In existing sliding mode control (SMC) methods, a disturbance observer (DOB) is employed to achieve disturbance rejection and reduce chattering, which is a major disadvantage associated with SMC and increases with increasing switching gain. However, the disturbance in a DOB associated with SMC is typically estimated using a control input that exhibits chattering. Although the existing methods can reduce chattering using SMCs with DOBs, the estimated disturbance comprises undesirable high-frequency components caused by the control input. In this article, a chattering attenuation disturbance observer (CADOB) is proposed to achieve chattering reduction in the SMC. A frequency spectrum analysis is performed for the control input, estimated disturbance, and controlled state to elucidate the effect of chattering in the control input on the estimated disturbance and controlled state obtained using existing methods. The proposed CADOB is designed to estimate the disturbance with a reduction in undesirable high-frequency components. The frequency response results demonstrate that the effect of chattering in the control input on the estimated disturbance can be reduced by using CADOB, while maintaining the disturbance estimation performance. Moreover, the performance of the CADOB is experimentally validated using SMC in permanent-magnet synchronous motors.

We have designed a nonlinear H ₂ controller for permanent magnet stepper motors. The proposed method consists of a new torque modulation scheme, a passive nonlinear observer, and a nonlinear H ₂ controller. The nonlinear torque modulation is incorporated to generate desired torque. The H ₂ controller and a passive nonlinear observer are independently designed. The use of the passive nonlinear observer allows operation based on only angular position without requiring an additional sensor. The nonlinear H ₂ controller is developed to improve transient response in the position control. Tracking performance is evaluated in the view point of a linear system. The control gains are linearly scheduled by using interpolation parameters based on a linear matrix inequality approach. A stability of the passive nonlinear observer is proven by using a passivity theorem. The proposed method improves transient response in position tracking and allows evaluation of performance criteria. The performance of the proposed method was validated by means of experimental comparison with a previous method.

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.