Wonhee Kim

Robust Multirate Control Scheme With Predictive Virtual Lanes for Lane-Keeping System of Autonomous Highway Driving

In this paper, we propose a new approach for a robust multirate lane-keeping control scheme with predictive virtual lanes. First, the multirate lane-keeping control scheme is proposed to improve the lane-keeping performance and to reduce the ripple in the yaw rate. To improve the lane-keeping performance on a curved road, the integral of the lateral offset error is added to the state feedback controller. A multirate Kalman filter (KF) has been developed to resolve the problems caused by slow lane detection due to the vision processing system. This multirate KF estimates vehicle states at a fast rate using a microprocessor. Utilizing the estimated states, the linear quadratic state feedback control operates at the same fast update rate of the microprocessor. Thus, a multirate control scheme can reduce the ripple in the yaw rate. Second, we propose a virtual lane prediction method that compensates for the momentary failure of lane detection from unexpected problems. If the camera sensor momentarily fails while obtaining lane information, the predicted virtual lane can be substituted for the lane detection using the camera sensor in the proposed control scheme. Thus, the proposed control scheme can normally operate when the lane information is momentarily unavailable. The performance of the proposed method was evaluated via experiments.

Design and Implementation of Simple Field-Oriented Control for Permanent Magnet Stepper Motors Without DQ Transformation

In this paper, a simple field-oriented control (FOC) without direct quadrature (DQ) transformation is proposed for position tracking of permanent magnet stepper motors (PMSMs). Conventional FOC methods require DQ transformation to linearize the mechanical dynamics for PMSMs. In this paper, a proportional-integral-derivative controller with velocity feedforward is developed to obtain the torque modulation required to track the desired position. In addition, a new commutation scheme is proposed to generate the desired currents with the torque modulation; this commutation scheme is equivalent to the microstepping where the desired currents have time-varying amplitudes with π/2 electrical phase advance. The proposed controller method is in the form of an FOC even though DQ transformation is not used. The proposed commutation scheme likens the PMSM to a two-phase permanent magnet synchronous motor. Experimental results validate the effectiveness of the proposed method.

Torque-Overlay-Based Robust Steering Wheel Angle Control of Electrical Power Steering for a Lane-Keeping System of Automated Vehicles

We propose a torque-overlay-based robust steering wheel angle (SWA) control method of electrical power steering (EPS) for a lane-keeping system of automated vehicles. The proposed method consists of an augmented observer and a nonlinear damping controller to guarantee the semiglobal uniform ultimate boundedness of the SWA tracking error using only SWA feedback. The key idea of the proposed method is that the system functions with unknown parameters and external disturbance, along with their derivatives, are combined into an augmented state variable for designing the nonlinear observer in the absence of Lipschitz conditions. The augmented observer is designed to estimate the full state and disturbance. The nonlinear damping controller is developed via backstepping to suppress the angle tracking error using the input-to-state stability property when the estimation error becomes large. Since the proposed method is designed based on torque overlay, a torque integration using basic functions of the EPS for SWA control is available for driver convenience. Furthermore, no modification of the EPS is required. The performance of the proposed method was validated through experimentation with a test vehicle.

Novel Position Detection Method for Permanent Magnet Stepper Motors Using Only Current Feedback

In this paper, a position detection method using only current feedback is proposed for permanent magnet stepper motors. Using the Lyapunov stability analysis of microstepping, we show that the approximate position can be determined by the interpolation of the measured currents. The position estimation error in the constant velocity period is analyzed using the position tracking error of microstepping. A new compensation filter is proposed to reduce the position estimation error due to the mechanical dynamics. The Heydemann correction and the gradient searching method are used for calibrating the current signals. 16 phase-shifted sinusoids are implemented for the interpolation of the currents. The performance of the proposed method was validated by experiment.

Lyapunov-based control in microstepping with a nonlinear observer for permanent magnet stepper motors

In this paper, we propose a Lyapunov-based control with a nonlinear observer in microstepping for permanent magnet stepper motors (PMSMs). Given static inputs to a PMSM, stability of the equilibrium points is studied in the sense of Lyapunov stability and their local asymptotic stability is proved using LaSalles theorem. From the stability analysis the principle of microstepping is verified. The Lyapunov-based controller was developed to regulate the desired phase current errors. For the implementation of the proposed controller a nonlinear observer is also designed using the Lyapunov method to estimate the full state of PMSM. And we analyze the stability of the closed-loop system. The Lyapunov-based controller and nonlinear observer do not require any transformation so that it could reduce the commutation delay. The proposed method is validated via experiments and its tracking performance was compared with that of the conventional microstepping. We used two position profiles to evaluate the performance of the proposed method. Overall more than a 40% improvement in tracking error was obtained. Furthermore, we achieved improved uniformity in the tracking error during the constant velocity period.

Lyapunov-based microstepping control of Sawyer motors with PID control

Proportional-integral-derivative (PID) controls have been widely used for Sawyer motors. The electrical dynamics are generally neglected in general PIDs control since the electrical dynamics are faster than the mechanical dynamics. However, when the current control is used, the phase currents are reduced by back-emf and have the phase lags due to inductances. Thus, the electrical dynamics should be considered to improve the performance of PID control. In this paper, Lyapunov-based microstepping control of Sawyer motors with PID control is developed for improved performance of PID control. The proposed method consists of PID and Lyapunov-based controller. PID controllers make the desired forces and torque to track the position profiles of x and y with regulation of yaw. And the commutation scheme from the desired forces and torque to the desired phase currents are used. For the design of Lyapunov-based control, the stabilities of the equilibrium points are studied using Lyapunov method. Then, Lyapunov-based control is designed to compensate back-emfs and phase lags. Furthermore, the proposed method guarantees the exponential stabilities of desired currents for PID control. And, the closed-loop system is analyzed. The proposed method considering the electrical dynamics is designed without any coordinate transformation. Therefore, it could reduce the commutation delay. Simulation results show that the tracking performance of PID controller is improved by the proposed method.

High gain observer based nonlinear position control for electro-hydraulic servo systems

We present a high gain observer-based nonlinear position control for electro-hydraulic servo systems. We design passivity based control for improve tracking performance. The passivity based control needs the full states information. Since the electro-hydraulic servo system has nonlinearities, we designed a modified high gain observer to estimate its states without the transformation for normal form. To reduce the effect of nonlinear terms, we use a high gain technique. We analyze the stability of the closed-loop system using the singular perturbation method. Simulations show that the proposed controller has better position tracking performance than a standard PI controller.

Passivity-Based Control With Nonlinear Damping for Type 2 STATCOM Systems

This paper presents a passivity-based control (PBC) for a type 2 static synchronous compensator (STATCOM) based on an Euler-Lagrange model. The proposed method is designed based on a Lyapunov function by considering dissipation to improve transient performance. An additional nonlinear damping term is designed to regulate the capacitor voltage. It is guaranteed that the equilibrium point of the system is locally exponentially stable in the operating range. The performance of the proposed method is validated via a 100 Mvar STATCOM system connected to the 345-kV grid system in SimPowerSystems, MATLAB/Siumlink. To compare with the input-output feedback linearization method, the proposed control method has improved convergence and reduction of oscillations of the active current and DC voltage, as shown in simulation results. Lastly, it shows that the proposed method is robust to model mismatches as the variation of the grid voltage and the degradation of the capacitance.

Position control of a permanent magnet stepper motor by MISO backstepping in semi-strict feedback form

In this paper, we present a recursive application of multiple-input single-output (MISO) backstepping for the position tracking of permanent magnet stepper motors (PMSMs) in the form of semi-strict feedback. This backstepping method does not use direct-quadrature (DQ) transformation but it turns out that the MISO backstepping is equivalent to field oriented control (FOC). In the dynamics of a PMSM, the quadrature current can be regarded as the input to the mechanical dynamics of PMSM for realization of FOC. In the proposed controller, however, virtual velocity is designed to track the desired position while the desired current vector is designed to track the virtual velocity. Since the proposed controller requires full state information, assuming position and currents measurement available, a new reduced order observer with a state augmentation for load torque is developed. The global exponentially of tracking error is guaranteed by using a composite Lyapunov function. In addition, we show that the estimator and controller gains can be independently tuned due to principle of separation. Simulation results validate the effectiveness of the proposed method.

Observer-based variable structure control in microstepping for permanent magnet stepper motors

In this paper, we propose observer-based variable structure control (VSC) in microstepping for permanent magnet stepper motors (PMSMs) without position feedback. The back-emfs of the currents dynamics are defined as the disturbance terms. The observers for the back-emf estimation are designed. The proposed observers are in the form of the high pass filter. Observer-based VSC is developed to guarantee local exponential stability of the desired currents for microstepping by only currents feedback. The proposed controller is robust to back-emf. The proposed controller does not require any transformation so that it could reduce the commutation delay. Experimental results show that the proposed method results in improvement in position tracking over the microstepping with proportional and integral current feedback. Since proposed method guarantees local exponential stability of the desired currents required for microstepping, overall more than 60% improvement in tracking error was obtained in experimental results. And the tracking error ripple is also reduced.