To improve the position estimation performance of the permanent magnet synchronous motor (PMSM) drive system, a novel quasi-super-twisting observer (QSTO) combined with the enhanced quadrature phase-locked loop (Q-PLL) is presented in this paper. Different from the discontinuous signum function used in conventional sliding mode observer, the proposed QSTO with continuous nonsmooth terms is employed to estimate the back electromotive force (EMF), which significantly reduces the negative impact of the chattering phenomenon. After acquiring the EMF signal from the QSTO, an effective enhanced Q-PLL is utilized to alleviate the low-order harmonic components generated by inverter nonlinearities and flux spatial harmonics. Comparative experimental results demonstrate the satisfactory performance of the proposed sensorless control strategy.

Stepper motors are used in satellites for various drive operations that are achieved by custom designs. This paper presents a stepper motor driver for satellite systems. It takes rotor position and phase current as inputs and employs a current subdivision method with back-propagation neural network (BPNN) to achieve constant current control of the motor. The driver can ensure the smooth operation and the positioning accuracy of the motor with a filter wheel that is 0.1944 $\mathrm{kg}·{\mathrm{m}}^2$ in the moment of inertia and satisfy self-adaption of the load without system parameter identification. Compared to the previous scheme, the proposed scheme can reduce the power consumption by about $21.15\%$ when the motor runs at 2 $\mathrm{r}/\mathrm{s}$, which is beneficial to the reduction in the size and the mass of some power supply modules. The performances of the developed driver are implemented on a field programmable gate array (FPGA) circuit board. The experimental results are conducted to verify the claims presented. The proposed scheme can be extended to other stepper motor systems with large moment of inertia loads within spacecraft.

To enable the optical remote sensing satellite to flexibly adjust the camera’s focal length for clearer imaging, a low-power position monitoring and control system suitable for space environments is designed, which is highly significant for aerospace devices with limited energy resources. A novel constant voltage drive circuit is proposed for driving the stepper motor. The differential linear driving and receiving circuit is presented to collect data from the linear encoder. By using the linear encoder to provide feedback on the current focal length, both open-loop and closed-loop focusing functions are achieved. The performances of the designed system are implemented on a field programmable gate array (FPGA) circuit board. The experimental results demonstrate that the developed system consumes approximately 1.4W of power, has a strong load-carrying capacity, and achieves a focusing control precision of ±0.0004mm over the entire motion range of −6mm to +6mm .