Encoders are one of the critical parts in an electric drive system. In safety critical applications like an air plane a redundant and robust sensor-less controller with an approval in aviation is required. This paper presents a hysteresis current controller, which is implemented on a FPGA. We simulated the switching action and the controller dynamics and measured it on a test bench. We describe the transients excited by the switching action analytically. Although transients are excited at the switching moment, a stable operation of the machine is ensured. The results of simulation and measurement of the switching action show a maximal deviation of 6% in the stator current amplitude. The excited transients describe a sinusoidal shape for the rotor speed. The analytical solution of the oscillation amplitude deviates from the measured results by a maximum of 14%. The oscillation frequency is 24% up to 35% smaller, depending on the operating point. The differences are due to the assumption of phase currents with a constant amplitude. It is shown that the dq-current components follow the constant torque hyperbola, if the current reference amplitude changes. In case of a load torque change they will move on the constant stator current circle and turning clockwise for a load torque decrease and counter clockwise for an increase. Due to the working principle of the controller, the current distortion is significant and is measured to 29% in a defined operating point. The measurement results validate the simulation results. The implemented hysteresis current controller can be used to improve the redundancy of a control structure.