Design of sliding mode controller for three phase grid connected multilevel inverter for distributed generation systems

Design and implementation of constant frequency sliding mode current control for three phase grid connected Nine Level Multilevel Inverter is presented for distributed generation systems and power quality applications. Limitations in present design of sliding mode controller for grid connected systems are discussed and method to overcome these limitations is proposed. Proposed constant frequency sliding mode control retains the advantages of good dynamic response as in hysteresis control, better reference tracking capability and robustness like predictive control. This current controller has the advantages in constant switching frequency and less sensitivity to parameter variations and non linear loads. Among three well-known multilevel inverter topologies, diode clamped topology is the most common type of converter which is widely used in Wind turbine and photovoltaic applications, as the component device rating and number can be reduced. The proposed controller for multilevel diode clamped inverter is validated through Matlab simulation with inverter performance indices like Reference current tracking (steady state error), Dynamic response(change in grid current reference), Current and Voltage THD and also stability of the controller under non linear load variation is validated with the help of phase plane trajectory. Hence The proposed controller is expected to be an attractive solution for grid connected inverter application which includes distributed generation, power quality as well as it is expected to serve drives application.