JP2006042484A - Drive device of brushless dc motor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a drive device of a brushless DC motor that can effectively utilize a switching function of a transistor in an inverting circuit, and can surely transmits an inputted and PWM-modulated speed command signal even if a voltage fluctuation occurs. <P>SOLUTION: In the drive device 12 that controls the number of rotations of the brushless DC motor 10 by a drive current from an inverter circuit 16, the speed command signal that is amplitude-modulated by a speed command signal conversion circuit 22 is input to a drive circuit 18 that controls the inverter circuit 16, and the speed command signal conversion circuit 22 is constituted of a comparison circuit 28, the inverting circuit 30 and an integration circuit 32. The speed command signal that is inputted from an external circuit 14 and PWM-modulated is input to the comparison circuit 28. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a drive device for controlling a DC brushless motor by an inverter circuit.

Conventionally, a drive current is supplied from an inverter circuit to each stator winding of a three-phase brushless DC motor, and this inverter circuit is controlled by a position detection circuit that detects and outputs the position of the rotor of the brushless DC motor. The position signal and the speed command signal from the outside are combined to perform PWM modulation to control the rotational speed (see, for example, Patent Document 1).
JP 2004-15986 A

  The external speed command signal is a PWM-modulated signal, and speed control is performed based on the PWM-modulated speed command signal. A circuit diagram of such a driving apparatus 100 is shown in FIG.

  The PWM-modulated speed command signal input from the external circuit (microcomputer) 102 is input to the inverting circuit 106 via the filter circuit 104. In the inverting circuit, the polarity of the speed command signal is inverted and output to the integrating circuit. The integration circuit 108 integrates the PWM-modulated speed command signal and converts it into an amplitude-modulated speed command signal.

  The speed command signal thus converted to amplitude modulation is PWM-modulated once more based on the triangular wave to generate a speed command signal. As described above, after the speed command signal input by PWM modulation is converted into amplitude modulation, the PWM modulation is further performed by converting the carrier wave of the input PWM modulated speed command signal into a logic circuit that controls the inverter circuit. This is for conversion to a corresponding carrier frequency.

  In the drive circuit 100 in FIG. 3, the inverting circuit 106 is configured to be an open collector of a transistor, and when the power supply voltage Vcc applied to the transistor Q1 of the inverting circuit 106 varies or when the offset voltage of the external circuit 102 varies. In addition, the switching function of the transistor Q1 (that is, entering the cutoff region and the saturation region) is lost, and the transmission characteristic of the PWM-modulated speed command signal is deteriorated.

  In view of the above problems, the present invention can effectively utilize the switching function of the transistor in the inverting circuit, and can reliably transmit the input PWM-modulated speed command signal even when voltage fluctuation occurs. Provided is a brushless DC motor drive device.

  The invention according to claim 1 is an inverter circuit that supplies a drive current to a stator winding of each phase of a brushless DC motor, and a position detection that detects a rotational position of the rotor of the brushless DC motor and outputs a position signal. A speed command signal conversion circuit for converting a speed command signal PWM-modulated by a first carrier wave input from an external circuit into an amplitude-modulated speed command signal, and the amplitude-modulated speed Based on the command signal and the triangular wave from the triangular wave oscillation circuit, a speed PWM modulation circuit that generates a speed command signal PWM-modulated by the second carrier wave, a speed command signal PWM-modulated by the second carrier wave, and A logic circuit for outputting a control signal based on the position signal and a switching signal for each switching element of the inverter circuit based on the control signal. In the brushless DC motor driving apparatus, the speed command signal conversion circuit compares the speed command signal PWM-modulated with the first carrier wave with a reference voltage value by a comparator, A comparison circuit that outputs a pulse signal when the speed command signal is equal to or higher than the reference voltage value, an inversion circuit that inverts the polarity of the pulse signal from the comparison circuit by a switching function of a transistor, and an inversion of polarity from the inversion circuit A brushless DC motor driving device comprising: an integrating circuit that integrates a pulse signal to perform amplitude modulation and outputs the amplitude-modulated speed command signal.

  The invention according to claim 2 is the brushless DC motor driving device according to claim 1, wherein a filter circuit is arranged between the comparison circuit and the external circuit.

  In the brushless DC motor driving apparatus of the present invention, a comparison circuit is provided in the preceding stage of the inverting circuit for inverting the polarity of the pulse signal, and the speed command signal input in the comparison circuit is compared by the reference voltage and the comparator, Since the speed command signal is output as a pulse signal at the time of output, even if the power supply voltage fluctuates, the pulse signal output from the comparator is only ON and OFF, so the transistor switching function is effectively utilized. be able to. Even when the offset voltage fluctuation of the external circuit occurs, the offset voltage can be compensated for by the comparator as described above. Therefore, the transmission characteristic of the speed command signal can be improved.

  Hereinafter, a drive device 12 for a brushless DC motor (hereinafter simply referred to as a motor) 10 according to an embodiment of the present invention will be described with reference to FIGS. 1 and 2.

(1) Configuration of Drive Device 12 The configuration of the drive device 12 will be described with reference to FIG.

  The drive device 12 controls rotation, stop, and rotation speed of the motor 10 based on a speed command signal from an external circuit (for example, a microcomputer) 14, and includes an inverter circuit 16, a drive circuit 18, a position detection circuit 20, and a speed. A command signal conversion circuit 22 is included.

  The inverter circuit 16 is a full bridge inverter circuit composed of six switching elements (for example, MOS-FETs), and supplies a drive current to each stator winding 24 of the three-phase motor 10.

  The speed command signal conversion circuit 22 converts the PWM-modulated speed command signal input from the external circuit 14 into an amplitude-modulated speed command signal and outputs it to the drive circuit 18.

  The position detection circuit 20 outputs a position signal indicating the position of the rotor to the drive circuit 18 based on an output signal from the Hall IC provided in the vicinity of the rotor of the motor 10.

  Based on the amplitude-modulated speed command signal from the speed command signal conversion circuit 22 and the position signal from the position detection circuit 20, the drive circuit 18 sets each speed of the inverter circuit 16 so that the rotation speed corresponds to the speed command signal. A switching signal is supplied to the gate terminal of the switching element.

(2) Configuration of Speed Command Signal Conversion Circuit 22 The configuration of the speed command signal conversion circuit 22 will be described with reference to FIG.

  As shown in FIG. 2, the speed command signal conversion circuit 22 includes a filter circuit 26, a comparison circuit 28, an inversion circuit 30, and an integration circuit 32. Each circuit will be described in more detail with reference to FIG.

  The speed command signal output from the external circuit 14 is a PWM-modulated signal, and in this case, PWM-modulated with the first carrier wave. The frequency of the first carrier wave is, for example, 300 Hz.

  The speed command signal PWM-modulated by the first carrier wave (hereinafter referred to as the first speed command signal) is input to the filter circuit 26. The filter circuit 26 removes noise or the like in the first speed command signal and outputs it to the comparison circuit 28.

  In the comparison circuit 28, the first speed command signal from which noise is removed is input to the plus terminal of the comparator 34, and the reference voltage obtained by dividing the power supply voltage Vcc by the resistors R52 and R53 is input to the minus terminal. To do. When the first speed command signal equal to or higher than the reference voltage value is input by the comparator 34, a pulse signal is output from the output terminal.

  The pulse signal output from the comparator 34 is input to the inverting circuit 30 and input to the base terminal of the transistor Q1. Then, a pulse signal whose polarity is inverted from that of the pulse signal is output from the emitter terminal. The reason why the polarity of the pulse signal is inverted in the inversion circuit 30 in this way is that the external circuit 14 has a switching transistor Q2 that performs polarity inversion at the output portion thereof. The reason why the transistor Q2 is present is to remove the influence of disturbance or the like when the first speed command signal is output.

  The pulse signal whose polarity is inverted by the inverting circuit 30 is input to the integrating circuit 32. This pulse signal is amplitude-modulated according to the pulse width PWM-modulated by the first carrier wave, and is output as an amplitude-modulated speed command signal (hereinafter referred to as a second speed command signal).

(3) Configuration of Drive Circuit 18 The configuration of the drive circuit 18 will be described with reference to FIG.

  The drive circuit 18 includes a speed PWM modulation circuit 36, a triangular wave oscillation circuit 38, a logic circuit 40, and an output circuit 42. As described above, the second speed command signal is input to the speed PWM modulation circuit 36 from the speed command signal conversion circuit 22. The speed PWM modulation circuit 36 performs PWM modulation based on the triangular wave having the frequency of the second carrier wave output from the triangular wave oscillation circuit 38. The frequency of the second carrier wave for PWM modulation is, for example, 18 KHz. The speed command signal PWM-modulated from the external circuit 14 (that is, the first speed command signal) is converted into an amplitude-modulated speed command signal (that is, the second speed command signal), and the third speed command signal is converted into the third speed command signal. Further, the reason for the PWM modulation to make the speed command signal in the second carrier wave (hereinafter referred to as the third speed command signal) is that the frequency of the carrier wave that can be handled by the logic circuit 40 is the first carrier wave output from the external circuit 14. It is because it does not adapt. Specifically, the first carrier wave of the speed command signal output from the external circuit 14 is 300 Hz and too low, and it is necessary to convert this to a high frequency of 18 KHz.

  In the logic circuit 40, the position signal from the position detection circuit 20 is compared with the third speed command signal, and feedback is performed so that the rotation speed detected in the position signal is always the rotation speed corresponding to the third speed command signal. The control signal is output to the output circuit 42.

  The output circuit 42 outputs a switching signal to the gate terminal of each switching element of the inverter circuit 16 based on the input control signal.

  As a result, the rotational speed of the motor 10 can be feedback controlled in response to the first speed command signal input from the external circuit 14.

  In the speed command signal conversion circuit 22, by providing the comparison circuit 28, the pulse signal output from the comparator 34 is ON (for example, 5V) and OFF (for example, 0V) even when the power supply voltage Vcc fluctuates. Therefore, the switching function of the transistor Q1 can be used effectively. Further, even when the offset voltage fluctuation of the external circuit 14 occurs, the offset voltage of the pulse signal can be compensated by setting the reference voltage value of the comparator 34 as described above. Therefore, the transmission characteristic of the speed command signal of the motor 10 can be improved.

  The present invention is suitable, for example, as a drive device for a brushless DC motor used as a drive source for a blower, an electric tool, or the like.

It is a block diagram of the drive device which shows one Embodiment of this invention. It is a circuit diagram of a speed command signal conversion circuit. It is a circuit diagram of a conventional speed command signal conversion circuit.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Motor 12 Drive apparatus 14 External circuit 16 Inverter circuit 18 Drive circuit 20 Position detection circuit 22 Speed command signal conversion circuit 24 Stator winding 26 Filter circuit 28 Comparison circuit 30 Inversion circuit 32 Integration circuit 34 Comparator 36 Speed PWM modulation circuit 38 Triangle wave Oscillation circuit 40 Logic circuit 42 Output circuit

Claims (2)

An inverter circuit for supplying drive current to the stator windings of each phase of the brushless DC motor;
A position detection circuit for detecting a rotational position of the rotor of the brushless DC motor and outputting a position signal;
A speed command signal conversion circuit that converts a speed command signal PWM-modulated by a first carrier wave input from an external circuit into a speed command signal that is amplitude-modulated and outputs the speed command signal;
A speed PWM modulation circuit that generates a speed command signal PWM-modulated by a second carrier wave based on the amplitude-modulated speed command signal and the triangular wave from the triangular wave oscillation circuit;
A logic circuit that outputs a control signal based on the speed command signal PWM-modulated by the second carrier wave and the position signal; and an output circuit that supplies a switching signal to each switching element of the inverter circuit based on the control signal When,
In the drive device of the brushless DC motor having
The speed command signal conversion circuit is
A comparison circuit that compares a speed command signal PWM-modulated with the first carrier wave with a reference voltage value by a comparator, and outputs a pulse signal when the speed command signal is equal to or higher than the reference voltage value;
An inverting circuit for inverting the polarity of the pulse signal from the comparison circuit by a switching function of a transistor;
An integration circuit that performs amplitude modulation by integrating the polarity-inverted pulse signal from the inversion circuit, and outputs it as a speed command signal that is amplitude-modulated;
A drive device for a brushless DC motor, comprising: The brushless DC motor drive device according to claim 1, wherein a filter circuit is disposed between the comparison circuit and the external circuit.

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