JPH027831A - Protective circuit for inverter - Google Patents

Abstract

PURPOSE:To cope properly with a fault by judging the cause of the fault based on the time relation between a time point when overcurrent occurs and a time point when under voltage occurs at the load side. CONSTITUTION:Protective circuits 18, 28 monitor the load side voltage and the inverter input current continuously and judge which of the under voltage or the overcurrent has occurred earlier. Upon occurrence of fault in a bus 5 or a load 6, a metering potential transformer 7 detects voltage drop of the bus 5 at first. Since current flowing through a filter reactor 15 increases subsequently, overcurrent detected through a current transformer 12 or 22 lags behind voltage drop and an overcurrent protective operation command is fed from the protective circuit 18 or 28 to an inverter 13 or 23. In case of an internal abnormality of inverter, the current transformer 12 or 22 detects overcurrent at first and an interruption command signal is fed to an interrupter 17 or 27 in order to isolate the abnormal inverter from the bus 5.

Description

[Detailed Description of the Invention] [Field of Industrial Application] This invention determines whether an overcurrent generated in an inverter device is caused by a load or an abnormality inside the inverter, and identifies the cause. The present invention relates to a protection circuit for an inverter device that takes corresponding measures.

[Conventional technology]

An inverter that converts DC power into AC power includes a DC power source such as a rectifier that receives AC power from a commercial $ source in order to obtain this DC power, and harmonics contained in the AC power output by this inverter. It comes with a filter that absorbs and removes components to create a sine waveform, and a circuit breaker that switches on and off the AC power output from this filter. Therefore, these DC power supplies, inverters, filters, and circuit breakers will be collectively referred to as an inverter device.

In such inverter devices, in order to protect the semiconductor switching elements that make up the inverter, if it is detected that the current flowing through the inverter has exceeded a predetermined value, the inverter voltage is reduced. More and more methods are being adopted to eliminate overcurrent.

[Problem 8 to be solved by the invention] When the inverter device independently supplies AC power to a load, there is no particular problem even if the above-described overcurrent protection method is adopted. However, when a plurality of sets of the above-mentioned inverter devices are connected in parallel to each other and operated, the following problems occur. In other words, if the cause of an inverter's overcurrent is not the load, but an abnormality inside the inverter that causes the overcurrent, it would be better to disconnect the inverter from the grid. First, the voltage of the inverter is reduced, which affects other inverter devices operating in parallel, resulting in a major drawback in that the output voltage of the parallel operating system is lost.

Therefore, the load current given to the load from the inverter devices running in parallel is detected, and the overcurrent value of this load current is calculated.
By comparing the overcurrent values of individual inverter devices,
A method is used to determine whether the cause of the overcurrent in the inverter is the load or something inside the inverter.

However, this method also requires four current transformers for detecting load current.

If a ground fault or short circuit occurs on the in side of the image point, for example, on the bus bar, there is a disadvantage that the above-mentioned discrimination method cannot be applied.

Therefore, the purpose of this invention is to be able to reliably determine whether the cause of overcurrent that occurs in the inverter is on the load side or inside the inverter in any case, and to be able to deal with the cause. It is to make it.

[Means to solve the problem]

In order to achieve the above object, the protection circuit of this invention includes:
In an inverter device consisting of an inverter that converts direct current to alternating current, a filter that shapes the waveform of the alternating current output by the inverter, and a switch installed between the filter and the load, the current flowing to the inverter is means for detecting that the current has reached an overcurrent of a predetermined value or more;
Means for detecting that the voltage on the load side of the switch has become an undervoltage below a set value, and means for instructing the inverter to perform overcurrent protection operation if an overcurrent is detected after detecting the undervoltage, and means for detecting undervoltage. A logic circuit that instructs the switch to open if an overcurrent is previously detected.

[Function] Since the inverter device is equipped with a filter composed of a reactor and a capacitor in order to shape the waveform of the output alternating current, the present invention provides overcurrent detection means at the front stage of the filter. Furthermore, if an undervoltage detection means is installed after the filter, there will be a time difference between the overcurrent detection point and the undervoltage detection point. Undervoltage is detected and then overcurrent is detected, but in the case of an abnormality inside the inverter, overcurrent is detected first and as a result, undervoltage occurs, so the timing of such operations may be delayed. The purpose of this system is to determine the cause of failure based on the information and perform protective actions corresponding to this cause of failure.

〔Example〕

FIG. 1 is a main circuit connection diagram showing an embodiment of the present invention, and shows a case where two sets of inverter devices are operated in parallel.

In FIG. 1, the first inverter device 10 includes a DC power source 11, an inverter 13 that converts the DC power from the DC type #11 into AC power, and a transformer 14 that insulates and transforms this AC power. , a filter consisting of a filter reactor 15 and a filter capacitor 16 for absorbing and removing harmonic components contained in AC power and shaping it into a sinusoidal waveform, and a circuit breaker 17 for opening and closing this AC power. and a protection circuit 18. Similarly, the second inverter device 20 includes a DC power supply 21, an inverter 23, a transformer 24, and a filter reactor 25.
It consists of a filter consisting of a filter capacitor 26, a circuit breaker 27, and a protection circuit 28.

The first inverter device 10 and the second inverter device 20 are connected in parallel to each other by a bus bar 5, and the AC output from both inverter devices 10 and 20 is parallel. X power is supplied to the load 6 via this bus 5.

In the present invention, the voltage on the load side is detected by the voltage transformer 7 connected to the bus 5, and the protection circuits 18 and 2
A circuit is provided to send a voltage signal to 8. Further, the first inverter device 10 is provided with a circuit in which the input terminal of the inverter 13 is detected by the current transformer 12, and this current signal is manually input to the protection circuit 18. Similarly, the second inverter device 20 is provided with a circuit that detects the input current of the inverter 23 with a current transformer 22 and sends the current signal to the protection circuit 28.

The protection circuits 18 and 28 constantly monitor the voltage and inverter input current on the load side that are input to each,
When an undervoltage below a set value and an overcurrent above a predetermined value occur, it is determined which of the two occurred first.

For example, when an accident such as a short circuit occurs on the bus 5 or the load 6, the voltage on the bus 5 first decreases, and the voltage transformer 7 detects this. Thereafter, the current in the filter reactor 15 forming the filter increases according to a certain time constant, so the overcurrent detected by the current transformer 12 or 22 lags behind the voltage drop. Therefore, in this case, a command is output from the protection circuit 18 or 28 to cause the inverter 13 or 23 to perform an overcurrent protection operation.

In addition, in the case of an internal abnormality in the inverter, the current transformer 12 or 22 will first detect the overcurrent, so in order to immediately disconnect the abnormal inverter from the bus 5, a shutdown command is issued to the circuit breaker 18 or 28. A signal will be issued.

FIG. 2 is a control block diagram showing the inside of the protection circuit 18 used in the embodiment circuit shown in FIG.

As shown in FIG. 2, the protection circuit 18 inputs the voltage signal IA from the instrument transformer 7 that detects the bus voltage, and the current signal IB from the current transformer 12 that detects the inverter input current. The overcurrent protection operation signal 1c is output to the inverter I3, and the cutoff command signal ID is output to the circuit breaker 17. For this purpose, an undervoltage detection system consisting of a rectifier 31, a voltage setting device 32, and a voltage comparator 33 is used. means, rectifier 34 and current setting device 35 and t
overcurrent detection means consisting of a current comparator 36;
Furthermore, a reset switch 30 and three AND elements 41
．． 42.43 2 <7) OR element 44.47, D flip-flop 45 and Sl'? flip flop 46
This protection circuit 18 is provided with a logic circuit composed of a delay element 48 and a delay element 48 .

D flip-flop 45 and SR flip-flop 46
are both reset by operating the reset switch 3o. When a short circuit occurs on the load side, first, the bus voltage decreases below the set value via the voltage comparator 33, the AND element 41, and the D flip-flop 4.
5, and then the current comparator 36 outputs an AND element 42 indicating that the inverter current has exceeded a predetermined value.
The D flip-flop 45 is sent to the D flip-flop 45 via the D flip-flop 45.
An overcurrent protection operation signal IC is sent to the inverter 13 via the inverter 7.

In addition, overcurrent caused by an internal abnormality in the inverter is applied from the current comparator 36 to the SR flip-flop 46 via the AND element 43, and this is set, so that the interrupt command signal ID is output to the circuit breaker 17 via the delay element 48. be done. Here, the delay element 48 is a D flip-flop 45
This is provided to time the operations of the SR flip-flop 46 and the SR flip-flop 46, and a very short delay time is sufficient.

FIG. 3 is a control block diagram showing the inside of a protection circuit 19 having a circuit configuration different from that of the protection circuit 18 shown in FIG. 2. In the protection circuit 19 shown in FIG. Except for the addition of a memory circuit 51 and a subtraction circuit 52, all other components have the same names, uses, and functions as those shown in FIG. 2, and thus their explanations will be omitted.

The protection circuit 19 shown in FIG. 3 includes a waveform memory circuit 51 that periodically stores the steady state waveform of the bus voltage taken in by the voltage transformer 7. The difference between the waveform and the actual instantaneous voltage waveform is subtracted by a subtraction circuit 52, and a voltage comparator 33
When this difference becomes larger than a certain level, AND element 4
1 so that changes in bus voltage can be detected.

[Effects of the Invention] According to the present invention, an overcurrent caused by an abnormality on the load side of an inverter device and an overcurrent caused by an abnormality inside the inverter can be detected at the time of occurrence of this overcurrent and on the load side. The protection circuit is configured to determine the cause of overcurrent occurrence based on the context of the point in time when the circuit voltage becomes undervoltage, and take appropriate measures to address the cause, so multiple inverters can be operated in parallel. Even if an overcurrent occurs when the equipment is running, appropriate measures can be taken, such as disconnecting only the abnormal equipment.
Inconveniences such as stopping the entire parallel operation system can be reduced as much as possible.

[Brief explanation of the drawing]

Fig. 1 is a main circuit connection diagram showing an embodiment of the present invention, Fig. 2 is a control block diagram showing the inside of the protection circuit used in the embodiment circuit shown in Fig. 2 is a control block diagram showing the inside of a protection circuit having a circuit configuration different from that shown in FIG. 2. FIG.

Claims (1)

[Claims] 1) An inverter device that includes an inverter that converts direct current to alternating current, a filter that shapes the waveform of the alternating current output by the inverter, and a switch installed between the filter and the load. means for detecting that the current flowing through the inverter has become an overcurrent of a predetermined value or more; means for detecting that the load-side voltage of the switch has become an undervoltage of a set value or less; and a logic circuit that commands the inverter to perform an overcurrent protection operation if an overcurrent is detected after the detection of the overcurrent, and a logic circuit that commands the switch to open the circuit if an overcurrent is detected before the detection of an undervoltage. protection circuit for inverter equipment.