JP3127183B2 - DC brushless motor drive controller - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a drive control device for a brushless DC motor used in an air conditioner or the like.

[0002]

2. Description of the Related Art A DC brushless motor is composed of a stator having a plurality of phase windings mounted thereon and a rotor having permanent magnets. This motor has a two-pole type and a four-pole type. In the two-pole type, a star-connected three-phase winding is mounted on the stator with a mechanical displacement of 120 ° relative to each other, and the rotor has one permanent magnet ( Magnetic poles N, S) are provided. In the four-pole system, two sets of three-phase windings, also in a star connection, are mounted on the stator with a mechanical displacement of 180 ° from each other.
Two permanent magnets are provided with a mechanical offset of 90 ° from each other.

The difference between the two-pole type and the four-pole type operation is that in the two-pole type, one cycle of the mechanical angle of the rotor corresponds to the energization of one cycle of the electrical angle of the three-phase winding. The point is that one cycle of the mechanical angle of the rotor corresponds to energization for two cycles of the electrical angle of the winding.

When such a DC brushless motor is driven, a switching circuit having a plurality of switching elements and a DC voltage circuit for applying a DC voltage to the switching circuit are prepared. As the DC voltage circuit, a rectifier circuit that rectifies an AC voltage is used, and the rectifier circuit and the switching circuit constitute a so-called inverter circuit. Then, the position of the rotor is sequentially detected, and each switching element of the switching circuit is turned on and off in accordance with the detected position, so that energization to each phase winding of the motor is sequentially switched, and driving is performed. You.

In this inverter circuit, a shunt resistor for current detection is inserted into a connection line between the rectifier circuit and the switching circuit, and overcurrent protection for the inverter circuit is performed by current detection via the shunt resistor. . That is, the current flowing through the shunt resistor is detected,
When the detected current exceeds the set value, the operation is immediately stopped upon judging that an overcurrent has occurred, and the elements of the switching circuit are protected.

[0006]

During the operation of the motor, the position of the rotor and the energization of each phase winding may not be well matched. So-called step-out. When this step-out occurs, an extra reflux current is generated due to the magnetic action between the phase winding of the stator and the permanent magnet of the rotor, and there is a concern that the switching circuit element may be destroyed.

[0007] The present invention has been made in view of the above circumstances,
An object of the present invention is to provide a highly safe DC brushless motor drive control device capable of immediately detecting a step-out of a motor and protecting elements of a switching circuit.

[0008]

SUMMARY OF THE INVENTION The present invention provides a DC brushless motor including a stator having a plurality of phase windings and a rotor having a permanent magnet, a switching circuit having a plurality of switching elements, and a switching circuit having a plurality of switching elements. Means for applying a DC voltage, a drive control device for a DC brushless motor for driving a motor by turning on / off each switching element while sequentially detecting energization to each phase winding while detecting the position of the rotor. , A detecting means for detecting a current flowing in a direction opposite to the normal direction flowing between the DC voltage circuit and the switching circuit, and a control means for stopping the operation when the detected current exceeds a set value.

[0009]

In the drive control device for a DC brushless motor according to the present invention, when the motor loses synchronism, a current flows in the switching circuit in a direction opposite to the normal direction. This reverse current is detected, and when it exceeds a set value, the operation is stopped.

[0010]

An embodiment of the present invention will be described below with reference to the drawings. In FIG. 1, reference numeral 1 denotes a DC brushless motor, which includes a stator (not shown) having star-connected three-phase windings Lu, Lv, and Lw, and a rotor (not shown) having permanent magnets.

An inverter circuit 3 is connected to a three-phase AC power supply 2. The inverter circuit 3 includes a rectifier circuit 4 and a switching circuit 5. The rectifier circuit 4 has a diode bridge 6 and a smoothing capacitor 7.

The switching circuit 5 has a series circuit of an upstream switching element and a downstream switching element provided for three phases, and includes transistors Tu + and Tu- as U-phase upstream and downstream switching elements and V-phase switching elements. Transistors Tv + and Tv-, and transistors W + and Tw- for the W phase. A DC voltage from the rectifier circuit 4 is applied to these series circuits. Note that a damper diode D for preventing back electromotive force is connected in parallel to each transistor.

In the inverter circuit 3, a shunt resistor 8 is inserted and connected to a negative connection line between the rectifier circuit 4 and the switching circuit 5. The non-connection end of the phase winding Lu is connected to an interconnection point of the transistors Tu + and Tu− in the switching circuit 5. The non-connection end of the phase winding Lv is connected to the interconnection point of the transistors Tv + and Tv-. The non-connection end of the phase winding Lw is connected to the interconnection point of the transistors Tw +, Tw-.

Reference numeral 10 denotes a position detection circuit for detecting the position of the rotor, which has comparators 11, 12, and 13. The terminal voltage of the phase winding Lu is input to the non-inverting input terminal (+) of the comparator 11. The terminal voltage of the phase winding Lv is input to the non-inverting input terminal (+) of the comparator 12. The terminal voltage of the phase winding Lw is input to the non-inverting input terminal (+) of the comparator 13. And
The reference voltage Vd is input to the inverting input terminals (-) of the comparators 11, 12, and 13. The reference voltage Vd is set to half the level of the output voltage of the rectifier circuit 4.

The comparators 11, 12, and 13 output a logical "0" signal when the input voltage to the non-inverting input terminal (+) is lower than the reference voltage Vd, and output the signal to the non-inverting input terminal (+). When the voltage is equal to or higher than the reference voltage Vd, a logic "1" signal is output.

The outputs of the comparators 11, 12, and 13 are output from the control unit 3
0 is supplied. The control unit 30 controls the phase windings Lu, Lv, L
The voltages induced in w are monitored through the comparators 11, 12, and 13, and the drive signal for each transistor of the switching circuit 5 is created while detecting the position of the rotor based on the change in the induced voltage. These drive signals are supplied to the bases of the respective transistors of the switching circuit 5.

Shunt resistor 8 in inverter circuit 3
The current detection circuit 20 is connected to both ends. The current detection circuit 20 has a forward current detection circuit 21 and a reverse current detection circuit 22.

The forward current detecting circuit 21 detects a normal forward current I ₁ flowing through the shunt resistor 8 and determines whether or not the detected current I ₁ exceeds a set value Ia. The reverse current detection circuit 22 detects a current I ₂ flowing in the shunt resistor 8 in a direction opposite to the normal direction, and determines whether the detected current I ₂ exceeds a set value Ib.

The outputs of the forward current detecting circuit 21 and the reverse current detecting circuit 22 are sent to an abnormality detecting circuit 23. When the forward current detection circuit 21 determines that the detection current I ₁ is equal to or greater than the set value Ia, the abnormality detection circuit 23 determines that the reverse current detection circuit 22 determines that the detection current I ₂ is greater than or equal to the set value Ib. Are performed, each of them is determined to be abnormal, and an abnormality detection command is sent to the control unit 30.

Upon receiving the abnormality detection command from the abnormality detection circuit 23, the control unit 30 immediately stops the driving of the switching circuit 5, and resumes the driving of the switching circuit 5 a predetermined time after that.

FIG. 2 shows a specific example of the forward current detecting circuit 21 and the reverse current detecting circuit 22. Forward current detection circuit 2
Reference numeral 1 denotes a configuration in which the voltage across the shunt resistor 8 due to the forward current I ₁ is applied to the light emitting diode 41a of the photocoupler 41 through an integrating circuit, and when the forward current I ₁ exceeds the set value Ia, the light emitting diode 41a Emits light. Reverse current detector circuit 22 is configured to apply a voltage across the shunt resistor 8 by reverse current I ₂ in the light emitting diode 51a of the photocoupler 51 through the integrating circuit, a situation where the reverse current I ₂ exceeds the set value Ib , The light emitting diode 51a emits light.

Although not shown, the photocouplers 41 and 51 include phototransistors that operate by receiving light from the light emitting diodes 41a and 51a, and these phototransistors are provided in the abnormality detection circuit 23 as a notification unit.

Since it is difficult to cause the light emitting diodes 41a and 51a to emit light only by the voltage generated at the shunt resistor 8, a battery power supply 60 for assisting the operating voltage is provided in the current detection circuit 20.

Next, the operation of the above configuration will be described with reference to the flowchart of FIG. First, in order to perform two-phase energization from the phase winding Lu to the phase winding Lv, two transistors, the upstream transistor Tu + and the downstream transistor Tv-, are turned on. And the transistor T on the upstream side
u + is turned on, and the downstream transistor Tv- is turned on and off.

When a magnetic field is generated in the phase windings Lu and Lv, a rotational torque is generated in the rotor due to an interaction between the magnetic field and the magnetic field generated by the permanent magnet, and the rotor starts to rotate. At this time, a voltage is induced in one of the non-energized phase windings Lw due to the magnetic action accompanying the rotation of the permanent magnet. The induced voltage to the phase winding Lw is compared with the reference voltage Vd in the comparator 13, and the comparison output is sent to the control unit 30. The control unit 30 changes the logical level of the comparison output (the induced voltage and the reference voltage Vd).
Are detected as the reference position for the rotation of the rotor.

When the rotation reference position is detected, the phase winding Lu, L
The commutation from the two-phase energization to v to the two-phase energization to the phase windings Lu and Lw is performed.

That is, in order to carry out two-phase conduction from the phase winding Lu to the phase winding Lw, the upstream transistor T
The two timings of u + and the transistor Tw− on the downstream side are the ON timing. The transistor Tu + on the upstream side is turned on and off, and the transistor Tw- on the downstream side is turned on.

When a magnetic field is generated in the phase windings Lu and Lw, a rotational torque is generated in the rotor due to an interaction between the magnetic field and the magnetic field generated by the permanent magnet, and the rotor continues to rotate. At this time, due to the magnetic action accompanying the rotation of the permanent magnet, one phase winding L
A voltage is induced in v. The induced voltage on the phase winding Lv is compared with the reference voltage Vd in the comparator 12, and the comparison output is sent to the control unit 30. The control unit 30 detects a change point of the logical level of the comparison output (a point where the induced voltage and the reference voltage Vd intersect) as a rotation reference position of the rotor.

When the rotation reference position is detected, the phase windings Lu, L
The commutation from the two-phase energization to w to the two-phase energization to the phase windings Lv and Lw is performed.

That is, in order to carry out two-phase conduction from the phase winding Lv to the phase winding Lw, the upstream transistor T
The two timings, v + and the downstream transistor Tw-, are turned on. Then, the upstream transistor Tv + is turned on, and the downstream transistor Tw− is turned on and off.

Similarly, commutation is repeated with a delay of 30 electrical degrees from the detection of the rotation reference position, and the rotation of the rotor is continued. Thus, when the motor 1 is operating, a current flows through the shunt resistor 8. Among these currents, the forward current I ₁ is detected by the forward current detection circuit 21, and the reverse current I ₂ is detected by the reverse current detection circuit 22.

[0032] During normal operation of the motor 1 is not that forward current I ₁ exceeds the set value Ia, also reverse current I ₂ is small. For some reason, the forward current I ₁ becomes excessive,
When it exceeds the set value Ia, an abnormality detection command is sent from the abnormality detection circuit 23 to the control unit 30. Then, the driving of the switching circuit 5 is immediately stopped, and the operation of the motor 1 is stopped. With this stop, the overcurrent is released, and each transistor of the switching circuit 5 is protected.

After a predetermined time from the stop, the driving of the motor 1 is automatically restarted. When step-out occurs in the motor 1, as shown in FIG. 4, the forward current I ₁ (+ side in the figure) increases, and the reverse current I ₂ (− side in the figure) also increases. It has been experimentally confirmed that the increase in the reverse current I ₂ appears remarkably only at the time of step-out.

When the reverse current I ₂ exceeds the set value Ib (for example, 14 A), an abnormality detection command is sent from the abnormality detection circuit 23 to the control unit 30. Then, the driving of the switching circuit 5 is immediately stopped, and the operation of the motor 1 is stopped. By this stop, the reverse current I ₂ is released, and each transistor of the switching circuit 5 is protected.

After a predetermined time from the stop, the driving of the motor 1 is automatically restarted. FIG. 5 shows the current waveform when the operation is stopped based on the increase in the reverse current I ₂ expanded in the time direction.
It is.

FIG. 6 shows a current waveform at the time of step-out in the conventional device. An increase in the forward current (+ side) is detected as an overcurrent, but a reverse current (-side) is detected. I couldn't do that. In this case, the operation of the motor 1 can be temporarily stopped by detecting the overcurrent in the forward direction, but the reverse current has been increasing from before that point, and a considerable load is placed on each transistor of the switching circuit 5. It will take.

On the other hand, in this embodiment, since detecting the increase in the reverse current I ₂ which is a characteristic at the time of loss of synchronism by the reverse current detector circuit 22, it is possible to release the reverse current I ₂ immediately switching It is safe for each transistor of the circuit 5. In the above embodiment, the case where the switching element of the switching circuit 5 is a transistor has been described as an example. However, the present invention can be similarly implemented with other elements.

[0038]

As described above, according to the present invention, detecting means for detecting a current flowing in the switching circuit in a direction opposite to the normal direction, and control means for stopping the operation when the detected current exceeds a set value, Therefore, when a step-out occurs in the motor, it is possible to detect the step-out immediately and to provide a drive control device for a DC brushless motor which is excellent in safety and can protect the elements of the switching circuit.

[Brief description of the drawings]

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

FIG. 2 is a block diagram of a specific example of a current detection circuit in the embodiment.

FIG. 3 is a flowchart for explaining the operation of the embodiment.

FIG. 4 is a waveform chart showing a forward current and a reverse current at the time of step-out in the embodiment.

FIG. 5 is a waveform diagram showing a main part of FIG. 4 in an enlarged manner in a time direction.

FIG. 6 is a waveform diagram showing a forward current and a reverse current at the time of step-out in the conventional device.

[Explanation of symbols]

1: DC brushless motor, 3: Inverter circuit, 4:
Rectifier circuit, 5 switching circuit, 10 position detection circuit, 20 current detection circuit, 21 forward current detection circuit,
22: reverse current detection circuit, 23: abnormality detection circuit, 30
... Control unit.

Claims (1)

(57) [Claims] 1. A DC brushless motor comprising a stator having a plurality of phase windings and a rotor having a permanent magnet, a switching circuit having a plurality of switching elements, and means for applying a DC voltage to the switching circuit. A drive control device for a DC brushless motor that drives the motor by sequentially turning on and off each of the switching elements while detecting the position of the rotor to sequentially switch energization to each phase winding; A drive control device for a DC brushless motor, comprising: detection means for detecting a current flowing in a direction opposite to a normal direction, and control means for stopping operation when the detected current exceeds a set value.