Design of decentralized variable structure stabilizers for multimachine power systems

Variable structure (VS) stabilizers possess the advantages of better transient response, insensitivity to plant parameter variations, etc. In general, variable structure controls involve measurements from all the states, which is not possible in a multimachine power system (MMPS). In this paper, the switching planes for the variable structure stabilizers are selected in such a way that computation of switching planes involves local state variables only. The coefficients of the switching plane equation are determined using the Riccati equation approach. Through the approximation of neglecting non-diagonal blocks of the state space matrix, at the design stage, a decentralized Variable Structure stabilizer (VS stabilizer) is obtained. To accept the switching plane so obtained, a check of the closed loop eigenvalues is made with the actual state space matrix. After computation of the switching plane, the variable gains are also selected in such a way that control signal computation involves only local state variables. This is possible as the gains of nonlocal state variables are small compared with local variables. The response of the system with variable structure stabilizers indicates that the system performance is improved.

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