HF parameter identification using test current injection for sensorless control of a synchronous reluctance machine (SynRM)

An increasing number of sensorless control methods are being developed for a recently rediscovered machine type: synchronous reluctance machines (SynRMs). The advantage of sensorless control methods is that the position sensor can be omitted. Many alternative methods are conceivable, but in all of them, it is impossible to observe and estimate the electrical rotor position at standstill and at low speed without additional excitation via high-frequency (HF) test signals. To calculate the position information from the current or voltage response of these test signals, a detailed machine model is necessary. The challenge is to identify the parameter of the machine model that characterises the HF machine behaviour. Thus, there is a need to find a proper identification method and to analyse these HF parameters for different HF test signal frequencies and amplitudes. Thereby, one can determine which test signal frequencies and amplitudes are best suited for sensorless control of SynRMs. Therefore in this paper an HF parameter identification method is described and the corresponding measurement results for a SynRM are analysed. A test current signal injection method is used. Different test signal frequencies and amplitudes, as well as the position dependencies, are compared. It can be concluded that, first a appropriate test signal frequency and amplitude combination has to be selected that offers enough voltage reserve to control the fundamental behaviour of the machine. Moreover, the HF parameters should be measured exactly for the combination used because there is a dependency of the HF parameters on the test signal frequency and amplitude that is significant but not equally strong. Position averaged measured values ensure high-precision HF parameter results. SynRMs are suitable for saliency-based sensorless control methods based on test signal injection because they have an inherent machine parameter saliency due to their rotor design.