JPS6056399B2 - Motor drive circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a drive circuit for a DC motor, and is particularly suitable for use in a drive circuit for a brushless DC motor.

A conventional method for reducing torque ripple in brushless DC motors has been to use a trapezoidal wave-shaped magnetization pattern for the rotor magnet used to form the field so that the magnetic flux linkage with the coil in the energized area is almost constant. It is being However, with this method, it is difficult to make the flux linkage completely constant in the energized area, and a drop in torque occurs near the shoulder of the trapezoidal wave, resulting in torque ripple. Furthermore, by forming a trapezoidal wave-like magnetization pattern, the effective magnetic flux may be reduced. In addition, the magnetization pattern of the rotor magnet is sinusoidal, and a sinusoidal current is applied to the first and second phase coils, which are provided at an interval of 900 electrical degrees, in accordance with the magnetic flux linkage with these coils. Constant torque motors are known that allow the flow of . That is, the magnetic flux linkage φm sin θ(
φm: constant) and current flowing through this coil Imsinθ (
Im: constant), T1=Im・φms1n
A torque of 2θ (constant) is generated, and T
2) A torque of ・Im·φm−cos”θ is generated. Therefore, the resultant torque is Tl+T0=1mφm, and a constant rotational torque independent of the rotation angle θ of the rotor is obtained. However, in such constant-torque motors, it is difficult to make the magnetization pattern accurately sinusoidal, and the circuit configuration is complicated because it is necessary to flow a sinusoidal current through each coil. There is.
The present invention has been made in view of the above-mentioned problems, and includes an arithmetic circuit equipped with a Hall element as a feedback loop for detecting the magnetic flux density interlinked with the coil of a DC motor.
The coil is configured to flow a drive current in accordance with a signal inversely proportional to the interlinkage magnetic flux density obtained from the arithmetic circuit. With this configuration, it is possible to obtain a substantially constant rotational torque that is unrelated to the interlinkage magnetic flux density of the coil, which changes depending on the rotation angle of the motor. Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic block diagram showing one embodiment of a motor drive circuit according to the present invention.

In FIG. 1, the rotational position of a rotor of a motor 1 is detected by a Hall element 2 that detects leakage magnetic flux of a field magnet of the rotor.

The Hall element 2 forms a feedback loop of the arithmetic circuit 3, and the Hall element 2 and the arithmetic circuit 3 constitute a divider 4. Further, the arithmetic circuit 3 is supplied with a motor speed adjustment voltage Vs. As a result, from the output of the divider 4, an output signal e=k is inversely proportional to the interlinkage magnetic flux density Bθ=f(bθ) of the motor coil and proportional to the speed adjustment voltage.
-ゝ- is obtained f(BO).

Note that the motor speed adjustment voltage Vs is a servo voltage or a constant DC voltage for controlling the speed of the motor. The output signal e of the divider 4 is supplied to the switching circuit 6,
Based on this signal, a coil switching signal corresponding to the rotation angle of the rotor is generated.

Further, the signal e is supplied to the voltage-current converter 5, and as a result, a drive current 1=IOVS/f(BO) (IO: constant) proportional to the voltage signal e flows through the transistor 7. Therefore, the rotational torque generated by the current 1 flowing through the coil and the interlinkage magnetic flux Bθ of this coil is (K: constant/Z
: Number of coil turns).

That is, the rotational torque T is determined by the coil's interlinkage magnetic flux density Bθ=f(
BO), and if the motor speed adjustment voltage S is constant, it is possible to obtain a substantially constant rotational torque that is independent of the rotation angle θ of the motor. Fig. 2 is a circuit diagram of a motor drive circuit in which the present invention is applied to a drive circuit of a three-phase, one-phase brushless DC motor, and Fig. 3 shows the waveforms of each part of Fig. 2 and the rotational torque of the motor. It is a graph.

In FIG. 2, Hall elements 2a, 2b, and 2c as rotor position detection elements are placed close to the magnet at a predetermined interval (for example, 120 mm intervals) so as to detect leakage magnetic flux of the rotor magnet of the motor. However, it is attached to the stator side. For this reason, these Hall elements 2a
, 2b, 2c are provided with coils 25a as shown in FIG. 3a.
, 25b, 25c, for example, a leakage magnetic flux density KlBa, which is proportional to the sinusoidal magnetic flux density Ba, Bb, Bc,
KlBb and klBc (k1: constant) act. Regarding the A phase of the three-phase drive circuit, the output of the Hall element 2a is also amplified by the operational amplifier 15a.

The output of the operational amplifier 15a is supplied to the summing point Aa via the resistor 13a, where it is added to the servo voltage -Vs supplied via the resistor 14a, and then the output is sent to the operational amplifier 16a.
supplied to The output of the operational amplifier 16a is fed back to one current terminal of the Hall element 2a via a resistor 10a, and the other current terminal of the Hall element 2a is grounded via a resistor 11a. Therefore, the operational amplifier circuit including the Hall element 2a as a feedback loop constitutes the divider 4a as a whole. Note that the remaining B-phase and C-phase dividers 4b
, 4c also have a similar configuration. FIG. 4 is a diagram showing the principle of the dividers 4a to 4c.

As shown in FIG. 4, the multiplier π serves as a feedback loop for the operational amplifier A, and in this multiplier π, the output E of the operational amplifier A. and the product E of external input E2. e2 is calculated. The output EOe2 of the multiplier π and the external input e1 are added together via the respective resistors R and then supplied to the operational amplifier A. Therefore, the input of operational amplifier A becomes e1+EOe2, and assuming that amplifier A has a gain of 0, the operational circuit of FIG. 4 is in a stable state when e1+EOe2=0. That is, the output of operational amplifier A is
S-2, and a signal inversely proportional to the input E2 of the multiplier π is obtained.

Therefore, the dividers 4a to 4c shown in FIG. 2 calculate the reciprocal of the coil flux linkage B.theta. based on the above-mentioned principle. In FIG. 2, a current 13 approximately proportional to the output voltage Ea of the operational amplifier 16a flows through the Hall element 2a via the resistor 10a.

Note that the sum of the resistance value of the resistor 10a and the resistance value of the resistor 11a connected to the other current terminal of the Hall element 2a is set to a value sufficiently larger than the internal impedance of the Hall element 2a. Therefore, even if the internal impedance of the Hall element 2a changes due to the magnetoresistive effect, the voltage Ea
An operating current 11 approximately proportional to flows through the Hall element 2a. For this reason, the above current 1. , and the output terminals in a direction perpendicular to both the magnetic flux density KlBa acting on the Hall element 2a.

The output current a of the Hall element 2a is supplied to a differential amplifier 15a having a negative feedback resistor 12a, and a predetermined voltage E″a=K
After being amplified to 4eaBa (K4: constant), resistor 13
a to the summing point Aa. Also, this additional point A
DC voltage -Vs (servo voltage) is supplied to a through a resistor 14a. And the addition point M is the operational amplifier 1
The positive input terminal of the operational amplifier 16a is grounded. These resistors 13a and 14
a is selected to have the same value. Therefore, for example, divider 4
For a, the potential of the addition point Aa is zero, that is, E″a=
A closed loop operates so that Vs. That is, for example, E
When ``a'' is smaller than Vs, the voltage at point Aa becomes -Δv, and this voltage is inverted and amplified by the operational amplifier 16a.

Therefore, the output Ea of the operational amplifier 16a increases by +Δe, and the operating current 1a of the Hall element 2a also increases in accordance with the increase in the output Ea. Therefore, the output Ea of the Hall element 2a also increases and is maintained at E″a=Vs.
>Ea, the voltage at point Aa becomes +Δv, and this voltage is inverted and amplified by the operational amplifier 16a to produce the output voltage E. decreases by Δe. Therefore, the operating current of the Hall element 2a decreases, and the output Ea of the Hall element 2a decreases, and is maintained at E''a=Vs. Therefore, (K5: constant), the output voltage of the operational amplifier 16a E. is the voltage V
s, and proportional to the reciprocal of the interlinkage magnetic flux density Ba of the coil 25a (FIG. 3b).

Similarly, for the dividers 4b and 4c, the operational amplifier 16b
, 16c output voltages Eb and eO are respectively E,=K5■s/
Bb. ．． eO=K5Vs/Bc, which is proportional to the voltage S and proportional to the reciprocal of the interlinkage magnetic flux densities Bb and Bc of the coils 25b and 25c (Fig. 3b). The output voltages Ea, eb, and ec of the dividers 4a, 4b, and 4c are output from transistors 17a and 17a, respectively.
It is supplied to the bases of 17b and 17c.

As a result, inverted and amplified voltage signals Fa, Fb, and Fc as shown in FIG. 3c are obtained from the collectors of the transistors 17a, 17b, and 17c. Note that in the negative polarity portion of the signals Ea, e, ec shown in FIG. 3B, the transistors 17a to 17c are cut off. These voltage signals Fa, Fb, Fc are applied to resistors 20a, 20b, 20c.
are supplied to the bases of transistors 21a, 21b, and 21c, respectively.

These transistors 21a, 21b, 21c have their load resistances 22a, 22b, 22c and a common emitter resistance 2.
Since the transistors 24a, 24b, 24b, and 3 together form a differential amplifier, the collectors of each transistor are switched by 1200 as shown in FIG.
The current switching signals Ha, Hb, which have a level lower by the base-emitter voltage of 24c and have no overlapping portions,
Hc is formed. These current switching signals Ha, Hb,
Since Hc is supplied to the bases of drive transistors 24a, 24b, and 24c, respectively, these transistors
The three-phase coils 25a and 25 are turned on alternately, one by one.
A driving current is sequentially applied to the terminals b and 25c. Further, from the common emitter resistor 23, voltage signals Fa,
A signal G proportional to the maximum level between Fb and Fc is obtained.

This signal G is supplied to the base of a transistor 26, and from the collector of this transistor 26 a signal J whose polarity is inverted as shown in FIG. 3f is obtained. This signal J has voltage signals El, eb, and eO of transistors 17a and 17b.
, 17c, synthesized by the emitter circuit of the differential amplifier, and then inverted again by the transistor 26, so it is proportional to the composite signal of these voltage signals El, e, , eO. . Therefore, the signal J is expressed as (K6: constant) as a function of the coil flux linkage density BO=f(bθ) (f(bθ) is a function of the rotation angle θ) and the servo voltage Vs.

This signal J is supplied to a voltage-to-current conversion circuit 5 comprising an operational amplifier 30, resistors 31 and 33, and a transistor 32.

Therefore, a current 1 (VU) corresponding to the voltage level of the signal J flows through the transistor 32 (IO: constant).

Therefore, a current i expressed by the above formula is sequentially passed through each of the coils 25a, 25b, and 25c in an amount of 1200. That is, coil 2 currents 1a, Ib, and Ic are respectively applied. Therefore, the rotational torque T generated by this current i and the interlinkage magnetic flux density Bθ of each coil is (K: constant/Z: number of turns of the coil).

That is, the rotational torque of the motor is
It is unrelated to the interlinkage magnetic flux density 5c = f (bθ) and is determined according to the speed adjustment voltage Vs. Therefore, no matter what magnetization pattern the rotor magnet has, if the speed adjustment voltage Vs is constant, a nearly constant rotational torque that is independent of the rotation angle θ of the motor can be obtained, as shown in FIG. 3h. be able to. Therefore, torque ripple can be extremely reduced, and a motor without coking can be obtained. As described above, the present invention detects the magnetic flux density linking to the coil of a DC motor using a Hall element, obtains an output inversely proportional to the interlinking magnetic flux density from a calculation circuit equipped with the Hall element as a feedback loop, and performs the calculation. A drive current corresponding to the output is passed through the coil.

Therefore, the product of the magnetic flux density linking to the coil and the drive current flowing through this coil can always be kept constant, and therefore, the product is almost independent of the coil flux linkage density, which changes depending on the rotation angle of the motor. A constant rotational torque can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a schematic block circuit diagram showing an embodiment of a motor drive circuit according to the present invention, and FIG. 2 is a circuit diagram of a motor drive circuit in which the present invention is applied to a brushless DC motor of a three-phase one-phase energization system. FIG. 3 is a graph showing the waveforms of each part in FIG. 2 and the rotational torque of the motor, and FIG. 4 is a diagram of the principle of the divider. In addition, in the symbols used in the drawings, 2a to 2c.
...Hall element, 4a to 4c...Divider,
5...It is a voltage-to-current converter.

Claims (1)

[Claims] 1 Equipped with an arithmetic circuit including a Hall element as a feedback loop for detecting the magnetic flux density interlinking with the coil of the DC motor, and applying a drive current to the coil in accordance with a signal inversely proportional to the interlinking magnetic flux density obtained from the arithmetic circuit. A motor drive circuit configured to allow current to flow.