Direct Torque Control with Space Vector Modulation (DTC-SVM) of ...
Direct Torque Control with Space Vector Modulation (DTC-SVM) of ...
Direct Torque Control with Space Vector Modulation (DTC-SVM) of ...
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<strong>Control</strong> methods <strong>of</strong> PM Synchronous motor<br />
4.2 Field oriented control (FOC)<br />
During many years a DC motor has been mostly used. Because <strong>of</strong> simple control<br />
method, which based on fact that flux and torque can be controlled separately using<br />
current control loop <strong>with</strong> PI controllers. However the weak point <strong>of</strong> this drive was DC<br />
motor, which could not worked in aggressive or volatile environment and required<br />
cyclical maintenance. This disadvantages has been eliminated, when instead <strong>of</strong> DC<br />
machine a three phase PMSM motor were used.<br />
In searching new control method for induction machine in 1971 was developed vector<br />
control method known as field oriented control (FOC) [31,38,49]. This method allows<br />
control the flux and the torque in the AC machine in similar way as for DC motor. It<br />
was achieved by transform current vector in stationary reference frame ( α,<br />
β ) into new<br />
coordinate system ( dq) , <strong>with</strong> respect to rotor (magnet) flux vector. So the flux<br />
produced by permanent magnet is frozen to the direct axis <strong>of</strong> the rotor (see Fig. 4.4).<br />
q−axis<br />
β −axis<br />
I s<br />
I sq<br />
δ I<br />
γ I<br />
I sd<br />
γ m<br />
Ω s<br />
Ψ PM<br />
d−axis<br />
α −axis<br />
Figure 4.4 <strong>Vector</strong> diagram illustrated the principle <strong>of</strong> FOC.<br />
Further, stator current vector can be split into two current components: flux current I sd<br />
and torque producing current I sq<br />
. In analogy to separate commutator motor, the flux<br />
current components corresponds to excitation current and torque-producing current<br />
corresponds to the armature current. Therefore, the goal <strong>of</strong> the control system is to<br />
reference the<br />
I<br />
sd_<br />
ref<br />
,<br />
sq_<br />
ref<br />
I stator current components in respect to requirement <strong>of</strong><br />
references torque and flux. The flux and torque producing stator current references are<br />
obtained on the output <strong>of</strong> the reference current generation block (see Fig. 4.5).<br />
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