Voltage and frequency droop control of a microgrid in islanded modes

Nowadays, there are increased amount of distributed generation and renewable resources (including geothermal, ocean tides, solar and wind) used in the microgrid systems, which are connected via the power inverters. Microgrid is a concept that the systems include at least one distributed generation resources and local loads can switch to islanded power distributed systems, [1]. Duo to the small scale of microgrid, the voltage and frequency of system will carry more severe fluctuations then the larger grids, which will be able to stable these fluctuations via the wider systems, [9]. The inverters can provide the stability and redundancy to the power systems. For the normally working of the high current electronic devices, it is deviation that several inverters operate in parallel in the systems, [3]. The inverter control methods which should be able to bring the reliable and efficient electricity to microgrid system have attracted much attention in recent years. Various droop control methods are regarded as the effective solving technique in conventional generation system. The droop control strategy is associated with using local power to detect the load changes of complex powers in the system and adjusting the outputs, automatically, [2]. The advantage of droop control method is to allow the distributed generators in the system can operate without external mechanism communications, [3]. No mechanical communication means the system can adjust and share the loads among distributed generators (connected via inverters) automatically when the loads change happen. This is based on the calculation of droop control characteristics. The droop control uses the real power to adjust the frequency of loads, and vary the reactive power to vary the voltage of loads. However, droop control scheme are different when the impact of complex impedance is considered. The experimental simulation results will be presented to illustrate how the droop control scheme impacts the power distributions of parallel-connected inverters