Supressão de corrente parasita em rolamentos de motor Brushless DC acionado por inversor PWM
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Data
2022-05-04
Autores
Parigi Filho, Éder Aparecido
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Editor
Universidade Estadual Paulista (Unesp)
Resumo
O acionamento e controle de um motor de corrente contínua sem escovas (Brushless DC motor), é realizado por meio da utilização de um inversor de frequência com modulação por largura de pulso (PWM - Pulse Width Modulation). Devido à alta frequência de chaveamento deste inversor, capacitâncias parasitas são estabelecidas ao longo do motor permitindo a circulação de correntes parasitas. Estas correntes ao circularem pelos rolamentos do motor podem causar erosão eletrostática nas pistas dos rolamentos, gerando vibrações indesejadas e reduzindo substancialmente a vida útil dos mesmos. O objetivo deste trabalho foi o estudo de abordagens para a mitigação destas correntes parasitas em motores Brushless, comumente designados de motores BLDC. Mais especificamente, a partir do estudo das abordagens para a mitigação disponíveis na literatura, bem como o estudo e ensaio de um motor Brushless de pequena potência (1,01 cv), abordagens para a mitigação das correntes parasitas foram estudadas levando em consideração suas vantagens e desvantagens num cenário industrial. Utilizando uma ponte RLC e ensaios em laboratório, as capacitâncias parasitas foram medidas. Buscando valores comparativos, as capacitâncias também foram determinadas usando equações eletromagnéticas a partir das dimensões mecânicas do motor BLDC. De posse das capacitâncias parasitas e da tensão de eixo medida, especificou-se uma nova capacitância interna de forma a estabelecer uma alta reatância entre o eixo e carcaça do rotor reduzindo substancialmente as amplitudes das correntes parasitas de modo comum nos rolamentos do motor. São apresentados resultados de simulações utilizando as capacitâncias medidas, com e sem a introdução desta nova capacitância entre o eixo e a carcaça do motor. Por meio do comportamento da tensão de eixo e corrente nos rolamentos, mostra-se que há a mitigação desta corrente parasita. Conclui-se que tal abordagem apresenta as seguintes contribuições: mitiga a corrente de descarga nos rolamentos de motores Brushless com eficiência; contribui de forma direta para o aumento da vida útil dos motores em estudo; dispensa o uso de abordagens que apresentam a necessidade de manutenção periódica como, por exemplo, as escovas no eixo e/ou graxas condutivas nos rolamentos. Como desvantagem dessa abordagem cita-se o aumento de uma etapa no processo de produção do motor.
The drive and control of a brushless direct current motor is performed using a frequency inverter with pulse width modulation (PWM). Due to the high switching frequency of this inverter, parasitic capacitances are established along the motor allowing eddy currents to circulate. These currents, when circulating through the motor bearings, can cause electrostatic erosion in the bearing runway, generating unwanted vibrations and substantially reducing their useful life. The objective of this work was the study of approaches for the mitigation of these eddy currents in Brushless motors, commonly called BLDC motors. More specifically, from the study and testing of a small power Brushless motor (1.01 cv), approaches to the mitigation of eddy currents were evaluated taking into account their advantages and disadvantages in an industrial setting. Using an RLC bridge and laboratory tests, stray capacitances were measured. Looking for comparative values, the capacitances were also determined using electromagnetic equations from the mechanical dimensions of the BLDC motor. In possession of the eddy capacitances and the measured shaft voltage, a new internal capacitance was achieved in order to establish a high reactance between the shaft and the rotor frame, substantially reducing the amplitudes of the common mode eddy currents in the motor bearings. Simulation results are presented using the measured capacitances, with and without the introduction of this new capacitance between the shaft and the motor frame. Through the behavior of the shaft voltage and current in the bearings, it is shown that this eddy current is mitigated. It is concluded that such an approach presents the following contributions: it mitigates the discharge current in Brushless motor bearings efficiently; contributes directly to increasing the useful life of the engines under study; eliminates the use of approaches that require periodic maintenance, such as brushes on the shaft and/or conductive greases on the bearings. As a disadvantage of this approach, the increase of one step in the engine production process can be cited.
The drive and control of a brushless direct current motor is performed using a frequency inverter with pulse width modulation (PWM). Due to the high switching frequency of this inverter, parasitic capacitances are established along the motor allowing eddy currents to circulate. These currents, when circulating through the motor bearings, can cause electrostatic erosion in the bearing runway, generating unwanted vibrations and substantially reducing their useful life. The objective of this work was the study of approaches for the mitigation of these eddy currents in Brushless motors, commonly called BLDC motors. More specifically, from the study and testing of a small power Brushless motor (1.01 cv), approaches to the mitigation of eddy currents were evaluated taking into account their advantages and disadvantages in an industrial setting. Using an RLC bridge and laboratory tests, stray capacitances were measured. Looking for comparative values, the capacitances were also determined using electromagnetic equations from the mechanical dimensions of the BLDC motor. In possession of the eddy capacitances and the measured shaft voltage, a new internal capacitance was achieved in order to establish a high reactance between the shaft and the rotor frame, substantially reducing the amplitudes of the common mode eddy currents in the motor bearings. Simulation results are presented using the measured capacitances, with and without the introduction of this new capacitance between the shaft and the motor frame. Through the behavior of the shaft voltage and current in the bearings, it is shown that this eddy current is mitigated. It is concluded that such an approach presents the following contributions: it mitigates the discharge current in Brushless motor bearings efficiently; contributes directly to increasing the useful life of the engines under study; eliminates the use of approaches that require periodic maintenance, such as brushes on the shaft and/or conductive greases on the bearings. As a disadvantage of this approach, the increase of one step in the engine production process can be cited.
Descrição
Palavras-chave
Supressão de corrente parasita, Motor Brushless DC, Corrente de rolamento, Inversor PWM, Eddy current suppression, Brushless DC motor, Bearing current, PWM inverter