Dynamic voltage stability enhancement of a microgrid with different types of distributed energy resources

Increasing energy demand is stressing the generation and transmission capabilities of power systems. Due to continuous growth and deregulation in electric power grid, voltage stability is the main problem concerning utilities. The limited fossil fuel based resources and the rising public awareness of environmental protection has created growing interest in renewable energy resources. Utilization of Distributed Energy Resources (DER) has the ability to meet these growing demands, while protecting the environment from greenhouse gas emission and promoting clean energy. DERs are connected to power systems at the distribution voltage levels and the concept of microgrid has been used for the interconnection. Most of the DERs (such as fuel cells, photovoltaic arrays, micro-turbines, etc.) cannot produce reactive power. Thus, they cannot support voltage stability during dynamic state. Having a large number of non-dispatchable, electronically-interfaced and renewable energy based DERs with the output power fluctuations makes microgrid system weak from the voltage stability standpoint. Proper voltage controllers should be designed to maintain the voltage stability of microgrids. Micro Grid Voltage Stabilizer (MGVS) was proposed in literature for voltage stability control of micro-grids which takes a weighted average of voltage deficiencies at the load buses and generates a control signal that determines the reactive power generations of the reactive sources. The performance of MGVS was studied (by other authors) for the case of constant power loads and reactive sources of inertial (rotating) type. However, microgrids are supplied by both inertial and non-inertial (converter-interfaced) distributed generators (DGs). In addition, load profiles can vary from polynomial loads to dynamic loads. All these components have to be considered for a realistic approach regarding voltage stability problems for a real microgrid environment. This dissertation is extending the study of the existing MGVS for the case of microgrid systems with more realistic loads (combined dynamic and polynomial loads) in presence of both inertial and non-inertial DGs. In addition, an improved alternative controller (called Extended Microgrid Voltage Stabilizer or EMGVS) with systematic parameter calculation methods is proposed. The effectiveness of EMGVS is investigated with a dynamic simulation for a microgrid test system in case of major disturbances or outages in both grid-connected and islanded modes of operation. The results show, with the addition of the proposed EMGVS, the dynamic voltage profile of the microgrid system at load buses is improved and enhanced reasonably.