A new topology for commutation torque ripple reduction in brushless direct current motor drives

During the commutation period in brushless direct current motors (BLDCMs), discrepancies between the rise and fall times of the incoming and outgoing phase currents lead to the generation of current and torque ripples. These ripples, known as commutation torque ripple (CTR), result in adverse effects such as speed fluctuations, knocking, vibration, and acoustic noise. These phenomena significantly restrict the utilization of BLDCMs in high-performance servo systems. Theoretically, CTR can be eliminated by equalizing the rise and fall times of the commutated phase currents. When these durations are balanced, torque ripple is effectively nullified, in accordance with Kirchhoff's current law (i_a+i_b+i_c=0). It also means that the inverter's direct current (DC) bus voltage (V_bus) for the BLDCM is equal to 6 times the sinusoidal back electromotive force (emf, E) generated by the BLDCM. The BLDCM's back emf value is directly proportional to the motor speed. Therefore, it is satisfied that at low speeds V_bus>6E and at high speeds V_bus<6E. While it is sufficient to simply apply pulse width modulation (PWM) to the phase current to reduce the CTR at low speeds, a higher voltage is needed to reduce the CTR at high speeds. Considering this, an auxiliary boost circuit topology that will control the bus voltage amplitude for reducing the CTR at high speeds is presented in this thesis. The proposed topology is connected between the input DC power supply and the three-phase inverter. The capacitor in the circuit is charged during the normal conduction period. During the commutation period, the charged capacitor is connected in series with the DC power supply via the switch circuitry to increase the DC bus voltage and the DC bus voltage (V_bus) is raised to a value equal to 6 times the back emf. To evaluate the performance of the proposed method, simulation and experimental studies were conducted at the Matlab®/Simulink® environment. For the practical implementation, digital signal processor (DSP) of EzDSP TMS320F28335 was utilized. According to the results of the simulation and experimentation, the proposed method could achieve an improvement up to %57.14 for the commutation torque ripple and a %57.2 for the commutation time comparing with the traditional method.