JP5370904B2 - Motor drive circuit - Google Patents

Description

  The present invention relates to a motor drive circuit having a function of overload protection and ground fault protection of a motor such as a brushless DC linear motor.

  When an overload is applied to the motor, a large abnormal current flows, preventing overheating of the motor windings, or a ground fault that causes the potential of a line not at ground potential to fall to ground potential. In order to prevent a ground fault from flowing through an overcurrent, a protection circuit that cuts off by an unbalanced current is provided between the output part of the drive circuit and the motor load (winding).

  For example, in the motor drive circuit shown in FIG. 3, in order to protect the motor from overload, a switching circuit 2 that converts a DC voltage supplied from the main power supply 1 into a drive current of a predetermined frequency by a semiconductor switch element and this drive An alarm fuse 40 having an alarm contact is inserted in the middle of the power supply line 3 for supplying current to the winding of the motor 6, and when the fuse is blown, a spring provided in the fuse holder is expanded, and an alarm contact (auxiliary contact) Is made, the detection circuit 50 detects the disconnection of the fuse, and inputs the detection signal to the control circuit 70 to interrupt the switching operation. However, alarm fuses are expensive, large, and have limited capacity, so it is conceivable to use fuses that are small and inexpensive and do not have alarm contacts.

Further, as shown in FIG. 4, the containers fuse 41 in the middle of the feed line 3 for connecting the winding of the switching circuit 2 and the motor 6 connected to the main power supply 1 is provided, preceding fuse and the control circuit 7 0 The disconnection detection circuit 51 is connected between the current control signal and the difference between the current control signal for driving the motor and the current (actual current) flowing through the power supply line with the detection circuit 51 is compared with the reference value. If it exceeds, that output a fusing detection signal indicating that the fuse 4 1 is blown to the control circuit 70 can be considered. However, with such a detection method, if the current is small, such as during initial setting driving, the differential voltage is always below the reference value, so the motor is restarted after a fuse blown (fuse blown) due to overcurrent. Then, since an overcurrent cannot be detected, there is a problem that the motor is operated in an abnormal state and is damaged.

  In addition to the above, a disconnection detection circuit that does not use an alarm fuse is described in, for example, Patent Documents 1 to 3.

  An electric motor drive device described in Patent Document 1 includes a smoothing circuit unit that absorbs fluctuations in a DC voltage converted by a converter unit that converts commercial power into DC power, and AC power having a desired frequency in a DC manner. An inverter unit for converting to an electric motor, a fuse for preventing an overcurrent from flowing in the motor, a disconnection detection circuit connected in parallel to the fuse, and a CPU for controlling the inverter unit. The AC input photocoupler for detecting the disconnection and the resistor for limiting the current flowing through the diodes 8 to 10 are connected in series.

  In the power conversion device described in Patent Document 2, a main circuit fuse blow detection resistor is connected in parallel to the main circuit fuse, and a signal indicating a change in the voltage between both ends of the resistor is sent to the photocoupler in the control microcomputer unit. The main circuit fuse blown detection signal is taken into the control microcomputer via an insulating circuit part constituted by the above, and the blowout of the main circuit fuse is detected.

  In the fuse blow detection circuit described in Patent Document 3, the secondary circuit has an L output when the power is turned on, and when the fuse is broken, the photo of the first and second photocouplers 3 and 4 is output. Although a potential difference is generated between the transistors, the transistor is prevented from being turned on by eliminating the potential difference. Therefore, the output terminal is in the same L output state as when the power supply is turned on. I am trying to output.

Japanese Patent Laying-Open No. 2007-252170 (page 4, FIG. 1) JP 2003-333860 A (page 4, FIG. 1) Japanese Patent Laying-Open No. 2003-281990 (pages 2 and 3, FIG. 1)

Although the above-described conventional fuse disconnection detection circuit can detect the fusing of a fuse without using an alarm fuse, the following points are desired to be improved. In the disconnection detection circuit described in Patent Document 1, a photocoupler is connected to a main power supply (high voltage) via an inverter (operated by current from the main power supply), and because of the high voltage, a fuse is caused by overcurrent. It is dangerous to operate the inverter unit after a break has occurred, with secondary damage such as an electric shock, but if the inverter unit is not operated, it is impossible to detect the disconnection of the fuse due to overcurrent. Even when the inverter is operating, if all the fuses are disconnected or the power supply line to the motor winding is interrupted due to disconnection or loosening of the power plug, no current flows through the diode of the photocoupler and the disconnection detection circuit operates. Since it does not operate, there is a problem that the disconnection of the fuse cannot be detected.

  The disconnection detection circuit described in Patent Document 2 has a problem that the disconnection between the inverter unit and the motor cannot be detected because the main circuit fuse is connected between the rectifier and the inverter unit.

  The disconnection detection circuit described in Patent Document 3 has a problem that the cost increases because photocouplers are provided in the front and rear stages of the fuse.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a motor drive circuit capable of reliably detecting a disconnection of a fuse by using a fuse having no disconnection detection function.

  In order to achieve the above object, a motor drive circuit according to the present invention includes a switching circuit that generates a drive current by switching a DC voltage obtained by rectifying a commercial AC power supply, and the switching circuit and a motor winding. A fuse in a container inserted in the middle of a power supply line connecting between the two, a disconnection detection circuit connected in parallel with the fuse, and an operation of the drive switch based on a detection signal of the disconnection detection circuit In the motor drive circuit having a control circuit, the disconnection detection circuit includes a DC power supply, a photocoupler including a light emitting diode connected to the DC power supply, a phototransistor that outputs a detection signal to the control circuit, and an output of the light emitting diode. It has a resistor connected in series to the terminal and a diode whose cathode side is connected to the feed line. The one in which the features.

  In the present invention, the switching circuit is connected to each winding of a linear motor having a three-phase winding, and the disconnection detection circuit can be provided in parallel with a fuse inserted in the middle of each power supply line.

  According to the present invention, the disconnection detection circuit is connected in series to a DC power supply, a photocoupler including a light emitting diode connected to the DC power supply, a phototransistor that outputs a detection signal to the control circuit, and an output terminal of the light emitting diode. Therefore, the disconnection detection signal can be output only when the fuse is blown by an overcurrent, thereby improving the reliability of the disconnection detection circuit. it can. Further, when applied to a linear motor having a plurality of loads (multi-phase coils), an overcurrent can be detected even when all the fuses provided in each power supply line are blown.

  Hereinafter, details of the present invention will be described with reference to the accompanying drawings.

  FIG. 1 is a diagram showing a drive circuit according to a first embodiment of the present invention, and FIG. 2 is a diagram showing a drive circuit according to a second embodiment of the present invention.

[First Embodiment]
As shown in FIG. 1, the drive circuit includes a power supply circuit 1 (converter) that obtains a DC voltage by smoothing an AC voltage (for example, three-phase 200 V) supplied from a commercial AC power source after full-wave rectification, and this DC voltage. A switching circuit 2 for converting the alternating current voltage (drive current) to a predetermined frequency; a feed line 3 for supplying the drive current to a load (winding of the motor 6); and a fuse 4 connected in the middle of the feed line 3; And a disconnection detection circuit 5 for detecting that it has blown, and a control circuit 7 for outputting a detection signal output from the disconnection detection circuit 5 to the switching circuit 2.

  Each part of the drive circuit can be configured as follows, for example. As the fuse 4, it is possible to use a commercially available fuse with a conductor portion housed in an insulating container such as a glass tube or a ceramic tube.

  The switching circuit 2 includes switching elements that are turned on and off by direct current output from the power supply circuit 1, for example, MOSFETs 21 and 22, and is an inverter that converts a direct current into an alternating current of a predetermined or variable frequency to generate a drive current.

  The disconnection detection circuit 5 is connected in parallel with the fuse 4, a DC power source 8 connected to the front stage of the fuse 4, a photocoupler 9 including a light emitting diode 91 and a phototransistor 92, a resistor 10, and a rear stage of the fuse 4. A diode 11 is connected on the cathode side, and these components are connected in series.

  The control circuit 7 applies the disconnection detection signal output from the disconnection detection circuit 5 to the switching circuit 2 and controls its operation. That is, when a normal drive current is supplied to the motor, the control circuit 7 applies a positive voltage to the gate of the MOSFET and a current flows from the drain to the source (the drive current flows to the power supply line). On the other hand, when a disconnection detection signal is input, no voltage is applied to the gates of the MOSFETs 21 and 22 so that the drive current does not flow through the power supply line.

  The operation of the disconnection detection circuit 5 is as follows.

  When the fuse 4 is not blown, the potentials at both ends of the fuse 4 are the same, so that a current flows through the light emitting diode 91, the phototransistor 92 is turned on, and the photocoupler 9 is activated, so that the control circuit 7 No disconnection detection signal (H level voltage) is output. Therefore, the drive current output from the switching circuit 2 is supplied from the power supply line 3 to the motor 6 as it is.

  When the drive current becomes excessive and the fuse 4 is blown, the current from the DC power supply 8 to the light emitting diode 91 is cut off, so that the light emitting diode 91 is turned off and the phototransistor 92 is turned off. Accordingly, a disconnection detection signal is output from the phototransistor 92. When this disconnection detection signal is input to the control circuit 7, the switching operation of the switching circuit 2 is interrupted, so that the motor 6 can be stopped. Here, the current from the plus (+) side of the DC power supply 8 flows from the anode to the cathode of the light-emitting diode 91 and restricts the current via the resistor 10, and is connected to the anode side of the diode 11 to connect the fuse 4 from the cathode side. The motor returns to the minus (−) side of the DC power source 8 via the, so that the motor operation is not hindered.

  Since the disconnection detection circuit 5 uses an inexpensive and compact fuse that does not have an alarm contact, the drive circuit can be reduced in cost and size. In particular, since the motor operates with a DC power supply that is different from the power supply circuit for supplying drive current to the motor, the motor is not connected due to poor connection of the wiring system (for example, poor contact between the plug and socket or disconnection of the plug). When stopped, the disconnection detection signal that detects the blow of the fuse is not output, and the disconnection detection signal can be output only when the fuse is blown by an overcurrent, improving the reliability of the disconnection detection circuit be able to.

  Further, even when the motor operation is stopped (the switching circuit does not operate), disconnection can be detected, and safety can be improved. Further, there is an advantage that even when the drive current during the initial setting drive is small, it is possible to reliably detect that the fuse is blown by operating the disconnection detection circuit 5.

[Second Embodiment]
An example in which the above drive circuit is applied to a brushless DC linear motor having a plurality of movers (multiphase coils) will be described with reference to FIG. In FIG. 2, parts having the same functions as those in FIG. 1 are denoted by the same reference numerals except for subscripts (alphabet letters). This linear motor is, for example, a movable coil type linear motor having a permanent magnet as a field magnet and an armature having a multiphase coil (for example, a three-phase coil) as a mover, and a sine wave (for example, a phase difference of 120 degrees). Sine wave).

  The drive circuit shown in FIG. 2 includes power supply lines 3a, 3b, and 3c that connect the switching circuits 2a, 2b, and 2c connected to the power supply circuit 1 and coils of each phase (U phase, V phase, and W phase) of the motor. It has fuses 4a, 4b, 4c connected in the middle, disconnection detection circuits 5a, 5b, 5c, and a control circuit 7 for controlling the drive of the motor.

[Switching circuit]
The switching circuit 2a includes switching elements such as MOSFETs 21a and 22a that are turned on / off by a direct current obtained by smoothing an alternating current (for example, three-phase 200V) supplied from a commercial alternating-current power supply after full-wave rectification. The switching circuit 2a, for example, compares a carrier signal (such as a sawtooth wave or a triangular wave) with a reference voltage by a comparator, generates a PWM signal (a pulse width modulated control signal) based on the difference voltage, and based on this PWM signal, the MOSFET 21a , 22b can be alternately turned on and off to obtain a drive current having a predetermined frequency. Since the other switching circuits 2b and 2c have the same configuration as the switching circuit 2a, the description thereof is omitted.

[Disconnection detection circuit]
The disconnection detection circuit 5a includes a DC power supply 8a connected to the front stage of the fuse 4, a photocoupler 9a including a light emitting diode 91a and a phototransistor 92a, a resistor 10a, and a diode 11a connected in series therewith, and the fuse 4a The cathode side of the diode 11a is connected to the subsequent stage. Since the other disconnection detection circuits 5b and 5c have the same configuration as the disconnection detection circuit 5a, description thereof is omitted.

  The operation of the disconnection detection circuit 5a (same for 5b and 5c) is as follows.

  When the fuse 4a is not blown, the potentials at both ends of the fuse 4a are the same, so that a current flows through the light emitting diode 91a, the phototransistor 9b is turned on, the photocoupler 9 is activated, and the control circuit 7 is turned on. No disconnection detection signal (H level voltage) is output. Therefore, the drive current output from the switching circuit 2a is supplied as it is from the power supply line 3a to the load 60a.

  When the drive current becomes excessive and, for example, the fuse 4a is blown, the current of the light emitting diode 91a is cut off from the DC power supply 8a, so the light emitting diode 91a is turned off and the phototransistor 92b is turned off. Therefore, a disconnection detection signal is output from the phototransistor 91b. When this disconnection detection signal is input to the control circuit 7, the switching operation of the switching circuit 2a is interrupted, so that the motor can be stopped.

  As described above, the disconnection detection circuit shown in FIG. 2 is not limited to the case where any of the fuses 4a, 4b, 4c is blown, and can reliably detect even when all the fuses are blown. The motor can be prevented from being damaged due to abnormal operation. Further, it is possible to reliably detect that the fuse has been blown even when the drive current during the initial setting drive is small.

It is a figure which shows the drive circuit for motors concerning the 1st Embodiment of this invention. It is a figure which shows the drive circuit for motors concerning the 2nd Embodiment of this invention. It is a figure which shows the example of the conventional motor drive circuit. It is a figure which shows the other example of the conventional motor drive circuit.

Explanation of symbols

1: power supply circuit, 2, 2a, 2b, 2c: switching circuit, 21, 21a, 21b, 21c, 22, 22a, 22b, 22c: MOSFET, 3: power supply line, 4: fuse in container, 5: disconnection detection circuit , 6: motor, 60a, 60b, 60c: coil, 7: control circuit, 8: DC power supply, 9, 9a, 9b, 9c: photocoupler, 91, 91a, 91b, 91c: photodiode, 92, 92a, 92b , 92c: phototransistor, 10, 10a, 10b, 10c: resistor, 11, 11a, 11b, 11c: diode

Claims (2)

A power supply circuit that generates a DC voltage obtained by rectifying a commercial AC power supply, a switching circuit that generates a drive current by switching the DC voltage, and a power supply that connects the switching circuit and a motor winding possess a fuse inserted in the middle of the line, and disconnection detecting circuit for detecting that the fuse is blown, and a control circuit for controlling the switching operation based on a detection signal of the disconnection detecting circuit, wherein the disconnection detection emitting circuit is connected in parallel with the fuse, which is connected to a DC power source for operating the disconnection detecting circuit connected to the power supply line of the switching circuit side with respect to the fuse, in series with the DC power supply a photocoupler consisting of a phototransistor to output a diode and the detection signal to the control circuit, the light emitting diode Motor, characterized in that it comprises a resistor connected in series to a de output terminal, and said cathode-side are connected in series to the resistor is connected to the power supply line of the winding side of the motor with respect to the fuse diode Drive circuit. Winding of the motor is a winding of each phase of the linear motor having three-phase windings, connecting the disconnection detection circuit to the feeding line which connects the windings of the respective phases and the switching circuit 2. The motor drive circuit according to claim 1, wherein:

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