Model Predictive Control For High-Power Low-Switching Frequency Grid-connected Inverters

The development of different types of new energy power generation, such as photovoltaics and wind turbines, has provided great opportunities for the implementations of high-power inverters. Howere, in these high-power low switching frequency inverter applications, control strategy has always been a hot and difficult research topic.With the development of fast and powerful digital signal processors (DSPs) and microprocessors, finite control set model predictive control (FCS-MPC) has receiving more and more attentions in the control of high-power grid-connected inverters. Howere, at the present state of the art, for the FCS-MPC system of the conventional three-phase grid-connected inverters with output LCL-filter, how to achieve stable and efficient operation is still in the theoretical research stage.In this paper, a three-phase grid-connected inverter with output LCL-filter is selected as the control obeject and hysteresis model predictive control (HMPC), which is a variant of FCS-MPC, is selected as the research control scheme. Firstly, in order to ensure the stable operation of the control system, two aspects of the research have been done in this paper. On the one hand, the resonance characteristics of the system with LCL filter based on the HMPC are analyzed and an active damping (AD) scheme is then given. On the other hand, the impacts of the modeling error on the system stability and average switching frequency are analyzed in detail. Then a new switching frequency-adaptive control scheme which uses the average switching frequency to adjust the parameter value of the predictive model online is presented. The new control scheme can keep the average switching frequency within an acceptable operational margin, whilst improving the stability of the control system. Secondly, in order to ensure the efficient operation of the control system, a new method to combine the discontinuous modulation strategy and the HMPC is proposed. The proposed new method can make the phase corresponding to the maximum phase current producing a clamping area. Finally, through the simulation analysis and experimental verification, the results show that the proposed control scheme is effective.