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
The used Luenberger observer for the PMSM back emf in the stationary αβ frame is described as [63,64,67]
where ^ is the estimated value; Ls is the stator inductance, assuming that Ls = Ld; and Kiα, Kiβ, Keα, Keβ, are observer gains (when using symetrical motor Kiα = Kiβ = Ki, Keα = Keβ = 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 ...