Jason Lai

Operation principles of bi-directional full-bridge DC/DC converter with unified soft-switching scheme and soft-starting capability

A new bi-directional dual full-bridge DC/DC converter with a unified soft-switching scheme and soft-start capability is proposed in this paper. A simple voltage clamp branch is used to limit transient voltage across the current-fed bridge and realize zero-voltage-switching (ZVS) in boost mode operation, while achieving hybrid zero-voltage/zero-current switching (ZVZCS) for the voltage-fed bridge in buck mode operation. The theory of operations including soft-start-up process is discussed in this paper.

Design, implementation, and experimental results of bi-directional full-bridge DC/DC converter with unified soft-switching scheme and soft-starting capability

The PWM control, design and implementation issues of the bi-directional dual full-bridge DC/DC converter with a unified soft-switching scheme and soft-start capability, which was proposed in a companion paper, are presented in this part of the two-paper sequel. Test results on a 5 kW prototype converter, which is connected between a 12 V battery and a high voltage bus, and targeted for alternative energy applications, validate the secure operation, high reliability and superior efficiency of the proposed converter topology.

Efficiency considerations of load side soft-switching inverters for electric vehicle applications

This paper critically evaluates the efficiency of load side soft-switching inverters for electric vehicle (EV) drive applications. Five types of load side soft-switching inverters are studied, including the auxiliary resonant commutated pole inverter (ARCP), the zero-current-transition (ZCT) inverter, the zero-voltage-transition (ZVT) inverter with coupled inductors (ZVTCI), the ZVT inverter with a single switch (ZVTSS), and the ZVT inverter with a single inductor (ZVTSI). Loss categorization methods are developed using simplified device models in order to reveal the mechanism of efficiency improvement. It is shown that the ZVTSI and the ZVTSS have poor efficiency performance compared to the hard-switching inverter because of the extra turn-off of main switches and the nonzero-current-switching for the auxiliary devices. The ARCP, the ZCT inverter and the ZVTCI show substantial energy savings. Besides, the variable timing soft-switching control can further increase efficiency in ZVT inverters.

A novel three-phase zero-current-transition and quasi-zero-voltage transition (ZCT-QZVT) inverter/rectifier with reduced stresses on devices and components

This paper proposes a new soft-switching strategy for three-phase inverter and rectifier applications. All the main switches and auxiliary switches are turned on and turned off under zero-current-transition (ZCT) conditions. Compared to existing ZCT techniques, the diode reverse recovery is reduced, and the main switch turn-on voltage is reduced to less than the DC link voltage from full DC link voltage-referred to as quasi-zero-voltage-transition (QZVT). In addition, the current stress in the auxiliary switches is reduced and evenly distributed, and the resonant capacitor voltage stress is reduced to 1.3/spl sim/1.4 times the DC link voltage from twice the DC link voltage. The operational principle, state plane analysis, and design aspects are described. Both simulation and experiment results are provided for verification. Based on the proposed technique, finally presented is an application example of three-phase soft-switching inverter for electric vehicle propulsion.

A high-frequency 1.5 MVA H-bridge building block for cascaded multilevel converters using emitter turn-off thyrister

This paper proposes a 1.5 MVA H-bridge building block (HBBB) using the newly developed emitter turn-off (ETO) thyristor to demonstrate the superior performance of the ETO. The modular HBBB is intended to be used in high-power cascaded multilevel voltage source converters for reactive power compensation applications. Because of theirs identical layouts, the HBBB are easily manufactured for both the building block itself and for the whole system. Whenever the power requirement of the system needs to be changed, the HBBBs are simply added into or taken away from the system without redesigning the HBBB component ratings. The hardware configuration as well as component selection and design of the HBBB are presented. This paper also proposes the new air-core snubber inductor design, which lowers losses and is lighter in weight than the conventional iron-core inductor. An ETO-based 1.5 MVA HBBB prototype has been implemented and tested in inverter mode. Experimental results indicate that the proposed ETO-based HBBB with the snubber components operates effectively at high frequency and high power.

A simplified control scheme for zero voltage transition (ZVT) inverter using coupled inductors

A new soft-switching control scheme for zero voltage transition (ZVT) inverter using coupled inductors is proposed in the paper. By applying this new control scheme, the ZVT inverter has several salient features: simple fixed timing control for the auxiliary switches does not require any load information, thus eliminates the needs of current for soft-switching operation; all the main and auxiliary switches are under soft-switching condition; the auxiliary circuit current level is adaptive to the load current, thereby minimizing the conduction loss. The operating principle and design procedures are presented in the paper. Simulation results verify the validity of the proposed scheme.

1500 V, 4 amp 4H-SiC JBS diodes

This paper reports the detailed design, fabrication and characterization of 1500 V, 4 Amp 4H-SiC JBS diodes. 2D device simulations show that a grid spacing of 4 /spl mu/m results in the most optimum trade-off between the on-state and off-state characteristics. JBS diodes with linear and honeycombed p/sup +/ grids, Schottky diodes and implanted PiN diodes fabricated alongside show that while 4H-SiC JBS diodes behave similar to Schottky diodes in the on-state and switching characteristics, they show reverse characteristics similar to PiN diodes. Measurements on 4H-SiC JBS diodes indicate that the reverse recovery time (/spl tau//sub n/) and associated losses are near zero even at a rev. dI/dt of 75 A//spl mu/sec. Based on measured waveforms, detailed loss models on diode switching were established for a high frequency switching power supply efficiency evaluation. A DC/DC converter efficiency improvements of 3-6% were obtained over the fastest, lower blocking voltage silicon diode when operated in the 100-200 kHz range.

Comprehensive evaluation of auxiliary resonant commutated pole inverter for electric vehicle applications

A 50 kW auxiliary resonant commutated pole inverter (ARCPI) is built and experimentally investigated for the electric vehicle (EV) application. The key performance aspects such as the efficiency and EMI noise have been compared between the ARCPI and the hard-switching inverter. The theoretical analysis is also presented to give the insightful view of the actual performance of the ARCPI for the EV application.

An IGBT and MOSFET gated SiC bipolar junction transistor

A high voltage 4H-SiC bipolar junction transistor (BJT) has been developed with 16 A, 600 V rating. This paper presents a new base drive structure for the SiC BJT for inverter application. The driver consists of one IGBT and one MOSFET to help turn-on and turn-off of the SiC BJT transistor in a Darlington like configuration. Instead of using conventional proportional current driven method for optimal driving bipolar transistor, the proposed base drive method can adaptively drive SiC BJT at near-saturated condition based on voltage balance of V/sub be/ and V/sub ce/. The IGBT and MOSFET gated transistor structure (IMGT) can significantly improve BJT switching behavior. Basic design principle is presented with simulation results. The proposed IMGT driver scheme is also verified by experimental results for both Si and SiC BJT. With the proposed driver scheme, the SiC BJT have the turn-on time of less than 0.5 /spl mu/s and turn-off time of less than 0.2 /spl mu/s under test condition of 300 V 15 A. Further work still needed for reducing conduction loss of SiC BJT.

A low-cost three-phase zero-current-transition inverter with three auxiliary switches

Most existing three-phase soft-switching inverters with less than six auxiliary switches have fundamental drawbacks in performance. Those with six auxiliary switches have potentially good performance, but with penalties of high cost and large space. This paper proposes a new zero-current-transition (ZCT) inverter topology that reduces the number of auxiliary switches from six to three, without increasing the device power rating or requiring any additional components, for electric vehicle propulsion. With considerable reduction in cost and size, the performance of existing ZCT inverters remains as desired. At main switches and auxiliary switches are turned off under zero-current conditions, and main switches are turned on under a near zero-current condition. Meanwhile, the ZCT implementation does not modify normal space vector modulation (SVM) schemes. A 10 kW prototype has been built and tested to verify the fundamental principle and simulation results.