PERFORMANCE ANALYSIS OF UPS INVERTERS SYSTEM

Abstract

U ninterruptible power supply (UPS) systems are used to provide uninterrupted, reliable, and high-quality electrical power to various sensitive loads in electrical power system. UPS system not only provides uninterrupted power but also improves quality of electrical power. UPS systems provide protection against under-voltage, overvoltage, voltage sag, and voltage swell. They also suppress line transients and harmonic disturbances. Generally, an ideal UPS system should be able to deliver uninterrupted power and, simultaneously, provide the necessary power conditioning for the particular power application. Applications of UPS systems include medical facilities, life supporting systems, data storage and computer systems, emergency equipment, telecommunications, industrial processing, and on-line management systems. Information technology (IT) or information technology enabled services (ITeS), such as, banking, financial services and insurance, telecom, healthcare, education, and manufacturing sectors rely heavily on UPS systems. In addition to protection against power outage, UPS systems filter out many types of mains disturbances including electrical noise and voltage sags and brownouts, spikes, surges and supply frequency changes – all of which can cause loss of data or hardware damage if allowed through to the IT equipment. In the first chapter the various configurations of UPS systems are discussed. The advantages and disadvantages of each configuration are discussed. Afterwards, the square-wave operation of single-phase full-bridge VSI is discussed along with its disadvantages and the need to go for sinusoidal pulse-width modulation. The sinusoidal PWM operation is discussed for both unipolar and bipolar switching schemes. The reasons for preferring unipolar switching scheme over bipolar switching scheme are discussed. In the second chapter the disadvantages of sinusoidal pulse width operation are discussed along with the need for an output low-pass L-C filter. In continuation to the same the design criteria for output low-pass L-C filter are discussed. In the third chapter, the mathematical model of single-phase full-bridge voltage-source inverter is derived. The need for closed-loop operation of inverter is discussed followed by the single-loop voltage-mode control technique. The concept of active damping (AD) and active damping with feed-forward (ADFF) is discussed so as to minimize the effect of disturbance input, i.e., load current. In the fourth chapter various closed-loop control techniques for single-phase full-bridge voltage-source inverter are discussed and compared. Single-loop and multi-loop control techniques are discussed along with voltage-mode control and current-mode control. The performance of various closed-loop control techniques is discussed for both linear and non-linear load. The various results are obtained with the help of MATLAB and Simulink. The criteria for designing outer voltage controller and inner current controller in case of multi-loop current mode control are also discussed.