Transient stability of distributed generators in the presence of energy storage devices

Several small-scale distributed generators DGs have been recently used in power and distribution systems. Placement of such small-generators to the power grid has numerous economical and environmental advantages. However, high penetration level of these devices could also have a significant impact on the voltage and angle stability limits of the system. This can be partly attributed to the fact that most DGs are inertia-less generators or sometimes having small inertia. Therefore, in non-conventional power systems where DGs are present, the overall system inertia will significantly decrease. Such low inertia may lead to loss of synchronism during abnormal fault conditions and large disturbances. One method to compensate for the reduced system inertia is to connect short-term energy storage to the DG bus. The entire unit is termed as virtual inertia or Virtual Synchronous Generator VSG. This paper introduces a methodology for stability enhancement of non-conventional power systems. The method utilizes the concept of virtual inertia to account for the transients that usually take place on power system. A control algorithm was integrated to the storage device that is connected to the DG bus through bidirectional DC-DC converter and DC-AC converter. The method was demonstrated on a 5-bus power system.