Discrete PLL control for single-phase fuel cell grid connected system

Utility-signal information, such as frequency and phase angle, is very important in many industrial systems. Especially in the power electric grid connection application, the PLL control is used to synchronize the inverter current to the grid voltage to make the power factor as high as possible. However, for a single-phase system, the utility-signal information is much more difficult to acquire than three-phase system. Generally, the frequency and phase angle of a single-phase voltage are obtained by detecting the zero-cross point. Yet, this method cannot provide the utility-voltage information instantaneously and is very sensitive to noise. Another PLL topology based on quadrature two phase frequency detection method is proposed to improve the former method. But its dynamic response for the frequency change is not so satisfying and the choice of the type of components is much more complex. Accordingly, a novel discrete PLL based on the mean value PID control with automatic gain control is proposed in this paper. The proposed method is programmed in C language and compiled to MEX32 executable file as a RTW S-function, and is verified by simulation in Simulink environment. The algorithm uses automatic gain control to optimize the performance of the PID controller, and its performance is also demonstrated by the simulation result of a two-loop feedback fuel cell grid connection system model.