Electricity: motive power systems – Limitation of motor load – current – torque or force
Patent
1996-04-18
1998-09-08
Ip, Paul
Electricity: motive power systems
Limitation of motor load, current, torque or force
318138, 318254, H02P 606
Patent
active
058049398
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a brushless D.C. motor driving and controlling method and apparatus therefor. More particularly, the present invention relates to a brushless D.C. motor driving and controlling method and apparatus which drive a brushless D.C. motor using voltage-fed inverters, and to electrical equipment which employs a brushless D.C. motor as a driving source which is driven and controlled by the brushless D.C. motor driving and controlling apparatus.
BACKGROUND ART
A brushless D.C. motor is known as a motor having higher efficiency in comparison to an A.C. motor. The rotor of a brushless D.C. motor is equipped with permanent magnets instead of rotor windings, therefore secondary copper losses caused by currents flowing in the rotor windings is eliminated.
It is known that a brushless D.C. motor has a remarkable efficiency improving effect in comparison to an A.C. motor when the brushless D.C. motor has a medium or small capacity which is equal or less than several tens kW.
In a brushless D.C. motor driving system having such capacity, voltage-fed inverters or current control type inverters are employed as inverters for driving a brushless D.C. motor. Wherein, the current control type the inverters has a main circuitry arrangement which is the same to that of voltage-fed inverters, and controls the inverters so as to determine a motor current to be a desired value.
A system which drives a brushless D.C. motor using the voltage-fed inverters, is mainly used on devices which require efficient power consumption (improvement in efficiency), and is manufactured in large quantities, such as air conditioners, vacuum cleaners, electric washers and others. Therefore, a waveform having a conducting interval which is 120.degree. by electrical angle, is employed as a waveform control in inverters from the point of view of easiness in controlling. And, a system is employed which has a simple arrangement and which is cheap. (refer to "Microcomputer-Controlled Brushless Motor Without a Shift-Mounted Position Sensor", T.Endo et. al., IPEC-Tokyo'83,pp.1477-1488,1983: "Controlling Apparatus of a Brushless D.C. Motor", Nagata et. al., Japanese Patent Laid Open Gazett Tokuganhei 5-72197: "P.M.Brushless Motor Drives:A self-Commutating System without Rotor-Position Sensors", P.Ferraris et. al.,Ninth Annual Symposium-Incremental Motion Control Systems and Devices,pp.305-312,1980) Further, Magnetic pole position detection by detection of induced voltages of a motor, or by a magnetic pole position detection sensor having a simple arrangement and employing Hall elements and the like is employed in detecting magnetic pole position of a brushless D.C. motor. A rotational position sensor which is expensive, such as a rotary encoder and the like, is not employed as it is not economical.
A system which drives a brushless D.C. motor using the current control type inverters, is typically applied to machine tools, servo-motor for an industrial robot, and others which require rapid torque response and the low torque ripple.
In this system, a closed loop arrangement is employed in which a control circuitry determines output voltages of inverters so that current waveforms are the desired waveforms. This is so because the currents and torques of a brushless D.C. motor are functions of rotational position and are in proportional relationship. Therefore, the system has an expensive system arrangement which employs a precision sensor for detecting rotational position of a motor, current detectors for accurately controlling motor currents and a controller which can perform high-speed processing. Further, output voltages of inverters continuously vary because the inverters are controlled instantaneously in response to the conditions of the motor.
In the system in which a brushless D.C. motor is driven using conventional voltage-fed inverters, a switch of each phase of inverters is turned on for only an electrical angle of 120.degree. in spite of positive and negative electrical angles of 180.degree., respective
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Kimura Taizou
Ooyama Kazunobu
Yamai Hiroyuki
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