An Improved Power-Quality 30-Pulse AC–DC for Varying Loads

ABSTRACT:

This paper presents the design and analysis of a novel 30-pulse ac–dc converter for harmonic mitigation under varying loads. The proposed 30-pulse ac-dc converter is based on a polygon connected autotransformer with reduced magnetic. The proposed ac–dc converter is able to eliminate lower than 29th order harmonics in the ac supply current. The resulting supply current is near sinusoidal in shape with low total harmonic distortion and a nearly unity power factor. Moreover, the design of an autotransformer is modified to make it suitable for retrofit applications, where presently a 6-pulse diode bridge rectifier is used. To validate the proposed approach, various power-quality indices are presented under varying loads. The proposed ac–dc converter is found to be suitable for retrofit applications with a large load variation and where harmonic reduction is more stringent. The laboratory prototype of the proposed autotransformer-based 30-pulse ac–dc converter is developed and test results are presented which validate the developed design procedure and the simulation models of this ac–dc converter.

KEYWORDS:

1.      Auto transformer

2.      Multipulse ac–dc converter

3.      Polygon connection

4.      Power-quality (PQ) improvement.

SOFTWARE: MATLAB/SIMULINK

CIRCUIT  DIAGRAM:

EXPECTED SIMULATION RESULTS:

CONCLUSION:

A new 30-pulse ac–dc converter-feeding varying load has been designed, modeled, simulated, and developed to demonstrate its improved performance. The proposed 30-pulse ac–dc converter consists of a reduced rating polygon-connected autotransformer for producing the desired phase shifted voltages and is suitable for retrofit applications, where presently a 6-pulse diode-bridge rectifier is used. It has resulted in the elimination of a lower than 29th harmonic in the supply current. The proposed ac–dc converter has resulted in a THD of supply current of less than 5% in a wide operating range of the load with nearly unity power factor operation. The proposed converter results in the reduction in rating of the magnetics, leading to savings in weight, size, volume, and, finally, the overall cost of the converter system. The results obtained on the developed converter configuration also validate the simulated models and the design procedure.

REFERENCES:

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