Electricity: motive power systems – Switched reluctance motor commutation control
Patent
1996-03-25
1998-04-14
Ro, Bentsu
Electricity: motive power systems
Switched reluctance motor commutation control
318437, 318438, 318721, 318722, H02P 608
Patent
active
057396507
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a motor system capable of high efficiency operation as well as a control method for a motor.
BACKGROUND ART
Brushless DC motors have conventionally been researched and developed for their application to various fields, and also put into practical use, taking advantage of their capability that no secondary copper loss is involved so that enhancement in efficiency is theoretically possible.
The method for controlling brushless DC motors to high efficiency can be classified roughly into the following two: torque-to-current ratio is increased, by detecting the instantaneous value of the motor current; and voltage-fed inverter is controlled in response to the detected rotation speed so that the inverter output voltage relative to the phase of the motor counter-electromotive voltage is brought to a phase that allows the brushless DC motor to be driven at around the maximum output.
In the above (i) method, when a brushless DC motor in which a permanent magnet is mounted on the surface of the rotor (hereinafter, referred to as surface-magnet DC motor) is adopted, the motor current is controlled so that the d-axis current (a current in the same direction as that of the gap magnetic flux) that is irrelevant to torque generation is reduced to zero (see "Theory and Practical Design of AC servo systems," Sugimoto et al., published by Sogodenshi Shuppansha K. K., p. 74). Also, when a brushless DC motor in which a permanent magnet is mounted so as to be buried inside the rotor (hereinafter, referred to as buried-magnet DC motor) is adopted, the motor current is controlled based on the fact that the generated torque is the sum of magnet torque (a torque proportional to the q-axis current, which is a current in a direction perpendicular to that of gap magnetic flux) and reluctance torque (a torque proportional to the product of d- and q-axis currents), in such a way that optimum values for the d- and q-axis currents are obtained through the steps of detecting the load status (torque) and sequentially performing arithmetic operations to calculate the optimum values of the d- and q-axis currents (see "High Efficiency Control of Brushless DC Motors for Energy Saving," Morimoto et al., T.IEE Japan, Vol. 112-D, No. 3, '92, in particular, Equations (14) and (15)).
The method (i) allows easy application to such fields as would demand high-speed torque response, for example, brushless DC motor drive systems used in machine tools, industrial robots, and the like, where a voltage-fed inverter is previously provided with an instantaneous current detector to implement a high-speed current control system so that there is no need of providing a special device for high efficiency. It is because the current response becomes generally equal to the torque response in brushless DC motors that the high-speed current control system is implemented. This allows a high-speed torque response to be realized.
Meanwhile, the brushless DC motor drive system in household electrical appliances such as air conditioners, washers, and cleaners is based on a simple control system in which the voltage waveform is controlled by only a voltage-fed inverter in response to a position signal derived from detecting the position of the rotor of the brushless DC motor. Therefore, the above (i) method, if applied, would make it necessary not only to newly provide an instantaneous current detector but also to enhance the control operation function, particularly when a buried-magnet DC motor is adopted. As a result, a high-performance microcomputer needs to be substituted for or be added to an existing microcomputer, which incurs a great increase in cost.
In view of these and other problems, it has been proposed to adopt such a constitution for brushless DC motor drive systems in household electrical appliances such as air conditioners, washers, and cleaners that the voltage-fed inverter is controlled so that the phase of the inverter output voltage relative to the phase of the motor counter-electromotive voltage wil
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Kimura Taizou
Kitano Nobuki
Nishijima Kiyotaka
Ooyama Kazunobu
Yamagiwa Akio
Daiken Industries Ltd.
Ro Bentsu
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