Development Of High Frequency Isolated Grid-connected Inverter

As the key component of the photovoltaic power system, grid-connected photovoltaicinverter played a crucial role in the development and utilization of solar energy. Under thisbackground, the principle and design of grid-connected photovoltaic inverter was deeplystudied and researched in this paper. A1.5kW high-frequency isolated grid-connectedphotovoltaic inverter based on DSP control was successfully designed.The main circuit of high-frequency isolated grid-connected inverter contained two stages.The first stage was phase-shift soft-switching circuit and the second stage was full-bridgeinverter. The topology and operating principle of the two stages were analyzed in detail andthe crucial parameters of the main circuit were also selected and designed.The hardware and software control system of the grid-connected inverter based on DSPcontrol were designed systematically. The hardware control system included DSP minimumsystem, AD sampling circuit, driving circuit and various protection circuits. The whole idea ofthe software design was presented and the flow chart of the main program and interruptprograms were given. Besides, the method of PWM generation and digital phase-locked loopwere analyzed.By analyzing the control strategies of grid-connected, double closed-loop control methodwas chosen as the system control strategy, which included the outer loop of doubleclosed-loop with PI control and the inner loop with deadbeat current control. Then theprinciple of PI control and deadbeat current control were respectively analyzed in detail.Based on the characteristics of solar cells, the mechanism of maximum power pointtracking was expounded. The perturbation and observation method and the incrementalconductance method were discussed at emphasis. It was of great significance to avoid thegeneration of islanding which may cause serious problem. Passive detection method whichcombines the active frequency shift method and the active phase shift method was applied toobtain the minimum blind zone.An experiment platform was established for the high-frequency isolated grid-connected inverter and the experiment results showed that the grid-connected inverter had goodperformance of output current with low total harmonic distortion and high power factor. Thefunctions of MPPT and anti-islanding were proved to be feasible and effective, which verifiedthe practicality and reliability of the system control.