Research On The Control Technology Of Parallel Inverter

Parallel inverters can expand capacity and realize redundancy in power supply system, so they are now considered as one of the most important part in the field of inverter technology. The parallel inverters can expand the capacity so that they greatly improve the power system's flexibility and thus the system's volume and weight are remarkably reduced. The current stress of the power switch is considerably lessened which means higher reliability, lower cost and higher power density. Because of the redundancy, the parallel system can improve the reliability furthermore.This paper mainly studies the parallel technology of the single phase inverter and presents a parallel strategy in which there is no power line connection but digital line connection among the inverter modules. This control strategy can be easily realized and the control effect is good.Different power circuits and control strategy of the single phase inverter in parallel condition are first analyzed, and half-bridge inverter is selected as the power circuit and current hysteresis control is selected as the control strategy.By the means of theory, simulation and experiment, the second part of this paper is then analyzed which is on the equivalent output resistance and inductance of the selected inverter and the effect to the output voltage's amplitude and phase caused by the different values of the inverter's component. It is concluded that by selecting certain precision level components, the difference of the output voltage amplitude is much greater than that of the output voltage phase.How the parallel inverters share the output power is analyzed and a completely different conclusion is got that the output active power's difference and passive power's difference of two parallel inverters are relative to both the output voltage amplitude's difference and output voltage phase's difference of the two parallel inverters.The parallel strategy is presented which is Based on Phase Synchronizing and Amplitude Modulating. Phase Synchronizing means synchronizing the phase of the reference voltage; Amplitude Modulating means modulating the amplitude of the reference voltage in according to the difference of the output current. Two amplitude modulating control strategies are presented which are the pre-circulating current amplitude modulating and the circulating current amplitude modulating. These two amplitude modulating control strategies are contrasted and it is found that the later one is better than the former one.Finally it is explained how the inverter circuit and the digital control circuit are design.