Discrete-time compensating control of a stepper motor for an active control lever

Control levers for command setting are widely used, e. g. as thrust control in marine or aviation applications. Actually these levers are equipped with a mechanical brake to avoid movements of the lever in case of vibrations. Special control points are indicated to the user by mechanical detents. The basic idea of an active lever is to create a force feedback to the user which depends on the current situation of the system, e.g. if the user wants to reduce the thrust and the system recognizes a risk to stall the airplane then a high counterforce is applied against the movement of the lever. Detents or break characteristics can also be simulated by the active lever which is typically driven by a DC motor. The basic idea presented in this paper is to use a stepper motor which is able to produce high detent torques even in the case of a power blackout. Field oriented control by means of a discrete-time compensating controller is applied to the current control loop. This paper focuses on the nonlinear mathematical model of the stepper motor and the design of a discrete-time decoupling compensating current controller. Due to the small electrical time constant of the motor and a limited sampling rate, quasi continuous control design of a PI controller does not produce satisfactory results.