JP7684038B2 - Inrush current limiting circuit and inrush current limiting method for motor drive power supply circuit - Google Patents

Description

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

AC motors such as synchronous motors and induction motors are used to drive each axis of an industrial robot, but the servo drivers that drive and servo control these motors are equipped with inverter functions and are usually supplied with DC power. This DC power is obtained by rectifying the AC power supplied from an external AC power source, for example a commercial AC power source that is single-phase, 200/230V, 50/60Hz, using a rectifier circuit such as a full-wave rectifier circuit, and smoothing it with a smoothing capacitor. Here, a circuit including a rectifier circuit and a smoothing capacitor (capacitor) installed on the output side of the rectifier circuit is called a power supply circuit. The power supply circuit is started, for example, by closing the contacts of a main circuit relay inserted in the conductor connecting the external power source and the power supply circuit.

When a power supply circuit is started without sufficient charge being 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 a method of inserting an inrush current limiting resistor between the rectifier circuit and the smoothing circuit in the power supply circuit, providing a switch or relay to short both ends of the resistor, starting the power supply circuit with the switch or relay open, and shorting both ends of the resistor by the switch or relay after a certain amount of charge has accumulated in the smoothing capacitor, i.e., after the smoothing capacitor has been charged to a certain extent. Regarding the timing of shorting both ends of the inrush current limiting resistor, Patent Document 1 discloses providing an input voltage detection circuit that detects the voltage at the connection point between the output of the rectifier circuit and the inrush current limiting resistor, and a charging voltage detection circuit that detects the charging voltage of the smoothing capacitor, and shorting the resistor based on a comparison between the difference between the voltages detected by both detection circuits and a predetermined value. Patent Document 3 discloses shorting both ends of the inrush current limiting resistor when a predetermined delay time has elapsed since the charging voltage of the smoothing capacitor reached a predetermined value.

Japanese Patent Application Publication No. 3-27721 Japanese Patent Application Publication No. 3-22867 Japanese Unexamined Patent Publication No. 166779/1983

In the techniques disclosed in Patent Documents 1 to 3, even if there is no longer a need to limit the inrush current, both ends of the resistor for limiting the inrush current may not be short-circuited. For example, when the voltage of the AC power input to the power supply circuit drops, the inrush current itself is small, so it is possible to short-circuit both ends of the resistor for limiting the inrush current earlier, but the techniques disclosed in Patent Documents 1 to 3 cannot handle 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 techniques disclosed in Patent Documents 1 to 3 cannot handle such a case. When a motor is provided as a load on the power supply circuit, it is common to start the motor after shorting both ends of the resistor for limiting the inrush current in order to avoid the effect of the voltage drop in the resistor for limiting the inrush current and to prevent excessive heat generation by this resistor. Therefore, if the timing of shorting both ends of the resistor for limiting the inrush current is unnecessarily delayed, the timing of starting the motor will also be delayed accordingly.

The object of the present invention is to provide an inrush current limiting circuit and an inrush current limiting method that limit the inrush current in a power supply circuit for driving a motor, while enabling the motor to start sooner after the power supply circuit starts.

The inrush current limiting circuit of the present invention is an inrush current limiting circuit for limiting an inrush current at the start of a power supply circuit used to drive a motor, the power supply circuit having a rectifier circuit and a smoothing capacitor provided on the output side of the rectifier circuit, and the power supply circuit being supplied with AC power from an external power source, the inrush current limiting circuit comprising: a resistor inserted between the external power source and the input of the power supply circuit; a shorting relay having contacts capable of shorting both ends of the resistor; a main circuit relay provided between the resistor and the external power source for supplying and cutting off AC power from the external power source to the power supply circuit; a first voltage detector for detecting the voltage of the AC power supplied to the power supply circuit at a position closer to the external power source than the main circuit relay; a second voltage detector for detecting a charging voltage of the smoothing capacitor; and control means for controlling the contacts of the shorting relay to change from open to closed when a difference between a peak value of the voltage of the AC power and a charging voltage of the smoothing capacitor becomes equal to or less than a threshold value based on the detection results of the first voltage detector and the detection results of the second voltage detector when the contacts of the main circuit relay change from open to closed in response to an input of a safety output signal to start supplying the AC power to the power supply circuit.

Whether the smoothing capacitor provided on the output side of the rectifier circuit is sufficiently charged, i.e., whether the inrush current limiting resistor provided on the input side of the rectifier circuit may be shorted, can be determined by whether the charging voltage of the smoothing capacitor is sufficiently close to the peak value of 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, the charging voltage of the smoothing capacitor is measured by the second voltage detector, and both ends of the inrush current limiting resistor are shorted based on these measurement results, so that both ends of the resistor can be shorted at the shortest timing regardless of fluctuations in the voltage of the supplied AC power, and therefore the start timing of the motor, which is the load of the power supply circuit, can be advanced.

In the inrush current limiting circuit of the present invention, the first voltage detector is provided with the function of detecting the waveform of AC power, and when the shorting relay is used to control the shorting of the resistor for limiting the inrush current, the shorting relay contacts can be controlled to close in synchronization with the zero crossing points in the waveform of the AC power based on the detection results of the first voltage detector. In this configuration, the shorting relay contacts are closed at a timing close to the zero crossing points, so that the current flowing through the contacts is reduced at the moment the contacts are closed, thereby suppressing wear on the contacts.

In the inrush current limiting circuit of the present invention, a main circuit relay that supplies and cuts off AC power from the external power source to the power supply circuit is provided between the resistor for limiting the inrush current and the external power source , and the first voltage detector is provided closer to the external power source than the main circuit relay. By providing the first voltage detector closer to the external power source than 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 can be controlled by a control means, and when the control means is about to start supplying AC power to the power supply circuit, the main circuit relay can be controlled so that the contacts of the main circuit relay are closed in synchronization with the zero crossing point in the waveform of the AC power based on the detection result of the first voltage detector while keeping the contacts of the short circuit relay open. By controlling the main circuit relay in this way, the contacts of the main circuit relay are closed at a timing near the zero crossing point, so that the current flowing through the contacts is reduced at the moment the contacts are closed, and wear of the contacts of the main circuit relay can be suppressed.

In the inrush current limiting circuit of the present invention, the control means may, after controlling the contacts of the short-circuit relay to be closed, notify the motor control means that controls the driving of the motor that it is now possible to start the motor. Since the motor control means is notified by this notification that the resistor for limiting the inrush current has been short-circuited, it is possible to start the motor immediately after the resistor is short-circuited, thereby shortening the time until the motor starts.

The inrush current limiting method of the present invention is an inrush current limiting method for a power supply circuit used to drive a motor, which is supplied with AC power from an external power source, has a rectifier circuit and a smoothing capacitor provided on the output side of the rectifier circuit, and limits the inrush current at the start of the power supply circuit, the method detecting the voltage of the AC power supplied to the power supply circuit at a position closer to the external power source than a resistor inserted between the external power source and the input of the power supply circuit, detecting the charging voltage of the smoothing capacitor, and when the contacts of a main circuit relay provided between the resistor and a measurement point of the AC power voltage and which supplies and cuts off AC power to the power supply circuit from the external power source change from open to closed in response to the input of a safety output signal to start the supply of AC power to the power supply circuit, based on the detected AC power voltage and charging voltage, 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 , the method controls the contacts of a short-circuit relay to change from open to closed to short -circuit the resistor.

In the inrush current limiting method of the present invention, when the supply of AC power to the power supply circuit begins in response to the input of a safety output signal, both ends of the inrush current limiting resistor are short-circuited based on the AC voltage supplied to the power supply circuit from an external power source and the charging voltage of the smoothing capacitor. Therefore, both ends of the inrush current limiting resistor can be short-circuited at the shortest possible timing, regardless of fluctuations in the voltage of the supplied AC power, and therefore the start-up timing of the motor, which is the load of the power supply circuit, can be advanced.

In the inrush current limiting method of the present invention, the waveform of the AC power is also detected when the voltage of the AC power is detected, and when control is performed to short-circuit the resistor for limiting the inrush current, control can be performed to close the contacts of the short-circuiting relay that shorts both ends of the resistor in synchronization with the zero-crossing point in the AC power waveform. When controlled in this manner, the contacts of the short-circuiting relay are closed at a timing near the zero-crossing point, so that the current flowing through the contacts is reduced at the moment the contacts are closed, and wear on the contacts can be suppressed.

Furthermore, in the inrush current limiting method of the present invention , when attempting to start supplying AC power to the power supply circuit, the contacts of the main circuit relay can be controlled to close in synchronization with the zero crossing point of the AC power waveform while keeping the contacts of the shorting relay open. By controlling the main circuit relay in this way, the contacts of the main circuit relay are closed at a timing close to the zero crossing point, so that the current flowing through the contacts at the moment they are closed is reduced, thereby suppressing wear on the contacts of the main circuit relay.

In the inrush current limiting method of the present invention, after control is performed to short-circuit the resistor for limiting the inrush current, a motor control means that controls 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 shorting the resistor, thereby shortening the time until the motor starts.

The present invention provides an inrush current limiting circuit and an inrush current limiting method that limit the inrush current in a power supply circuit for driving a motor, while allowing the motor to start sooner after the power supply circuit starts.

1 is a block diagram showing a configuration of an inrush current limiting circuit according to an embodiment of the present invention; 2 is a timing chart illustrating an operation of the inrush current limiting circuit shown in FIG. 1 .

Next, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows the configuration of an inrush current limiting circuit according to an embodiment of the present invention. In the illustrated circuit, a power supply circuit 15 is provided to which AC power is supplied from an external power source, for example, an AC power source 10 which is a commercial power source. The power supply circuit 15 is provided with a full-wave rectifier circuit 16 which rectifies the supplied AC power, and a smoothing capacitor 17 which smoothes the pulsating current output by the full-wave rectifier circuit 16. The power supply circuit 15 is provided to output DC power to drive, for example, the motors 32 of each axis of an industrial robot. In the illustrated example, the DC power obtained by the power supply circuit 15 is supplied to a servo driver 31 which 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 in response to a command from a motor control unit 30 which controls the drive of the motor 32 based on an external command.

Between the AC power source 10 and the power supply circuit 15, a main circuit relay 12 is provided to supply and cut off AC power from the AC power source to the power supply circuit 15. In an industrial robot, the motor 32 must not be driven unless certain safety conditions are met. Therefore, the main circuit relay 12 closes its contacts in response to a safety output signal from a safety judgment circuit (not shown) that judges whether certain safety conditions are met, and supplies AC power from the AC power source 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 gives a certain delay time. Between the main circuit relay 12 and the power supply circuit 15, a resistor 13 is provided to limit the inrush current that will flow to the smoothing capacitor 17 when the power supply circuit 15 is started, and a short-circuit relay 14 having contacts for shorting both ends of the resistor 13 is provided. Furthermore, an AC voltage detector 11 is provided at a position closer to the AC power source 10 than the main circuit relay 12 to measure the voltage of the AC power supplied from the AC power source 10 to the power supply circuit 15. A DC voltage detector 19 is provided on the load side (the servo driver 31 side in the illustrated example) of the short circuit protection fuse 18, which measures the output voltage of the power supply circuit 15, i.e., the charging voltage of the smoothing capacitor 17. The AC voltage detector 11 and the DC voltage detector 12 correspond to the first voltage detector and the second voltage detector, respectively.

When the power supply circuit 15 is started, the contacts of the short-circuit relay 14 are generally open and the contacts of the main circuit relay 12 are closed. Then, AC power from the AC power source 10 is supplied to the power supply circuit 15 through the resistor 13 for limiting the inrush current, and the charging voltage of the smoothing capacitor 17 rises. After that, when the smoothing capacitor 17 is sufficiently charged, the contacts of the short-circuit relay 14 are closed, and AC power from the AC power source 10 is supplied to the power supply circuit 15 through the contacts of the short-circuit relay 14 without passing through the resistor 13 for limiting the inrush current. The fact that the smoothing capacitor 17 is sufficiently charged means that 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, assuming that the forward voltage drop in the full-wave rectifier circuit 16 can be ignored. 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, so it is not possible to determine whether the smoothing capacitor 17 has become fully charged by only paying attention to the charging voltage of the smoothing capacitor 17.

Therefore, the inrush current limiting circuit of this embodiment is equipped with a control unit 20 that controls the contact of the short-circuit relay 14 to change from open to closed 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, for example, configured with a CPU (Central Processing Unit) or a microprocessor, and corresponds to a control means. More specifically, the control unit 20 determines the peak value of the AC power from the voltage value detected by the AC voltage detector 11, and drives the coil 14a of the short-circuit relay 14 to close the contact of the short-circuit relay 14 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. When the contact of the short-circuit relay 14 is closed, the contact of the main circuit relay 12 must already be closed and AC power must be supplied to the power supply circuit 15. In the configuration shown in FIG. 1, the AC voltage detector 11 is provided closer to the AC power source 10 than the main circuit relay 12, and even if the contacts of the main circuit relay 12 are open, the AC voltage detector 11 detects voltage, so it is not possible to determine whether AC power is actually being supplied to the power supply circuit 15 based on the detection result of the AC voltage detector 11. Therefore, in the circuit shown in FIG. 1, a safety output signal is supplied to the control unit 20 via a delay element 21, so that the control unit 20 can determine whether AC power is being supplied to the power supply circuit 15 via the main circuit relay 12 based on the safety output signal.

Figure 2 is a timing chart showing the operation of the inrush current limiting circuit of this embodiment. Assume that the power supply circuit 15 is for driving the motors 32 of each axis of an industrial robot and is provided in a robot controller (not shown) used to control 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. Note that when there is residual voltage in the smoothing capacitor 15, the charging voltage of the smoothing capacitor 15 in the initial state is not 0V.

To operate the robot, a servo ON command is first input to the robot controller. In the figure, the input of the servo ON command is shown as the command transitioning from OFF to ON. When the servo ON command is input, a safety judgment circuit (not shown) in the robot controller judges whether a predetermined condition for safety is met, and if the condition is met, it outputs a safety output signal by changing the safety output signal from OFF to ON. As a result, after a 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 AC power from the AC power source 10 is supplied to the power supply circuit 15 via the resistor 13 for limiting the inrush current. The DC output voltage of the power supply circuit 15, i.e., the charging voltage of the smoothing capacitor 17, gradually rises. Then, when this charging voltage approaches sufficiently close to the voltage of the AC power represented by the peak value, the control unit 20 controls the contact of the short-circuit relay 14 from open to closed.

In the inrush current limiting circuit of this embodiment, based on the voltage of the AC power supplied from the AC power source 10 to the power supply circuit 15 and the charging voltage of the smoothing capacitor 17, both ends of the resistor 13 are short-circuited by the short-circuiting relay 14 when the charging voltage sufficiently approaches the peak value of the AC power voltage. As a result, both ends of the resistor 13 for limiting the inrush current can be short-circuited in a short time regardless of voltage fluctuations on the AC power source 10 side, making it possible to shorten the time from starting up the power supply circuit 15 to starting up the motor 32.

The motor 32 is controlled by the motor control unit 30 via the servo driver 31, and the motor control unit 30 controls the start of the motor 32. As a more specific configuration for shortening the time until the motor 32 starts, the control unit 20 can notify the motor control unit 30 that the motor 32 can be started when the control unit 20 controls the short-circuit relay 14 to be closed. If the motor control unit 30 receives this notification and starts the motor 32, the time from the start of the power supply circuit 10 to the start of the motor 32 can be shortened. The motor control unit 30, which controls the drive of the motor 32 based on an external command, is composed of, for example, a CPU or a microprocessor.

When an AC voltage detector 11 capable of detecting the waveform of AC power is used, it is preferable that the control unit 20 detects the zero crossing points in the waveform of 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 points in synchronization with the cell crossing points. By closing the contacts of the short-circuit relay 14 at a timing near the zero crossing points in the waveform of AC power, the current flowing through the contacts becomes smaller at the moment the contacts are closed, thereby reducing wear on the contacts.

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 capable of detecting the waveform of AC power is used, the main circuit relay 12 is not controlled by the safety output signal itself, but the control unit 20 may control the contacts of the main circuit relay 12 to close when the safety output signal is output and synchronized with the zero crossing point of the AC power waveform. By closing the contacts of the main circuit relay 12 at a timing near the zero crossing point of the AC power waveform, the current flowing through the contacts becomes small at the moment the contacts are closed, thereby reducing wear on the contacts of the main circuit relay 12.

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 (8)

1. An inrush current limiting circuit for limiting an inrush current at the start of a power supply circuit used to drive a motor, the power supply circuit having a rectifier circuit and a smoothing capacitor provided on an output side of the rectifier circuit, the inrush current limiting circuit comprising:
a resistor inserted between the external power supply and the input of the power supply circuit;
a shorting relay having contacts capable of shorting both ends of the resistor;
a main circuit relay provided between the resistor and the external power source for supplying and cutting off the AC power from the external power source to the power supply circuit;
a first voltage detector that detects a voltage of the AC power supplied to the power supply circuit at a position closer to the external power supply than the main circuit relay ;
a second voltage detector for detecting a charging voltage of the smoothing capacitor;
a control means for performing control to change the contact of the short-circuit relay from open to closed when a difference between a peak value of a voltage of the AC power and a charging voltage of the smoothing capacitor becomes equal to or smaller than a threshold value based on a detection result of the first voltage detector and a detection result of the second voltage detector when a contact of the main circuit relay changes from open to closed in response to an input of a safety output signal to start supplying the AC power to the power supply circuit;
An inrush current limiting circuit comprising: The first voltage detector has a function of detecting a waveform of AC power,
2. The inrush current limiting circuit according to claim 1, wherein, when controlling the contacts of the short-circuit relay to change from open to closed, the control means controls the short-circuit relay so that the contacts of the short-circuit relay are closed in synchronization with a zero-crossing point in a waveform of the AC power based on a detection result of the first voltage detector. The main circuit relay is controllable by the control means,
3. The inrush current limiting circuit according to claim 2, wherein, when attempting to start supply of AC power to the power supply circuit in response to input of the safety output signal, the control means controls the main circuit relay so that the contact of the main circuit relay is closed in synchronization with a zero crossing point in a waveform of the AC power based on a detection result of the first voltage detector, while keeping the contact of the short - circuit relay open. 4. The inrush current limiting circuit according to claim 1, wherein after performing the control to change the contact of the short-circuit relay to the closed state, the control means notifies a motor control means that controls driving of the motor that the motor can be started. 1. A method for limiting an inrush current at the start of a power supply circuit that is supplied with AC power from an external power supply, has a rectifier circuit and a smoothing capacitor provided on an output side of the rectifier circuit, and is used to drive a motor, the method 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 the contact of a main circuit relay, which is provided between the resistor and a measurement point of the voltage of the AC power and performs supply and cut-off of AC power from the external power source to the power supply circuit, changes from open to closed in response to an input of a safety output signal to start supplying the AC power to the power supply circuit, control is performed to short-circuit the resistor when a difference between a peak value of the voltage of the AC power and a 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.
Inrush current limiting methods. When detecting the voltage of the AC power, a waveform of the AC power is also detected;
6. The inrush current limiting method according to claim 5 , wherein when the control to short-circuit the resistor is performed, control is performed to close contacts of a short-circuit relay that shorts both ends of the resistor in synchronization with a zero crossing point in a waveform of the AC power. 7. The inrush current limiting method according to claim 6, further comprising the steps of: when attempting to start supplying AC power to the power supply circuit , controlling so that the contacts of the main circuit relay are closed in synchronization with a zero crossing point in a waveform of the AC power, while keeping the contacts of the short-circuit relay open. 8. The inrush current limiting method according to claim 5 , further comprising the step of: notifying a motor control means that controls the driving of the motor that the motor can be started after the control for shorting the resistor is performed.

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