In this paper, the unbalanced current in the 12- pulse phase control AC/DC converters was studied. The 12- pulse A-Y type AClDC converter will keep a balanced voltage with 30″ phase shifted at the low coupling coefficient condition. But an unbalanced current will be obtained in the 12-pulse autotransformer phase shift AClDC converter at the low coupling coefficient condition. The theoretical phasor analysis of the unbalanced current was presented and a feedback controller was designed to overcome this problem. Finally, a 3 kW 12-pulse autotransformer phase shifted AClDC converter was implemented to demonstrate the theoretical analysis.
- 12 Pulse AClDC Converter
- Phase Controller
Fig. 1. Conventional 12-pulse AClDC converter.
(a) A-Y isolated transformer.
(b) Autotransformer phase shifted.
Fig. 2. 12-pulse phase control A-Y connected AC/DC converter.
Fig. 3. I;!-pulse phase control autotransformer connected AC/DC converter.
EXPECTED SIMULATION RESULTS:
Fig. 4 The output current io, and io, of 12-pulse phase control A-Y
typ: transformer ACDC converter with K=0.96 and a = 30″
Fig 5 The output current io, and io, of 12-pulse autotransformer
phase shift ACDC converter with K=0.96 and a = 30″.
Fig. 6 The output current of 12-pulse autotransformer connected
AC/DC converter with the controller
Fig. 7 Experimental results for a resistive load without controller
Fig. 8 Experimental results for a resistive load with controller
In this paper, the 12-pulse phase control ACDC converters with A-Y type and autotransformer type are analyzed and studied. The theoretical analysis is presented and the computer simulation results are performed. The 12- pulse A-Y type ACDC converter can function well under any firing condition. However, a serious unbalanced circulation current exists in the autotransformer connected ACDC converter at the non-unity coupling coefficient conditions. Finally, a 3 kW 12-pulse autotransformer phase controlled ACDC converter was implemented to demonstrate the theoretical analysis.
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