JP2597025Y2 - Inverter DC short circuit detection device - Google Patents

Description

[Detailed description of the invention]

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a DC short-circuit detection device for an inverter, which detects a DC short-circuit current generated when a switching element constituting the inverter is damaged.

[0002]

The Related Art FIG. 2, the inverter device smoothing the DC side of the inverter 1 (electrolytic) capacitors C ₁ and is disposed, is performed smoothing the DC voltage.

The switching elements TRU to TRY constituting the inverter 1 are alternately turned on without being turned on at the same time.
Although the device is turned OFF, if the device TRU is damaged and remains ON, for example, a DC short circuit occurs when the device TRX is turned ON. In this case, it is necessary to quickly detect the DC short-circuit current and stop the inverter device by failure.

[0004] Detection of the DC short-circuit current is performed by connecting the short-circuit current detecting circuit 2 to the detection level which is set by installing the current transformer CT1 for AC wiring portion of the electrolytic capacitor C ₁ .

When the smoothing capacitors CA and CB are separately provided for each of the plurality of inverters 1A and 1B as shown in FIG. 3A, the current transformers CTA and CTB are connected to each other. It is installed in the wiring portion of the capacitors CA and CB, and the output of each current transformer is input to the short circuit detection circuit 2 to detect a DC short circuit.

Further, current transformer to wiring portions likewise the smoothing capacitor C _1, CB may smoothing capacitor C _1, C ₂ for each phase of the inverter is divided installed as shown in FIG. 3 (b) CT1 and CT2 are installed to detect DC short circuit.

[0007]

In the conventional circuit shown in FIG. 2A, the detected current is IA + IB (IA and IB are alternating currents flowing through the capacitors CA and CB when normal).

If a DC short circuit occurs in the inverter 1A, the short-circuit current is reduced for a short time by the capacitor CA.
And the wiring impedance difference between CB and the inverter 1A, the current from the capacitor CAＣＡthe current flowing from the capacitor CB.

Assuming that the short-circuit current is K.IA (K is a coefficient), the detection current in the short-circuit current detection circuit 2 is K.IA
+ IB. Assuming that the normal current IA = IB, K ·
IA + IB = (K + 1) IA.

Similarly, assuming that the number of electrolytic capacitors installed separately is N, the detected current in a normal state is N · IA, and the detected current in a short circuit is (K + N−1) IA.

For example, if K = 5, the results are as shown in Table 1.

[0012]

[Table 1]

As described above, as the number N of dividing electrolytic capacitors (= the number of current transformers) increases, the difference between the short-circuited and normal detected currents becomes smaller. That is, as N increases, the detection set level of the short-circuit current detection circuit 2 approaches the normal level, so that a stable DC short-circuit detection operation cannot be expected (the same applies to the circuit of FIG. 3B).

The present invention has been made in view of such a conventional problem, and an object of the present invention is to reduce a DC short circuit without lowering a detection set level even when the number of current transformers is increased. An object of the present invention is to provide a DC short-circuit detection device for an inverter that can detect the short-circuit.

[0015]

In order to achieve the above object, the impedance short circuit detecting device according to the present invention is provided with a smoothing capacitor for each of a plurality of inverters having a common direct current or for each phase of the inverter. A current transformer is provided on each of the wirings of each smoothing capacitor, and an output of each current transformer is input to a short-circuit current detection circuit to detect a DC short circuit. Diodes are connected in the same direction between them.

[0016]

Each current transformer detects a current flowing through each smoothing capacitor. When a DC short circuit occurs, the output of the current transformer of the inverter or the inverter phase in which the DC short circuit has occurred increases due to a difference in wiring impedance. Since each diode is connected in the same direction between each current transformer and the short-circuit current detection circuit, only the maximum value in the output of each current transformer is input to the short-circuit current detection circuit, and the other current transformers Is not input to the short-circuit current detection circuit.

Therefore, the difference between the short-circuit time and the normal time of the detection current input to the short-circuit current detection circuit is not reduced by the output of the current transformer that does not output the maximum value. Therefore, it is possible to detect a DC short circuit without lowering the detection setting level of the short-circuit current detection circuit.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to the drawings.

In FIG. 1, 1A and 1B are inverters,
CA and CB are smoothing (electrolytic) capacitors connected to the DC side of the inverters 1A and 1B, CTA and CTB are current transformers for detecting current flowing through the smoothing capacitors CA and CB, R
A and RB are resistors connected to the secondary sides of the current transformers CTA and CTB, and 2 is a short-circuit current detection circuit connected to the output sides of the current transformers CTA and CTB via diodes DA and DB.

As described above, since the diodes DA and DB are connected between the current transformers CTA and CTB and the short-circuit detection circuit 2, the short-circuit current detection circuit 2 includes the current transformers CTA and C
Current transformer in which the maximum current flows in TB, for example, CTA
Of the current transformer CTA other than the current transformer CTA
The output of TB does not enter.

Therefore, when a DC short circuit occurs in the inverter 1A, the DC short circuit current K · IA (IA is a normal battery, K is a coefficient) can be detected without being affected by the output of the current transformer CTB.

In the above embodiment, the number N of the smoothing capacitors is two. When the number N is three or more, similarly, only the output of the current transformer in which the maximum current flows is short-circuited. Since the signal is input to the current detection circuit 2, even if the number N of the smoothing capacitors (= the number of current transformers) N increases, the difference between the short-circuit detection and the normal detection does not decrease.

Therefore, the detection set level in the short-circuit current detection circuit 2 can be set sufficiently higher than the level at the time of normal operation, so that the DC short-circuit can be reliably detected.

In the above embodiment, the number of inverters is plural. However, even when an electrolytic capacitor is provided for each phase of the inverter as shown in FIG. It goes without saying that a DC short circuit can be similarly detected by connecting diodes between the current detection circuits.

[0025]

The present invention is configured as described above, and has the following effects.

(1) The DC short circuit is detected by extracting only the output of the current transformer in which the maximum current is flowing among the current transformers for detecting the current of each of the divided smoothing capacitors. Therefore, it is possible to reliably detect a DC short circuit without lowering the detection level.

(2) Since the diodes are simply connected between the conventional current transformers and the short-circuit detection circuit, the structure is simple.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention.

FIG. 2 is a circuit diagram showing a DC short-circuit detection device of a conventional inverter.

FIG. 3 is a circuit diagram showing a conventional DC short-circuit detecting device of an inverter in which a smoothing capacitor is divided and installed.

[Explanation of symbols]

1, 1A, 1B ... inverter 2 ... short-circuit current detecting circuit _{C 1, C 2, CA,} CB ... smoothing capacitor CT1, CT2, CTA, CTB ... current transformer DA, DB ... diode TRU～TRY ... switching element

Claims (1)

(57) [Scope of request for utility model registration] 1. A smoothing capacitor is provided for each of a plurality of inverters having a common direct current or for each phase of the inverter, and a current transformer is provided on a wiring of each smoothing capacitor, and an output of each current transformer is provided. In the one that is input to the short-circuit current detection circuit to detect a DC short circuit, a diode is connected in the same direction between each of the current transformers and the short-circuit current detection circuit, and the short-circuit current detection circuit is connected to the output of each current transformer. DC short-circuit detection device for an inverter, wherein only the maximum value of the short-circuit is detected.