RESEARCH ARTICLE Nitin Kumar SAXENA, Ashwani Kumar SHARMA Estimation of composite load model with aggregate induction motor dynamic load for an isolated hybrid power system © Higher Education Press and Springer-Verlag Berlin Heidelberg 2015 Abstract It is well recognized that the voltage stability of a power system is affected by the load model and hence, to effectively analyze the reactive power compensation of an isolated hybrid wind-diesel based power system, the loads need to be considered along with the generators in a transient analysis. This paper gives a detailed mathematical modeling to compute the reactive power response with small voltage perturbation for composite load. The composite load is a combination of the static and dynamic load model. To develop this composite load model, the exponential load is used as a static load model and induction motors (IMs) are used as a dynamic load model. To analyze the dynamics of IM load, the fifth, third and first order model of IM are formulated and compared using differential equations solver in Matlab coding. Since the decentralized areas have many small consumers which may consist large numbers of IMs of small rating, it is not realistic to model either a single large rating unit or all small rating IMs together that are placed in the system. In place of using a single large rating IM, a group of motors are considered and then the aggregate model of IM is developed using the law of energy conservation. This aggregate model is used as a dynamic load model. For different simulation studies, especially in the area of voltage stability with reactive power compensation of an isolated hybrid power system, the transfer function ΔQ=ΔV of the composite load is required. The transfer function of the composite load is derived in this paper by successive derivation for the exponential model of static load and for the fifth and third order IM dynamic load model using state space model. Keywords isolated hybrid power system (IHPS), compo- site load model, static load, dynamic load, induction motor load model, aggregate load 1 Introduction An isolated far located remote area where the availability of grid connected power supply is almost impossible and uneconomical; a wind-diesel based isolated hybrid power system (IHPS) is most promising to provide continuous, efficient, economical and reliable electrical energy [1]. In such a system, wind and diesel based electrical sources may be operated by induction generators and synchronous generators respectively. The advantages of such a hybrid system have been explored [2,3]. Apart from balancing the electric power supply and demand, the ancillary services are also important issues for the system operations. The reactive power issue is one of them [4]. When the load and/ or input reactive power demand fluctuates, the voltage will also change. Without any compensation, this voltage variation may go beyond the voltage permissible range and therefore such power would not be acceptable for end users [5], and therefore static and dynamic compensation techniques are required. Electrical energy generation and consumption is a combined process for any power system. In previous works based on the IHPS, the dynamics of wind and diesel based generators have been depicted in detail. However, the load dynamics have not been considered in detail and even ignored by considering the static load model in the system [6]. Loads, however, have a significant impact on a system. It has been concluded that the voltage stability of a power system and choice of compensation techniques signifi- cantly depends on the selection of the load model and its parameters [7]. To effectively analyze the dynamics of the IHPS, the loads need to be considered along with the generators in a transient analysis. Power system planners and operators attempt to accurately model loads in order to analyze their systems. However, it is very difficult to Received December 17, 2014; accepted March 25, 2015 Nitin Kumar SAXENA (✉), Ashwani Kumar SHARMA Deptment of Electrical Engineering, NIT Kurukshetra, Haryana 136119, India E-mail: nitinsaxena.iitd@gmail.com Front. Energy DOI 10.1007/s11708-015-0373-7