JPH08266086A - Method and device for controlling speed of dc brushless motor - Google Patents

Abstract

PURPOSE: To provide a speed controlling device of a DC brushless motor whereby the rotation in the case of its low-speed driving can be made stable. CONSTITUTION: Driving currents are made to flow in armature coils Lu-Lw of a DC brushless motor from a DC power supply B via an inverter circuit 3. A switching circuit 20 is provided between a power supply terminal 3a of the inverter circuit 3 and the DC power supply B. The duty ratio of the ON-OFF of the switching circuit 20 is so controlled that in the case of the starting of the motor, a power supply voltage VB applied to the power supply terminal 3a of the inverter circuit 3 is made high, and in the case of the constant-speed driving of the motor, it is made lower than its value in case of the starting of the motor.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a speed control method for controlling the speed of a DC brushless motor to which a drive current is supplied through an inverter circuit, and a speed control device used for implementing the method.

[0002]

2. Description of the Related Art For controlling the speed of a DC brushless electric motor driven through an inverter circuit, for example, the structure shown in FIG. 3 is adopted. FIG. 3 shows a speed control device for controlling the speed of a DC brushless electric motor. In FIG. 3, 1 is a stator having three-phase armature coils Lu to Lw and a rotor having a magnet field (see FIG. A DC brushless electric motor 2 and a load of the electric motor requiring a driving torque τ, and three-phase armature coils Lu to L.
w is star-connected. PS is a position detector that detects the rotational angular position of the rotor of the electric motor 1, and RE is a rotary encoder that generates a pulse signal each time the electric motor 1 rotates a minute angle.

The position detector PS is, for example, a magnetic sensor such as a Hall element or a magnetoresistive element which is arranged at intervals of 120 degrees and detects the polarity (N pole or S pole) of the magnetic pole of the rotor. A position detection signal that takes a different state [for example, an H level (high level) or an L level (low level or zero level)] is output depending on the polarity of the existing magnetic pole. In this example, it is assumed that the position detector PS is composed of three Hall elements arranged at 120 ° intervals so as to detect the polarities of the magnetic poles of the rotor at the center positions of the three magnetic poles of the stator. In this case, as shown in FIGS. 4A to 4C, the three Hall elements constituting the position detector PS have the position detection signals eu, ev and the level detection signals eu and ev whose levels change with the change of the rotation angle θ. Output ew.

Reference numeral 3 denotes an inverter circuit. In the illustrated inverter circuit, switches Tu to Tw and Tx to Tz, which are semiconductor switching elements capable of on / off control, are connected in a three-phase bridge, and switches Tu to Tw.
, And Tx to Tz respectively, and diodes Du to Dw and Dx to Dz connected in antiparallel to each other.
In the illustrated example, the switches Tu to Tw and Tx to Tz are N.
It consists of PN transistor and switches Tu to Tw.
Each of the switches is rendered conductive when an H level (high level) signal is applied to the bases of the transistors forming each of Tx and Tx.

The connection point between the emitter of the transistor forming the switch Tu and the collector of the transistor forming the switch Tx, the connection point of the emitter of the transistor forming the switch Tv and the collector of the transistor forming the switch Ty, and the switch Tw. The connection points between the emitter of the transistor that forms the switch and the collector of the transistor that forms the switch Tz are output terminals 3u, 3v, and 3w of the inverter circuit, and these output terminals have three-phase armature coils Lu to Lw. The terminal on the opposite side of the neutral point is connected. The inverter circuit 3 has a positive electrode side DC power supply terminal 3a and a negative electrode side DC power supply terminal 3b. The positive electrode side DC power supply terminal 3a is connected to a positive electrode terminal of a DC power supply B such as a battery whose negative electrode is grounded, and a negative electrode side. The DC power supply terminal 3b is grounded.

In the inverter circuit 3, the switches Tu to Tw on the upper side of the bridge circuit and the switches Tx to Tz on the lower side are driven so that they are turned on one by one in a predetermined order. The drive current supplied to the armature coils Lu to Lw is commutated to rotate the electric motor 1.

Reference numeral 4 denotes a microcomputer, which receives the position detection signals eu to ew output by the position detector PS as an input and instructs a phase to be excited by a predetermined program stored in a ROM (not shown). Phase pattern signals Su, Sv, Sw and Sx, Sy
, Sz to output the phase pattern output means 5.
These phase pattern signals are respectively switches Tu to Tw.
And Tx to Tz are signals that determine whether to turn on or off, and in this example, the phase pattern signals Su to Sw.
And Sx to Sz are in the H level state, the corresponding transistors TRu to TRw and TRx to TR are provided.
It is supposed to indicate that z should be turned on. These signals Su, Sv, Sw and Sx, Sy, S
Waveforms of z are shown in Fig. 4 (D), (E), and (F), respectively.
And (I), (H), and (G).

Phase pattern signals Su, Sv, Sw and Sx
, Sy, Sz can be obtained by applying a predetermined logical operation to the position detection signals eu to ew. For example, the signal S
u can be obtained by taking the logical product of the position detection signal eu and the negative signal of the position detection signal ev, and the drive signal Sv is the logical product of the position detection signal ev and the negative signal of the position detection signal ew. It can be obtained by taking.

Phase pattern signals Su to Sw and Sx to Sz
Is input to the inverter drive unit 6, and the inverter drive unit 6 drives the drive signals Su ′ to Sw ′ according to the phase pattern signal.
, And Sx'-Sz ', and supply these drive signals to the bases of the transistors constituting the switches Tu-Tw and Tx-Tz, respectively. Since these drive signals are pulse-width modulated by the PWM control unit described later, they have a pulse waveform which is intermittent at a predetermined duty ratio. In the illustrated example, the drive signal Su when the duty ratio is 100%
The waveforms of'-Sw 'and Sx'-Sz' are the same as the waveforms of the phase pattern signals Su-Sw and Sx-Sz, respectively.

When the above drive signal is applied to the inverter circuit, the switches Tu to Tw and Tx to Tz become (Tu
, Ty), (Tu, Tz), (Tv, Tz), (Tv
, Tx), (Tw, Tx), (Tw, Ty), (Tu,
The combination of Ty), ... turns on in sequence, and Lu →
Lv, Lu → Lw, Lv → Lw, Lv → Lu, Lw → L
The drive current is commutated as u, Lw → Lv, ... And the electric motor is rotated.

The output of the rotary encoder RE is input to the speed detection unit 7 and converted into a speed detection signal (digital signal) indicating the actual rotation speed of the electric motor, and the speed detection signal is input to the microcomputer 4. The microcomputer includes a speed setting means 8 for giving a set rotation speed of the electric motor according to a predetermined program stored in the ROM,
The speed deviation detecting means 9 and the manipulated variable calculating means 10 are realized. The speed deviation detecting means 9 calculates a deviation between the rotation speed of the electric motor detected by the output of the speed detecting unit 7 and the set rotation speed, and outputs a speed deviation signal indicating the deviation. The manipulated variable calculating means 10 performs proportional, differential and integral calculation (PID calculation) on the deviation detected by the speed deviation detecting means to determine the drive current that needs to be supplied to the armature in order to reduce the deviation to zero. The amount that gives the value (average value) is calculated as the manipulated variable. This manipulated variable may directly give the magnitude of the drive current or may give the duty ratio of the drive signal.

A signal indicating the operation amount calculated by the operation amount calculation means 10 is input to the PWM control unit 11. P
The WM control unit 11 pulse-width modulates at least one of the drive signals Su'-Sw 'and Sx'-Sz' so that a predetermined drive current given by the calculated manipulated variable is passed through the armature coils Lu-Lw. To do. As a result, the drive current required to match the rotational speed of the electric motor with the set rotational speed is applied to the electric motor, and the rotational speed of the electric motor is maintained at the set rotational speed.

FIG. 5 shows a rotation speed N when the rotation speed of the brushless DC motor is controlled by the above speed control device.
It shows the relationship between [rpm] and load torque τ [N · m]. The straight line a in the figure shows the characteristic when the load torque τ is increased with the duty ratio of the drive current being 100%. When the load torque is τ o, the duty ratio of the drive current is 100%. Rotation speed of electric motor is Nm
It shows that it rotates with. When operating at a rotational speed lower than Nm with respect to the load torque τo, the duty ratio of the drive current will be reduced.
Here, if the rotation speed of the electric motor is proportional to the average value of the drive current, the rotation speed is, for example, N with respect to the load torque τo.
In order to set o, the duty ratio Do of the drive current is Do
= No / Nm.

[0014]

In the above speed control device, when the power supply voltage of the DC power supply is high, a relatively large torque ripple occurs when switching the excitation phase. This torque ripple does not cause a problem when the electric motor rotates at high speed, but it causes a decrease in torque when the electric motor rotates at low speed, and this torque ripple causes a problem that the rotational fluctuation at low speed becomes large. It is conceivable to lower the power supply voltage in order to lower the torque ripple, but if the power supply voltage is lowered, the drive current will be insufficient at startup and it will not be possible to obtain the prescribed starting torque.
It may not be possible to supply sufficient braking current during braking.

Further, in the above speed control device, if the power supply voltage is set sufficiently high in order to allow a sufficient starting current to flow, the duty ratio of the drive current must be made extremely small during low speed operation (see FIG. 5). In the example shown, it is necessary to set Do = No / Nm), so that the control width of speed control (change width of drive current) cannot be made wide, and rotation speed control is sufficient for fluctuations in load torque. However, there is a problem in that the fluctuation of the rotation speed of the electric motor becomes large.

An object of the present invention is to provide a speed control method and apparatus for a DC brushless motor, which can prevent the fluctuation of the rotation speed from increasing at a low speed operation and can perform a stable operation. Especially.

[0017]

According to the speed control method of the present invention, an inverter circuit having a bridge circuit constituted by connecting a plurality of switching elements, which conducts while a drive signal is applied, in a bridge connection, is a DC power source and a DC brushless. A PWM control unit that is provided between the armature coil of the electric motor and the drive current supplied to the armature coil through the inverter circuit is provided to control the duty ratio of the drive current to rotate the electric motor. A method of performing a constant speed operation for maintaining a speed at a set rotation speed, and in the present invention, a DC power supply voltage applied to a power supply terminal of an inverter circuit at the time of starting the motor is required to flow a predetermined starting current. The DC power supply voltage is set to a value lower than the value at start-up when the motor is running at a constant speed.

The DC power supply voltage during constant speed operation of the electric motor may be constant, but it is preferable to change the DC power supply voltage in accordance with the rotation speed of the electric motor so that the value corresponds to the operating speed. Good.

The speed control device of the present invention used for carrying out the above method has a bridge circuit constituted by connecting a plurality of switching elements, which are connected in a bridge manner while a drive signal is applied, with a DC power supply. An inverter circuit that is provided between the armature coil of the electric motor and supplies a predetermined drive current to the armature coil, an inverter drive unit that supplies a drive signal to a switching element of the inverter circuit, and a rotational speed of the electric motor is detected. Speed detecting section, speed deviation detecting means for detecting a deviation between the rotational speed detected by the speed detecting section and the set rotational speed, and an armature for reducing the deviation detected by the speed deviation detecting means to zero. To the armature through an inverter circuit and a manipulated variable calculating means for calculating the amount of drive current that needs to be supplied to the armature as the manipulated variable. An inverter PWM control unit that pulse-width modulates a drive signal supplied from the inverter drive unit to the switching element of the inverter circuit so that the value of the drive current is equal to the value given by the operation amount calculated by the operation amount calculation unit, At the time of starting the motor, the DC power supply voltage given to the power supply terminal of the inverter circuit is set to the value required to flow the starting current, and during constant speed operation, the DC power supply voltage is lower than the value at start up and is commensurate with the set rotation speed. And a power supply voltage control unit that changes the DC power supply voltage applied to the power supply terminal of the inverter circuit according to the operating condition of the electric motor.

The power supply voltage control unit includes, for example, a switch element that maintains an ON state while an ON signal is supplied, and a switch provided to turn on / off the voltage supplied from the DC power supply to the power supply terminal of the inverter circuit. Circuit,
A switch drive unit that gives an ON signal to the switch circuit, a voltage setting means that gives a set value of a DC power supply voltage given to the power supply terminal of the inverter circuit, and a voltage value of the actual DC voltage given to the power supply terminal of the inverter circuit. A voltage deviation detecting means for detecting a deviation from a set value given by the voltage setting means, and a duty ratio for calculating an on / off duty ratio of the switch circuit necessary for reducing the deviation detected by the voltage deviation detecting means to zero. And a PWM control unit for voltage control that pulse-width modulates an ON signal given to the switch circuit from the switch drive unit so as to turn on and off the switch element of the switch circuit with the duty ratio calculated by the duty ratio calculation unit. To be done. In this case, the voltage setting means sets the DC power supply voltage applied to the power supply terminal of the inverter circuit at the time of starting the motor to a value necessary for flowing the starting current, and the DC power supply voltage during constant speed operation is lower than the value at the start. In addition, the set value of the voltage is changed according to the operating condition of the electric motor so that the value corresponds to the set rotational speed.

The power supply voltage control unit sets the DC power supply voltage applied to the power supply terminal of the inverter circuit at the time of starting the electric motor to a value required to flow the starting current, and sets the DC power supply voltage at the time of constant speed operation at the time of starting. It is not limited to the above configuration as long as it can be controlled to be lower than the above. For example, a voltage divider circuit that divides the output voltage of the DC power supply to generate a plurality of voltages is provided, and a plurality of voltages obtained from the voltage divider circuit are selectively applied to the power supply terminals of the inverter circuit (high at start-up). The voltage may be selected, and a low voltage may be selected during constant speed operation). Further, a plurality of power supply ICs that generate different output voltages by PWM controlling the output voltage of the DC power supply are provided, and a plurality of voltages obtained by the plurality of power supply ICs are selectively applied to the power supply terminals of the inverter circuit. It can also be configured.

[0022]

As described above, when the power supply voltage of the inverter circuit is set to a low value during constant speed operation, the torque ripple that occurs when switching the excitation phase can be reduced, so that a torque shortage occurs during low speed operation. Can be prevented, and low-speed operation can be stably performed.

As described above, by setting the power supply voltage during constant speed operation to a low value commensurate with the operation speed, it is possible to prevent the duty ratio of the drive current from becoming too small during constant speed operation, particularly during low speed operation. In addition, it is possible to prevent the change width of the duty ratio of the drive current with respect to the load change from becoming too small, to improve the controllability, and to reduce the speed change due to the load change.

[0024]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an embodiment of the present invention. In FIG. 1, parts that are the same as the parts of the speed control device of FIG. In this embodiment,
A switch circuit 20 is provided between the DC power supply B and the power supply terminal 3 a of the inverter circuit 3. The switch circuit 20 includes a switch element such as a transistor that maintains an ON state while an ON signal is supplied from the drive unit 21, and turns on / off the voltage supplied from the DC power supply B to the power supply terminal 3a of the inverter circuit.

The voltage VB between the power supply terminals 3a and 3b of the inverter circuit 3 is converted into a digital signal by the analog / digital converter (A / D converter) 22 and input to the microcomputer 4.

In this embodiment, in addition to the phase pattern output means 5, the speed setting means 8, the speed deviation detecting means 9 and the manipulated variable calculating means 10, the microcomputer 4 further comprises:
The voltage setting means 23 for giving the set value of the power source voltage of the inverter circuit 3, the detected value of the power source voltage of the inverter circuit 3 given from the A / D converter 22, and the set value of the power source voltage set by the voltage setting means 23. The voltage deviation detecting means 24 for detecting the deviation of the switch circuit 20 and the duty ratio calculating means 25 for calculating the on / off duty ratio of the switch circuit 20 necessary for reducing the deviation detected by the voltage deviation detecting means 24 to zero. .

The duty ratio calculated by the duty calculating means 25 is given to the PWM control section 26, and the PWM
The control unit pulse-width modulates the ON signal given from the drive unit 21 to the switch element of the switch circuit 20 so as to turn on and off the switch element of the switch circuit 20 at the calculated duty ratio.

Therefore, the output voltage of the DC power supply B is turned on and off at the calculated duty ratio, and the DC power supply voltage applied to the power supply terminal 3a of the inverter circuit 3 is the voltage setting means 2.
It is kept at the value set by 3.

The voltage setting means 23 sets the DC power supply voltage VB given to the power supply terminal 3a of the inverter circuit 3 to a value necessary for supplying the starting current when the motor is started, and the DC power supply voltage VB is started at the constant speed operation. The value of the voltage is changed in accordance with the operating condition of the electric motor so that the value is lower than the value of and the value corresponds to the operating speed set by the speed setting means 8.

Further, in this embodiment, the detected value of the power supply voltage VB supplied from the A / D converter 22 is the manipulated variable calculating means 10.
The operation amount calculation means 10 calculates the operation amount that gives the duty ratio of the drive current according to the value of the power supply voltage VB. Other points are the same as those of the conventional speed control device shown in FIG.

In the present embodiment, the switch circuit 20
The drive unit 21, the A / D conversion unit 22, the voltage setting unit 23, the voltage deviation detection unit 24, the duty ratio calculation unit 25, and the PWM control unit 26 cause the inverter circuit 3 to operate when the electric motor is started. Set the DC power supply voltage applied to the power supply terminals to the value necessary to flow the starting current, and to keep the DC power supply voltage lower than the value at start-up and to a value commensurate with the operating speed during constant-speed operation. A power supply voltage control unit configured to change the DC power supply voltage applied to the power supply terminal according to the operating condition of the electric motor is configured.

FIG. 2 shows the speed control device of the present embodiment.
The relationship between the rotation speed N and the load torque τ when the value of the DC power supply voltage VB applied to the power supply terminal 3a of the inverter circuit 3 is changed is shown. The power supply voltage VB decreases in the order of, and the straight line a indicates that the on / off duty ratio of the switch circuit 20 is 100.
% (When the output voltage of the DC power supply B is directly used as the power supply voltage of the inverter circuit 3). The output voltage of the DC power supply B is set to a sufficiently high value so that a sufficient drive current can flow when the electric motor is started.

In the present embodiment, the load torque is τ when the duty ratio of ON / OFF of the switch circuit 20 is 100%.
When a load of o is driven, assuming that the duty ratio D of the drive current supplied to the armature coils Lu to Lw is 100%, the motor can obtain a rotation speed Nm4 (the load voltage τo at the power supply voltage at that time). It rotates at the maximum rotation speed. By decreasing the ON / OFF duty ratio of the switch circuit 20 and decreasing the power supply voltage VB as shown by the straight line B → C → D in FIG. 2, the duty ratio of the drive current becomes 1
The rotation speed at 00% decreases as Nm3 → Nm2 → Nm1. When the output voltage of the DC power source B is directly used as the power source voltage of the inverter circuit 3, in order to perform low speed operation with the rotation speed of the motor set to No, the duty ratio Do of the drive current is set to No / Nm4 (duty of the drive current). If the ratio is proportional to the rotation speed),
A problem occurs that the duty ratio of the drive current becomes too small. However, as shown by the straight line B → C → D in FIG.
As B is decreased, the duty ratio Do of the drive current required to operate at the rotation speed No with respect to the load torque τo increases as No / Nm3 → No / Nm2 → No / Nm1. . Therefore, during constant speed operation, if the power supply voltage VB applied to the power supply terminal 3a of the inverter circuit 3 is reduced to a value commensurate with the operating speed, the duty ratio of the drive current supplied to the armature coil can be controlled. The size of the suitable range can be set, and the controllability can be improved by preventing a state in which the variation width of the duty ratio of the drive current is insufficient with respect to the load variation.

For example, in the example shown in FIG. 2, when the load requiring the torque τo is operated at the rotation speed No, the power supply voltage VB is set so as to obtain a characteristic like a straight line d or c. When operating at the rotation speed Nm1, the power supply voltage VB may be set so that the characteristic such as the straight line C or the line B can be obtained.

Further, as described above, if the power supply voltage of the inverter circuit 3 is lowered during constant speed operation (during steady operation other than startup), the torque ripple generated when switching the excitation phase can be reduced. It is possible to prevent a decrease in torque when the operating speed is low, and to stably perform low speed operation.

In the above embodiment, the duty ratio of ON / OFF of the switch circuit 20 is set to 100% at the time of starting the electric motor, but the driving current in the reverse direction from the DC power source to the armature coil (the driving current of the polarity for reversing the electric motor). It is preferable to set the ON / OFF duty ratio of the switch circuit 20 to 100% also when the electric current is applied to brake the electric motor.

In the above embodiment, the power supply voltage VB applied to the power supply terminal of the inverter circuit 3 is feedback-controlled to stabilize the power supply voltage VB. However, the voltage of the DC power supply B is stable. In that case, it is not always necessary to feedback control the power supply voltage VB, and the ON / OFF duty ratio of the switch circuit 20 may be determined so as to obtain the voltage set by the voltage setting means 23.

In the above description, the power supply voltage VB is changed stepwise to a value commensurate with the operating speed, but the power supply voltage VB may be continuously changed according to the rotation speed.

In the above embodiment, the switch circuit 20 is used.
The drive unit 21, the A / D conversion unit 22, the voltage setting unit 23, the voltage deviation detection unit 24, the duty ratio calculation unit 25, and the PWM control unit 26 constitute a power supply voltage control unit. This power supply voltage control unit is provided with a voltage dividing circuit that divides the output voltage of the DC power supply to generate a plurality of voltages,
When starting the electric motor, a higher voltage of the plurality of voltages obtained from the voltage dividing circuit is selected and applied to the power supply terminal of the inverter circuit, and at the time of constant speed operation, the lower one of the voltages obtained from the voltage dividing circuit is selected. A voltage may be selected and applied to the power supply terminal of the inverter circuit.

Further, a plurality of power supply ICs for PWM-controlling the output voltage of the DC power supply to generate different output voltages are provided, and a plurality of voltages obtained by the plurality of power supply ICs are selected according to operating conditions. The voltage may be applied to the power supply terminal of the inverter circuit.

In the above embodiment, the voltage setting means 23 is
Although the setting value of the power supply voltage VB is determined according to the rotation speed set by the speed setting means 8, the setting value of the power supply voltage VB is determined according to the speed detection signal obtained from the speed detection unit 7. May be.

Further, in the above embodiment, the manipulated variable calculating means 1
0 calculates the operation amount which gives the duty ratio of the drive current according to the detected value of the power supply voltage VB obtained from the A / D converter 22, but the power supply voltage set by the voltage setting means 23 is set. You may make it calculate the operation amount which gives the duty ratio of a drive current according to a value.

The preferred embodiments of the present invention have been described above. The main aspects of the invention disclosed in this specification are as follows.

(1) An inverter circuit having a bridge circuit formed by connecting a plurality of switching elements that are conductive while a drive signal is applied is bridge-connected between the DC power source and the armature coil of the DC brushless motor. A PWM controller for pulse-width modulating the drive current supplied to the armature coil through the inverter circuit,
In a speed control method for a DC brushless electric motor, which controls a duty ratio of a driving current to perform a constant speed operation for maintaining the rotational speed of the electric motor at a set rotational speed, in starting the electric motor and in an armature coil of the electric motor. When applying a braking drive current in the direction opposite to the drive current to perform braking, the DC power supply voltage applied to the power supply terminal of the inverter circuit is set to a large value necessary to flow a predetermined starting current and braking current, and A method for controlling the speed of a DC brushless motor, wherein the DC power supply voltage is set to a value lower than the values at the time of starting and braking during constant speed operation of the motor.

(2) An inverter circuit having a bridge circuit formed by connecting a plurality of switching elements, which conducts while a drive signal is applied, in a bridge connection, is provided between the DC power source and the armature coil of the DC brushless motor. A PWM controller for pulse-width modulating the drive current supplied to the armature coil through the inverter circuit,
In a speed control method for a DC brushless electric motor, which controls a duty ratio of a driving current to perform a constant speed operation for maintaining the rotational speed of the electric motor at a set rotational speed, in starting the electric motor and in an armature coil of the electric motor. When applying a braking current in the direction opposite to the drive current to apply braking to the electric motor, the DC power supply voltage applied to the power supply terminal of the inverter circuit is set to a large value necessary to flow a predetermined starting current and braking current. Changing the DC power supply voltage according to the rotation speed of the electric motor so that the DC power supply voltage is lower than the values at the time of starting and braking during the constant speed operation of the electric motor, and is a value commensurate with the operating speed. A method for controlling a speed of a DC brushless electric motor, characterized by:

(3) A bridge circuit is formed by connecting a plurality of switching elements that are connected in a bridge manner while a drive signal is applied, and is provided between the DC power source and the armature coil of the DC brushless motor. The output of the inverter circuit that supplies the drive current to the armature coil and the output of the position detector that detects the rotational angle position of the rotor of the electric motor to perform commutation of the drive current supplied to the armature coil. Phase pattern output means for generating a phase pattern signal for determining an excitation phase of the armature coil, an inverter drive section for providing a drive signal to a switching element of the inverter circuit according to the phase pattern signal, and the direct current A speed detection unit for detecting the rotation speed of the brushless motor, and a deviation between the rotation speed detected by the speed detection unit and the set rotation speed is detected. Speed deviation detecting means, and an operation amount calculating means for calculating, as an operation amount, an amount that gives a value of a drive current that needs to be supplied to the armature coil in order to reduce the deviation detected by the speed deviation detecting means to zero. And an inverter for pulse-width modulating the drive signal so that the value of the drive current supplied from the DC power supply to the armature coil through the inverter circuit becomes equal to the value given by the operation amount calculated by the operation amount calculation means. A DC brushless system including a PWM control unit, which implements the phase pattern output unit, the speed deviation detection unit, and the manipulated variable calculation unit by a microcomputer to perform a constant speed operation for maintaining the rotation speed of the electric motor at a set rotation speed. In a speed control device for an electric motor, a braking current in a direction opposite to a drive current is applied to the armature coil of the electric motor when the electric motor is started. When braking the electric motor, the DC power supply voltage applied to the power supply terminal of the inverter circuit is set to a large value necessary for supplying the starting current and the braking current, and the DC power supply voltage is started at the constant speed operation. A power supply voltage control unit is provided that changes the DC power supply voltage applied to the power supply terminal of the inverter circuit according to the operating condition of the electric motor so that the value is lower than the operating time and the value during braking and that is suitable for the operating speed. A speed control device for a DC brushless electric motor.

(4) The power supply voltage control unit is provided with a switching element that maintains an ON state while an ON signal is supplied, and is provided to turn on / off the voltage supplied from the DC power supply to the power supply terminal of the inverter circuit. Switch circuit, a switch drive section for giving an ON signal to the switch circuit, voltage setting means for giving a set value of the power supply voltage of the inverter circuit, and an actual DC voltage given to the power supply terminal of the inverter circuit. A voltage deviation detecting means for detecting a deviation between a voltage value and a set value given by the voltage setting means, and an on / off duty ratio of the switch circuit necessary for making the deviation detected by the voltage deviation detecting means zero. And a duty ratio calculation means for calculating the duty ratio of the switch circuit based on the duty ratio calculated by the duty ratio calculation means. A voltage control PWM control unit for pulse-width modulating an ON signal given to the switch circuit from the switch driving unit so as to turn on and off the switch element, wherein the voltage setting unit starts the electric motor and an electric machine of the electric motor. When a braking current in the direction opposite to the drive current is applied to the child coil to apply braking to the electric motor, the DC power supply voltage applied to the power supply terminal of the inverter circuit is set to a value necessary to pass the starting current and the braking current. When the constant speed operation, the DC power supply voltage is lower than the value at the time of starting and braking, and the set value of the voltage is changed according to the operating condition of the electric motor so as to be a value commensurate with the operating speed. The speed control device for a DC brushless motor according to the above item 3, which is characterized.

[0048]

As described above, according to the present invention, the power supply voltage control unit for controlling the power supply voltage applied to the power supply terminal of the inverter circuit is provided so as to be applied to the power supply terminal of the inverter circuit during low speed operation. Since the power supply voltage is set to be lower than the starting value, the torque ripple generated when switching the excitation phase can be reduced. Therefore, it is possible to prevent a situation where the torque becomes insufficient during low speed operation, and it is possible to stably perform low speed operation.

Further, according to the present invention, when the power supply voltage during constant speed operation is set to a low value commensurate with the operation speed, the duty ratio of the drive current is prevented from becoming too small during low speed operation, and the drive current with respect to load fluctuations is prevented. Since it is possible to prevent the change width of the duty ratio from becoming too small, it is possible to improve the controllability and reduce the speed fluctuation due to the load fluctuation.

[Brief description of drawings]

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

FIG. 2 is a diagram showing a relationship between a rotation speed of an electric motor and a load torque when the speed control device according to the embodiment of FIG. 1 is used, using a power supply voltage of an inverter circuit as a parameter.

FIG. 3 is a configuration diagram showing a configuration of a conventional speed control device.

FIG. 4 is a waveform diagram showing the relationship between the output of the position detector of the brushless DC motor and the phase pattern signal that determines the excitation phase.

FIG. 5 is a diagram showing a relationship between a rotation speed of an electric motor and a load torque when a conventional speed control device is used.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Brushless DC motor 2 Load 3 Inverter circuit 4 Microcomputer 5 Phase pattern output means 6 Inverter drive section 7 Speed detection section 8 Speed setting means 9 Speed deviation detection means 10 Manipulation amount calculation means 11 PWM control section 20 Switch circuit 21 Switch drive section 22 A / D conversion section 23 Voltage setting means 24 Voltage deviation detection means 25 Duty ratio calculation means 26 PWM control section

Claims (4)

[Claims] 1. An inverter circuit having a bridge circuit constituted by connecting a plurality of switching elements, which are conductive while a drive signal is applied, in a bridge connection, is provided between a DC power source and an armature coil of a DC brushless motor, and
A PWM control unit for pulse-width modulating the drive current supplied to the armature coil through the inverter circuit is provided, and the constant speed operation is performed to maintain the rotation speed of the electric motor at the set rotation speed by controlling the duty ratio of the drive current. In the speed control method for a DC brushless motor, the DC power supply voltage applied to the power supply terminal of the inverter circuit at the time of starting the motor is set to a value required to flow a predetermined starting current, and when the motor is running at a constant speed, A method for controlling the speed of a DC brushless motor, characterized in that the DC power supply voltage is set to a value lower than the value at startup. 2. An inverter circuit having a bridge circuit configured by connecting a plurality of switching elements, which are conductive while a drive signal is applied, in a bridge connection, is provided between a DC power supply and an armature coil of a DC brushless motor, and
A PWM control unit for pulse-width modulating the drive current supplied to the armature coil through the inverter circuit is provided, and the constant speed operation is performed to maintain the rotation speed of the electric motor at the set rotation speed by controlling the duty ratio of the drive current. In the speed control method for a DC brushless motor, the DC power supply voltage applied to the power supply terminal of the inverter circuit at the time of starting the motor is set to a value required to flow a predetermined starting current, and when the motor is running at a constant speed, A method for controlling the speed of a DC brushless motor, characterized in that the DC power supply voltage is changed according to the rotation speed of the electric motor so that the DC power supply voltage is lower than the value at the time of starting and is a value commensurate with the operating speed. 3. A bridge circuit having a plurality of switching elements connected in a bridge connection that conducts while a drive signal is being applied, the bridge circuit being provided between the DC power source and the armature coil of the DC brushless motor. An inverter circuit for supplying a drive current to the armature coil, an inverter drive unit for applying a drive signal to a switching element of the inverter circuit so as to perform commutation of the drive current supplied to the armature coil, and the DC brushless A speed detection unit for detecting the rotation speed of the electric motor, a speed deviation detection unit for detecting a deviation between the rotation speed detected by the speed detection unit and a set rotation speed, and a deviation detected by the speed deviation detection unit to zero. An operation amount calculating means for calculating, as an operation amount, an amount giving a value of a drive current that needs to be supplied to the armature coil in order to: A PWM controller for an inverter that pulse-width modulates the drive signal so that the value of the drive current supplied from the DC power supply to the armature coil through the inverter circuit becomes equal to the value given by the operation amount calculated by the operation amount calculation means. In a speed control device for a DC brushless motor for performing a constant speed operation for maintaining the rotation speed of the electric motor at a set rotation speed, a DC power supply voltage applied to a power supply terminal of the inverter circuit is started when the electric motor is started. A DC power supplied to the power supply terminal of the inverter circuit so that the DC power supply voltage has a value required to flow a current, is lower than the value at the time of start-up during constant speed operation, and is a value commensurate with the operating speed. A DC brushless power source is provided with a power supply voltage control unit that changes the voltage according to the operating condition of the electric motor. Motivation speed control device. 4. The power supply voltage control unit is provided with a switch element that maintains an ON state while an ON signal is supplied, and is provided to turn on / off the voltage supplied from the DC power supply to the power supply terminal of the inverter circuit. A switch circuit, a switch driver that gives an ON signal to the switch circuit, a voltage setting unit that gives a set value of a power supply voltage of the inverter circuit, and a voltage of an actual DC voltage given to a power supply terminal of the inverter circuit. A voltage deviation detecting means for detecting a deviation between a value and a set value given by the voltage setting means, and an on / off duty ratio of the switch circuit necessary for making the deviation detected by the voltage deviation detecting means zero. A duty ratio calculating means for calculating, and a switch ratio of the switch circuit based on the duty ratio calculated by the duty ratio calculating means. A voltage control PWM control unit for pulse-width modulating an ON signal given to the switch circuit from the switch driving unit so as to turn on and off the switch element, and the voltage setting unit is a power supply terminal of the inverter circuit when the motor is started. The DC power supply voltage given to the value required to flow the starting current, during constant speed operation the DC power supply voltage is lower than the value at the time of starting, and the voltage of the voltage so as to be a value commensurate with the operating speed. The speed control device for a DC brushless motor according to claim 3, wherein the set value is changed according to the operating condition of the electric motor.