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08/08/2017 HYU News > Academics


Founding Father of the Pragmatic Application of Stepping Motors

Professor Chung Chung-choo (Department of Electrical and Biomedical Engineering)


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Every moving object needs a power plant. In the industrial world, permanent magnet stepper motors are widely used, which are designed with permanent motor (PM) rotors that are commanded by electrical pulses. In his paper “Nonlinear H2 Control for a Nonlinear System with Bounded Varying Parameters: Application to PM Stepper Motors,” Chung proposes a new nonlinear H2 controller for the PM motors that can increase the efficiency both in its speed and practicality.

Chung is the pioneer in South Korea to discover new methods of applying nonlinear H2 control for a nonlinear system.

Utilization of the PM motors vary from household purposes such as printers to industrial purposes such as gas systems and cars. Since its earlier usage from the 1970s, these motors have thrown questions to scientists and engineers on its formula. “Despite the fact that these motors are popularized in the industry, there are constraints in the PM motors, such as speed restriction,” said Chung.
To solve this problem, engineers have discovered the DQ (direct quadrature) transformation of the motors which is a tensor that rotates the reference frame of a element vector matrix to simplify the analysis of it. “My research team has found that DQ is comparatively inefficient in terms of energy saving and cost control. Thus, we detected a new mathematical method to replace the DQ transformation,” said Chung.
Often times, engineers used the linear system to control the PM motors. A linear motor is an electric motor that has its stator and rotor unrolled, so that instead of producing a torque, it produces a linear force along its length. However, linear motors are not necessarily straight, which causes restrictions in speed. “Formula of the linear system consists of homogeneity and additivity, and the main point of our research was to minimize the relationship between them using the H2 control system,” emphasized Chung. This FOC (Field Oriented Control) with the H2 system went through an experiment with other traditional methods for a comparison. “The results were outstanding as more simplified version of mathematical calculation and less usage of sensors beforehand were required, while the tracking errors and energy cost were reduced respectively,” said Chung.

The green line of case 3, which uses the FOC (Field Orientation Control) of the H2 control shows the extreme distinction in tracking errors. 
(Photo courtesy of Chung)

The most desired application of this method is on the intelligence vehicle, which is a car that can drive by itself without any interference of a driver. “Learning about the motion control, which is the main issue of my paper, is the most important criteria of designing a self-driving vehicle. This study allowed me to grow this industry rapidly in five years,” astonished Chung. Currently, Chung’s research lab for the intelligence vehicle based on motion control is the best in Korea which acquire all the knowledge on the sensors, actuators, and control algorithms.
Chung’s passion for science was conspicuous from the days he used to make a radio on his own. When he started gaining interests in engineering, motion control grabbed his sight. “The stepping motors and their control system are fundamental technologies. I thought that developing them into pragmatic applications would be exciting,” reminisced Chung.
Currently, Chung is passionately contributing to the scientific and technological advancement. For the visible result, he had launched the IEEE (Institute of Electrical and Electronics Engineers) ‘s CDC (Conference on Decision and Control) conference at Jeju Island, South Korea. “This is the first time ever that the CDC conference is being held in South Korea and I consider this the greatest achievement of my academic life so far,” smiled Chung.

Chung is currently working on developing more advanced intelligence vehicles.

Chung’s everlasting hope for his students is that they could study both science and liberal arts. “I wish South Korean educational system could teach students to embrace the joy of learning. This will eventually rear the bright sprouts of Korea,” said Chung.

Kim Ju-hyun
Photos by Choi Min-ju
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