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Accurate and timely fault diagnosis of the rotating rectifier for a wound-rotor synchronous starter/generator is of great importance to improve system reliability. In the generation mode of the system, there is one idle stator winding of the main exciter. The terminal voltage characteristic of the idle stator winding is analyzed, and a novel fault diagnosis method for the rotating rectifier in the generation mode of the system is proposed. In this method, two feature voltages, namely, the maximum peak voltage and any other peak voltage of the idle stator winding terminal voltage are extracted through voltage sequence reconstruction to calculate the feature ratio for fault detection. The corresponding rotor position obtained by an inherent position sensor where the maximum peak voltage occurs is collected to determine the faulty diode location. The experimental results verify the feasibility and effectiveness of the proposed fault diagnosis method.

To utilize the full potential of the direct matrix converter (DMC) and improve the output waveform quality, a three-level output strategy for conventional 3 × N ( N ≥3) DMCs is presented, where three-level output voltages are achieved without any changes in the topology. In this developed strategy, the DMC is treated as a two-stage converter that consists of a fictitious rectifier and a neutral-point clamped (NPC) three-level inverter. By applying a phase-shifted carrier modulation strategy to the rectifier and a modified carrier-based double-signal pulsewidth modulation strategy to the NPC inverter, sinusoidal input and output, reduced switching losses, and controllable input power factors are achieved in conventional 3 × N DMCs. The developed three-level output strategy improves output waveform quality while sacrificing input performance to some extent. Finally, the effectiveness of the developed strategy is verified by both simulations and experimental results.

This paper presents general modeling approaches to achieve accurate real-time simulation of high switching frequency converters. The proposed methods are based on the direct mapped method (DMM) and make use of decoupling techniques when appropriate. The DMM links state variables to diode statuses and provides an exact and noniterative solution to network equations. An electric vehicle battery charger (EVBC) test case comprised of a full bridge rectifier, an interleaved boost, and a three-phase LLC is used to demonstrate the high accuracy achieved by the proposed methods compared to a conventional approach. FPGA implementations are proposed and shown to achieve from 75 ns to 175ns real-time simulation time-steps for this test case circuit, allowing its accurate simulation while switched at 200 kHz. To further validate the effectiveness of the FPGA-based simulator, a resonant boost converter is also implemented and simulated in real-time.

This paper proposes a primary-side linear control strategy to realize the constant current (CC)/voltage (CV) charging for the wireless power transfer (WPT) system, based on the LCC-N circuit. Different from the conventional compensation topology used in control strategies, this paper combines magnetic integration structure on the primary side and non-compensation topology on the secondary side. Firstly, the LCC-N magnetic integration and non-compensation topology is introduced. An improved parameters identification method considering the non-pure resistive input impedance characteristics of the rectifier is proposed to identify the current, voltage and equivalent resistance of the load, based on the LCC-N topology. In the process of identification, the relationship between the input impedance of the rectifier and the load is needless. Then, according to the LCC-N output characteristics and identified load parameters, the relationship between the input voltage and load current and voltage is simplified to linear through the linear superposition of fundamental wave and third harmonic. A linear control strategy on the primary side is proposed to achieve CC/CV output. Finally, a 1 kW WPT prototype is built. The experimental results show that the maximum error of the output current and voltage are 1.8% and 1.2% during the CC and CV charging, respectively.

This paper proposes digitally controlled power management circuit (PMC) for vibration energy harvesting in vehicle suspension system. The PMC is tested with a mechanical motion rectifier based electromagnetic energy harvester that converts from bi-directional vibration to unidirectional rotation, with improved energy harvesting performance and efficiency. Topology of one-stage DC-DC converter is adapted, and it is digitally controlled while considering the uncertainty of vibration sources. In order to efficiently transfer the harvested power to the electrical load, the algorithm of digital controller is designed to have four operation modes, which are impedance matching mode, voltage regulation mode, generator protection mode, and low power mode, for increasing the PMC efficiency while reducing the power consumption of controller. Experimental results show that proposed circuit can successfully operate and switch between the four operation modes. In the evaluation of PMC performance with 2mm and 2Hz excitation, the efficiency of proposed one-stage power converter is 86%. The total power consumption of controller in active mode and low power mode are 109 mW and 2.52 mW respectively while harvesting about 3W vibration energy.

With the rapid and extensive development of wireless communication and low power electronics, electromagnetic wireless power harvesting (WPH) draws more and more attention. As the core component for RF-to-DC power conversion, its characteristics determine the performance of the overall system. To obtain as much DC energy as possible, ambient electromagnetic energy with various frequencies should be efficiently rectified. Therefore, its important to widen the operating bandwidth of the rectifier. According to the theoretical analysis of the Schottky diode, it can be found that if the harmonic components generated by the diode can be fed back through a specific approach for rectifying, the bandwidth of the rectifier will be effectively improved. Therefore, a broadband rectifier has been proposed based on the previous principle. For validation, a wideband rectifier based on Schottky diode SMS7630 had been designed, fabricated and measured. When the input power level is 0 dBm, the conversion efficiency of the implemented rectifier is larger than 40% from 0.4 GHz to 2.6 GHz within a relative bandwidth of 146.67%, exhibiting an ultra-wide bandwidth compared with existing state-of-the-art configurations.

This article presents an interleaved boost rectifier for power factor correction (PFC) that operate in the continuous conduction mode (CCM) and is grounded on the switching cell with switching frequency modulation (SC-SFM). The input current naturally follows the shape of the input voltage, which is a resistive input characteristic (voltage follower). In the proposed converter, only one output voltage control loop is required. Moreover, the proposed topology has a wide range of soft commutation and no reverse recovery when the diodes block. This article presents the operating principle, a mathematical analysis of the converter, and four topological variations. In addition, experimental results of a 1-kW rectifier prototype with four different switch technologies (MOSFET, CoolMOS, SiC and IGBT), are discussed and their operational characteristics are demonstrated.

In this paper, a novel zero-voltage switching (ZVS) full-bridge converter is proposed to overcome the disadvantages of traditional phase-shifted full-bridge (PSFB) converter. In the proposed converter, a half-bridge (HB) converter with center-tap rectifier (CTR) is integrated into the traditional PSFB converter by sharing the lagging-leg switches and output filter. The HB converter operates with full duty cycle to ensure continuous energy transmission and the output voltage is regulated by adjusting the phase-shifted time of FB converter. The proposed converter has many advantages such as reduced filter requirement, wide ZVS range and low primary circulating current. In addition, the rectifier in the proposed converter is composed of a full-bridge rectifier (FBR) section and a CTR section. This feature makes the proposed converter well appropriate for the medium output voltage applications. Key operation principle and characteristics are fully discussed in this paper. The effectiveness of proposed converter is verified using a 1.2-kW prototype circuit with 280 V input voltage and 60-120 V output voltage.

Traditional wireless power transfer (WPT) systems usually adopt the triple-phase-shift (TPS) control method to maintain a constant output voltage, track the maximum system efficiency point (MEPT), and achieve zero-voltage-switching (ZVS) operation for various applications. However, these three targets are achieved at the cost of high reactive power on both primary and secondary sides, especially under light-load conditions, leading to low efficiency. This has become one of the challenges that hinder a further deployment of WPT technologies in practice. To address this vital problem, in this paper, how the reactive power lowers the system efficiency is revealed based on a mathematical model established. Then, a hybrid modulation control strategy based on a proper selection between the full-bridge and half-bridge modes of the inverter and active rectifier is developed. Besides, a detailed analysis of the switching boundary, i.e., selecting full-bridge or half-bridge, is provided. Finally, an experimental prototype is constructed to verify the effectiveness of the proposed control method. Experimental results show that the proposed method can reduce the reactive power, maintain a constant output voltage, and realize the MEPT and ZVS operation, with high efficiencies up to 94.29% in a wide load range.

The hybrid LCC/VSC cascaded HVDC (HC-HVDC) scheme, in which the LCC is adopted as rectifier, and one LCC in series with multiple paralleled VSC based MMCs is adopted as inverter, combines the advantages of both LCC and VSC-MMC technologies. Presently, a HC-HVDC project is planned to deliver the power from Baihetan to Jiangsu in China. One of the major challenges is to suppress the DC overcurrent issue of VSC-MMCs especially under commutation failure condition of LCC at inverter side. Based on Baihetan-Jiangsu project under construction, the model of HC-HVDC system is developed in PSCAD/EMTDC. In the system, the rectifier employs a dual 12-pulse LCC, while the inverter adopts a hybrid scheme, i.e., one LCC converter in series with three paralleled VSC-MMC converters. This paper addresses the main cause and feature of the DC overcurrent, then proposes an overcurrent suppression control method for HC-HVDC system based on fuzzy clustering and identification approach. And the system transient performances with the proposed control approach are evaluated under AC fault conditions. The results show that the proposed approach can not only suppress the DC overcurrent following the commutation failure to a certain extent, but also improve the post-fault recovery performance of the overall system.

The existence of inrush current poses a significant problem during the start-up process within three-phase voltage-source rectifiers. To address this problem, this study proposes a strategy to suppress the inrush current effectively based on the virtual-resistor- control method, while preventing the increase in cost of the system and complexity of the algorithm. First, a mathematical model is established based on the dq coordinate frame, and the primary cause of the inrush current is analyzed. Then, the design process of the virtual-resistor-control method is detailed. Finally, the accuracy and effectiveness of the proposed method are verified by simulations and experiments. The results show that the inrush current can be more than two times the rated current before the addition of the virtual resistor. The start-up process can be realized without the inrush current after the addition of the virtual resistor, it does not need to increase hardware costs, there is no secondary inrush current, and the sensitivity of the parameters and the complexity of control are low.

In this paper, a series-series wireless power transfer (WPT) system combined with an inverse coupled current-doubler rectifier (ICCDR) is proposed, as a very appropriate WPT topology for high current applications. The ICCDR uses an autotransformer to reduce the losses on the rectifier stage, which is suitable for high current low voltage output applications. Furthermore, a comprehensive comparison between the proposed WPT system with ICCDR and the traditional WPT system with diode rectifier is presented. In the proposed WPT system, the primary parameter configuration and circuit behavior keep the same, while the secondary side altered, contributing to a volume reduction on the resonant capacitor. The system overall efficiency and power density are improved significantly. Accordingly, a 10kW 400V/48V WPT prototype for battery charging is constructed and tested to validate this proposal. The output voltage is in the range between 38 Vdc and 55 Vdc, and the rated output current is 200A. The overall efficiency of the proposed system reaches 94%, improving 2% efficiency with 220W energy saving with respect to the traditional diode-rectifier system, when 9.5kW output power is delivered. Theoretical analysis and experimental results have verified that the proposed system shows great advantages in high power WPT applications.

As for bidirectional LLC converter, conventional pulse frequency modulation is typically adopted in the reverse mode resulting in a low voltage gain of reverse LLC. Then the bus voltage may be lower than peak grid voltage, which causes the buck-type inverter cannot output 220 Vac and poses series challenge for bidirectional operation. A bidirectional synchronous / asynchronous rectifier control is proposed for wide battery voltage applications in LLC converter. In the forward mode, the secondary-side switching devices are regulated as synchronous rectifiers (SRs) and a simplified model is built to calculate the SR on-time. In the reverse mode, with the same conduction time, the turn-on instants of primary-side and secondary-side switches are asynchronous and controlled with a delay angle. The proposed control not only achieves the forward LLC SR function with low microcontroller calculation resources, but also helps the reverse LLC obtain high voltage gain. A 6.6-kW SiC bidirectional LLC charger was built. By using the proposed control, the forward LLC efficiency improves 0.2% compared to conventional SR method. In the reverse mode, the LLC voltage gain is up to 1.33 so that the charger can output 220 Vac in the wide battery voltage range of 200 V~500 V.

During the typical constant current (CC) charging process, the supercapacitor has a pretty wide-range load variation. However, an inductive power transfer (IPT) converter can only maintain high efficiency within a certain load range around its optimum load point. Once the supercapacitor load resistance is far away from the optimum point, which usually happens in low charging power levels, i.e., the smaller load resistances, the IPT converter will suffer from the dramatic efficiency degradation and thus a step-up load transformation is required throughout the whole charging process. In this paper, a novel current-controlled semi-active rectifier (CCSAR) based IPT converter is proposed to fulfill this requirement. The characteristic of step-up load transformation is firstly identified and implemented by controlling the conduction angle of the CCSAR to enhance the efficiency in the charging process. The desired charging CC is then regulated by tuning the operating frequency of the IPT inverter. To coordinate these two objectives, a bivariate control is adopted here to achieve fast, direct and precise current output with enhanced efficiency performance over the whole load range during the CC charging process. Finally, experiment results validate the theoretical analysis well.

Nowadays, the scale of power grid is remarkably increasing and there is a continuous reinforcement of AC–DC hybrid systems. Thus, the single-phase grounding fault currents on the AC grid-side of rectifier and inverter stations increase significantly, which may exceed the capacity limit of the circuit breakers. The large short-circuit currents would result in problems during equipment selection and threaten the safety of equipment and personnel. To solve such issue, the effect of the converter transformer on the single-phase grounding fault current on the grid-side is analyzed. The mechanism of high short-circuit current in DC near region is revealed. Also, the feasibility of neutral point earthing via small reactor at HVDC converter transformer to suppressing the single-phase grounding fault current is verified. In addition, the principle of selecting the suitable small reactor is summarized. The results show that the neutral point earthing via small reactor at converter transformer can effectively limit the single-phase grounding fault current on the AC-side. However, it would lead to an increase of overvoltage at the neutral point of HVDC transformer. Therefore, neutral grounding by small reactor might be implemented when the insulation level is satisfied.

Vibration energy harvesting using multiple piezoelectric transducers (multi-PZTs) can increase its output power and environmental adaptability. At present, there are still few researches on multi-input interface circuits for multi-PZTs, especially those using the parallel synchronized switching harvesting on inductor (PSSHI) technique. Therefore, this article presents a self-powered dual-inductor MI-PSSHI-VDR interface circuit. It can process multi-PZT voltages with arbitrary phases input. The measurements demonstrate that the prototyped MI-PSSHI-VDR circuit can extract a peak power of 1.93 mW from four PZTs under an excitation of 1.5 g and 75.5 Hz. The energy integration efficiency and energy extraction efficiency of the prototyped circuit are 93.2% and 75.1%. Compared with a multi-input full-bridge rectifier, the proposed circuit can achieve 3.22 power improvement and 3.58 voltage improvement, which grasps a good balance between the indexes of peak output power and load voltage range. Additionally, the MI-PSSHI-VDR circuit is easy to implement and shows a good scalability, which can be an alternative solution for multi-PZTs energy harvest

Integrated generator-rectifier architecture has been shown to substantially improve power density, efficiency and reliability of the electric drivetrains in wind turbines. From a power-electronic perspective, the architecture processes a majority share of the incoming power through passive diodes operating at the generator’s fundamental frequency. This paper presents a design methodology of a 10 MW generator, which involves a specific low-reactance generator to minimize the commutation voltage drop at the passive rectifiers as well as prevent power imbalance between different generator ports. Appropriate phase shifts between the multiple passive ports to eliminate the need for a dc-link capacitor improve the drivetrain reliability. The proposed design adopts a slotless permanent magnet (PM) generator, where the reactance is greatly constrained by eliminating the stator slots. In addition, a Halbach PM-array structure reduces the reactance by removing the rotor back iron. The design methodology uses these features along with a multi-objective optimization framework to maximize power density and efficiency while retaining a low reactance. Co-simulation of the generator and integrated power electronics shows that the proposed architecture is suitable for off-shore wind generators. Finally, a subscale generator is tested to verify the low-reactance design of the proposed generator.

This paper presents an improved full-bridge converter with a five-diode rectifier. The primary side circuit is composed of a full bridge with two transformers and two split capacitors. On the secondary side, five diodes are employed in the rectifier stage. By using the asymmetrical PWM signals, this converter can realize the ZVS of all switches and reduce the circulating current. The two transformers share the load power equally in whole load range. Compared with the other dual-transformer-isolated-full-bridge converters, the transformers in the proposed converter are easy to optimize because of the load power equal sharing. Furthermore, the output filter inductance is reduced, which reduces the loss and volume. According to the loss analysis, the proposed converter has higher efficiency compared with some other DC-DC converters. The experimental results of a prototype with 300-400V input voltage and 250V/4A output verify the performance of the proposed converter.

In this paper, a four-phase 8/10-pole dual armature-winding variable flux reluctance generator (DAW-VFRG) with double-redundant rectifier circuit is proposed for onboard generator. The proposed generator integrating four-phase VFRG and dual armature winding structure improves fault-tolerant capability and power density. Based on the airgap field harmonics analysis and winding function theory, the no-load back-EMF model and winding inductance model are deduced for determining the optimal stator/rotor pole combination. In addition, based on magnetic energy comparison, the influence of the connection categories between two sets of armature windings and rectifier circuits on output capability is also investigated when the saturation effect is considered. The key design parameters are globally optimized to improve the output capability and fault-tolerant capability simultaneously. Moreover, the electromagnetic performance of the proposed DAW-VFRG under both normal and fault condition is evaluated and compared with single armature-winding VFRG with half bridge rectifier. Finally, two prototypes are manufactured and tested to validate the finite-element predictions.

In the acdcac converter system, the second harmonic current (SHC) is generated by the acdc rectifier and the dcac inverter. If the SHC propagates to the intermediate dcdc converter, the current stress of the power switches will be increased, and the conversion efficiency will be degraded. Therefore, it is necessary to suppress the SHC in the dcdc converter. In this paper, the generation and propagation mechanism of the SHC in the acdcac converter system is analyzed. Then, from a perspective of control bandwidth and dc-bus port impedance, the basic ideas for reducing the SHC in the dcdc converter with different control targets are proposed. Based on that, the virtual-impedance-based control scheme is proposed to increase the input impedance and output impedance of the dcdc converter simultaneously. The realization and design guideline of the virtual impedance are also presented. Finally, a single-phase 3-kVA acdcac converter system is fabricated and tested in the lab. The experimental results are provided to verify the effectiveness of the proposed SHC reduction control scheme.

To integrate large-scale islanded onshore wind power with different sizes, this paper proposes an integration system based on the cascaded hybrid HVDC transmission system, which consists of LCC and several MMCs in series connection at the DC side of the rectifier. A large-scale wind farm is connected with one LCC and one MMC while several medium-scale wind farms are connected with MMCs directly. Owing to the hierarchical integration arrangement, the operating flexibility can be improved with reduced capacity and the number of step-up interfacing transformers. A resilient DC voltage control is proposed for the integration system to adaptively redistribute power among the converters during wind power fluctuations. Firstly, the topology and operating characteristics of the wind power integration system are introduced. Then, a resilient DC voltage control is proposed to ensure stable operation during wind power curtailments. Finally, a simulation model of the hybrid cascaded HVDC transmission system is built in PSCAD/EMTDC to verify the effectiveness. The research results show that the system provides a new option for long-distance transmission of large-scale islanded wind power.

Vienna rectifier, which is a non-generative-boost type rectifier, is widely employed in electric vehicle charging system. Nevertheless, the Vienna rectifier faces the challenge of current distortion elimination, current ripple mitigation and neutral-point (NP) voltage balance. As these problems are mutually coupled, the conventional finite control set model predictive control (FCS-MPC) methods cannot solve these problems properly. To address these issues, a three-layer double vectors FCS-MPC method is proposed. In the first layer of the proposed FCS-MPC method, the sectors are divided and the candidate vectors are selected to reduce the current distortion. In the second layer of the proposed FCS-MPC method, the double vectors with optimal duty cycles are adopted to reduce the current ripples. In the third layer of the proposed FCS-MPC method, the NP voltage is balanced by selecting the redundant P-type small vector or N-type small vector. Through the proposed method, the current distortion elimination, current ripple mitigation and NP voltage balancing are realized at the same time. The effectiveness of proposed method has been verified by simulation and experiment.

A novel Cuk-based bridgeless rectifier is proposed for receiving side of wireless power transfer (WPT) system. The proposed converter can not only help improve overall efficiency, but also is with features of wide power modulation range and very low output current ripple. In terms of the output current source characteristics of series-series-compensated WPT system, a bridgeless rectifier and a Cuk converter are combined and an input inductor of Cuk converter is cut down to form the proposed single-stage converter. Besides, a synchronous operation method is derived for the proposed converter to realize the optimal working point of transmission power and efficiency. Operation principles of the converter and its impact on performance of WPT system are analyzed. Also, design methods for system parameters are given. A prototype is built up to verify the feasibility of the proposed topology and the operation method. It is noted that the proposed converter can well adjust the output power of WPT system to realize the desired working point via adjusting the duty cycle at different transfer distances and loads.

As the increase of power and voltage level of back-to-back three-level NPC converters, the high-amplitude and high-frequency common-mode voltage (CMV) has become an urgent problem. To address this, a CMV elimination method based on PWM pulse alignment for back-to-back three-level NPC converter is proposed. On this basis, a neutral-point potential balance method based on zero-sequence voltage (ZSV) is also proposed. In order to decouple the CMV elimination and the neutral-point potential balance, a same optimal ZSV is injected into both the rectifier and inverter sides and the CMV elimination will not be affected. Simulation and experiments are presented to verify the effectiveness of the proposed method.

An integrated generator–rectifier system is a promising architecture to harvest energy in offshore wind turbines. The system processes the majority of the incoming power using reliable, efficient, and inexpensive passive diodes operating at the generator line frequency. Elimination of capacitors at the diode rectifiers’ output by appropriately phase shifting the voltages of a multiport generator further improves the reliability of the overall architecture. This article creates a generalized framework to evaluate the interactions among different generator ports, diode-bridge rectifiers, and the active rectifier that is used to control the power flow. The framework enables quantifying the effect of integration on the dc bus power ripple and power imbalance among different generator ports. An exemplary winding layout is proposed that ensures theoretically zero interaction between the passive ports, although all the ports are mounted on a magnetic structure. A 10-MW integrated generator–rectifier design and simulation proves the accuracy of the framework using coupled circuit and finite-element simulation. Finally, a laboratory prototype shows the realization of the winding layout. The proposed inductance-matrix-based framework can be used to evaluate other winding layouts to estimate the effect of magnetic coupling on the performance of the system.

Multi-port solid-state transformer (SST) characterized by high scalability is expected to be widely used in AC/DC hybrid microgrid. However, the DC bus voltage deviation and dynamic response speed are two key issues in its application. Therefore, a model predictive direct power control (MPDPC) of the three-port SST (TPSST) is proposed. Compared with the traditional PI-based method, the oscillation of the DC bus voltage is inhibited, and the steady-state performance is improved with the MPDPC method. Moreover, a direct power path is incorporated into the control system in order to integrate the rectifier and dual active bridge (DAB) stage. This power path delivers the power required by the load to the DAB stage and the rectifier stage for power control, thereby improving the dynamic response of the system in the process. Besides, since the MPDPC strategy is a control scheme for the whole system, the design of the control system is simplified. Finally, a low power prototype has been built and tested, and the experimental comparison with the traditional voltage control (TVC) and model predictive voltage control (MPVC) method verifies the efficiency improvement of the proposed control strategy.

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.

Considering the weakness of the conventional physical model of power diodes in the rectifier design, an improved lumped-charge model is presented in this paper to achieve both high accuracy and high efficiency in the simulation of power electronic equipment. To improve the convergence of the physical model simulation in the rectifier circuit, the transmission-line-theory is implemented in the model. Furthermore, a dynamic partition method is implemented in the model to achieve high accuracy of the transient characteristics of the diode during the level transition of the rectifier, with reducing the number of numerical solutions through reallocation of computing resources. Compared with the conventional model, the simulation error is decreased. This successfully adopts the physical model to realize both equipment-level simulation and high accuracy of device simulation in the design of the rectifier and RC snubber circuit. The experimental results show that the error of the proposed model is less than 10% and 5% the minimum, which is a maximum 30% decreasing compared with that of the conventional model. The half-cycle (500μs) simulation of the rectifier circuit with 10 and 20 power diodes cost 18s and 33s.

A novel driving circuit for a current doubler synchronous rectifier to inductive power transfer (IPT) applications is proposed in this paper using only auxiliary windings in the existent rectifier output filter inductors to drive the active switches. The proposed synchronous rectifier (SR) overcomes the limitations of the traditional driving schemes because it does not require any processing, analog circuits, gate drivers circuits or current measurement, normally used in the conventional SR applied to IPT systems. The proposed configuration presents a simple and robust operation considering usual parametric variation in IPT systems, such as coupling factor, misalignment, load variation and component tolerances. Moreover, the same size and weight of the conventional diode rectifier board is maintained due to the simplicity of the self-driven circuit. The proposed configuration allows increasing the global efficiency by reducing the conduction losses of the output rectifier and previous stages. A resonant circuit design procedure using an iterative process to find the maximum efficiency point considering the self-driven SR is proposed to maximize the global system efficiency. A 100 W resonant series-parallel IPT prototype is developed to validate the performance of the proposed self-driven SR circuit presenting a maximum global efficiency equal to 94.8%.

This paper proposes a wide output voltage range LLC resonant converter based on topology reconfiguration method (TRM). First, with different driving signals two operational modes of inverter circuit and rectifier circuit of the proposed topology are analyzed respectively. On this basis, the converter in whole voltage range has three variable operating modes considering voltage gain by different combination between two kinds of inverting modes and two kinds of rectifying modes. Thus compared with conventional LLC converter, the voltage gain range can be extended by four times within the same switching frequency range using TRM plus pulse-frequency modulation (PFM). Comprehensive analysis of circuit states and soft-switching condition in these three modes are presented. Moreover, design of voltage area division in three modes is discussed to arrive a better tradeoff between efficiency and power density. A design flowchart is given to help to implement an efficiency optimization algorithm. In addition, a smooth mode transition technique is proposed to avoid the rapid frequency change during reconfiguring modulation strategy. Finally, a 2kW 100V-900V output prototype is built, and main experimental results are provided to verify the effectiveness of the proposed topology and topology reconfiguration method.

This paper proposes a family of two-to-three-phase AC-AC indirect matrix converters with an open-end rectifier stage (IMCORS) which are direct AC-AC converters, having no energy storage element at their DC-link. The IMCORSs are the first indirect matrix converters (IMC) with an open-end rectifier stage, creating a new category of IMC. The IMCORS is a full-controlled and partial-bidirectional power flow converter. By replacing four active/controlled switches of the rectifier stage of the IMCORS with four diodes, two new configurations are proposed with reduced active switch count, resulting in reduced costs and increased efficiency. Also, by adding an inverting link to the DC-link of the rectifier stage of the IMCORS (which enables the bidirectional power flow operation), another converter is proposed. The IMCORSs topologies are suitable for wind energy conversion systems (WECS). The zero DC-link current commutation and the space vector modulation (SVM) applied to the proposed converters provide a unity power factor for the input system, reduction of power losses, and decrease the complexity of the commutation when compared to classical matrix converters. The proposed converters are verified by simulation and experimentally using a 1.7 kW/liter prototype operating at 1 kW.

Radio frequency energy harvesting (RFEH) is very attractive for the Internet of things (IoT) and self-powered micro-systems such as wearable biomedical devices and wireless sensor networks. This paper proposes, analyzes, and implements a new RF-DC converter in standard 130 nm CMOS technology. The developed converter is designed and optimized for ultra-low-power IoT and wearable biomedical applications using the 900 MHz ISM band. The proposed 10-stage cross-connected rectifier compensates the transistors threshold voltage by using both dynamic and static bias compensation techniques. An analytical model of the rectifier based on the MOSFET transistor equations is presented, allowing optimization of the rectifier as a function of the number of stages and transistors sizing, improving the sensitivity and the input power range of the converter. The measurement results demonstrate a sensitivity of -25.5 dBm for 1 V output across a 5-MΩ resistive load and -29 dBm for a 100 MΩ load, which is better than the best previously reported results. The measured peak end-to-end efficiency of the proposed harvester is 42.4% at -16 dBm input power, delivering 2.19 V to a 450 kΩ load.

A novel high switching frequency isolated voltage-fed hybrid bridge combining semiactive rectifier dc–dc converter is introduced for unidirectional power flow and wide voltage gain. Three potentially appropriate working patterns are elaborated, including ideal output power derivation, current stress analysis, working voltage matching, output power distribution, soft switching characteristics, etc. In consideration of the optimization of the minimum of the root-mean-square value of the leakage inductor current, two truly applicable working patterns are selected. Meanwhile, based on the consideration of soft switching, a segmented control strategy is implemented on it. With the optimization of current stress and the realization of soft switching, the converter can theoretically realize higher efficiency operation. Eventually, the effectiveness of the proposed converter and the control strategy is verified by a 1 kW prototype.

This article proposes a condition monitoring scheme for the dc-link capacitors used in ac/dc/ac pulsewidth-modulation converters based on the signal injection, which can estimate capacitance in real time when both the rectifier and the inverter are in normal operation. First, a low-frequency signal is injected into the dc-link voltage, and its effects on the total harmonic distortion (THD) of the input current are analyzed. Accordingly, a suitable injection frequency is selected to keep the THD of input current within limits prescribed by the IEEE standard. Then, a novel calculation method of capacitor current without any dc-link current sensor is given, where the converter system is still in normal operation and different inverter operations are both taken into consideration. Finally, capacitance estimation based on the slide discrete Fourier transform is introduced. At the end of this article, experiments have been done to validate the correctness of the conclusion and effectiveness of the proposed scheme.

A backpack energy harvester converts mechanical energy associated with the oscillation of the backpack during human walking, into electric energy. It can be a very promising solution for supplying portable devices, especially in outdoor activities, disaster relief, and military applications. In this article, a backpack energy harvesting system that is able to self-adapt its operating condition to maximize the extracted power while supplying a dc load is presented and studied, analytically and experimentally. It is based on a mechanical motion rectifier that converts the up-and-down oscillation of the backpack into a unidirectional rotation of a dc generator. The generator output voltage is regulated by a power electronic interface implementing a maximum power point tracking technique to maximize the extracted power. Experimental results confirm the tracking ability of the proposed system and show the advantages with respect to other wearable energy harvesting systems published in the literature.

This article presents a secondary side voltage and current estimation method in the wireless power transfer (WPT) systems on the basis of the load parameter identification. In the application of limited space and weight, it is difficult to arrange sensors to monitor the high frequency voltages and currents in the WPT secondary side. Compared with the conventional methods, joint estimation of several secondary side voltages and currents is achieved in this article to monitor WPT electrical stress, based on only the RMS value of one primary side measured voltage. First, equivalent circuit model of WPT system with the dual-side LCC compensation networks and rectifier load is established. Then, T-type equivalent circuit of the coils and compensation capacitors is adopted to simplify the model. Moreover, the relationship between the RMS value of the primary side measured voltage and system equivalent load resistance is obtained and simplified for the load parameter identification. Furthermore, the secondary side voltage and current estimation method is proposed based on the identified system equivalent load resistance. Finally, a WPT prototype is developed and the experimental results indicate that the proposed method can achieve high estimation accuracy under the conditions of battery load voltage change, inverter phase-shift angle variation and coil misalignment.

Inductive power transfer (IPT) systems with multiple output voltages are potential to supply a variety of loads simultaneously. This article proposes an IPT system with multiple semiactive rectifier cells (SARCs) connected in series at the receiver (Rx) side. These SARCs are independent of each other and their output voltages can be regulated individually with single receiver coil, which reduces the cost and volume. The proposed IPT configuration has the advantages of high flexibility, simple control, and no cross regulation. Considering that the SARC may cause additional reactance and lead to detuning of the Rx side, variable inductor is introduced to ensure the full tuning condition. Thus, the proposed IPT system can maintain zero phase angle operation with unity power factor in the whole load range, minimizing the reactive power losses. In addition, both primary inverter and the SARCs can achieve zero voltage switching. To verify the feasibility and validity of the proposed IPT system, an experimental prototype with two outputs of 640 W/150 V and 400 W/120 V is built.

A typical battery charging process consists of a constant-current (CC) charging phase which is followed and completed by a constant-voltage charging phase. Moreover, replacing the CC charging by constant-power (CP) charging can eliminate thermal problems and enhance the cycle life of the battery. This work aims to maximize the system efficiency of a single-stage inductive power transfer (IPT) charger by minimizing the overall losses using a CP charging scheme. The single-stage CP IPT charger employs series-series compensation and adopts an active rectifier on the secondary side. Based on a time-domain model, the conditions of zero voltage switching (ZVS) and minimum circulating reactive power are derived. Then, the power losses in the magnetic coupler, inverter and active rectifier are analyzed and optimized under CP output condition. Combining the conditions of ZVS, minimum circulating reactive power, and minimum overall losses, we propose a novel optimal control strategy to maintain CP output and maximum efficiency throughout the charging process. In addition, the proportional integral controller is not needed. Finally, a 120-W experimental prototype is built to verify the performance of the proposed control strategy. Experimental results demonstrate high precision CP output and an efficiency of around 87.5 $\%$ for the proposed single-stage inductive power transfer battery charger.

In this article, a single-stage wireless power receiver featuring continuous dc output current, good output regulation, and high conversion efficiency is presented. The topology is achieved via the integration of a diode rectifier circuit into a pair of interleaved buck converters, of which overlapped components are removed. With this, component count (diode's number) reduction is achieved without affecting the combined operation of rectification and voltage regulation. Moreover, its output inductor pair can be conveniently incorporated in integrated-magnetics form to reduce magnetic size. For control, it adopts an ac-input-current-synchronized modulation scheme, which hybridizes phase-shift modulation (PSM) and pulse-width modulation (PWM) control. The PSM enables consistently zero-voltage-switching turn- on of switches and zero-current switching turn- off of diodes for mitigating switching loss, while the PWM modulation performs good regulation of the output voltage of the rectifier. Experimental results of our constructed 100-kHz, 12-V output voltage, 35-W output power prototype show a fairly constant dc output current with 71% current ripple reduction as compared with that of a regular single-phase buck converter, good output regulation with less than 1% regulation error, and efficient ac–dc conversion with a peak efficiency of 96%.

A phase-shift modulated converter with two full bridges at primary side and rectifier diodes in hybrid combination at secondary side is proposed in this article. Due to the proposed symmetrical modulation strategy, two full-bridges always equally share the total system power rating, and thus the VA rating of two transformers is minimized. The circulating currents decay to zero in the zero state, contributing to reduce the conduction loss and duty-cycle loss. Zero-voltage or zero-current switching is achieved for all switches over whole input voltage range with an auxiliary inductor. The rectifier output voltage is synthesized of two controlled transformer secondary voltages all the time, which achieves the same output current ripple suppression effect as the conventional input-parallel output-parallel full-bridge converters with interleaved control scheme, and reduces the voltage stress of rectifier diodes. These advantages make the converter suitable for wide input voltage range applications. In this article, the operation principle and steady-state analysis of the proposed converter are illustrated in detail. Experimental results with 220–460 V input voltage are demonstrated to verify the advantages.

The article overviews residential and building-integrated photovoltaic (PV) module types. It demonstrates that existing dc–dc converter technologies do not allow building a universal interface microconverter because of wide dispersion of the parameters. However, the absence of universal microconverters limits the widespread adoption of PV modules despite great benefits for energy-efficient buildings and restrains the deployment of residential PV-based dc microgrids. Based on the design requirements formulated, a new approach utilizing a boost half-bridge front-end inverter and a three-mode reconfigurable rectifier (RR) is proposed. The article describes the operating principle of the derived converter. The RR allows keeping the duty cycle of the input side within a favorable range of acceptable efficiencies. An experimental prototype rated for 360 W was assembled and tested in the entire operating range. The experimental results prove the ultrawide input voltage range of over 1:20 and demonstrate the capability of the proposed concept to interface different PV module types while enabling their shade-tolerant operation.

Hybrid HVDC system, which comprises a line commutated converter (LCC) at rectifier side and a voltage source converter (VSC) at inverter side, is drawing wide attention due to its high reliability and economic benefit. For such a new transmission technology, the system characteristics are not comprehensively studied, and inappropriate control parameters may be coherent to system instability. This paper puts forward a novel coherence analysis procedure which analyzes system stability based on a verified hybrid HVDC small-signal model. For the first time, the procedure is proposed to capture the coherence relationships between the system characteristics and control parameters. The analysis results reveal: the circuit and control parameters can highly affect the oscillatory modes and even cause instability. Moreover, the variation of grid Short Circuit Ratio (SCR) at LCC rectifier side trades off the response speed and damping of the oscillatory modes - under low SCR, large proportional and small integral coefficients of the LCC DC current control are suggested to enhance response performance. Also, the increase of VSC DC capacitance reduces the mode response speed - for a large capacitance, large proportional and small integral coefficients of the VSC DC voltage control shall be set to guarantee system stability.

In this article, we describe the research and development of a 3 kV active rectifier for a 4 MW aerospace generator drive system demonstrator. The converter is fed by a multiphase high-speed/high-frequency permanent magnet generator. The main aim of the work is to demonstrate for the first time the feasibility of an MW-class generator system meeting future hybrid-electric propulsion requirements. A concept with multiple and isolated three-phase systems feeding different power buses is proposed to meet the availability requirements. Multiple converters (one for each three-phase system) are connected in series and/or in parallel to achieve the rated power and dc-link voltage. This article describes the key design concepts and the development and testing of the converter to meet the challenging application requirements. Reduced power tests are carried out on a full-scale 4 MW converter prototype, validating the proposed design. The work represents a step forward in terms of voltage, power, and output frequency with respect to the state-of-the-art.

This article presents the analysis and implementation of a predictive control method for dc-link regulation and voltage balance in a cascaded modular reduced dc-link solid-state transformer (SST). Passive components like bulky dc links limit the power density of power converters, especially medium-voltage (MV) SST. Reduced dc-link or low-inertia converters can dramatically reduce the size, cost, and weight by tolerating larger dc-link ripples and improve the reliability with electrolytic capacitor-less dc link. However, a small dc link leads to tight coupling between the input and the output stages, which is a challenge for control design. In stacked low-inertia converters (SLIC), the low-inertia converter modules are stacked for MV applications, resulting in coupling between the modules and making the control more challenging. A new model predictive control method that can achieve deadbeat regulation on the dc link without weighting factors has been proposed to address this novel problem. This article focuses on analyzing the condition of the low-inertia dc link up to 80% ripple, the robustness of the control under parameter mismatches, high-order terms, and important implementation issues, such as model-based sampling and computation delay compensation. Significantly, the high-order terms are introduced because of the large dc-link ripple. These high-order terms are unique to the SLIC and negligible in conventional high-inertia converters. A discrete-time large-signal model is built to capture the dc-link's nonlinear dynamics, and the eigenvalues of a small-signal Jacobian matrix are analyzed with Floquet theory to evaluate stability, using the modular soft-switching SST (M-S4T) as an example of the SLIC. Simulation and experimental results of an MVDC M-S4T verify the analysis and the predictive control method. Finally, the general application of the predictive control to low-inertia converters is compared against a conventional PI controller using a reduced dc-link active-front-end rectifier as an example.

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.