분할형 성형코어의 자속밀도 향상에 따른 모터효율 특성평가

Abstract

ABSTRACT

A Study on Evaluation of Motor Efficiency due to Improved Magnetic Flux Density of Divide Type Powder Molding Core

By Park, Yong-Sun Advisor : Prof. Cha, Yong-Hun, Ph.D. Department of Mechanical Engineering Graduate School of Chosun University

The representative cases of eco-friendly vehicles include the hybrid and fuel cell vehicle in addition to the electric vehicle driven by an electric motor. The electric motor application technology, the key one among the above technologies, represents the eco-friendly vehicle technology, so the technological demand for it is increasing. In the world motor technology sector, ultra-small, high speed, high efficiency, high power and automobile diet-oriented products tend to rapidly grow, and especially as an interest in the environment is rising, eco-friendly products are forming a new market. Also the restriction is strengthened and technology is developed actively in order to lower the demand and power consumption for such R&D. For the development of 10kw100kw graded BLDC motor, which is a driving motor of electric vehicles, not only electric vehicle motor producers but also home electronic appliance and industrial motor producers start to be engaged in the research and business for product development and quality enhancement. It is because the BLDC motor has no brushes, so electric and mechanical noises are low, and it is easy to make the BLDC motor high speed, and reliability is high, and maintenance is not needed, thus like this the BLDC motor has more merits as an electric vehicle driving motor than the general DC and AC motor. Therefore despite the demerit that the BLDC is expensive, its life span and efficiency is so good that it is paid the researcher's attention as an electric vehicle driving motor. Today, the rare earth permanent magnet has a very wide range of applications, so it became an important basic matter. The development of various electronic industries and the increase in the motor output are bringing about the changes from a DC motor with brushes into a brushless motor and in the case of a built-in magnet, from the ferrite magnet into the Nd-Fe-B(Neodium) sintered magnet. The rare earth permanent magnet is necessarily used for developing the high performance motor required for performance improvement and weight lightening. For the BLDC core, the permanent magnet is used, and in general, mostly the ferrite magnets are used but in this case the torque is small per volume. To improve this demerit, the rare earth magnet with high energy efficiency is used, which brings about not only a higher expense but also around 60 % of motor manufacturing cost. Since the rare earth metals are limited in their deposits worldwide, studies as following are activated; makes the interval between crystal grains of Nd-Fe-B sintered magnet smaller from 5 ㎛ to 1.1 ㎛ to enhance the coercivity so that the used quantity of dysprosium should be reduced. In this study as a driving method of high efficiency BLDC motor for electric vehicles, a Hall sensor, encoder, and resolver, etc. were used to select the sensorless control method, and it aimed to develop the Stater of the BLDC core components into the divide type. To enhance the performance efficiency of the high efficiency BLDC motor, the powder molding product was developed, and it aimed to verify the performance in relation regarding motor efficiency according to the residual magnetic flux density of molding core, through the motor dynamo system. The Nb-Fe-B magnet, one of rare earth metals, is excellent in the residual magnetic flux density and coercivity, etc. more than other rare earth metals, but its temperature characteristics are quite poor that the flux density is severly falling due to temperature changes, which makes it difficult to be used for green car motor development. To overcome such a demerit and enhance motor efficiency, obtaining the molding core with the highest value of residual magnetic flux density of powder molding core is main target in this study. The motor for powder molding core component with a different residual magnetic flux density was also produced and it was intended to verify, through a dynamo test, how this produced core product affects the BLDC motor performance efficiency. Through theses series of test processes, it aimed to develop the supply type driving system that will be applied to a green car, and the results of the study are as follows:

1. For measurement of maximum output test result, the inverter input was measured as 310 input voltage (VDC), and motor output as 40.386 torque (Nm), 3,233 rated revolutions (rpm), and 9.24 rated output (kw).

2. The Vickers hardness test on the molding density and core surface was performed for produced BLDC divide type powder molding core. As the result, molding density was measured in range of 7.1∼7.5, while average Vickers hardness was in range of 557～584(Hv). It confirmed that the measurement value of hardness increased as the density of molding core increased.

3. The test on residual magnetic flux density was performed in range of 10,000∼12,970 Br when maximum workable temperature is 80～120℃ and hard condition temperature is 200℃. As result, the residual magnetic flux density was measured higher as density and hardness of powder molding core increased.

4. As result of performance evaluation with Dynamometer test on divide type powder molding, the maximum efficiency was 93% when the maximum molding density was 7.48 and the maximum residual magnetic flux density was 12,970 Br. As the molding density and residual magnetic flux density of a core increased, the higher performance efficiency of the motor was measured.

5. Based on the result of performance evaluation on divide type powder molding core, BLDC motor was produced and had performance evaluation done. As the result, the maximum efficiency was 93.0% when the maximum torque is 40.386N.m, speed is 3,233rpm, voltage is 220.03V, and watt is 9.24k. Its excellence in performance as controller and motor was confirmed as it satisfied the efficiency of regular electric car’s motor, which is 92∼94%.

Given the above, the BLDC motor running is possible not only in a certain torque area but also a ceratin output area and at a wide range of running speed; thus, the forthcoming studies are expected to continue. In terms of the response, switching frequency, high frequency content of the output current, and linearity of control, etc., the BLDC motor is applied to various drive systems as an excellent control algorithm. Thus regarding the high performance and high efficiency electric vehicle BLDC motor and drive system, these technologies can be applied widely to the companies related to vehicle component companies, and these technologies are expected to contribute to developing the forthcoming eco-friendly vehicles.