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Title: Current source dc-dc and dc-ac converters with continuous energy flow
Author: Badawy, Ahmed Darwish
Awarding Body: University of Strathclyde
Current Institution: University of Strathclyde
Date of Award: 2015
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This work considers current sourced powerelectronic converters. The thesis classifies and presents several new single-phase and three-phase differential-mode current source inverters that evolve from the basic dc-dc converter topologies. The switched, large-signal, and small-signal models of these converters are presented, and used to develop control strategies for the proposed differential-mode inverters, considering their inversion and rectification modes. The viability of each differential mode inverter/rectifier is validated using simulations and experimentation. The performances of different proposed buck, boost, and buck-boost current source inverters are discussed and compared in terms of efficiency, total harmonic distortion, input current ripple, capacitor stresses, and control complexity. Some of the proposed current source inverters offer buck-boost capability (can operate with output voltage less or greater than the input dc voltage), which is suited for grid-connected operation of single-stage three-phase buck-boost inverters. Phase variables and synchronous frame controllers are used to provide satisfactory inverter operation in inversion and rectification modes. The inherent low-order harmonic currents in the input and output of the proposed converters (predominantly, negative sequence 2nd order harmonic) are supressed using PI and PR controllers. Also, interleaved carriers are used to reduce the input current ripple of the three-phase inverters. The proposed converters can operate over a full control range from 0 to unity power factor, with power flow in both directions (unlike the conventional six-pulse current inverter). Additionally, a nonlinear control strategy, sliding mode control, is implemented with to achieve faster dynamic inverter response during faults as well as elimination of dccurrent injection into ac grid. This is necessary during unbalanced operation. Operation of single-phase differential-mode buck-boost inverters is presented, including suppression of the 2nd order harmonic in the input dc current by two methods. In the first, active suppression of the 2nd harmonic uses a power electronic circuit. The second method manipulates the modulating signal in combination with a relatively large capacitor to trap the oscillating power that causes the 2nd order harmonic to appear input dc link current. The two single-phase harmonic suppression approaches are compared.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral