Characteristics comparison of high-frequency multilevel inverter connected with filter inverters

This paper presents a characteristics comparison of a high-frequency multilevel inverter connected with small-capacity filter inverters. In general, PWM inverters require a low-pass filter in order to reduce switching harmonics. However, in the high-frequency systems such as class D power amplifiers, the cutoff frequency of the low-pass filter must be set at high frequency. Thus, harmonic distortion of the output voltage is enlarged to a harmful level. Increasing the number of output voltage levels is effective in reducing the harmonic distortion of the output voltage and the low-pass filter size. The proposed systems consist of a five-level inverter and several cascade-connected low-voltage full bridge inverters without any external DC power sources for filtering the output voltage. The five-level inverter generates a stepwise waveform with five-level voltage, and the low-voltage filter inverter superimposes harmonic components to compensate for the voltage waveform distortion. Therefore, the proposed system can reduce its total switching loss and can increase the number of the output voltage levels. In this paper, the effectiveness of the proposed systems is verified through several experiments. 2007 Wiley Periodicals, Inc.