Research On Parallel And Protection Technology Of High-power Single-phase Inverter

Based on two single-phase voltage-controlled inverters, the paper established the mathematical model of inverter and its parallel control system, then studies and analyzes the parallel system and protection methods. Through digital controlling, the paper researches waveform control strategy, digital phase-locked loop, voltage regulator through power error as well as protection strategy.The paper establishes the mathematical model of singer-phase inverter, analyzes factors makes distortion in the waveform, then propose a control scheme for high-power inverter. The paper introduces the principle of PID control and repetitive control, according to the 60KW single-phase inverter, the method of combining PID control and repetitive control is designed in the paper, then it's verified through simulation with Matlab.Through analyzing the parallel system, the paper reveals vector error of output voltage is the real reason of circulating current. Output impedance is another factor affecting the magnitude of circulating current. But if inverter is controlled with close-loop of voltage, the output impedance will decrease, and the feature of circulating current will change too, so there is contradiction between circulating current control and close-loop control.According to the 60KW inverter, the paper proposes a scheme based on distribute logic for parallel system control. Using digital phase-locked loop can make the phase of all inverters be the same, controlling the power error can make the magnitude be the same. Through these control strategy, there will be little circulating current, and all the inverters distribute power on average.The paper introduces protection methods for inverter, including overload protection, over-voltage protection, over-temperature protection and current limiting protection, primary on the latter two. Temperature transmitter and temperature transform current are design on the paper, too. DSP can gain the temperature of system on the time, and then it can protect the inverter from high temperature. The paper propose a strategy of current limiting combining hardware protection and software protection, which make the inverter always work even it's impacted by high-current. The paper also gives a improving strategy to limit output current for parallel system.According to the strategy for controlling parallel system and protecting inverters, it was tested on two 60KW inverters. The theoretic results and control strategy proposed on the paper are verified by the experimental results.