Study On Control Strategy Of SL-qZSI Photovoltaic Grid-Connected System Based On Improved MPC

As a key link of solar power system,photovoltaic grid-connected inverter is the core of energy conversion and control.Compared with the traditional two-stage inverter,the switched-inductor quasi Z source inverter uses a unique shoot-through state to boost the voltage and eliminate dead time,which is beneficial to reducing the cost of photovoltaic power generation and outputting a higher quality waveform.Model predictive control,as an advanced control strategy,can make up for the complex multi-variable control and difficult modulation of switched-inductor quasi Z source inverter.Therefore,the model predictive control strategy is very suitable for switched-inductor quasi Z source inverter.In addition,the problem of delay time of model predictive control algorithm reduces the waveform quality of controlled variables,so it is imperative to improve the model predictive control algorithm.In summary,the study on model predictive control strategy of switched-inductor quasi Z source inverter is carried out in the following three aspects.(1)Firstly,based on the topologies study of the through and non shoot through state of the switched-inductor quasi Z source inverter,the boosting principle is revealed.By studying the principle and the design method of model predictive control strategy,the design method of model predictive control strategy for switched-inductor quasi Z source inverter is determined.(2)Then,through the topology analysis of the AC side and DC side of the photovoltaic grid-connected system of the switched-inductor quasi Z source inverter,the prediction models of grid-connected current,capacitor voltage and inductor current are established and the evaluation criterion is built by constructing the cost function.In this way,the flow of model predictive control algorithm for switched-inductor quasi Z source can be formed.The simulation results show that the model predictive control strategy proposed,which means that it is very suitable for the switched-inductor quasi Z source inverter.(3)Finally,through two improved model predictive control algorithms,the delay time of the traditional model predictive control algorithm is reduced,thereby reducing the oscillation of the controlled variables.Because the values of inductance prediction model are consistent in the non shoot through state,the first improved algorithm uses this characteristic to prejudge whether the shoot-through state is the optimal switching state or not by establishing the subcost function of the inductance current.As a result,the calculation of a variety of non shoot through states can be minimized,thus reducing the delay time.The second improved algorithm is based on the two-step prediction model,and can eliminate the delay time by selecting the next optimal switching state in advance.The simulation results also demonstrate the effectiveness of the two improved algorithms.By realizing the model predictive control strategy of switched-inductor quasi Z source inverter and improving the delay time of model predictive control algorithms,the multivariable control of switched-inductor quasi Z source inverter is realized simply and the effect is ideal.It is shown that the switched-inductor quasi Z source inverter can play a greater role in photovoltaic power generation.