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an investigation of dual stator winding induction machines

an investigation of dual stator winding induction machines

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It should be noted that at <strong>an</strong>y time the power flowing in the converters could be bi-<br />

direction with the same hardware topology. For example, the voltage source converter<br />

shown in Figure 1.1 is called as voltage source inverter when power is flowing from dc<br />

side to ac side <strong>an</strong>d it c<strong>an</strong> also be called as voltage source rectifier when power is flowing<br />

from ac side to dc side. The power direction is dominated by the direction <strong>of</strong> dc current in<br />

the voltage source converter while dc voltage direction is unch<strong>an</strong>ged.<br />

Energy conversion in converters is achieved by the Pulse Width Modulation (PWM)<br />

technique. The turn on <strong>an</strong>d turn <strong>of</strong>f time <strong>of</strong> each switching device is calculated from a<br />

control scheme <strong>an</strong>d when these PWM pluses are applied, the fundamental voltages<br />

embedded in the output PWM voltages are the same as the desired ones. The PWM<br />

technique c<strong>an</strong> be generally divided into Carrier-based PWM (CPWM) <strong>an</strong>d Space Vector<br />

PWM (SVPWM). In the CPWM method, the modulation signals which contain certain<br />

magnitude, frequency <strong>an</strong>d <strong>an</strong>gle information are compared with a high frequency carrier<br />

signal to generate the switching pulses. The pulses are “one” when modulation signals are<br />

larger th<strong>an</strong> the carrier signal <strong>an</strong>d “zero” when modulation signal are smaller th<strong>an</strong> carrier<br />

signal. However, the turn on <strong>an</strong>d turn <strong>of</strong>f times <strong>of</strong> each device are calculated <strong>an</strong>d then<br />

sent to the PWM generator directly in the SVPWM method.<br />

The development <strong>of</strong> fast switching devices in power converters <strong>an</strong>d microcontrollers<br />

provides the possibility <strong>of</strong> implementing complex control schemes to the <strong>induction</strong><br />

machine. Generally speaking the variable speed control <strong>of</strong> <strong>an</strong> <strong>induction</strong> machine c<strong>an</strong> be<br />

classified into two main categories: scalar control <strong>an</strong>d vector control.<br />

The scalar control is the first control scheme applied to the <strong>induction</strong> machine. The<br />

const<strong>an</strong>t volts per Hertz (Const<strong>an</strong>t V/Hz) control is the simplest <strong>an</strong>d most robust scalar<br />

5

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