Sensorless control of induction machines by combining fundamental wave models with transient excitation technique

In industrial applications, when high dynamic performance is required, the induction machine is operated under field oriented control. This implies the knowledge of the machine main flux position at any time instant. In practical operation, the flux is calculated with mathematical models considering only the fundamental wave behavior of the machine. To maintain a stable operation of such a scheme even at zero electrical frequency, the rotor position has to be known, measured by a mechanical rotor shaft sensor. Many sensorless control methods have been suggested to omit this sensor since it decreases the drives reliability and increases the costs. Sensorless schemes using fundamental wave models are based on a voltage integration. They show a good performance at high speed but fail at low and zero electrical frequency due to the low signal to noise ratio and parameter uncertainties. Other methods are evaluating parasitic effects in the machine response to a transient or high frequency excitation. This allows a calculation of the flux- or rotor position independent from the fundamental frequency. The approach given in this paper attempts to combine both methods to provide an excellent performance of the sensorless control scheme in the whole frequency range. Therefore, the fundamental wave model is stabilized at low frequencies by a method using a transient excitation method