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High Performance Control of AC Drives with Matlab / Simulink Models by Jaroslaw Guzinski, Atif Iqbal, Haitham Abu-Rub

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8.3 Sensorless Control of PMSM

The rotor speed and produced torque can be computed using the Luenbergera back emf observer. Assuming that the dynamics of the mechanical system are much slower than the dynamics of the electric variables, we may assume that the motor back emf does not change during an observer sampling period, so that

(8.49) equation

(8.50) equation

The used Luenberger observer for the PMSM back emf in the stationary αβ frame is described as [63,64,67]

(8.51) equation

(8.52) equation

(8.53) equation

(8.54) equation

where ^ is the estimated value; Ls is the stator inductance, assuming that Ls = Ld; and K, K, K, K, are observer gains (when using symetrical motor K = K = Ki, K = K = Ke).

The state variables in the observer are stator currents iα, iβ; however, the back emf signals eα, eβ are disturbances that should be identified in the observer. The block showing such an operation is illustrated in Figure 8.14 ...

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