Abstract:

In DC microgrids based on photovoltaic and energy storage systems, the bidirectional DC-DC converter is a key interface between the energy storage equipment and DC bus, and its performance under the large signal disturbance of photovoltaic output power and load directly affects the stable operation of the DC bus. Therefore, a nonsingular terminal sliding mode control strategy based on a nonlinear disturbance observer is proposed in this study. First, the state-space model of the bidirectional DC-DC converter system is transformed into Brunovsky's standard form using the exact feedback linearization method based on differential geometry theory, and the disturbances are estimated using the nonlinear disturbance observer as the compensation channel. Moreover, we design a nonsingular terminal sliding mode controller and analyze the stability, as well as convergence, of the proposed control strategy based on Lyapunov stability theory. Finally, we perform simulations to prove the effectiveness of the proposed control strategy. The simulation results show that compared with typical nonlinear control methods in the literature, the proposed control strategy has a fast response time, small overshoot, and steady-state error under the large signal disturbance of photovoltaic output power and load.

Key words: DC microgrid, bidirectional DC-DC converter, nonsingular terminal sliding mode control, nonlinear disturbance observer