The Reasearch Of The Fast Robust Composite Control Method For Three-Phase Photovoltaic Grid-connected System And Device Development

Since the 21st century,humanity's demand for energy is growing while environmental pollution and energy crisis become increasingly prominent.It is imperative to develop renewable energy and adjust energy structure.In view of the advantages such as sufficient energy supply,extensive application,clean and environmental friendly power generation process,photovoltaic power generation system has become a research hotspot.Based on the project of "50kW three-phase photovoltaic grid-connected inverter study”,this paper has a further study in DC/AC control technology,MPPT control technology and device development technology.Firstly,the main circuit uses single-stage non-isolated topology after introducing a series of grid-connected topologies such as the fundamental frequency isolation type,high frequency isolation type,multi-level non-isolated type,single-stage non-isolated and analyzing their advantages and disadvantages,respectively.And then the equivalent transformation model from three-phase full bridge to single-phase half bridge is deduced.Combined with theoretical calculation and engineering experience,and based on the equivalent transformation model,it determines the electrical parameters of the power device,DC-side capacitor and filter inductor in the main circuit.Secondly,based on the area equivalent principle,it analyzes and improves traditional deadbeat control parameters,using the predicted average grid voltage instead of the instantaneous sampling to calculate that improves the accuracy of control parameters effectively.A fast robust PWM method is proposed to achieve equivalent duty cycle by loading duty cycle parameters twice in one control cycle,which effectively solves the delay problem caused by the traditional one-step-control method,improves the critical stability gain of system and enhances the dynamic response.A maximum power tracking(MPPT)control method with hysteresis adaptive variable step is proposed,which can provide the adaptive tracking step based on the hysteresis power fluctuation.The proposed MPPT control method has a higher control precision and faster response speed,which effectively solves the contradiction between control precision and response speed in the traditional maximum power tracking control method.Then,the control structure with digital signal processor(DSP)as the core processor is put forward.And the main hardware circuit and their working principle including power module,AD sampling circuit,zero-crossing capture,fault detection human-computer interaction is introduced in the control system with three-phase photovoltaic grid-connected inverter.Furthermore,the flow charts of main program,interrupt program,protection program,and communication program are proposed in this paper.Finally,a simulation model for three-phase photovoltaic grid-connected power generation system is established and a 50kW three-phase photovoltaic grid-connected inverter prototype is designed.In addition,a practical experiment platform that simulates photovoltaic arrays is also proposed and built for the inverter prototype experiment.Simulation and experimental results verify the effectiveness of the proposed methods.