Parallel operation of one-cycle controlled grid connected three-phase inverters

Parallel operation of three-phase grid connected inverters extends the power range to a much higher level and allows modular design. However, current sharing and circulating current among the modules are the potential problems. This paper studies these phenomena within two paralleled inverters and proposes a new parallel operation method based on one-cycle control (OCC) with combined vector operation and bipolar operation. With some minor addition to the original OCC circuit and a simple add-on communication path among the individual modules, the current is properly shared among all the inverters and the circulating current is limited to an acceptable range, while the OCC advantages, such as constant switching frequency, no multipliers, and simple circuitry, are preserved. Two OCC inverters of 1.5 kW each were built and tied together using the proposed parallel operation method. Experiments have shown the simplicity and the effectiveness of this method.