Electricity: motive power systems – Switched reluctance motor commutation control
Patent
1992-07-13
1994-07-19
Shoop, Jr., William M.
Electricity: motive power systems
Switched reluctance motor commutation control
318138, 323314, G05F 316
Patent
active
053312597
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a brushless drive circuit which supplies a power to a brushless motor while switching the power supply to the driving coils of the motor in the respective phases in a sequential order by what is called a soft switching technique which employs smooth or rounded coil driving waveforms. More particularly, the invention pertains to a circuit for preventing saturation of output transistors which are used to switch the power supply to the driving coils of the brushless motor.
BACKGROUND ART
There has been proposed a brushless motor drive circuit of the type supplying a power to the brushless motor by applying to the driving coils of motor driving current waveform with dulled or rounded inflection points, in the respective phases, in an attempt to reduce a noise generation caused by abrupt or acute changes in driving current waveform due to the inherit abrupt power-supply switching in each driving coil. However, with such drive circuit, when a power transistor becomes saturated upon starting a motor or during its uncontrolled drive, the switching waveform (i.e. the driving current waveform applied to each driving coil) is distorted or becomes unsmooth, resulting in lowering its motor noise reduction effect.
One possible technique that has been proposed to solve this problem is a technique for detecting the state of the power transistor which is about to be saturated and limiting a control current so as to limit power supply to the transistor, thereby preventing saturation. This technique is disclosed in Japanese Patent Laid-Open Gazette No. 56188/88 of a patent application filed in the name of the applicant of the present application. Referring now to FIG. 6, a brief explanation will be made thereof.
In FIG. 6, the power supply to three-phase driving coils L.sub.1, L.sub.2, and L.sub.3 is controlled by power transistors Qa, Qb, Qc, Qd, Qe and Qf via a pre-driver 2. The pre-driver 2 combines together or synthesizes rotor position sensed signals from position sensors (not shown) into a 120.degree. switching signal which supplies power for a 120.degree. period in a 180.degree. interval or zone, thereby dulling or rounding this signal waveform at its inflection points to obtain a soft switching waveform, which is used to control each of the transistors Qa to Qf, effecting a power supply control for each of the driving coils L.sub.1 to L.sub.3.
The current to each of the driving coils L.sub.1 to L.sub.3 flows into a current detecting resistor Re, which generates a voltage proportional to the incoming current, and the voltage is applied to an inverting input of a current feedback amplifier Af. On the other hand, when a current flows to a resistor Ra via a transistor Qg, a voltage proportional to this current is induced in the resistor Ra and is applied to a non-inverting input of the amplifier Af. A control amplifier Ac amplifies a difference between a control reference voltage Vref, defined by the ratio between resistors Rc and Rd, and a control signal voltage Vctl, to provide a control current Ictl. The control current Ictl flows to the ground via a resistor Rb and a transistor Qj and, at the same time, defines a current which flows in the collector of a transistor Qh via the base of a transistor Qi, and in accordance with this collector current, the base current of a transistor Qg is controlled to thereby determine the above-mentioned current Ictl which is the collector current of the transistor Qg. The control current Ictl of the control amplifier Ac is set such that it will ultimately become equal to the current Ictl which flows in the resistor Ra.
Diodes Da, Db and Dc have their cathodes connected to the driving coils L.sub.1, L.sub.2 and L.sub.3, respectively, and have their anodes all connected to an output terminal of the control amplifier Ac.
Now, let is be assumed that the motor is placed under constant speed control. If the rotational speed of the motor decreases, the control voltage Vctl will be raised to increase the speed and also the control current I
REFERENCES:
patent: 4227127 (1980-10-01), Fukaya et al.
patent: 4428040 (1984-01-01), Yamashiro et al.
patent: 4608524 (1986-08-01), Yokobori
patent: 4742281 (1988-05-01), Nakano et al.
patent: 4751463 (1989-06-01), Higgs et al.
patent: 4987352 (1991-01-01), Ishii
Cabeca John W.
Sankyo Seiki Mfg. Co. Ltd.
Shoop Jr. William M.
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