Proposing a New Hybrid Model for LFC and AVR Loops to Improve Effectively Frequency Stability Using Coordinative CPSS

Abstract

In order to get an accurate insight to load frequency control (LFC) issue in a realistic environment, taking into account the possible interactions between the frequency and voltage control loops is important. To obtain a realistic results, a complete dynamic model including the LFC and excitation control loops is required. In current article, a novel hybrid dynamic model is presented to analyze the mutual effects between the LFC and automatic voltage regulator (AVR) loops. For this purpose, the linearized LFC system is developed to include the excitation control system. So, a linearized Phillips-Heffron model of a single machine infinite bus (SMIB) power system is mixed with a single area LFC system model. A conventional power system stabilizer (CPSS) is also considered in the excitation control loop to improve the LFC performance. The proposed hybrid dynamic model is presented for a single area multi-unit power system incorporating gas, reheat thermal and hydro units with regarding the physical limitations of generation rate constraint (GRC) and governor dead-band (GDB). In the proposed hybrid dynamic model, the adjustable parameters of the CPSS and LFC loop are adjusted simultaneously using an improved particle swarm optimization (IPSO) technique under a 0.01 pu step load perturbation. Moreover, the system dynamic responses under a small-signal disturbance in reference voltage of the AVR is evaluated. Simulation results show that by employing this hybrid model, the damping performance of LFC system is augmented due to effective contribution of the CPSS in mitigation of the area low frequency oscillation (LFO).