Haiwen Liu

Bio: Haiwen Liu is an academic researcher from University of Tennessee. The author has contributed to research in topics: Inverter & Power electronics. The author has an hindex of 4, co-authored 5 publications receiving 174 citations. Previous affiliations of Haiwen Liu include Intertek.

Hybrid cascaded multilevel inverter with PWM control method

Abstract: A hybrid cascaded multilevel inverter with PWM method is presented in this paper. It consists of a standard 3-leg inverter (one leg for each phase) and H-bridge in series with each inverter leg. It can use only a single DC power source to supply a standard 3-leg inverter along with three full H-bridges supplied by capacitors. Multilevel carrier- based PWM method is used to produce a five-level phase voltage. The inverter can be used in hybrid electric vehicles (HEV) and electric vehicles (EV). A simulation model based on PSIM and MATLAB/SIMULINK is developed. An experimental 5 kW prototype inverter is built and tested. The results experimentally validate the proposed PWM hybrid cascaded multilevel inverter.

Power electronics for distributed energy systems and transmission and distribution applications

Abstract: Power electronics can provide utilities the ability to more effectively deliver power to their customers while providing increased reliability to the bulk power system. In general, power electronics is the process of using semiconductor switching devices to control and convert electrical power flow from one form to another to meet a specific need. These conversion techniques have revolutionized modern life by streamlining manufacturing processes, increasing product efficiencies, and increasing the quality of life by enhancing many modern conveniences such as computers, and they can help to improve the delivery of reliable power from utilities. This report summarizes the technical challenges associated with utilizing power electronics devices across the entire spectrum from applications to manufacturing and materials development, and it provides recommendations for research and development (R&D) needs for power electronics systems in which the U.S. Department of Energy (DOE) could make a substantial impact toward improving the reliability of the bulk power system.

Comparison of fundamental frequency and PWM methods applied on a hybrid cascaded multilevel inverter

Abstract: This paper presents a hybrid cascaded multilevel inverter for electric vehicles (EV) / hybrid electric vehicles (HEV) and utility interface applications. The inverter consists of a standard 3-leg inverter (one leg for each phase) and H-bridge in series with each inverter leg. It can use only a single DC power source to supply a standard 3-leg inverter along with three full H-bridges supplied by capacitors or batteries. Both fundamental frequency and high switching frequency PWM methods are used for the hybrid multilevel inverter. An experimental 5 kW prototype inverter is built and tested. The above two switching control methods are validated and compared experimentally.

Hybrid multilevel inverter with single DC source

Abstract: A hybrid multilevel inverter model based on PSIM and MATLAB/SIMULINK is presented in this paper. It consists of a standard 3-leg inverter (one leg for each phase) and H-bridge in series with each inverter leg. The inverter can be used in hybrid electric vehicles (HEV) and electric vehicles (EV). The co-simulation model is employed in order to take full advantage of different power electronics simulation software. Specifically, the main circuit model is developed using PSIM, and the control model is developed using MATLAB/SIMULINK. An experimental 5-level hybrid inverter is tested, which is controlled by multilevel carrier-based PWM signals. The simulation yields a good estimation for the test results of the inverter.

Potential Applications and Impact of Most-Recent Silicon Carbide Power Electronics in Wind Turbine Systems

Abstract: Power electronics is an enabling technology found in most renewable energy generation systems. In a wind turbine system, it plays an important role in system integration, power quality, and reliability control. Moreover, the fast growth of wind energy poses the increasing need for high-power, low-loss, and fast-switching power electronic devices in order to reduce the system complexity and cost, and improve reliability and compactness. Among the technologies addressing this need, silicon carbide (SiC) power electronics as the most-recent technology stands out because of its superior voltage blocking capabilities and fast switching speeds. As the research samples of SiC power switches become available, it is possible to discuss the design of a wind turbine system using SiC devices and estimate its performance based on the characteristics of practical devices. Therefore, considering the high-power density and high voltage capability of SiC power devices and the recent trend on wind turbine converters, this chapter focuses on the studies of the application of SiC power devices in a full-scale wind turbine converter. First, the characteristics of the most recent devices are obtained through tests. Then, wind turbine system modeling including models for the major electrical components such as generator, power converter, etc., is discussed in detail. Next, the potential benefits from the use of SiC devices in a wind turbine system are explored by a comparison study of the SiC converter and its Si counterpart. Results are presented and analyzed at different wind speeds, temperatures, and switching frequencies. The conclusions drawn from these studies verify that the application of SiC converters in wind turbine systems can improve the wind system power conversion efficiency and reduce system size and cost due to the low-loss, high-frequency, and high-temperature properties of SiC devices even for one-for-one replacement for Si devices. It is also pointed out that the application of SiC devices may enable medium converter technology for wind turbine applications when such devices become available. In this way, substantial improvement can be achieved. The chapter is organized as follows: Section 4.1 introduces the present status of wind energy and power electronics. It briefly reviews the electrical technologies used in wind turbine systems such as generator, power converter technology, and power electronics suitable for wind turbine applications. It also summarizes the future trends on wind turbine systems. Section 4.2 focuses on studies of the application of SiC power devices in a full-scale wind turbine converter, including discussions on the present SiC device characteristics, system modeling, simulations of two wind turbine systems with the same components expected for the power converters (One is with SiC power converter, and the other is with a Si power converter). Section 4.3 draws the conclusions and discusses the future work.

A Survey on Cascaded Multilevel Inverters

Abstract: Cascaded multilevel inverters synthesize a medium-voltage output based on a series connection of power cells which use standard low-voltage component configurations. This characteristic allows one to achieve high-quality output voltages and input currents and also outstanding availability due to their intrinsic component redundancy. Due to these features, the cascaded multilevel inverter has been recognized as an important alternative in the medium-voltage inverter market. This paper presents a survey of different topologies, control strategies and modulation techniques used by these inverters. Regenerative and advanced topologies are also discussed. Applications where the mentioned features play a key role are shown. Finally, future developments are addressed.

A Single-Phase Multilevel Inverter Using Switched Series/Parallel DC Voltage Sources

Abstract: A novel multilevel inverter with a small number of switching devices is proposed. It consists of an H-bridge and an inverter which outputs multilevel voltage by switching the dc voltage sources in series and in parallel. The proposed inverter can output more numbers of voltage levels in the same number of switching devices by using this conversion. The number of gate driving circuits is reduced, which leads to the reduction of the size and power consumption in the driving circuits. The total harmonic of the output waveform is also reduced. The proposed inverter is driven by the hybrid modulation method. In this paper, the circuit configuration, theoretical operation, Fourier analysis, simulation results with MATLAB/SIMULINK, and experimental results are shown. The experimental results accorded with the simulation results.

A Switched-Capacitor Inverter Using Series/Parallel Conversion With Inductive Load

Abstract: A novel switched-capacitor inverter is proposed. The proposed inverter outputs larger voltage than the input voltage by switching the capacitors in series and in parallel. The maximum output voltage is determined by the number of the capacitors. The proposed inverter, which does not need any inductors, can be smaller than a conventional two-stage unit which consists of a boost converter and an inverter bridge. Its output harmonics are reduced compared to a conventional voltage source single phase full bridge inverter. In this paper, the circuit configuration, the theoretical operation, the simulation results with MATLAB/SIMULINK, and the experimental results are shown. The experimental results accorded with the theoretical calculation and the simulation results.

Extended multilevel converters: an attempt to reduce the number of independent DC voltage sources in cascaded multilevel converters

Abstract: The cascaded multilevel converters are the most favorable topologies of multilevel converters. However, they have the main disadvantage of using multiple independent dc voltage sources. This study proposes new cascaded multilevel converter topologies in which the number of independent dc voltage sources is reduced. In the proposed topologies, for a specific number of voltage levels, the number of dc voltage sources is halved. Beside the number of dc voltage sources, in one of the proposed topologies the number of switches is also reduced in comparison with that of the conventional cascaded multilevel converter. A new modified pulse-width modulation method is presented to control the proposed topologies. Also, a method for compensating non-ideality of the dc voltage sources is presented. Simulation results using PSCAD software as well as experimental results from a laboratory-scale prototype are presented to verify the proposed multilevel converters.

A single phase multilevel inverter using switched series/parallel DC voltage sources

Abstract: A novel multilevel inverter with a small number of switching devices is proposed. It consists of an H-bridge and an inverter which outputs multilevel voltage by switching the dc voltage sources in series and in parallel. The proposed inverter can output more number of voltage levels in the same number of the switching devices by using this conversion. The number of gate driving circuits is reduced, which leads to the reduction of the size and power consumption in the driving circuits. The total harmonic of the output waveform is also reduced. The proposed inverter is driven by the hybrid modulation (HM) method. In this paper, the circuit configuration, the theoretical operation, Fourier analysis, simulation results with MATLAB/ SIMULINK and the experimental results are shown. The experimental results accorded with the simulation results.