Joonhyuk Kang

Robust position control of AC servo motors

In this paper, we propose a robust position control scheme for AC servo motors. We adopt a disturbance torque suppresser to eliminate the effects of the disturbance torque and variation in moment of inertia, thus the proposed controller has improved robustness. We can, thereby, reduce position errors due to the disturbances. Some simulation and experimental results are presented to demonstrate the superior position tracking performance of the proposed controller over the conventional proportional-integral (PI) and feedforward controller.

Feedback-linearizing control of hybrid step motors

In this paper, we propose a feedback-linearizing control method for hybrid step motors. Our controller consists of a current tracking controller and a torque controller. In particular, our torque controller contains a function that can be chosen freely under some constraints imposed by the physical limitation in stator currents. Any controller that can make the generated torque of a hybrid step motor linear to the torque command always can be represented by our torque controller with a specific choice of the free function. As an example for optimal choices of the free function, we present a method of determining the free function that gives minimal power loss due to stator resistance. We also present a method of obtaining the full dynamic model of a hybrid step motor. Prior works consider the special cases when the torque component due to variable reluctance is negligible or sinusoidal. Our results in this paper can be applied equally well to these special cases.<<ETX>>

New feedforward control of brushless DC motors (BLDCM) using a novel disturbance suppresser

In this paper, we propose a new feedforward control scheme for the control of brushless DC motors. We adopt a novel disturbance torque suppresser to eliminate the effects of the disturbance torque, uncertain inertia moment, and nonlinear friction, so that the new controller makes the velocity error zero at any state even when the moment of inertia and viscous friction are varying. We can, thereby, overcome the drawbacks of the conventional proportional and integral (PI) and feedforward controller. Some simulation and experimental results as well as mathematical performance analysis are presented to demonstrate the superior tracking performance of our controller over the conventional PI controllers and feedforward controllers.

Full digital controller of permanent magnet AC servo motor for industrial robot and CNC machine tool

A method which fully controls current and speed of the permanent magnet AC servomotor in the discrete time domain with high dynamic performance and wide bandwidth is discussed. The current controller, which controls motor current in the stationary d-q coordinates, consists of a nonlinear feedback controller compensating back EMF, a phase lead compensator, and a PI controller with gains varying according to motor speed. The final output of the current control algorithm is pulsewidth modulated through comparison with a digital triangular carrier signal to produce a PWM waveform. To obtain accurate estimation of motor speed, a speed observer is utilized in the speed control loop. Furthermore, a repetitive controller is applied in order to compensate errors in the position transducer. To investigate the control performance, the full digital servo control algorithm is applied to a SCARA robot with four degrees of freedom through execution on the control system based on the one-chip microprocessor.<<ETX>>