Modeling and Analysis of Single-Phase Modified Unipolar Sinusoidal PWM Inverter with Compensator

Abstract

Minimzation of total harmonic distortion in the case of Pulse Width Modulation (PWM) based inverters for non-linear loading condition is a prime factor in the improvisation of the overall response of the system. In this paper, modeling and analysis of multiple feedback loop control systems for single-phase modified unipolar Sinusoidal Pulse Width Modulation (SPWM) inverter with a proper designed inductive and capacitive output filter. A new control scheme is utilized in the design which senses the capacitor current used in the filter circuits and the same current is used as an inner current feedback loop. To ensure the regulated sinusoidal load voltage, a feedback loop considering voltage of the outer loop is integrated. The power stage transfer functions between capacitor current, current reference and output voltages that are required to design the feedback compensators are derived using Mason’s gain formula and signal flow graph. The control design is accomplished using single input single output (Siso) tool, which is provided in MATLAB/SIMULINK to observe the results of change in gain control values to the system’s transient response and stability. To appraise the execution of the designed compensators, the PWM inverter is designed and simulated for linear (resistive) and non-linear (rectifier) loads with an output power of 700 W at 230 V AC. From the simulation results, the designed compensator exhibits a good transient response and inverter output is stable with infinite gain margin and 0.5% harmonic distortion for non-linear load conditions. With the proposed design, the load voltage recovery time of less than 0.5 ms has been achieved for 700 W load step.