JPH0697833B2 - Overvoltage protection device for thyristor converter - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an overvoltage protection device for a thyristor converter used for DC power transmission and the like.

[Technical background of the invention and its problems]

A thyristor converter configured by connecting thyristors in series or in series-parallel is widely used as a high-voltage thyristor converter even in a high-voltage field such as DC power transmission and reactive power compensator. By the way, the thyristor converter needs so-called overvoltage protection against a surge voltage that intrudes from the outside, for example, a lightning impulse voltage or a switching impulse voltage. Therefore, in the past, high voltage thyristor converters have been provided with overvoltage protection using an arrester and overvoltage protection by the ignition function of the thyristor itself.

FIG. 5 is a circuit diagram showing the configuration of a conventional overvoltage protection device for a thyristor converter using an arrester. In the figure, only one arm of the three-phase bridge converter is shown in the thyristor converter, and the others are omitted. The serially connected thyristors 1 forming the arm are connected in series to the reactor 2. The reactor 2 acts to suppress the voltage gradient dv / dt and the current gradient di / dt of the thyristor 1.
Further, the thyristor 1 is connected in parallel with a snubber circuit 3 for equalizing high-frequency voltage and a DC voltage dividing resistor 4 for equalizing DC voltage. In addition, the arm (hereinafter,
The arrester 5 made of a non-linear resistor is connected in parallel to the thyristor valve). The arrester 5 suppresses the surge voltage below the withstand voltage of the thyristor valve and protects the thyristor valve from damages from the surge voltage intruding from the outside. By the way, the surge voltage intrusion into the thyristor valve occurs randomly at an arbitrary phase regardless of the operating state of the thyristor valve. Figure 6 shows
It is a time chart which showed the phase relation which surge voltage invades into a thyristor valve at the time of reverse conversion operation.
(A) shows the gate signal of a thyristor valve, (b) shows the voltage of a thyristor valve. Also, (c) to (e) are
FIG. 4 is an enlarged view showing a part of the time relationship of the voltage of the thyristor valve shown in (b), in which the broken line shows the surge voltage V _s entering the thyristor valve for various intrusion phases. . That is, (c) shows that when the surge voltage V _s enters the thyristor valve after time t ₃ ,
(D) shows the surge voltage intrusion between times t ₂ and t ₃ , and (e) shows the surge voltage intrusion between times t ₁ and t ₂ . In the figure, in the state of (c), the carrier of the thyristor after energization has completely disappeared, and since only the surge voltage below the protection level of the arrester is applied to the thyristor valve, the thyristor valve can sufficiently withstand the surge voltage. On the other hand, in the state of (e), since the carriers have not disappeared after energization, the thyristor valve is destroyed by the surge voltage entering the thyristor valve. The state of (d) is
In the intermediate state between (c) and (e), the thyristor valve may or may not withstand surge voltage intrusion. As described above, the effect of the surge voltage on the thyristor valve depends on what phase of the thyristor valve at the time of operating the surge voltage, and what value the forward withstand voltage of the thyristor valve has just after energization. It will be different depending on.

FIG. 7 is a waveform chart showing the relationship between the characteristics of the forward withstand voltage V _w of the thyristor valve and the protection level V _{p of the} arrester in each operation mode of the thyristor valve. (A) shows the case where the operation mode is reverse conversion, (b) shows the case of forward conversion, and (c) shows the case of floating, that is, the case where the AC signal is applied to the thyristor valve but the gate signal is not applied to the thyristor. ing. In the figure, the forward withstand voltage V _w of the thyristor valve is zero or low not only during energization but also immediately after energization due to the existence of carriers in the thyristor. On the other hand, after energization, the forward withstand voltage gradually recovers as the carriers decay, and reaches a constant withstand voltage V _w after a predetermined time. Therefore, the withstand voltage characteristic of the thyristor valve changes according to each operation mode as shown by the broken lines in (a) and (b).

By the way, when the thyristor valve is overvoltage-protected by the arrester, basically, the protective effect is not produced unless the protection level V _{p of the} arrester is set smaller than the withstand voltage V _w of the thyristor valve. However, as described above, the withstand voltage characteristic of the thyristor valve changes depending on each operation mode of the thyristor valve. For example, immediately after energization, V _p becomes larger than V _w , and the protection coordination of the arrester for protecting the thyristor valve is broken. .

That is, in FIG. 7, the arrester does not work for overvoltage protection of the thyristor valve in the shaded portions of (a) and (b). On the other hand, in the floating state without energization, that is, in the case of (c), V _p is always smaller than V _w , and the thyristor valve is effectively protected by the arrester. Therefore, when the overvoltage protection coordination immediately after energization is broken, if a surge voltage such as a lightning surge enters from the outside, the thyristor valve cannot withstand the surge voltage and will be destroyed, leading to a serious failure. Had.

[Object of the Invention]

The present invention has been made to solve the above problems, and a thyristor converter capable of protecting a thyristor valve from damage due to overvoltage against surge voltage intruding from the outside even immediately after energization of the thyristor valve. It is intended to provide an overvoltage protection device.

[Outline of Invention]

The present invention generates a reference signal function related to the recovery characteristic of the forward withstand voltage of the thyristor converter immediately after the energization of the thyristor, detects an overvoltage of the arm of the thyristor converter, and detects the reference signal function. When the overvoltage is larger than the withstand voltage of the thyristor converter, the arm of the thyristor converter is ignited, and the thyristor converter is protected against the surge voltage invading from the outside. It is designed for overvoltage protection.

〔Example〕

FIG. 1 is a circuit diagram showing the configuration of the first embodiment of the present invention.
Similar to that shown in FIG. 5, the configuration of only one of the thyristor arms of the three-phase bridge converter is shown.
The description of other arms is omitted. The plurality of thyristors 1 forming the arm are connected in series with each other, and further the reactor 2 is connected in series. Here, one of the plurality of thyristors 1 is a representative thyristor 11, and a snubber circuit 3 and a DC voltage dividing resistor 4 are connected in parallel to each of the thyristors 1 including the representative thyristor 11. The light-emitting elements 71 and 72 are connected in parallel to the DC voltage dividing resistor 4 of the representative thyristor 11 in opposite polarities. Further, the gate signal 141 is supplied to the gate of each thyristor 1 including the representative thyristor 11 from the gate signal amplifier 14 provided corresponding to each thyristor 1. A power supply voltage is supplied to the gate signal amplifier 14 from the corresponding anode of the thyristor 1 via the resistor 13, the light receiving element 12 as a signal input means is connected, and an optical signal is applied via the light guide 61. On the other hand, in the thyristor valve in which the thyristors 1 including the representative thyristor 11 are connected in series, the arrester 5 is connected in parallel, and the overvoltage detection circuit in which the resistor 20 and the light emitting element 21 are connected in series is connected in parallel. A diode 22 for reverse voltage protection is connected in parallel to the light emitting element 21.

The light emitting elements 71, 72, 21 and the light receiving element 12 described above are respectively received by the light receiving elements 91, 92, 2 via the light guides 81, 82, 23, 61.
4 and the light emitting element 6 are optically connected.

The light emitting element 71 detects the forward voltage of the thyristor element and emits light, and applies an optical signal to the light receiving element 91 forming the light receiving circuit 101 via the light guide 81.

Similarly, the light emitting element 72 detects the reverse voltage of the thyristor element and applies an optical signal via the light guide 82 to the light receiving element 92 forming the light receiving circuit 102. The light receiving circuit 101 supplies the forward voltage detection signal 103 to the gate signal generator 15. Further, the light receiving circuit 102 supplies the reverse voltage detection signal 104 to the gate signal generator 15 and the reference signal generator 26. The gate signal generator 15 is supplied with a gate command signal 151 for performing normal firing of the thyristor valve, and at the same time, a gate command signal during overvoltage for performing ignition during overvoltage immediately after energization.
152 has been entered. Here, the gate signal generator 15 includes a light emitting element 6 corresponding to the thyristor 1 including the representative thyristor 11, and supplies an optical signal to the light receiving element 12 of the gate signal amplifier 14 via the light guide 61. On the other hand, a reference signal generator to which the reverse voltage detection signal 104 of the light receiving circuit 102 is added.
A gate command signal 151 for performing a normal firing is further added to the 26, and an output signal 261 of the reference signal generator 26 is added.
Is supplied to one input terminal of the comparator 27. Comparator 27
An overvoltage detection signal 251 output from a ground level light receiving circuit 25 including a light receiving element 24 is supplied to the other input end of the. Here, an optical signal output from the light emitting element 21 of the overvoltage detecting circuit is supplied to the light receiving element 24 via the light guide 23. The comparator 27 compares the output signal 261 with the overvoltage detection signal 251, and the overvoltage detection signal 251 outputs the output signal.
When it is larger than 261, a gate command signal 152 at the time of overvoltage for causing ignition at the time of overvoltage immediately after the energization is supplied to the gate signal generator 15.

The reference signal generator 26 is a signal related to the forward withstand voltage characteristic of the thyristor valve immediately after energization, based on the gate command signal 151 and the reverse voltage detection signal 104 input thereto.
Generates 261. That is, the reference signal generator 26 determines the energization state from the gate command signal 151, and also determines from the reverse voltage detection signal 104 that it is just after energization, and by inputting the reverse voltage detection signal 104, the forward direction of the thyristor valve. The reference signal function related to the voltage recovery characteristic of is output as the output signal 261. At this time, the reference signal function is set lower than the forward voltage recovery characteristic of the thyristor valve.

The operation of this embodiment will be described below.

First, the reference signal generator 26 inputs the reverse voltage detection signal 104 detected from the representative thyristor 11 and the gate command signal 151 to output the reference signal function in the forward direction immediately after energization, and outputs the output of the thyristor valve. It is added to the comparator 27 after lowering it in consideration of the margin corresponding to the ability. The comparator 27 uses the reference signal function 261 and the overvoltage detection signal 251 obtained by detecting the surge voltage actually applied to the thyristor valve with the light emitting element 21.
When the surge voltage is higher than the reference value, the gate command signal 152 is supplied to the gate signal generator 15, and the thyristor valves are simultaneously ignited by using the thyristor's ignition function. In this way, overvoltage protection of the thyristor converter is performed.At this time, the reference signal function 261 output by the reference signal generator 26 simulates the forward voltage resistance characteristic of the thyristor valve immediately after energization. Therefore, even if the phase relationship in which the surge voltage enters the thyristor valve changes, the thyristor can be sufficiently protected from overvoltage breakdown within the range of the withstand voltage of the thyristor.

Hereinafter, a more detailed operation will be described with reference to FIG. FIG. 2 is a time chart showing the waveform of each part of the present embodiment, (A) is a floating time chart, that is, a time chart in which a gate signal is not input to the thyristor while an AC input is applied to the thyristor valve, (B) is a time chart when the operation mode is reverse conversion. In the figure, (a) is a voltage waveform of the thyristor valve, (b) is a gate command signal (reference numeral 151 in FIG. 1),
(C) is a reverse voltage detection signal (reference numeral 104 in FIG. 1), (d)
Is a reference signal function output by the reference signal generator (reference numeral 261 in FIG. 1), and (e) is an overvoltage detection signal (reference numeral 25 in FIG. 1).
1) and (f) show a gate command signal (reference numeral 152 in FIG. 1) at the time of overvoltage, and (g) shows a gate signal (reference numeral 141 in FIG. 1) of each thyristor. In the floating state of (A), since there is no energization, the reference signal function 261 has a constant output corresponding to the protection level V _p . On the other hand, during the operation of (B), the reference signal function 261 once becomes zero immediately after energization (t = t _{1 in the} figure), and then increases as a time function signal corresponding to the forward withstand voltage of the thyristor. At t = t ₃ , the reference signal function 261 returns to a value corresponding to the protection level V _p in the floating state.
Note that, the level of V _p is V _p, i.e. protection level equal to or slightly higher arrester 5 in Figure 7.
Now, suppose that the surge voltage intrudes in the vicinity of t = t ₂ shown in FIG. 2 (B). If an overvoltage signal having a waveform as shown by a broken line in (e) is generated in the overvoltage detection signal 251, and the signal is larger than the reference signal function 261 related to the withstand voltage of the thyristor valve shown in (d), At the time of middle t = t ₂ , the comparator 27 generates the gate command signal 152 as shown by the broken line (f). As a result, the gate signal 140 indicated by the broken line in (g) is input to each thyristor, the thyristors are simultaneously fired, and the thyristor valve is reliably protected from damage due to surge voltage. That is, in the thyristor, the withstand voltage in the forward direction becomes smaller than the withstand voltage V _{w in the} other period from the time t = t ₀ to t = t ₃ (the period of T _C + T _{F in} the figure) of (B). Therefore, the overvoltage protection is performed by the gate function only during the period of T _C + T _F. Regarding the period T _C , the gate command signal shown in FIG.
151) will be supplied, so additional protection only needs to be provided for the period T _F. The overvoltage protection of the thyristor during the period other than the above period is performed by the arrester.

Next, a second embodiment will be described with reference to FIGS. 3 and 4. FIG. 3 is a block diagram showing the configuration of the main part of this embodiment, and FIG. 4 is a time chart for explaining its operation. 3 is different from the configuration of the embodiment shown in FIG. 1 in that the light receiving circuit 252 for inputting the optical signal detecting the overvoltage through the light guide 23 receives not only the overvoltage,
The steepness of the rising edge of the input signal that detected the overvoltage, that is, dv / d
Also, t can be detected, and the light receiving circuit 252 supplies the signal 253 whose steepness is detected to the reference signal generator 262. Then, the reference signal generator 262 is adapted to supply the reference signal function 263 of different rising edge to the comparator 27 according to the signal 253. That is, the reference signal generator 262, as shown in FIG. 4, responds to the detection signal 253 of the steepness (dv / dt) detected by the light receiving circuit 252 when the dv / dt is dv ₁ / dt. When the rising edge of the signal function is g ₁ , and when dv / dt is dv ₂ / dt, g is g ₂ , dv / dt
When dt is dv ₃ / dt, g is g ₃ (where dv ₁ / dt <dv ₂ / dt <dv
₃ / dt), the rising edge g of the reference signal function 263 is determined, and the reference signal function 263 is supplied to the comparator 27. On the other hand, the forward withstand voltage of the thyristor valve after energization is generally affected by the rising steepness (dv / dt).
Withstand voltage is low. Therefore, according to the present embodiment, the reference signal generator 262 supplies the reference signal function 263 having a rising edge in which the steepness (dv / dt) is also added to the comparator 27,
Since the reference signal function 263 and the overvoltage detection signal 251 are compared and used as the gate command signal 152, the thyristor converter can be protected against overvoltage with higher accuracy.

In the description of the first and second embodiments, the floating, forward, and reverse conversion operation modes have been described, but the overvoltage protection of the present embodiment is not limited thereto.
It goes without saying that the same phenomenon that occurs immediately after the current is interrupted during operation or immediately after the bypass pair is energized can also be applied. Further, in the above embodiment, the reference voltage generator, the overvoltage detection circuit including the light receiving circuit and the comparator are provided in units of the thyristor valve, and the light receiving circuit system is also included to perform processing at the ground level. By providing the means for performing the overvoltage detection and the signal processing of each thyristor as a unit, the detection and the processing can be performed for each thyristor unit, and the same effect as the above embodiment can be realized.

Further, in the description of the above embodiment, the steady value V _p of the reference signal function output by the reference signal generator is set to be equal to or higher than the protection level of the arrester, but the protection is set by the following. The range of functions can be changed optimally. That is, the steady output V of the reference signal generator
_{When p} is made larger than the protection level of the arrester, the protection in the steady state is made by the arrester, and when the steady output V _p of the reference signal generator is made equal to the protection level of the arrester,
When the steady state protection is overvoltage protection by the arrester or the gate of the present invention, and when the steady output V _p of the reference signal generator is smaller than the protection level of the arrester, the steady state protection is overvoltage by the gate of the present invention. Can be protected.

〔The invention's effect〕

As described above, in the present invention, focusing on the fact that the forward withstand voltage of the thyristor valve immediately after energization becomes low and that it changes with time, the function output related to the withstand voltage recovery characteristic,
If the overvoltage detection signal is larger than the function output, the thyristor gate firing function is used to simultaneously fire the thyristors to protect the thyristor from destruction due to overvoltage. Therefore, it is possible to provide a thyristor converter capable of reliably performing overvoltage protection against a surge voltage applied immediately after energization of the thyristor valve.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing the configuration of the first embodiment of the present invention, FIG. 2 is a time chart for explaining the operation of the same embodiment, and FIG. 3 is a configuration of the second embodiment of the present invention. FIG. 4 is a time chart for explaining the operation, FIG. 5 is a circuit diagram showing the configuration of a conventional device, FIG. 6 is a time chart for explaining the operation of the conventional device, and FIG. The figure is also a time chart for explaining the operation of the conventional apparatus. 1, 11 ... Thyristor, 2 ... Reactor, 3 ... Snubber circuit,
4 ... DC voltage dividing resistance, 5 ... arrester, 6,21,71,72 ... light emitting element, 23,61,81,82 ... light guide, 12,24,91,92 ... light receiving element, 14 ... gate signal amplifier, 15 ... Gate signal generation circuit,
25, 101, 102 ... Light receiving circuit, 26 ... Reference signal generating circuit, 27 ... Comparator.

Claims (2)

[Claims] 1. A reference signal generating means for generating a reference signal function related to a recovery characteristic of a forward withstand voltage of a thyristor converter immediately after energization of the thyristor, and an overvoltage detection for detecting an overvoltage of an arm of the thyristor converter. Means, and comparing means for comparing the reference signal function with the output of the overvoltage detection means, so as to fire the arm of the thyristor converter when the output of the overvoltage detection means is greater than the reference signal function. An overvoltage protection device for a thyristor converter characterized by the above. 2. The overvoltage detecting means includes steepness determining means for determining a rising steepness of a detected signal, and the reference signal generating means outputs a reference signal function in accordance with a determination result of the steepness determining means. The overvoltage protection device for a thyristor converter according to claim 1, characterized in that it is a means for changing the waveform.