JPS6111057B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an overvoltage protection device that effectively suppresses surge voltage that enters from the alternating current or direct current side of a semiconductor power conversion device.

2. Description of the Related Art Conventionally, as a surge voltage absorption circuit for a semiconductor power conversion device, circuits such as those shown in FIGS. 1 and 2 have been used. In the one shown in Fig. 1, a CR absorber 2 consisting of a capacitor and a resistor is provided between the lines on the secondary side of the transformer 1, and a CR absorber 3 is also provided in parallel to the diode D that constitutes the power converter. A CR absorber 4 is also provided on the output side. The one in Fig. 2 has a diode clipper circuit 5 on the secondary side of the transformer 1, a CR absorber 6 connected in parallel to the thyristor SCR constituting the power converter, and a lightning arrester 7 on the output side of the converter.
It has been established.

However, these conventional examples have the following drawbacks.

(b) In the one in Figure 1, CR absorbers 2, 3,
The loss of the resistor 4 is large, and consideration must be given not only to this loss but also to cooling.

(b) Since the CR absorbers 2, 3, 4, and 6 and the diode clipper circuit 5 have a series circuit of a capacitor and a resistor as their main components, it is not possible to expect the same suppressing effect against surge voltages of all frequencies.

(c) The lightning arrester 7 shown in FIG. 2 has a high discharge starting voltage, which is disadvantageous for the insulation design of the converter.

In order to solve these drawbacks, a method of using nonlinear overvoltage suppressing elements such as a discharge gap, a nonlinear resistor, a Zener diode, and a Celecia arrester in place of the CR absorber 2 has been considered, but this also has the following effect. This causes various problems.

(a) Nonlinear overvoltage suppression elements generally not only have a small discharge withstand capacity, but are also considered to be somewhat less reliable than capacitors. Therefore, in order to put it into practical use, protection measures such as connecting a fuse in series with the nonlinear overvoltage suppressing element are taken to prevent accidents such as deterioration and short circuits, but the input voltage of the converter is high (for example, 3000 V or more). In this case, there is no suitable semiconductor protection fuse (a special fuse that does not generate overvoltage when it blows).

(b) When the deterioration is shortened, the secondary side of the transformer is short-circuited,
This may result in a DC short circuit, but complex wiring is required to withstand the large current that flows at this time.

The present invention has been made to eliminate the above-mentioned conventional drawbacks, and an object thereof is to provide an overvoltage protection device for a semiconductor power conversion device that is highly reliable, inexpensive, and highly effective in suppressing surge voltage.

Embodiments of the present invention will be described below with reference to the accompanying drawings.

In the embodiment shown in FIG. 3, a series circuit consisting essentially of both nonlinear overvoltage suppressing elements and a capacitor is provided between the AC side lines of a semiconductor power converter, and a unidirectional nonlinear overvoltage suppressing element and a capacitor are provided on the DC side of the converter. A series circuit is provided. here,
Two breakdown diodes (Zener diodes or controlled door avalanche diodes) connected in anti-series are used as the bidirectional nonlinear overvoltage suppression element, and a breakdown diode is used as the unidirectional nonlinear overvoltage suppression element. That is, in FIG. 3, the series circuit of anti-series connected breakdown diodes B ₁ and B ₂ and capacitor C ₁ is on the AC side of the semiconductor power converter. Connected to the secondary side of transformer 1, breakdown diode B ₃ on the DC side of the converter
and a series circuit with capacitor C ₂ are connected. In addition, in parallel to the diode D that constitutes the conversion device,
CR absorber 3 is connected.

When the server voltage enters from the AC side or DC side of the converter, when the surge voltage reaches a predetermined level, the breakdown diodes B ₁ , B ₂ ,
B ₃ limits its value. At this time, the capacitor
If the capacitances of C ₁ and C ₂ are set to a very large value, they can be regarded as a short circuit in response to a surge voltage. On the other hand, during steady state, the breakdown diode B ₁ ,
B ₂ and B ₃ have almost no loss, and capacitors C ₁ and C ₂
Since the capacitors C 1 and C 2 can be considered to be in an open state compared to the capacitors C ₁ and C ₂ , almost no voltage is applied to the capacitors C 1 and C 2 and only an extremely small current flows.

Therefore, for example, compared to the capacitor constituting the CR absorber 2 in FIG. 1, the capacitor shown in FIG.
Since _C1 only needs to have a small voltage rating, it is also possible to use a relatively large capacitor. Also, in case the breakdown diodes B ₁ , B ₂ ,
Even if _B3 deteriorates and short-circuits, the short-circuit current can be suppressed by capacitors _C1 and _C2 , and if the capacitances are appropriately selected, it is possible to continue operation of the converter.

Note that a bidirectional breakdown diode may be used instead of the anti-series connected breakdown diode.

In the embodiment shown in FIG. 4, a Y-connection circuit is provided in which one arm is composed of a series circuit of a breakdown diode B ₄ and a capacitor C ₃ on the AC side of the semiconductor power converter, and the converter is connected in the same way as in FIG. A series circuit consisting of a breakdown diode _B3 and a capacitor _C2 is provided on the DC side. Since the operation is almost the same as that in FIG. 3, the explanation thereof will be omitted.

In FIG. 5, a discharging resistor R ₁ is connected to the capacitor C ₃ of FIG. 4. Even with this configuration, there is no loss in resistor _R1 because capacitor _C3 is not constantly charged.

In the embodiment shown in Fig. 6, a series circuit of a breakdown diode B5 and a capacitor _C4 is connected to the output side of a diode bridge circuit BRG connected to the AC side of the semiconductor power exchange device, and a series circuit of a breakdown diode _B5 and a capacitor C4 is
Connect a resistor R ₂ in parallel to C ₄ , a breakdown diode B ₃ and a capacitor on the DC side of the converter
This is a series circuit of _C2 connected. Even with this configuration, the same effect as the embodiment shown in FIG. 3 can be obtained.

The embodiment shown in FIG. 7 includes a capacitor C ₅ connected in parallel to a thyristor SCR constituting a semiconductor power converter, a breakdown diode B ₆ connected in anti-series,
A series circuit consisting of B ₇ and a low impedance resistor R ₃ is connected, and a diode D ₁ and a light emitting diode P are further provided in parallel with the resistor R ₃ . For example, if the voltage during reverse recovery of a thyristor exceeds a certain level, the breakdown diode
B ₆ or B ₇ limits its value, and in this case capacitor C ₅ can be considered as a short circuit. During steady state, the breakdown diodes B ₆ and B ₇ are considered to be in an open state, and almost no voltage is applied to the capacitor C ₅ . Therefore, the same effect as the embodiment shown in FIG. 3 can be obtained. Also, breakdown diode B ₆ ,
When _B7 deteriorates and short-circuits, the current flowing through capacitor _C5 generates a voltage across resistor _R3 , which causes current to flow through light-emitting diode P, which emits light. The photoelectric conversion circuit PE detects this light and detects an abnormality. Detected. Therefore, when no abnormal signal is output from the photoelectric conversion circuit PE, the overvoltage protection device is working normally, and the reliability of the device is improved.

Although a breakdown diode is used as the nonlinear overvoltage suppressing element in the above-described embodiment, it is of course possible to use other elements with similar characteristics.

As is clear from the above explanation, since the overvoltage protection device of the present invention is composed of a series circuit of a nonlinear overvoltage suppression element and a capacitor, almost no loss is generated from the nonlinear overvoltage suppression element during steady state, and compared to a capacitor. The capacitor becomes almost open, and the current flowing through the capacitor is small, allowing the use of a large capacitance capacitor. Furthermore, when an overvoltage is applied, the nonlinear overvoltage suppression element limits its value, and even if the nonlinear overvoltage suppression element deteriorates and shorts, the capacitor can suppress the short circuit current, allowing the conversion device to continue operating. Therefore, the conventional drawbacks are wiped out, and
Costs can be drastically reduced.

[Brief explanation of the drawing]

Figures 1 and 2 are circuit diagrams showing conventional examples, and Figure 3 is a circuit diagram showing a conventional example.
4, 5, 6 and 7 are circuit diagrams showing embodiments of the present invention. 1...Transformer, 2,3,4,6...CR absorber, 5...Diode clipper circuit, 7...Surge arrester, _C1 , _C2 , _C3 ...Capacitor, _B1 , _B2 ,
B ₃ , B ₄ , B ₅ , B ₆ , B ₇ ... Breakdown diode, D, D ₁ ... Diode, SCR ... Thyristor, R ₁ , R ₂ , R ₃ ... Resistor, P ... Light emission Diode, PE...photoelectric conversion circuit.

Claims (1)

[Scope of Claims] 1. A series circuit consisting of a nonlinear overvoltage suppressing element and a capacitor is provided between at least one line on the AC side or the DC side of the semiconductor power conversion device to suppress surge voltage entering the semiconductor power conversion device. An overvoltage protection device for a semiconductor power conversion device, characterized in that: 2. A semiconductor power converter characterized in that a series circuit consisting of a nonlinear overvoltage suppressing element and a capacitor is provided in parallel with each thyristor constituting the semiconductor power converter to suppress surge voltage entering the semiconductor power converter. Equipment overvoltage protection device. 3. A series circuit consisting of a nonlinear overvoltage suppressing element and a capacitor is provided on the output side of the diode bridge circuit connected to the AC side of the semiconductor power converter to suppress surge voltage entering the semiconductor power converter. An overvoltage protection device for a semiconductor power conversion device characterized by: