Overvoltage Suppression Strategy for Electrolytic Capacitorless Drives Using Sliding Mode Controller Based on Improved Variable Rate Reaching Law

The advantage of a permanent magnet synchronous motor (PMSM) electrolytic capacitorless drives lies in its small volume and long service life, as its dc-link uses small capacitance film capacitors. However, during the regenerative braking process of the motor, small capacitance film capacitors are prone to cause overvoltage in the dc-link. The PI regulators are widely used in traditional overvoltage controllers. However, the PI regulator depends on the system model. As the deceleration amplitude and deceleration rate of the motor increase, the voltage control loop gradually becomes unstable, which may lead to the failure of overvoltage suppression. For the purpose of improving the response speed and stability of the voltage control circuit, a sliding mode voltage controller (SMVC) utilizing an improved variable rate convergence law (IVRRL) is proposed in this article. Firstly, the mathematical model is established for the q-axis current and dc-link voltage. Then, SMVC is designed using exponential reaching law (ERL). To reduce the conflict between convergence speed and chattering suppression, a SMVC based on IVRRL is proposed. The convergence and stability of IVRRL have been proven. Finally, the proposed SMVC is validated on the experimental device of a PMSM electrolytic capacitorless drives.