Internal Model Principle Method to Robust Output Voltage Tracking Control for Single-Phase UPS Inverters With Its SPWM Implementation

Abstract

This article investigates output voltage tracking control, and harmonic distortion suppression in single-phase voltage-source uninterruptible power supply (UPS) inverters with an <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$LC$</tex-math></inline-formula> -filter. The control scheme is based on sensing the output voltage across the UPS load, and using the voltage tracking error in a feedback loop of the internal model principle (IMP) framework. A robust controller is designed to drive <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$LC$</tex-math></inline-formula> -filter to operate with an adjustable amplitude, and adaptive resonant frequency. Specifically, the proposed controller basically employs an internal model with a filter to examine the incremental dynamics of the voltage tracking error, and regulate the voltage modulating signal in sine pulse width modulation (SPWM). With such a stable operation of the controlled UPS system, the inverter is able to achieve fast dynamics of voltage tracking, which results in the minimum harmonics while approaching the zero-error steady state under the external loads. The Matlab/Simulink simulation, and experimental validation are both provided for the prototype controlled UPS inverter under the closed-loop operation. It is shown that the controller offers improved performance over the existing schemes. By merely using the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">voltage error</i> to adjust the output voltage, the controlled inverter produces nearly perfect sinusoidal voltage at moderate switching frequency under a wide range of filter parameters, and consequently, the UPS operation has excellent dynamic response with both high voltage utilization of the DC source, and high power quality.