Search

Ultrafast charging can help increase the adoption of battery electric vehicles (BEVs) as it solves the prime issues of range anxiety and long charging time. However, for conventional 400 V battery systems, these high charging currents can become infeasible due to cable limitations and thermal issues. Fortunately, 800 V systems can provide higher charging power capacity at lower current levels, better enabling ultrafast charging. The emerging shift to 800 V systems from 400 V systems requires careful design considerations for the on-board charger (OBC). This article fills a gap in the literature by performing a comprehensive review of state-of-the-art 800 V passenger BEV OBC topologies and control, focusing primarily on 1-phase topologies as the majority of residential charging connections are 1-phase. This article also reviews the main design challenges for 800 V OBCs and relevant industrial products, and provides a discussion of related future trends.

The modular multilevel converter (MMC) can integrate distributed energy systems (DES), such as a battery energy storage system, to expand its functionalities and carry out multiple simultaneous tasks. However, a DES induces power imbalances within the MMC, which affects the operating currents and voltages of the converter. This phenomenon has been partially covered in recent works, but an analytical analysis has not yet been carried out to see the behavior and implications in different MMC-DES applications. This article introduces a novel analytical analysis of the power imbalances between MMC clusters. It pioneers the development of general equations and imbalance capability metrics, enabling the assessment of maximum currents and voltages supported by the MMC clusters. The developed tools allow the evaluation of any MMC-DES application regarding the current and voltage rating requirements of MMC clusters. The analysis shows that the MMC operating mode can substantially restrain or enlarge its imbalance capacity, affecting its suitability for different DES applications. While it needs around 33% current overrating in the worst imbalances, under some operating modes it can reach most imbalances without requiring current overrating. The ac compensation mode is much more capable of achieving imbalances than the dc compensation mode, reaching 88.37% and 16.74% of the imbalance points, respectively, without requiring any overrating.

It is well-known that the accurate measurement of input voltage and current, as the feedforward and feedback terms, plays a crucial role in the nonlinear controller design for power factor compensation of an AC-DC boost converter. This paper addresses the problem of the simultaneous estimation of the input voltage and current from the output voltage in a full-bridge AC-DC boost converter. In the lossless model of the system, those variables are unobservable from the output voltage when the control input is zero. To overcome this, the system dynamics are immersed in a proper form by a new filtered transformation. The phase and amplitude of the input voltage, along with the input current, are globally estimated from the output voltage by a fifth-dimensional estimator. Unlike some existing results, the stability of the proposed estimator does not rely on a priori knowledge about the parasitic resistances and is guaranteed exponentially under the persistence of excitation conditions on the control signal. An application of the proposed estimator is presented in conjunction with a dynamic controller to form a sensorless control algorithm that does not require any sensor on the input side and controls the system only by the feedback from the output voltage. Processor-in-the-loop (PIL) studies conducted by OPAL-RT OP 5700 are used to assess the performances of the proposed estimator and controller.

An improved modulation method is proposed for two parallel three-level interleaved rectifiers to reduce current harmonics and high-frequency zero-sequence circulating current, which uses sinusoidal pulse width modulation. First, a model of the two parallel rectifiers is constructed, and the main factor affecting the line current performance and zero-sequence circulating current is discussed. Second, the current harmonics are the priority optimization target to guarantee better line current performance. Finally, an exchange of the large common-mode voltage between two converters is made to reduce the high frequency zero-sequence circulating current based on the low current harmonics. Performance comparisons between the proposed method and existing methods in terms of total current harmonics, zero-sequence circulating current value and switching loss are made in the experiment, which confirm the effectiveness of the proposed method.

LLC resonant converter is widely used due to its soft switching, high power density, and high efficiency. To incorporate the merits of the LLC resonant tank into a three-phase single-stage ac/dc converter, this article proposes a three-phase single-stage ac/dc converter based on Swiss rectifier and three-level LLC topology. It takes advantage of the high-efficiency Swiss rectifier to convert three-phase ac voltages into three variable dc voltages and interface a three-level LLC resonant circuit. With help of the LLC resonant tank, all the high-frequency three-level switches achieve soft switching. To both regulate the output voltage and achieve three-phase power factor correction, the frequency modulation in combination with the duty cycle control strategy is employed by splitting the resonant current into three parts and then forming three phase sinusoidal currents. The proposed converter's detailed operation principles, steady-state characteristics, and design considerations are given. Finally, a 10 kW experimental prototype with three-phase 220 Vac inputs and 500 Vdc output is built to verify the effectiveness and feasibility of the proposed topology and its control strategy. [ABSTRACT FROM AUTHOR]

This article proposes a planar magnetic integration technique that combines the grid inductors and transformer in the single-stage E-capless electric vehicle charger into one core. The proposed integration technique reduces the number of magnetic components; therefore, the cost, total magnetic core loss, and volume can be significantly reduced. Using the integrated structure, the overall converter power density increases up to 11.1% compared to the nonintegrated one. This article also presents a detailed analysis of the optimal printed circuit board (PCB) winding arrangement considering both ac resistance and winding stray capacitance. Due to the high dc resistance of PCB winding, Litz wire was also considered for the proposed integrated structure. The effectiveness of the proposed structure was validated by implementing it on a 3.7-kW prototype of a single-stage ac–dc converter. Results show that the prototype with the proposed integrated structure achieved higher efficiency with both PCB winding and Litz wire. Peak efficiency of 97.17% and 6.55-kW/L power density were achieved. [ABSTRACT FROM AUTHOR]

A dual three-phase active bridge (D3AB) power factor correction (PFC) rectifier features two dc ports, i.e., one on the primary side, which is not isolated from the mains, and the second, which is galvanically isolated dc port on the secondary side. A model for calculating the conducted electromagnetic interference (EMI) noise of a 7.5-kW D3AB PFC rectifier operating from a 400 V $_\mathrm{rms}$ line-to-line mains and generating dc output voltages of $V_{\mathrm{dc,1}} =$ 800 V and $V_{\mathrm{dc,2}} =$ 400 V is presented in this article. The EMI model takes into account the implications of the power levels provided at the primary- and secondary-side dc ports, i.e., $P_{1}$ and $P_{2}$ , respectively, on the conducted EMI noise and is used to design an EMI filter for a hardware prototype of the D3AB converter topology, which is volume-optimized for the considered specifications. The designed filter has a volume of $0.17\,\text{dm}^{3} = 10.\text{4}\;\text{ in}^{3}$ ($0.09\text{ dm}^{3} = 5.5\text{ in}^{3}$ for the differential mode filter and $0.08\text{ dm}^{3} = 4.9\text{ in}^{3}$ for the common mode filter part). As part of the experimental verification of the model, the conducted EMI noise of the hardware prototype is measured under two different workload scenarios, i.e., $P_{1} = \text{4}\;\text{ kW}$ , $P_{2} = \text{2.5}\;\text{ kW}$ and $P_{1} = 0$ , $P_{2} = 6.5\text{ kW}$. Measurements show that the level of conducted EMI noise increases with increasing load on the secondary side, which is consistent with the predictions of the noise model. The complete hardware prototype achieves sinusoidal mains currents with a power factor of $\lambda = 0.994$ and a total harmonic distortion of currents lower than $5.6\%$ at the considered loads and complies with the CISPR 11 class A quasi-peak conducted EMI limit. [ABSTRACT FROM AUTHOR]

This article presents full-bridge resonant ac/dc converter that minimizes switching loss over entire grid voltage cycle. By using the voltage fluctuation at T-type voltage doubler, the existing hard-switched components are turned-off with almost zero-voltage switching at high instantaneous output power and with less than half of the output voltage at low instantaneous output power. Moreover, no instantaneous reactive current flows through the circuit under wide variations of grid voltages and loads. Furthermore, the proposed converter has balanced loss distribution over the primary-side and secondary-side switches, which ensures high power transfer capability with improved overall switch utilization. A 1-kW prototype is developed and tested to demonstrate the circuit functionality. Finally, the efficiency improvement is investigated; comparisons show the benefit of the proposed converter over conventional converters that use unfolders. [ABSTRACT FROM AUTHOR]

This article presents a quasi-single-stage current-fed resonant ac–dc converter having improved heat distribution. Secondary-side switches are turned off with the voltage closed to zero at high instantaneous power and with the voltage closed to the half of the output voltage at low instantaneous power. Switching losses at the primary-side bottom switches are reduced; this change improves the heat distribution over the switches. The primary-side duty-cycle fixed at 0.5 results in negligible input current ripple; this trait can significantly reduce the size of filter inductor at the grid side. Experimental results show the effectiveness of the proposed ac–dc converter and its improved heat distribution against a conventional solution. [ABSTRACT FROM AUTHOR]

Grid impedance plays a significant role in the performance and design considerations of nonlinear devices like Variable Frequency Drive (VFD). VFD operates across domestic, industrial, and residential applications under different grid configurations and capacities including renewables. IEEE 519 standard recommends grid short circuit ratio and thereby grid impedance as an index for the individual and overall current harmonic performance of the connected utilities. This research investigation details a comprehensive approach for an online dynamic grid impedance estimation and may also give an insight into the hardware implementation within a VFD to achieve optimum performance and reliability during installation. A VFD of 250 kW is used for real-time measurements and simulation with varying grid configurations to determine grid impedance and lifetime of the DC capacitors. A fuzzy model is developed based on the established knowledge base for the estimation of the grid impedance of a generic grid. The fuzzy model is further enhanced to estimate the lifetime of the DC capacitor.

A recently introduced Dual Three-Phase Active Bridge Converter (D3ABC) provides two three-phase ac ports (ac${}_{1}$ and ac${}_{2}$), two dc ports (dc${}_{1}$ and dc${}_{2}$), and galvanic isolation between the ports ac${}_{1}$, dc${}_{1}$ (primary side) and ac${}_{2}$, dc${}_{2}$ (secondary side). Previously documented studies confirm that the D3ABC is generally capable of transferring power between all four ports. However, it has been found challenging to operate the converter if ac voltages with different line frequencies, $f_{1} \ne f_{2}$, are present at the ports ac${}_{1}$ and ac${}_{2}$. Such operation causes Low-Frequency (LF) power pulsations in the converter's dc links, leading to fluctuating dc link voltages and distorted phase currents. In this paper, a new duty-cycle dependent phase shift modulation scheme is proposed that eliminates such LF power pulsations and substantially increases the theoretical maximum transmittable power between primary and secondary sides compared to previous work. The new modulation scheme is developed on the basis of analytical considerations, which are supported by the results of numerical calculations, and verified by means of circuit simulations and experimental results. A hardware demonstrator originally designed for a rated power of $\text{8}\,$kW when operated from ac${}_{1}$ to dc${}_{2}$ at the European low-voltage ac mains ($V_{\mathrm{ac,1}} = \text{230}\,{\rm V}$ line-to-neutral rms, $V_{\mathrm{dc,1}} = \text{800}\,{\rm V}$, $V_{\mathrm{dc,2}} = \text{400}\,{\rm V}$) is used for experimental verification. Since the operation with $f_{1} \ne f_{2}$ leads to an increase of the currents in the converter, the experimental verification is conducted at half voltages and for a reduced power of $\text{2}\,$kW that is transferred from ac${}_{1}$ to ac${}_{2}$ at substantially different primary-side and secondary-side line frequencies of $f_{1} = \text{50}\,$Hz and $f_{2} = \text{77}\,$Hz. The measured results agree well with the simulated results. In particular, the dc link voltages show almost constant waveforms, which confirms the correct operation of the proposed modulation scheme.

Investigations of the dynamic behaviour of power electronic components integrated into electric networks require suitable and established simulation methodologies. Real-time simulation represents a frequently applied methodology for analyzing the steady-state and transient behavior of electric power systems. This work introduces a guideline on how to model power electronics converters in digital real time simulators, taking into account the trade-off between model accuracy and the required computation time. Based on this concept, possible execution approaches with respect to the usage of central processing unit and field-programmable gate array components are highlighted. Simulation test scenario, such as primary frequency regulation and low voltage ride through, have been performed and accuracy indices are discussed for each implemented real-time model and each test scenario, respectively. Finally, a run-time analysis of presented real-time setups is given and real-time simulation results are compared. This manuscript demonstrates important differences in real-time simulation modelling, providing useful guidelines for the decision making of power engineers.

Conventionally, the benchmark proportional-integral control method is implemented to realize power factor correction and output voltage regulation of single-phase ac/dc converters. However, the performance is deteriorated due to the influence of uncertainties and disturbances, e.g., periodic input voltage and load variation. Concerning this problem, this article proposes a model-free control (MFC) strategy of single-phase ac/dc converters. The MFC principle is revisited and a frequency response analysis is presented for the algebraic estimators of uncertainties and disturbances. Consequently, the closed-loop performance of MFC systems is allowed to be analyzed in frequency domain via classical linear control theory. Based on the theoretical results, the model-free current and voltage control systems are synthesized in detail to achieve control objectives of the converter. Simulation results demonstrate the performance of MFC systems in reference tracking and disturbance rejection. The feasibility and validity of the presented MFC strategy for single-phase boost ac/dc converters is also confirmed experimentally as compared to the benchmark scheme. [ABSTRACT FROM AUTHOR]

This article proposes a system, which comprises an isolated, nonresonant single-stage ac–dc converter with variable frequency control. One of the main contributions of this article is that the proposed system ensures a stable dc-link voltage independent of power flow, which improves the reliability of the system. Moreover, it eliminates the capacitor imbalance issue when using pulsewidth modulation control in bridgeless, nonresonant single-stage converters. Due to this, a minimal output capacitance is needed to regulate the output current in low output voltage applications tightly. The proposed system shows high flexibility in controlling the current waveforms, which enables soft switching for all turn-on instants of the switches. A new equivalent circuit is introduced to study the steady-state operation of the proposed system accurately. Experimental and simulation results are provided for a $250 \, \mathrm{W}$ prototype to demonstrate the superior performance of the proposed system. [ABSTRACT FROM AUTHOR]

For three-phase ac–dc converters, load disturbances, and parameter uncertainties cause large fluctuations of the dc-link voltage, even resulting in system instability. In order to cope with this problem, the disturbance observer-based finite-time control (DOFTC) is put forward in this article, where the finite-time disturbance observer is designed to fast and accurately estimate disturbances. Subsequently, the stability of the ac–dc converter closed-loop system is analyzed and theoretically proved. Finally, experimental results verify the effectiveness of the DOFTC strategy, where good dynamic and steady-state performance is achieved under load disturbance and parameter uncertainties. Compared with the enhanced state observer-based sliding mode control and adaptive control method, the proposed DOFTC method not only reduced the fluctuations of the dc-link voltage by at least 55% but also improved the transient response. [ABSTRACT FROM AUTHOR]

Since LLC converter is capable of naturally creating the soft-switching condition to improve the overall efficiency, it is widely used in dc–dc applications. Using LLC resonant tank to realize soft switching for three-phase ac–dc converters would be a very promising solution to high efficiency and low cost ac–dc conversion, an LLC-based three-phase single-stage ac–dc converter was configured by taking advantage of three-phase voltage feature $ u_{\mathrm a}$ + $ u_{\mathrm b}$ + $ u_{\mathrm c}$ = 0 and incorporating three bidirectional switches. Because of time-varying feature of three-phase voltages, the input voltage of the converter to the LLC resonant tank is no longer a symmetrical square wave, but a time-varying and asymmetrical three-level waveform, which makes the analysis of the resonant circuit behavior much complicated. Some traditional analysis methods, such as fundamental harmonic approximation and its variants, are impossible to deal with. To overcome this analysis obstacle, this article proposes a numerical analysis method to analyze the time-varying three-level LLC resonant tank for this converter. According to the monotonous change of LLC input voltage in one fundamental cycle, it calculates and determines the time durations of three phases and the corresponding operation modes in each switching cycle. And this numerical analysis method is used to calculate the numerical relationship between the two control variables (switching frequency $ f_{\mathrm s}$ and duty cycle $ D_{\mathrm M}$) of this converter and the voltage gain and power level, which is a guideline for the design of the resonant tank parameters and control strategy of the LLC-based three-phase single-stage ac–dc converter. Finally, the time-varying waveforms of $ f_{\mathrm s}$ and $ D_{\mathrm M}$ obtained by numerical calculation well match the PSIM simulation results, and a 3.3-kW three-phase 220Vac input and 48Vdc output prototype was built to verify the effectiveness of the proposed numerical analysis method and the feasibility of the control strategy. [ABSTRACT FROM AUTHOR]

A DC distribution system integrated with electric vehicle charging stations (EVCSs) is typically constructed to satisfy the large power exchange demand of electric vehicles (EVs). However, the stochastic operating state of the EVCSs results in difficulties in the stability analysis of the DC distribution system. In this study, a linearized model of the DC distribution system connected with multiple EVCSs is established, which considers the charging and the discharging states of the EVCSs. Based on the similarity transformation, this study theoretically verifies the generalized conclusion that a DC distribution system has a higher possibility of instability if the EVCSs are in the charging rather than the discharging state, and that the system stability is the worst if all the EVCSs operate at the maximum charging state. Moreover, a method to quickly evaluate the stability region of the DC distribution system is proposed. It can provide a numerical instability risk estimation of a complex DC distribution system considering all the possible states of the EVCSs. Lastly, the conclusions are validated by two SIMULINK cases, and the application of the numerical instability risk estimation to the DC distribution system is demonstrated. [ABSTRACT FROM AUTHOR]

Ground fault diagnosis is difficult to carry out in dc–ac systems due to the presence of power electronics. Additionally, it is common that neither relays could protect efficiently these systems as ac devices are not prepared to actuate under dc currents and vice versa. Previous studies were able to detect if the fault was in ac or dc but the faulty point still being incognita. This article presents a ground fault location method for the ac side of dc–ac systems that complements previous detection methods. It is based on a grounding resistor connected between the midpoint of the dc bus and ground. Then, an instantaneous voltage window record is analyzed into a histogram, obtaining two representative voltage peaks that are correlated. These values are the one with most repetitions and the one with most amplitude. Attending to a coefficient defined by these two parameters, the fault location can be estimated. The effectiveness of this method has been corroborated with simulations and experimental tests in a 140 kW dc–ac converter, achieving promising results. [ABSTRACT FROM AUTHOR]

This paper presents a reduced-stage three-phase isolated AC/DC converter topology used for auxiliary power units (APUs) in avionics and electric vehicle (EV) applications. Traditional two-stage cascaded AC/DC converters are widely used for these applications due to their ease of implementation and simple control schemes. With the objective of improving the power density of the APUs, the proposed converter achieves reduction in the number of active power devices along with a smaller DC link capacitance by implementing an unconventional structure with a bandpass filter, to allow only the required frequency components to transfer the rated power. To accurately characterize the proposed converter, a detailed formulation of the filter design for the circuit along with mathematical derivation of the control scheme is presented. In terms of achieving enhancement in the overall efficiency, a comparative study is presented that focusses on the conduction and switching losses incurred in the proposed topology as compared to the state of the art (SOA) two-stage AC/DC conversion topologies. The analyses portray efficiency improvement of 0.8% for a 6 kW rated load, with significant reduction in active device losses. Additionally, to support the formulations and derivations, simulation studies and experimental verifications are also presented. The results show an input power factor of 0.9918 (lagging) with a conversion efficiency of 97.6%, a tightly regulated output voltage with less than 1% peak-peak ripple and the input current total harmonic distortion (THD) of as low as 1.57%. [ABSTRACT FROM AUTHOR]

This article focuses on the dynamic optimization of the operating conditions of two types of ac–dc converters, a diode bridge rectifier and a full bridge active rectifier, which are used for interfacing regenerative rail vehicle suspensions based on ac electromagnetic generators. A theoretical analysis shows that, for both types of converters, the optimal operating conditions, leading to the maximization of the extracted power, can be predicted from the measurement of the generator speed. In particular, as regards the diode bridge rectifier, it is shown that the optimal value of the dc side voltage is related to the generator speed. As regards the active full-bridge rectifier, it is shown that a relationship exists between the optimal converter duty cycle and the generator speed. Experimental results validate the proposed theoretical models both in case of ideal constant generator speeds, and in case of more realistic time-variable generator speeds. The proposed analysis enables the design of high-performance speed-driven maximum power point tracking techniques for regenerative vehicle suspensions. [ABSTRACT FROM AUTHOR]

These days, demand for small volume and low cost of the home automation device is getting higher and higher. Converter with single-stage scheme has advantages of simple structure, low cost, and small theoretical volume, but it often suffers bad output accuracy in low output voltage applications. This brief proposes a constant voltage compensation circuit for AC/DC converters to improve the output accuracy which can also be used in a BUCK AC/DC converter with low output voltage. To verify the feasibility of the proposed compensation method, a BUCK controller based on the proposed circuit is implemented in Episil $0.5~\mu \text{m}$ /40V-HVCMOS process and occupies a die size of $0.99{\times }0.8$ mm2. By the help of the proposed circuit, the output accuracy of the prototype with single-stage structure, which has advantages of small volume and low cost, can reach as high as those converters with multi-stage structure. Test results show that the load regulation of the prototype is about 1.3% with 3.3V output and less than 0.9% with 5V and 12V outputs. [ABSTRACT FROM AUTHOR]

This article proposes a control system of a three-phase grid-connected power converter, operating in the rectifier mode, which achieves the unity power factor target, i.e., unbalanced and distorted current instead of sinusoidal one for grid voltage imbalance and harmonics. Such a target is known from active power filters control, but it has not been used for power supply devices yet. Thanks to that, the three-phase converter is seen as resistive load by the utility grid, and active power is consumed with minimal possible rms current, keeping current asymmetry corresponding to the voltage asymmetry during unbalanced dips. Intentional introduction of current harmonics is not trivial from the point of view of both reference signals calculation and control system structure, because in the classical approach, it would require resonant terms in controller structure. Additionally, grid voltage asymmetry introduces another oscillating component, which imposes other resonant terms in the controller. The transformation presented in this article allows to achieve desirable current harmonics and asymmetry with the use of two proportional-integral controllers, one in each controlled axis. This article presents theoretical principles of the new transformation, control system structure as well as simulation and experimental tests of a three-phase converter utilizing this idea. [ABSTRACT FROM AUTHOR]

This article proposes a bridgeless push–pull resonant ac–dc converter featuring naturally balanced switching loss at the primary side. The proposed converter employs a current-fed push–pull structure and two rectifier diodes at the primary side and a series resonance circuit at the secondary side. By incorporating two rectifier diodes, a diode bridge can be removed from the grid side of the proposed converter, and thereby that the number of components and primary-side conduction loss are reduced. One major advantage of the proposed converter is balanced loss distribution over one cycle of grid voltage, which guarantees high power transfer capability with enhanced overall switch utilization. The series-resonant circuit provides zero-current switching turn-off at the output diode, thereby reducing the reverse recovery loss. The operating principles and theoretical derivations of the converter are discussed in detail. The validity and performance of the proposed converter are verified using a prototype with 1.65 kW output power. [ABSTRACT FROM AUTHOR]

Ferroelectric Class II ceramic capacitors allow for highly compact converter realizations, but are showing relatively high losses for large-signal excitations which must be taken into account in the system dimensioning. Recent literature introduced the iGSE-CQ, a Steinmetz model based on the macroscopic capacitor Q-U hysteresis, allowing to accurately predict the losses of X7R capacitors. However, the model is specific for each single device, i.e., is insufficient to characterize losses in devices of the same series and manufacturer, which are employing the same dielectric material but with different voltage rating or nominal capacitance value. In this publication, based on basic physical properties we propose a new Steinmetz model, the iGSE-CX based on the relative dielectric material D-E hysteresis, which is applicable to all devices of a capacitor series. The iGSE-CX loss modeling technique is demonstrated for the TDK X7R, the TDK X7T, as well as the Knowles Syfer X7R series. Finally, the iGSE-CX is employed to estimate the large-signal losses of the capacitors of a three-phase inverter and shown to offer sufficient accuracy for a first power circuit design.

The increasing importance of cascaded multilevel converters (CMCs), and the sub-category of modular multilevel converters (MMCs), is illustrated by their wide use in high voltage DC connections and in static compensators. Research is being undertaken into the use of these complex pieces of hardware and software for a variety of grid support services, on top of fundamental frequency power injection, requiring improved control for non-traditional duties. To validate these results, small-scale laboratory hardware prototypes are often required. Such systems have been built by many research teams around the globe and are also increasingly commercially available. Few publications go into detail on the construction options for prototype CMCs, and there is a lack of information on both design considerations and lessons learned from the build process, which will hinder research and the best application of these important units. This paper reviews options, gives key examples from leading research teams, and summarizes knowledge gained in the development of test rigs to clarify design considerations when constructing laboratory-scale CMCs.

Triangular-current-mode (TCM) modulation guarantees zero-voltage-switching across the mains cycle in AC-DC power converters, eliminating hard-switching with a minor ${\approx} {30}{\%}$ penalty in conduction losses over the conventional continuous current mode (CCM) modulation scheme. TCM-operated converters, however, include a wide variation in both switching frequency and switched current across the mains cycle, complicating an analytical description of the key operating parameters to date. In this work, we derive an analytical description for the semiconductor bridge-leg losses in a TCM AC-DC converter, including the rms current and/or conduction losses, switching frequency, and switching losses. For SiC mosfets, we introduce a new loss model for switching losses under zero-voltage-switching, which we call “residual ZVS losses”. These losses include the constant $C_\text{oss}$ losses found in previous literature but must also add, we find, turn-off losses that occur at high switched currents. The existence and modeling of these turn-off losses, which are due to currents flowing through the Miller capacitance and raise the inner gate source voltage to the threshold level and accordingly limit the voltage slew rate, are validated on the IMZA65R027M1H 650V SiC mosfet. The complete loss model – and the promise of TCM for high power density and high efficiency – is validated on a 2.2 kW hardware bridge-leg demonstrator, which achieves a peak 99.6$\%$ semiconductor efficiency at full load. The proposed, fully-analytical model predicts bridge-leg losses with only 12$\%$ deviation at the nominal load, accurately including residual ZVS losses across load, modulation index, and external gate resistance.

This article presents a novel simplified method to implement the finite set - model predictive control technique for photovoltaic generation systems connected to the ac network. This method maintains the advantages of the conventional finite set - model predictive control, such as fast response, simple implementation, and easy understanding; but it also eliminates the use of a cost function and hence the weighting factors, instead, it finds the optimal operating state directly from the model and the discrete number of valid states of the converter. Although the proposed algorithm does not compute a cost function, it is able to select the inverter state that minimizes the tracking error by using a hexagonal convergence region. The main advantage of this technique is to reduce the computational cost in 43% of the algorithm that selects the best state, presenting a simple and complete algorithm without compromising the predictive control performance. The proposed algorithm properly operates under various conditions such as changes in the network frequency and changes in the system parameters.

Multicell converters, based on power cells that use low-voltage semiconductors, implement AC motor drives for medium-and high-voltage applications. These converters feature an input multipulse transformer, which performs low-frequency harmonics cancelation generated by three-phase diode rectifiers in the power cells. Despite this advantage, the multipulse transformer is bulky, heavy, expensive, and must be designed according to the number of power cells required by a specific case, limiting the modularity of the topology. This work proposes a multicell converter based on power cells that requires a standard input transformer and uses active front-end rectifiers controlled by employing a finite control set-model predictive control algorithm. The proposed approach emulates the multipulse transformer harmonic cancelation owing to the predictive algorithm operation combined with input current references that are phase-shifted for each active front-end rectifier. Simultaneously, the DC voltages of the power cells are regulated and equalized among the cells using PI regulators. Experimental results confirm the feasibility of the proposed system as input currents in each Multicell AFE rectifier with a unitary displacement factor, and a low THD of 1.87% was obtained. It is then possible to replace the input multipulse transformer with standard ones while reducing the copper losses, reducing the K factor, and extending the modularity of the power cell to the input transformer.

Designing an efficient, compact, and optimized electromagnetic interference (EMI) filter for the next generation high-frequency switched mode power converter while maintaining a small form factor with high power density, requires adequate research and development effort. This article presents a systematic as well as unified approach to design the EMI filter for any power electronic converter, particularly for three-phase ac–dc active boost rectifier systems. Since the differential mode (DM) filter stage consumes a major part of the EMI filter volume and weight, DM filter design optimization is a necessary yet challenging task to attain a higher power density. This article theoretically demonstrates the design steps for choosing the appropriate filter component values and number of filter stages to achieve the smallest volume of the DM EMI filter. Furthermore, to design an optimized common mode (CM) filter stage, a research effort has been made for estimation of the CM noise corner frequencies followed by multiconstraint volume optimization through a detailed mathematical noise modeling of the converter. While the validation of the proposed design methodology is done through MATLAB simulation, an experimental verification is also performed by designing the optimized EMI filter for a 2.3-kW proof of concept of a three-phase boost power factor correction converter to comply with the stringent EMI requirements of DO-160F standard. [ABSTRACT FROM AUTHOR]

In this article, analysis and design of a 3.3-kW isolated single-stage three-phase buck-type rectifier for aircraft applications is presented. The operating principle and modulation method of the proposed rectifier are introduced. The advantageous zero-voltage switching (ZVS) feature in all of the switching transitions is analyzed. A comparison with the VIENNA Rectifier III is done, being different both in the phase-leg implementation and the modulation sequence. A detailed rectifier design guideline is discussed and losses estimations are provided aiming at reaching 93.7% overall efficiency, including the EMI (electromagnetic interference) filter. Simulation waveforms are presented. Finally, experimental results obtained with the designed 3.3-kW hardware demonstrator are provided. The results verify achievement of ZVS in all of the switching transitions from full load down to 50% of nominal load, while exhibiting 1.9% THD $_I$ (total harmonic distortion) and 0.9996 PF (power factor) at nominal power, ultimately showing very good agreement to the simulation results. This article is accompanied by a video demonstrating experimental operation of the proposed rectifier at nominal input voltage, output voltage, and output power. [ABSTRACT FROM AUTHOR]

Figures-of-Merit (FOMs) are widely-used to compare power semiconductor materials and devices and to motivate research and development of new technology nodes. These material- and device-specific FOMs, however, fail to directly translate into quantifiable performance in a specific power electronics application. Here, we combine device performance with specific bridge-leg topologies to propose the extended FOM, or X-FOM, a Figure-of-Merit that quantifies bridge-leg performance in multi-level (ML) topologies and supports the quantitative comparison and optimization of topologies and power devices. To arrive at the proposed X-FOM, we revisit the fundamental scaling laws of the on-state resistance and output capacitance of power semiconductors to first propose a revised device-level semiconductor Figure-of-Merit (D-FOM). The D-FOM is then generalized to a multi-level topology with an arbitrary number of levels, output power, and input voltage, resulting in the X-FOM that quantitatively compares hard-switched semiconductor stage losses and filter stage requirements across different bridge-leg structures and numbers of levels, identifies the maximum achievable efficiency of the semiconductor stage, and determines the loss-optimal combination of semiconductor die area and switching frequency. To validate the new X-FOM and showcase its utility, we perform a case study on candidate bridge-leg structures for a three-phase 10 kW photovoltaic (PV) inverter, with the X-FOM showing that (a) the minimum hard-switching losses are an accurate approximation to predict the theoretically maximum achievable efficiency and relative performance between bridge-legs and (b) the 3-level bridge-leg outperforms the 2-level configuration, despite utilizing a SiC MOSFET with a lower D-FOM than in the 2-level case.

For three-phase AC-DC power conversion, the widely-used continuous current mode (CCM) modulation scheme results in relatively high semiconductor losses from hard-switching each device during half of the mains cycle. Triangular current mode (TCM) modulation, where the inductor current reverses polarity before turn-off, achieves zero-voltage-switching (ZVS) but at the expense of a wide switching frequency variation (15× for the three-phase design considered here), complicating filter design and compliance with EMI regulations. In this paper, we propose a new modulation scheme, sinusoidal triangular current mode (S-TCM), that achieves soft-switching, keeps the maximum switching frequency below the 150 kHz EMI regulatory band, and limits the switching frequency variation to only 3×. Under S-TCM, three specific modulation schemes are analyzed, and a loss-optimized weighting of the current bands across load is identified. The 2.2 kW S-TCM phase-leg hardware demonstrator achieves 99.7% semiconductor efficiency, with the semiconductor losses accurately analytically estimated within 10% (0.3 W). Relative to a CCM design, the required filter inductance is 6× lower, the inductor volume is 37% smaller, and the semiconductor losses are 55% smaller for a simultaneous improvement in power density and efficiency.

Renewable energy has gained significant attention of researchers in the last years, mainly due to the importance of using unlimited energy sources to supply homes, industries, cities and countries. In this context, this document focuses on the solar injection by employing a neutral point clamped (NPC) topology together with utilization of a maximum power point tracking (MPPT) and space vector modulation (SVM) techniques. Model predictive control (MPC) is employed to manage the currents and track their references. The proposed algorithms do not employ a cost function to decide which voltage to apply resulting in a spread frequency spectrum, and instead, a concentrated SVM spectrum is imposed. Notwithstanding, the DC link capacitors voltage balance is ensured and the computational burden is notably reduced as compared to traditional Finite Set Model Predictive Control (FS-MPC). Nevertheless, the consistent results are a consequence of the critical analysis that shows the feasibility of the proposal and guarantees the good performance of the entire system in simulated and experimental platforms.

At present, it is safe to say that the future belongs to sustainable technologies. Electric vehicles are one of the most representative sustainable solutions for mobility. Some of the many advantages they offer are a clean operation, a profit gain from a possible power return to the grid in vehicle to grid applications, grid power support, etc. As it is expected, an increase in the production of electric cars, and other battery-based systems, lead to an increment in battery chargers. Therefore, energy distributors must deal with many different schemes in the grid and with the amount of energy demanded from a fleet of cars and other electric vehicles. This paper deals with the modeling of AC/DC battery chargers by identifying the transfer functions in any operating condition without knowing the specific details inside those chargers. This approach is called black-box modeling and the strategy is based on the information provided by the input and output variables of the charger. The research illustrates the flexibility of the model to work with single-phase and three-phase AC/DC chargers which are linked to on-board and off-board charging stations. An extensive set of tests is shown, verifying the accuracy of the proposed models in a wide variety of operating conditions.

This article is concerned with the design of a finite-time disturbance-observer-based integral terminal sliding mode controller for the effective performance of three-phase synchronous rectifiers. The proposed control technique is developed based on the conventional synchronous reference frame model of the three-phase grid-connected converter, and the system dynamics is described in terms of a time-varying non-linear state equation. The variation of DC-load is considered as a disturbance. Therefore, a combination of a fast disturbance observer and an integral terminal sliding mode controller is utilized to produce the reference value of the direct axis for the current control loop. In this research, by employing Lyapunov stability theorem in the theoretical analysis and by numerical simulations, it is confirmed that the proposed closed-loop system is stable and the states converge to desired values in finite time even in the presence of load disturbance and control input saturation. The integral terminal sliding mode controller is utilized to maintain a robust performance along with a faster response of the converter. In order to demonstrate the performance ability of the proposed control scheme under real condition, an AC power source, impregnated with low order harmonics, is assumed. A real-time laboratory setup of the synchronous rectifier has been developed successfully, and the effective performance of the proposed control technique is fully proven.

The Swiss-type rectifier (SR) uses harmonic injection circuit and two dc–dc converters to help three-phase uncontrolled rectifier bridge to achieve better power factor correction (PFC). By applying the full-bridge topology to the dc structure, both the soft switching and the high-frequency galvanic isolation can be achieved. However, two full-bridge structures are required to realize the PFC principle of SR. That means the current flows through at least four switches and two transformers during the power conduction or freewheeling period. There are improvements in both conduction loss and core utilization. Thus, an optimized single-stage isolated Swiss-type ac/dc converter based on a single full-bridge with midpoint-clamper is proposed. Only one full-bridge structure is used to improve the conduction loss and core utilization. Two bidirectional voltage clampers are used to implement the PFC principle of the SR. The performance of the proposed converter has been verified by experiments. A total of 95.4% efficiency under half rated power and 5% input current THD under rated power have been achieved under a 10-kW 380 Vac input/400 Vdc output prototype with 90 kHz switching frequency. [ABSTRACT FROM AUTHOR]

This article presents a reduced-order generalized proportional-integral observer based resonant super-twisting sliding mode controller (RST-SMC) for the three-phase ac–dc converters. On the contrary to utilizing the proportional-integral controller in regulating the dc-link voltage, which may cause large undershoot/overshoot under the disturbance, the proposed voltage control strategy for the dc-link has high disturbance rejection ability and the settling time has been greatly reduced. In addition, the proposed RST-SMC in the current control loop not only preserve the merits of the sliding mode controller but also achieve the current tracking without steady-state error in the stationary αβ frame. The effectiveness of the proposed method has been verified by a lab-constructed experimental prototype. [ABSTRACT FROM AUTHOR]

This paper presents a unified power flow algorithm for large and complex mixed ac/dc power systems based on the partitioning of power grids, a version of the two-level Newton method, and the modified nodal analysis formulation. Partitioning significantly increases numerical efficiency without altering the accuracy of the power flow solution. This approach can be applied to any combination of multiple dc and possibly non-synchronized ac systems. It considers the steady-state interaction of ac and dc systems for a wide range of converter representations and control functions. Simplification of elements within the converter stations is not required. Both dc and ac-side converter losses are adequately accounted for by using a generalized converter loss model. The steady-state converter equations are derived in their most general form, with the ac and/or dc-side power exchange or voltages defined as controlled quantities. [ABSTRACT FROM AUTHOR]

A high-frequency link three-phase ac/dc converter based on matrix converter is widely studied because of its small size of passive components, and some modulation methods have been proposed. However, these methods have not achieved zero-voltage-switching (ZVS) and sinusoidal line currents under bidirectional operation with PQ control. This article presents a new modulation method to realize ZVS and sinusoidal line currents under bidirectional operation by accurate control parameters (duty cycle and phase shift) for high-frequency link bidirectional three-phase ac/dc dual-active-bridge (DAB) converter. The converter can realize ZVS by phase-shift-modulation similarly to the dc/dc DAB converter. The line currents have nonlinear characteristics to phase shift and duty cycle. Therefore, the proposed method uses a nonlinear mathematical model to determine the accurate duty cycle and phase shift in order to realize sinusoidal line currents. The accurate duty cycle and phase shift are determined by real-time numerical calculation. Experimental results employing a 1-kW laboratory prototype verify the capability to control active and reactive power with sinusoidal line current. It is confirmed that the proposed method can realize the sinusoidal line current with total harmonic distortion of less than 4% under the bidirectional operating condition at the rated power. [ABSTRACT FROM AUTHOR]

With the development of electrified railway, harmonic resonance accidents occur from time to time. Based on the mechanism of resonance, a harmonic resonance suppression radical method by impedance reshaping is proposed. Thus, the equivalent impedance of the train position is significantly reduced. Compared with the traditional method of improving harmonic current, this method of impedance reshaping can not only suppress the resonance caused by its own harmonic, but also suppress the resonance caused by other trains or other unknown harmonic sources. Harmonic impedance of the train in the resonant frequency is reshaped by detecting the resonance voltage and controlling the auxiliary converter harmonic current. The resonance identification and parameter settings of the impedance reshaping control are also discussed. The proposed harmonic resonance suppression strategy is fully tested with an auxiliary converter control in a simulation trains-network system model. The performance of the proposed strategy is further evaluated on the experimental platform. Both the results verify the effectiveness and feasibility of the proposed strategy. The application of SiC devices makes it effective to suppress the resonance of thousands of hertz. The experiment was validated in two cases. One is the resonance caused by the harmonic current of the train itself. The second is the resonance caused by the harmonic current of trains in other locations. In both cases, the train using impedance reshaping method can ensure that the resonance of its position is effectively suppressed.

This paper covers the theoretical background as well as chosen selected experimental results obtained for two AC current generators connected to voltage source inverters working in parallel. Inverters were connected in parallel via their intermediate direct current circuits by means of auctioneering diodes which select higher voltage source, and then directly to a DC power network. The selected real-time control algorithm for a digital signal processor and a field programmable gate array was used to achieve the proper excitation of two different types of alternators: a squirrel-cage generator denoted as and a self-excited synchronous generator. Another task for the excitation system was to maintain the proper level of direct current link voltage and stable power distribution between both generators rotating at changing speeds. The windings of alternators were fed with the use of so-called machine side inverters. The asynchronous generator was a voltage source inverter driven with the use of a sensorless multiscalar algorithm based on the current machine model, whereas the self-excited synchronous generator worked on the field oriented control principle. To prove the robustness of the chosen algorithm, different types of load were applied while during the parallel work of the generators and inverters.

Two new three-phase high-power-factor rectifiers using an interleaved discontinuous conduction mode (DCM) boost converters in a three-level configuration are proposed in this paper. The input currents waveforms follow the input voltages waveforms without a current control loop and the input currents present low current ripple without additional input filter due to the interleaved operation. The main advantage of the proposed rectifiers is the low voltage stress with the voltage applied across all semiconductors and output filter capacitors lower than the output voltage. A high gain rectifier version is presented in a hybrid configuration, including resonant voltage multiplier cell. The structures use only two active switches and current sensors and current control loops are not necessary, becoming a possible solution for low power and low cost applications. The low voltage stress operation and the reduction of the switch current stress due to the interleaved operation allows the reduction of the switches conduction losses of the DCM operation. The experimental results obtained from two prototypes are presented and efficiency equal to 97.26% is obtained for the three-level converter (Vi = 127 V/P = 2 kW) and 94% for the hybrid configuration (Vi = 64 V/P = 1 kW).

This article proposes a unidirectional cascaded topology of a power rectifier. It is composed of a three-leg cell with half-controlled legs series connected with one H-bridge cell per phase. The dc links of the H-bridge cells operate with floating capacitors. The floating capacitor voltages regulation is solved by means of the common-mode voltage manipulation. Control and pulsewidth modulation strategies are presented to regulate the capacitor voltages and grid currents. The design of passive elements is also shown. The topology has its harmonic distortion content, semiconductor losses, and average switching frequency values compared to those of conventional solutions. Experimental results validate the proposed topology and strategy. [ABSTRACT FROM AUTHOR]

In this research article, new investigation and comprehensive analysis is done on the current distortion effects of dc link inductor and capacitor in variable frequency drive (VFD). Shunt active filter (SAF) is the most prominent solution for harmonic mitigation at the point of common coupling in the power distribution system. However, SAF connectivity reduces the grid impedance (ZTH) seen at the input of six pulse diode bridge rectifier in VFD. Commutation behavior of the diode rectifier is changed due to this grid impedance variation resulting in increased harmonic current distortion (THDi) at the input of the rectifier bridge. This effect increases the ripple current of dc capacitor, dc link inductor losses, and diode rectifier conduction losses. This study investigates the drive dc link inductor and capacitor lifetime reduction with and without SAF, under various grid operating conditions of 3% voltage unbalance and 8% predistortion. Moreover, the high frequency (2–9 kHz) impact on dc link inductor core and copper losses is detailed. A 250 kW VFD with SAF of 180 A capacity is used for test measurement under various operating conditions. Current distortion effects are analyzed, and test results are compared with MATLAB simulation. Grid impedance variation due to SAF and its effect on the reliability of the VFD front-end components were not covered in detail in any of the earlier research. Lifetime estimation of dc link inductor and capacitor due to grid impedance variation is one among the significant outcomes of this investigation. [ABSTRACT FROM AUTHOR]

RMS current load is one of the most important design criteria for the dc-link capacitors of voltage source converters. In the literature, determination of this rms current load is well documented for state-of-the-art modulation schemes, such as space vector modulation. But the methods presented cannot be applied for direct current control algorithms. Therefore, this article introduces a new approach especially for direct current controllers, which reflects and compares to the state-of-the-art calculation method for space vector modulation. As direct current control is a feedback control, no closed-form solution can be given. Instead, the dc-link capacitor rms current load is determined by an iterative calculation scheme as a function of the modulation level and the phase angle. Although the scheme presented is applied to a three-phase two-level voltage source converter, it can be adapted to any voltage source converter topology. An example is presented applying the calculation method to one specific direct current control algorithm. The calculated results are verified via a digital simulation model as well as test bench measurements showing good correlation. For correct comparison, different effects are considered and discussed between simulation, calculation, and measurement results. These contain transients, the commutation process between insulated gate bipolar transistor (IGBT) and diode, the current-dependent voltage drop of the semiconductors, and the stationary current error of the hysteresis control. The dc-link capacitor current load for space vector modulation is calculated analytically as a reference by using the state-of-the-art method. The comparison of results obtained in this article and the reference are very similar, which is discussed in the conclusion. [ABSTRACT FROM AUTHOR]

Due to the large relative permittivity of Class II dielectrics, ceramic capacitors (CCs) from these materials promise significant volume and weight reductions in inverter and rectifier sine-wave filters, and are especially attractive in mobile applications that demand ultrahigh power density. While previous literature found large low-frequency losses in these components, no extensible loss model was proposed to accurately characterize these ferroelectric losses. In this article, we take advantage of prior art on ferromagnetic components in power electronics to propose a Steinmetz parameter-based loss modeling approach for X7R CCs, named the Improved Generalized Steinmetz Equation for CCs, or iGSE-C. This model is verified using the Sawyer–Tower circuit to measure losses in a commercially available X7R capacitor across excitation magnitude, dc bias, temperature, excitation frequency, and harmonic injection. Losses are shown to scale according to a power law with charge, with the resulting Steinmetz coefficients valid across dc bias and slightly varying as the temperature is increased. The iGSE-C accurately predicts losses for typical nonsinusoidal phase voltage waveforms with an error under 8%. Finally, the loss modeling technique is demonstrated for the sine-wave output filter of a bridge-leg arrangement with both low- and high-frequency excitations, with total capacitor losses predicted within 12% accuracy. [ABSTRACT FROM AUTHOR]

This letter proposes a half-bridge bidirectional isolated matrix-based ac/dc converter for compact ac/dc power conversion applications. The converter can control not only the dc voltage or current, but also the power factor of the ac current with a single conversion stage, which helps to achieve a higher power density with a lower complexity. The converter operates with zero-voltage switching or zero-current switching in all switches. Hence, the switching frequency of the converter can be increased higher, leading to smaller passive components. Besides the simple circuit, the modulation scheme derived from time domain analyses is also easy to implement. The proposed topology has been verified by experimental results for a 2-kW SiC-based prototype. A high efficiency of 96.8% was achieved at a full load condition. The current total harmonic distortion (THD) is lower than 4% and the power density is 1.8 kW/dm3. [ABSTRACT FROM AUTHOR]

In this article, an ac/dc converter based on the stacked boost circuit and dual-mode LLC circuit is proposed. In the power factor correction (PFC) part, two boost circuits are stacked to halve the input voltage and the inductor can be shared. The stacked boost circuit can achieve PFC and soft-switching characteristics with open-loop control with the complementary driving signal. In the dc/dc part, a dual-mode LLC circuit is adopted based on two stacked half-bridge structure. The proposed ac/dc converter can be utilized in wide input voltage variation conditions. A prototype is proposed in the laboratory and the experimental results verify the feasibility of the proposed converter. [ABSTRACT FROM AUTHOR]

When not all the converters are enabled in a parallel ac/dc power conversion system, some current flows through the disabled converters. This current not only distorts the current waveform of the ac side but also causes extra loss and unintended power flow from the ac to the dc side. In this article, the reason for this current flow is identified, and the total current according to the number of paralleled converters and its operating conditions are analyzed. A new pulsewidth modulation (PWM) method is proposed to minimize the current. And, the zero-sequence voltage and the consequent current flowing through the disabled converters under the proposed PWM method are compared to those under the conventional PWM methods. As a result, it was identified that discontinuous space vector PWM (DPWM) is not a proper PWM method because it causes a large current at some operating conditions. According to both simulation and experimental results, the magnitude of the current flows through disabled converters under the proposed PWM was about 40% less than that under sine PWM and DPWM, and it was about 10% less than that under continuous space vector PWM. [ABSTRACT FROM AUTHOR]

This article presents a modular low current ripple electrolysis power supply topology based on multiphase high-frequency inverter and its control method. The topology of the electrolysis power supply consists of ac–dc converter and dc–dc converter. Among them, the dc–dc converter is composed of a plurality of modular small-capacity dc–dc conversion modules connected in parallel. Each dc–dc conversion module is composed of a half-bridge high-frequency inverter and a full-wave rectifier. By controlling the output voltage of the high-frequency inverter in each dc–dc conversion module and staggering the equal phase angle in sequence, the low-frequency harmonic components in the dc voltage at the output terminals of multiple dc–dc conversion modules are eliminated. Finally, simulation and experimental results show that the proposed electrolysis power supply can provide low ripple current for the load, which provides technical guarantee for the production of high-quality electrolytic copper foil. [ABSTRACT FROM AUTHOR]