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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Voltage source PWM inverter for PMSM supply<br />
3.3 <strong>Space</strong> vector based pulse width modulation (PWM) methods<br />
In voltage source inverter the transistors are controlled in a on-<strong>of</strong>f fashion. In order to<br />
obtain a suitable duty cycle for each switches the technique pulse <strong>with</strong> modulation is<br />
used. The modulation methods [18,21,22,23,24,26,28,29,30] have the influence on:<br />
wide range <strong>of</strong> linear operation, low content <strong>of</strong> higher harmonics in voltage and current,<br />
low frequency harmonics, minimal number <strong>of</strong> switching to decrease switching losses in<br />
the power components.<br />
The most important factor in PWM mode is modulation index defined as the ratio <strong>of</strong> the<br />
reference voltage amplitude value to the maximum voltage amplitude value during sixstep<br />
operation (see Fig 3.17) and is given by:<br />
M<br />
U<br />
ref<br />
= (3.8)<br />
2<br />
U<br />
DC<br />
π<br />
where the<br />
U<br />
DC<br />
is the DC link voltage (for three phase six diodes rectifier is 560 V ).<br />
The modulation index varies between 0-1 and can be divided into two regions: the<br />
linear ( 0< M ≤ 0.907) and the nonlinear ( 0.907 < M ≤ 1) as is shown in Fig. 3.17.<br />
Im<br />
U3(010)<br />
U 2(110)<br />
End <strong>of</strong> overmodulation<br />
region (six-step mode)<br />
2<br />
π<br />
Umax<br />
= U DC<br />
⇒ M = 1<br />
sector = 2<br />
sector = 3<br />
2<br />
U<br />
3 dc<br />
U ref<br />
End <strong>of</strong> linear region<br />
U<br />
max<br />
= U DC<br />
⇒ M = 0.907<br />
3<br />
U 4<br />
(011)<br />
sector = 4<br />
U 0<br />
(000)<br />
U 7<br />
(111)<br />
sector = 5<br />
θ ref<br />
T1<br />
U<br />
1<br />
Ts<br />
sector = 1<br />
sector = 6<br />
Re<br />
U (100) 1<br />
nonlinear<br />
(overmodulation) region<br />
linear region<br />
U 5 (001)<br />
U 6 (101)<br />
Figure 3.17 <strong>Space</strong> vector diagram <strong>of</strong> the available switching vectors.<br />
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