A Study on CLLC-SMES System Based on the Passivity Control Strategy

SMES systems as power compensation devices can effectively improve the transient stability of the power system. Due to the nonlinear and strongly coupled characteristics of the compensation device, an effective transfer function cannot be established, such that the traditional PI control by the linearization cannot accurately describe the complex nonlinear system. In this paper, a passive control strategy is introduced for the SMES System based on CLLC resonant converter to solve the problems that the traditional PI control cannot accurately describe the complex nonlinear system and the parameters’ settings are complicated. First, according to KVL and KCL, the mathematical model of the SMES system based on the CLLC resonant converter in the (d, q) coordinates is derived and established. Second, based on passive control theory, the port-controlled dissipation Hamiltonian model of CLLC-SMES is given. Third, combined with the passivity of SMES, the energy equation is established and the active and reactive power are analyzed respectively for the balanceable expectation, and then the energy equation is solved to obtain the drive signal of the switch tube. Fourth, the stability of the passive controller is verified by the Lyapunov equation, and the feasibility of the passive control strategy of CLLC-SMES is verified by simulation. The results show that compared with the traditional PI control strategy, the power compensation system based on the passive control strategy does not need to establish the transfer function and the parameters are simple to adjust. It can not only track the active and reactive power commands quickly and accurately but also improve the transient state of the power system effectively.