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

Direct Torque Control with Space Vector Modulation
Chapter 5
DIRECT TORQUE CONTROL WITH SPACE VECTOR MODULATION
(DTC-SVM)
5.1 Introduction
The DTC-SVM greatly improves torque and flux performance by:
• Achieved fixed switching frequency,
• Reduced torque and flux ripples.
The main idea of DTC-SVM is based on analyze of the torque equation
M
Assuming that the Ld = Lq = Ls
e
3 Ψ sin
2 s
ΨPM
δΨ Ψs
( Lq
−Ld)sin2δ
Ψ
= pb[ − ]
(5.1)
2 L
2L L
d d q
M
e
3 Ψs
ΨPM
sinδ = pb[ Ψ
]
(5.2)
2 L
From equation (5.2) we can see that for constant stator flux amplitude
by permanent magnet
Ψ
PM
s
Ψ
s
and flux produced
, the electromagnetic torque can be changed by control of the
torque angle δ Ψ
. This is the angle between the stator and rotor flux linkage, when the stator
resistance is neglected. The torque angle, in turn, can be changed by changing position of the
stator flux vector θ Ψ s
in respect to PM vector using the actual voltage vector supplied by
PWM inverter.
In the steady state, δ Ψ
is constant and corresponds to a load torque, whereas stator and rotor
flux rotate at synchronous speed. In transient operation, δ Ψ
varies and the stator and rotor
flux rotate at different speeds (Fig. 5.1).
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