Certain investigation on power converters for low power drive application

Abstract

In today s world we are moving towards technology aided lifestyle where electrical and electronic appliances play a vital role. These devices are operated by an electric drive. Induction motors are predominantly used in applications that require simplicity and ruggedness. Induction motor based electric drives are characterized by low power factor and low efficiency when operated below half the rated power. BLDC motor is a promising technology which is replacing the induction motor based electric drives due to its high efficiency, silent operation, compact size, high reliability and low maintenance features. BLDC drives are used in various applications like household appliances, automobiles, transportation, aerospace equipment, power tools, toys, healthcare equipment, sophisticated position control applications and mediumsize industrial drives. Recently, efficiency and cost are the major concerns in designing and developing low-power application drives like mixers, fans, blowers, refrigerators, air conditioners and other household devices. As energy consumption has gained importance all over the world, organizations like International Electrotechnical Commission (IEC) has implemented the strict regulation on power quality issues and energy conservations of electrical and electronic equipment and appliances. BLDC motors are not self-starting; it requires a power electronic interface for its operation. The BLDC motor is fed by a three-phase Voltage Source Inverter (VSI) whose firing angle is controlled by the feedback obtained from the rotor position; the VSI gets a dc supply from a single phase rectifier through a smoothening capacitor. The power electronic interface along with the smoothing capacitor consumes pulsating current from the sources due to the rectification process. This pulsating current causes various power quality issues like low power factor and harmonics. The power quality issues cause losses thereby the overall system efficiency reduces. In order to overcome the power quality of the system, various power factor circuits such as non-isolated converters like boost, buck-boost, Cuk converters and isolated converters like Half-bridge and Full-bridge, flyback, forward, SEPIC, Cuk, Zeta, Push-pull converters are being used. These converters are operated in continuous and discontinuous conduction mode by current and voltage control respectively. In this thesis, the induction motor based drive fed by boost converter for power factor correction is considered. Next step involves the power factor correction simulated using MATLAB and BLDC drive is fed by the buck-boost converter, Cuk converter, and SEPIC converter. SEPIC converter fed BLDC motor is analyzed by two control schemes, one with PI controller and the other with the Fuzzy control scheme. The performance of the proposed SEPIC fed BLDC using PI controller shows reduction of the peak over shoot and settling time in both DC-link voltage and in motor speed is obtained. On the other hand fuzzy logic controller has presented additional decrease in settling time and speed error while compared with the PI controller. newline