Three Phase-Lock Loop Design And Photovoltaic Grid-Connected Inverter Control

With the development of the global economy, energy shortages, ecological deterioration of the environment and other issues have become increasingly prominent. Many countries used wind, solar and other renewable energy sources as the primary means to respond to the dual challenges of the new century. The dual challenges including energy resource and climate change. The amplitude and phase information of grid voltage is the reference of gird-connected inverter control and power flow control. A high performance PLL system can not only track grid transient changes quickly and accurately but also extract the positive sequence component of grid voltage. It can provides reference signal for gird-connected inverter. Therefore, study of phase-locked loop system has a very important practical significant.This article focused on analysis and discussion of grid-connected PV control technology. Focused on maximum power tracking, grid-connected control and phase lock under unbalance grid voltage. This article gave a deep theoretical analysis.This article studied the works, the basic structure and the mathematical model of a photovoltaic grid-connected inverter. It also completed analysis of grid inverter controller, designed a grid-connected inverter control system and deduced the algorithm of control system parameter tuning. Using Proportional Resonant Controller completed the three-phase photovoltaic grid-connected inverter control under coordinate system of the two-phase.This article focused on power flow control of a photovoltaic gird-connected inverter under unbalance grid voltage, and design of a phase-locked loop tracking system. The main idea is using the opposite rotation of two groups of Park transform, and cross decoupling transformation results. Ultimately to obtained the fundamental positive sequence phase of the three-phase grid voltage under unbalanced conditions.Next, this article applied the designed three-phase locked loop to photovoltaic grid-connected inverter and created a simulation model in MATLAB, to verify the performance of the inverter controller. Validation through prototype testing, test results showed that the three-phase locked loop has achieved the synchronization requirements of the PV inverter system and gained a unit power factor for the inverter.Finally, this article used Verilog language to complete the design of FPGA-based three phase-locked loop. First, the modular design of the three-phase PLL, and then implemented the phase detector, loop filter and the numerically controlled oscillator functions. And after the top-level connection, complete the design of the entire three-phase PLL. This article used the Modelsim simulation tool, completed simulation of the designed three-phase PLL. After analysis of the simulation results, showed that the designed three-phase PLL has achieved system synchronization performance requirements. At the same time it verified stability and viability of the system.