Introduction to Design of Power System Stabilizer to Improve Small Signal Stability Project:

Power system stabilizer is the remedial solution for instability caused by signals because of damping in the system. The design followed in constructing such a system has been adopted from Heffron-Phillip’s model. The modified Heffron-Phillip’s model which is simulated by using MATLAB/SIMULINK has proved to be a better option as compared to the conventional power system stabilizer.

Features of Heffron-Phillip’s model

With increasing demand of electricity and ensuring system stability performance at low frequency oscillations, the damping torque needs to be increased. The Heffron-Phillip’s modified model which is based upon Bode-plot technique, does not depend on external parameters.

Single Machine connected Infinite Bus

The model consists of generator excitation system and AC network which is similar.

Modified Heffron-Phillip’s Model

The model is based on linearizing the system. The system establishes a relation between the transfer function for the model and excitation of the system.

Power System Stabilizer

The parameters involved in the system are PSS gain (Ks), Wash out circuit, Compensator and limiter. The form of the system establishes a dependency on the number of the lead-lag stages. In cases of a dynamic compensator the form of the system is equal to the gain.The washout function should be considered while assessing the performance of PSS. The value of this function should be high enough to allow signals to pass through unaffected.

Performance of stabilizer

Single Machine connected Infinite Bus/SMIB test system is used here. Bode plot is drawn comparing the transfer functions. Mathematical equations infer the stabilizer gain for the system.Graphs also depict the fault obtained at the bus containing the transformer. It is cleared by tripping. The comparison of the response in same, strong and weak show variations in power factor but oscillations are effectively damped.


The modified Heffron-Phillip’s model can be used and tested on multi-machine systems.

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