HARMONIC REDUCTION FOR SINGLE-PHASE UNINTERRUPTIBLE POWER SUPPLY INVERTER

Numerous control strategies for Uninterruptible Power Supply (UPS) inverters have been proposed, with the primary objectives of voltage tracking, stability, and maintaining a perfect sinusoidal waveform even under nonlinear loads, varying loads, and the presence of disturbances. A proposed method is two Multiple Loop Control (MLC) with an outer voltage control loop tracking the reference voltage and an inner current control loop to reduce the steady-state error of the load voltage, reduce harmonics in the main circuit current, and improve system efficiency. The controller's robustness based on the Lyapunov function is proven by sudden load changes and variations in the reference voltage along with the presence of noise. The fundamental principles of Lyapunov's theorem are applied to the state equations to calculate the switching function for generating Pulse Width Modulation (PWM) to reduce harmonics in UPS. Simulations and experiments were conducted using MATLAB-Simulink. Results demonstrated that the UPS output voltage and current can track the reference values from low to high, regardless of sudden load changes or reference voltage variations, and in the presence of noise. The total harmonic distortion (THD) of the current was significantly reduced to 0.04%, meeting the IEEE-519 standard.