H_∞ robust control of load frequency in diesel-battery hybrid electric propulsion ship

Considering the load frequency fluctuation in the shipboard integrated power system caused by such stochastic uncertainty as wind, wave and current, the battery is adopted here to compensate for the difference between diesel generator output power and ship demand power, and the secondary frequency control is used for the diesel generator to guarantee the power balance in the shipboard integrated power system and suppress the frequency fluctuation. The load frequency control problem is modeled as a state space equation, the robust controller is designed by selecting the appropriate sensitivity function and complementary sensitivity function based on the H_∞ mixed sensitivity principle, and the controller is solved by the linear matrix inequality(LMI)approach. The amplitude frequency characteristics denote the reasonability of the designed controller and the design requirement is satisfied by the impact of the impulse signal. The simulation results show that, compared with the classical PI controller, the controller designed by the H_∞ robust method can significantly suppress frequency fluctuation under stochastic uncertainty, and improve the power variation of the diesel generator, battery and state of charge(SOC). The robust stability and robust performance of the power system are also advanced.