Research On The Control Of Grid-connected Inverter

Nowadays, on account of the problems of environmental pollution and exhaustion of energy sources, the new energy application has been a hot spot that most countries compete against each other to develop. In this paper, grid-connected technology is studied based on a three-phase grid-connected inverter.This paper analyzes the grid-connected power generation system and the different structures of the inverter system. According to the requirements of the design, this paper selected the appropriate topology, introduced the various types of phase-locked loop and definited requirements of the grid system on the phase-locked loop, which laid a good foundation for the next study of the entire system.Combined with control objectives of grid-connected inverter, this paper makes an analysis on the grid mode and finally chooses a direct current-grid method. This paper also briefly describes the commonly used modulation method for grid-connected inverter.Based on the analysis of the structure and principle of a single synchronous reference coordinate system software phase-locked loop (SSRF SPLL), this paper establishes its mathematical model to analyze the steady-state and dynamic performance of the system, give the distorted voltage system tracking error, and make a simulation study by using matlab software. Since the results show that in the case of voltage distortion, the phase lock accuracy is not satisfactory; this paper uses the notch method and filtering method on phase-locked loop to improve the properties.The operational principle of symmetrical component method-based EPLL-SSRF SPLL, is presented. The structure model of EPLL-SSRF SPLL is established, and the impact of the dynamic parameters on its performance is studied. Simulation results have verified the good performance of EPLL-SSRF PLL under the voltage distortion.Based on the theoretical analysis and simulation, this paper designes the hardware system based on the DSP digital control, including power circuit, IGBT drive circuit and control circuit, draw the circuit schematic and PCB map and build a test system of the main power circuit.This paper introduces system software design based on the DSP control, including SPWM algorithm implementation and presents coordinate transformation based on the software lock-in algorithm and so on. According to the algorithm, this paper designes various parts of the flow chart and applies CCS2.2software and C language software to programming.