The DC motor has broadened its role in many industrial parts. To control the speed for DC motor, the system usually requires the motor speed. However, there are many problems in case of using speed sensors. A sensor requires a mounting space on the motor, reduces the reliability, and increases cost of the drive system.
This paper proposes a new speed control method for DC motor, which requires neither shaft encoder nor speed estimator. The proposed scheme is based on decreasing armature current gap between a numerical model and an actual motor. By supplying the identical instantaneous voltage to both model and motor in the direction of reducing the armature current difference, the rotor approaches to the model speed, that is, reference value.
DC motor can be considered as a system whose inputs are field & armature voltage and outputs are field & armature current and armature velocity. As the numerical model whose electric parameters are the same as those of the actual motor is adopted, the armature rotating speed can be converged to the setting value by controlling voltages and currents on both sides to be equalized.
The simulation and experiment results indicate good speed and load responses and also show accurate speed changing performance.