| Summary: | 碩士 === 國立臺灣科技大學 === 電機工程系 === 99 === In this thesis, the thyristor rectifiers are applied to the 18-pulse converter system and a DC side injection strategy is proposed to directly inject the compensation currents at the DC side of the 18-pulse converter for improving the overall AC line condition with various delay angles. The digital signal processor (TMS320F2812) is applied as the core of control in this thesis for feeding back the parameters in system, calculating the compensation commands, and generating the triggering signals for thyristor rectifiers and three-phase inverter. In the proposed scheme, the delta/delta/double polygon phase-shifting transformer is deployed to offer three three-phase voltage sources with ±20° phase-shift to the three thyristor rectifiers and their outputs are connected to the inter-phase transformer for generating the 18-pulse DC output voltage. A three-phase current-controlled inverter directly injects compensation currents into these outputs for improving AC line condition. Besides the advantage of the low kVA rating [2.409%Po (pu)], the three-phase inverter used in the proposed DC side injection strategy connects to the 18-pulse converter system in parallel. Therefore, when the inverter malfunctions, the system can still work with the traditional 18-pulse converter. In this thesis, a DC side injection strategy is proposed for 18-pulse converter systems and modified with the constraints of the latching current and the holding current when applying thyristors. The two modified compensation strategies are compared in simulation. The proposed compensation strategy is highly proper for preexisting 18-pulse converter systems to operate on the occasions demanding lower harmonics or to apply thyristors for controlling output voltage. The compensation strategy can compensate with various delay angles. A 3kW prototype is built for test. Both simulation and experimental results demonstrate the validity of the proposed scheme.
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