An experimental study of frequency droop control in a low-inertia microgrid

Abstract

The use of distributed generation in microgrid systems is becoming a popular way to provide a reliable source of electricity to critical loads. Efforts in disaster relief operations and national defense applications require a mobile, scalable power grid that is easily constructed and robust enough to handle radical system changes. These microgrids are usually built using low-inertia generators that are portable and can easily adapt to a rapidly changing environment. Despite the benefits of low-inertia generation, the drawback is that large load steps can cause a system to become unstable, losing synchronism and damaging both generators and loads. A control system is necessary to bring stability while providing efficient and robust electricity to the microgrid.

A droop control scheme uses only local power to detect changes in the system and adjust the operating points of the generators accordingly. The droop control uses the real power out of a generator to calculate the ideal operating frequency. This relaxing of a stiff frequency allows the microgrid to dampen the fast effects of changing loads, increasing the stability of the system. Droop control is reviewed and simulations will be used to determine the effectiveness of the droop controller as well as alternative forms of the traditional droop control. Experimental results are presented detailing how the droop gain affects power distribution and system stability.