Modeling and Control of Utility Interactive Inverters

As alternative energy sources become more competitive with traditional energy sources, the proliferation of distributed generation sources that interface to the electric utility grid continues. Most of the alternative energy sources either produce dc directly (solar photovoltaics or fuel cells) or create dc before inversion to the utility (wind or hydroelectric turbines). The dc electric energy is injected into the ac utility through an inverter. The resulting ac electric energy has to be compatible with the energy within the ac utility system at the point where the inverter is connected to the utility system. The control, design, and operation of the inverter must meet the applicable standards. This paper provides an overview of modeling and control of the inverter system that interfaces with the utility grid. Recent advancements in the state of the art are presented along with practical implementations. Simulation and experimental test results are provided to emphasize concepts and illustrate issues. Embedded control of the inverter is assumed to be implemented through digital control techniques. Algorithms are given in general form for application to single- and three-phase inverters with any number of levels.