Development Of High Frequency Photovoltaic Micro-grid Key Equipment

With the highly development of industrialization, the demand of power is continuously increasing. In modern power industry, micro-grid based on distributed generation of renewable energy is thriving as a new way to distribute power. With the large-scale development of micro-grid, a more distributed and efficient way of power transfer is needed to make the power transmission more environmentally friendly and economical. Thus, the application of High Frequency Alternating Current(HFAC) technology in micro-grid is gaining more and more attention. In actual operation, a high-frequency photovoltaic(PV) micro-grid system should be low costs, high efficiency and high reliability. Based on these features, a prospect of 1.5k W single-phase 400 Hz inverter and a prospect of 3k W single-phase PV grid-connected inverter are developed in this paper.At the beginning, this paper presents an overview of the background and prospect of PV power generation, as well as the current development of micro-grid both at home and abroad. The advantages and prospects of HFAC technology applying in micro-grid are also pointed out in this paper. Then, the Maximum Power Point Tracking(MPPT) control strategy of PV power generation is analyzed. Besides, the PWM control strategy of the 400 Hz inverter is studied, as well as the overall control strategy of the PV grid-connected inverter, PLL technology and the inverter grid-connected current control method. Finally, in this paper, the system hardware and software design are elaborated, which includes the designs of main circuit, control circuit, detection circuit, protection circuit, auxiliary power supply and software development flow. Experiment programs are carried out to verify the performance of the designed inverters in this paper.To improve the energy utilization efficiency of the system, an in-depth study of the MPPT control algorithm is conducted. And based on the fixed-step Perturbation and Observation(P&O) method, an adaptive variable-step P&O method is adopted in this paper. In order to filter out the output harmonics of the 400 Hz inverter, the SHE-PWM control algorithm is presented. Thus, the complex circuits like multilevel topology or cascade-connected structure don’t need to be adopted in the main circuit. To improve the tracking control accuracy of the PV grid-connected inverter output current, PR controller is adopted to achive zero steady-state error tracking control of the grid-connected current. To reduce the disturbance on grid-connected current due to grid voltage, the gird voltage feed-forward compensation is also added.According to the design concepts mentioned above, a 400 Hz inverter based on the analogy chip controller and a photovoltaic grid-connected inverter based on dual DSP controllers are developed. Corresponding tests are completed and good experimental results are obtained. According to the experimental results, the design approach is feasible in this paper.The research in this paper was supported by the project of National Natural Science Foundation of China(51177050)--Distributed renewable energy technology research based on the high frequency alternating current technology.