Power flow control of a single distributed generation unit with nonlinear local load

Distributed generation units with small energy sources, such as fuel cells, micro-turbines, and photovoltaic devices, can be connected to utility grid as alternative energy sources besides providing power to their local loads. The distributed generation units are interfaced with utility grid using three phase inverters. With inverter control, both active and reactive power pumped into the utility grid from the distributed generation units can be controlled. Reactive power flow control allows the distributed generation units to be used as static var compensation units besides energy sources. This paper presents a distributed generation unit control technique which provides robust voltage regulation with harmonic elimination under island running mode and decoupled active and reactive power flow control under grid-connected mode. The control technique, which combines discrete-time sliding mode current control, robust servomechanism voltage control, and integral power control, enables seamless switching between island mode and grid-connected mode and guarantees sinusoidal line current waveform under nonlinear local load. The P Q coupling issue is addressed and the stability of the power control loop is proved using Lyapunov direct method.