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Unregulated CLLC converters have significant potential for dc transformers and two-stage battery chargers due to their high efficiency and bidirectional capability. In these applications, unregulated CLLC converters are usually designed to have their switching frequency fixed at resonance for maximum efficiency. However, the resonant frequency drifts from the designed value due to resonant tank parameter deviations, which leads to a decrease in efficiency for unregulated converters. To address this issue, this article proposes the bidirectional resonant frequency and a unified tracking algorithm. By analyzing the generalized resonant frequency equations in depth, an interesting feature is discovered for CLLC converters: forward mode and backward mode achieve maximum efficiency at an identical (but not constant) frequency. Thus, this unique frequency is defined as bidirectional resonant frequency (BRF). As the BRF varies with parameter deviations, a unified bidirectional tracking algorithm is proposed, which unifies the tracking of bidirectional maximum efficiency points into the tracking of a BRF. The introduction of the BRF combined with the unified tracking algorithm provides a simple, accurate, and low-cost solution for bidirectional resonance tracking of unregulated CLLC converters. Finally, experimental results show that unified bidirectional tracking and efficiency improvement are achieved under parameter deviations. [ABSTRACT FROM AUTHOR]

Three-phase CLLC resonant converters provide higher power conversion capability as compared to half-bridge and full-bridge structures. In addition to the unique features of CLLC converters for bidirectional applications, the three-phase structure provides significantly reduced output current ripple (smaller output capacitor), parallel power processing (reduced components size and current peak stress), and better thermal distribution (smaller heatsinks). However, with practical, i.e., nonzero, resonant component tolerances, these benefits are normally less, and sometimes significantly less than expected in the ideal case. In this article, the unbalanced behavior of the converter with 15 unknown resonant components is identified and analyzed. A new analysis methodology is proposed to investigate the worst-cases of current-sharing among above 32 000 possible scenarios in three-phase CLLC resonant converters. In addition, this article shows that phase-shifting techniques can be effective to mitigate the unbalanced behavior of the converter. The proposed analysis in this article helps to determine the highest admissible tolerance in the components to keep the converter working within a certain range of unbalanced behavior without requiring any balancing techniques. The proposed analytical framework is verified with experimental and simulation results of a 3-kW bidirectional three-phase CLLC experimental prototype. [ABSTRACT FROM AUTHOR]

Charge control for resonant converters introduces an inner feedback loop that improves the system dynamic characteristics. However, small-signal modeling is not as straightforward with charge-controlled resonant converters as it is with current mode hard-switching topologies, due to the nature of resonant behavior. Conventional small-signal models for charge-controlled resonant converters are developed based on the converter input and output energy balance. This simplified approach overlooks the dynamics of the magnetizing inductor current and generates errors in small-signal frequency response. To improve the analytical model and enable high-bandwidth design, this article proposes a new methodology for modeling charge-controlled resonant converters. The energy stored in the resonant tank is analyzed using the theory of extended describing function, which accounts for the effect of the magnetizing current. This methodology applies to a wide range of charge control variants, such as bang-bang charge control and hybrid-hysteretic control. To demonstrate the modeling procedure, this article considers a high-order, five resonant-component half-bridge CLLC resonant converter as a case study. The proposed analytical model is applied to a 1 kW, 400-V/3.3-A power supply prototype for simulation and experimental validation. The proposed model successfully predicts the frequency response of the resonant converter across frequency and load conditions, providing rapid frequency-domain evaluation in the design process. [ABSTRACT FROM AUTHOR]

The rapid expansion of distributed energy resources has led to increasingly complex systems with numerous power converters. Accurate converter loss prediction in large grids and microgrids is essential for financial and reliability evaluation. Existing system-level analysis focuses on distribution losses and oversimplifies converter losses by assuming fixed efficiency. However, converter losses are highly variable under different operating conditions. Moreover, commercially-available multidomain simulation tools are too slow to be applied to system-level analysis. To provide computationally simple loss prediction under all operating conditions, the rapid loss estimation (RLE) equation is proposed. First, the real operating conditions of the converter are determined for the intended application. Then, accurate loss information is extracted from detailed converter behavior in multidomain simulations. Finally, the RLE equation is obtained: a parametric equation, which is fast enough for system-level simulation while capturing the converter's complexity at different operating conditions. A dc microgrid with three different converters, one each for solar generation, electric vehicle charging stations and battery storage, is considered to highlight the benefits of the proposed loss estimation tool. [ABSTRACT FROM AUTHOR]

Three-phase LLC resonant converters can handle much higher power compared to half-bridge and full-bridge LLC converters, which makes them suitable for levels 2 and 3 battery charger applications. In addition to the unique features of LLC resonant converters, the three-phase structure provides higher power capacity and higher power density at higher power levels in comparison with single-phase structures. Although single-phase LLC resonant converters were thoroughly investigated in the literature for many different applications, limited work has been done on three-phase LLC converters. Unexplored problems with three-phase LLC resonant converters include issues with their limited gain range and also their poor light-load efficiency. In this article, a modified three-phase LLC resonant converter with a new phase-shedding strategy is proposed. With the proposed modified topology and phase-shedding strategy, the wide gain range needed for covering the recovery zone of charging Li-ion batteries is realized. Moreover, with the proposed phase-shedding strategy, a significant efficiency improvement with light-load absorption charging is achieved. A 3-kW prototype was developed to validate the performance of the proposed converter. [ABSTRACT FROM AUTHOR]

In the past ten years, LLC resonant converters have become a mainstream topology for dc/dc power conversion, and multiple design tools have been developed for this topology, including controllers, regulators, soft-switching techniques, etc. While many tools are available for designing this converter, techniques for accurately determining power losses in the inverter mosfets of the topology based on time-domain analysis have not been fully explored yet. Precise power loss estimation is fundamental to determine the thermal behavior of the switches before the converter is built, which accelerates and optimizes the thermal management design process. In addition, accurate methods of estimating conduction losses, which are dominant in this topology, switching losses, and body diode losses are lacking in the literature. This paper proposes a method for enhancing power loss estimation in LLC inverter mosfets based on time-domain analysis of the converter. Moreover, a detailed characterization of mosfet's conduction losses ($P_{\text{cond}}$), switching losses ($P_{\text{sw}}$), and body diode losses ($P_{\text{diode}}$), including the effects of different parameters such as gate-source voltage ($V_{\text{GS}}$), junction temperature ($T_{j}$), drain current ($\displaystyle I_{D}$), and drain-source voltage ($V_{\text{DS}}$), is presented, which can further improve power loss assessment in this topology. The developed method based on time interval analysis replaces the simplistic first-harmonic approximation (FHA), which allows for improved power loss calculations. Further improvement is obtained with the detailed characterization of the switching device. As verified by simulation and experimental results, the proposed estimation tool provides a significant boost in accuracy for power loss determination when compared to the existing method for power loss estimation using FHA. [ABSTRACT FROM AUTHOR]

With the increasing demand for flat displays, slim telecom/IT power supplies, and portable devices, the use of planar transformers (PTs) is becoming mandatory to achieve slim, compact converter designs. In particular, PTs present a significant opportunity to replace tall and bulky wire-wound transformers in industry standard LLC converters. However, the common-mode (CM) noise generated by PTs remains a significant obstacle to make LLCs effective. The CM noise issues are originated by large capacitances in overlapping primary and secondary layers of PTs, leading to serious electromagnetic interference issues. This paper develops a new winding method to overcome CM noise in LLC PTs. By minimizing noise, the proposed method prevents the use of bulky CM chokes, helping to keep a slim/flat form factor for LLC converters with high-power density. As well, the proposed winding method maintains low ac resistance and leakage inductance, two desirable features in high-efficiency transformers. The paper explains the root cause of CM noise in LLC PTs and develops a comprehensive method that targets all sources of CM noise in the transformer and is applicable to any type of PTs. The proposed winding method successfully shields problematic turns with high $dv/dt$ and overlaps the turns with the same $dv/dt$. As a result, circulating currents between primary and secondary (which are known as CM noise) are prevented, which leads to significant reduction of the converter's noise. Experimental results show that the proposed PT generates 11–20 dBμV less CM noise than a traditional PT with the same parasitic capacitance, which is the result of using the proposed winding method. [ABSTRACT FROM AUTHOR]

Synchronous rectification (SR) for LLC resonant converters has been developed to enhance the power conversion efficiency and achieve high-power-density design. Conventional SR driving strategies can be categorized as current-driven methods, $v_{\text{DS-ON}}$ sensing methods, and alternative approaches. The current-driven methods widely adopt current transformers (CTs) to sense the rectifier current and generate the SR driving signals. The CTs are lossy and bulky, which is unfavorable to high-power-density design. The $v_{\text{DS-ON}}$ sensing methods remove the current sensors by sensing the voltage across the on-state resistor of the SR mosfet, yet the sensed signal is small and prone to be offset by the inductive voltage induced from parasitic components. Most alternative approaches avoid sensing noise-sensitive signals; however, the operating range is narrow due to the limited information from the converter. This paper proposes an SR driving strategy based on the resonant capacitor voltage (RCV) to address those issues. The RCV SR driving strategy does not require current sensors. The sensed RCV is insensitive to the parasitic effects. In addition, the RCV strategy controls the SR on-time effectively over a wide range of operating frequency and loading conditions. Simulation and experimental results of a 650-W/24-V LLC converter are presented to validate the effectiveness of the proposed RCV strategy. Compared with the conventional $v_{\text{DS-ON}}$ sensing method, the on-time error caused by the parasitic effect is greatly reduced, which improves the power conversion efficiency and reduces the SR mosfet temperature. [ABSTRACT FROM AUTHOR]

Due to its simplicity, the hard-switching boost converter is widely used in many applications, such as renewable energy and power factor correction. The power density of the converter can be increased with smaller magnetics; however, this requires an increase in the switching frequency. Therefore, it is necessary to provide soft-switching conditions to minimize the switching losses. In this paper, a new resonant step-up converter and the associated analysis are presented. The proposed interleaved LC resonant boost converter provides soft switching for all of the semiconductor elements even under light loading conditions. Small inductors with discontinuous conduction mode (DCM) currents can be used because the interleaving behavior ensures a continuous input current with low ripples. The interleaving also reduces the output capacitor ripple current. Burst mode operation has been applied to improve the efficiency of the converter during light loading conditions. Detailed design methodology and the control strategies are provided. To show the validity of the theoretical analysis, experimental results are provided for a 400-W prototype, and are compared to a benchmark conventional interleaved boost converter with the same components. Substantial efficiency improvements are achieved for different loads and voltage gains, particularly under light loading conditions. [ABSTRACT FROM AUTHOR]

The interest in distributed generators (DGs), especially those associated with renewable energies, has increased in recent years. The number of functionalities that their commonly associated voltage source inverters (VSIs) can deal with is rising, harmonic currents compensation being one of them. VSI control is in charge of accomplishing the different capabilities, and it must be done without exceeding the limited and variable dc voltage margin, if undesirable effects want to be avoided. If limitations are reached, capabilities will be reduced in order to remain within the limitations. At the same time, as the number of DGs is also increasing, when capabilities are not able to be coped with exclusively one VSI, the cooperation among VSIs appears as a solution. A key point is to establish a strategy in this kind of topology when one of the VSI is brought to its limits. In this paper, a new strategy is proposed, where even under limited situation VSIs always try to inject the maximum power extracted from the DG and achieve the harmonic compensation (multifrequency) by cooperation among the different parallel VSIs. Newest multifrequency saturation strategies are studied, modified, and applied to cooperative applications. Simulations, hardware in the loop (HiL), and experimental results are included and compared. [ABSTRACT FROM AUTHOR]

In this paper, a thorough thermal analysis is carried out in order to find an analytical three-dimensional (3-D) frequency-dependent thermal model of planar transformers (PTs) used in high-frequency power converters. Because of the tendency of having higher power density as well as miniaturization of power converters, the components have to work near their thermal limit margins. This issue is more critical for planar magnetics in LLC converters due to their variable high-frequency operation, making thermal modeling and heat transfer analysis tools necessary. The proposed 3-D frequency thermal model is obtained based on the lumped parameters network (LPN) according to different thermal resistances of the PT including convection, conduction, and radiation heat exchanges. It should be noted that not only the 3-D geometry effect of the core is applied to the proposed model, but thermal surface resistances are also considered to model the high-frequency operation effect. Moreover, the lumped capacitance thermal model is used to analyze the transient thermal variation of the transformer. The LLC resonant converter with two PTs, including EE58/11/38 and ER51/10/38 planar cores, is considered to show the compatibility of the proposed 3-D-frequency LPN model. In addition, the temperature distribution of different parts of the transformers is evaluated using finite element method modeling and compared with the proposed 3-D frequency-dependent LPN model. Experimental results confirm the improved accuracy of the proposed LPN model and show the proposed model predicts the temperature distribution in PTs with an error of less than 3%. Considering the improved accuracy and low computational time of the method, the proposed 3-D frequency-dependent model is a powerful and fast design tool to evaluate the temperature distribution for different designs, and so can be used to effectively optimize the transformer from thermal point of view. [ABSTRACT FROM AUTHOR]

In order to further reduce losses in LLC resonant converters, the use of synchronous rectifiers (SRs) in the output rectifier is desirable. Analysis and detection of the conduction angles of the SRs used in an LLC converter are the main challenges in synchronous rectification. This paper develops a new time-domain theoretical analysis, called homopolarity cycle, enabling synchronous rectification in LLC resonant converters with the use of a low-cost polarity-based sensing technique. The homopolarity cycle considerably reduces the complexity of the LLC converter's analysis, relates the conduction angles of the SRs to the gate driving signals of the inverter switches and the polarity of the rectifier voltage, and finally introduces a low-cost polarity-based sensing technique. A synchronous rectification control algorithm, called homopolarity cycle modulation (HCM), is proposed, which only needs to sense the polarity of the rectifier voltage, which is simple to measure and immune to noise. A simple graphical plane, named the homopolarity, is introduced to provide information about the SRs’ conduction angles. The proposed HCM method is validated by experimental and simulation results. Unlike the conventional synchronous rectification technique, the results have shown that the proposed HCM synchronous rectification method has a flat synchronous rectification coverage from light to full loading conditions while using a simple sensing strategy. [ABSTRACT FROM AUTHOR]

Photovoltaic cells require maximum power point tracking (MPPT) algorithms to ensure that the amount of power extracted is maximized. True seeking, direct duty cycle control MPPT algorithms are a simple and straightforward solution that can provide high tracking efficiency. In these algorithms the duty cycle is traditionally modified to reach a new steady state prior performing a new MPPT iteration. Therefore, the MPPT update period must be larger than the converter's settling time to reach a new steady state, which limits the dynamic tracking performance. This paper proposes a novel direct duty cycle control method that does not require the converter to achieve steady state in between MPPT updates. The proposed method benefits from the natural oscillations occurring in the converter to obtain extreme dynamic tracking improvements while maintaining simple implementation with no need of employing temperature or irradiance sensors. The scheme being introduced combines MPPT concepts with large-signal geometric control to achieve a reliable, high-performance solution very suitable for applications with rapidly changing irradiance, such as wearable technology and rooftop electric vehicle (EV). The theoretical analysis is supported by detailed mathematical procedures and validated by simulations and experimental results. [ABSTRACT FROM AUTHOR]

Three-phase $LLC$ resonant converters can handle very high power levels beyond the capabilities of half-bridge and full-bridge $LLC$ topologies. Among other characteristics, three-phase $LLC$ structures reduce output current ripple (small output filter), enable parallel power processing (low peak current), and provide good thermal distribution. However, all these key advantages can be severely compromised due to passive components tolerances, leading to undesired current balance issues in three-phase $LLC$ resonant converters. Tolerances in resonant tank passive components are inevitable and lead to unequal peak currents between phases, uneven temperature distribution, and large output current ripple. This paper investigates the imbalances in three-phase $LLC$ converters and proposes a novel trigonometric current balancing (TCB) technique using phasor analysis. In this strategy, the required input voltage phase angles are calculated to achieve balanced phase currents, even under severe unbalanced conditions. In some cases, the output filter current ripple is reduced to less than half. The methodology is verified with a 3-kW experimental prototype, which validates the analytical framework and effectiveness of TCB. [ABSTRACT FROM AUTHOR]

Flyback and forward converters are two commonly used topologies for isolated low-power applications. These converters are simple and cost effective and provide galvanic isolation, which make them desirable for low-power levels. In order to enhance the performance of these converters, planar transformers (PTs) can be used that feature lower height, considerably lower leakage inductance, excellent thermal characteristics, and repeatability. Selecting a proper winding arrangement for a PT is a significant challenge, in particular given the large capacitances involved in flat structures. While interleaved structures significantly reduce the ac resistance and leakage inductance of PTs, they also lead to very large interwinding capacitance, which produces significant levels of undesired common-mode (CM) noise that causes EMI problems. Reducing interwinding capacitance by using noninterleaved structures is not an ideal solution to the CM noise problem because of its side effects. Instead, this paper tackles the problem by proposing the concept of paired layers. According to this concept, there are layers in the primary and secondary sides that have the same dv/dt, and therefore, their overlapping does not generate CM noise. These layers can be used to design highly interleaved structures that not only have very low ac resistance and leakage inductance, but also generate almost zero CM noise, although they may have a very large interwinding capacitance. In addition, a detailed parasitic capacitance model of PTs is proposed, which analytically validates the proposed concept and method. The experimental results show that the proposed PTs not only have very low ac resistance and leakage inductance, but also generate extremely low levels of CM noise. Considering that the proposed PT has interwinding capacitance equal to \text{700 pF} , it is very interesting to see that it generates significantly less CM noise than does a traditional wire-wound transformer that has only \text{10-pF}$ parasitic capacitance. Therefore, the proposed method gives designers the opportunity to minimize ac resistance and leakage inductance by using highly interleaved structures, without having to worry about CM noise caused by large interwinding capacitance. [ABSTRACT FROM AUTHOR]

LLC resonant converters suffer from a startup inrush current that may push power switches beyond the safe operating area. The conventional method of limiting the startup inrush current is to adopt the frequency decrement method; however, doing so, results in the overdesign of magnetic components and the gate driver circuit, sluggish startup response, and circulating current in light and no-load conditions. To tackle these problems, this paper proposes a nonlinear controller called the average geometric controller (AGC), offering low-cost implementation requirements. The proposed controller uses the advantages of a new LLC average large-signal model, in order to analyze the large-signal nature of the converter. Studying the average nature of LLC converters enables the use of low-bandwidth sensors, and lower sampling rates, while improving the system performance. In addition to limiting the startup inrush current without employing a very high switching frequency, the proposed AGC provides an extreme dynamic startup response for LLC converters, with near zero voltage overshoot. In order to validate the theoretical analysis, experimental results of an LLC converter are presented using the proposed controller. Comparative experimental analysis is performed with a conventional method for limiting inrush current. Moreover, the accuracy of the average large-signal model is experimentally validated. [ABSTRACT FROM PUBLISHER]

The advancements in dc microgrids and the increase in distributed generation systems have led to a new trend toward the coexistence of multiple power converters from different sources (renewable, storage, etc.) supplying a variety of loads of different natures in a weak network. The loads can behave as passive loads (resistances) or be implemented by tightly regulated power converters, leading to constant power load (CPL) behavior. The CPLs present a characteristic negative incremental resistance that can alter the response of the system, even causing instability. In this work, a novel embedded technique based on a digital lock-in amplifier is proposed that enables the real-time detection of the dynamic impedance present in a power converter. The proposed technique uses a very efficient algorithm, along with standard sensors available in the converter, to measure the magnitude and phase of the dynamic load, and uses this information to improve the performance of the converter. A sample application of the proposed technique in an adaptive control system is described. Although the total output power of the converter is independent of the nature of the load, the converter's dynamic response is not. The interaction of the CPL, passive load, and control loop will determine not only the stability but also the transient response. The proposed instrument allows the incremental load of the converter to be accurately measured while reducing the complexity and sensor requirements, and improving the performance of the controller. Simulations of the proposed technique are presented to illustrate its behavior. Experimental results for different kinds of loads are presented to validate the proposed strategy. [ABSTRACT FROM PUBLISHER]

The optimal management of energy generation/consumption in modern distribution systems has gained attention in the smart grid era. This paper presents optimized and coordinated strategies for performing and assessing energy management in multi-microgrid systems. The energy management process is formulated for multi-microgrid systems that simultaneously incorporate several energy generation/consumption units, including different types of distributed generators (DGs), energy storage units, electric vehicles (EVs), and demand response. Due to the probabilistic nature of some loads (e.g., EVs) and generators (e.g., wind turbine and photovoltaic (PV) modules), a novel probabilistic index is defined to measure the success of energy management scenarios in terms of cost minimization. Moreover, by using the new index, common types of energy controllers, such as DGs, storage units, EVs and demand side management are implemented simultaneously and individually, in a system, and the effect of each addition on the defined index and on operational costs is investigated. Finally, the robustness of the process to the load and generation prediction errors is investigated. [ABSTRACT FROM AUTHOR]

In recent years, with a higher penetration of renewable distributed generators into the ac grid network, the risk of grid instabilities and vulnerabilities has increased. This paper proposes grid support strategies that can be used to alleviate the grid frequency–voltage variations, which are indicators of the imbalance between power generation and consumption within an ac network. The proposed strategies to support grid stability in the event of frequency–voltage variation go beyond recent standards and provide extended functionalities. The preconfigured set points of active power-frequency P(f) strategy features the control of the converter's power flow direction with an adjustable power gradient transition between grid-feeding and force charge as grid loading, in response to grid frequency deviation. The distributed power generators are represented by an energy storage converter, with the capacity to discharge and charge the electrical energy storage (EES) element, primarily for grid support purposes. The EES energy storage is configured for later usage when the grid requires active power support, under line frequency deviation, used under normal conditions, or during on-peak tariff high-demand daytime hours (energy shifting for TOU, ac load shave). In addition to grid support enhancement, the P(f) strategy is combined with reactive power-voltage Q(v ) control to attempt to correct frequency and voltage deviations in a collective impact of distributed generators operation for grid stabilization purposes. The P(f) − Q (v) strategy provides an automatic active/reactive power generate/receive preconfigured control, in response to frequency–voltage deviations, in order to support the grid and prevent network instabilities. The proposed control strategy for local frequency assist and voltage assist is applicable for single and three-phase grid converters interfaced with energy storage systems. Simulations and experimental results, obtained using a single-phase 6 kVA four-quadrant EES converter, are presented to validate the proposed P( f) and Q(v) grid support strategies. [ABSTRACT FROM AUTHOR]

Linear controllers and small-signal modeling techniques have been used for over 40 years to control power electronic converters around the equilibrium operating point. Outside the quiescent area, the shortcomings of linear controllers are well known and include uncertain large-signal transient behavior and sluggish dynamic/recovery response. In particular, resonant converters have inherent large-signal behavior, making the transient performance of small-signal linear controllers poor. This paper develops a geometric controller based on large-signal modeling to achieve enhanced dynamic response of the series resonant converter (SRC). The proposed modeling strategy provides detailed insight into the behavior of the SRC and creates an analytical framework to successfully perform geometric control. A new geometric control law is mathematically derived using average circular trajectories producing accurate and fast dynamics during startup, sudden load or reference changes. In order to validate the theoretical analysis, experimental and simulation results of an SRC are presented and compared to those of a linear and a nonlinear controller. The dynamic response is, on average, over 100 times faster than that of the designed linear controller, while overshoot is virtually eliminated. [ABSTRACT FROM AUTHOR]

With the widespread growth of slim portable electronics, research into planar spiral windings for wireless power transfer (WPT) battery charging systems has gained a lot of attention due to their low profile, reproducibility, and manufacturability. The major design goal for windings in WPT systems is high-quality factor (Q) for a given inductance. This study presents a new method to improve Q by using a nonunity track-width-ratio (TWR) geometrical arrangement in conjunction with increasing the inner radius of winding to make an improved hollow planar spiral winding. The inductance regulation of this technique combined with its exceptional improvements in Q make it a superior choice for resonant WPT systems. Inductance and resistance models are provided in order to assess the Q improvement. A 5-W, 110–200-kHz WPT system was built and tested based on the wireless power consortium Qi standard to confirm the advantages of the improved windings on the transmission efficiency of the system. An increase from 70% to 90% are observed from employing the proposed winding technique designed using the provided models. [ABSTRACT FROM AUTHOR]

Photovoltaic (PV) power converters and maximum power point tracking (MPPT) algorithms are required to ensure maximum energy transfer between the PV panel and the load. The requirements for the MPPT algorithms have increased over the years—the algorithms are required to be increasingly accurate, fast, and versatile, while reducing the intrusiveness on the overall performance of the PV panel and converter. The family of hill-climbing algorithms such as incremental conductance (InCond) and perturb and observe (P&O) has gained popularity given their simplicity and accuracy, but it requires the injection of a perturbation that changes the operating point even in steady state and are prone to errors during changing environmental conditions. In recent literature, the use of the switching ripple has been proposed to replace the perturbation in the hill-climbing algorithms given its inherent presence in the system and speed. The constant work toward smaller and faster ripples presents challenges to the signal detection involved in this kind of algorithm. This paper develops and implements a new InCond MPPT technique based on switching ripple detection using a digital lock-in amplifier (LIA) to extract the amplitude of the oscillation ripple even in the presence of noise. The use of this advanced technique allows to push forward the reduction of the ripple in order to virtually eliminate the oscillation in steady state maximizing the efficiency. The accurate detection allows for adaptive-step features for fast tracking of changing environmental conditions while keeping the efficiency at maximum during the steady state. Detailed mathematical analysis of the proposed technique is provided. Overall, the use of the proposed LIA allows to push the reduction of the ripple even more while keeping accuracy and delivering superior performance. Simulations and experimental results are provided for the proposed technique and the InCond technique in order to validate the proposed approach. [ABSTRACT FROM PUBLISHER]

The control of boost-derived converters presents a special challenge due to its non-minimum phase behavior, forcing a slow transient response when traditional linear techniques are employed. In order to improve the dynamic behavior, more complex controllers have been proposed (e.g., adaptive, nonlinear, boundary, etc.), but the improvements introduced by each one of them cannot be objectively assessed in the absence of a theoretical performance limit standard reference. This work introduces a benchmarking tool based on the evaluation of the converters’ performance under start-up, load current, and input voltage step-up/step-down transients. Six performance indices are defined using the theoretical performance limits as reference. In this way, the converters’ dynamic performance can be quantitatively assessed in six different aspects, enabling a thorough benchmarking procedure. The ideal parameters are found by exploring the performance limits of boost converters, providing valuable insight into the behavior of the topology. These reference parameters are found in a normalized domain and characterized by closed-form expressions, providing simple, intuitive, and general results valid for any combination of LC parameters and voltage levels. The characterization of the dynamic performance limits is validated by experimental results. The proposed benchmarking procedure is illustrated by evaluating the dynamic performance of two different dc–dc boost converters. [ABSTRACT FROM PUBLISHER]

Dual active bridge converters enable bidirectional power flow in buck and boost operating modes. This paper presents an advanced switching sequence and burst-mode strategy to balance conduction, switching, and magnetic losses under light, medium, and heavy loading conditions, leading to improved operating efficiency. The implementation of the switching sequence employs the natural state-plane trajectories of the converter and contributes to higher efficiency and the ability to perform burst mode. The proposed switching sequences improve the overall efficiency of the converter by enabling soft switching and adjusting the frequency to match the minimum RMS transformer current in the full operating range. Furthermore, it incorporates a fully controlled burst-mode switching sequence for light loading conditions to further extend the efficiency gains. As a result, maximum efficiency is obtained by taking advantage of all the possible switching structures of the converter. The analysis provides insight into the natural trajectories of the converter, which produce soft-switching transitions and enable the converter structures to achieve the target operating point directly. Simulation and experimental results are presented to validate the benefits of the switching sequence and illustrate the burst-mode operation. [ABSTRACT FROM PUBLISHER]

In order to recover and fully charge batteries in electric vehicles, smart battery chargers should not only work under different loading conditions and output voltage regulations (close to zero to 1.5 times the nominal output voltage), but also provide a ripple-free charging current for battery packs and a noise-free environment for the battery management system (BMS). In this paper, an advanced $LLC$ design procedure is investigated to provide advantageous extreme regulation and eliminate detrimental burst mode operation. A modified, special $LLC$ tank driven by both variable frequency and phase shift proves to be a successful solution to achieve all the regulation requirements for battery charging (from recovery, bulk, equalization, to finish). The proposed solution can eliminate the negative impact of burst mode noises on the BMS, provide a ripple-free charging current for batteries in different states of charge, reduce the switching frequency variation, and facilitate the EMI filter and magnetic components designs procedure. In order to fully consider the characteristics of the full bridge $LLC$ resonant converter, especially the output voltage regulation range and soft transitions of the MOSFETs in the fixed frequency phase shift mode, a new set of analytical equations is obtained for the $LLC$ resonant converter with consideration of separated primary and secondary leakage inductances of the high frequency transformer. Based on the proposed strategy and analytical equations, multivariate statistical design methodology is employed to design and optimize a 120 VDC, 3-kW battery charger. The experimental results exhibit the excellent performance of the resulting converter, which has a peak efficiency of 96.5% with extreme regulation capability. [ABSTRACT FROM PUBLISHER]

Electric vehicles make use of energy storage systems, such as batteries and/or ultracapacitors to power the electric power drive train, as well as auxiliary automotive system for control, safety, and comfort. This relatively complex power structure can be described as a distributed multiconverter system. The constant power behavior of tight-speed controllers in the vehicle's traction system and tightly regulated dc-dc converters connected to the HV-DC bus produces instability effects. This paper proposes a simple and practical geometric control, using circular switching surfaces, to address constant power load instability in electric vehicle's power systems. The proposed switching surfaces provide a solution in the geometrical domain to constant power loading conditions, while achieving outstanding dynamic response compared to state-of-the-art controllers. The controller is implemented in a bidirectional Buck + Boost cascade converter as a battery charge/discharge unit and ensures reliable system operation. The predictable and consistent behavior of the converter with constant power load is presented by analyzing the system curves in the normalized state plane with the switching surfaces employed. Simulation and experimental results on a scaled 1-kW Buck + Boost cascade converter validate the proposed switching surfaces and predictions regarding the converter's behavior under constant power loading conditions. [ABSTRACT FROM AUTHOR]

The demand for electric vehicles has expanded rapidly for both industrial and transportation applications. In parallel, new battery technologies capable of deeply discharging and powering electric vehicles over long periods of time have been introduced and made available in the market. Due to the increasing complexity of charging algorithms, battery chargers are exposed to demanding operating requirements. Chargers should not only work under different loading conditions (from absolutely zero to maximum output power) but also regulate a wide output voltage range (from near zero to 1.5 times nominal voltage). In this paper, a multiresonant L3C2 resonant converter is introduced that can cover nearly all of the regions in the battery V-I plane, from near zero output voltage, zero output current to maximum output power. By adding one capacitor, the topology is able to extend the operating frequency beyond the LLC topology and achieve significant regulation improvements. Near free-ripple charging current for batteries charging is achieved in different states of charge without using burst mode operation, effectively increasing the battery life cycle. In addition, soft transitions are obtained for all the switches (MOSFETs and diodes) resulting in high efficiency, reliability, power density, and low-noise operation of the charger. A complete set of simulation and experimental results, extracted from a 96-VDC 950-W L3C2 resonant converter, demonstrates the characteristic features of the proposed topology for battery charger applications, while providing a comparative example with the LLC topology. [ABSTRACT FROM AUTHOR]

With the increase of wireless power transfer (WPT) systems for home and industrial electronic applications, planar spiral winding design techniques are gaining attention due to their low profile, reproducibility, and manufacturability. The major design goal for windings in WPT systems is a high quality factor (Q) for a given inductance. This paper establishes a new method to improve and analyze Q by using a nonunity track-width-ratio geometrical arrangement. The results are applicable for a variety of planar spiral winding families and make full use of the ability to change the width of the traces to improve Q for wireless powered applications. In order to simplify the analysis and provide generality, a unified dimensional system framework is also proposed, covering the racetrack geometry and its derivatives—circular, rectangular, generalized octagonal, and traditional racetrack windings. The resulting dimensional system provides an accurate geometrical description of the windings to obtain high Q and a simple set of manufacturing specifications. Details and derivations of this new method to calculate inductance, dc resistance, and ac resistance estimation to obtain improved Q are presented. A comprehensive set of experimental measurements confirms the validity of the dimensional system and the improvements in Q for wireless powered applications. [ABSTRACT FROM AUTHOR]

Traditional linear techniques are widely used for the control of basic dc–dc converters due to their simple implementation. However, due to the small-signal validity range of the models employed, the converters usually perform poorly under large transients, and the dynamic response can be improved only to a limited extent in order to ensure a stable behavior. On the other hand, faster dynamic response can be achieved with boundary controllers, which require faster sensors and more powerful processors. A novel control scheme that combines the advantages of fixed-frequency pulsewidth modulation with state-plane geometric analysis is introduced to obtain fast and reliable large-signal response. The natural evolution of the average state variables is described by a large-signal unified model, which provides the basis to develop a reliable nonlinear control scheme. The proposed technique is suitable for implementation in low-cost digital signal processors, using low-bandwidth sensing stages, and it features fast, sleek, and consistent dynamic response with constant switching frequency. Since the model developed accurately predicts the large-signal behavior, reliable and predictable responses can be obtained at any operating point. In this way, the transient response obtained shows reduced, consistent, and well-determined peaks in inductor current and capacitor voltage, avoiding magnetic saturation and system failures even during extremely large transients. Furthermore, the maximum rating specifications for the reactive components can be reduced, which, combined with the low requirements for sensors and processors, lowers the implementation cost and makes the controller a very appealing alternative for high-volume applications. The contributions made to the theoretical and applied field are valid for any combination of reactive components due to the normalized approach adopted. The theoretical concepts are supported by detailed mathematical procedures. The proposed theory and controller are validated by experimental results. [ABSTRACT FROM PUBLISHER]

For reliability reasons, the employment of small film capacitors instead of electrolytic ones is an interesting alternative for the dc-link in single-phase inverters for fuel cell applications. Due to the low capacitance that can be accomplished at an acceptable cost using this technology, there are large low-frequency voltage fluctuations (100/120 Hz and harmonics) in the dc-link caused by the double-frequency power transfer. By allowing these variations in the bus, the capacitor bank absorbs the current ripple from the inverter to avoid detrimental oscillations in the fuel cell. Traditional control strategies for inverters are usually designed to operate with nearly constant input voltage and are not able to effectively handle large (e.g., ) low-frequency input voltage fluctuations. This paper introduces the analysis of a swinging bus in the context of fuel cell standalone applications (i.e., voltage-source inverters) and proposes a nonlinear control approach to operate inverters with very large input voltage swing: the natural switching surface (NSS). Under the proposed scheme, the inverter presents excellent dynamic and steady-state characteristics, even at moderate switching frequency (e.g., 3.6 kHz). In order to illustrate the superior performance of the NSS, a comparison to a proportional-resonant (PR) controller is performed. Unlike the linear compensator, the NSS is able to reject the large bus voltage oscillations and achieve high-quality output voltage with low total harmonic distortion (THD). Simulation and experimental results are provided to illustrate the behavior of the swinging bus and to validate the NSS control scheme under the proposed demanding operating conditions. [ABSTRACT FROM AUTHOR]

Maximum power point tracking (MPPT) strategies in photovoltaic (PV) systems ensure efficient utilization of PV arrays. Among different strategies, the perturb and observe (P&O) algorithm has gained wide popularity due to its intuitive nature and simple implementation. However, such simplicity in P&O introduces two inherent issues, namely, an artificial perturbation that creates losses in steady-state operation and a limited ability to track transients in changing environmental conditions. This paper develops and discusses in detail an MPPT algorithm with zero oscillation and slope tracking to address those technical challenges. The strategy combines three techniques to improve steady-state behavior and transient operation: 1) idle operation on the maximum power point (MPP); 2) identification of the irradiance change through a natural perturbation; and 3) a simple multilevel adaptive tracking step. Two key elements, which form the foundation of the proposed solution, are investigated: 1) the suppression of the artificial perturb at the MPP; and 2) the indirect identification of irradiance change through a current-monitoring algorithm, which acts as a natural perturbation. The zero-oscillation adaptive step P&O strategy builds on these mechanisms to identify relevant information and to produce efficiency gains. As a result, the combined techniques achieve superior overall performance while maintaining simplicity of implementation. Simulations and experimental results are provided to validate the proposed strategy, and to illustrate its behavior in steady and transient operations. [ABSTRACT FROM PUBLISHER]

This paper presents a boundary control scheme for dual active bridge (DAB) converters using the natural switching surface (NSS). The implementation of a curved switching surface for DAB converters is a new area of research undertaken in this paper. The proposed technique brings the benefit of unprecedented dynamic performance, already developed for nonisolated topologies (e.g., buck and boost), to this more complex isolated topology. The analysis provides insight into the natural trajectories of the DAB converters and creates an accurate framework in the normalized geometrical domain. As a result, the physical limits of the converter under study become evident. Those physical limits are exploited by employing the NSS to obtain fast transient response under start-up, sudden load transients, and reference change. In addition, fixed-frequency operation is one of the key features of the proposed control scheme, which allows optimizing the design of the high-frequency transformer. Experimental results are presented to validate the NSS for DAB converters and illustrate the benefits of the normalization technique. [ABSTRACT FROM AUTHOR]

This paper presents the use of a high-performance boundary controller for the full-bridge zero-voltage-switching topology. An enhanced dynamic response is obtained by employing the natural switching surface (SS), which is thoroughly derived in the normalized geometrical domain. The advantages of the normalization are the simple graphical representation, the generality for any combination of parameters, and the mathematical simplicity. Recently, nonisolated basic topologies have benefited from advancements in boundary control. The analysis and derivation in this work bring the benefit of outstanding dynamic performance to this isolated topology. As demonstrated in this work, the relationship between the leakage and output filter inductances makes the formulation of the natural trajectories for isolated converters possible. The resulting SS provides an excellent dynamic response during start-up, reference change, and sudden output loading conditions. Experimental results are presented to illustrate the characteristics and advantages of the control scheme and the converter operation with fixed switching frequency. [ABSTRACT FROM AUTHOR]

A swinging bus scheme is investigated in this paper to eliminate undesirable low-frequency ripple current reflection in fuel cells. The swinging bus is thoroughly characterized under various loading conditions to establish a behavioral model. As a result, a general control scheme and signal processing for buck- and boost-derived power converters are obtained. A digital filter in the form of a moving averaging filter proves to be a fundamental component of the control loop, a significant practical advancement in control for low-frequency ripple elimination. A formal mathematical demonstration is included and experimental results are presented to validate the technique and illustrate its benefits. [ABSTRACT FROM AUTHOR]

Planar transformers provide a light-weight and low-profile solution for power electronic converters with highly reproducible parameters and simple manufacturability. Parasitic inductances, capacitances, and resistances in planar magnetics are difficult to model due to the complex interactions between the physical winding arrangement of each layer and the core geometry (track width, air gap, clearance, etc.). These nonlinear and multivariate magnetic devices play a key role in defining the performance of traditional, soft-switching, and resonant converters by ruling behaviors such as ringing, self-resonant frequency, conduction losses, and the current rate of change in these converters. In this paper, a methodology for determining parametric models for leakage and magnetizing inductance, inter- and intrawinding capacitances, and the winding resistance of small planar transformers is presented using a variety of winding arrangements. The models are employed to shape the winding design to control parasitic elements in order to optimize soft-switching and resonant converters. A central composite design based on the design of experiment methodology is employed on finite element simulations to provide the comprehensive models. Results from physical verification on a planar Ferroxcube ER18/3.2/10-3F3 core set are provided and show excellent correlation between models and verification tests. The method is later employed to effectively design an LLC resonant converter, which is also experimentally verified to illustrate the benefits of the proposed method. The methodology can be employed to characterize and design planar transformers and to predict their performances as part of a variety of power electronic converters. [ABSTRACT FROM PUBLISHER]

This study presents the application of the natural switching surface (NSS) to control single-phase power factor correctors (PFCs). The proposed boundary control scheme provides tight regulation and enhanced dynamic characteristics. The analysis is performed in the normalized geometrical domain to provide valuable graphical insight and generality. Low-frequency ripple effects are included as part of the converter reference to improve its behavior in steady state and load transient operation. In addition to the complete characterization of the system, a method to obtain fixed-frequency operation is presented by employing discrete-step references. The resulting switching surface (SS) provides fast output voltage regulation and input current dynamics, and low input harmonic distortion, achieving steady state in only a few switching actions under sudden load disturbances. The enhanced qualities of the natural SS are confirmed with simulation and experimental results of a 300 WPFC. [ABSTRACT FROM AUTHOR]

This paper presents a set of novel soft-switching techniques to increase the power conversion efficiency in fuel cell (FC) systems using a full-bridge topology. For this purpose, a special right-aligned modulation sequence is developed to minimize conduction losses while maintaining soft-switching characteristics in the MOSFETs. Traditional auxiliary elements in the primary, such as series inductors that are impractical for realizing due to the extreme input current, are avoided and reflected to the output of the rectifier to minimize circulating current and generate soft transitions in the output diodes. As a result, the proposed combined techniques successfully reduce conduction losses, minimize reverse-recovery losses in the output rectifiers, minimize transformer ringing, and ensure low stress in all the switches. The high efficiency is maintained in the entire range of loading conditions (0%–100%) while taking into consideration remarkable challenges associated with FC power conversion: high input current, low voltage and poor regulation, and wide range of loading conditions. A detailed analysis of the techniques for efficiency gains are presented and a phase-shift zero-voltage switching topology is employed as a reference topology to highlight the mechanisms for performance enhancement and the advantages in the use of the special modulation. Experimental results of a 1-kW power converter are presented to validate the efficiency gains, illustrate the benefits of the special modulation, and demonstrate the soft-switching transitions. [ABSTRACT FROM PUBLISHER]

This paper presents an embedded frequency response analyzer for fuel cells (FCs) based on a robust measurement technique with simple implementation. A frequency response analysis technique provides valuable information of different electrochemical processes that occur inside the FC. The measurement system is implemented on a low-cost digital signal processor to perform frequency response and impedance tracking. The small-size and low-power consumption allows this special device to be embedded into the FC controller or power conditioning stage. The system is capable of measuring automatically the frequency response of the FC at different operating points, even when the FC is operating with a load. These measurements can be used to characterize the FC at the design stage and to perform online monitoring of the FC state during a continuous operation. The proposed instrument uses the lock-in amplification technique, which allows very accurate and precise measurements even in the presence of high noise levels. The proposed hardware and signal processing technique are described in this paper, including the experimental result of a 1.2-kW proton exchange membrane FC system. [ABSTRACT FROM AUTHOR]

A curved switching surface (SS) for inverters control with superior characteristics is geometrically derived in this paper. In order to avoid inaccuracies introduced by simplification or assumptions, the analysis is performed entirely using a versatile geometrical method in the normalized domain. Unlike previous approaches, both the output voltage and the capacitor current are considered as varying references to establish a more accurate control law with enhanced performance. The proposed normalization technique provides remarkable insight into the behavior of system, the leading to a pure geometrical treatment that is general and applicable to any possible inverter. As a result of a rigorous analysis, a control law for inverters defined as natural SS is proposed and thoroughly characterized. In addition to the enhanced dynamic response, fixed-frequency operation is one of the key features of the proposed control scheme. In order to formally demonstrate fixed-frequency operation, a transformation from the natural SS to its pulsewidth modulation (PWM) equivalent is performed, revealing duality between boundary control using curved SS and traditional PWM. This is a significant advancement toward the unification and understanding of traditional modulation against modulation produced by curved SSs. Finally, an additional novel concept is explored: operation in mixed monopolar and bipolar mode using the natural SS. This new mixed operating mode overcomes physical limitations of the inverter structure in monopolar mode around the region of zero voltage cross (both the problem identification and solution are investigated). Experimental results of a 1.5-kVA inverter operating at fixed moderate frequency are presented to validate the natural SS performance, illustrate the benefits of the normalization technique, and demonstrate the monopolar and mixed operating mode. [ABSTRACT FROM AUTHOR]

A general procedure for the selection of a curved switching surface (SS) to control buck-type converters is presented in this letter. The analysis is based on the normalized representation of ideal SSs for different loading conditions. The normalization process leads to a unique representation of the SSs for any possible buck converter. A set of graphics in three dimensions is introduced to give a spatial sense of the behavior of the converter and its control requirements during transients. As a result of the investigation, a switching surface referred to in this letter as the natural unloaded SS is selected, providing excellent transient behavior and no overshoot during startup. For any buck converter with typical parameters, this control scheme produces, in one switching action, a minimum of 99 % of the desired output voltage. The general concept of using second-order SS is also geometrically analyzed in this letter to clarify its characteristic features and disadvantages. Experimental results for a typical buck converter are presented to illustrate the transient behavior of the converter during startup and sudden load changes. The results confirm the virtues of the control scheme. [ABSTRACT FROM AUTHOR]

Three-phase pulsewidth modulated converters are usually controlled to achieve sinusoidal currents in the grid side and tight voltage regulation in the dc-link capacitor. The implementation of linear controllers based on small-signal models is a well-established solution for these converters. However, the dynamic performance can be improved only to a limited extent and it deteriorates under different operating conditions which may result in the uncontrollability of the dc-bus voltage during transients. In this work, a state-plane model and control strategy are introduced to improve the dc-link dynamics for three-phase converters. The proposed method provides fast, reliable, and consistent transient responses under the entire operating range, including rectifier and inverter modes. First, a normalized model that describes the natural dynamic behavior of the converter is derived and represented in the state-plane. In this way, the dynamic evolution of the operating point is described in a graphical domain as circular trajectories with well-defined characteristics. The insight provided by these natural trajectories is used to develop a control strategy to improve the dc-link dynamics by selecting a unique combination of circular paths to solve the transients. As a result, the operating point follows well-defined trajectories to achieve fast and consistent dc-link voltage responses under a wide operating range. The effectiveness and feasibility of the proposed control strategy are validated by several simulation and experimental results. [ABSTRACT FROM AUTHOR]

Three-phase pulsewidth-modulated converters require closed-loop controllers to meet the performance requirements and to achieve reliable responses over the entire operating range. Conventionally, by using the synchronous reference frame (SRF) representation, different linear and nonlinear control strategies have been proposed to improve the converter's dynamic performance. However, the achieved improvements cannot be objectively assessed due to the absence of a performance limit standard reference of the converter's dynamics. In this article, the theoretical minimum time solutions for three-phase converters in the SRF are derived and analyzed, providing an objective reference point for the system's dynamic performance evaluation. The normalized dynamic model of the converter in the SRF is derived and combined with the time-optimal control principle to find the theoretical minimum transient time solutions. The state-plane representation of these minimum time responses enables a straightforward and comprehensive interpretation of the converter's dynamic behavior, and it simplifies the derivation of closed-form expressions that characterize the minimum time transient parameters. The introduced analysis, minimum time dynamic responses, derived transient's expressions, and dynamic performance evaluation are validated by simulation and experimental results. [ABSTRACT FROM AUTHOR]

Wide-bandgap and silicon power semiconductor devices require advanced pulsewidth gate-driver capability to successfully convert power for high-performance operation. In this article, a simplified forward isolated resonant converter structure with an integrated planar transformer is proposed, a cost-effective solution which eliminates the need of an output filter inductor while rearranging the clamp circuit for reduced component ratings and voltage stress. The first design option uses a simple back-to-back Zener diode voltage clamp circuit for low-power dc–dc isolated power supply applications. The second design employs a lossless voltage-clamped converter with auxiliary energy-recovering winding with an application example for an isolated gate-driver power supply. Through analysis of the converter, the switching frequency has been selected in relationship to the transformer inductance and the equivalent circuit capacitance for the benefit of soft-switching power device transitions. The proposed resonant converter structure features an integrated planar transformer designed with a specific layer disposition to ensure low interwinding capacitance. The converter offers isolated supplies for a gate-driver power devices pair, such as half-bridge SiC devices. The simulation and experimental results are obtained from a gate-driver application platform to demonstrate the validity of the proposed isolated dc–dc converter design and integrated planar transformer with a total conversion efficiency of 87.7%. [ABSTRACT FROM AUTHOR]

Utility power lines voltage levels vary in different geographical locations, ranging from 208 to 480 Vrms. Power factor correction (PFC) converters are typically designed for a particular input voltage and do not accept a wide range of line voltages. This results in multiple product designs and revisions and increased production costs to accommodate the various ac voltage levels used around the world. A PFC converter capable of coping with a wide input voltage range, from 90 Vrms up to 530 Vrms, would significantly decrease costs and streamline development. In this article, an extended input voltage range PFC converter is proposed, which provides a high and almost flat efficiency curve throughout the entire operating voltage range with an 800 VDC bus voltage. The proposed converter has a flexible bridgeless structure with simple control, low-current ripples, low common mode noise, and startup inrush current handling capabilities. Theoretical analysis and waveforms are discussed and experimental results for a 2-kW prototype are given, thereby validating the expected behavior. The operation of the proposed extended input voltage range PFC converter is also compared to the traditional totem-pole PFC showing more than 1% efficiency improvements at full load and a higher power factor in the proposed design. [ABSTRACT FROM AUTHOR]

Fringing losses play a detrimental role in high-frequency transformers. The tendency toward higher power density and miniaturization of power converters leads to higher switching frequency and enforces the use of low-profile components such as gapped planar transformers. Due to the air gap, lower magnetizing inductance and better regulation of LLC (Lm, L2, Cs) can be achieved, but fringing fluxes can also be induced, resulting in extra magnetic losses and more hotspots. These losses are highly dependent on the frequency and the core material, so it is critical to model them for gapped planar transformers in LLC resonant converters, which operate at high frequencies and use ferrite material. In this article, fringing losses for gapped ferrite transformers in LLC converters are thoroughly modeled in order to provide a precise prediction regardless of the materials and core geometries. The proposed method provides an accurate and compact formula for predicting the fringing losses of planar transformers. This formula is obtained based on the finite-element method so as to consider and evaluate different design parameters. An LLC resonant converter with different planar transformers is implemented to show the compatibility of the proposed model. Experimental results show the higher accuracy of the proposed model compared to traditional ones and confirm that the proposed loss model can be applied to diverse core shapes. In addition, the gradient descent method is used to calibrate the theoretical and experimental results. Moreover, temperature deviations of the transformer due to the fringing losses are measured and evaluated both experimentally and theoretically to show the accuracy of the proposed loss formula. Due to the proposed model's higher accuracy, an improved design procedure for planar transformers is obtained, adding substantial value for design engineers. [ABSTRACT FROM AUTHOR]

In past years, LLC resonant converters have become a mainstream topology for dc–dc power conversion due to their advantages, such as the superior efficiency obtained with the soft switching of MOSFETs. In order to further improve the efficiency of the converter, synchronous rectification (SR) can be implemented as an alternative for diode rectification. As a result, the vast majority of the literature related to this field of study presents different LLC SR control algorithms, which aim to improve the operation of the rectification. Unlike prior work on SR controllers, this paper contributes to the area of power loss estimation using rectifier current equations (RCE). The developed method based on time-domain analysis of SR currents provides a new analytical framework to characterize the behavior of SR. Implications in SR power losses of different time delays are investigated using the developed loss estimation method. In addition, different converter design parameters, such as choice of inductance ratio, can be analyzed. The RCE captures the true discontinuous and complex behavior of SR, which is often oversimplified by the conventional first-harmonic approximation (FHA). As a result, the proposed method facilitates the design of LLC resonant converters and provides increased precision in SR power loss estimation when compared to FHA, and in a considerably faster fashion when compared with precise yet computationally intensive simulation software. This paper is validated with simulation and experimental results. [ABSTRACT FROM AUTHOR]

Boost-based converters are used in a variety of non-isolated step-up applications, such as power factor correctors, because of their simplicity. The power density of these converters can be increased in higher switching frequencies, which reduces the size of the magnetic elements. This increases the switching losses, but that can be solved by soft-switching techniques. This paper proposes a resonant bridgeless power factor correction converter that provides soft switching for all of the semiconductors. The proposed structure can provide zero voltage switching for the switches and zero current switching for the diodes. In the proposed structure, the input current is inherently sinusoidal with low total harmonic distortion, even with small inductances. Therefore, a high input power factor is achieved without requiring a current control loop in the circuit. This reduces the complexity of the control circuit. An experimental prototype has been constructed to investigate the validity of the claims. Experimental results show near-unity power factor, as well as $\text{2}\%$ efficiency improvement at full load when compared to a conventional interleaved boost converter with the same components. [ABSTRACT FROM AUTHOR]

Three-phase solar inverters can be operated with different modulation strategies such as sinusoidal pulsewidth modulation (SPWM), space vector modulation (SVM), and third-harmonic injection PWM (THIPWM). The selection of the modulation strategy can significantly affect photovoltaic (PV) leakage currents and power losses and compromise the inverter performance. This paper presents a detailed analysis of traditional and modified modulation effects on power semiconductor losses and PV leakage current. The research focuses on a three-phase three-level T-type neutral point clamped (3L-TNPC) solar inverter. A detailed exploration of traditional SPWM and SVM is presented, and a new modified modulation strategy referred to as two-triplen harmonic injection PWM (2THIPWM) is proposed, which can substitute the SVM scheme. Analytical expressions are derived for the proposed 2THIPWM strategy, which can be used for the SVM power-loss approximation. The comparison between 2THIPWM and SPWM shows a conduction-loss difference greater than the 5% normalized range. The modulation strategies are discussed with respect to the PV common mode current signature, and specific design techniques in modulation lead to reduced leakage currents for safety compliance. The theoretical and experimental results obtained using a 3L-TNPC solar inverter are presented to evaluate the modulation strategies and their impact on performance. [ABSTRACT FROM AUTHOR]

LLC resonant converters have gained popularity in a wide number of industrial applications due to their high efficiency and power density. Common applications of these converters are battery chargers, electric vehicles, and high-efficiency power supplies, which require tight output voltage regulations. However, traditional averaging techniques employed in pulse width modulation converters cannot be employed for LLCs. As a consequence, designing linear controllers for these types of converters requires complex analysis or applying empirical methods. This paper proposes a simple and straightforward methodology for designing linear controllers for LLC resonant converters. A dual-loop control scheme including an inner current loop and an outer voltage loop is introduced. A simplified second-order equivalent circuit is employed to derive all the relevant equations for designing the compensators. Simulations and experimental results using a 150-W platform are employed to validate the theoretical analysis. [ABSTRACT FROM AUTHOR]

In the past two decades, the operating voltage of photovoltaic (PV) installation has increased in order to reduce current ratings and system installation costs. Such a large number of PV panels in series (e.g., 1000–1500 V systems) lead to wide variations of PV voltage due undesirable effects such as shading, soiling/dust, aging, and hot surface temperature. A partial shade would normally shut down solar inverters, unless a boost stage is added to the system input to ensure a proper dc-link operating voltage for the inverter. A boost input stage can double the input voltage operating range to extract maximum power under any possible shading and temperature condition. In this paper, a new PV string boost topology arrangement is proposed in the form of a miniboost used for three-phase grid-connected converters. The string miniboost increases the dc voltage range to extend power extraction under shading and low irradiance conditions and only requires to process a fraction of the rated power. The proposed cost-effective solution is further improved by using the inverter peak power envelope at boundary operation, resulting in expanded energy extraction beyond existing techniques. A design procedure to optimally size the miniboost and the peak-power envelope is presented along with a comparative analysis, under different irradiance levels, to illustrate the advantages in energy extraction obtained with the proposed PV string miniboost solution under low voltage and boundary operation. Furthermore, improved efficiency operation schemes and issues of common-mode current are discussed, and three mitigation design techniques intended for three-phase, three-level inverter transformerless topology are presented. Simulations and experimental results using a dual miniboost dc–dc stage and three-phase three-level neutral point clamped inverter are presented to validate the proposed dc-bus extension range and system design. [ABSTRACT FROM AUTHOR]