Youngwoo Lee

Sliding mode control based on singular perturbation theory for position tracking of permanent magnet stepper motors

In this paper, we propose sliding mode control (SMC) based on singular perturbation theory (SPT) for position tracking of permanent magnet stepper motors (PMSMs). Separate time scale is a characteristic of the singular perturbation method. Therefore, singular perturbation theory can be applied to the position tracking control of PMSMs because the dynamics of PMSMs is separated into slow and fast dynamics. The proposed method consists of torque modulation, commutation scheme, and SMC. Torque modulation was developed to generate the desire currents. For position control, the SMC was proposed only position feedback without any other observer. The simulation results validate the performance of the proposed method.

Phase-Compensated Microstepping for Permanent-Magnet Stepper Motors

This paper presents a phase-compensated microstepping (PCMS) for permanent-magnet stepper motors in order to overcome the steady-state position error (SSPE) limitation of conventional microstepping without position feedback. An additional phase to compensate for the SSPE is injected into the desired currents for PCMS. Proportional-integral (PI) current feedback with feedforward is proposed in order to guarantee the desired currents for PCMS. Given a desired position error and a desired velocity, the additional phase is calculated in order to ensure the desired position error. In the proposed method, the structure of the PI current feedback with feedforward is not modified, and the additional phase can be obtained by a linear interpolation with an offline generated lookup table. Therefore, it can be easily applied to existing industrial applications without any costs for additional hardwares. The experimental results validate the effectiveness of the proposed method.

Proximate In-Phase Current Estimator to Reduce Torque Ripple in Permanent-Magnet Stepping Motor

This paper proposes microstepping via a proximate in-phase current estimator (PIpCE) to improve position control performance with reduced torque ripples in permanent-magnet (PM) stepping motors. In conventional microstepping control, low-pass filters (LPFs) are used to filter out measurement noise resulting from the implemented current feedback loops. However, the phase lag caused by LPFs can degrade position control performance. In this paper, we propose a current tracking controller with PIpCE. The globally uniformly ultimately bounded current tracking error is proved via the Lyapunov theory. The proposed PIpCE also enhances current tracking performance over that of the conventional method. The proposed controller not only reduces the torque ripple caused by the phase lag but also increases the operational range of microstepping by pushing the electromechanical resonance frequency to a high-frequency region. We experimentally validated the effectiveness of the proposed method and observed that this method provides uniform position tracking performance without step-out or speed reversal, even in high-speed operation.

Enhanced nonlinear damping for a class of singularly perturbed interconnected nonlinear systems

In this paper, we propose a method of enhanced nonlinear damping control for a class of singularly perturbed interconnected nonlinear systems (SPINSs). Instead of simply canceling out the interconnection between slow and fast subsystems, the proposed method transforms SPINS into a feedback connection of two output strictly passive subsystems. Then, enhanced nonlinear damping is implemented to improve the transient behavior of slow subsystem. The proposed method provides weighting factors for each tracking error which enable the energy function to be designed to shape the tracking performance for each state. We also design an augmented state observer to estimate unknown disturbances and unmeasurable states. Using a composite Lyapunov function, we prove that the origin of the tracking error dynamics is globally exponentially stable. It is also analyzed that the tracking errors are globally uniformly ultimately bounded for a time-varying bounded disturbance. Experiments were performed to evaluate the tracking performance of the proposed method and our results validate the effectiveness of the proposed method.

Nonlinear H 2 control for position tracking of permanent magnet stepper motors

In this paper we propose nonlinear H2 control for position tracking of permanent magnet stepper motors. The nonlinear H2 control based on linear parameter-varying (LPV) synthesis for permanent magnet stepper motors (PMSM) is formulated to improve transient response in the position control and to reduce energy consumption. The proposed method consists of a new nonlinear torque modulation with a commutation scheme and LPV gain scheduling current controller. The position control problem for PMSMs is reformulated into the LPV system optimal problem. PMSM, nonlinear system, is analyzed as LPV systems which depend on online accessible time-varying parameters which provide real-time information. The control gain scheduling is determined using H2 control based on linear matrix inequality (LMI) approach. Since the proposed method is designed based on optimal control with gain scheduling based on LPV synthesis, the proposed method obtains both improved transient response in the position control and reduced energy consumption. The performance of the proposed method was validated by the comparison with previous method via simulations.

Improved electrochromic device performance from silver grid on flexible transparent conducting electrode prepared by electrohydrodynamic jet printing

Flexible transparent conducting electrodes (TCEs) are promising for use in electrochromic devices (ECDs), owing to their flexibility to operate in nonplanar configuration. The successful introduction of indium tin oxide (ITO)-coated glass into rigid and planar display devices made ITO on a transparent polymer film an attractive option for flexible devices. However, the flexible characteristic of the ITO film is compromised by its higher surface resistance compared to that of ITO glass. Here, we report printing silver grid on ITO film using an electrohydrodynamic (EHD) jet method, varying the grid pitch. This mask-free method to introduce silver grids onto ITO was used for ECD fabrication. The results showed improvements in colour quality and response time that are attributed to the enhanced conductivity of the silver grid ITO film under low-voltage (1.0 V) operation. Our approach can be used to improve soft ECDs by improving the performance of flexible TCEs.

H ∞ control based on LPV for load torque compensation of PMSM

This paper proposes H∞ control based on linear parameter varying (LPV) systems for load torque compensation of the permanent magnet synchronous motors (PMSMs). The proposed method consists of torque modulation, commutation scheme and LPV H∞ controller. The dynamics of PMSMs was represented as the LPV systems depend on varying parameters. By the LPV modeling, we designed H∞ controller. Stability is proven by Lyapunov theorem. Finally, simulations are performed to show that the proposed method has a good performance of load torque compensation.

A Simplified Nonlinear Control for Sawyer Motors based on Singular Perturbation Theory

In this paper, we propose the nonlinear control based on singular perturbation theory for position tracking and yaw regulation of Sawyer motor. The method of singular perturbation is characterized by the existence of slow and fast transients in the system dynamics. Thus, we can apply to singular perturbation at sawyer motor due to separated motor dynamics into slow and fast dynamics. The proposed method so as to decouple error dynamics consist of auxiliary control. The controller is developed in order to guarantee the desired position and yaw regulation without current feedback or estimation. Simulation results validate the adequation of proposed method.

Robust nonlinear damping backstepping with augmented observer for position control of permanent magnet stepper motors

We innovate an approach to position control, a robust nonlinear damping backstepping with augmented observer for position control of permanent magnet stepper motors (PMSMs). The proposed method requires only position feedback and nominal value of Km over JL among PMSM parameters. We propose new 3rd order single-input single-output PMSM dynamics that consist of position, velocity, and acceleration using a commutation scheme. Instead of separated phase A and B current dynamics, the actual torque dynamics are proposed. The external disturbance, acceleration dynamic, and uncertainty of Km over JL are regarded as a disturbance. In order to estimate the position, the velocity, the accleration, and the disturbance, an augmented observer is designed. A nonlinear damping backstepping is developed to suppress a position tracking error increased as the estimation error of the disturbance is increased. This approach simplifies the design process such that the control algorithm is suitable for real time control. The performance of the proposed method was validated via experiments.

Nonlinear H 2 control of Sawyer motors

In this paper we propose a nonlinear H2 control to improve transient response in the position control and to reduce energy consumption for the position tracking of Sawyer motors. The proposed method consists of a nonlinear torque modulation with a commutation scheme and gain scheduling LPV controller. The position control problem for the Sawyer motor is reformulated into the LPV system optimal problem. The nonlinear models of the Sawyer motors are analyzed as a LPV system. However, in LPV formulation, each vertex to guarantee the controllability should be chosen because of relationship between tracking motion and yaw motion. Hence, stabilizing the inner-loop system with state feedback controller is designed to solve above problem. The control gain scheduling is determined by using H2 control based on linear matrix inequality (LMI) approach. Since the proposed method is designed based on optimal control with gain scheduling based on LPV synthesis, the proposed method obtains both improved transient response and reduced energy consumption in the position control.