Analysis of Single Phase AC-DC SEPIC Converter using Closed Loop Techniques

Abstract

This paper proposes single phase AC-DC SEPIC converter using closed loop techniques for domestic and industrial applications. The Single Ended Primary Inductor Converter (SEPIC) is a type of DC-DC converter allowing the electrical potential (voltage) at its output to be greater then, less then, or equal to that of its input. A SEPIC converter is similar to the BUCK-BOOST and BOOST-BUCK converter, but has advantages of having non-inverted output (The polarity of the output voltage is same as that of the input). There are two types of techniques, open loop and closed loop technique. In open loop, a non-isolated SEPIC converter is used. This has lower power factor and high THD. Hence the closed loop technique is used to improve power factor and THD. The control techniques are voltage follower approach and average current control technique. By using the above techniques the power quality parameters will be improved when compared to open loop. The simulation of SEPIC converter is done by using the software tool PSIM (Power Simulation). I.INTRODUCTION Power conversion is converting electric energy from one form to another, converting between AC and DC or just varying the voltage and frequency or some combination of these. The power conversion systems can be classified according to the type of input and output power  AC to DC (Rectifier)  DC to AC (inverter)  DC to DC (DC to DC converter)  AC to AC (AC to AC converter) DC to DC converters are important in portable electronic devices such as cellular phones and laptop computers, which are supplied by power from batteries mainly. The majority DC to DC converters also control the output voltage. AC to DC converters (rectifier) is an electrical device that converts alternating current (AC), which periodically reverses direction, to direct current (DC), which flows in only one direction. The process is well-known as rectification. Rectifiers have several uses, however are often found serving as components of DC power supplies and high-voltage direct current power transmission systems. Rectification may well serve in roles other than to generate direct current for use as a source of power. Because of the alternating nature of the input AC sine waves, the method of rectification only produces a DC current that, while unidirectional, consists of pulses of current. Several applications of rectifiers, such as power supplies for television, radio and computer equipment, necessitate a steady constant DC current (as would be produced by a battery).Normally AC-DC conversion is carried out by simply rectifying the AC input and the rectified output voltage is filtered by means of a large valued capacitance to get a nearly constant DC output voltage. In this conversion, the input AC supply current is drawn in narrow pulses since the capacitor voltage value is nearly constant. This narrow pulse current of high peak, results in power quality problems to nearby consumers, which include higher value of THD on supply current, higher THD of input supply voltage, lower value of power factor and displacement factor and poor distortion factor. These large harmonic currents are undesirable because they not only produce distortion of AC line voltage but also result in conducted and radiated electromagnetic interference (EMI). The problem becomes more serious particularly when several drive units are connected to single phase supply where the input power pulsates at twice the frequency. Recent international regulations governing the power quality and harmonic currents pollution limits at the utility have placed an increased emphasis on the application of improved power quality AC-DC converters to feed the load. For ideal sine wave line voltage, harmonic currents do not contribute to active power, this