A design method for a thyristor discharge switch with a rated voltage of 15kV

Abstract

The present invention relates to a 15kV thyristor discharge switch system, which belongs to the field of thyristor discharge switches. It is composed of four light-controlled thyristors T2563N80TOH, a dynamic voltage-equalizing RCD circuit, a static voltage-equalizing circuit and a transient voltage protection circuit to form a thyristor discharge switch with a rated voltage of 15kV, a maximum operating voltage of 30kV and a maximum discharge current of 93kA. The voltage level controlled by the thyristor is improved by connecting a single thyristor in series, and a suitable external protection circuit structure is designed to solve the problems of dynamic voltage-equalizing, static voltage-equalizing and synchronization faced by the series thyristor structure. A method for improving the voltage level and improving dynamic and static voltage-equalizing is provided for a thyristor switch system.

Description

Technical Field

[0001] The present invention relates to a thyristor discharge switch technology. This paper determines a series thyristor switch protection circuit scheme by analyzing the dynamic and static voltage-sharing measures of the existing series thyristor structure. Background Art

[0002] As the most commonly used semiconductor switching device, thyristor generally has excellent current carrying capacity, allowing the current to pass from hundreds of amperes to thousands of amperes. Single thyristor is widely used in occasions with low repetition frequency, low voltage but large current. The voltage resistance and current capacity of thyristor components are the highest, and after long-term testing, it is proved that the electrical performance of thyristor is stable. It is the main basic switching component in the field of high-voltage pulse and large-current discharge equipment. At present, one of the main problems faced by thyristor is the dynamic and static voltage balancing problem. Therefore, it is necessary to select reasonable voltage balancing protection circuit structure parameters according to different voltage levels, current capacities and different frequency occasions to make up for the problem of uneven performance of the device itself and protect the thyristor components. Summary of the invention

[0003] In order to solve the problem that the voltage level of a single thyristor is not enough to meet the requirements of the power system, as well as the dynamic voltage balancing problem and the static voltage balancing problem, the purpose of the present invention is to design a 15kV thyristor discharge switch, which is achieved through the following technical solutions:

[0004] (1) First, select the thyristor electrical device based on the thyristor's own characteristics;

[0005] (2) Select a trigger circuit with better synchronization to reduce the dynamic voltage balancing problem caused by the inconsistent time of the thyristor conduction process;

[0006] (3) By selecting reasonable voltage-equalizing protection circuit structure parameters for different voltage levels, current capacities and different frequencies, the problem of unbalanced device performance can be compensated and the thyristor components can be protected. These protection circuits can effectively improve the series voltage-equalizing effect, reduce the voltage rise rate across the thyristor and protect the thyristor components.

[0007] Furthermore, this design will conduct a theoretical analysis on the working characteristics of high-voltage series thyristors, determine the circuit scheme, and achieve dynamic and static voltage equalization of series thyristors by selecting a suitable external protection circuit structure.

[0008] A method for designing a thyristor discharge switch with a rated voltage of 15 kV, characterized in that it comprises the following steps:

[0009] Step 1: Select suitable static voltage-equalizing circuit components by calculating the withstand voltage of the static voltage-equalizing circuit;

[0010] Step 2: Select appropriate dynamic voltage-equalizing circuit components by calculating the withstand voltage of the dynamic voltage-equalizing circuit;

[0011] Step 3: Select appropriate overvoltage suppression circuit components by calculating the withstand voltage of the overvoltage suppression circuit;

[0012] Step 4: Calculate the withstand voltage of the overvoltage suppression circuit. By analyzing its voltage equalization measures, synchronization strategy and triggering method, design a 15kV thyristor discharge switch circuit diagram with thyristors in series;

[0013] Step 1 specifically includes: under the premise of only considering the static voltage-equalizing circuit without considering other protection circuits, assuming that the entire switch voltage is UT, the voltage across a single thyristor is recorded as UT1 to UT4, and the leakage current IRRM of the selected photo-controlled thyristor when working at the rated repetitive peak voltage URRM is known to be 23mA, assuming that the maximum leakage current difference ΔITmax between the two thyristors is 1mA, and this difference exists between the first and second thyristors, and the leakage current of other thyristors is the same as that of the second thyristor. At this time, the current on the static voltage-equalizing resistor is I1R1 to I4R1, then:

[0014]

[0015] From the above formula, we can get:

[0016] U T =nU T1 -(n-1)R S ΔI T

[0017] When the thyristor operates at the highest off-state voltage, the maximum value of R1 can be obtained as:

[0018]

[0019] In addition, the static voltage-equalizing resistor should meet the requirement that the maximum power on it cannot be greater than its rated power:

[0020] P1≥(U T / n) 2 / R S

[0021] Substitute the data and solve for R S ≤5000kΩ,P1≥2.81W;

[0022] Through data comparison, it can be known that the selected static voltage-equalizing resistor meets the above requirements;

[0023] Step 2 specifically includes: In the RCD circuit, the presence of the diode during the charging process short-circuits the dynamic voltage-equalizing resistor. When the dynamic voltage-equalizing capacitor is charged, a large current may be generated. This current is caused by the asynchronous opening of the thyristors in series. Assuming that the first thyristor is opened 1μs later than the other three thyristors, the voltage across the first thyristor is:

[0024]

[0025] Substitute the data to get U max The value is 6kV. In fact, due to the delay process when the thyristor is turned on, U max The value will be greater than 6kV. Driven by this voltage, the charge will quickly flow into the capacitor to generate a surge current. It can be inferred that the greater the difference in the thyristor turn-on time, the greater the surge current value will be. Therefore, selecting a capacitor with a withstand voltage of 8000V can meet the requirements.

[0026] Since the time for the thyristor switch to complete the conduction process is very short, it can be seen from the thyristor data sheet that the delay time of T2563N is 5μs, so it can be regarded as the voltage across the capacitor always maintaining the voltage when the switch is not turned on, that is, U / n. After the switch is turned on, the dynamic voltage-equalizing capacitor will discharge to the light-controlled thyristor through the dynamic voltage-equalizing resistor. For the convenience of calculation, it can be regarded as a uniform discharge of the capacitor;

[0027] At this time, the following equation can be obtained from the voltage relationship:

[0028]

[0029] Where U c1 is the voltage across the dynamic voltage-equalizing capacitor, U1 is the voltage across the thyristor T1; t1 is the time required for the thyristor T1 to change from the blocking state to the fully conducting state, which is 6μs, and the value of t is 0≤t≤t1;

[0030] According to the above formula, we can get:

[0031]

[0032] According to the above formula, the maximum current of the circuit is 250A, and the selected resistor meets the requirements;

[0033] Step three specifically includes: the selection principle of TVS voltage suppression diode is that the reverse breakdown voltage is not less than the maximum allowable working voltage of the circuit, the maximum clamping voltage is not greater than the maximum safe voltage of the circuit, and the maximum allowable working voltage across a single thyristor is 3.75kV. If the maximum allowable working voltage is exceeded, the TVS voltage suppression diode will enter a breakdown state, which will increase the leakage current in the circuit and affect the normal operation of the circuit. The maximum clamping voltage must be less than the maximum allowable safe voltage of the circuit, 7.5kV, that is, under the maximum clamping voltage, no components in the circuit will be damaged.

[0034] As described above, the present invention designs a design method for a thyristor discharge switch with a rated voltage of 15 kV. The effects of the present invention are as follows:

[0035] The present invention analyzes the working principle and working process of light-controlled thyristors, connects the voltage of a single thyristor in series, improves the voltage level of the thyristor discharge switch, and calculates the withstand voltage of the static and dynamic voltage-equalizing circuit and the overvoltage suppression circuit. While selecting suitable circuit components, it also solves the problems of dynamic and static voltage-equalizing and synchronization faced by the series thyristor structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 It is a static voltage equalization circuit diagram;

[0037] Figure 2 This is the RCD buffer circuit diagram;

[0038] Figure 3 This is the schematic diagram of the thyristor switch circuit;

[0039] Figure 4 This is a schematic diagram of the mechanical structure of a 15kV thyristor discharge switch;

[0040] In the figure, 1 is a water-cooled heat sink, 2 is a light-controlled thyristor, 3 is an insulating plate, 4 is a water-cooled radiator, 5 is a connecting plate, 6 is an insulating spacer, 7 is a dynamic voltage-equalizing capacitor, and 8 is nuts and bolts. DETAILED DESCRIPTION

[0041] The following describes the implementation methods of the present invention through specific examples. The specific implementation methods of the present invention may be varied and may have other implementation methods and applications. It should be noted that the illustrations provided in the following embodiments are only schematic illustrations of the basic concept of the present invention. Therefore, the illustrations only show components related to the present invention rather than the number, shape and size of components in actual implementation. In actual implementation, the type and proportion of each component may be changed arbitrarily, and the component layout type may also be more complicated.

[0042] Figure 1The figure shows a static voltage-equalizing circuit diagram. The thyristors are connected in series through an external circuit to make the voltages at both ends of each tube tend to be consistent. In a stable forward or reverse blocking state, a voltage-equalizing resistor is connected in parallel to each series device. Without considering the difference in leakage current between units, four voltage-equalizing resistors with the same resistance are used to make the voltage borne by each thyristor the same. In order to achieve the voltage-equalizing effect, the static voltage-equalizing resistor needs to be much smaller than the leakage resistance of the thyristor.

[0043] Figure 2 The figure shows the RCD snubber circuit diagram. In order to reduce the current rise rate on the thyristor, a snubber circuit is connected in parallel at both ends of the thyristor, and a fast diode is connected in parallel with the dynamic voltage-equalizing resistor. This can achieve a better overvoltage suppression effect and effectively prevent circuit oscillation.

[0044] Figure 3 The circuit diagram of the series part of this design is shown. There are four series units in total. Each thyristor level contains a light-controlled thyristor T2563N80TOH, a static voltage-equalizing resistor RS composed of two RI80X-1W resistors in series, a dynamic voltage-equalizing capacitor C1 composed of two STM-3000-0.82 capacitors in series, a dynamic voltage-equalizing diode D2 composed of four diodes in parallel, a dynamic voltage-equalizing resistor R composed of a 251AEC151KDS resistor, and a transient voltage suppression circuit composed of 10 TVS tubes SMAJ440CA. Through calculation, it can be obtained that the reverse breakdown voltage of the TVS voltage suppression circuit composed of 10 SMAJ440CA in series is greater than 4.92kV, and the maximum clamping voltage is 7.13kV. It meets the requirements of the operating voltage of the series thyristor switch of 3.75kV and the maximum allowable safety voltage of 7.5kV.

[0045] Figure 4The figure shows the mechanical structure of the switch. The overall structure is press-fit. The upper and lower connecting plates, the thyristor and the heat sink are press-fitted by nuts and PEEK bolts with insulating sleeves using professional installation tools. Since the tip of the metal nut surface will cause uneven electric field distribution, the nut should be wrapped with semi-conductive tape to reduce the impact of tip discharge on the insulation performance of the switch. Static equalizing resistors, dynamic equalizing resistors, TVS suppression tubes and fast diodes in the dynamic equalizing circuit are composed of multiple smaller components connected in series and parallel. In order to increase the heat dissipation efficiency and reduce the size of the switch, these resistors and diodes are directly connected to the heat sink. This structure greatly increases the heat dissipation area and reduces the noise generated by mechanical vibration when the device is flowing. The dynamic voltage-equalizing capacitor is tightly fixed with a mounting frame and insulating spacers. The height difference between the capacitor and the thyristor and the heat sink is supplemented by the insulating spacers. Adjacent thyristor units are connected with thin copper strips. The bolts must be installed with insulating sleeves during actual installation, and the nuts must be wrapped with semiconductor tape after installation. Such a structure is pressed and tightened with professional tools to ensure that the device will not be damaged due to extrusion. The switch greatly saves space and provides convenience for transportation and installation.

[0046] The above embodiments are merely illustrative of the principles and effects of the present invention, and are not intended to limit the present invention. Anyone familiar with the art may modify or alter the above embodiments without departing from the spirit and scope of the present invention.

Claims

1. A design method for a thyristor discharge switch with a rated voltage of 15kV. Features: The steps include: Step 1: Select suitable static voltage-equalizing circuit components by calculating the withstand voltage of the static voltage-equalizing circuit; Step 2: Select appropriate dynamic voltage-equalizing circuit components by calculating the withstand voltage of the dynamic voltage-equalizing circuit; Step 3: Select appropriate overvoltage suppression circuit components by calculating the withstand voltage of the overvoltage suppression circuit; Step 4: Calculate the withstand voltage of the overvoltage suppression circuit. By analyzing its voltage equalization measures, synchronization strategy and triggering method, design a 15kV thyristor discharge switch circuit diagram with thyristors in series; Step 1 specifically includes: under the premise of only considering the static voltage-equalizing circuit without considering other protection circuits, assuming that the entire switch voltage is UT, the voltage across a single thyristor is recorded as UT1 to UT4, and the leakage current IRRM of the selected photo-controlled thyristor when working at the rated repetitive peak voltage URRM is known to be 23mA, assuming that the maximum leakage current difference ΔIT max between the two thyristors is 1mA, and this difference exists between the first and second thyristors, and the leakage current of other thyristors is the same as that of the second thyristor. At this time, the current on the static voltage-equalizing resistor is I1R1 to I4R1, then: From the above formula, we can get: U T =nU T1 -(n-1)R S ΔI T When the thyristor operates at the highest off-state voltage, R 1 The maximum value is: In addition, the static voltage-equalizing resistor should meet the requirement that the maximum power on it cannot be greater than its rated power: P 1 ≥(U T / n) 2 / R S Substitute the data and solve for R S ≤5000kΩ,P 1 ≥2.81W; Through data comparison, it can be known that the selected static voltage-equalizing resistor meets the above requirements; Step 2 specifically includes: In the RCD circuit, the presence of the diode during the charging process short-circuits the dynamic voltage-equalizing resistor. When the dynamic voltage-equalizing capacitor is charged, a large current may be generated. This current is caused by the asynchronous opening of the thyristors in series. Assuming that the first thyristor is opened 1μs later than the other three thyristors, the voltage across the first thyristor is: Substitute the data to get U max The value is 6kV. In fact, due to the delay process when the thyristor is turned on, U max The value will be greater than 6kV. Driven by this voltage, the charge will quickly flow into the capacitor to generate a surge current. It can be inferred that the greater the difference in the thyristor turn-on time, the greater the surge current value will be. Therefore, selecting a capacitor with a withstand voltage of 8000V can meet the requirements. Since the time for the thyristor switch to complete the conduction process is very short, it can be seen from the thyristor data sheet that the delay time of T2563N is 5μs, so it can be regarded as the voltage across the capacitor always maintaining the voltage when the switch is not turned on, that is, U / n. After the switch is turned on, the dynamic voltage-equalizing capacitor will discharge to the light-controlled thyristor through the dynamic voltage-equalizing resistor. For the convenience of calculation, it can be regarded as a uniform discharge of the capacitor; At this time, the following equation can be obtained from the voltage relationship: Where U c1 is the voltage across the dynamic voltage balancing capacitor, U 1 For thyristor T 1 Voltage across the two ends; t 1 For thyristor T 1 The time required from the blocking state to the fully conducting state is 6 μs, and the value of t is 0 ≤ t ≤ t 1 ; According to the above formula, we can get: According to the above formula, the maximum current of the circuit is 250A, and the selected resistor meets the requirements; Step three specifically includes: the selection principle of TVS voltage suppression diode is that the reverse breakdown voltage is not less than the maximum allowable working voltage of the circuit, the maximum clamping voltage is not greater than the maximum safe voltage of the circuit, and the maximum allowable working voltage across a single thyristor is 3.75kV. If the maximum allowable working voltage is exceeded, the TVS voltage suppression diode will enter a breakdown state, which will increase the leakage current in the circuit and affect the normal operation of the circuit. The maximum clamping voltage must be less than the maximum allowable safe voltage of the circuit, 7.5kV, that is, under the maximum clamping voltage, no components in the circuit will be damaged.

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