JPS6033748Y2 - Element abnormality detection circuit for forward conversion circuit - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to an element abnormality detection circuit for detecting an abnormality in a semiconductor rectifying element in a bridge type forward conversion circuit using semiconductor rectifying elements. The present invention relates to a detection circuit suitable for detecting a short-circuit failure of a rectifier in the case of a rectifier.

FIG. 1 is a conventional circuit diagram in which an element abnormality detection circuit is provided in a full-wave rectifier circuit using a diode bridge.

The full-wave rectified outputs from the diodes D1 to D4 are smoothed by a smoothing capacitor C8 and applied to the load as a power supply or DC detection voltage.

Abnormalities in the diodes D□ to D4 are detected by the voltage applied to the relay Ry□ provided between the DC output terminals P and N.

Here, when the load is removed, the smoothing capacitor C8
Since there is almost no discharge circuit (only the energizing current of relay Ry), the voltage between PN is 72 times the AC power supply voltage e regardless of whether the rectifier circuit configuration is a full-wave rectifier circuit or a half-wave rectifier circuit.

However, in the case of a full-wave rectifier circuit, P
NN voltage drop is small and cannot be detected by relay Ry1, whereas in the case of a half-wave rectifier circuit, voltage drop is large and relay Ry□ is deenergized and detection is possible.

Now, if one of the diodes D□ to D is short-circuited, it corresponds to a half-wave rectifier circuit, and when a load is applied, an element abnormality can be detected by relay Ry1.

If two of diodes 1 to D are short-circuited, PN
Since no voltage is generated between them, relay Ry1 can detect an element abnormality.

Therefore, the element abnormality detection circuit using the relay Ry□ cannot detect an abnormality in one diode until a load is applied.

If the AC input side of the rectifier circuit is a potential transformer (PT), a short circuit in one diode will cause a short circuit current to flow in the rectifier circuit, causing another diode in the short circuit to fail, resulting in a short circuit failure. This is the same as if two diodes were short-circuited, and an element abnormality in relay Ry1 can be detected even when there is no load.

However, when the input is a current transformer (CT), the short circuit current is small, so the short circuit only occurs in one diode, and the relay R
Element abnormality cannot be detected until a load is applied to y1.

In this way, in the element abnormality detection circuit shown in Fig. 1, when no load is applied, the AC input side is connected to a current transformer (CT
), it was not possible to detect a short-circuit failure in one semiconductor rectifying element when no load was applied.

An improved conventional circuit is shown in FIG.

In the figure, a 1-winding polarized relay is added, and the coil 1 is connected in parallel with the diode D1 and the coil 2 is connected in parallel with the diode D4 so that the coil 1 and the coil 2 have opposite polarities. is the driving force of coil 1 and coil 2
When one of the diodes is short-circuited, the balance between the driving force and the suppressing force is lost, and an abnormality is detected by operating the polarized relay.

Note that the AC input side is shown as a transformer @l1CT.

The element abnormality detection operation will be explained below. First, when all diodes D1 to D4 are normal, in the positive half wave from the current transformer IT, voltage (e to vc) is applied to coil 1, and voltage (e-vc) is applied to coil 2.
vc) Voltage is applied and both are excited, but they cancel each other out and the polarized relay does not operate.

In addition, (e ~ VC), if e>VC, e appears and V
If C>e, it means that vc appears.

In the negative half-wave, coils 1 and 2 are connected to diodes D1. D4
Since both coils 1 and 2 are short-circuited, no voltage is applied to both coils 1 and 2, and the relay is inoperative.

In this way, under normal conditions, both coils are excited every half wave.

Next, when the diode D1 is short-circuited, the coil 1 is short-circuited by the diode D1 in the positive half wave, and since VC is applied to the coil 2, the polarized relay operates to detect an abnormality.

It should be noted that during negative half-waves, the relay is inactive as in normal times, and the relay detects an abnormality at positive half-wave timing.

Similarly, when diode D4 is short-circuited, Vc is applied to positive half-wave coil 1, and the relay with coil 2 short-circuited operates.

Next, when diode D2 is short-circuited, Vc is applied to coil 1 in the negative half wave, and coil 2 is short-circuited by diode D4, so the relay operates.

Note that during the positive half-wave, it is inactive, which is the same as during normal operation.

Similarly, when diode D3 is short-circuited, coil 1 is short-circuited at diode D1 during the negative half wave, and Vc is applied to coil 2, causing the relay to operate.

Also, in the positive half wave, it is inactive as in the normal state.

In this way, even when the AC input side is a current transformer, when any one of the diodes D□ to D is short-circuited, the polarized relay is activated by either the positive or negative half-wave, and the diode abnormality is detected. can be detected.

However, the detection circuit shown in FIG. 2 requires an expensive two-winding polarized relay, and has a short lifespan because it is constantly energized.

In addition, since it is constantly excited, it is necessary to adjust the resistors aR1 and R2 to appropriate values to maintain a balance so as not to malfunction during normal operation, and this adjustment work is time-consuming.

The purpose of this invention is to detect an abnormality in a single semiconductor rectifying element by adding one commonly used relay and a simple resistance circuit, and also to make it possible to detect an abnormality in a single semiconductor rectifying element, and also to eliminate the need for adjustment because the relay is not energized during normal operation. An object of the present invention is to provide an element abnormality detection circuit.

FIG. 3 shows an embodiment of the present invention.

A resistor #3 is connected between AC input sides A and B of the rectifier circuit. A series circuit of R4 is provided, and a neutral point C is formed by making the resistance values of resistors R3 and R1 the same.

Similarly, a resistor R5 is installed between P and N on the DC circuit side of the rectifier circuit.
? A series circuit of R6 is provided, and a resistor of 15? The resistance value of R6 is made the same to form a midpoint resistance.

And between neutral points C and D is relay R3' for element abnormality detection.
2 are provided.

This relay Ry2 is a normal DC relay.

In such a configuration, when all of the diodes D□ to D4 are normal, the potential difference between the neutral points C and D is zero, so the relay Ry2 is not excited.

This will be explained in detail below.

(i) When the voltage between A and 8 is smaller than the voltage between P and N during a positive half wave, all diodes D to D are in a non-conducting state, so no current flows between neutral points C and D. C and D have the same potential.

(ii) When the voltage between A and 8 is smaller than the voltage between P and N in the positive half wave, the diode D2. D3 becomes conductive,
A and P, B and N are at almost the same potential, C and D are at the same potential, and relay Ry2 does not operate.

(iii) When the voltage between A and 8 is smaller than the voltage between P and N during a negative half wave, the result is the same as in case (i) above.

(iv) When the voltage between A and 8 is greater than the voltage between P and N in the negative half wave, diode D4. D□ becomes conductive, and A
and N and B and 2 become almost the same potential, and the above (ii
) is the same as in the case of

As described above, when all of the diodes D□ to D4 are normal, the potential between C and D becomes the same under any condition, and no current flows through the relay RJ2, so it does not operate.

Next, when diode D0 causes a short-circuit failure, CT is short-circuited in the positive half wave, a potential difference is generated between C and D, and relay Ry2 detects an abnormality.

In the negative half wave, it becomes inoperable as in the normal state.

This will be explained in detail below.

(i) In the positive half wave, A and B are short-circuited through D1 to D3, so the voltage between them becomes zero.

If the impedance of relay Ry2 is the resistance R3, R6
If it is very large compared to , the potential of C will be almost the same as that of A and B.

By the way, since Do is short-circuited, A and N are at the same potential, and a voltage is applied between C9D and N.

D. The voltage between N is the voltage between P and N, that is, the DC output voltage Vc
Since it is above, a voltage of Vc/2 is applied between C9D and Ry2 operates.

The current path is P since Dl is short-circuited and D is conductive.
-D-C-A (and B)-N.

In addition, other circuits such as the one shown in Fig. 4a, R3=R
4=RA, R5=R6=RD, and the coil impedance of relay R3'2 is Z, then a becomes as shown in b.

At b, the current I flowing through relay Ry2 is c ■”2(Z+RA)+R8 (1),
If the resistors R3, R4, and R5°RstZ are set so that the value of ◯ is larger than the minimum operating current value of the relay RY2, the relay Ry2 operates and can detect an abnormality in the element.

In addition, if R3~Rs < Z, the above formula (1) becomes IJψ・・・・・・(2) Therefore, the above conditions can be determined by selecting relay Ry2.

(ii) If the voltage between A and 8 is smaller than the voltage between P and N during the negative half wave, the potentials of A and N will be the same because diode D1 is shorted, increasing the impedance Z of relay Ry2. Therefore, the potential difference between C9D is P
, N is equal to the value obtained by subtracting the chamber pressure between A and B, and a current flows through relay Ry2.

(iii) When the voltage between AB is greater than the voltage between P and N in the negative half wave, diode D4 becomes conductive and B.

1 and between A and N, the potentials of C and D also become the same, and no current flows through relay Ry2.

FIG. 5 shows voltage and current waveforms at various parts.

Similarly, when diode D2 causes a short-circuit fault, relay R3'2 is inactive during the positive half-wave, as it is during normal operation, but during the negative half-wave, relay R3'2 is inactive, but during the negative half-wave, D4. Since CT is shorted at D2, C,
A potential difference is created between D, current flows through the path P-A(B)-C-D-N, and relay Ry2 is activated.

Furthermore, when diode D3 causes a short-circuit failure, relay Ry is inoperative during the positive half-wave as in the normal state, but during negative half-wave, D3. Since Dl is short-circuited, a potential difference is created between C and D, and current flows through the path P-D-C-B(4)-N, and relay Ry2 is activated.

Also, when the diode D4 causes a short-circuit failure, the positive half wave causes the diode D2. Since CT is short-circuited at D4, a potential difference is created between Ct and D, and current flows through the path P-B(A)-C-D-N, and relay Ry2 is activated.

In the negative half wave, the relay R3'2 is inoperative as in the normal state.

As described above, when each of the diodes D□ to D4 is short-circuited, the relay Ry2 operates even when no load is applied, and an abnormality can be detected.

Note that if the return time of relay RY2 is sufficiently longer than the half cycle time, no beat will occur and the relay will operate perfectly.

Furthermore, even in the case of a relay with a short recovery time, if a capacitor is added to both ends of the coil, the voltage applied to the relay Ry2 can be smoothed and its operation can be stabilized.

According to this embodiment, a normal DC relay can be used as the relay R3'2, and since it is not energized during normal operation, its life can be extended.

Further, there is no need to adjust the operation and non-operation of the relay Ry2 using a resistor circuit, and the configuration of the detection circuit becomes simple.

In the embodiment, a case where the present invention is applied to a single-phase AC rectifier circuit is shown, but the present invention is not limited thereto, and can also be applied to a multi-phase AC rectifier circuit such as a three-phase AC rectifier.

As explained above, the present invention is a commonly used 1
The configuration of two DC relays and a simple resistance circuit has the effect of detecting an abnormality in a single semiconductor rectifying element.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram showing a conventional element abnormality detection circuit, Fig. 2 is a diagram showing another conventional detection circuit, and Fig. 3 is an embodiment of an element abnormality detection circuit of a forward conversion circuit according to the present invention. 4a and b are equivalent circuit diagrams for explaining the operation of FIG. 3, and FIG. 5 is a diagram showing voltage and current waveforms at various parts when the diode D□ in FIG. 3 is short-circuited. It is. CT...Current transformer, D□~D4...Diode, Ryl, Ry2...Relay, co...
... Smoothing capacitor, L ... Load, R1 ~
R...Resistance.

Claims (1)

[Scope of utility model registration request] In a bridge type forward conversion circuit that uses a diode rectifier and has a smoothing capacitor on the DC side, there is a resistor circuit that forms a neutral point on the AC input side of the forward conversion circuit, and a neutral point on the DC output side of the forward conversion circuit. and a relay provided between the neutral points of both of the resistance circuits, and detects a short-circuit abnormality in the diode rectifying element by actuation of the relay. detection circuit.