Direct Torque Control with Space Vector Modulation (DTC-SVM) of ...

Sensorless Speed Direct Torque Control with Space Vector Modulation (DTC-SVM)
Where lim is the limited value. Please note that lim should be set at reference stator
flux amplitude
lim =Ψ
s _ ref
equal Ψ
PM
.
From Eq. 6.18 it can be observed that when one of the stator flux linkage components
Ψ
sα
or Ψ
sβ
exceeds the limit, it causes in distortion of the output waveform.
6.4 Electromagnetic torque estimation
The PMSM motor output torque is calculated based on the equations (2.51), (2.52),
(2.55), (2.58) presented in Chapter 2, which for stator oriented coordinate system can be
written as follows:
3
M
e
= pb( Ψs αIsβ −Ψ
sβIsα
)
(6.19)
2
It can be seen that calculated torque is dependent on the current measurement accuracy
and stator flux estimation method. In practice current measurement is performed with
high accuracy ( ≤ 1% with 150kHz frequency bandwidth) using, for example, LEM
sensors.
6.5 Rotor speed estimation methods
6.5.1 Overview
High performance operation of motion sensorless PMSM drives depends mainly on
accurate knowledge of rotor PM flux magnitude, position and speed. The rotor position
estimation methods can be classified into two major groups:
• motor model based,
• rotor saliency based techniques.
The rotor saliency based approach is suitable only for the Interior PMSM (see Fig. 1.2 c
and d). Motor model based approach detect the back EMF vector, which includes
information about position and speed, using either open loop models/estimators
[81,85,86] or closed loop estimators/observers [70, 73,74,96,97,100]. Also adaptive
observers [72,92,98,83] and Extended Kalman Filters (EKF) [67,73] have been
proposed for motor position and speed estimation. These methods, however, are
computationally intensive and require careful design and proper initialization.
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