18-07-2011, 12:41 PM
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Design Of Power System Stabilizer To Improve Small Signal Stability By Using Modified Heffron-Phillip’s Model
Abstract:
One of the major problems in power system operation is related to small signal instability caused by insufficient damping in the system. The most effective way of countering this instability is to use auxiliary controllers called Power System Stabilizers, to produce additional damping in the system. Generally Heffron-phillip’s Model of a synchronous machine is commonly used for the small signal stability analysis. A Modified Heffron-Phillip’s (K-constant) Model is derived for the design of Power System Stabilizers; knowledge of external parameters, such as equivalent infinite bus voltage and external impedance value are required for designing a conventional power system stabilizer, Modified Heffron-Phillip’s Model power system stabilizer. The efficiency of the proposed design technique and the performance of the stabilizer has been evaluated over a range of operating and system conditions and the performance of the proposed Modified Heffron-Phillip’s Model is much better than the conventional power system stabilize.. The proposed work describes the ‘Design of Power System Stabilizer by using Modified Heffron-Phillip’s model’ is simulated by using MATLAB/SIMULINK.
Keywords: Modified Heffron-Phillip’s model (Mod HP), Heffron-Phillip’s model (HP), Power System Stabilizers (PSS), Single Machine connected Infinite Bus (SMIB).
1. Introduction
Electric power systems are highly nonlinear systems and constantly experience changes in generation, transmission and load conditions. With the enormous increase in the demand for the electricity almost all major transmission networks in the world are operated close to their stability limits. In such systems fast excitation control plays a crucial role. The synthesis of effective excitation controllers for all operating conditions still remains a difficult task due to the following reasons.
1) Large variations of the possible operating conditions.
2) Large variety of disturbances that can occur in various
Parts of the power systems.
3) Variation of plant parameters as result of power network configuration changes.
In such systems fast excitation control plays a crucial role. The excitation controllers are designed to regulate the terminal voltage. Automatic voltage regulators also enhance the overall stability of the system. Over the years a variety of design procedures and algorithms have been proposed for the design of power system stabilizers for different models of power system.
In order to reduce this instability effect and improve the system stability performance it is useful to introduce supplementary stabilizing signals at low frequency oscillations, to increase the damping torque of the synchronous machine [1], [2], [3]. Different approaches have been proposed in the literature to provide the damping torque required for improving the stability, the first proposed method is the conventional power system stabilizer [4] it is based and design the Bode plot technique, second method proposed Modified Heffron-Phillip’s power system stabilizer, it is based on the Bode plot technique [5]. Generally conventional power system stabilizer is use the information of external parameters, such as equivalent infinite bus voltage and external impedance values. In this Modified Heffron-Phillip’s method, information available at the secondary bus of the step up transformer is used to set up a Modified Heffron-Phillip’s Model.
2. Modelling of System
System is treated as in this model is SMIB. Modelling of SMIB consisting the generator, excitation system, AC network etc. A SMIB power system model as shown in Fig. 1 is used to obtain the Modified Heffron-Phillip’s model parameters.
