Fixed Switching Frequency Sliding-Mode Control Methodology for Single-Phase LCL-Filtered Quasi-Z-Source Grid-Tied Inverters

Abstract

This paper presents a fixed frequency sliding mode control methodology for single-phase grid-tied LCL filtered quasiz-source inverters (qZSI). In the presented methodology, a smoothing process is applied to the sliding surface function so as to eliminate the chattering and achieve the fixed switching frequency. The smoothing process is conducted by passing the sliding surface function through a narrow boundary layer. An expression is determined analytically to determine the value of boundary layer thickness. To alleviate the steady state error arising due to the smoothing process, a PR controller is employed to process the grid current error and determine the capacitor voltage reference needed in the SMC. The shoot through control of the qZSI is achieved by using the simple boost control technique. Computer simulations verify a good steady state and dynamic responses, as well as robustness and sinusoidal grid current with low total harmonic distortion achieved at fixed switching frequency.