JP2009278734A - Voltage control circuit and motor driving device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a voltage control circuit and a motor driving device which prevent direct-current voltage raised by regenerative power from fluctuating with repeated increase and decrease and prevents a motor rotationally driven by a drive circuit supplied with direct-current voltage from being repeatedly accelerated and decelerated. <P>SOLUTION: When direct-current voltage Ea exceeds a predetermined voltage and divided voltage Eb from a voltage divider circuit 31 exceeds a Zener voltage Ez of a Zener diode 36, a PNP transistor 34 operates in an active region and a voltage detection circuit 30 outputs detection voltage corresponding to the divided voltage Eb. The detection voltage from the voltage detection circuit 30 is input to the gate of an FET 42 in a discharge circuit 40 through a diode 43. A braking resistor 41 and the FET 42 are connected in series between direct current buses P and N. The amount of current Ibr flowing through the braking resistor 41 is linearly adjusted by the FET 42 according to the detection voltage. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a voltage control circuit that suppresses a DC voltage of a power supply circuit that supplies power to a drive circuit that drives a motor from being increased due to regenerative power from the motor, and a motor drive device including the voltage control circuit. .

  FIG. 3 is a circuit diagram showing a configuration of a conventional motor driving device. In the figure, reference numeral 101 denotes a motor drive device, which is supplied with an AC voltage from an AC power supply 70 and drives a brushless DC motor 80 with a speed reducer. The AC power source 70 is connected to the three input terminals R, S, and T of the motor driving device 101 and supplies a three-phase AC voltage to the motor driving device 101. The brushless DC motor 80 with a speed reducer has a speed reducer 82 attached to the output shaft of the brushless DC motor 81. The brushless DC motor 81 is rotationally driven by a three-phase driving voltage or driving current of U phase, V phase and W phase input from the motor driving device 101.

  The motor drive device 101 includes a converter circuit 10 that converts an AC voltage from the AC power supply 70 into a DC voltage, a smoothing capacitor 20 that smoothes the converted DC voltage, and a drive voltage or drive current that drives the brushless DC motor 81. An output inverter circuit 50 is provided. In addition, the conventional motor drive device 101 operates the voltage control circuit 140 that suppresses the DC voltage output from the converter circuit 10 from being increased by the regenerative power from the brushless DC motor 81 and the voltage control circuit 140 to operate. The control power supply circuit 130 is provided.

  The AC voltage of the three-phase AC supplied from the AC power supply 70 is rectified by the converter circuit 10, and the rectified DC voltage is supplied to each circuit of the motor driving device 101 via two power supply wirings. In the following, of the two power supply wirings, the high-potential side output wiring is referred to as a DC bus P, and the low-potential side output wiring is referred to as a DC bus N. The DC voltage output from the converter circuit 10 is smoothed by the smoothing capacitor 20 connected between the DC buses P and N and supplied to the inverter circuit 50. The inverter circuit 50 is turned on / off in accordance with a control signal supplied from a control circuit (not shown), converts the input DC voltage into a three-phase driving voltage or driving current, and outputs it to the brushless DC motor 81. As a result, the brushless DC motor 81 rotates.

  The brushless DC motor 81 generates regenerative power when a load torque is applied in the rotation direction or when a load having a large inertia is decelerated. The regenerative power generated by the brushless DC motor 81 returns to the inverter circuit 50 and charges the smoothing capacitor 20 through the diode in the inverter circuit 50, so that the DC voltage between the DC buses P and N rises.

  The conventional voltage control circuit 140 includes a braking resistor 141 and an NPN bipolar transistor (hereinafter referred to as an NPN transistor) 142 connected in series between the DC buses P and N. Specifically, one end of the braking resistor 141 is connected to the DC bus P, the other end is connected to the collector of the NPN transistor 142, and the emitter of the NPN transistor 142 is connected to the DC bus N. Further, a protective diode 143 is connected in parallel to the NPN transistor 142 (the cathode of the diode 143 is connected to the collector of the NPN transistor 142, and the anode of the diode 143 is connected to the emitter of the NPN transistor 142). ). Further, although not shown, the voltage control circuit 140 includes a circuit that detects a DC voltage between the DC buses P and N and drives the NPN transistor 142 according to the detection result. This circuit determines an increase in the DC voltage between the DC buses P and N by comparing the DC voltage supplied from the control power supply circuit 130 with the DC voltage between the DC buses P and N.

  4A and 4B are schematic diagrams for explaining the operation of the conventional voltage control circuit 140. FIG. 4A shows a change in the DC voltage Ea between the DC buses P and N, and FIG. 4B shows a brake resistor 141 in FIG. The change of the flowing current Ibr is shown. When the brushless DC motor 81 is normally rotating, the DC voltage Ea is maintained at the voltage value e1. When a regenerative current is generated in the brushless DC motor 81 and the DC voltage Ea rises and reaches the voltage value e3 (see t1, t3, t5,... Ty in the figure), the voltage control circuit 140 includes the NPN transistor 142. Is made conductive. As a result, when the current flows through the braking resistor 141 and the DC voltage Ea decreases and the DC voltage Ea falls below the voltage value e2 (see t2, t4, t6,..., Tz in the figure), the voltage control circuit 140 is The NPN transistor 142 is turned off, and the current flowing through the braking resistor 141 is cut off. Therefore, the voltage control circuit 140 can suppress fluctuations due to regenerative power so that the DC voltage Ea does not exceed the voltage value e3.

  In Patent Document 1, voltage detection means for outputting an output voltage corresponding to voltage fluctuation of a DC circuit, voltage comparison means for comparing the output voltage and the voltage of the DC circuit, and output of the amplified voltage comparison means There has been proposed a voltage suppression circuit that includes a semiconductor switch that operates in response to a voltage and a suppression resistor that is connected to and disconnected from the DC circuit by the semiconductor switch. Compared to the conventional circuit, this voltage suppression circuit can omit the insulation of the circuit that controls the suppression resistor and the hysteresis of the comparator, so that the cost can be greatly reduced.

  In Patent Document 2, a regenerative power consumption circuit composed of a series circuit of a first resistor and a voltage control element connected in parallel between both ends of a smoothing capacitor in a DC power supply circuit, and a parallel connection between both ends of the smoothing capacitor. A series circuit of the zener diode and the second resistor, and conduction means for driving the voltage control element of the regenerative power consumption circuit to conduct when the voltage difference between both ends of the second resistor is equal to or greater than a predetermined value. An electric motor control circuit has been proposed. In this control circuit, when the power supply voltage is increased by the regenerative power and the voltage across the second resistor becomes equal to or higher than the set value, the voltage control element is driven to conduct, and the regenerative current flows through the first resistor. The regenerative power is consumed in the resistor, and it is possible to avoid the voltage immediately after the regenerative operation from being significantly higher than the supply power voltage.

In Patent Document 3, current detection means for detecting the direction and current value of a current output from a converter unit that converts alternating current into direct current, regenerative power discharging means for discharging regenerative power, and detection signals of the current detection means Based on this, an inverter device has been proposed that includes a control unit that operates a regenerative power discharging unit when the direction of current is on the regeneration side and the current value exceeds a set value. Since this inverter device performs on / off control of the regenerative power discharging means in accordance with the direction and current value of the main circuit current, it is possible to suppress the increase and fluctuation range of the main circuit voltage even during the deceleration operation.
JP 59-110385 A Japanese Patent Laid-Open No. 2-74182 JP-A-5-344742

  In the conventional motor drive device 101 shown in FIG. 3, when the DC voltage Ea rises due to regenerative power as shown in FIG. 4, the DC voltage Ea fluctuates between the voltage values e2 and e3 and repeats increasing and decreasing. For example, when the motor driven by the motor drive device 101 is an induction motor, and the motor drive device 101 is configured to control the frequency of the induction motor (the rotational speed is controlled by the frequency), the DC voltage Ea is shown in FIG. Even if it fluctuates in this way, the rotation speed does not fluctuate.

  However, when the motor driving device 101 drives the brushless DC motor 81, the rotational speed of the brushless DC motor 81 varies according to the DC voltage Ea. Therefore, when the DC voltage Ea repeatedly increases and decreases as shown in FIG. The DC motor 81 repeats acceleration and deceleration. Particularly in this case, since the DC voltage Ea is higher than the voltage value e1 at which the brushless DC motor 81 performs normal rotation, the brushless DC motor 81 repeatedly accelerates and decelerates at a higher rotational speed or rotational speed than usual. .

  The brushless DC motor 80 with a speed reducer has a gear wheel that meshes with a pinion provided on the output shaft of the brushless DC motor 81, for example, in order to make the rotational speed and torque of the brushless DC motor 81 suitable for actual use. The brushless DC motor 81 and the speed reducer 82 are integrated. Since the brushless DC motor 80 with a reduction gear is often used when driving a load having a large inertia, the regenerative power is periodically generated, the voltage control circuit 140 is operated, the DC voltage Ea repeatedly increases and decreases, and the brushless The DC motor 81 often repeats acceleration and deceleration.

  When the brushless DC motor 81 repeatedly accelerates and decelerates, the tooth surface of the pinion provided on the output shaft of the brushless DC motor 81 and the tooth surface of the gear wheel of the speed reducer 82 that meshes with the pinion tooth surface. For this reason, there is a possibility that the pinion and the gear wheel are deteriorated and destroyed, and there is a problem that the life of the brushless DC motor 80 with a reduction gear is shortened. Further, when the brushless DC motor 81 repeatedly accelerates and decelerates, the output shaft of the speed reducer 82 repeatedly accelerates and decelerates accordingly, so that there is a possibility that the output shaft of the speed reducer 82 and the fastening portion of the mechanical load are deteriorated. .

  In addition, the conventional voltage control circuit 140 needs to appropriately select the resistance value of the braking resistor 141 in order to suppress pinion of the brushless DC motor 80 with a reduction gear and gear wheel rattling. FIG. 5 is a schematic diagram for explaining the operation when the resistance value of the braking resistor 141 is reduced in the conventional voltage control circuit 140. FIG. 5A shows the change in the DC voltage Ea between the DC buses P and N. FIG. (B) shows the change in the current Ibr flowing through the braking resistor 141. When the resistance value of the braking resistor 141 is reduced, the current Ibr flowing through the braking resistor 141 increases, so that the DC voltage Ea decreases more quickly and the brushless DC motor 81 decelerates faster. Therefore, when the resistance value of the braking resistor 141 is reduced, pinion and gear wheel rattling are more likely to occur, and the brushless DC motor 80 with a reduction gear is more likely to be deteriorated and destroyed. On the contrary, when the resistance value of the braking resistor 141 is increased, there is a possibility that the increase of the DC voltage Ea cannot be sufficiently suppressed when the regenerative power generated by the brushless DC motor 81 is large. For this reason, there is a problem that the resistance value of the braking resistor 141 must be selected in consideration of the characteristics of the load driven by the brushless DC motor 80 with a speed reducer.

  When the AC power supply 70 is stopped and no AC voltage is supplied to the motor drive device 101, when the brushless DC motor 80 with a reduction gear is rotated by an external force, the brushless DC motor 81 acts as a generator, Since the generated power charges the smoothing capacitor 20 through the diode of the inverter circuit 50, the DC voltage Ea rises. However, in the conventional motor drive device 101, the control power supply circuit 130 cannot operate unless the AC voltage is supplied from the AC power supply 70, and the voltage control circuit 140 cannot be operated. There is a problem that you can not.

  Since the voltage suppression circuit described in Patent Document 1 is configured to turn on / off the semiconductor switch and control the connection / disconnection of the suppression resistor, the DC voltage fluctuates similarly to the conventional motor driving device 101 described above. May occur. Since the control circuit for the electric motor described in Patent Document 2 is also configured to flow a regenerative current through the first resistor by turning on a transistor which is a voltage control element, there is a possibility that the DC voltage fluctuates similarly. Further, the inverter device described in Patent Document 3 is said to be able to keep the fluctuation range of the DC voltage narrow by controlling so as to increase the regenerative power discharge operation duty in proportion to the detected current value. However, details of such a control method are not mentioned.

  The present invention has been made in view of such circumstances, and an object of the present invention is to output a detection voltage corresponding to the voltage value of the DC voltage when the DC voltage exceeds a predetermined voltage. In this configuration, the DC voltage is adjusted by linearly adjusting the energization amount of the resistor in accordance with the detected voltage so that the DC voltage increased by regenerative power does not fluctuate repeatedly. Another object of the present invention is to provide a voltage control circuit capable of preventing a motor driven to rotate by a drive circuit to which a DC voltage is supplied from repeating acceleration and deceleration.

  Another object of the present invention is to provide a configuration in which a bipolar transistor outputs a detection voltage in accordance with a potential difference between a divided voltage obtained by dividing a DC voltage and a Zener voltage of a Zener diode. When the DC voltage fluctuates beyond the predetermined voltage specified by the above, it is possible to output a linear detection voltage corresponding to the fluctuation of the DC voltage, and linearly adjust the energization amount of the resistor of the discharge circuit Another object of the present invention is to provide a voltage control circuit that can output a detection voltage for the voltage detection circuit.

  Another object of the present invention is to provide a configuration in which a field effect transistor as an adjustment element connected in series to a resistor for discharging is operated linearly in accordance with a detected voltage, thereby energizing the resistor. An object of the present invention is to provide a voltage control circuit capable of linearly adjusting the amount.

  Another object of the present invention is to provide a configuration including the above-described voltage control circuit in addition to a power supply circuit that converts an AC voltage into a DC voltage and a drive circuit that drives the motor by supplying the DC voltage. Thus, a motor drive device that suppresses a voltage increase due to regenerative power, prevents a DC voltage from fluctuating repeatedly, and prevents a motor driven to rotate by a drive circuit from repeatedly accelerating and decelerating is provided. It is in.

  The voltage control circuit according to the present invention is a voltage control circuit that suppresses a voltage increase caused by regenerative power from the motor of a DC voltage supplied from a power supply circuit to a motor drive circuit, and the DC voltage exceeds a predetermined voltage. A voltage detection circuit that outputs a detection voltage corresponding to the DC voltage, a resistor connected between a high-potential side output and a low-potential side output of the power supply circuit, and a detection voltage of the voltage detection circuit And a discharge circuit having an adjustment element for linearly adjusting the energization amount of the resistor.

  In the present invention, the voltage detection circuit for detecting the fluctuation of the DC voltage supplied to the motor drive circuit outputs a detection voltage corresponding to the voltage value when the DC voltage exceeds a predetermined voltage. That is, when the DC voltage exceeds a predetermined voltage, the detection voltage output from the voltage detection circuit is a linear voltage value corresponding to the voltage value of the DC voltage. A discharge circuit having a resistor connected between a high potential output and a low potential output of a power supply circuit to discharge a DC voltage linearly varies the amount of current flowing to the resistor according to the detection voltage output by the voltage detection circuit. To adjust the DC voltage. Rather than digitally controlling the energization of the resistor as a conduction / non-conduction, steep fluctuations in the DC voltage can be suppressed by linearly adjusting the energization amount according to the detected voltage. As a result, the voltage increase of the DC voltage can be suppressed so that the DC voltage increased by the regenerative power does not fluctuate repeatedly.

  Further, in the voltage control circuit according to the present invention, the voltage detection circuit has one end connected to a voltage dividing circuit that divides the DC voltage, a Zener diode that defines the predetermined voltage, and a voltage dividing point of the voltage dividing circuit. A resistor having the other end connected to the cathode of the Zener diode; an emitter connected to the voltage dividing point of the voltage dividing circuit; a base connected to the cathode of the Zener diode; And a PNP-type bipolar transistor that outputs the detection voltage from a collector in accordance with a voltage difference.

  In the present invention, the voltage detection circuit operates the bipolar transistor in the active region using the voltage dividing circuit for dividing the DC voltage and the Zener diode. Specifically, the emitter of the bipolar transistor is connected to the voltage dividing point of the voltage dividing circuit, the base of the bipolar transistor is connected to the cathode of the Zener diode, and the base and emitter of the bipolar transistor are connected by a resistor. As a result, a voltage across the resistor (potential difference between the divided voltage of the voltage dividing circuit and the Zener voltage of the Zener diode) is applied between the base and emitter of the bipolar transistor, and the detection voltage corresponding to the divided voltage is applied to the bipolar transistor. Output from the collector. Therefore, the voltage detection circuit is a voltage corresponding to the divided voltage obtained by dividing the DC voltage when the DC voltage exceeds the predetermined voltage and the potential difference between the divided voltage and the Zener voltage exceeds the threshold voltage for operating the bipolar transistor. Can be output as a detection voltage. The detection voltage output from the voltage detection circuit is not a voltage that changes digitally, but a voltage that changes linearly according to the divided voltage (that is, according to the DC voltage).

  The voltage control circuit according to the present invention is a field effect transistor in which the adjustment element is connected in series to the resistor, and a voltage corresponding to the detection voltage is input to a gate, and the discharge circuit includes the electric field It is characterized by having a resistor and a capacitor connected in parallel between the gate and the source of the effect transistor.

  In the present invention, a field effect transistor is connected in series to a resistor for discharging a direct current voltage, and the detection voltage of the voltage detection circuit is input to the gate of the field effect transistor so that the field effect transistor is in a linear region (or non-linear). Operating in the saturation region). Thereby, the energization amount of a resistor can be adjusted linearly. A resistor and a capacitor are connected in parallel between the gate of the field effect transistor and the low potential side output of the power supply circuit. Thereby, when the output of the detection voltage from the voltage detection circuit is stopped, the electric charge stored in the capacitor is discharged through the resistor, so that the potential of the gate of the field effect transistor can be lowered smoothly.

  The motor drive device according to the present invention includes a power supply circuit that converts an alternating voltage into a direct current voltage and outputs the drive voltage, a drive circuit that is supplied with the direct current voltage output from the power supply circuit and drives the motor, Or a single voltage control circuit.

  In the present invention, the motor drive device includes a power supply circuit that converts an AC voltage into a DC voltage and a drive circuit that drives the motor by supplying the DC voltage, and includes the voltage control circuit described above to control the DC voltage. As a result, the DC voltage does not fluctuate repeatedly, and the voltage control circuit can suppress an increase in the DC voltage due to regenerative power, so that the motor driven by the drive circuit repeats acceleration and deceleration. Absent.

  In the case of the present invention, when the DC voltage exceeds a predetermined voltage, the voltage detection circuit outputs a detection voltage corresponding to the voltage value of the DC voltage, and the discharge circuit energizes the discharging resistor according to the detection voltage. Since the DC voltage increased by the regenerative power can be prevented from fluctuating repeatedly so that the DC voltage rise can be suppressed, the DC voltage is supplied. It is possible to prevent the motor from being driven such that the drive circuit repeats acceleration and deceleration.

  As a result, when the motor driven by the drive circuit is, for example, a brushless DC motor with a speed reducer, the tooth surface of the pinion provided on the output shaft of the motor and the tooth surface of the gear wheel of the speed reducer cause rattling. Therefore, the brushless DC motor with a speed reducer can be prevented from being deteriorated and destroyed, and the life of the brushless DC motor with the speed reducer can be extended. In addition, it is possible to prevent the output shaft of the motor (or the output shaft of the speed reducer) and the fastening portion of the mechanical load from being deteriorated due to repeated acceleration and deceleration of the output shaft. Therefore, the life of the device equipped with the motor and the motor driving device can be extended.

  In the conventional power supply control circuit, it is necessary to appropriately select the resistance value of the resistor that discharges the DC voltage in accordance with the characteristics of the motor and the characteristics of the load that is fastened to the motor. Since the control circuit can perform feedback control so that the DC voltage is constant and linearly adjust the energization amount of the resistor, the DC voltage can be controlled regardless of the resistance value of the resistor. Therefore, it is not necessary to select a resistance value according to the characteristics of the motor and the characteristics of the load, etc., and it is possible to cope with various motors and their loads with one type of resistor. The versatility of the apparatus can be improved.

  Further, the power supply control circuit of the present invention does not require a control power supply circuit provided in the conventional power supply control circuit, and therefore is a case where regenerative power is generated by the motor when the supply of AC voltage is stopped. Moreover, the voltage rise by regenerative electric power can be suppressed.

  Hereinafter, the present invention will be specifically described with reference to the drawings showing embodiments thereof. FIG. 1 is a circuit diagram showing a configuration of a motor drive device according to the present invention. In the figure, reference numeral 1 denotes a motor drive device, which is supplied with an AC voltage from an AC power source 70 and drives a brushless DC motor 80 with a speed reducer. The AC power supply 70 is connected to the three input terminals R, S, and T of the motor driving device 1 and supplies a three-phase AC voltage to the motor driving device 1.

  The brushless DC motor 80 with a speed reducer is obtained by, for example, attaching a speed reducer 82 having a gear wheel that meshes with a pinion provided on the output shaft of the brushless DC motor 81, and integrating the brushless DC motor 81 and the speed reducer 82. The rotational speed and torque of the brushless DC motor 81 can be made suitable for actual use by the speed reducer 82. The brushless DC motor 81 is rotationally driven by a three-phase driving voltage or driving current of U phase, V phase, and W phase input from the motor driving device 1. The brushless DC motor 81 has a built-in position detector that detects the position of the rotor. The detection result of the position detector is fed back to the motor driving device 1, so that the motor driving device 1 is connected to the brushless DC motor 81. However, the position detector of the brushless DC motor 81 and the feedback path to the motor driving device 1 are not shown.

  The motor drive device 1 includes a converter circuit 10 that converts an AC voltage from an AC power supply 70 into a DC voltage, a smoothing capacitor 20 that smoothes the converted DC voltage, and a drive voltage or drive current that drives the brushless DC motor 81. An output inverter circuit 50 is provided. Further, the motor drive device 1 according to the present invention includes a voltage control circuit 3 that suppresses an increase in the DC voltage output from the converter circuit 10 due to regenerative power from the brushless DC motor 81. 3 includes a control power supply circuit 130 for operating the voltage control circuit 140. The voltage control circuit 3 according to the present invention requires such a control power supply circuit. And not.

  The AC voltage of the three-phase AC supplied from the AC power supply 70 is rectified by the converter circuit 10, and the rectified DC voltage is output from two power supply wirings, and each circuit of the motor drive device 1 is connected via these wirings. Supplied to. In the following description, of the two power supply wirings, the high potential side output wiring is referred to as a DC bus P, and the low potential side output wiring is referred to as a DC bus N. The converter circuit 10 includes six diodes 11 to 16, and two diodes 11 and 12, two diodes 13 and 14, and two diodes 15 and 16 connected in series are connected to a DC bus. This is a configuration of a full-wave rectifier circuit connected in parallel between P and N. Specifically, the cathode of the diode 11 is connected to the DC bus P, the anode of the diode 11 is connected to the cathode of the diode 12 and the input terminal R, and the anode of the diode 12 is connected to the DC bus N. The cathode of the diode 13 is connected to the DC bus P, the anode of the diode 13 is connected to the cathode of the diode 14 and the input terminal S, and the anode of the diode 14 is connected to the DC bus N. Similarly, the cathode of the diode 15 is connected to the DC bus P, the anode of the diode 15 is connected to the cathode of the diode 16 and the input terminal T, and the anode of the diode 16 is connected to the DC bus N. Since the diodes 11 to 16 always apply a voltage to the DC buses P and N in the same direction, the AC voltage from the AC power supply 70 can be rectified by the converter circuit 10 and converted into a DC voltage. .

  The DC voltage that has been full-wave rectified and output by the converter circuit 10 is smoothed by the smoothing capacitor 20 connected between the DC buses P and N, and is supplied to the inverter circuit 50. Since the output voltage that has been full-wave rectified by the converter circuit 10 has a pulsating component, the smoothing of the smoothing capacitor 20 can supply a DC voltage having no (or little) pulsating component to the inverter circuit 50.

  The inverter circuit 50 includes six NPN transistors 51 and diodes 52. Two pairs of NPN transistors 51 connected in series are connected in parallel between the DC buses P and N, respectively. A diode 52 is connected to the NPN transistor 51 in parallel. Specifically, the collector of one NPN transistor 51 is connected to the DC bus P, the emitter of this NPN transistor 51 is connected to the collector and output terminal of another NPN transistor, and the emitter of the other NPN transistor 51 is connected to the DC bus N. Three connected series circuits are connected in parallel. Each NPN transistor 51 has a collector connected to the cathode of a diode 52 and an emitter connected to the anode of the diode 52.

  The base of each NPN transistor 51 is connected to a control circuit (not shown), and each NPN transistor 51 is turned on / off in accordance with a control signal supplied from the control circuit. The control circuit generates six control signals based on the detection result of the above-described position detector built in the brushless DC motor 81 and outputs the generated control signals to each NPN transistor 51. As a result, the six NPN transistors 51 are turned on / off at an appropriate timing, and three-phase drive voltages or drive currents of the U phase, the V phase, and the W phase can be output to the brushless DC motor 81.

  When the brushless DC motor 80 with a speed reducer is normally rotated (powering), the AC voltage supplied from the AC power source 70 is rectified by the converter circuit 10 and converted into a DC voltage, and further smoothed by the smoothing capacitor 20. To the inverter circuit 50. The inverter circuit 50 turns on / off the NPN transistor 51 in accordance with a control signal given from the control circuit, converts the given DC voltage into a three-phase drive voltage or drive current, and outputs it to the brushless DC motor 81. As a result, the brushless DC motor 81 rotates.

  The brushless DC motor 81 generates regenerative power when a load torque is applied in the rotation direction or when a load having a large inertia is decelerated. When the regenerative power generated by the brushless DC motor 81 returns to the inverter circuit 50, the current due to the regenerative power charges the smoothing capacitor 20 through the diode 52 and increases the DC voltage between the DC buses P and N. At this time, in the motor drive device 1 according to the present invention, the voltage control circuit 3 can suppress an increase in the DC voltage.

  The voltage control circuit 3 according to the present invention includes a voltage detection circuit 30 that detects an increase in DC voltage, and a discharge circuit 40 that suppresses an increase in DC voltage due to discharge. The voltage detection circuit 30 includes a voltage dividing circuit 31 including two resistors 32 and 33 connected in series between the DC buses P and N. Specifically, the resistor 32 of the voltage dividing circuit 31 has one end connected to the DC bus P and the other end connected to one end of the resistor 33. The resistor 33 of the voltage dividing circuit 31 has one end connected to the other end of the resistor 32 and the other end connected to the DC bus N. The connection point of the resistors 32 and 33 is a voltage dividing point that divides a DC voltage, and the voltage at the voltage dividing point is a divided voltage that forms the output of the voltage dividing circuit 31.

  The voltage dividing point of the voltage dividing circuit 31 is connected to the emitter of a PNP bipolar transistor (hereinafter referred to as a PNP transistor) 34 included in the voltage detecting circuit 30, and the base of the PNP transistor 34 via a resistor 35. Is connected. The cathode of the Zener diode 36 is connected to the base of the PNP transistor 34, and the anode of the Zener diode 36 is connected to the DC bus N. The collector of the PNP transistor 34 forms the output terminal of the voltage detection circuit 30 that mainly controls the detection voltage, and is connected to the discharge circuit 40.

  In the voltage detection circuit 30, when the divided voltage by the voltage dividing circuit 31 exceeds the Zener voltage of the Zener diode 36 (that is, a predetermined voltage defined by the Zener voltage and the resistance value of the voltage dividing circuit 31 is changed to DC. When the voltage exceeds), a base current flows through the PNP transistor 34 according to the voltage difference between both ends of the resistor 35, and the collector voltage according to the divided voltage and the collector-emitter voltage of the PNP transistor 34 is detected voltage. Is output as The detection voltage output from the voltage detection circuit 30 continuously changes as the DC voltage changes when the DC voltage exceeds a predetermined voltage.

  The discharge circuit 40 includes a braking resistor 41 connected in series between the DC buses P and N, and an N-channel field effect transistor (hereinafter referred to as FET (Field Effect Transistor)) 42. Specifically, one end of the braking resistor 41 is connected to the DC bus P, the other end is connected to the drain of the FET 42, and the source of the FET 42 is connected to the DC bus N.

  The detection voltage of the voltage detection circuit 30 is input to the gate of the FET 42 via the diode 43, and a capacitor 44 and a resistor 45 are connected in parallel between the gate and source of the FET 42. Specifically, the collector of the PNP transistor 34 of the voltage detection circuit 30 is connected to the anode of the diode 43, and the cathode of the diode 43 is connected to the gate of the FET 42. One end of the capacitor 44 is connected to the gate of the FET 42, and the other end is connected to the DC bus N. Similarly, one end of the resistor 45 is connected to the gate of the FET 42, and the other end is connected to the DC bus N.

  In the discharge circuit 40, when the detection voltage of the voltage detection circuit 30 is input to the gate of the FET 42 via the diode 43, and the gate voltage exceeds the cut-off voltage of the FET 42, the FET 42 becomes conductive and a drain current flows. When a current flows through the limiting resistor 41, an increase in DC voltage can be suppressed. Since the FET 42 operates linearly according to a continuously changing gate voltage and can linearly change the drain current, the amount of current flowing through the limiting resistor 41 can be adjusted linearly. . Further, by connecting the capacitor 44 and the resistor 45 in parallel between the gate and the source of the FET 42, the gate voltage of the FET 42 can be changed smoothly even when the detection voltage of the voltage detection circuit 30 changes sharply. That is, the detection voltage can be smoothed and input to the FET 42.

  Next, the operation of the voltage control circuit 3 will be described with reference to a voltage waveform, a current waveform, and the like. 2A and 2B are schematic diagrams for explaining the operation of the voltage control circuit 3 according to the present invention. FIG. 2A shows a change in regenerative power generated by the brushless DC motor 80 with a speed reducer, and FIG. The change of the DC voltage Ea between the buses P and N is shown, (c) shows the change of the drain voltage Ed of the FET 42, (d) shows the change of the gate voltage Eg of the FET 42, and (e) shows the braking resistor 41. The change of the current Ibr flowing through is shown.

  In the example shown in FIG. 2A, the period between time 0 and tr is a power running state in which the brushless DC motor 80 with a speed reducer is normally rotating, and no regenerative power is generated. At time tr, the brushless DC motor 80 with a reduction gear shifts to a regenerative state, the regenerative power increases during the period from time tr to t3, and the regenerative power remains constant during the period from time t3 to t4. In the period of t5, the regenerative power decreases. Thereafter, after time t5, the brushless DC motor 80 with a reduction gear shifts to a power running state and no regenerative power is generated. The operation of the voltage control circuit 3 when the brushless DC motor 80 with a speed reducer operates in the example illustrated in FIG. The motor drive device 1 shown in FIG. 1 may cause power loss in each circuit regardless of whether the brushless DC motor 80 with a speed reducer is in a power running state or a regenerative state. Therefore, in the following description, power loss other than in the discharge circuit 40 is ignored. However, in the motor drive device 1, power loss other than in the discharge circuit 40 is sufficiently smaller than power consumption in the braking resistor 41 and the FET 42 of the discharge circuit 40.

  It is assumed that the DC voltage Ea, in which the AC voltage is rectified by the converter circuit 10 and smoothed by the smoothing capacitor 20 during the powering state period from time 0 to tr, has a voltage value e1. At this time, when the divided voltage obtained by dividing the DC voltage Ea by the voltage dividing circuit 31 of the voltage detection circuit 30 is Eb, the divided voltage Eb is Eb <Ez with respect to the Zener voltage Ez of the Zener diode 36. As described above, the resistance values of the resistors 32 and 33 of the voltage dividing circuit 31 are set. Therefore, since the PNP transistor 34 is cut off and the detection voltage of the voltage detection circuit 30 is not output, the gate voltage Eg of the FET 42 of the discharge circuit 40 becomes 0 V, and the FET 42 is non-conductive. Does not flow (Ibr = 0).

  At time tr, the brushless DC motor 80 with a reduction gear changes to the regenerative state, and the current due to the regenerative power generated in the brushless DC motor 81 charges the smoothing capacitor 20, and the DC voltage Ea increases as the regenerative power increases. It starts to rise from the value e1. Therefore, the divided voltage Eb of the voltage dividing circuit 31 rises. However, when the condition of Eb <Ez is satisfied, the PNP transistor 34 is cut off, so that the gate voltage Eg of the FET 42 is 0V. Since the FET 42 is non-conductive, no current flows through the braking resistor 41.

At time t0, the DC voltage Ea reaches the voltage value e2, and the divided voltage Eb of the voltage dividing circuit 31 reaches the Zener voltage Ez of the Zener diode 36 (Eb = Ez). Thereafter, when the DC voltage Ea further rises and the divided voltage Eb exceeds the Zener voltage Ez (Eb> Ez), a current flows through the resistor 35 of the power supply detection circuit 30, and the following ( A base-emitter voltage V _BE (negative value) represented by Formula 1 is applied.
V _BE = Ez-Eb (1 formula)
In accordance with the base-emitter voltage V _BE , a base current Ib (negative value) flows through the PNP transistor 34, and the PNP transistor 34 operates in the active region. The voltage value e2 is a voltage value defined by the Zener voltage Ez of the Zener diode 36 and the resistance values of the resistors 32 and 33 of the voltage dividing circuit 31, and the voltage detection circuit 30 has a DC voltage Ea of a predetermined voltage. The operation is started by detecting that the value e2 has been exceeded.

When the DC voltage Ea further increases due to an increase in regenerative power, the divided voltage Eb of the voltage dividing circuit 31 further increases, and the absolute value of the base-emitter voltage V _BE further increases. As a result, the absolute value of the base current Ib of the PNP transistor 34 increases, and the absolute value of the collector-emitter voltage V _CE (negative value) of the PNP transistor 34 decreases. At this time, the collector voltage Ec of the PNP transistor 34 is expressed by the following (Equation 2), and increases as the DC voltage Ea increases.
Ec = Eb + V _CE (2 formulas)

  Further, the collector voltage Ec of the PNP transistor 34 expressed by (Expression 2) is input to the discharge circuit 40 as a detection voltage. As a result, a current flows through the diode 43 to the parallel circuit of the capacitor 44 and the resistor 45, so that the gate voltage Eg of the FET 42 increases as the collector voltage Ec increases. However, until the gate voltage Eg exceeds the cut-off voltage Voff of the FET 42, the FET 42 is non-conductive and no current flows through the braking resistor 41.

  When the regenerative power further increases and the DC voltage Ea further rises and the DC voltage Ea exceeds the voltage value e3 at time t1, the gate voltage Eg of the FET 42 of the discharge circuit 40 rises and exceeds the cut-off voltage Voff. The FET 42 becomes conductive. As a result, a drain current flows through the FET 42, and thus the current Ibr begins to flow through the braking resistor 41.

Thereafter, since the regenerative power increases, the DC voltage Ea further exceeds the voltage value e3, the divided voltage Eb of the voltage dividing circuit 31 further increases, and the base current Ib of the PNP transistor 34 operating in the active region. The absolute value of becomes even larger. Along with this, the absolute value of the collector-emitter voltage V _CE of the PNP transistor 34 becomes small, so the collector voltage Ec rises from (Equation 2), and the gate voltage Eg of the FET 42 of the discharge circuit 40 rises. As the gate voltage Eg increases, the drain current of the FET 42 increases, and the current Ibr flowing through the braking resistor 41 increases.

At this time, the electric power W consumed by the braking resistor 41 and the FET 42 of the discharge circuit 40 is expressed by the following (Expression 3) or (Expression 5).
W = Ea × Ibr (3 formulas)
Ibr = (Ea−Ed) / (resistance value of braking resistor 41) (Expression 4)
From (Formula 3) and (Formula 4),
W = Ea × (Ea−Ed) / (resistance value of braking resistor 41) (Expression 5)

  By increasing the current Ibr flowing through the braking resistor 41, an increase in the DC voltage Ea is suppressed, and the power consumption W of the braking resistor 41 and the FET 42 represented by (Equation 3) or (Equation 5) at time t2, The regenerative power generated by the brushless DC motor 81 becomes equal. As a result, the DC voltage Ea converges to the voltage value e4. After that, even if the regenerative power of the brushless DC motor 81 increases, the increase in the DC voltage Ea due to the increase in the regenerative power is fed back to the voltage detection circuit 30 and the current Ibr flowing through the braking resistor 41 increases. Can be consumed by the braking resistor 41, the DC voltage Ea is kept constant at the voltage value e4.

  During a period in which the regenerative power from time t3 to t4 is constant, the constant regenerative power is consumed by the braking resistor 41. Therefore, the current Ibr flowing through the braking resistor 41 is a constant value of the current value Ibr1. The DC voltage Ea is kept constant at the voltage value e4. At this time, the PNP transistor 34 operates in the active region, and the FET 42 flows a drain current corresponding to the gate voltage Eg.

In the period in which the regenerative power from time t4 to t5 decreases, the voltage fed back to the voltage detection circuit 30 also decreases when the DC voltage Ea decreases, so the divided voltage Eb of the voltage dividing circuit 31 decreases. Due to the decrease of the divided voltage Eb, the absolute value of the base-emitter voltage V _BE of the PNP transistor 34 becomes smaller than that of (Equation 1), the absolute value of the base current Ib becomes smaller, and the collector-emitter voltage V _CE (negative The absolute value of () is greater. Therefore, from (Equation 2), the collector voltage Ec of the PNP transistor 34, that is, the detection voltage decreases, the gate voltage Eg of the FET 42 to which the collector voltage Ec is applied via the diode 43 decreases, and the drain current of the FET 42 decreases. Therefore, the current Ibr flowing through the braking resistor 41 decreases. That is, when the regenerative power decreases, the power W consumed by the braking resistor 41 and the FET 42 decreases, so that the DC voltage Ea is kept constant at the voltage value e4.

  At time t5, the brushless DC motor 80 with a reduction gear changes from the regenerative state to the power running state, and the brushless DC motor 81 does not generate regenerative power. As the regenerative current disappears, the DC voltage Ea gradually decreases due to the power consumed by the braking resistor 41 and the FET 42 and the power consumed by the inverter circuit 50 for driving the brushless DC motor 81.

During the period from time t5 to time t6, the divided voltage Eb of the voltage dividing circuit 31 is lowered by the drop of the DC voltage Ea, and the absolute value of the base current Ib (negative value) of the PNP transistor 34 operating in the active region. As a result, the absolute value of the collector-emitter voltage V _CE (negative value) of the PNP transistor 34 increases. Therefore, from (Equation 2), the collector voltage Ec of the PNP transistor 34 decreases and the gate voltage Eg of the FET 42 of the discharge circuit 40 decreases, so the current Ibr flowing through the braking resistor 41 decreases.

  At time t6, when the DC voltage Ea drops to the voltage value e3 and the gate voltage Eg of the FET 42 of the discharge circuit 40 drops below the cut-off voltage Voff, the FET 42 becomes non-conductive and the current Ibr flowing through the braking resistor 41 is cut off. (Ibr = 0).

Thereafter, when the DC voltage Ea further decreases due to the electric power consumed for driving the brushless DC motor 81 through the inverter circuit 50, and the DC voltage Ea decreases to the voltage value e2 at time t7, the divided voltage Eb of the voltage dividing circuit 31. Decreases to the Zener voltage Ez of the Zener diode 36 (Eb = Ez). Therefore, from (Expression 1), the base-emitter voltage V _{BE of} the PNP transistor 34 becomes 0, and the PNP transistor 34 operating in the active region is cut off.

  The detection voltage of the voltage detection circuit 30 is not input to the discharge circuit 40 due to the interruption of the PNP transistor 34. At this time, since the electric charge stored in the capacitor 44 of the discharge circuit 40 is discharged through the resistor 45, the gate voltage Eg of the FET 42 falls smoothly. As described above, when the capacitor 44 and the resistor 45 are connected in parallel between the gate and the source of the FET 42 of the discharge circuit 40, the detection voltage of the voltage detection circuit 30 (the collector voltage Ec of the PNP transistor 34) changes sharply. Even so, the change in the gate voltage Eg of the FET 43 can be smoothed. Therefore, the FET 42 operates smoothly and linearly, and the current Ibr flowing through the braking resistor 41 also changes smoothly.

  Thereafter, the DC voltage Ea is reduced to the voltage value e1 by the power consumed to drive the brushless DC motor 81 through the inverter circuit 50 (time t8), and the DC voltage Ea is changed until the brushless DC motor 80 with a speed reducer shifts to the regenerative state. Is kept constant at the voltage value e1.

  In the motor drive device 1 according to the present invention having the above configuration, when the DC voltage Ea exceeds the predetermined voltage (voltage value e2), the voltage detection circuit 30 detects the detection voltage (collector voltage Ec) corresponding to the voltage value of the DC voltage Ea. ) And the discharge circuit 40 linearly adjusts the energization amount of the braking resistor 41, so that the DC voltage Ea is a constant value even when the brushless DC motor 80 with a speed reducer is in a regenerative state. Since the feedback control can be performed so as to be (voltage value e4), the fluctuation of the DC voltage Ea is small, and the DC voltage Ea can be suppressed from rising to the voltage value e4 or more. Thereby, since the fluctuation | variation of the rotational speed of the brushless DC motor 81 is small, it can prevent that the tooth surface of the pinion provided in the output shaft of the brushless DC motor 81 and the tooth surface of the gear wheel of the reduction gear 82 raise | generate a tooth ratchet. . Further, it is possible to prevent the output shaft of the speed reducer 82 and the fastening portion of the mechanical load from deteriorating due to repeated acceleration and deceleration of the output shaft. Therefore, the lifetime of the device in which the brushless DC motor 80 with a reduction gear and the motor driving device 1 are mounted can be extended.

  Further, the voltage control circuit 3 of the present invention can perform feedback control so that the DC voltage Ea is constant and linearly adjust the energization amount of the braking resistor 41 by the FET 42. Regardless of the resistance value, the DC voltage Ea can be controlled. Therefore, there is no need to select a resistance value of the limiting resistor 41 according to the characteristics of the brushless DC motor 81 and the characteristics of the load fastened to the speed reducer 82, and various motors using one type of the same limiting resistor 41. In addition, the versatility of the voltage control circuit 3 and the motor drive circuit 1 can be improved.

  Further, when the brushless DC motor 80 with a speed reducer is rotated by an external force when the supply of the AC voltage from the AC power supply 70 is stopped, the speed reducer 82 acts as a speed increaser for the brushless DC motor 81. The brushless DC motor 81 acts as a generator for the motor driving device 1. The electric power generated by the brushless DC motor 81 charges the smoothing capacitor 20 through the diode 52 of the inverter circuit 50. Even if the voltage between the DC buses P and N rises due to this, the voltage control circuit 3 can be activated to suppress the voltage rise. Since the motor driving device 1 of the present invention does not require the control power circuit 130 provided in the conventional motor driving device 1 shown in FIG. 3, the AC voltage supply by the AC power source 70 is stopped. Even in this case, an increase in voltage between the DC buses P and N can be suppressed.

  In the present embodiment, the motor drive device 1 is configured to drive the brushless DC motor 80 with a speed reducer, but is not limited thereto, and is configured to drive a brushless DC motor without a speed reducer. Alternatively, it may be configured to drive other motors. Further, the configurations of the converter circuit 10 and the inverter circuit 50 shown in FIG. 1 are merely examples, and the present invention is not limited to this.

It is a circuit diagram which shows the structure of the motor drive device which concerns on this invention. It is a schematic diagram for demonstrating operation | movement of the voltage control circuit which concerns on this invention. It is a circuit diagram which shows the structure of the conventional motor drive device. It is a schematic diagram for demonstrating operation | movement of the conventional voltage control circuit. It is a schematic diagram for demonstrating operation | movement at the time of making resistance value of a braking resistor small in the conventional voltage control circuit.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Motor drive device 3 Voltage control circuit 10 Converter circuit (power supply circuit)
20 smoothing capacitor 30 voltage detection circuit 31 voltage dividing circuit 32, 33 resistor 34 PNP transistor (bipolar transistor)
35 Resistor 36 Zener diode 40 Discharge circuit 41 Braking resistor (resistor)
42 FET (regulating element, field effect transistor)
43 Diode 44 Capacitor 45 Resistor 50 Inverter circuit (Drive circuit)
80 Brushless DC motor with reduction gear 81 Brushless DC motor (motor)
82 Reducer Ea DC voltage Eb Divided voltage Ez Zener voltage Eg Gate voltage P DC bus (High potential side output)
N DC bus (low potential side output)

Claims (4)

In a voltage control circuit that suppresses a voltage increase caused by regenerative power from the motor of a DC voltage supplied from a power supply circuit to a motor drive circuit,
A voltage detection circuit that outputs a detection voltage corresponding to the DC voltage when the DC voltage exceeds a predetermined voltage;
A discharge having a resistor connected between the high-potential side output and the low-potential side output of the power supply circuit, and an adjustment element that linearly adjusts the energization amount of the resistor according to the detection voltage of the voltage detection circuit A voltage control circuit comprising: a circuit. The voltage detection circuit includes:
A voltage dividing circuit for dividing the DC voltage;
A Zener diode defining the predetermined voltage;
A resistor having one end connected to the voltage dividing point of the voltage dividing circuit and the other end connected to the cathode of the Zener diode;
A PNP-type bipolar transistor having an emitter connected to a voltage dividing point of the voltage dividing circuit, a base connected to the cathode of the Zener diode, and outputting the detection voltage from a collector according to a voltage difference between both ends of the resistor The voltage control circuit according to claim 1, further comprising: The adjustment element is a field effect transistor that is connected in series to the resistor, and a voltage according to the detection voltage is input to a gate;
The voltage control circuit according to claim 1, wherein the discharge circuit includes a resistor and a capacitor connected in parallel between a gate and a source of the field effect transistor. A power supply circuit that converts an AC voltage into a DC voltage and outputs it;
A drive circuit for driving the motor by being supplied with a DC voltage output from the power supply circuit;
A motor drive device comprising: the voltage control circuit according to claim 1.

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