Research On Control Of Photovoltaic Power Generation System Based On Energy Storage Quasi Z-source Cascaded H-bridge Inverter

Solar photovoltaic power generation is easily affected by environmental conditions and has intermittent and instability.As the core component connecting photovoltaic cells and users power grid,the structure,reliability and efficiency of inverter play a vital role in the whole system.The photovoltaic system structure of cascaded H-bridge has the characteristics of high efficiency,small filter volume,low cost and easy modularization.The inverter topology of Quasi-Z source has high stability,efficiency and economy for switching devices,but the application of a single photovoltaic cell has the defect of low output voltage.Therefore,this thesis studies the multi-level inverter（ES-qZS-CMI）with energy storage Quasi-Z source cascaded H-bridge topology.It integrates energy storage system,Quasi-Z source network and cascaded multi-level inverter,and has unique advantages in photovoltaic power generation system.Firstly,this thesis introduces the working principle of ES-qZS-CMI,and establishes the mathematical models of DC component and double frequency component of photovoltaic power generation system based on the traditional mathematical model of ESqZS-CMI.The mathematical model considers the influence of photovoltaic panel terminal capacitance and energy storage battery on frequency doubling at the same time,so that the parameters of two capacitors and two inductors in the traditional symmetrical structure do not need to be equal respectively.After randomly selecting three groups of different impedance network parameters,the effectiveness of the model is verified by the comparison of model calculation and simulation results.Secondly,according to the light sufficiency of the system,a comprehensive control strategy suitable for high light intensity operation and low light intensity operation is proposed to reduce the impact of insufficient light on photovoltaic cell power generation and ensure the normal operation of the system under unstable external conditions.Then,aiming at the high control complexity of the system under the traditional master-slave control and centralized control strategy,an ES-qZS-CMI model switch driven predictive control algorithm is proposed,so as to reduce the control links of the system,achieve the effect of multi-threaded cooperation of multiple control objectives and avoid the complexity of control links.Finally,aiming at the battery protection of energy storage system,a battery SOC balance control method is proposed to stabilize the power fluctuation of the system and prevent the damage to the battery caused by the rapid reduction of charge.