Design Of Three-Phase Grid-Connected Inverter For Fuel Cell

The fuel cell generation is one of the key solutions to the energy crisis we are facing now days. As the most important part of the fuel cell generation, the three-phase grid-connected inverter affects directly the performance of the generation and the quality of the grid energy. A lot of research has been done in this paper about the three-phase grid-connected inverter and the main content as follows:Based on the requirements, the author did a deep investigation on the main circuit topological structures, the output current filter and the control method and proposed the overall solution.The author compared the characteristics of several typical filters, proposed the LCL-filter as the output current filter for its good depression on switching ripples and harmonics and an passive damping method, cascading a damping resister with the filtering capacity to stabilize the system. And calculate all the parameters of the LCL-filter.Based on the mathematical model, a control method based on grid voltage phaser orientation is proposed. There are two control loops, the inner grid side current loop for the steady accuracy and fast dynamic performance and the outer voltage loop to determine the output active power. The model in dq frame was decoupled as to control the active and reactive current. Space vector PWM was proposed as to increase the efficiency of the DC line and to decrease the switching power consumption.To guarantee a good grid voltage phase and frequency tracking performance under different conditions such as three-phase voltage unbalance, phase jump or frequency shift, software phase locked loop (SPLL) based on symmetrical components and frame transformation was prosed. That’s to separate the positive sequence from the grid voltage and then transform it into the dq frame for the PI controller to lock the phase.All the method proposed above are modeled and simulated in MATLAB and the results are correct.