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

Abstract

The limitations of classical carrier wave-based pulse width modulation (PWM) techniques prevent themfromensuringgoodoutputqualityformulti-levelinverters.Thispaperproposesanewslidingmodecontrol(NSMC)method for controlling cascaded H-bridge multi-level inverters (CHB-MLIs) to improve the output quality of theinverter, reduce the common-mode (CM) voltage with high-order harmonics, and achieve stable and robustnesscontrolfortheCHB-MLIs.TheNSMCmethodmodulatesthePWMpulsesforthemulti-levelinverterbycomparingthecontrolsignalu(t)andthecomparatorlevelswithoutusingcarrierwavetechniques.Thisapproachfacilitatestheformation of a control signal u(t) which can be flexibly adjusted to optimize the generation of PWM pulses. Toreducethechatteringproblemaroundthesliding-modesurfaceathighfrequenciesandtoincreasespeedconvergence, the integral sliding-mode surface integrated with a continuous control law is used to design thecontroller. Additionally, a first-order low-pass filter (LPF) with a variable cut-off frequency is added to the controllawtoimprovestabilityandreduceoscillationcausedbyrapidandlargechangesintheloadcurrentamplitude.ThestabilityofthecontrolsystemisvalidatedbytheLyapunovtheory.Simulationandexperimentaltestswereperformedon the same cascaded H-bridge five-level inverter (CHB-5LI) with an R-L load. The results show that the proposedNSMC method is robust and performs better efficiently for multi-level inverter control systems. Furthermore, theoutput 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 b eachieved by the proposed NSMC method.