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BrushLess Direct-Current (BLDC) motors are characterized by high efficiency and reliability due to the fact that the BLDC motor does not require power to the rotor. The rotor of the BLDC motor consists of permanent magnets. When examining the waveform of the current supplied to the motor windings, significant current ripple was observed within one power cycle, where the optimum value would be the constant value of this current during one power cycle. The variability of this current in one motor supply cycle results from the variability of the electromotive force induced in the motor winding. The paper presents a diagram of the power supply system consisting of an electronic commutator and a DC/DC converter made by the authors, and a proposed modification of the power supply system reducing the current pulsation of the motor windings and thus the possibility of reducing energy losses in the motor windings. The paper presents numerous results of measurements which showed a significant reduction in energy losses in the case of low-load operation.

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Dc tram traction voltage is obtained by rectifying grid ac voltage with help of transformer-rectifier sets. In Poland typically 6-or 12-pulse systems are used. 24-pulse system may be achieved by parallel operation of two Yyd transformers with primary windings arranged as zigzag. This paper deals with 24-pulse system design using cost-effective transformer with partially integrated secondary windings. Generation of secondary side voltages is explained. We prove that in spite of secondary phase voltages being of correct magnitude and shift angle, this transformer will never operate with more than 12 pulses. Results of computer simulations are verified by lab tests results.Index Terms -rectifier transformer, commutation, multiphase transformer.978-1-4673-0142-8/12/$26.00 ©2012 IEEE