Abstract: Aiming at the non-linear, large inertial, uncertain parameters and multi-disturbances of the main steam temperature object in power plants, a mixed H₂/H_∞ optimal PID control scheme was designed. The multiplicative perturbed boundary of the H_∞ and the effective range of the PID controller parameters were given under the system being closed-loop stability. An improved gravitational search algorithm was proposed in order to obtain optimum performance indicators. The effectiveness of the algorithm was supported through testing on typical test functions, then the algorithm was applied to optimize the parameters of the main steam temperature system Mixed H₂/H_∞ optimal PID controller. Simulation results show that the optimized main steam temperature control system has good control quality, and unknown disturbance can be overcome, and has strong robustness.

Key words: mixed H₂/H_∞ control, gravitational search algorithm, main steam temperature system, PID control, robust stability