Estimating the orientation error with injected test signals for sensorless field oriented control of induction machines using magnetic anisotropies

A method for sensorless control of induction machines is proposed to estimate the field angle error using continuous excitation signals. Effects, which are present during a misalignment between the real world and model value, are used to estimate the error and correct it. Main flux oriented machine model equations, which take into account the magnetic anisotropies of the machine, are used to show the effect of a mismatch between the real and the model angle. These equations are simplified to only show the relevant terms in respect to high frequency test signals. By this it is possible to estimate the expected amplitude of injected test signals with greatly reduced computational effort. Simulation results are presented to show the validity of these assumptions. With the effects of an orientation error on a test signal described, a way to correct this error is discussed. For this, test signal components are extracted and used in a simple, but effective, control structure to minimize the error. By this it is also possible to estimate the main-flux angle of the machine. Simulation results are presented to show the performance of this method. Measurements on a test bench were carried out to show that these effects can be used in a practical application and also to validate the proposed method. This is done for standstill and with low rotor speeds.