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an investigation of dual stator winding induction machines

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proposed. The switching frequency is kept const<strong>an</strong>t <strong>an</strong>d satisfactory dynamic<br />

perform<strong>an</strong>ce c<strong>an</strong> be achieved. Three control schemes for parallel connected PWM<br />

rectifiers have been proposed <strong>an</strong>d the system perform<strong>an</strong>ces <strong>of</strong> the three proposed<br />

controllers have also been compared.<br />

In the parallel voltage source inverter area, different system configurations have been<br />

studied in [9.9]. The control strategy for parallel operation <strong>an</strong>d the system protection<br />

methods have been discussed in detail. In [9.10], a simple control scheme that regulates<br />

the current <strong>of</strong> each inverter independently has been used. Current instability has been<br />

reported when a <strong>dual</strong>-<strong>winding</strong> three-phase motor was driven by parallel connected<br />

voltage source inverters. It was discovered that the nonlinearities <strong>of</strong> the system, including<br />

the modulator, inverter <strong>an</strong>d machine, result in a chaotic tr<strong>an</strong>sient into the instability,<br />

which is not predictable or repeatable. Parallel connected five-level PWM inverters have<br />

also been studied in [9.11] to increase the power rating <strong>of</strong> the inverter system. The dc<br />

current was found to be controllable by me<strong>an</strong>s <strong>of</strong> phase shifting <strong>of</strong> the injected third order<br />

harmonics.<br />

Very few published papers have focused on the use <strong>of</strong> series connected ac-dc boost<br />

rectifiers when compared to the relatively large body <strong>of</strong> work on paralleled ac-dc boost<br />

converters [9.1-9.5, 9.7-9.11]. In [9.1], both parallel <strong>an</strong>d series connected AC-DC<br />

rectifier systems using hysteresis current control have been studied <strong>an</strong>d stability <strong>an</strong>alysis<br />

results based on a very simplified converter model have also been shown under unity<br />

power factor condition.<br />

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