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 />
Chapter 3 VOLTAGE SOURCE PWM INVERTER FOR PMSM SUPPLY<br />
3.1 Introduction<br />
The block scheme <strong>of</strong> an adjustable speed drive (ASD) commonly used in industrial<br />
applications to supply three-phase AC motor is presented in Fig. 3.1.<br />
Three-phase<br />
grid<br />
Rectifier<br />
DC link<br />
filter<br />
Inverter<br />
AC motor<br />
Choke<br />
Figure 3.1 Basic scheme <strong>of</strong> adjustable speed AC motor system.<br />
An ASD is supplied from three or single phase grid. It consists <strong>of</strong> a diode rectifier, DC<br />
link filter and an inverter. The rectifier converts supply AC voltage into DC voltage.<br />
The DC voltage is filtered by a capacitor in the DC link. The inverter converts the DC<br />
to an variable voltage, variable frequency AC for motor speed or (torque/current)<br />
control.<br />
The rectifier section <strong>of</strong> an ASD, called the front end, is responsible for generating<br />
current harmonics into the power supply system. Therefore, to reduce the total harmonic<br />
distortion (THD) <strong>of</strong> phase current it is necessary to add additional choke inductances.<br />
There are generally to way how insert choke inductances (see Fig. 3.2).<br />
a)<br />
b)<br />
L F<br />
D 1<br />
D3<br />
D5<br />
D 1<br />
D3<br />
D5<br />
L F<br />
L F<br />
C F<br />
U DC<br />
C F<br />
U DC<br />
L F<br />
D 2<br />
D4<br />
D6<br />
D 2<br />
D4<br />
D6<br />
L F<br />
Fig. 3.2 Three phase diode rectifier <strong>with</strong> smoothing choke: a) at the input b) at the DC link side.<br />
By adding a choke inductance at the input <strong>of</strong> rectifier gives the significant harmonic<br />
reduction. Some drive manufactures are starting to include this choke inductance in the<br />
DC link <strong>of</strong> the drive, providing the same harmonic current reduction benefit.<br />
Regarding to power electronics standards IEEE Std 519 it is recommended that<br />
production <strong>of</strong> harmonics should be less than 5%. It is a trend to replace the diode<br />
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