Electricity: motive power systems – Switched reluctance motor commutation control
Patent
1997-02-25
1998-06-16
IP, Paul
Electricity: motive power systems
Switched reluctance motor commutation control
318138, 318439, H02P 616
Patent
active
057676410
DESCRIPTION:
BRIEF SUMMARY
This application is a 371 of PCT/DE95/01106 filed Aug. 22, 1995.
PRIOR ART
The invention relates to a circuit and a method for the actuation of a brushless DC motor.
Such a DC motor is disclosed, for example, in EP-A-0 482 913. For the actuation of the brushless DC motor, the rotational position of its rotor is determined by picking up the zero passages of the back electromotive force induced in the stator windings by the rotating rotor. Subsequently, a signal generator generates a trapezoidal signal which, after amplification, is applied to the respective stator windings so as to effect a smooth current commutation of the stator windings. This accomplishes a quiet running of the motor.
SUMMARY AND ADVANTAGES OF THE INVENTION
The present invention provides an improved circuit and method for actuating a brushless DC motor with the circuit having a triangular signal oscillator for generating a triangular voltage as a function of commutation pulses resulting from the position of the rotor of the DC motor, a sampling and hold circuit for sampling and holding a holding voltage from the curve of the triangular voltage as a function of time at the moment of the commutation, and a differential amplifier for amplifying the differential voltage between the received triangular voltage and the holding voltage, with the output signal of the differential amplifier being supplied to a final stage of the control circuit for actuation of the motor.
The method according to the invention involves actuating a brushless DC motor with a periodic voltage whose curve as a function of time is formed by voltage blocks of a specific length having rising and falling slopes, and wherein the steepness of the slopes is set by varying the amplification of a differential amplifier at whose output the periodic voltage appears.
The circuit according to the invention as described above and the method according to the invention offer the advantage that the steepness of the current slopes of the individual voltage blocks can be varied. This results in a reduction of the commutation noise. Furthermore, flat slopes can be set, thus ensuring a quiet running of the motor. Moreover, flatter slopes offer the advantage of smaller induction peaks when the current pulses are turned off. Thus, the evaluation of the voltages induced in the three phases of a brushless DC motor is facilitated and an operation without Hall sensors becomes possible. Advantageous modifications and improvements of the circuit and of the method according to the invention are described and disclosed.
It is advisable to use an additional adder in the circuit for adding a voltage U block to the value Ul of the sampled and held triangular voltage, with the difference between the triangular voltage and the sum of holding voltage Ul and block voltage U block being amplified in the differential amplifier. In addition to the option of setting the slope steepness, this also allows a reduction of the length of the individual voltage blocks and thus a quiet running at low speeds due to very flat actuation slopes and, at the same time, an improvement of the efficiency at higher speeds because of the option of allowing current gaps between the individual voltage blocks.
A further advantage is that the circuit can be easily realized in an integrated circuit. In order to "break" the peaks of the triangular voltage, the upper setting limit of the differential amplifier is selected advantageously such that it is lower than the maximum amplified value of the triangular voltage. This results in a horizontal voltage curve as a function of time of the amplified signal during the time in which the amplified differential voltage exceeds the upper setting limit of the differential amplifier. This also increases the efficiency.
For a flexible and simple setting of the length of the voltage blocks, the value of the added block voltage U block is between zero and the maximum value of the triangular voltage. This allows a setting in which the block length is not reduced, i. e., current gaps during t
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Kern Robert
Soellner Michael
Ip Paul
Robert & Bosch GmbH
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