A Modified Lyapunov-Function Based Control Scheme for Three-Phase Three-Level Two-Leg Grid-Tied NPC Inverter

Abstract

In this paper, a three-phase three-level two-leg neutral point clamped (NPC) grid-tied inverter is proposed. Since, the proposed inverter topology has only two three-level legs, it employs totally eight active switches and four clamp diodes. Thus, advantages of the multi-level inverter are achieved with reduced switch count. In addition, a modified Lyapunov-function based control scheme (LFBCS) is derived and applied to the proposed topology. A control law is determined by using Lyapunov's direct method with only grid current feedback. Then, the control law is modified with an additional capacitor voltage feedback to damp the oscillations introduced by the complex conjugate poles of the LCL filter. Whereas ensuring the global stability of the system, the proposed modified LFBCS also improves the transient response of the system. The operation of the inverter topology and performance of the proposed controller are proved through MATLAB/Simulink simulations. Simulation results prove that all three-phase currents are balanced and in sinusoidal waveform, and current harmonics distortion is obtained as 1.07% which is in the limits of international standards.