Abstract
Cascade H-bridge (CHB) inverter is an attractive choice for integration of DC sources of different nature, e.g., for distributed generation with energy storage, photovoltaic generation, etc. In general, non-equal DC voltage sources can affect the total harmonic distortion (THD) of the CHB by introducing undesirable low-frequency subharmonics. This paper investigates different level-shifted (LS) and phase-shifted (PS) pulse width modulation (PWM) strategies for single- and three-phase cascade H-bridge inverters with non-equal DC sources from the load current THD minimization perspective. The best current quality is provided by LS PWM, as reported in the literature. The paper provides a simple time domain explanation of LS PWM superiority. However, PS PWM may be a preferable choice for practical applications due to fair power and loss sharing across individual H-bridges. The paper explains how to obtain the best current quality by PS PWM carriers’ order arrangement (DC sources switching sequence selection).
Highlights
Nowadays, multilevel inverters (MLIs) are widely used, since they offer improved output waveforms, smaller grid filter size, lower total harmonic distortion (THD), and reduced electromagnetic interference (EMI), compared to their two-level inverter counterparts [1,2,3,4,5,6]
Many recently published papers deal with the estimation of voltage and current THD in multilevel inverters
The scientific community has shown a significant interest in voltage and current THD analyses for both multilevel pulse width modulation (PWM) and staircase modulation over the past years
Summary
Multilevel inverters (MLIs) are widely used, since they offer improved output waveforms, smaller grid filter size, lower total harmonic distortion (THD), and reduced electromagnetic interference (EMI), compared to their two-level inverter counterparts [1,2,3,4,5,6]. Analytical solutions for the voltage THD of multilevel PWM single- and three-phase inverters were obtained in [7] in asymptotic approximation (high switching-to-fundamental frequency ratio). Experimental tests have been carried out in [8] to verify the calculation and analytical developments of voltage and current THDs in the case of three-, five-, and seven-level single-phase PWM inverters. The paper starts with a generalization of asymptotic current THD formulas for a single-phase multilevel inverter withlevels uniform levels [8] for non-uniform voltage level distribution. In applicable to a single-phase CHB inverter with LS PWM and non-equal DC sources. THD current calculation methodology for non-uniform voltage levels allows evaluating current Though it is difficult implement in practice (PWM band matching to source voltages is required), the calculated.
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