Research On MW-level Grid-connected Photovoltaic Inverter

Large-scale photovoltaic power station is the current domestic main form of renewable energy power generation. MW-level photovoltaic (pv) grid-connected inverter is considered to be an important research direction due to its superiorities of high efficiency, high power, high reliability. This thesis mainly discusses the design of MW level photovoltaic grid-connected inverter and the control strategy of low voltage ride through. The main research works are introduced as follows.Firstly, the design of power module is important and difficult for MW photovoltaic grid-connected inverter. In order to facilitate assembly and maintenance, power module adopts the modular design. Stray inductance is taken into account in the design of the power module. The design of DC capacitance, absorbing circuit, paralleling current-sharing circuit and water cooling are given. In addition, the feasibility and reliability of the power module are verified by simulation and module testing.Secondly, this thesis analyzes the control strategy of MW photovoltaic grid-connected inverter and the design of LCL filter. The double closed loop control strategy based on grid voltage orientation and parameter selection of the LCL filter are discussed. The stability of the system and the design correctness of the LCL filter are verified by the simulation and experimental results.Thirdly, in terms of the PV system commom mode leakage current, this thesis analyzes leakage generation principle and factors. On this basis, the improved SVPWM modulation strategy and the common mode rejection filter are discussed and comparison. Subsequently, common mode rejection filter circuit is designed and verified by experiment results.Fourthly, the control strategies of low voltage ride through are analyzed and studied under both symmetrically and asymmetrically voltage sags conditions. Control strategies of reactive power compensation and positive and negative sequence extraction are discussed and verified by experimental results.Finally, the performance of prototype is tested including THD, power factor, system efficiency, temperature rise and low voltage ride through. Experimental results show that MW photovoltaic grid-connected inverter can meet the design requirements.