Research On Control Strategy Of Two Stage Inverter

In the two-stage single-phase inverters, because the first-stage power converters provide the second-stage inverters with second harmonic power, it will generate the second harmonic current fluctuation in the first-stage power converter. This paper takes a two-stage single phase inverter with a Boost converter in front as an example to study the control strategies for the suppression of the second harmonic fluctuations of the inductor current of the Boost converter as output voltage waveform control of inverter with nonlinear load is a hot research topic in inverter control, this article has also launched a corresponding research on it.First of all, the paper analyzes the working principle of the Boost converter and the conduction mechanism of second harmonic current when Boost converter is with an inverter load. On this basis, designing Boost converter circuit parameters, building small signal mathematical model of Boost converter and designing basic double closed loop controller.Secondly, this article derives and analyzes the transfer function of the output current of Boost converter to the inductor current under dual-loop control. Two methods were proposed to suppress the second harmonic fluctuations inductor current: method 1, connecting a band stop filter with its center frequency is 100Hz in voltage loop. method 2, adding a bandpass filter feedback in the current feedback channel, Wherein the first method obtains the optimal suppression effect.Then , this paper carried out a research Aiming inverter with nonlinear load. Because the output current of inverter with nonlinear load is discontinuous, and the inverter Alternatively works in the no-load and light load, heavy three conditions. So in the design of dual-loop controllers, three different conditions are considered, each condition is divided into two cases,the current inner loop decoupling and not decoupling, and six groups of different controllers were designed.After that, on the basis of double closed loop control, the inverter output current was regard as a kind of disturbance. Based on this view point, this article respectively proposes load current feed-forward method on the stationary coordinate system and the dq coordinate system to suppress the effect of load current on output voltage. The design method of the feed-forward controller is analyzed in detail. Through frequency domain analysis,feed-forward control reduces the inverter output impedance, so this method can suppress the effect of output current on the output voltage. As a comparison, the control strategy of double closed loop and repetitive control is introduced, and the design method of the repetitive controller is introduced in detail.In the end, the simulation verification and analysis are carried out to verify the correctness of the theoretical analysis and the effectiveness of the proposed control strategy.