The Design And Control Of PSS Based On The Damping Torque Theory

The paper gives a detailed demonstration of damping torque theory in power systems.Based on this theory,coordinated design method is used to design the PSSs.The commonly adopted strategy for the coordinated design is to convert the design to a problem of parameter optimization by setting up an objective function.Thus parameter setting of PSSs can be carried out by searching the optimum of the objective function in the parameter space of PSSs.In this paper,a simple method of coordinated design of PSSs is proposed.Hence for the coordinated design of M PSSs in a multi-machine power system,the simplification is the reduction of dimension of parameter space of PSSs to M.Thus efficiency of searching the optimum of objective function of PSSs design is increased with the reduced dimension of parameter space.Proposed method of coordinated design in the paper is in two steps.Firstly by taking the damping torque contributions of a PSS to all synchronous generators in a multi-machine power system into consideration,and parameters of each of multiple PSSs are set for the PSS to supply the most damping to the electromechanical oscillation mode of interests.It is proved in the paper the setting can ensure the supply of damping to be most efficient.Parameters of all PSSs are set in a sequence.Secondly,the gain of all PSSs is set in coordination by parameter optimization.The optimal searching is in the M dimensional parameter space of M PSSs.An example multi-machine power system with multiple PSSs to be installed is presented in the paper to demonstrate and validate the method proposed in the paper.In order to give a deeper demonstration of this method,various forms of commonly-used objective functions are tested and compared.This paper also shows the collection of parameters in three-dimensional figure and in these figures,we can find a combination to minimize the sum of gains.Detailed examination of optimum for each form of objective functions is carried out to provide an insight into the connections of optimum with the objective functions in the coordinated design of multiple PSSs.As we know the common parameters optimum of PSSs would be nonlinear.There would exist multiple extreme values.In order to solve the problem,an artificial intelligence algorithm—fish swarm algorithm is used to optimize the parameters of PSSs.An example of power grid of Jiangsu Province installed with multiple PSSs and UPFCs is presented to validate the fish swarm algorithm method proposed in the paper.In the end,we compare and analyze the impact of PSSs and damping controllers installed in UPFC to the electromechanical oscillation mode of interests.The results show that the effects of damping controller installed on the UPFC are not significant.Hence,the parameters of PSSs are designed without damping controllers installed on the UPFC.Based on the design,system was simulated again in the BPA.It can be seen from the simulation that such design method can improve the stability of the system significantly.