Droop Control of Parallel Inverters with LCL Filter and Active Damping in Stand-alone Operation

-Because of the acute shortage of conventional energy resources, renewable energy harness is gaining attention. Voltage source inverter forms the interface to feed the power from the renewable source to utility. In order to increase the modularity of the system, the use of several parallel inverters of reduced rating is preferred. An effective control strategy to maintain the amplitude and frequency of output voltages of each inverter at the specified values is necessary, in order to avoid circulating currents and to share load currents proportionally. When inverters are connected in parallel without communication each inverter should be able to form the grid. This paper presents a simple and effective droop control strategy for two three phase inverters to develop a grid. Each inverter is assigned with an LCL filter at the output and active damping. The control strategy consists of two control loops, an outer voltage control loop and inner current control loop.