Research On Phase-locked Loop Of Photovoltaic Grid-connected Inverter

To relieve the energy crisis, the development and utilization of renewable clean energy to achieve sustainable development has become a major task faced by countries around the world together, new energy sources such as solar power grid become inevitable trend. Grid inverter technology to ensure the inverter to the power grid in synchronous operation, must want to detect the phase of voltage and frequency of power grid. Lock power grid frequency and phase of phase-locked loop technology is good or bad will directly affect the performance of the inverter. Quickly and accurately detecting grid amplitude, phase and frequency information is low voltage across and the islands of the important guarantee of detection. In order to ensure the grid inverter work normally under non-ideal grid voltage must study the high-performance phase-locked circuit trace detection technology. Therefore, the study of phase locked loop technique has very important practical significance.Thesis research three-phase grid inverter topology structure.establish the mathematical model of three-phase grid inverter. On this basis, the three-phase grid inverter control technology. Selects the current inner ring double closed loop control strategy of voltage loop to the grid inverter grid current grid index requirements.Analyzing the working principle of phase-locked loop, three-phase grid inverter phase-locked loop model is set up. Comparison and analysis of single synchronous reference frame phase-locked loop (SSRF-PLL), based on the symmetrical component method of single synchronous reference frame phase-locked loop (EPLL-SSRF-PLL) and decoupled double synchronous reference frame phase-locked loop (DDSRF-PLL) the advantages and disadvantages. Simulation study of SSRF PLL, based on the symmetrical component method of SSRF PLL and DDSRF-phase-locking performance of PLL.To adopt decoupled double synchronous reference frame phase-locked loop (DDSRF PLL) to obtain the grid point of view, for the grid inverter output current to the power grid voltage of the same frequency and phase state of interconnection. Will be decoupled double synchronous reference frame phase-locked loop (DDSRF-PLL) model is applied to three-phase photo voltaic (pv) grid inverter system, under the non-ideal grid voltage (symmetric and asymmetric voltage drop, voltage frequency offset, power grid voltage harmonics and unbalanced three-phase voltage) power grid adaptive simulation research, validation decoupled double synchronous reference frame phase-locked loop (DDSRF-PLL) the correctness of the model and the effectiveness of the phase-locking performance.