Symmetrical Cascaded Switched-Capacitor Multilevel Inverter Based on Hybrid Pulse Width Modulation

Lingling Cao,Shikai Chen,Yuanmao Ye,Jiefeng Lin

doi:10.3390/en14227643

Abstract

Multilevel inverters have been widely used in various industrial applications such as renewable energy generation and electric vehicles. An improved circuit of symmetrical cascaded switched-capacitor multilevel inverter is proposed so that the reactive power is absorbed by its power supply instead of capacitors. Then, a special hybrid pulse width modulation strategy combing level-shifted pulse width modulation (LS-PWM) and phase-shifted pulse width modulation (PS-PWM) was developed for the inverter. With this modulation algorithm, the power between cascaded units is automatically balanced, and the voltage of the capacitor in each unit is also automatically balanced to the dc input voltage. In addition, the optimized capacitor voltage ripple makes it possible to use a smaller capacitor to produce a better output voltage waveform. Theoretical analysis, simulation and experimental results show that the equivalent switching frequency of the cascaded multilevel inverter is twice the original frequency so that the output voltage harmonics are only distributed near even multiples of the carrier frequency.

Highlights

Recently, multilevel inverters have been widely used in photovoltaic power generation, energy vehicles and high voltage DC (HVDC) transmission since it offers the advantage of low voltage stress across switching devices on the occasion of high voltage application and generates a sinusoidal output waveform with reduced harmonic distortion at low switching frequency [1,2]
In order to verify the effectiveness of the proposed symmetrical switched-capacitor multilevel inverter and its hybrid pulse width modulation, a simulation model was built in PSIM
Since the RMS value of output voltage in each unit is measured the same as 66 V, it can be deduced that the power of each cascaded unit is equal, and the power between two cascaded units is automatically balanced.1M0 oof r1e5over, the capacitor voltage is balanced to the dc input voltage by using hybrid PWM

Summary

Introduction

Multilevel inverters have been widely used in photovoltaic power generation, energy vehicles and high voltage DC (HVDC) transmission since it offers the advantage of low voltage stress across switching devices on the occasion of high voltage application and generates a sinusoidal output waveform with reduced harmonic distortion at low switching frequency [1,2]. In [20], a new SC cell consisting of four switches, two diodes and two capacitors is proposed to produce more output voltage levels. A hybrid pulse width modulation combining level-shifted pulse width modulation (LS-PWM) and phase-shifted pulse width modulation (PS-PWM) was developed for the symmetrical cascaded switched-capacitor multilevel inverter With this modulation algorithm, the power between cascaded units as well as the voltage of the capacitor in the SC cell is automatically balanced, and the capacitor voltage ripple is effectively minimized. The output power of each unit approaches, and power balancing is realized automatically

Capacitor Voltage Ripples

Simulation Verification

Conclusions