This paper develops a circuit model and controllers of fuel cell based distributed generation systems (DGS) in a standalone AC power supply. Dynamic model of the fuel cell is considered. To boost low output DC voltage of the fuel cell to high DC voltage and compensate for its slow response during the transient, two full-bridge DC to DC converters are adopted and their controllers are designed: a unidirectional full bridge DC to DC boost converter for the fuel cell and a bidirectional full-bridge DC to DC buck/boost converter for the battery. For a three-phase DC to AC inverter, a discrete-time state space model in the stationary dq reference frame is derived and two discrete-time sliding mode controllers are designed: voltage controller in the outer loop and current controller in the inner loop. To demonstrate the proposed circuit model and control strategies, a simulation test-bed using Matlab/Simulink is developed and various results are given.