Adaptive integral backstepping control and stability analysis of a three‐level neutral point clamped inverter for single‐stage grid‐tied photovoltaic systems

Abstract

Abstract This paper presents an advanced control technique for a single‐stage grid‐tied photovoltaic (PV) system, including a three‐level neutral point clamped inverter with an LCL filter. The control objectives are threefold: (i) achieving power factor correction (PFC) by ensuring a sinusoidal grid current in phase with the grid voltage; (ii) transferring maximum PV power to the grid and tightly regulating the DC bus voltage; (iii) maintaining capacitor voltages balance to ensure proper power exchange. The control design entails several difficulties, namely: (i) the system's inherent nonlinearity and high dimensionality; (ii) the uncertainty in some system parameters; (iii) the numerous unmeasurable state variables and parameters. The considered control problem is dealt with by synthesizing a multi‐loop adaptive controller featuring three main cascaded loops. The fast inner loop utilizes an integral backstepping control alongside the formal Lyapunov technique for PFC achievement. The outer loop incorporates a filtered proportional‐integral (PI) regulator for DC bus voltage adjustment to its maximum power point reference. The auxiliary balancing loop implements a PI regulator for neutral‐point voltage stabilization. The control system is further enhanced with an adaptive observer for online estimation of network voltage and impedance parameters. The closed‐loop system stability is formally established through system averaging analysis. MATLAB/Simulink simulations demonstrate the performance of the suggested adaptive controller under varying operating conditions, and comparative studies confirm its supremacy over different other inner loop controllers.