**ABSTRACT:**

** **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.

**KEYWORDS:**

- 12 Pulse AClDC Converter
- Phase Controller
- Autotransformer

**SOFTWARE:** MATLAB/SIMULINK

**BLOCK DIAGRAM:**

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

**CONCLUSION:**

** **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.

** ****REFERENCES:**

** **

**S.**Choi, A. Jouanne, P. Enjeti and**1.**Pitel, “New Polyphase Transformer Arrangements with Reduced kVA Capacities for Harmonic Current Reduction in Rectifier Type Utility Interface,“ IEEE PESC, 1995.

**S.**Choi, P. N. Enjeti, H. Lee and I. J. Pitel, “A New Active Interphase Reactor for 12-Pulse Rectifiers Provides Clean Power Utility Interface,” IEEE IAS, pp.2468-2474, 1995.

- G. Oliver, G. E. April, E. Ngandui and C. Guimaraes, “Novel Transformer Connection to Improve Current Sharing on High Current DC Rectifier,” IEEE
**IAS,**pp.986-962, 1993.

**S.**Miyairi, etc.al, “New Method for Reducing Harmonic Involved in Input and Output of Rectifier with Interphase Transformer,” IEEE Trans.**On**Industry Applications, Vol. IA-22, No.5, pp.790- 797, SepIOct, 1986.

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