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Browsing Articles by Author "Choi, Han Ho"
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Item Open Access A Nonlinear Sliding Mode Controller for IPMSM Drives with an Adaptive Gain Tuning Rule(2015) Jung, Jin-Woo; Dang, Dong Quang; Vu, Nga Thi-Thuy; Justo, Jackson John; Do, Ton Duc; Choi, Han Ho; Kim, Tae HeoungThis paper presents a nonlinear sliding mode control (SMC) scheme with a variable damping ratio for interior permanent magnet synchronous motors (IPMSMs). First, a nonlinear sliding surface whose parameters change continuously with time is designed. Actually, the proposed SMC has the ability to reduce the settling time without an overshoot by giving a low damping ratio at the initial time and a high damping ratio as the output reaches the desired setpoint. At the same time, it enables a fast convergence in finite time and eliminates the singularity problem with the upper bound of an uncertain term, which cannot be measured in practice, by using a simple adaptation law. To improve the efficiency of a system in the constant torque region, the control system incorporates the maximum torque per ampere (MTPA) algorithm. The stability of the nonlinear sliding surface is guaranteed by Lyapunov stability theory. Moreover, a simple sliding mode observer is used to estimate the load torque and system uncertainties. The effectiveness of the proposed nonlinear SMC scheme is verified using comparative experimental results of the linear SMC scheme when the speed reference and load torque change under system uncertainties. From these experimental results, the proposed nonlinear SMC method reveals a faster transient response, smaller steady-state speed error, and less sensitivity to system uncertainties than the linear SMC methodItem Open Access Adaptive PID Speed Control Design for Permanent Magnet Synchronous Motor Drives(2014) Jung, Jin-Woo; Leu, Viet Quoc; Do, Ton Duc; Kim, Eun-Kyung; Choi, Han Ho; Leu, Viet QuocThis paper proposes an adaptive proportionalintegralderivative (PID) speed control scheme for permanent magnet synchronous motor (PMSM) drives. The proposed controller consists of three control terms: a decoupling term, a PID term, and a supervisory term. The first control term is employed to compensate for the nonlinear factors, the second term is made to automatically adjust the control gains, and the third one is designed to guarantee the system stability. Different from the offline-tuning PID controllers, the proposed adaptive controller includes adaptive tuning laws to online adjust the control gains based on the gradient descent method. Thus, it can adaptively deal with any system parameter uncertainties in reality. The proposed scheme is not only simple and easy to implement, but also it guarantees an accurate and fast speed tracking. It is proven that the control system is asymptotically stable. To confirm the effectiveness of the proposed algorithm, the comparative experiments between the proposed adaptive PID controller and the conventional PID controller are performed on the PMSM drive. Finally, it is validated that the proposed design scheme accomplishes the superior control performance (faster transient response and smaller steady-state error) compared to the conventional PID method in the presence of parameter uncertaintiesItem Open Access An Adaptive Voltage Control Strategy of Three- Phase Inverter for Standalone Distributed Generation Systems(2012) Do, Ton Duc; Leu, Viet Quoc; Choi, Young-Sik; Choi, Han Ho; Jung, Jin-WooThis paper proposes an adaptive control method of three-phase inverter for standalone distributed generation systems (DGSs). The proposed voltage controller includes two control terms: an adaptive compensating term and a stabilizing term. The adaptive compensating control term is constructed to avoid directly calculating the time derivatives of state variables. Meanwhile, the stabilizing control term is designed to asymptotically stabilize the error dynamics of the system. Also, a fourth-order optimal load current observer is proposed to reduce the number of current sensors and enhance the system reliability and cost effectiveness. Stability of the proposed voltage controller and the proposed load current observer is fully proven by using Lyapunov theory. The proposed control system can establish good voltage regulation such as fast dynamic response, small steady state error, and low total harmonic distortion (THD) under sudden load change, unbalanced load, and nonlinear load. Finally, the validity of the proposed control strategy is verified through simulations and experiments on a prototype DGS testbed with a TMS320F28335 DSP. For a comparative study, the feedback linearization for multi-input and multi-output (FLMIMO) control scheme is implemented and its results are presented in this paperItem Open Access Nonlinear Optimal DTC Design and Stability Analysis for Interior Permanent Magnet Synchronous Motor Drives(2015) Do, Ton Duc; Choi, Han Ho; Jung, Jin-WooThis paper presents a nonlinear optimal direct torque control (DTC) scheme of interior permanent magnet synchronous motors (IPMSMs) based on an offline approximation approach for electric vehicle (EV) applications. First, the DTC problem is reformulated in the stationary reference frame in order to avoid estimating the stator flux angle, which the previous DTC schemes in the rotating stator reference frame require. Thus, the proposed DTC method eliminates the Park’s transformation and consequently it reduces the computational efforts. Particularly, since the estimated stator flux angle is not accurate in low speed range, the proposed method that does not need this information can significantly improve the control performance. Moreover, a nonlinear optimal DTC algorithm is proposed to deal with the nonlinearity of the IPMSM drive system. In this paper, a simple offline θ-D approximation technique is utilized to appropriately determine the controller gains. Via an IPMSM test-bed with a TI TMS320F28335 DSP, the experimental results demonstrate the feasibility of the proposed DTC method by accomplishing better control performances (e.g., more stable in low speed region, much smaller speed and torque ripples, and faster dynamic responses) compared to the conventional proportionalintegral (PI) DTC scheme under various scenarios with the existence of parameter uncertaintiesItem Open Access SDRE-Based Near Optimal Control System Design for PM Synchronous Motor(IEEE, 2011) Do, Ton Duc; Choi, Han Ho; Jung, Jin-WooThis paper presents a nonlinear optimal speed controller based on a state-dependent Riccati equation (SDRE) for permanent magnet synchronous motor (PMSM). An SDREbased near optimal load torque observer is also proposed to provide the load torque information for the controller. In both designs, the stability is analytically proven and Taylor series method is used to find an approximate solution because the SDRE cannot be directly solved. The SDRE-based optimal controller and observer can ensure better control performance such as no overshoot and fast transient response in speed tracking than the linear conventional controllers such as LQ regulator and PI controller even under the variations of the model parameters and load torque. The proposed SDRE-based control strategy is implemented on a PMSM testbed using TMS320F28335 DSP. The simulation and experimental results are given to prove the feasibility of the proposed control schemeItem Open Access θ-D Approximation Technique for Nonlinear Optimal Speed Control Design of Surface-Mounted PMSM Drives(2015) Do, Ton Duc; Choi, Han Ho; Jung, Jin-WooThis paper proposes nonlinear optimal controller and observer schemes based on a θ-D approximation approach for surface-mounted permanent magnet synchronous motors (PMSMs). By applying the θ-D method in both the controller and observer designs, the unsolvable Hamilton–Jacobi–Bellman equations are switched to an algebraic Riccati equation and statedependent Lyapunov equations (SDLEs). Then, through selecting the suitable coefficient matrices, the SDLEs become algebraic, so the complex matrix operation technique, i.e., the Kronecker product applied in the previous papers to solve the SDLEs is eliminated. Moreover, the proposed technique not only solves the problem of controlling the large initial states, but also avoids the excessive online computations. By utilizing a more accurate approximation method, the proposed control system achieves superior control performance (e.g., faster transient response, more robustness under the parameter uncertainties and load torque variations) compared to the state-dependent Riccati equation-based control method and conventional PI controlmethod. The proposed observer-based control methodology is tested with an experimental setup of a PMSM servo drive using a Texas Instruments TMS320F28335 DSP. Finally, the experimental results are shown for proving the effectiveness of the proposed control approach