Inrush Current Limiting Circuit and Inrush Current Limiting Method for Motor Driving Power Supply Circuit

Abstract

To provide an inrush current limiting circuit that has a rectifier circuit and a smoothing capacitor, and that limits an inrush current in a power source circuit for driving a motor so that the motor can be started quickly after the power source circuit is started.SOLUTION: An inrush current limiting circuit includes a resistor 13 that is inserted between an external AC power source 10 and an input of a power source circuit 15, and is for limiting inrush currents, a short circuit relay 14 having a contact point for short-circuiting both ends of the resistor 13, an AC voltage detector 11 that detects voltage of AC power at a position closer to the AC power source 10 than the resistor 13, a DC voltage detector 19 that detects a charging voltage for a smoothing capacitor 16 in the power source circuit 15, and a control unit 20 that performs control to change an opened state of the contact point of the short circuit relay 14 to a closed state on the basis of both a detection result obtained by the AC voltage detector 11 and a detection result obtained by the DC voltage detector 19.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a circuit and a method for limiting an inrush current in a power supply circuit for driving a motor.

Background Art

[0002] AC motors such as synchronous motors and induction motors are used for motors that drive each axis of industrial robots. Servo drivers that drive and servo-control these motors have an inverter function and are usually supplied with DC power. The DC power is obtained by rectifying AC power supplied from an external AC power source, for example, a commercial AC power source of single-phase, 200 / 230V, 50 / 60Hz, with a rectifier circuit such as a full-wave rectifier circuit and smoothing it with a smoothing capacitor. Here, a circuit including the rectifier circuit and the smoothing capacitor (capacitor) provided on the output side of the rectifier circuit will be referred to as a power supply circuit. The power supply circuit is started, for example, by closing the contacts of the main circuit relay inserted into the wire connecting the external power source and the power supply circuit.

[0003] When the power supply circuit is started with insufficient charge accumulated in the smoothing capacitor, a large inrush current flows. As a method for limiting the inrush current at startup, Patent Documents 1 to 3 disclose inserting a resistor for inrush current limitation between the rectifier circuit and the smoothing circuit in the power supply circuit, and providing a switch or relay so as to short-circuit both ends of this resistor. The power supply circuit is started with the switch or relay open, and after a certain amount of charge has accumulated in the smoothing capacitor, that is, after the smoothing capacitor has been charged to a certain extent, both ends of the resistor are short-circuited by the switch or relay. Regarding the timing of short-circuiting both ends of the resistor for inrush current limitation, Patent Document 1 discloses providing an input voltage detection circuit for detecting the voltage at the connection point between the output of the rectifier circuit and the resistor for inrush current limitation, and a charging voltage detection circuit for detecting the charging voltage of the smoothing capacitor, and short-circuiting the resistor based on a comparison between the difference in the voltages detected by both detection circuits and a predetermined value. Patent Document 3 discloses short-circuiting both ends of the resistor for inrush current limitation when a predetermined delay time has elapsed after the charging voltage of the smoothing capacitor has reached a predetermined value.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0005] In the technologies disclosed in Patent Documents 1 to 3, even when there is no need to limit the inrush current, the both ends of the resistor for inrush current limitation may not be short-circuited. For example, when the voltage of the AC power input to the power supply circuit decreases, since the inrush current itself is small, it is possible to short-circuit the both ends of the resistor for inrush current limitation earlier, but the technologies disclosed in Patent Documents 1 to 3 cannot cope with such a case. Similarly, when the power supply circuit is started with a voltage remaining in the smoothing capacitor, the smoothing capacitor will be charged earlier, but the technologies disclosed in Patent Documents 1 to 3 cannot cope with such a case. When a motor is provided as a load of the power supply circuit, in order to avoid the influence of the voltage drop in the resistor for inrush current limitation and also to avoid excessive heat generation of this resistor, it is common to start the motor after short-circuiting the both ends of the resistor for inrush current limitation. Therefore, if the timing of short-circuiting the both ends of the resistor for inrush current limitation is unnecessarily delayed, the timing of starting the motor will be delayed accordingly.

[0006] An object of the present invention is to provide an inrush current limiting circuit and an inrush current limiting method that can start a motor earlier after starting of a power supply circuit while limiting the inrush current in the power supply circuit for driving the motor.

Means for Solving the Problem

[0007] The inrush current limiting circuit of the present invention is an inrush current limiting circuit that limits the inrush current at the start of a power supply circuit in a power supply circuit that has a rectifier circuit to which AC power is supplied from an external power supply and a smoothing capacitor provided on the output side of the rectifier circuit and is used for driving a motor, and includes a resistor inserted between the external power supply and the input of the power supply circuit, and a short-circuit relay having a contact that can short-circuit the both ends of the resistor, A main circuit relay provided between a resistor and an external power supply for supplying and interrupting AC power to a power supply circuit from the external power supply, and the main circuit relay a first voltage detector that detects the voltage of the AC power supplied to the power supply circuit at a position closer to the external power supply, and a second voltage detector that detects the charging voltage of the smoothing capacitor, When the contact of the main circuit relay changes from open to closed in response to the input of a safety output signal and the supply of the AC power to the power supply circuit starts,Based on the detection result of the first voltage detector and the detection result of the second voltage detector, control means is provided for performing control to change the contact of the short-circuit relay from open to closed when the difference between the peak value of the voltage of the AC power and the charging voltage of the smoothing capacitor becomes equal to or less than the threshold value.

[0008] Whether the smoothing capacitor provided on the output side of the rectifier circuit is sufficiently charged, that is, whether it is possible to short-circuit the inrush current limiting resistor provided on the input side of the rectifier circuit can be determined by whether the charging voltage of the smoothing capacitor is sufficiently close to the peak value in the AC power supplied to the rectifier circuit. In the inrush current limiting circuit of the present invention, When the supply of AC power to the power supply circuit starts in response to the input of a safety output signal, The voltage of the AC voltage supplied from the external power source to the power supply circuit is measured by the first voltage detector, and the charging voltage of the smoothing capacitor is measured by the second voltage detector. Based on these measurement results, both ends of the inrush current limiting resistor are short-circuited. Therefore, regardless of the voltage fluctuation of the supplied AC power, both ends of the resistor can be short-circuited at the shortest timing, and accordingly, the starting timing of the motor, which is the load of the power supply circuit, can be advanced.

[0009] In the inrush current limiting circuit of the present invention, the first voltage detector is provided with a function of detecting the waveform of the AC power. On this basis, when performing control to short-circuit the inrush current limiting resistor by the short-circuit relay, based on the detection result of the first voltage detector, it is possible to control the contact of the short-circuit relay to be closed in synchronization with the zero-crossing point in the waveform of the AC power. In this configuration, since the contact of the short-circuit relay is closed at a timing near the zero-crossing point, the current flowing through the contact at the moment the contact is closed becomes small, and the loss of the contact can be suppressed.

[0010] In the inrush current limiting circuit of the present invention, a main circuit relay for supplying and interrupting the AC power from the external power source to the power supply circuit is provided between the inrush current limiting resistor and the external power source. and The first voltage detector is is provided on the side of the external power source rather than on the side of the main circuit relay. isBy providing the first voltage detector on the side of the external power supply rather than on the side of the main circuit relay, it becomes possible to control the main circuit relay according to the detection result of the first voltage detector. For example, the main circuit relay is made controllable by a control means. When the control means attempts to start supplying AC power to the power supply circuit, while keeping the contacts of the short-circuit relay open, based on the detection result of the first voltage detector, the main circuit relay can be controlled so that the contacts of the main circuit relay close in synchronization with the zero-crossing point in the waveform of the AC power. By controlling the main circuit relay in this way, since the contacts of the main circuit relay close at a timing near the zero-crossing point, the current flowing through the contacts at the moment of closing the contacts becomes small, and the wear of the contacts of the main circuit relay can be suppressed.

[0011] In the inrush current limiting circuit of the present invention, after the control means performs control to change the contacts of the short-circuit relay to closed, it may notify the motor control means for controlling the drive of the motor that the motor can be started. Since the motor control means is informed by this notification that the resistor for inrush current limiting has been short-circuited, after the short-circuit of the resistor, the motor can be started immediately, and the time until the motor starts can be shortened.

[0012] The inrush current limiting method of the present invention is an inrush current limiting method for limiting the inrush current at the start of a power supply circuit having a rectifier circuit supplied with AC power from an external power supply and a smoothing capacitor provided on the output side of the rectifier circuit and used for driving a motor. The method includes detecting the voltage of the AC power supplied to the power supply circuit at a position closer to the external power supply than a resistor inserted between the external power supply and the input of the power supply circuit, detecting the charging voltage of the smoothing capacitor, A contact of a main circuit relay provided between a resistor and a measurement point of the voltage of AC power for supplying and interrupting AC power to a power supply circuit from an external power supply changes from open to closed in response to the input of a safety output signal, and when the supply of AC power to the power supply circuit starts, the detected voltage of the AC power and the charging voltage to and based on this, when the difference between the peak value of the voltage of the AC power and the charging voltage of the smoothing capacitor becomes equal to or less than a threshold value change the contact of the short - circuit relay from open to closed performing control to short-circuit the resistor.

[0013] In the inrush current limiting method of the present invention, When the supply of AC power to the power supply circuit starts in response to the input of a safety output signal,Based on the voltage of the alternating current voltage supplied from an external power source to a power supply circuit and the charging voltage of a smoothing capacitor, both ends of a resistor for inrush current limitation are short-circuited. Therefore, regardless of fluctuations in the voltage of the supplied alternating current power, both ends of the resistor for inrush current limitation can be short-circuited at the shortest timing. Along with this, the starting timing of a motor, which is a load of the power supply circuit, can be advanced.

[0014] In the inrush current limitation method of the present invention, when detecting the voltage of alternating current power, the waveform of the alternating current power is also detected. When performing control to short-circuit the resistor for inrush current limitation, control can be performed such that the contacts of a short-circuit relay that short-circuits both ends of the resistor are closed in synchronization with the zero-crossing point in the waveform of the alternating current power. By performing control in this way, since the contacts of the short-circuit relay are closed at a timing near the zero-crossing point, the current flowing through the contacts at the moment the contacts are closed becomes small, and the loss of the contacts can be suppressed.

[0015] Furthermore, in the inrush current limitation method of the present invention electric When attempting to start the supply of alternating current power to the power source circuit, control can be performed such that the contacts of the main circuit relay are closed in synchronization with the zero-crossing point in the waveform of the alternating current power while the contacts of the short-circuit relay are kept open. By controlling the main circuit relay in this way, since the contacts of the main circuit relay are closed at a timing near the zero-crossing point, the current flowing through the contacts at the moment the contacts are closed becomes small, and the loss of the contacts of the main circuit relay can be suppressed.

[0016] In the inrush current limitation method of the present invention, after performing control to short-circuit the resistor for inrush current limitation, the motor control means for controlling the driving of the motor may be notified that the motor can be started. By receiving such a notification, the motor control means can start the motor immediately after the resistor is short-circuited, and the time until the motor starts can be shortened.

Advantages of the Invention

[0017] According to the present invention, it is possible to obtain an inrush current limiting circuit and an inrush current limiting method that can start the motor earlier after the start of the power supply circuit while limiting the inrush current in the power supply circuit for driving the motor.

Brief Description of the Drawings

[0018]

Figure 1

Figure 2

Embodiments for Carrying Out the Invention

[0019] Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows the configuration of the inrush current limiting circuit according to an embodiment of the present invention. In the illustrated circuit, a power supply circuit 15 to which AC power is supplied from an external power supply, for example, an AC power supply 10 which is a commercial power supply, is provided. The power supply circuit 15 is provided with a full-wave rectifier circuit 16 for rectifying the supplied AC power, and a smoothing capacitor 17 for smoothing the pulsating current output by the full-wave rectifier circuit 16. The power supply circuit 15 is provided to output DC power and drive motors 32 of each axis of, for example, an industrial robot. In the illustrated example, the DC power obtained by the power supply circuit 15 is supplied to a servo driver 31 that drives and servo-controls the motor 32 via a short-circuit protection fuse 18. The servo driver 31 drives the motor 32 using the supplied DC power according to a command from a motor control unit 30 that performs drive control of the motor 32 based on an external command.

[0020] A main circuit relay 12 for supplying and interrupting AC power from an AC power supply 10 to a power supply circuit 15 is provided between the AC power supply 10 and the power supply circuit 15. In an industrial robot, since the motor 32 must not be driven unless predetermined safety conditions are satisfied, the main circuit relay 12 closes its contacts in response to a safety output signal from a safety determination circuit (not shown) that determines whether the predetermined safety conditions are satisfied, and supplies AC power from the AC power supply 10 to the power supply circuit 15. The safety output signal is applied to the coil 12a of the main circuit relay 12 via a delay element 21 that provides a predetermined delay time. A resistor 13 is provided between the main circuit relay 12 and the power supply circuit 15 to limit the inrush current that will flow through the smoothing capacitor 17 when the power supply circuit 15 is started up. Further, a short-circuit relay 14 having contacts for short-circuiting both ends of the resistor 13 is provided. Further, an AC voltage detector 11 for measuring the voltage of the AC power supplied from the AC power supply 10 to the power supply circuit 15 is provided at a position closer to the AC power supply 10 than the main circuit relay 12. A DC voltage detector 19 for measuring the output voltage of the power supply circuit 15, that is, the charging voltage of the smoothing capacitor 17, is provided on the load side (the side of the servo driver 31 in the illustrated example) of the short-circuit protection fuse 18. The AC voltage detector 11 and the DC voltage detector 12 respectively correspond to a first voltage detector and a second voltage detector.

[0021] When generally starting up the power supply circuit 15, with the contacts of the short-circuit relay 14 open, the contacts of the main circuit relay 12 are closed. Then, the AC power from the AC power supply 10 is supplied to the power supply circuit 15 via the inrush current limiting resistor 13, and the charging voltage of the smoothing capacitor 17 rises. After that, when the smoothing capacitor 17 is fully charged, the contacts of the short-circuit relay 14 are closed so that the AC power from the AC power supply 10 is supplied to the power supply circuit 15 through the contacts of the short-circuit relay 14 without passing through the inrush current limiting resistor 13. That the smoothing capacitor 17 is fully charged means that, ignoring the forward voltage drop in the full-wave rectifier circuit 16, the charging voltage of the smoothing capacitor 17 is sufficiently close to the peak value of the AC power supplied to the power supply circuit 15. If there is a voltage fluctuation on the AC power side, the charging voltage in the fully charged state of the smoothing capacitor 17 also fluctuates. Therefore, just focusing on the charging voltage of the smoothing capacitor 17 alone, it is impossible to determine whether the smoothing capacitor 17 has reached the fully charged state.

[0022] Therefore, the inrush current limiting circuit of the present embodiment includes a control unit 20 that performs control to change the contact of the short-circuit relay 14 from an open state to a closed state based on the detection result of the AC voltage detector 11 and the detection result of the DC voltage detector 19. The control unit 20 is constituted by, for example, a CPU (Central Processing Unit) or a microprocessor and corresponds to a control means. More specifically, the control unit 20 obtains the peak value of the AC power from the voltage value detected by the AC voltage detector 11, and when the difference between the charging voltage of the smoothing capacitor 17 detected by the DC voltage detector 19 and the peak value becomes equal to or less than a predetermined threshold value, the coil 14a of the short-circuit relay 14 is driven so as to close the contact of the short-circuit relay 14. When closing the contact of the short-circuit relay 14, it is necessary that the contact of the main circuit relay 12 is already closed and AC power is supplied to the power supply circuit 15. In the configuration shown in FIG. 1, the AC voltage detector 11 is provided on the AC power supply 10 side with respect to the main circuit relay 12. Even when the contact of the main circuit relay 12 is open, the AC voltage detector 11 detects the voltage. Therefore, based on the detection result of the AC voltage detector 11, it is impossible to determine whether AC power is actually supplied to the power supply circuit 15. Therefore, in the circuit shown in FIG. 1, a safety output signal is supplied to the control unit 20 via the delay element 21, and the control unit 20 can determine whether AC power is supplied to the power supply circuit 15 based on the safety output signal via the main circuit relay 12.

[0023] FIG. 2 is a timing chart showing the operation of the inrush current limiting circuit of the present embodiment. It is assumed that the power supply circuit 15 is for driving the motors 32 of the respective axes of the industrial robot and is provided in a robot controller (not shown) used for controlling the robot. In the initial state, the contacts of the main circuit relay 12 and the short-circuit relay 14 are open. In this initial state, the AC power supply 10 itself is operating, and in the figure, the AC input voltage indicates the voltage of the AC power supplied from the AC power supply 10 to the power supply circuit 15 detected by the AC voltage detector 11. When there is a residual voltage in the smoothing capacitor 15, the charging voltage of the smoothing capacitor 15 in the initial state does not become 0V.

[0024] To operate the robot, first, a servo ON command is input to the robot controller. In the figure, the input of the servo ON command is indicated by the transition of the command from OFF to ON. When the servo ON command is input, a safety determination circuit (not shown) in the robot controller determines whether a predetermined condition for safety is satisfied. If the condition is satisfied, the safety output signal is changed from OFF to ON and the safety output signal is output. As a result, after the delay time by the delay element 21, the contact of the main circuit relay 12 changes from OFF (open) to ON (closed). At this point, the contact of the short-circuit relay 14 remains open, and the AC power from the AC power supply 10 is supplied to the power supply circuit 15 via the inrush current limiting resistor 13. The DC output voltage of the power supply circuit 15, that is, the charging voltage of the smoothing capacitor 17, gradually increases. When this charging voltage sufficiently approaches the voltage of the AC power represented by the peak value, the control unit 20 controls the contact of the short-circuit relay 14 to change from open to closed.

[0025] In the inrush current limiting circuit of the present embodiment, based on the voltage of the AC power supplied from the AC power supply 10 to the power supply circuit 15 and the charging voltage of the smoothing capacitor 17, when the charging voltage sufficiently approaches the peak value of the voltage of the AC power, both ends of the resistor 13 are short-circuited by the short-circuit relay 14. As a result, both ends of the inrush current limiting resistor 13 can be short-circuited in a short time regardless of the voltage fluctuation on the AC power supply 10 side, and the time from the start of the power supply circuit 15 to the start of the motor 32 can be shortened.

[0026] The motor 32 is controlled by the motor control unit 30 via the servo driver 31, and it is assumed that the motor control unit 30 controls the startup of the motor 32. As a more specific configuration for shortening the time until the startup of the motor 32, when the control unit 20 controls the short-circuit relay 14 to be closed, it can notify the motor control unit 30 that the startup of the motor 32 has become possible. If the motor control unit 30 receives this notification and starts the motor 32, the time from the startup of the power supply circuit 10 to the startup of the motor 32 can be made shorter. Note that the motor control unit 30 that performs drive control of the motor 32 based on an external command is configured by, for example, a CPU or a microprocessor.

[0027] When an AC voltage detector 11 that can also detect the waveform of AC power is used, the control unit 20 preferably detects the zero-crossing point in the waveform of the AC power and drives the coil 14a of the short-circuit relay 14 so as to close the contacts of the short-circuit relay 14 at a timing near the zero-crossing point in synchronization with the zero-crossing point. By closing the contacts of the short-circuit relay 14 at a timing near the zero-crossing point in the waveform of the AC power, the current flowing through the contacts at the moment of closing the contacts becomes small, so that the wear of the contacts can be reduced.

[0028] As described above, the main circuit relay 12 is controlled to close the contacts by the safety output signal. Since the safety control signal is also supplied to the control unit 20, when an AC voltage detector 11 that can also detect the waveform of the AC power is used, instead of controlling the main circuit relay 12 by the safety output signal itself, the control unit 20 may perform control to close the contacts of the main circuit relay 12 at a timing when the safety output signal is output and in synchronization with the zero-crossing point of the waveform of the AC power. By closing the contacts of the main circuit relay 12 at a timing near the zero-crossing point in the waveform of the AC power, the current flowing through the contacts at the moment of closing the contacts becomes small, so that the wear of the contacts of the main circuit relay 12 can be reduced.

Explanation of Reference Numerals

[0029] 10…AC power supply, 11…AC voltage detector, 12…main circuit relay; 13…resistor; 14…short-circuit relay; 15…power supply circuit; 16…full-wave rectifier circuit; 17…smoothing capacitor: 18…short-circuit protection fuse; 19…DC voltage detector; 20…control unit; 21…delay element; 30…motor control unit; 31…servo driver, 32…motor.

Claims

1. An inrush current limiting circuit that has a rectifier circuit supplied with AC power from an external power source and a smoothing capacitor provided on the output side of the rectifier circuit, and that limits the inrush current at the start of the power circuit used for driving a motor, comprising: a resistor inserted between the external power source and the input of the power circuit; a short-circuit relay having a contact that can short-circuit both ends of the resistor; a main circuit relay provided between the resistor and the external power source for supplying and interrupting the AC power from the external power source to the power circuit; a first voltage detector that detects the voltage of the AC power supplied to the power circuit at a position closer to the external power source than the main circuit relay; a second voltage detector that detects the charging voltage of the smoothing capacitor; control means for controlling the contact of the short-circuit relay to change from open to closed when the difference between the peak value of the voltage of the AC power and the charging voltage of the smoothing capacitor becomes equal to or less than a threshold value based on the detection result of the first voltage detector and the detection result of the second voltage detector when the contact of the main circuit relay changes from open to closed in response to the input of a safety output signal and the supply of the AC power to the power circuit starts; An inrush current limiting circuit having the above.

2. The first voltage detector has a function of detecting the waveform of the AC power, The control means controls the short-circuit relay so that the contact of the short-circuit relay closes in synchronization with the zero-crossing point in the waveform of the AC power based on the detection result of the first voltage detector when performing control to change the contact of the short-circuit relay from open to closed. The inrush current limiting circuit according to Claim 1.

3. The main circuit relay is controllable by the control means, When the control means attempts to start supplying the AC power to the power circuit in response to the input of the safety output signal, the control means keeps the contact of the short-circuit relay open and controls the main circuit relay so that the contact of the main circuit relay closes in synchronization with the zero-crossing point in the waveform of the AC power based on the detection result of the first voltage detector. The inrush current limiting circuit according to Claim 2.

4. After performing the control to change the contact of the short-circuit relay to closed, the control means notifies motor control means for controlling the driving of the motor that the motor can be started. The inrush current limiting circuit according to any one of Claims 1 to 3.

5. An inrush current limiting method for limiting an inrush current at startup of a power supply circuit having a rectifier circuit supplied with AC power from an external power supply and a smoothing capacitor provided on the output side of the rectifier circuit and used for driving a motor, comprising: detecting a voltage of the AC power supplied to the power supply circuit at a position closer to the external power supply than a resistor inserted between the external power supply and an input of the power supply circuit; detecting a charging voltage of the smoothing capacitor; when a contact of a main circuit relay provided between the resistor and a measurement point of the voltage of the AC power and for supplying and interrupting the AC power from the external power supply to the power supply circuit changes from open to closed in response to an input of a safety output signal and the supply of the AC power to the power supply circuit starts, performing control to short-circuit the resistor when a difference between a peak value of the voltage of the AC power and the charging voltage of the smoothing capacitor becomes equal to or less than a threshold value based on the voltage of the AC power and the charging voltage; An inrush current limiting method.

6. detecting also a waveform of the AC power when detecting the voltage of the AC power; performing control such that a contact of a short-circuit relay for short-circuiting both ends of the resistor closes in synchronization with a zero-cross point in the waveform of the AC power when performing control to short-circuit the resistor, the inrush current limiting method according to claim 5.

7. When attempting to start supplying AC power to the power supply circuit, performing control such that the contact of the main circuit relay closes in synchronization with a zero-cross point in the waveform of the AC power while keeping the contact of the short-circuit relay open, the inrush current limiting method according to claim 6.

8. notifying motor control means for controlling driving of the motor that the motor can be started after performing control to short-circuit the resistor, the inrush current limiting method according to any one of claims 5 to 7.

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