A novel composite control method based on disturbance observer for the precision suspension of a voltage-controlled active magnetic bearing (AMB) system is presented in this study. The voltage-controlled AMB system always suffers from the mismatched disturbances, which act on the system via different channels from the control inputs. In this study, we reconstruct a new system, which is equivalent to the original voltage-controlled AMB dynamical system. The reconstructed system targets to divide the mismatched disturbances into the matched component and the mismatched component. The matched component is attenuated by the feedback robust controller, and the mismatched component is rejected on the basis of disturbance observer. Both simulations and experiments demonstrate the effectiveness in rejecting the mismatched disturbances on the voltage-controlled AMB system in a magnetically suspended control moment gyro. The proposed control method handles the mismatched disturbances from the state variable and preserves the nominal performance of the baseline robust controller to the best.

Rotor imbalance causes undesirable synchronous vibrations of displacement, force and torque. An active vibration control (AVC) method achieving the minimum vibration force and torque within a desired vibration displacement is presented in an active magnetic bearing (AMB) system. First, the dynamics of the AMB system with static imbalance and dynamic imbalance are introduced, and the dimensional displacement relationships of the rotation, geometric and inertial axes of the rotor are described. Demands of the AVC are analyzed, and the results indicate that the rotation axis has to be controlled to move along the center line and the inclination direction of the geometric axis and the inertial axis, respectively. Then the synchronous vibration displacement is identified with a general notch filter, and a feedforward controller is designed to control the rotation axis by providing a synchronous control current. A gain phase modifier (GPM) is proposed to achieve a precise synchronous control current and to compensate the gain and phase errors caused by the power amplifier. The GPM is incorporated into the feedforward controller to formulate two closed loops, which can adaptively tune the gain and phase of the synchronous control current, respectively. Finally, simulations and experiments have been carried out to indicate the effectiveness of the proposed approach, which can be widely used since vibrations of displacement, force and torque can be controlled simultaneously to satisfy various requirements.

Harmonic currents, which are caused by rotor imbalance and sensor runout in active magnetic bearing (AMB) systems, can induce undesirable harmonic vibrations and superfluous power consumption. To analyze and reduce these harmonic currents, a comprehensive model of the AMB system is developed and a repetitive control method is proposed. First, dynamics of the four radial degrees-of-freedom rotor with the rotor imbalance and the sensor runout are introduced, and electrical equations of the AMB control system including power amplifiers and motion induced voltage (MIV) are described. Next, how synchronous and multiple harmonic vibration forces and torques, which result from the harmonic currents through both the current stiffness and the displacement stiffness, are induced by static imbalance, dynamic imbalance, and the sensor runout through controllers and the MIV, are explained and analyzed in detail. Then the AMB system is divided into two subsystems related to translational and rotational motions, respectively. The dynamic equations for the two coupled rotational motions of the rotor are combined into a complex function. The rotor imbalance and the sensor runout are transformed to input disturbances of the power amplifiers, and a repetitive control method is proposed to suppress these periodic disturbances by reducing the harmonic currents. Finally, the validity of the proposed method is demonstrated by simulations with MATLAB and experiments on a test rig of a magnetically suspended control moment gyro. It is superior to existing techniques due to the comprehensive AMB model and the effective control method with a short computation time.

Foot-mounted inertial navigation with zero velocity update (ZUPT) is commonly used in pedestrian positioning. To suppress the accumulating position error owing to the low-cost inertial sensor, classical dual-foot pedestrian navigation method provides the compensation using the two feet's relative step length, whose values can be set an upper bound constraint or measured by ranging sensors. However, it suffers from low improvement and poor wearability. In this study, the two sensors are distributed on the toe and ankle of the same leg. The sensor-to-sensor position is unchangeable with the lower limb segments. This makes the uncoupled two subsystems be related. Through gait analysis, the step is divided into the stance and swing phases. For each phase, positions, velocities, and the related characteristics of the toe and the ankle are analyzed and modeled, respectively. A Kalman filter is constructed to fuse the position and velocity observations according to the geometric constraints and the foot vector. The Mahony filter by fusing the inertial sensor and magnetometer is adopted for the attitude improvement. Several experiments at low and high walking velocities on the plane and upstairs are carried out to verify the proposed method. The results show that compared with the conventional single-inertial measurement unit (IMU) ZUPT and dual-IMU two-foot constraint methods, the position and heading errors have been well suppressed.