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The following paper investigates and analyses the electromagnetic processes in an electrical drive system composed of a power source, a power inverter and a brushless dc (BLDC) motor using known pulse-width modulation (PWM) methods. Investigated modulation techniques are: unipolar modulation of the upper transistors (PWM-TOP) and bottom transistors (PWM-BOT), symmetrical PWM-PWM, modulation type PWM-ON and ON-PWM, and bipolar PWM-ON modulation indicated with PWM-ON-BIP. The voltage source inverter is considered as DC-DC buck power converter, when BLDC is operated in motor mode. On the basis of summarized equivalent circuits, the analytical expressions are received for the electromagnetic processes in the system by the different modulation techniques. The efficiency of the system battery-inverter-machine for each discussed modulation is experimentally investigated and compared. These results are also compared with the efficiency of the BLDC driven with vector control. A MATLAB/SIMULINK model is proposed to implement these modulations and to analyze the obtained results. From this model, the harmonic composition of the phase currents for each modulation is investigated.

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