JPH0660296U - Inverter DC short-circuit detector - Google Patents

Abstract

(57) [Abstract] [Purpose] Detects a DC short circuit without lowering the detection setting level even if the number of current transformers increases. [Configuration] Multiple inverters 1 with common DC P and N
Smoothing capacitors CA and CB are installed for each of A and 1B, current transformers CTA and CTB are provided in the wiring of each capacitor, and the output of each current transformer is input to the short-circuit current detection circuit 2 to detect a DC short circuit. In this case, the diodes DA and DB are respectively connected in the same direction between the current transformers CTA and CTB and the detection circuit 2 so that only the maximum value of the outputs of the current transformers is input to the short-circuit current detection circuit 2. None, direct current short-circuit without lowering the detection setting level of short-circuit current detection circuit 2 by preventing the difference between the detection current short circuit and the normal state from becoming small by the output of another current transformer that does not output the maximum value. To detect.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to a DC current short-circuit detecting device for an inverter, which detects a DC short-circuit current generated when a switching element forming the inverter is damaged in the inverter device.

[0002]

[Prior art]

Referring to FIG. 2, in the inverter device, a smoothing (electrolytic) capacitor C ₁ is installed on the DC side of the inverter 1 to smooth the DC voltage.

The switching elements TRU to TRY forming the inverter 1 are alternately turned on and off without being turned on at the same time. For example, when the element TRU is damaged and remains on, the element TRX is turned on. DC short circuit occurs. In this case, it is necessary to promptly detect the DC short-circuit current and stop the failure of the inverter device.

The detection of this DC short-circuit current is carried out by installing a current transformer CT1 for AC in the wiring portion of the electrolytic capacitor C ₁ and connecting it to a short-circuit current detection circuit 2 having a detection level set. .

Due to the configuration of the inverter device, when the smoothing capacitors CA and CB are separately installed for each of the plurality of inverters 1A and 1B as shown in FIG. 3A, the current transformers CT A and CTB are provided. Is installed in the wiring portion of each capacitor CA, CB, and the output of each current transformer is input to the short-circuit detection circuit 2 to detect a DC short circuit.

Further, as shown in FIG. 3B, when the smoothing capacitors C ₁ and C ₂ are separately installed for each phase of the inverter, the current transformers are similarly connected to the wiring portions of the smoothing capacitors C ₁ and CB. CT1 and CT2 are installed to detect a DC short circuit.

[0007]

[Problems to be solved by the device]

 In the case of the conventional circuit of FIG. 2 (a), 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 short-circuited in a short time due to the difference in wiring impedance between the capacitors CA and CB and the inverter 1A >> the current from the capacitor CA >> the capacitor CB. It becomes the electric current flowing from.

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

Similarly, when the number of divided electrolytic capacitors is N, the normal detection current is N · IA and the short-circuit detection current is (K + N−1) IA.

For example, when K = 5, Table 1 is obtained.

[0012]

[Table 1]

As described above, as the number of divided electrolytic capacitors (= the number of current transformers) N increases, the difference between the detected currents at the time of a short circuit and at the time of normal operation becomes smaller. That is, as N increases, the detection setting level of the short-circuit current detection circuit 2 approaches the normal level, and 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 the above-mentioned conventional problems, and an object thereof is to prevent a DC short circuit without lowering the detection setting level even if the number of current transformers increases. Another object of the present invention is to provide a DC short-circuit detection device for an inverter that can detect it.

[0015]

[Means for Solving the Problems]

 In order to achieve the above object, the impedance DC short-circuit detection device according to the present invention is provided with a smoothing capacitor for each of a plurality of inverters having a common DC or for each phase of the inverter, and the smoothing capacitor of each smoothing capacitor is installed. In the case where each current transformer is provided in the wiring and the output of each current transformer 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 current transformer and the short-circuit current detection circuit. It is connected to.

[0016]

[Action]

 Each current transformer detects the current flowing through each smoothing capacitor. When a DC short circuit occurs, the output of the current transformer of the inverter or inverter phase where the DC short circuit occurs due to the difference in wiring impedance increases. Since the diodes are 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 Do not input the output of the instrument to the short circuit current detection circuit.

Therefore, the difference between the detected current input to the short-circuit current detection circuit at the time of the short circuit and the normal state 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]

Embodiments 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, and CTA and CTB are currents flowing through the smoothing capacitors CA and CB. Current transformers RA, RB are resistors connected to the secondary side of the current transformers CTA, CT B, 2 is a short-circuit current detection connected to the output side of the current transformers CTA, CTB via diodes DA, DB Circuit.

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 CTB. Only the output of the current transformer, such as CTA, in which the maximum current is flowing is input, and the output of the current transformer CTB other than this current transformer CTA is not input.

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 smoothing capacitors is 2. However, when the number N is 3 or more, only the output of the current transformer in which the maximum DC short-circuit current flows is short-circuited as well. Since the current is input to the current detection circuit 2, even if the number of smoothing capacitors (= the number of current transformers) N increases, the difference between the detection at the time of short circuit and the detection at the time of normal does not become small.

Therefore, it becomes possible to reliably detect a DC short circuit by setting the detection setting level in the short-circuit current detection circuit 2 to be sufficiently higher than the normal level.

In the above embodiment, the number of inverters is plural, but even when an electrolytic capacitor is provided for each phase of the inverter as shown in FIG. 3B, it is short-circuited with each current transformer. It goes without saying that a DC short circuit can be similarly detected by connecting diodes between the current detection circuits.

[0025]

[Effect of device]

 Since the present invention is configured as described above, it has the following effects.

(1) The DC short circuit is detected by extracting only the output of the current transformer with the maximum current flowing out of the current transformers that detect the currents of the smoothing capacitors installed separately. Therefore, a DC short circuit can be reliably detected without lowering the detection level.

(2) The configuration is simple because diodes are simply connected between each conventional current transformer and the short-circuit detection circuit.

[Brief description of 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 detecting device for a conventional inverter.

FIG. 3 is a circuit diagram showing a conventional DC short-circuit detection device for an inverter in which smoothing capacitors are separately 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)

[Scope of utility model registration request] 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 for each smoothing capacitor wiring, and an output of each current transformer is provided. In the one for detecting a DC short circuit by inputting to the short-circuit current detection circuit, each 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 outputs the current of each current transformer. A DC short-circuit detection device for an inverter, characterized in that it detects only the maximum value of.