A Robust Control for Five-level Inverter Based on Integral Sliding Mode Control

The limitations of classical carrier wave-based pulse width modulation (PWM) techniques prevent them from ensuring good output quality for multi-level inverters. This paper proposes a new sliding mode control (NSMC) method for controlling cascaded H-bridge multi-level inverters (CHB-MLIs) to improve the output quality of the inverter, reduce the common-mode (CM) voltage with high-order harmonics, and achieve stable and robustness control for the CHB-MLIs. The NSMC method modulates the PWM pulses for the multi-level inverter by comparing the control signal u(t) and the comparator levels without using carrier wave techniques. This approach facilitates the formation of a control signal u(t) which can be flexibly adjusted to optimize the generation of PWM pulses. To reduce the chattering problem around the sliding-mode surface at high frequencies and to increase speed convergence, the integral sliding-mode surface integrated with a continuous control law is used to design the controller. Additionally, a first-order low-pass filter (LPF) with a variable cut-off frequency is added to the control law to improve stability and reduce oscillation caused by rapid and large changes in the load current amplitude. The stability of the control system is validated by the Lyapunov theory. Simulation and experimental tests were performed on the same cascaded H-bridge five-level inverter (CHB-5LI) with an R-L load. The results show that the proposed NSMC method is robust and performs better efficiently for multi-level inverter control systems. Furthermore, the output quality of the inverter is significantly improved compared to classical carrier wave-based PWM techniques, with a reduced CM voltage and fewer high-order harmonics, resulting in reduced losses and switching frequency. Therefore, the stability and strong robustness of the CHB-MLIs can be achieved by the proposed NSMC method.