Balancing Capacitor Voltages in 7-Level Single Phase Flying-Capacitor Wavelet Modulated Inverters

Abstract

This paper develops and tests a method for balancing capacitor voltages in 7-level flying-capacitor (FC) inverters, which are operated by the wavelet modulation (WM) technique. This multi-level inverter has two capacitors in each pole, whose voltages deviate due to changes in its loading level. In order to ensure that all switching elements experience identical voltage stresses and no circulating currents, the voltage across each capacitor has to be maintained very close to its reference value. The proposed method to balance the capacitor voltage is based on adjusting the scales of resolution segmented wavelet basis functions, which are used as switching signals to operate a 7-level FC inverter. The adjustments of the scales can vary the widths and locations of switching pulses produced by the WM technique. The proposed capacitor voltage method is structured using a proportional-integral controller to adjust the scales, thus balancing the capacitor voltages. The accuracy, effectiveness, and response speed of the proposed method to balance capacitor voltage are demonstrated through simulation and experimental test cases.