JP2652997B2 - Two-phase DC brushless motor drive circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a circuit for driving a DC brushless motor, which uses a resolver to detect the position of a rotor (rotor) and a stator (stator), using switching pulses.

[0002]

2. Description of the Related Art In a conventional DC brushless motor drive circuit using a resolver, an amplitude modulation circuit is provided in a stage preceding a resolver input, and a method of changing the amplitude of a resolver excitation signal is employed.

First, the operation of a two-phase DC brushless motor will be described with reference to FIG. 2 showing the principle of operation of this type of motor. In order to keep the torque generated by the motor constant irrespective of the positional relationship between the rotor and the stator, and to eliminate dead points (positions where torque is not generated and the motor cannot be started), the independent motor coils are shifted by 90 ° from each other. To generate sine and cosine phase fields. A resolver is used to detect the positional relationship between the rotor and the stator. When the rotation axis of the motor is connected to the axis of the rotor of the resolver excitation coil and an excitation signal is applied from an AC power supply to the excitation coil of the resolver, the sine and cosine functions of the resolver axis rotation angle 0 become two phases on the stator side. Thus, an output voltage having a different amplitude is obtained.

Here, when a current of Isin θ is applied to the sine-phase field coil and a current of Icos θ is applied to the cosine-phase field coil, the force F ′ acting on the permanent magnet of the rotor due to the sine-phase field coil becomes F '= a KIsin θ, generated torque T' is ^{T '= F'sin θ = KIsin 2} θ. Here, K is a torque conversion constant. Similarly, in the cosine phase, T ″ = F ″ co
Since a torque of sθ = KI cos ² θ is generated, a torque of T = T ′ + T ″ = KI (sin ² θ + cos ² θ) = KI is generated as a whole, and is uniform independently of the angle θ between the rotor and the stator. That is, it is necessary to apply a current proportional to the output of the resolver to the motor coil in each of the sine and cosine phases, and to apply an external current to the motor coil to control the generated torque T itself. 3 shows a conventional example of a two-phase DC brushless motor drive circuit, in which the sine phase is described (the same applies to the cosine phase). In this conventional example, a local oscillator 1 for generating a sine wave to be input to a resolver 2, and a control signal input terminal 8 to which a control signal for amplitude-modulating the resolver input signal is input.
And an amplitude modulation circuit 9 that changes the amplitude of the output of the local oscillator 1 in proportion to the control signal and outputs it to the resolver 2 and a DC brushless motor 7 (usually built-in).
A resolver 2 that amplitude-modulates and outputs an input wave in accordance with the rotation of the DC brushless motor 7, and demodulates a signal component of the rotation of the DC brushless motor 7 and a signal component of a control signal from the output of the resolver 2 (local oscillator 1). (A low-pass filter that cuts off the frequency component of the signal) is used. The demodulation circuit 3 generates a sawtooth wave having a constant period and constant amplitude. The demodulated signal output from the resolver is compared with the voltage level of the sawtooth wave. A pulse width modulation circuit 5 comprising a comparator 11 for generating a pulse train (hereinafter referred to as a PWM modulation signal) having a pulse width proportional to the demodulated signal output from the resolver.
And a chopper circuit 6 for turning on the DC brushless motor 7 in response to the PWM modulation signal to supply a current to the motor. The DC brushless motor 7 is connected to the resolver 2 described above. Next, the operation of this conventional example will be described. When the sine wave whose amplitude is modulated by the control signal is input to the resolver 2, a signal whose amplitude is further modulated according to the rotation of the DC brushless motor 7 is output, and the signal component of the rotation of the DC brushless motor 7 is demodulated. And a control signal are obtained. By performing PWM modulation by the comparator 11 using this signal and the sawtooth wave, a pulse train whose average duty is proportional to both the rotational position of the motor and the control signal is obtained. By choppering the motor supply current according to the pulse train, a current proportional to the motor rotation position and the control signal input terminal 8 is supplied to each of the sine and cosine phases of the DC brushless motor 7, and the motor rotation is proportional to the control signal. A torque independent of position is generated.

[0005]

In such a conventional motor drive circuit, the amplitude level of the resolver input is changed by the control signal. Therefore, as the amplitude level of the resolver input decreases (that is, the level of the control signal decreases). As a result, there is a disadvantage that the SN ratio remarkably deteriorates, and a disadvantage that the conversion characteristic of the resolver is not linear with respect to the amplitude level of the input, so that the linearity of the switching pulse duty of the motor with respect to the control signal is also impaired.

SUMMARY OF THE INVENTION An object of the present invention is to provide a DC brushless motor driving circuit which eliminates such a drawback and maintains the conversion characteristics of a resolver at its best.

[0007]

SUMMARY OF THE INVENTION The present invention provides a sine-phase field winding and a cosine-phase field winding of a two-phase DC brushless motor equipped with a resolver for detecting a relative position between a rotor and a stator. In a two-phase DC brushless motor driving device including a chopper circuit for chopping a current supplied to the resolver according to a given modulation signal, a local oscillator that supplies a carrier signal having a predetermined amplitude and a predetermined frequency to the resolver; A demodulation circuit for generating a voltage signal obtained by demodulating the generated signal, a voltage controlled oscillator controlled by the voltage signal to generate a frequency modulated wave, and a control signal corresponding to the generated torque of the two-phase DC brushless motor are provided. A control signal input terminal and a modulation signal generated by modulating a pulse width of a frequency modulation wave generated by the voltage-controlled oscillator according to the control signal. Characterized in that a pulse width modulation circuit for applying to the chopper circuit Te.

Here, instead of the pulse width modulation circuit, a modulation signal is generated by modulating the number of pulses of a frequency modulation wave generated by the voltage controlled oscillator according to a control signal supplied to the control signal input terminal. A pulse number modulation circuit applied to the chopper circuit may be used.

[0009]

A voltage-controlled oscillator is controlled by a voltage signal obtained by demodulating the output of a resolver to which a fixed signal having an attribute having the best conversion characteristic of the resolver is given, thereby obtaining a frequency-modulated signal. The pulse width of the frequency modulation signal is modulated according to a control signal relating to the motor torque, and is provided to a chopper circuit. The chopper circuit controls the motor supply current according to the given signal.

[0010]

An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a configuration diagram showing a sine phase component of this embodiment. In this embodiment, as shown in FIG.
A local oscillator 1 for generating a sinusoidal carrier signal having a constant amplitude and a constant frequency to be input to the DC brushless motor 7 is connected (usually built-in), and the input wave is amplitude-modulated according to the rotation of the DC brushless motor 7. Output resolver 2
A demodulation circuit 3 for demodulating a voltage signal as a signal component of motor rotation from the amplitude-modulated wave, and a voltage-controlled oscillator (hereinafter referred to as VCO) for generating a frequency-modulated signal by oscillating at a frequency proportional to the voltage signal. .) 4, a pulse width modulation circuit (hereinafter referred to as a PWM modulation circuit) 5 for generating a PWM modulation signal that changes the pulse width of the frequency modulation signal in proportion to the control signal input terminal 8, and a DC brushless signal by the PWM modulation signal. It comprises a chopper circuit 6 for supplying a current when the motor 7 is turned on, and a DC brushless motor 7 connected to the above-described resolver 2. The control signal input terminal 8 modulates the FM signal output from the voltage controlled oscillator 4 by PWM. I do.

That is, in this embodiment, as shown in FIG. 1, a sine-phase field winding and a cosine-phase winding of a two-phase DC brushless motor 7 equipped with a resolver 2 for detecting a relative position between a rotor and a stator. The current supplied to each field winding is
A local oscillator 1 that provides the resolver 2 with a carrier signal having a predetermined frequency and a predetermined frequency, and a resolver 2 are generated as means characterized by the present invention, which includes a chopper circuit 6 that performs chopping according to the applied modulation signal. A demodulation circuit 3 for generating a voltage signal obtained by demodulating the signal; and a voltage-controlled oscillator 4 controlled by the voltage signal to generate a frequency-modulated wave.
And a control signal input terminal 8 to which a control signal corresponding to the torque generated by the two-phase DC brushless motor 7 is provided, and the pulse width of the frequency modulation wave generated by the voltage controlled oscillator 4 is modulated in accordance with the control signal. A pulse width modulation circuit 5 is provided for generating a modulation signal and supplying the generated signal to a chopper circuit 6. In addition, the chopper circuit 6 generates a modulation signal obtained by modulating the number of pulses of the frequency modulation wave generated by the voltage control oscillator 4 in accordance with a control signal supplied to the control signal input terminal 8 instead of the pulse width modulation circuit 5. A given pulse number modulation circuit may be used.

Next, the operation of this embodiment will be described. When a carrier having a constant amplitude and a constant frequency is input to the resolver 2 connected to the DC brushless motor 7, a signal whose amplitude is modulated according to the rotation of the DC brushless motor 7 is output. When this is demodulated by the demodulation circuit 3, a signal component of the motor rotation is obtained. When this demodulated wave is input to the VCO 4, a frequency modulation signal whose frequency changes in accordance with the rotational position of the DC brushless motor 7 is obtained. The VCO output usually has a duty of 50%, but the pulse width modulation circuit 5 performs PWM modulation so that the pulse width is proportional to the control signal input terminal 8, so that
A pulse train whose average duty is proportional to both the rotational position of the motor and the control signal is obtained. By choppering the motor supply current by this pulse train, a current proportional to the motor rotation position and the control signal is supplied to the sine-phase and cosine-phase field coils of the DC brushless motor 7, and the motor rotation position is proportional to the control signal. Irrelevant torque is generated. Note that by using, for example, a rate multiplier circuit as the pulse width modulation circuit 5, the present invention can be implemented even if the number of pulses is changed instead of the width of each pulse. In this case, since the average duty of the pulse train is changed, it is a kind of pulse width modulation circuit in a broad sense.

[0013]

According to the present invention, as described above, since the resolver input is fixed at a constant amplitude and a constant frequency, it is sufficient to select an input of an amplitude and a frequency having the best conversion characteristics of the resolver. There is an effect that the influence of the deterioration of the SN ratio when the resolver input level decreases and the nonlinearity of the resolver conversion characteristic can be eliminated.

[Brief description of the drawings]

FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention.

FIG. 2 is an explanatory diagram showing the operation of a DC brushless motor.

FIG. 3 is a block diagram showing a configuration of a conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Local oscillator 2 Resolver 3 Demodulation circuit 4 Voltage controlled oscillator 5 Pulse width modulation circuit 6 Chopper circuit 7 DC brushless motor 8 Control signal input terminal 9 Amplitude modulation circuit 10 Sawtooth generation circuit 11 Comparator

Claims (2)

(57) [Claims] 1. A current supplied to a sine-phase field winding and a cosine-phase field winding of a two-phase DC brushless motor equipped with a resolver for detecting a relative position between a rotor and a stator is supplied. In a two-phase DC brushless motor driving device provided with a chopper circuit for chopping according to the modulated signal, a local oscillator for providing the resolver with a carrier signal having a predetermined frequency and a predetermined frequency, and a voltage signal obtained by demodulating a signal generated by the resolver A voltage-controlled oscillator controlled by the voltage signal to generate a frequency-modulated wave; a control signal input terminal to which a control signal corresponding to the generated torque of the two-phase DC brushless motor is provided; Generating a modulation signal obtained by modulating a pulse width of a frequency modulation wave generated by the voltage controlled oscillator in accordance with the signal, and providing the modulation signal to the chopper circuit; And a pulse width modulation circuit. 2. A modulation signal, which is obtained by modulating the number of pulses of a frequency modulation wave generated by the voltage controlled oscillator according to a control signal supplied to the control signal input terminal instead of the pulse width modulation circuit. 2. A two-phase DC brushless motor drive circuit according to claim 1, wherein a pulse width modulation circuit applied to said chopper circuit is used.