JPS6356188A - Drive circuit of brushless motor - Google Patents

Abstract

PURPOSE:To avoid too much energy to control a brushless motor and to cause no oscillation to a current feedback loop, by limiting the conduction to a driving coil when the coil minimum voltage drops and by keeping the coil minimum voltage more than the assigned minimum voltage. CONSTITUTION:Cathodes of each diode D1-D3 are connected to driving coils L1-L3, while an odes of each diode D1-D3 are connected to the output of a control amplifier Ac. The circuit section comprising each driving coil L1-L3 and diodes D1-D3 constitutes a coil minimum voltage detecting means 26 which detects the minimum voltage among voltages of driving coils L1-L3. The circuit section comprising a resistance R2, a transistor Q10 and diodes D1-D3 limits the current current to a current feedback amplifier Af as a current control means when the coil minimum voltage detected by the coil minimum votage detecting means 26 drops to the prearranged minimum voltage value, so that the conduction to transistors Q1-Q6 is limited to keep the coil minimum voltage at more than the minimum voltage value.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a drive circuit for a brushless motor that performs soft switching energization.

(Prior Art) In a brushless motor, when switching energization to each phase drive coil, in order to reduce noise generated by sudden changes in current of the drive coil when switching energization,
It has been proposed to perform soft switching energization by rounding the inflection points of the rectangular energization waveform to each phase drive coil. Patent application No. 187680 of the present applicant
The brushless motor drive circuit disclosed in Japanese Patent Application Laid-Open No. 61-85092 is one such example.

FIG. 5 shows an example of a conventional brushless motor drive circuit that performs soft switching energization as described above. In FIG. 5, the three Hall elements H form a sinusoidal waveform according to the relative positional relationship between the stator, which has three-phase drive coils L1, L2, and L3, and the rotor, which has multipolar magnetized magnets. These are rotary position detection elements that generate outputs, and the output signals of these Hall elements H are sent to three amplifiers ^H.
The signal is applied to the waveform synthesis circuit 20 via. The waveform synthesis circuit 20 synthesizes a three-phase rectangular wave pulse-like switching signal in an analog manner using the output signals of three amplifiers AH, and logarithmically compresses and inflects the output signal of each amplifier AH. A three-phase rectangular waveform soft switching signal with rounded points is synthesized. This soft switching signal is applied via the pre-driver 21 to the power transistors 01-Q6 that constitute the drive circuit, and each transistor 01-Q6 energizes each phase drive coil L1, L2, L3 with 120° switching to rotate the rotor. Drive.

The current flowing through each phase drive coil L1, L2, L3 is detected by a current detection resistor Rs, and the rotational speed of the rotor is detected by a speed detector. The control amplifier Ac amplifies the error between the output voltage Vctl of the speed detector and the speed reference voltage Vref to produce a current command signal, and the error between this and the voltage of the current detection resistor Rs is amplified by a current feedback amplifier. The output of this current feedback amplifier Af is fed back to the driver 21, and energization to each phase drive coil L1, L2, L3 is controlled.

According to the above conventional example, when all of the transistors 01 to Q6 are in an unsaturated state, that is, in a state where the motor speed can be controlled, the inflection point of the rectangular wave-like energization signal is as shown by A in FIG. The soft-switching energization of the coil is performed with the current being blunted, resulting in the effect that electrical noise and mechanical noise of the motor are reduced.

However, transistors 01 to Q6, which are in the uncontrollable region,
When entering the saturation region, the switching waveform is no longer soft as shown by B and C in FIG. 6, and the above effect disappears. As the saturation state progresses further, as shown by D in FIG. 6, the shoulder portion of the 120° energization waveform is also fully amplified, resulting in a 180° energization state, increasing the reactive current and deteriorating the motor efficiency. Therefore, in this conventional example, the transistor for supplying current to the coil becomes saturated when the motor starts up and rotates in an uncontrolled manner, causing the above-mentioned problem.

In order to prevent saturation of the coil current-carrying transistor during startup and uncontrolled rotation, a drive circuit as shown in FIG. 7 has been proposed. This is described in Japanese Patent Publication No. 61-11556,
The saturation of the transistors Q1 to Q6 that switch the energization to the drive coils L1, L2, and L3 is detected by the saturation detection means consisting of the diodes D4 to D6, the differential amplifier q8, and the port 9, and the voltage drop across the resistor R4 is detected by this saturation detection signal. The operation of the current control means V-1 that controls the current flowing through the transistors 04 to Q6 is modified using However, saturation of transistors 04 to Q6 is prevented.

(Problems to be Solved by the Invention) According to the brushless morph drive circuit described in Japanese Patent Publication No. 61-11556, the operation of the current control means V-I is corrected based on the saturation detection signal, and the coil is energized. Since the current feedback loop is directly controlled and the current feedback loop is attempted to be controlled in opposition to the command signal Ecr, it is unreasonable and there is a problem that oscillation is likely to occur in the current feedback loop.

The present invention has been made to solve the problems of the prior art described above, and prevents the saturation of the transistor for switching the current to the drive coil even during startup and uncontrolled rotation, and the soft Not only can the switching waveform be maintained, but also the control current input to the current control means can be limited to prevent saturation of the transistor, which allows for smooth control and prevents oscillations from occurring in the current feedback loop. The purpose of the present invention is to provide a brushless morph drive circuit that can perform the following steps.

(Means for Solving the Problems) The present invention utilizes a plurality of drive coils that generate magnetic force between themselves and a rotor magnet when energized to urge the rotor to rotate, and a rotor rotational position detection output from a position detection element. In a brushless morph drive circuit comprising a plurality of transistors that switch energization to the drive coil, and a current control means that controls the amount of energization to the drive coil by these transistors, the voltage of the plurality of drive coils is the lowest. coil minimum voltage detection means for detecting the voltage of the current control means, and when the minimum coil voltage detected by the detection means falls to a preset minimum voltage value, the control current is restricted from flowing into the current control means. The present invention is characterized by comprising current limiting means for limiting energization to the transistor to maintain the minimum coil voltage at or above the minimum voltage value.

(Function) A transistor switches energization to the drive coil in response to a detection signal from the position detection element, thereby urging the rotor to rotate. The current control means controls the amount of current applied to the drive coil by the transistor so that the rotational state of the rotor becomes a predetermined rotational state. A minimum voltage detection means detects the minimum voltage among the voltages of the plurality of drive coils. When the detected coil minimum voltage drops to a preset minimum voltage value, the current limiting means limits the flow of control current into the current controlling means, thereby limiting the energization to the transistor and preventing saturation of the transistor. do.

(Example) Hereinafter, an example of a brushless morph drive circuit according to the present invention will be described.

The embodiment shown in FIG. 1 is an example of a three-phase 120° switching energization system. In FIG. 1, a drive coil L1 with a three-phase configuration
, L2, and L3 are for rotating a rotor (not shown) by applying electricity. That is, the rotor has a multi-pole magnetized magnet, and each of the drive coils L1, L
2. By energizing L3 with 120° switching, a magnetic force is generated between it and the magnet to urge the rotor to rotate. As in the conventional example shown in FIG. The output signals of these three position detection elements are synthesized into a three-phase rectangular wave pulse-like switching signal by a 120° soft switching waveform synthesis circuit (not shown).

Here, the waveform synthesis circuit logarithmically compresses the output signal of the position detecting element to obtain a soft switching waveform in which the three-phase switching signal waveform is rounded at its inflection point.

The three-phase switching signals are applied via the pre-driver 25 to the bases of transistors 01 to Q6 forming the drive circuit. The transistors Q1 to Q6 are connected to the drive coil L1 having a three-phase configuration according to the three-phase switching signals.
Controls energization to L2 and L3 to urge the rotor to rotate.

The current flowing through each phase drive coil L1, L2, L3 flows into a current detection resistor Rs, and a voltage drop generated across the resistor Rs in response to this inflow current is applied to a current feedback amplifier serving as a current control means.

On the other hand, a voltage drop across the resistor R1 corresponding to the current 1ctl flowing through the resistor R1 through the transistor 07 is applied to the current feedback amplifier Af.

The current 1ctl flowing through the resistor R1 is set to be equal to the control current 1ctl of the control amplifier membrane.

The control amplifier Ac receives the control reference voltage Vref determined by the ratio of the resistor R3 and the resistor R4, and the control signal voltage Vctl.
A control current of 1ctl is output by amplifying the error. This control current 1ctl flows through the resistor R2 and the transistor O, and also flows to the base of the transistor Q9 to determine the collector currents of the transistor Q9 and the transistor O8, and controls the base current of the transistor Q7 according to this collector current. The current 1ctl, which is the collector current of the transistor Q7, is determined.

Therefore, the circuit constants are set so that the control current 1ctl of the control amplifier Ac is ultimately equal to the current flowing into the resistor R1.

The cathodes of diodes D1, D2, and D3 are connected to each of the drive coils L1, L2, and L3, respectively, and the anodes of each of the diodes D1, D2, and D3 are connected to a control amplifier Ac.
connected to the output of Each drive coil L1, L2, L
3 and diodes D1, D2, and D3 constitute coil minimum voltage detection means 26 that detects the minimum voltage among the voltages of the plurality of drive coils L1, L2, and L3. Further, the circuit portion shown in FIG. 2 including the resistor R2, the transistor QIO, and the diodes DI, D2, and D3 is configured so that the coil minimum voltage detected by the coil minimum voltage detection means 26 reaches a preset minimum voltage value. By limiting the flow of control current into the current feedback amplifier as a current control means when the transistor Q1
- constitutes a current limiting means that limits the energization to Q6 to maintain the minimum coil voltage above the minimum voltage value.

Next, the operation of the above embodiment will be explained.

When the motor is rotating, the control signal voltage Vctl is higher than the control reference voltage Vref (the control current Ictl flows due to the difference between Vctl and Vref, and the drive coils L1, L2, and L3 are energized according to this control current 1ctl). The motor is driven. When Vctl = Vref, the motor stops for one time.

Next, when the rotation of the motor is controlled, assuming that the rotation speed is constant, the control voltage Vctl is constant, but when the rotation speed decreases, the Vctl increases in an attempt to increase the speed, and the control voltage Vctl increases. rctl increases and the voltage drop across resistor R1 increases. Resistance I? When the voltage drop of 1 becomes higher than the voltage drop of resistor Rs, the current feedback amplifier Af controls the pre-driver 25 to increase the current, increasing the base current of transistors 01 to Q6 that constitute the drive circuit, thereby increasing the current of the drive coil. The amplitude of the voltage applied to L1, L2, and L3 is increased to increase the motor current, which is the sum of the currents flowing to each coil L1, L2, and L3, and the rotational speed of the motor is increased. Due to the increase in motor current, the resistance Rs
When the voltage drop across resistor R1 becomes high and this voltage drop becomes equal to the voltage drop across resistor R1, the current feedback amplifier Af balances and stops increasing the motor current any further, and the control voltage Vctl
is the original constant value, and the rotational speed is also the original constant speed.

Conversely, when the rotational speed of the motor increases, the control voltage Vctl drops in an attempt to reduce the speed, and the voltage drop across the resistor R1 becomes lower than the voltage drop across the resistor Rs, causing the current feedback amplifier Af to control the current through the driver 25. The base currents of the transistors 01 to Q6 are controlled to decrease, thereby narrowing the amplitude of the voltages applied to the drive coils L1, L2, and L3, thereby reducing the motor current and lowering the rotational speed of the motor. As a result, the voltage drop across the resistor Rs decreases, and when this voltage drop becomes equal to the voltage drop across the resistor R1, the motor current stops decreasing, the control voltage Vctl returns to its original constant value, and the rotational speed also returns to its original constant value. It becomes speed.

In this manner, when the rotational speed of the motor is controlled, a constant current loop is configured such that a constant current according to the control voltage Vctl always flows through the motor.

Next, operations at startup and uncontrolled rotation will be described. As shown in FIG. 2, the input terminal A of the control current Ictl of the resistor R2 and each diode D1, D2, D3
Since the potentials at the connection point B of the anodes are equal, the minimum voltage V1mi of the motor coil voltages of each phase appearing on any of the cathode sides C, D, and E of each diode D1, D2, and D3
The relationship between n and the voltage drop R2・IctL of the resistor R2, the voltage vr of the transistor old 0, and the voltage Vf, 2 of each diode D1, D2, D3 is Vlmin +Vf2 ≧1?2・Icth +Vf,
.

ν1m1n≧RE ・Ictl +Vfl −Vfz
becomes. Here, if vrl = Vf, 2, then V1
min≧R2·Ictl.

The R2·Ictl is a preset minimum voltage value, and can be set to a predetermined value depending on the value of the resistor R2. Now, when the control voltage Vctl rises and Ictl increases, the drive coil voltage amplitude expands and the coil minimum voltage V
1 min is coming down. When the coil minimum voltage V1min falls to the above-mentioned minimum voltage value R2·Ictl, that is, when Vlmin = R2·Ictl, the control current Ic flows into the coil from point B through diodes D1, D2, and D3, and the control current The increase in current Ictl is no longer transmitted to the current feedback amplifier ^f, and the coil minimum voltage V1
min will not fall any further.

As shown in FIG. 3, the drive coil voltage is Vcc
It changes with the same amplitude up and down with /2 as the center, the lowest value of the minimum coil voltage V1min is R2·Ictl, and the maximum coil voltage V1max is Vcc −R2·Ictl. Therefore, the coil voltage never reaches the ground level or the power supply voltage level Vcc, and each of the transistors 701 to 6 for switching energization to the drive coil can be operated in an unsaturated state.

According to the above embodiment, when the coil minimum voltage drops to a preset minimum voltage value, the current limiting means limits the energization to the transistor for switching the energization to the drive coil, and the coil minimum voltage becomes equal to or higher than the minimum voltage. Therefore, even during startup or uncontrolled rotation, soft switching energization can be realized and saturation of the transistor can be prevented, and the current limiting means can control the control current to the current controlling means. Since saturation of the transistor is prevented by limiting the inflow, control is easy and reasonable, and oscillations do not occur in the current control means, the transistor, etc.

If the lower limit of the minimum coil voltage V1min is set to a constant value as in the above embodiment, the load on the motor will increase, the motor current will increase, and the collectors of transistors Q1 to Q6 will
When the emitter voltage increases, the saturation point decreases, and as a result, the transistors 01 to Q6 may become saturated before reaching the lower limit of the coil minimum voltage V1min.

Therefore, if the current limiting means is configured as shown in Fig. 4 so that the coil minimum voltage V1min changes as a function of the motor current 1m, the transistors Ql-Q6 will be saturated even if the motor current 1m increases. will disappear.

In FIG. 4, a control current 1ctl from the control amplifier flows through a resistor R2, a transistor Q10, a resistor R5, a transistor Q12, a resistor R6, and also passes through one diode D4 to the diodes D1, D2, which serve as the coil minimum voltage detection means. It is now possible to flow into D3. The collector and base of transistor Q12 are connected to the base of transistor Qll.
The emitter of transistor old 0 is connected to the collector of ll.

A resistor Rs for detecting the motor current rm is connected to the emitter of the transistor Qll.

In the example of Fig. 4, if the voltage of each transistor and diode is Vf, then V1min≧R2-Ic+Vf+ (R5/R6)
・R51m+νf+R5-lm-2Vf =R2・Ictl+[(R5+R6)/R6]
・It becomes Rs-Im. Usually transistors 01-Q6
Since the saturation voltage of V1 is proportional to the motor current Im, it is desirable that the lower limit of the minimum coil voltage V1min is also changed in proportion to the motor current Im. In the example of Fig. 4, the coil minimum voltage V
1 min is as shown in the above equation, which can be changed as a function of motor current Im, and saturation of transistors 01 to Q6 can be prevented even if motor current Im becomes large.

The brushless motor drive circuit according to the present invention is not limited to a three-phase configuration as in the illustrated embodiment, but can be similarly applied to other phase configurations.

(Effects of the Invention) According to the present invention, when the coil minimum voltage falls to a preset minimum voltage value, the current limiting means limits the energization to the transistor for switching energization to the drive coil, and the coil minimum voltage is reduced to the above level. Since the voltage is maintained above the minimum voltage, soft switching energization can be realized even during start-up or uncontrolled rotation to prevent saturation of the transistor, and the current limiting means is connected to the current controlling means. Since saturation of the transistor is prevented by limiting the inflow of the control current, control is easy and reasonable, and oscillations do not occur in the current control means, the transistor, etc.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an embodiment of a brushless motor drive circuit according to the present invention, FIG. 2 is a circuit diagram showing a portion of the current limiting means in the same embodiment, and FIG. 3 is an operation of the current limiting means same as above. 4 is a circuit diagram showing another example of the current limiting means applicable to the present invention, FIG. 5 is a circuit diagram showing an example of a conventional brushless motor drive circuit, and FIG. 6 is the same as above. FIG. 7 is a waveform diagram showing the output of a transistor for switching current to a drive coil in a conventional example. FIG. 7 is a circuit diagram showing another example of a drive circuit for a conventional brushless motor. Ll, L2, L3... Drive coil, 01~Q6...
- Transistor, Af...Current feedback amplifier constituting current control means, 26...Coil minimum voltage detection means.・U・7 shaku 232 units・）4 Enclosure 7 Enclosure procedure amendment band June 22, 1986. 1. Indication of the case 1986 Patent Application No. 199333 2. Name of the invention Brushless motor drive circuit 3. Person making the amendment Relationship to the case Patent applicant name (223) Sankyo Seiki Seisakusho Co., Ltd. 4, Agent Address: 4-5-4 Kyodo, Setagaya-ku, Tokyo
"Detailed Description of the Invention" and 1 Drawing (1) "Rectangular wavy" in page 3, line 8 of the specification is r12.
Change it to 0'J. [2] “Soft” after “120°” in line 13 of the same page
join. [3) "Detector" in line 18 of the same page has been changed to "control circuit." (4) "Speed reference voltage" in line 18 of the same page has been changed to "control reference voltage."<5) Change "square wave pulse-like" from line 17 to line 18 of page 8 to "r120'soft". (6) Delete "through coil" from line 6 to line 7 on page 14. [7] From the 14th line to the 15th line of page 15, the phrase ``As a result of an increase in the collector-emitter voltage, the saturation point decreases'' has been changed to ``Because the saturation voltage increases.'' :8) Revise Figures 1 and 5 in the drawings as attached□
.

Claims (1)

[Claims] A rotor having a multi-pole magnetized magnet, a plurality of drive coils that generate magnetic force between the magnets when energized and urge the rotor to rotate, and a position detection element that detects the rotational position of the rotor. , a brushless motor drive circuit comprising: a plurality of transistors that switch energization to the drive coil based on the output of the position detection element; and a current control means that controls the amount of energization of the drive coil by these transistors; coil minimum voltage detection means for detecting the minimum voltage among the voltages of the drive coil; and control for the current control means when the minimum coil voltage detected by the detection means falls to a preset minimum voltage value. A drive circuit for a brushless motor, comprising: current limiting means for limiting current flow to the transistor to maintain the minimum coil voltage at or above the minimum voltage value.