Pengwei Sun

Cascade Dual Buck Inverter With Phase-Shift Control

This paper presents a new type of cascade inverter based on dual buck topology and phase-shift control scheme. The proposed cascade dual buck inverter with phase-shift control inherits all the merits of dual buck type inverters and overcomes some of their drawbacks. Compared to traditional cascade inverters, it has much enhanced system reliability thanks to no shoot-through problems and lower switching loss with the help of using power MOSFETs. With phase-shift control, it theoretically eliminates the inherent current zero-crossing distortion of the single-unit dual buck type inverter. In addition, phase-shift control and cascade topology can greatly reduce the ripple current or cut down the size of passive components by increasing the equivalent switching frequency. A cascade dual buck inverter has been designed and tested to demonstrate the feasibility and advantages of the system by comparing single-unit dual buck inverter, 2-unit and 3-unit cascade dual buck inverters at the same 1 kW, 120 V ac output conditions.

Cascade dual-boost/buck active-front-end converter for intelligent universal transformer

In this paper, a new cascade active-front-end converter based on dual-boost/buck converters is proposed for an intelligent universal transformer (IUT), which allows adjusting the power factor to control both the active and reactive powers between medium and low voltage levels. Compared to the traditional cascade H-bridge converter, it has much enhanced system reliability owing to no shoot-through problems and lower switching loss with the help of using power MOSFETs. In addition, a unified control scheme is proposed for active-reactive power control and individual voltage balancing control, which is modular and easy to implement. In the end, a laboratory three-unit cascade active-front-end converter based on the half-bridge dual-boost/buck converter is constructed and tested. The experimental results verified the feasibility and effectiveness of the proposed active-front-end converter and the unified control scheme for IUT.

Grid-Tie Control of Cascade Dual-Buck Inverter With Wide-Range Power Flow Capability for Renewable Energy Applications

This paper presents a grid-tie control system for cascade dual-buck inverter with both active and reactive power flow capability in a wide range under two types of renewable energy sources. A fuel-cell power-conditioning system (PCS) is a Type I system with active power command generated by balance of plant of each unit; and photovoltaic or wind PCS is a Type II system with active power harvested by each front-end unit through maximum power point tracking. Reactive power command is generated by distributed generation control site for both systems. Selective harmonic proportional resonant controller and admittance compensation controller are first introduced to cascade inverter grid-tie control to achieve better steady-state and dynamic performance. Detailed analysis and derivation of both control systems were conducted. A 1-kV·A cascade dual-buck inverter system was designed and interfaced to 120-V, 60-Hz grid to verify the control strategy. Pure active power, pure reactive power, and mixed power flow with leading and lagging angles were fully tested under steady-state and command-dynamic conditions for both systems. The experimental results proved the effectiveness of the designed grid-tie control for both systems.

A Hybrid-Switch-Based Soft-Switching Inverter for Ultrahigh-Efficiency Traction Motor Drives

This paper presents a hybrid switch that parallels a power MOSFET and an IGBT as the main switch of a zero-voltage switching inverter. The combination features the MOSFET conducting in the low current region and the IGBT conducting in the high current region, and the soft switching avoids the reverse recovery problem during the device turn-on. A custom hybrid switch module has been developed for a variable-timing controlled coupled-magnetic type ZVS inverter with a nominal input voltage of 325 V and the continuous output power of 30-kW for a traction motor drive. Experimental results of the hybrid-switch based inverter with the total loss projected by temperature indicate that the inverter achieves 99% efficiency at the nominal condition and demonstrate ultrahigh efficiency operation over a wide load range. At 375-V input, the maximum measured efficiency through temperature projection and loss separation analysis is 99.3%.

A 55-kW Three-Phase Inverter Based on Hybrid-Switch Soft-Switching Modules for High-Temperature Hybrid Electric Vehicle Drive Application

This paper presents a 55-kW three-phase inverter based on soft-switching modules for hybrid electric vehicle drives at high-temperature conditions. The main switch of the module is composed of the hybrid switch, which is composed of parallel IGBT and MOSFET. Highly integrated soft-switching modules have been employed to achieve switching loss as well as conduction loss reduction. The operation principle of the proposed inverter is analyzed in detail. Experimental evaluations of the inverter have been conducted through both inductive load and motor-dynamometer load at coolant temperatures ranging from 25°C to 90°C. Efficiency measurement using power meter showed that the peak efficiency is around 99%, and it drops slightly at lower speed and higher temperature conditions. To ensure measurement fidelity, a double-chamber differential calorimeter system was designed and calibrated for the inverter testing. Through long-hour testing, the measured efficiencies consistently showed 99% and higher. The soft-switching inverter has been operated reliably and demonstrated high efficiency at different temperature and test conditions.

High efficiency transformerless photovoltaic inverter with wide-range power factor capability

Photovoltaic (PV) inverter is the most important part for energy conversion, and the current research focus for PV inverter is high efficiency, high reliability, and low-output ac-current distortion. With considerable grid-connected PV installation in last few years, high penetration PV system is desired, which requires integrating PV inverter into grid regulation. New code in Germany already requires PV inverter providing system regulation and service for low voltage distribution system. One of obvious impact on PV inverter is reactive power generation requirement. Most state-of-the-art high-efficiency PV inverters that adopt single-stage topology only allow unity power generation but none of them are able to generate reactive power. This paper proposes a high-efficiency dual-buck full-bridge PV inverter for a wide range power factor operation. Additionally, a novel hybrid bipolar PWM method is proposed to achieve low ground leakage current and low output current distortion in the PV system. At last, simulation and experiment demonstrate that the proposed PV inverter system can provide a wide-range power factor operation with high efficiency, low ground leakage current, and low output current distortion.

High efficiency three-phase soft-switching inverter for electric vehicle drives

This paper presents a high efficiency three-phase soft-switching inverter for electric vehicle drives application. A 12kW three-phase soft-switching inverter using CoolMOS as the main device and IGBT as the auxiliary device has been designed and fabricated. The electric vehicle drive test system has been assembled with soft-switching inverter, induction motor and dynamometer. The soft-switching inverter has been tested with closed-loop torque direction control under speed reversal conditions. The measured efficiency of the inverter in a wide load range is above 98.5%. The calorimeter test at 12kW shows 98.8% efficiency.

Efficiency evaluation of a 55kW soft-switching module based inverter for high temperature hybrid electric vehicle drives application

This paper presents a 55kW three-phase softswitching inverter for hybrid electric vehicle drives at high temperature conditions. Highly integrated softswitching modules have been employed to achieve switching loss as well as conduction loss reduction. Detailed experimental evaluations of inverter efficiency have been conducted through both inductive load and motor-dynamometer load at coolant temperatures ranging from 25°C to 90°C. Efficiency measurement using power meter showed that the peak efficiency is around 99%, and it drops slightly at lower speed and higher temperature conditions. To ensure measurement fidelity, a double chamber differential calorimeter system was designed and calibrated for the inverter testing. Through long-hour testing, the measured efficiencies consistently showed 99% and higher. The soft-switching inverter has been operated reliably and demonstrated high efficiency at different temperature and test conditions.

Performance evaluation of high voltage super junction MOSFETs for zero-voltage soft-switching inverter applications

This paper evaluates three different 600V-level super junction (SJ) MOSFETs employed in zero-voltage soft-switching inverter applications. Inverter efficiency was measured and compared with the same inverter test setup by only changing different MOSFETs. Besides high efficiency requirement, better switching performance is also highly appreciated in various inverter applications. Comparison test was done on each super junction MOSFET to investigate its body diode reverse recovery and associated problems. Based on performance of both efficiency and reverse recovery related issues, a high voltage super junction MOSFET selection for softswitching inverter was suggested.

Cascade dual-buck full-bridge inverter with hybrid PWM technique

This paper presents a new type of cascade inverter, named cascade dual-buck full-bridge inverter. Compared to cascade H-bridge inverter, the proposed inverter has several advantages. First, it eliminates the possibility of shoot-through problems, which is the major failure of traditional voltage source inverters. Second, it does not need dead time, which fully utilizes the pulse width modulated voltage and transfers total desired energy to the load. In addition, it can use high-voltage power MOSFETs without the complexity of soft-switching assisting circuits to improve the system efficiency. In this paper, several PWM techniques are analyzed and compared, including bipolar PWM, unipolar PWM and phase-shifted PWM, when applied to the proposed inverter. It has been found out that a hybrid PWM technique with the combination of the two out of the three PWMs mentioned above leads to better performance of the cascade dual-buck full-bridge inverter in terms of less output current ripple and harmonics, no zero-crossing distortion, and higher efficiency. A prototype of the proposed inverter has been built and tested to verify the feasibility and effectiveness of the topology and the hybrid PWM technique.