DC-Link Capacitor Voltage Fluctuation Analysis of Four-Switch Three-Phase Inverter

This paper discusses a new modulation scheme and the dc-link capacitor voltage fluctuation of the four-switch three-phase inverter in detail. Based on the spectrum of the output switched voltage, the modulation scheme is realized by injected the certain term into the traditional modulating waveforms, which as a result produces the balanced output voltages. In order to determine the capacitor voltage fluctuation, the spectrum of the dc-link current is characterized which is also the important factor to determine the capacitor losses. It is found that the two capacitor voltages can converge autonomously if the traditional modulating waveforms are applied. While the proposed modulation scheme is applied, the fluctuation amplitudes of the two capacitor voltages will be dependent on the dc component of the capacitor voltage under condition where front-end diode rectifier is supplied. But for the storage battery supplied front-end, the two capacitor voltages share the same fluctuation amplitude. At the last, the analyses are verified by digital simulations in MATLAB/SIMULINK.