Abstract
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.
Highlights
The penetration of renewable energy sources is increasing in the power grid due to carbon reduction and environmental protection, and the demand for DC distribution networks such as low voltage direct current (LVDC), medium-voltage direct current (MVDC) distribution, and microgrids is increasing [1–4]
It can be seen that the zero-sequence circulating currents (ZSCCs) increased rapidly
It can be seen that when an additional disturbance occurred at 0.3 s, the ZSCCs of individual inverters sharply increased and the distortion of the output currents intensified
Summary
The penetration of renewable energy sources is increasing in the power grid due to carbon reduction and environmental protection, and the demand for DC distribution networks such as low voltage direct current (LVDC), medium-voltage direct current (MVDC) distribution, and microgrids is increasing [1–4]. The demand for high power conversion systems is increasing, and the parallel connection of inverters is a method mainly adopted for high power conversion. In a three-phase parallel inverter structure that shares a common DC bus and a common AC bus, there is a path through which the circulating currents can flow between the inverters connected in parallel, so that zero-sequence circulating currents (ZSCCs) appear [6–10]. Such ZSCCs cause problems, such as the distortion of output currents, increase in the current burden on switch devices, and electromagnetic interference (EMI)
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