Power Conversion Research Of Parallel DC/AC Converters

With the continuous development of modern power electronic technique, the multi-module parallel power converter technique becomes optimal extraction process for its high reliability and great power, so it's acknowledged to be one of the important fields of modern power converter technique. Multi-module parallel DC-AC converter is widely used in all the DC-AC, DC-DC and AC-DC parallel power converter technique but the difficulties arise in consistency of output voltage frequency, amplitude and phase.In this paper, the present situation of the parallel inverter control technology and theory was reviewed, it demand a higher level of static and dynamic characteristics of single inverter to parallel inverter runs normally, so a control method was analyzed for converter independent operation. A double-loop decouple control strategy based on d-q axis was researched and the output filter and the controller parameter were also produced. These studies provide basis for DC-AC parallel operation.According to whether there is a wire among modules the parallel control strategy can be divided into wire-parallel and wireless-parallel. The approach is based on droop control for wireless-parallel in this paper. Particularly, the critical methods to calculate output power and droop parameter were given, the design was analyzed by simulation. The distribution controlled inverter parallel system was mainly studies for wire-parallel. After analysis of the distribution parallel structure and the current sharing, the current equalizing bus bar was incorporated to get the output current of each inverter, and then the difference of average current and self-output current was calculated to revise the reference voltage and also brought to the inner current loop to improve dynamic response. The design was proved effectively by simulation.Based on theory analysis and simulation, two experimental prototypes are designed based on distribution parallel control. Experimental showed that the parallel circulation was suppressed and proved the method effectively.