JPH05130728A - Protective device for power converting apparatus - Google Patents

Abstract

PURPOSE:To economically execute protecting detections and improve the operational reliability of a thyristor valve by grasping the temperatures of the snubber resistor comprehensively on the basis of the information easily obtainable on the earth potential side. CONSTITUTION:The operation control angle a of a thyristor valve is inputted to operate on 'K1 K' sin<2>alpha' by the use of a sin conversion circuit 11, square-law circuit 12, multiplier 13 and K1XK' constant setter 23. On the other hand, an operation on 'K2 {thetaRM-(theta1+kId)}' is executed by the use of a K gain setter 21, multiplier 22, K, constant setter 23, and thetaRM constant setter 24 after obtaining the valve entrance temperature thetaRM' and direct current Id. The difference between this output and that of the multiplier 13 is inputted into an integrator 31. This integrator is functional only when the entrance is 'positive'. Then, the output of the thetaRM setter is added to the output of this integrator. The result is inputted into a comparator 41 to compare it with the detection level Q3 which is defined in advance by a setter 42. Thus, it becomes unnecessary to directly measure the temperatures of many numbers of snubber circuit resistors on the high potential side of the thyristor valve.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a protection device for a power conversion device, which is composed of a large number of thyristors and power conversion semiconductor elements.

[0002]

2. Description of the Related Art A snubber circuit of a power converter is located in a high potential portion and is required for each semiconductor element for conversion (hereinafter referred to as a thyristor). In addition, it is difficult to monitor because of the large number of snubber circuits.Although snubber circuit failure leads to thyristor element failure, there is a design margin such as thyristor element redundancy. No targeted protection detections were performed.

[0003]

In recent years, due to the advancement of the thyristor element failure detection technology for power converters, it has become possible to detect individual element failures of many thyristors used. In addition, the number of elements in series is reduced due to the improved performance of the protective lightning arrestor, and there is a tendency to reduce the number of redundant elements to improve the economic efficiency. In such a situation, it can be said that the importance of the snubber circuit protection, which may cause a device failure, in particular, the overstress protection of the snubber resistance is increasing. The present invention has been made in view of the above circumstances, and detects that the snubber circuit resistance of the power converter is in an overstress state, and provides a reliable power converter protection device. Has a purpose.

[0004]

In order to achieve the above object, according to the present invention, in a protection device for detecting an abnormal temperature rise of a snubber circuit resistor of a power conversion device, a heat generation amount of the snubber circuit resistor is provided. Is calculated as a function of the converter operation control angle, and the cooling heat quantity of the resistor is calculated from the specific heat capacity of the cooling medium for cooling the resistor and the temperature difference between the inlet and the outlet of the cooling medium of the resistor. Second means for calculating, third means for calculating the temperature rise of the resistor from the difference between the calorific value by the first means and the cooling heat quantity by the second means, and the temperature rise by the third means And a fourth means for generating an alarm output when the value is larger than a predetermined set value.

When the temperature rise of the snubber circuit resistor becomes larger than the predetermined value, the alarm output is generated by the fourth means, so that the abnormal temperature rise of the snubber circuit resistor can be detected.

[0005]

Embodiments will be described below with reference to the drawings. Figure 2
Is an AC / DC converter for DC power transmission, and is a 6-phase rectifier bridge 1
It is an example of the main circuit configuration of the group, which is a transformer for conversion 1 and six thyristor converters (referred to as thyristor valves) V _{1 to} V ₆ ,
Also, a valve arrester A _rr for protecting each thyristor valve is connected. The system AC voltage E ₁ is transformed into a voltage E ₂ by the transformer 1 and given to the bridge, and a DC voltage E _d is output by the operation of the thyristor valves V _{1 to} V ₆ . All of the thyristor valves V _{1 to} V ₆ have the same configuration, and each unit is usually configured by connecting a plurality of units called modules in series.

FIG. 3 shows the structure of a water-cooled thyristor valve having a four-module structure. M _{1 to} M ₄ are modules, and pure water for cooling is supplied in parallel to each module through the insulating pipe 2 and drained by the insulating pipe 3. FIG. 4 is a detailed view of FIG. 3, and each module usually has anode reactors 4 and 5 on the “in” and “out” sides of the electric circuit, and in the meantime, it is shown as one, but normally four About eight thyristors 6 are connected and arranged in series, and snubber circuits (7 and 8 circuits in the figure) are connected and arranged in parallel for each thyristor 6. An example of cooling the snubber circuit inside the module is shown in FIG. Pure water for cooling passes through the hatched portions in the figure. The thyristor is sandwiched by cooling fins 9 and cooled by pure water supplied from the insulating pipe 2.
After further cooling the thyristor 6, pure water for cooling is sent to the snubber water cooling resistor 8, and after cooling the resistor 8, it is drained through the insulating pipe 3.

As can be seen from the above description, there are as many snubber circuits as there are thyristors in the module of the high potential part, and it is economical to detect the temperature of each snubber resistor and output it to the ground potential side. Not a good idea. On the other hand, the snubber resistance needs to be used at a predetermined temperature or less, and thermal overstress causes a disconnection. The temperature of the resistor is governed by the current flowing through the resistor, that is, the thermal balance between the charging / discharging current of the snubber capacitor and the cooling water temperature. FIG. 6 shows the snubber resistance portion of FIG. 5. When this resistor is in a thermal equilibrium state, equation (1) holds and equation (1) is transformed into equation (2). The charging / discharging current of the snubber capacitor is given by Eq. (3).

[0008] Where i: snubber capacitor charging / discharging current R: snubber resistor resistance value k: constant gw: flow rate of cooling water per unit time (including coefficient of specific heat) θ ₁ : cooling water inlet temperature θ ₃ : cooling water outlet temperature Q _R: snubber specific heat capacity of the resistor theta _2: average snubber resistance temperature _{K 1 = kR / Q R K} 2 = gw / Q R K: constant (considering the overvoltage multiples during commutation) E _2; valve input AC voltage α: Valve delay control angle

Equation (3) shows the current flowing through the snubber capacitor 7 and the resistor 8 due to overvoltage in consideration of commutation oscillation voltage when commutating at the delay control angle α when the thyristor valve has an AC input voltage of E _2. There is. Therefore, considering equation (3), equation (2) becomes equation (4) below. In equation (4), the temperature of the resistor can be determined from the cooling water temperatures θ ₁ and θ ₃ of the snubber resistance, the AC voltage input to the thyristor valve, and the operation control angle. In particular, assuming that the secondary voltage E ₂ of the transformer 1 shown in FIG. 1 is kept constant, it can be expressed by the following equation (5) with K · E ₂ = K ′. In equation (5), the inlet water temperature of resistance θ
_{Since 1} cannot be measured in general, the following equation (6) is used instead. The resistance outlet water temperature is set to a value θ _RM, which is a maximum value in various design operation patterns plus a margin. From this idea, Eq. (5) becomes Eq. (7) shown below. Also, during normal operation of the thyristor valve, equation (7) becomes negative as shown in equation (8) below, but this is meaningless for protection judgment.

[0010] Where θ ₁ ′: valve inlet water temperature I _d : direct current k: constant

On the other hand, when the valve operation control angle α approaches 90 °, the equation (8) becomes positive and the temperature θ of the resistor changes with time.
₂ goes up. If the valve inlet water temperature θ ₁ ′ becomes low
It can be seen that the time when the equation (7) turns to positive is delayed and the increase in the snubber resistor temperature θ ₂ becomes slow. Therefore, by comparing whether or not the above-mentioned temperature θ ₂ has reached the temperature θ _s which is undesirably set, it can be used as protection detection of the snubber resistor.

FIG. 1 is a block diagram of an embodiment of a protection device for a power conversion device according to the present invention, which is a block expansion of the expression (7) in an analog expression. This can also be easily realized by digital arithmetic processing. In FIG. 1, the operation control angle α of the thyristor valve is input and the sin conversion circuit 11, the squaring circuit 12,
The multiplier 13 and K ₁ constant setter 14 × K '"K ₁ ·
K'sin ² α ”is calculated. On the other hand, the valve inlet water temperature θ ₁ ′ and the DC current I _d are obtained to obtain the k gain setter 21 and the multiplier.
22, K ₂ constant setter 23 and θ _RM constant setter 24 calculate “K ₂ {θ _RM − (θ ₁ ′ + kId)}”, and the difference from the calculated output of the multiplier 13 is calculated. As the input of the integrator 31. This integrator works only when the inlet is “positive” as already shown in Eq. (8). Then, the integrated output
Add the _RM setting output and input to the comparator 41.
It is compared with the detection level Q _s set in.

[0013]

As described above, according to the present invention, the snubber is obtained from the information easily obtained on the ground potential side without directly measuring the temperatures of the numerous snubber circuit resistors on the high potential side of the thyristor valve. It has the advantage of being able to comprehensively grasp the temperature of the resistance, economically detecting and detecting the protection, and contributes to the improvement of the operational reliability of the thyristor valve.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an embodiment of a protection device for a power converter according to the present invention.

FIG. 2 is a diagram showing an AC / DC conversion 6-phase bridge for DC power transmission as an example of a power conversion device.

3 is a schematic diagram of the configuration of the converter shown in FIG.

FIG. 4 is a view showing FIG. 3 as an electric circuit.

FIG. 5 is a conceptual diagram of cooling the thyristor and the snubber resistance in the module.

FIG. 6 is a diagram showing a snubber resistance in a module.

[Explanation of symbols]

11 Sine conversion circuit 12 Square circuit 13, 22 Multiplier 14 K ₁ · K'constant setter 21 k Gain setter 23 K ₂ constant setter 24 θ _RM constant setter 31 Integrator 41 Comparator 42 Detection Level Q _s setter

Claims (1)

[Claims] 1. A protection device for detecting an abnormal temperature rise of a snubber circuit resistor of a power converter, wherein a first means for calculating a heat generation amount of the snubber circuit resistor as a function of a converter operation control angle. Second means for calculating the cooling heat quantity of the resistor from the specific heat capacity of the cooling medium for cooling the resistor and the temperature difference between the inlet and outlet of the cooling medium of the resistor, and the heat generation by the first means. Third means for calculating the temperature rise of the resistor from the difference between the amount of heat and the amount of cooling heat by the second means, and an alarm output is generated when the temperature rise value by the third means is larger than a predetermined set value. A protection device for a power converter, comprising: a fourth means.