The Circulating Current Reduction Control Method for Asynchronous Carrier Phases of Parallel Connected Inverters

Parallel operation of inverters is one of the most effective and representative ways to increase system capacity. However, zero-sequence circulating currents occur due to the practical deviations of components constituting individual inverters in case of parallel connected inverters in which a common direct current (DC) or alternating current (AC) bus is shared. In particular, circulating currents of the high-frequency component as well as those of the low-frequency component are generated due to the asynchronization of the carriers of individual inverters. In order to suppress the circulating currents as such, the phases of the carriers should be shifted as much as the phase errors between the carriers to compensate for the phase errors. A difficulty in this phase compensation control is that when there are several pulse-width modulation (PWM) carriers, it is impossible to identify the phase of each carrier. In this paper, to overcome the problem, a method to specify the position of one of the many carriers and control the carriers and compensate for phase errors based on the relevant phase was proposed. In addition, this paper includes the analysis of circulating currents generated in the case of carrier phase errors and proposes a method to identify carrier phase errors and compensate for the relevant errors. The proposed method was verified through simulations and experiments.