Latest dual-gate (2G) monolithic bidirectional (MB) gallium nitride (GaN) enhancement-mode field effect transistors (e-FETs) enable a performance breakthrough of current DC-link inverters, e.g., in terms of power conversion efficiency, power density, cost and complexity. In fact, a single 2G MB GaN e-FET can replace the two anti-series connected conventional power semiconductors required in this inverter topology, realizing a four-quadrant (AC) switch with bidirectional voltage blocking capability and allowing controlled bidirectional current flow. Furthermore, as shown in this paper in case of three-phase (3-Φ) buck-boost (bB) current source inverter (CSI) systems comprising a DC-link current impressing buck-type DC/DC input stage and a subsequent boost-type 3-Φ current DC-link inverter output stage, a variable DC-link current control strategy, based on a Synergetic Control concept, can be applied to significantly reduce the switching losses occurring in the 3-Φ inverter. This strategy is denominated two-third pulse-width modulation (2/3-PWM), since by properly shaping the DC-link current with the input stage, the desired 3-Φ sinusoidal load phase currents can be generated by switching, in each switching period, only two out of the three phases of the output stage. Based on comprehensive circuit simulations and analytical calculations, a detailed explanation of the developed modulation and control schemes in different operating conditions is provided, and the reduction of losses enabled by 2/3-PWM is confirmed. Next, the seamless transition of the 3-Φ bB CSI system from 2/3-PWM to conventional 3/3-PWM is demonstrated. Finally, a 3.3 kW 3-Φ bB CSI system, applying 2/3-PWM and employing research samples of 2G MB GaN e-FETs in the 3-Φ inverter, is estimated to achieve an efficiency of 98.4% and a power density of 18 kW/dm3 (295 W/in3) at a switching frequency of 140 kHz.

This paper compares different space vector modulation (SVM) strategies for neutral-point voltage balancing (NPVB) control in three-level (3-L) T-type neutral-point-clamped (TNPC) inverters, and proposes an improved SVM trimmed for NPVB control in hybrid-switch-based 3-L TNPC inverter with the features of loss and common-mode voltage (CMV) reduction. The proposed SVM strategy uses a new principle of small vector selection and vector sequence, and thus, it can balance the neutral point (NP) potential and achieve soft-switching of clamping leg simultaneously. The paper includes detailed analysis for circuit commutation mode, loss breakdown, and common-mode voltage patterns under different operation conditions. The circuit simulations and experiments are carried out in the last part of this paper to validate the proposed SVM strategy.

In the photovoltaic (PV) plant, the parasitic capacitance between the PV panel and the ground (Cp) causes leakage current in the non-isolated systems. The case can be deteriorated in the rainy environment because the Cp increases dramatically due to the rainwater. The existing off-line methods are either through simulation or measurement by impedance analyzer, which are not easy to conduct on-site especially in the PV plant when it rains. The existing on-line capacitance measurement method is to measure the amplitude of the main components of voltage and current on the capacitance, but the measurement results are inaccurate because the parasitic resistance and inductance of the PV panels are not considered. This paper presents a simple on-line extraction method for the Cp, which is obtained through measurement of the oscillation period of the leakage current. In this way, the Cp can be obtained even the equipment is running. The principle is analyzed in a full-bridge case and the simulation and experiment are carried out for the verification. Finally, the Cp obtained in this method is compared with the 3D finite element simulation, the measurement by impedance analyzer and the existing on-line calculation method, which shows the accuracy of this proposed method.

A novel transformerless boost inverter for stand-alone photovoltaic generation systems is proposed in this paper. The proposed inverter combines the boost converter with the traditional bridge inverter. The switch S not only realizes the boost function but also participates in inverting process. The inverter has a higher voltage gain and good characteristics when the inductor L is operated in discontinuous mode (DCM) and the nonpolarized capacitor can be chosen as bus capacitor, which makes the volume smaller and the service life of the inverter is increased. The inverter consists of five switches in which only two switches are operated at high frequency state and a monopole sinusoidal pulse width modulation (SPWM) strategy is used. Therefore, the modulation strategy of switches is very simple and the switching loss is reduced. The principle of inverter is described in detail and mathematical models are built by small-signal analysis. Finally, the correctness of the theoretical analysis is verified by simulation and experiment.

The concepts of dual coupled inductors and voltage multiplier cell are integrated to derive a novel non-isolated interleaved high step-up boost converter in this paper. At the input, due to the interleaved dual coupled inductors and voltage multiplier cell, the converter inhibits current ripple and reduced voltage stress for the power devices; At the output, the secondary sides of the two coupled inductors are connected in series to achieve the purpose of much higher voltage gain and lower voltage stress on the power devices. Therefore, lower voltage rating MOSFETs and diodes can be selected to reduce both switching and conduction losses. In addition, the leakage inductance energy of two coupled inductors can be absorbed and recycled to the output, and the reverse-recovery problem of diodes can be effectively suppressed. Zero current switching (ZCS) turn-on is realized for the power switches to reduce the switching loss. The working principle and steady-state characteristics of the converter are analyzed in detail. The voltage balance of the output capacitors and input current sharing by two interleaved phases are realized through the double closed-loop control of voltage and current. Finally, a 400W laboratory prototype with 25~30V input and 400V output is built to verify the significant improvements of the proposed converter.

To avoid weight, size and cost constraints, on-board integrated charging devices use the traction system components. The hardware of traction system can work as functions of three bridges rectifier, single-phase PFC and so on. And the charging mode and traction mode of EVs operate in different time. So we can consider using the hardware of traction system to reconstruct a charger. The inverter can work as a rectifier and DC/DC converter can realize buck function in charging mode. Even the motor windings can be used as the grid-side filter inductors or an inductor in DC/DC converter by reconstructing the windings. Additional components may be needed to realize some functions in charging mode. When the motor windings and traction system are integrated into a charger, the weight, size and cost of on-board charger reduce. While, the integrated charger has some disadvantages, such as, the motor maybe rotates in charging mode, the charging power will be limited by the traction system. And the single-phase integrated charger has a problem that dc-side exists second harmonic ripples. The voltage ripple in dc-side is suppressed by a large capacitor or additional components. This paper introduces the topologies of on-board integrated charger for EVs. And a new single-phase integrated charger is proposed which can suppress the second harmonic ripple. The proposed system only needs a small additional capacitor and inductor. The paper is organized as follows. In Section II, the overview of integrated charger is given. Three groups including DC/DC converter, switched reluctance motor and alternating current motor are discussed respectively. A novel single-phase integrated charger based on AC motor is proposed in Section III. The operation of system is analyzed in detail. The experimental results are given in Section IV. Section V gives a conclusion.

This paper presents the detailed analysis and design of a soft-switching DC-DC converter called clamped-resonant interleaved boost converter (CRIB). This topology, thanks to a resonant L-C tank connected between the drain terminals of the switches of two interleaved boost cells, achieves zero-voltage and zero current commutations of all devices, independently of the load current, with a reduced dv/dt across the switches, making the converter suitable for high-frequency operation. Moreover, a proper no-load operation is proved, whenever the minimum voltage gain is higher than a given threshold. Differently from previous works on current-fed resonant converters, the presented theoretical analysis includes the effect of the input filter inductors, allowing to derive a simple design procedure to meet the given specifications. According to the outlined design steps, an experimental prototype was built, rated at 42~54V to 400V~300W. Measurements confirm the theoretical predictions, showing an efficiency above 96% at the nominal power in the whole input voltage range. Finally, the possibility to reduce the overall magnetic volume by coupling the two input inductors is demonstrated.

Conventionally, LLC resonant converter adopts frequency control (FC) or combine FC with phase shift control (PSC) to regulate the output voltage. However, for both control strategies, a variable switching frequency operation range is required, which makes the magnetic component and driver circuit design complicated. In this paper, the magnetic control (MC) or variable inductor control is adopted for the LLC resonant converter. Thanks to MC, constant switching frequency and duty cycle can be implemented for the primary switches. A comprehensive analysis of the magnetically controlled LLC resonant converter is presented, which includes the operation principle, voltage gain, and soft switching operation. Meanwhile, a design methodology for LLC resonant converter with MC is proposed, especially the design considerations for the variable inductor are discussed. By adopting the proposed design methodology, the zero voltage switching (ZVS) operation for the primary switches and the zero current switching (ZCS) operation for the secondary rectifier can be achieved. Finally, a 200W experimental setup is built to validate the theoretical analysis.