Development of an Input Power Factor Corrected Variable Speed Motor Drive System for the Electric Motor Drives Course

Content Provider	Semantic Scholar
Author	Lee, Shiyoung
Copyright Year	2011
Abstract	An active input power factor correction (IPFC) is introduced as a front-end converter for the variable speed induction motor drive (IMD) system. This paper provides the involvement of the system power quality which involves a high power factor (PF) and low total harmonic distortion (THD). The necessity for efficient utilization of generated electrical energy is growing in order to optimize the usage of utility power plant capacity. Moreover, awareness of minimizing harmonic contamination in the electric power line is rising due to the increased use of electronic equipment powered by an ac-to-dc bridge rectifier with large filter capacitors and/or a switchmode power supply (SMPS). The variable speed motor drive (VSMD) saves more electrical energy than the fixed motor drive under the assumption that both are operating on the same load factor. Almost all of the small VSMDs have no IPFC circuits to save their production costs. Emerging applications of fractional horsepower IMDs such as compressors, appliances, blowers, hand tools, and heating, ventilating, and air-conditioning (HVAC) invoke the urgency of studying the effects of the IPFC on the VSMDs. A three-phase inverter-fed IMD with a single-phase source and an active IPFC circuit is proposed in this paper to study the impact of IPFC circuit experimentally. The foremost subject in the study of an input PF corrected VSMD are the effects of an IPFC circuit on overall system efficiency and input PF. Empirical comparisons between the conventional bridge rectifier circuit and IPFC circuit in terms of PF and efficiency against motor speed are developed. The overall system performance with an IPFC circuit is better than the system performance without it in terms of harmonic contents and PF. The system efficiency, however, shows marginal inferiority with an IPFC circuit because the front-end IPFC circuit and the three-phase inverter are connected serially. It should be emphasized that the IMD with IPFC is desirable in utilizing the generated electrical energy effectively and minimizing the harmonic contamination. The developed system may be useful as a hands-on experiment for the Electric Drives course. In conclusion, various teaching components are defined with the developed IPFC-IMD system. Introduction to IPFC VSMD One of the most active research and development areas in the power electronics field is VSMD. As power semiconductor devices become cheaper, faster, and more reliable, the use of energy saving VSMDs in industry and residential applications has been increasing. VSMDs utilizing induction and dc motors make up the majority of industrial and domestic drives. Although these VSMDs require an initial investment and generate current harmonics, they provide significant improvements in performance such as better control, wider speed ranges, soft start, and enormous energy savings in various kinds of applications. The selection of VSMDs is an application-specific matter. There are many factors to be considered when we select VSMD systems, including cost, output torque, speed ranges, performance, and power ratings. The emerging requirement in the VSMD application for drawing near sinusoidal current from the utility and less harmonics injection into the utility lines is the motivation for investigating the P ge 22487.2 PF-corrected motor drive system. The impact of IPFC on system efficiency and power converter ratings will be studied for high volume but low-cost applications such as washers, dryers, refrigerators, freezers, hand tools, and process drives. The power ratings for most of these high volume applications are less than one-horsepower. All off-line VSMDs have rectifiers and storage capacitors in their front-ends to get dc voltage from an ac power source. This input circuitry lowers the PF of the VSMD systems and pollutes ac power systems. The PF is the ratio of real power in watts to apparent power in volt-amperes (VA). The PF becomes unity when the input ac current and voltage are sinusoidal and in phase. In an off-line VSMD system, the input current is distorted and even out of phase with input voltage, the power factor is less than unity, and less real power is transmitted to the load. However, the rms input current is increased due to the harmonic currents plus the current required by the load must still be carried, thus requiring the wiring of the ac power system to be heavier and more expensive than necessary 1 . The most common problem that disturbs ac power systems is caused by electric motors operating in industries. The inductive component of the motors causes the ac current to lag the ac voltage. This results in a low power factor. Assuming the loads are linear, the power factor can be corrected to near unity by connecting a bank of capacitors across the ac power line. The low PF gives rise to a number of serious problems in VSMD systems. The size of the input fuses and circuit breakers of the input circuitry must be increased. The distorted input current waveform, which causes interference with other equipment, must be filtered to reduce the magnitudes of harmonic frequencies. Consequently, to increase the output power from ac power systems, it is necessary to correct the PF. This substantially reduces peak and rms input current and makes it possible to achieve higher output power. With the proliferation of nonlinear loads such as SMPSs, standards agencies around the world are developing requirements for harmonic contents of the electronic power conversion systems to reduce the overall distortion on the main supply line. One of these standards is the IEC 1000-3-2 (same as EN 61000-3-2 published in 1995 and the latest version of IEC 555-2 published in 1982) 2 from International Electrotechnical Commission (IEC) to set the limits for input harmonic currents in the electrical equipment. The standard describes general requirements for testing equipment as well as the limits and the practical implementations of the test. For the purpose of harmonic current limitation, the standard divides electrical equipment into four classes as shown in Figure 1. Each class has different harmonic current limits. The balanced three-phase equipment and other electronic apparatus which is excluded one of three classes are included in the Class A classification. To apply a Class D limit, the following two requirements should be satisfied:  Input power should be less than 600 W.  Input current waveshape of each half cycle is within the envelope shown in Figure 2 for at least 95% of the duration of each half period.
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