Switching Frequency Derivation for the Cascaded Multilevel Inverter Operating in Current Control Mode Using Multiband Hysteresis Modulation

Abstract

In this paper, a generalized expression of the switching frequency is obtained for the cascaded H-bridge multilevel inverter tracking a reference current. The inverter is considered connected to the grid and operates in current control mode using the generalized algorithm of multiband hysteresis modulation. The results are derived based on the time-domain current error dynamics which is applicable for any levels of the cascaded multilevel inverter. The generalized expression explicitly shows the relationship between the instantaneous switching frequency with the net hysteresis band, system parameters, and number of levels. The expression can be used for the determination of the net hysteresis band required for a given desired effective maximum switching frequency for the multiband hysteresis modulation. The value of maximum, minimum, and average switching frequencies can be obtained from the instantaneous switching frequency expression. The results are useful for the design of the multiband hysteresis controller for tracking of the desired reference current and can be used to evaluate the performance characteristics of the multilevel inverter. The simulation and experimental verification of the results are obtained through single-phase, three- and five-level cascaded H-bridge inverters.