Commutation Torque Ripple Reduction in BLDC Motor Using Modified SEPIC Converter  and Three-level NPC Inverter

Abstract

This paper presents a new power converter topology  to suppress the torque ripple due to the phase current commutation of a brushless DC motor (BLDCM) drive system. A combination of a 3-level diode clamped multilevel inverter (3level  DCMLI), a modified single-ended primary-inductor converter (SEPIC), and a dc-bus voltage selector circuit are employed in the proposed torque ripple suppression circuit. For efficient suppression of torque pulsation, the dc-bus voltage selector circuit is used to apply the regulated dc-bus voltage from the modified SEPIC converter during the commutation interval.  In order to further mitigate the torque ripple pulsation, the 3level  DCMLI is used in the proposed circuit. Finally, simulation and experimental results show that the proposed topology is an attractive option to reduce the commutation torque ripple significantly at low and high speed applications.

EXISTING SYSTEM:

Various hybrid converter topologies have been proposed with a dc-dc converter to improve torque performance of 2level  inverter-fed BLDCM a buck converter has been employed between the dc supply and conventional 2-level inverter for the speed control of BLDCM, which can significantly reduce the torque ripple at lower speeds. A super-lift Luo-converter has been employed in front of the 2-level inverter to lift the dc-bus voltage to the desired value for the torque ripple suppression at high-speed work conditions a novel circuit topology with SEPIC converter and a switch selection circuit has been proposed for torque ripple suppression of BLDCM drive with dc-bus voltage control. To reduce the commutation torque ripple, a voltage control strategy has been proposed to equalize the slew rates of incoming and outgoing phase currents. A novel circuit topology has been proposed for torque ripple suppression of BLDCM drive system which is built by a 3level DCMLI with two SEPIC converters and a commutation voltage selection circuit an average torque control method using one-cycle control (ATC-OCC) has been proposed using dc-bus voltage and current measurements, without using back-EMF and accurate rotor position information. In order to suppress the torque ripple for BLDCM, a current optimization technique has been proposed in both conduction mode and commutation mode using integral variable structure control.

PROPOSED SYSTEM:

In most industrial low- and medium-power applications, a conventional 2-level inverter is a preferred choice. The multilevel-inverter driven ac machines are used in many industrial high power applications due to lower harmonic distortion of the output currents and operate with reduced dv/dt stress as compared to the 2-level inverter driven ac machines. The BLDCM is widely used in more electric aircraft (MEA) applications in a power range of 100kW to 150kW and dc-bus voltage is from 270Vdc or 540Vdc. The multilevel converters such as flying capacitor (FC) inverter, cascaded H-bridge (CHB) inverter, and neutral point-clamped (NPC) inverter have been widely used in high-power medium-voltage applications. For FC inverter, the  capacitor  clamping requires a large number of expensive and bulky capacitors to clamp the voltage. It requires a complex control for voltage tracking of capacitors, difficult to control pre-charging of capacitors to the same voltage level, and operates with poor efficiency. A 5-level CHB inverter has been proposed for harmonics and torque ripple suppression of BLDCM drive with current and speed closed loop control. This converter needs galvanically isolated dc source for each of the H-bridge. In recent years, the MOSFETbased 3-level DCMLIs are preferred to drive BLDCM for low  and  medium power applications, which produce low current THD in the stator windings, smaller voltage steps, reduced switching loss under high switching frequency  and lower  common mode voltage amplitude than conventional 2-level inverter. The 3-level DCMLI topology provides a significant reduction in ripple current for low inductance BLDCM without the need for very high switching frequency than 2-level inverter. Also, it operates with a lower number of DC sources and power semiconductor devices than FC multilevel inverter and CHB multilevel inverter.   In this paper, a novel converter topology is proposed to reduce the torque ripple of the BLDCM drive system. The proposed converter is composed a modified SEPIC converter and a MOSFET-based 3-level DCMLI. The modified SEPIC converter operates with high static gain and less switching voltage stress than classical DC-DC converters. Hence, the modified SEPIC converter is used in this proposed torque ripple suppression circuit and the duty cycle is adjusted to obtain the desired dc-bus voltage based on the spinning speed of the BLDCM. The 3-level DCMLI is used for further reduction of the current ripple and as well as the resultant torque ripple. The MOSFET-based voltage selector circuit is used to apply regulated dc-bus voltage for efficient commutation torque ripple suppression. Simulation and experimental results show that the proposed converter topology with the dc-bus voltage selector circuit significantly reduces the torque ripple during the commutation interval

CONCLUSION  

In this paper, a commutation torque ripple reduction circuit has been proposed using 3-level DCMLI with modified SEPIC converter and a dc-bus voltage selector circuit. A laboratory-built drive system has been tested to verify the proposed converter topology. The suggested dc-bus voltage control strategy is more effective in torque ripple reduction in the commutation interval.  The proposed topology accomplishes the successful reduction of torque ripple in the commutation period and experimental results are presented to compare the performance of the proposed control technique with the conventional 2 -level inverter, 3-level DCMLI, 2-level inverter with SEPIC converter and the switch selection circuitfed BLDCM. In order to obtain significant torque ripple suppression, quietness and higher efficiency, 3-level DCMLI with modified SEPIC converter and the voltage selector circuit is a most suitable choice to obtain high-performance operation of BLDCM.  The proposed topology may be used for the torque ripple suppression of BLDCM with the very low stator winding inductance.

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