JPH02155477A - Protective device for power converter - Google Patents

Abstract

PURPOSE:To increase the resistance value of a resistor for current limit charging, and to improve a current limiting effect while avoiding wasteful power consumption at the time of operation by installing an electromagnetic contactor in parallel with the resistor for current limit charging and providing a means controlling the opening and closing of the electromagnetic contactor. CONSTITUTION:An electromagnetic contactor 6 is mounted in parallel with a resistor 5 for current limit charging, and the opening and closing of the electromagnetic contactor 6 are controlled by a control circuit 9. The control circuit 9 transmits a control signal over the electromagnetic contactor 6 so that the electromagnetic contactor 6 is brought to an open state until the terminal voltage of a smoothing capacitor 3 reaches fixed voltage and the electromagnetic contactor 6 is closed when the terminal voltage reaches fixed voltage. Consequently, since currents are made to flow through the smoothing capacitor 3 through the resistor 5 for current limit charging when a power supply is connected or when the power supply is turned ON, excess inrush currents are not made to flow through the smoothing capacitor 3. Accordingly, an expensive circuit element such as a switching element is not broken.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a protection device for power converters such as inverters, and is particularly suitable for protecting circuit elements from inrush currents generated when connecting a power source or operating a power source. The present invention relates to a suitable power converter protection device.

[Conventional technology]

A power converter equipped with a forward converter connected to an AC power source, a DC intermediate circuit with a smoothing capacitor, and an inverse converter with a feedback diode can be damaged if the wiring is incorrectly connected to the power source, resulting in damage to expensive switching elements or freewheeling. Excessive current may flow through the diode and destroy it.

Furthermore, a similar problem may occur when an inrush current flows into the smoothing capacitor when the power is turned on. Therefore,
Conventionally, as described in Japanese Utility Model Application Publication No. 57-95097, a current-limiting charging (inrush current prevention) resistor was connected in series with a smoothing capacitor to prevent excessive ff1l from flowing into expensive switching elements and freewheeling diodes. That's what I do.

[Problem to be solved by the invention]

In order to suppress rush current, increasing the value of the current-limiting charging resistor connected in series with the smoothing capacitor is more effective. However, this current-limiting charging resistor is used only when the power supply is connected or at t'! ! This element is required only when the power is turned on, and is unnecessary during normal operation of the power converter. Therefore,
If the value of the current-limiting charging resistor is increased, a lot of wasted power will be consumed by this resistor during normal operation, resulting in poor efficiency. Furthermore, if this current-limiting charging resistance value is reduced to suppress wasteful power consumption, the effect of suppressing inrush current will be reduced. This is an unavoidable problem, and when deciding the value of this current-limiting charging resistor, it is necessary to take into consideration the amount of wasted power consumption and the capacity of the fuse installed between the AC power supply and the forward converter. There is the annoyance of not having to do so.

On the other hand, instead of using the current-limiting charging resistor as described above, a method is adopted in which fuses are blown when excessive current flows to cut off the rush current to the smoothing capacitor and protect the expensive elements. There is also an H position. In addition, a fuse resistor, for example, is used as the above-mentioned current-limiting charging resistor, and when the rush current to the smoothing capacitor becomes excessive, this current-limiting charging resistor is fused or burned out to protect other circuit elements. It is also possible to adopt the method. However, in such a case,
If a fuse or resistor blows when the power is connected or turned on, and the power conversion equipment does not operate, the operator may not be able to immediately know that the cause is a wiring error or inrush current, and take prompt measures. The problem is that it cannot be taken.

A first object of the present invention is to provide a power conversion device protection device that increases the current limiting effect by increasing the resistance value when using a current limiting charging resistor, and avoids wasteful power consumption during operation. It's about doing.

The second object of the present invention is to control the cause when a fuse or resistor is blown due to wiring error or inrush current when a current-limiting charging resistor is not used, or when a resistor that is easily blown out is used. An object of the present invention is to provide a power conversion device protection device that can notify a person.

[Means to solve the problem]

The first object is achieved by providing an electromagnetic contactor in parallel with the current limiting charging resistor and further providing means for controlling opening and closing of this electromagnetic contactor.

The second purpose is to provide a current detector between the smoothing capacitor and the inverter, and when the current value detected by the current detector exceeds the set current value, it will indicate that there is an incorrect connection, etc. And it will be achieved.

[Effect]

The electromagnetic contactor installed in parallel with the current-limiting charging resistor is opened by the 1-close control means only when the power is connected or turned on, and at other times the magnetic contactor is closed and connected to the current-limiting charging resistor. short circuit. As a result, the current to the smoothing capacitor can be suppressed only when necessary, so the value of the current-limiting charging resistor can be increased without depending on the capacity of the fuse installed between the AC power source and the forward converter. When operating,
Wasteful power consumption due to this resistance can be eliminated.

In addition, in the case of a device that does not use a current-limiting charging resistor and protects the circuit elements by cutting off the circuit when excessive current flows,
By displaying a message indicating incorrect wiring when an excessive current is detected by the current detector, the operator can immediately know that incorrect wiring is the cause, and can take prompt countermeasures.

〔Example〕

Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a configuration diagram of a power conversion device including a protection device according to an embodiment of the invention as claimed in claim 1.

In FIG. 1, a power converter 20 includes a forward converter 1 that converts alternating current into direct current, a smoothing capacitor 3 that smoothes the direct current output from the forward converter 1, and a smoothed direct current that converts the smoothed direct current into an arbitrary frequency. Inverter 2 that converts to AC of any voltage
It is equipped with Furthermore, it includes a driver 8 that drives the switching elements constituting the inverter 2, a control circuit 9 that controls the driver 8 and others, and a frequency setter 10 that sets the frequency of the AC output. Input terminals R, S, and T of this power converter 20 are connected to a commercial AC power source 7 via a fuse-free breaker (not shown), and an AC converter 4, which is a load, is connected to output terminals U, V, and W. It has become. However, if you are not a skilled person, you may end up connecting the output terminals U, V, and W to the commercial alternator R7. If such wiring is incorrectly connected, an inrush current will flow and destroy the expensive semiconductor elements and smoothing capacitors that make up the forward converter 1 and inverse converter 2. Even if connected to R, S, T, r
An excessive inrush current flows when t and R are turned on, which may similarly destroy semiconductor elements and the like. So this kind of rush N
For the purpose of current limiting, a current limiting charging resistor 5 is connected in series with the smoothing capacitor 3. However, current-limiting charging resistor 5
Merely providing this will cause problems such as wasteful power consumption as described above. Therefore, in the present invention, an electromagnetic contactor 6 is provided in parallel with the current-limiting charging resistor 5, and a control circuit 9 controls opening and closing of the electromagnetic contactor 6. In addition, a current detector 12 is installed between the load (AC generator) 4 and the output terminals U, V, and W to detect the load current and send it to the control circuit 9, and to detect the terminal voltage of the smoothing capacitor 3 and output it to the control circuit. I'm trying to send it to 9.

Furthermore, a display 13 is connected to the control circuit 9.

Then, the control circuit 9 receives the detection signal of the voltage detector 12,
Based on the smoothing capacitor 3 terminal voltage value and the set value signal of the frequency setter 10, the driver 8 is controlled and the electromagnetic contactor 6 is opened/closed.

In this embodiment, the smoothing capacitor 3, the current-limiting charging resistor 5, and the electromagnetic contactor 6 constitute a DC intermediate circuit.

The control circuit 9 sends a control signal to the electromagnetic contactor 6 to keep the electromagnetic contactor 6 open until the terminal voltage of the smoothing capacitor 3 reaches a predetermined voltage, and to close the electromagnetic contactor 6 when the voltage reaches the predetermined voltage. Send. Therefore, when the power supply is connected or when the power supply is connected, current flows through the smoothing capacitor 3 through the current-limiting charging resistor 5, so that no excessive rush current flows to the smoothing capacitor 3. Therefore, expensive circuit elements such as switching elements will not be destroyed. When the terminal voltage of the smoothing capacitor 3 gradually increases and reaches a predetermined voltage, the electromagnetic contactor 6 is closed and the resistor 5 is short-circuited. At this time, since the smoothing capacitor 3 has been charged to some extent, the charging current will not flow through the circuit for a period like when the power is turned on. Therefore, even if there is a connection error in the power supply, the switching element etc. The T4 magnetic contactor 6 will not be damaged by excessive current flowing through it, and the contacts of the T4 magnetic contactor 6 will not be damaged by sparks.

Further, if the connection is normal, the control circuit 9 will thereafter drive the driver 8 according to the required frequency setting value and operate the power converter 20, but the current-limiting charging resistor 5 will be in a short-circuited state. Therefore, this resistor 5 does not waste power. In this way, the current-limiting charging resistor 5 is short-circuited after the inrush current has subsided, so that a fuse-free breaker or the like with a resistance value that is infinitely large in capacity can be used as the current-limiting charging resistor 5. . The control circuit 9 judges the detected value of the current detector 12, and when it detects load fluctuation, sudden acceleration/deceleration, load short circuit, etc., it displays a message to that effect on the display 13.
to be displayed.

In the embodiment described above, the terminal voltage of the smoothing capacitor 3 was monitored to control the opening and closing of the electromagnetic contactor 6, but the present invention is not limited to such opening and closing control. Close for a predetermined time from when the power is connected or turn on R, for example, count 100m5, and before the predetermined time elapses, the electromagnetic contactor 6 is in the open state, and after the predetermined time has elapsed, the electromagnetic contactor 6 is closed to limit the current. The charging resistor 5 may be short-circuited. Even in this case, the same effect as in the above embodiment can be obtained.

FIG. 2 is a configuration diagram of a power conversion device including a protection device according to an embodiment of the invention as claimed in claim 2.

The power converter 21 according to this embodiment is different from the power converter shown in FIG. Instead, a DC current detector 11 is provided between the smoothing capacitor 3 and the inverter 2, and the control circuit 9 receives the detected value of the DC current detector 11. The current-limiting charging resistor 5 is made of a resistor that is easy to melt and burn out when an inrush current flows through the smoothing capacitor 3. Note that such power conversion may also be configured such that a fuse or the like provided elsewhere is fused by the rush current and cuts off the excessive current to the smoothing capacitor 3, without using the current-limiting charging resistor 5-. Even if an inrush current occurs in the device, the current-limiting charging resistor 5- and the fuse blow out to protect the circuit elements, but if this continues, the operator will have to worry about why the power conversion v&ll will not operate. Therefore, in this embodiment, the DC current detector 1
A horizontal value of 1 is used to determine whether the operation has stopped due to incorrect wiring, and the display 13 indicates that there is incorrect wiring or the vA current charging resistor 5-, fuse, etc. is blown due to an inrush current. This allows the operator to know the cause of the inoperability of the power conversion device.

In the embodiment shown in FIG. 2, a problem caused by an inrush current is determined by the detection value of the DC current detector 11, and a load current for detecting load fluctuation etc. is detected by the current detector 12. In other words, 1. Two current detectors are provided.

On the other hand, FIG. 3 shows the smoothing capacitor 3 and the inverse converter 2.
FIG. 2 is a configuration diagram of a protection circuit that displays an overcurrent of load current and an overcurrent caused by an inrush current using a detection signal from one current detector 11 provided between the two.

First, the active filter 30 removes noise from the detection signal of the current detector 11 . The detection signal from which noise has been removed is passed through the full-wave rectifier circuit 31 to the comparator CPI.
is input to the non-inverting input terminal of the comparator C.
Power is also input to the inverting input terminal of P2. Comparator CP
A first set reference potential ■1 is applied to the inverting input terminal of the comparator I, and a second set reference potential v2 is applied to the non-inverting input terminal of the comparator CP2. Furthermore, the set reference potential Vl,
P■ and NV given by dividing V2 by resistors R11, R12 and R14°R15 respectively indicate positive voltage and negative voltage,
With this configuration, when an overcurrent occurs due to load fluctuation or the like, the output level of the full-wave rectifier circuit 31 exceeds the first set reference potential V1, and a predetermined signal is output from the comparator CP1.

As a result, the load it current is displayed on the display 13 in FIG. 2. Also, when an inrush Wi flow occurs, the filter 3
0 output level is higher than the first setting reference potential ■l
The set reference potential ■2 is exceeded, and a predetermined signal is output from the comparator CP2. As a result, display 1 in Fig. 2
3. Inrush current is displayed. In addition, in this embodiment, negative uW
The reason why the full-wave rectifier circuit 31 is used to detect abnormalities in the i current is that the regenerative current flows in the opposite direction to the normal load current, so no matter which direction the R1 current flows. This is because abnormality can be determined by one comparator CPI.

〔Effect of the invention〕

According to the invention of claim 1, it is possible to use a resistor with a large resistance value as the current-limiting charging resistor, and moreover, when the current-limiting charging resistor is unnecessary, it is possible to avoid wasteful power consumption due to this resistor.

According to the invention of claim 2, the power is changed due to a connection error to the power supply or an inrush current when the power is turned on. If the device becomes inoperable, the cause is displayed, so the operator can take immediate countermeasures.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a power conversion device equipped with a protective H device according to an embodiment of the invention of claim 1, and FIG. 2 is a diagram of a power conversion device equipped with a protection device according to an embodiment of the invention of claim 2. FIG. 3 is a configuration diagram of a protective fi
It is a block diagram of a device. l... Forward variable 1 negative converter, 2... Inverse converter, 3... Smoothing capacitor, 4... AC converter (load), 5.5-...
Current-limiting charging resistor, 6... Magnetic contactor, 7... AC power supply, 8... Tribar, 9... Control circuit, 10...
Frequency setter, li...DC N current detector, 12...
Current detector, 13...Display device, 20.21...Power conversion device, 30...Noise filter, 31...Full wave rectifier circuit, R, S, T...Input terminal, U, V, W...
・Output terminal, R1~RIB...Resistor, C1...Capacitor, DI, D2...Diode, OPI~0P
3-...Operation amplifier, CPl, CF2...Comparator, PV...Positive potential, NV...Negative potential.

Claims (1)

[Claims] 1. A forward converter connected to an exchange power supply, a DC intermediate circuit having a smoothing capacitor and a current-limiting charging resistor connected in series thereto, and an inverse converter having a feedback diode. In the power conversion device, a magnetic contactor is provided in parallel with the current-limiting charging resistor, and a magnetic contactor is provided in parallel with the current-limiting charging resistor.
A power converter protection device comprising: an electromagnetic contactor control means for controlling closing. 2. In a power conversion device comprising a forward converter connected to an AC power supply, a DC intermediate circuit having a smoothing capacitor, and an inverse converter having a feedback diode, when the current flowing through the smoothing capacitor is larger than a predetermined current. a current interrupting means for interrupting current to the smoothing capacitor; a current detector provided between the smoothing capacitor and the inverter; and when a detected current value of the current detector exceeds a certain set current value. 1. A power converter protection device comprising: abnormal connection display means for displaying an abnormal connection state. 3. In claim 1 or claim 2, a current detector provided between a smoothing capacitor and an inverter or between a load and an inverter, and when the current detector detects an overcurrent, an overcurrent is detected. 1. A power converter protection device, comprising: means for displaying.