A voltage balancing device and power electronic switch

Abstract

The present invention provides a voltage balancing device and a power electronic switch. The voltage balancing device includes: a resistance module operating in a low current region and being capacitive, so that when the power device is turned on or off, the resistance modules connected in parallel in each layer of power device modules rapidly reduce their impedance after reaching their inflection point voltage, absorb overshoot voltage energy, and make the overvoltage amplitude at both ends of each series power device smaller than the device's withstanding peak voltage, thereby realizing dynamic voltage balancing protection of the power device during the turn-on or turn-off process and reducing the leakage current of the voltage balancing branch when the power electronic switch is turned off; the capacitance value of the capacitor module of each power device is arranged differently, so that when the power device is in the off state, the mutual capacitance deviation between the device modules of adjacent layers can be greatly reduced, thereby optimizing the static voltage distribution of the power device.

Description

Technical Field

[0001] The present invention relates to the technical field of power electronics, and in particular to a voltage balancing device and a power electronic switch. Background Art

[0002] Power electronic switches are widely used in applications such as controlled lightning arresters, static synchronous series compensators, and unified power flow controllers due to their excellent switching performance, fast operation, and flexible control capabilities. Power electronic switches often use multiple anti-parallel thyristors connected in series to achieve the required withstand voltage. However, in special scenarios such as controlled lightning arresters, the power electronic switch is used in combination with the arrester itself, and strict restrictions are placed on the leakage current and distributed capacitance of the power electronic switch to reduce the difficulty of voltage balancing design of the arrester itself. In the field of ultra-high voltage controlled lightning arresters, the total leakage current is required to be less than 4mA, of which the capacitive current is required to be less than 3mA. Therefore, the distributed capacitance of the power electronic switch itself needs to be strictly limited. Due to the inherent junction capacitance of thyristor devices and the different distributed capacitances of each layer of thyristors installed in series to ground and surrounding electrical equipment, these factors will lead to uneven voltage distribution in the power electronic switch, causing some thyristor devices in series to be overvoltage-exposed, resulting in premature overvoltage conduction of the thyristor with high voltage, causing deviations in the operating voltage of the entire switch. Thyristors with excessive voltage also have the risk of overvoltage breakdown, posing a risk to the safe and stable operation of the power electronic switch. Therefore, it is necessary to simultaneously consider both sufficiently small distributed capacitance and good voltage balancing performance of the power electronic switch.

[0003] Currently, thyristor valves used in reactive power compensation devices and high-voltage direct current transmission (HVDC) all utilize a high-current RC voltage-sharing method. This method uses RC series-parallel circuits for voltage balancing, utilizing the large capacitor in the RC series branch to absorb the thyristor's turn-on overshoot voltage. The impedance of the resistor branch is significantly smaller than the thyristor's impedance, allowing leakage current to flow through the resistor branch with a lower impedance when the thyristor is off, thereby achieving voltage balancing. Because the impedance of the RC branch is significantly smaller than the thyristor's impedance in the off state, this voltage-sharing method results in excessive leakage current in the thyristor switch, reaching several amperes. This makes it unsuitable for applications where strict restrictions on leakage current and voltage-sharing are imposed.

[0004] There is also a method of using metal oxide nonlinear resistors (hereinafter referred to as resistors) for voltage balancing. This method uses the voltage-limiting characteristics of the nonlinear resistor to limit the turn-on overshoot voltage of the thyristor, thereby protecting the series-connected thyristors. At the same time, the electrostatic capacitance characteristics of the resistor itself are used to act as a capacitor when the thyristor is turned off, which has a certain effect on improving the voltage distribution of the power electronic switch. However, in this method, the capacitance of the resistor itself is relatively small, and its capacitance value is comparable to the junction capacitance of the thyristor device. It relies solely on the inherent capacitance of the resistor itself to balance the voltage of the series-connected thyristors. In scenarios where there are many thyristor devices in series, their complex distributed capacitance makes it impossible to achieve the desired voltage balancing effect by relying solely on the resistor. Summary of the Invention

[0005] Therefore, the technical problem to be solved by the present invention is to overcome the defect that the voltage balancing device of the power electronic switch in the prior art cannot achieve the required voltage balancing effect, thereby providing a voltage balancing device and a power electronic switch.

[0006] In order to achieve the above object, the present invention provides the following technical solutions:

[0007] In a first aspect, an embodiment of the present invention provides a voltage equalizing device, comprising: a resistor module and a capacitor module, wherein the resistor module and the capacitor module are both connected in parallel with the power device; the resistor module operates in a low current region, and the resistor module is capacitive; the capacitance of the capacitor module of each power device is arranged differently according to the end face voltage of a composite body formed by parallel connection of each layer of power devices and the resistor module, the capacitance of each end face to ground, and the mutual capacitance between each end face.

[0008] In one embodiment, the resistor module includes at least one resistor sheet.

[0009] In one embodiment, when the resistor module includes at least two resistor sheets, the resistor sheets are connected in any one of series, parallel, or series-parallel connection.

[0010] In one embodiment, the continuous operating voltage of the resistance module is higher than the interlayer voltage of the power devices connected in series, and the sum of the maximum residual voltages of all the resistors in the resistance module is lower than the voltage tolerance of the connected power devices.

[0011] In one embodiment, the resistor is a metal oxide resistor.

[0012] In one embodiment, the calculation formula for the capacitance of the capacitor module is:

[0013]

[0014] Among them, C ii C is the capacitance of each end face to ground from bottom to top. ijis the mutual capacitance between the end faces of each layer, U i is the voltage under the ideal potential distribution of each end surface, C i It is the capacitance value of the capacitor module installed in each layer of power modules starting from the second layer from bottom to top, i = 2, 3, ... n, j = 1, 2, 3, ... n, and n is the number of power modules.

[0015] In one embodiment, when the capacitor module includes at least two capacitors, the capacitors are connected in series, in parallel, or in series and parallel.

[0016] In a second aspect, an embodiment of the present invention provides a power electronic switch, comprising: the voltage balancing device of the first aspect, and a plurality of power devices, wherein each power device is connected in parallel with a voltage balancing device, and the power devices are connected in series.

[0017] The technical solution of the present invention has the following advantages:

[0018] 1. The voltage balancing device power electronic switch provided by the present invention has a resistance module that operates in a low current region and is capacitive, so that when the power device is turned on or off, the resistance modules of the power device modules in parallel on each layer rapidly reduce their impedance after reaching their inflection point voltage, absorb overshoot voltage energy, and make the overvoltage amplitude at both ends of each series power device smaller than the device's withstanding peak voltage, thereby realizing dynamic voltage balancing protection of the power device during the turn-on or turn-off process and reducing the leakage current of the voltage balancing branch when the power electronic switch is turned off; the capacitance values ​​of the capacitor modules of each power device are arranged differently, so that when the power device is in the off state, the mutual capacitance deviation between the device modules of adjacent layers can be greatly reduced, thereby optimizing the static voltage distribution of the power device.

[0019] 2. The voltage balancing device and power electronic switch provided by the present invention utilize nonlinear resistors and ceramic voltage balancing capacitors for voltage balancing, which can significantly reduce the volume of the voltage balancing circuit compared to conventional RC voltage balancing circuits. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the specific embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0021] Figure 1 A composition diagram of a specific example of a pressure equalizing device provided in an embodiment of the present invention;

[0022] Figure 2 A schematic diagram of a resistor provided in an embodiment of the present invention;

[0023] Figure 3 An equivalent circuit diagram provided for an embodiment of the present invention;

[0024] Figure 4 A schematic diagram of a specific example of a method for installing a pressure equalizing device provided in an embodiment of the present invention;

[0025] Figure 5 An example of voltage unevenness coefficient of a 32-layer thyristor series power electronic switch equipped with a voltage equalizing device provided by an embodiment of the present invention;

[0026] Figure 6 An example of voltage non-uniformity coefficient of a 32-layer thyristor series power electronic switch using only resistor voltage balancing provided by an embodiment of the present invention;

[0027] Figure 7 A composition diagram of a specific example of a power electronic switch provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0028] The technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0029] In the description of the present invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings and are intended solely to facilitate and simplify the description of the present invention. They are not intended to indicate or imply that the devices or components referred to must have, be constructed, or operate in a specific orientation, and therefore should not be construed as limitations on the present invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0030] In the description of the present invention, it should be noted that, unless otherwise expressly specified or limited, the terms "installed," "connected," and "connected" should be understood in a broad sense. For example, they can refer to fixed connections, detachable connections, or integral connections; mechanical connections or electrical connections; direct connections or indirect connections through an intermediate medium; internal connections between two components; wireless connections or wired connections. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on specific circumstances.

[0031] In addition, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0032] Example 1

[0033] The embodiment of the present invention provides a pressure equalizing device, such as Figure 1 As shown, it includes: a resistance module 11 and a capacitance module 12.

[0034] like Figure 1 As shown, the resistance module 11 and the capacitance module 12 of the embodiment of the present invention are both connected in parallel with power devices, wherein the power devices include but are not limited to power transistors GTR, thyristors SCR and insulated gate bipolar thyristors IGBT, and can also be other switching devices with the same functions and performance.

[0035] During the dynamic process of turning on and off the power device, there is a problem of uneven instantaneous voltage distribution. The power device that is turned on late or turned off early will be subjected to severe overshoot voltage for a short time. Therefore, the resistance module 11 of the embodiment of the present invention operates in the low current area, and the resistance module 11 is capacitive, that is, after the resistance module 11 connected in parallel with the power device reaches its inflection point voltage, the impedance of the resistance module 11 decreases rapidly and absorbs the overshoot voltage energy, so that the overvoltage amplitude at both ends of the power device is less than the peak voltage that the device can withstand, thereby realizing dynamic voltage equalization protection of the power device during the turning on or off process.

[0036] The resistance module 11 of an embodiment of the present invention is composed of at least one resistor sheet, wherein, when the resistance module 11 is composed of only one resistor sheet, the resistor sheet is directly connected to the power device, and the maximum residual voltage value of the resistor sheet is lower than the voltage tolerance value of the connected power device, and its continuous operating voltage should be higher than the interlayer voltage of the series power device; and when the resistance module 11 is composed of at least two resistor sheets, all the resistor sheets can be connected in any one of series, parallel or series-parallel connection modes, and the number of resistor sheets on each branch of the circuit composed of all the resistor sheets is determined according to actual conditions and is not limited here. In addition, the sum of the maximum residual voltage values ​​of all the resistor sheets in the resistance module 11 is lower than the voltage tolerance value of the connected power device, and the continuous operating voltage of the resistance module 11 should be higher than the interlayer voltage of the series power device.

[0037] like Figure 2 As shown, the resistor sheet of the embodiment of the present invention adopts a cylindrical sheet structure to facilitate press-fitting with the power device to form a composite body, and the resistor sheet can be a metal oxide resistor sheet, for example: a zinc oxide resistor sheet, etc. Under the continuous operating voltage, the zinc oxide resistor sheet should operate in a small current range below 1mA.

[0038] In the embodiments of the present invention, power devices are mostly used in power electronic switches. The power electronic switch is composed of power devices connected in series. Under AC operating voltage, when the power electronic switch is in the off state, the leakage current is mainly capacitive current, and the resistive current accounts for a very small proportion. Therefore, under normal operating voltage, the static voltage distribution of the power electronic switch is closely related to the distributed capacitance matrix of the switch, as shown in formula (1).

[0039]

[0040] In formula (1), Q i For each power device, the quiescent voltage, C ii C is the capacitance to ground of the end face of the complex composed of the power device and the resistor module. ij is the mutual capacitance between the end faces of each layer, U i is the voltage under ideal potential distribution at each end surface, i=1,2,…n, j=1,2,3,…n, and n is the number of power modules.

[0041] However, due to the stray capacitance of metal components such as the flanges at both ends of the power electronic switch, the metal gaskets between the series power devices, and the metal plates between the thyristor valve sections, the different heights of the power devices in each layer relative to the ground, and the influence of surrounding electrical equipment, the mutual capacitance between adjacent layers of power devices varies, which in turn causes uneven voltages to be borne by the series power devices within the switch. Under normal operating voltage, the resistor module 11 operates in the low current range (e.g., the current range of less than 1 mA). The resistor module 11 is capacitive and can compensate for the difference in mutual capacitance between the power devices in each layer to a certain extent, but it is not sufficient to achieve a uniform voltage distribution across the series power devices in each layer. Therefore, the embodiments of the present invention can balance or offset the effects of height relative to the ground or stray capacitance by differentially configuring the capacitance of the capacitor modules 12 of each layer of power devices, reducing the deviation in mutual capacitance between adjacent layers of power devices, thereby optimizing the voltage distribution of each layer of power devices.

[0042] Specifically, the embodiment of the present invention arranges the capacitance of the capacitor module 12 of each power device in a differentiated manner based on the end-face voltage of each layer of power devices and the resistance module 11 in parallel to form a composite body, the capacitance of each end face to ground, and the mutual capacitance between each end face. The calculation formula for the capacitance of the capacitor module 12 of each layer of power devices is obtained using the node voltage method, which is specifically as follows:

[0043]

[0044] Among them, C ii C is the capacitance of each end face to ground from bottom to top. ij is the mutual capacitance between the end faces of each layer, U i is the voltage under the ideal potential distribution of each end surface, C iIt is the capacitance value of the capacitor module installed in each layer of power modules starting from the second layer from bottom to top, i = 2, 3, ... n, j = 1, 2, 3, ... n, and n is the number of power modules.

[0045] Now, we take a power electronic switch composed of five power devices connected in series as an example. Considering the ground capacitance and mutual capacitance of each end face, we get the equivalent circuit model of the power electronic switch after adding a voltage balancing device, as shown in the figure: Figure 3 As shown, the static voltage formula of the power electronic switch can be obtained according to formula (2) and formula (3), wherein the capacitance of the capacitor module 12 installed on one of the power devices is set to 0, and the capacitance of the installed capacitor module C2~C5 is obtained by reverse calculation according to formula (4).

[0046]

[0047] Since the capacitor modules 12 can be arranged differently in the embodiment of the present invention, the capacitance of the capacitor modules 12 connected to each power device can be different, such as Figure 4 As shown, the power device is not even equipped with the capacitor module 12 , wherein the power device ( T1 -Tn) is an anti-parallel diode as an example, MOV is a metal oxide resistor, and C is the capacitor module 12 .

[0048] When the power device needs to be equipped with a capacitor module 12, capacitors of corresponding capacitance values ​​can be selected to form the capacitor module 12, or multiple capacitors can be selected and connected in series, parallel, or series-parallel to form the capacitor module 12, which is not limited here.

[0049] The capacitor of the capacitor module 12 of the embodiment of the present invention can be a small cylindrical ceramic capacitor, and the continuous operating voltage of the capacitor module 12 should be greater than or equal to a preset multiple of the voltage between the layers of the series power devices, such as 1.3 times.

[0050] In order to further verify the effectiveness of the voltage equalization device of the embodiment of the present invention for the voltage equalization protection of the power electronic switch under the limitation of small leakage current, a power electronic switch composed of 32 layers of thyristors in series is now described in detail as an example. In the embodiment of the present invention, due to the constraint that the leakage current must not exceed 4mA, the power electronic switch cannot use the traditional RC absorption circuit as a voltage equalization measure. The method of the embodiment of the present invention is adopted in which each layer is connected in parallel with a metal oxide nonlinear resistor and a differential configuration of the voltage equalization capacitor, wherein 400pF voltage equalization capacitors are configured in parallel for layers 1-16, and no voltage equalization capacitors are configured for layers 17-32, so that the voltage unevenness coefficient of the power electronic switch voltage distribution in the off state is reduced to 7%, as shown in FIG. Figure 5 As shown in the figure, the measured leakage current is only 3.1mA, which realizes the optimization of the voltage balancing performance of the power electronic switch under the limitation of small leakage current. When only nonlinear resistors are used for voltage balancing, the measured voltage balancing coefficient is as follows: Figure 6As shown, its maximum uneven pressure coefficient reaches 18%.

[0051] Example 2

[0052] An embodiment of the present invention provides a power electronic switch, such as Figure 7 As shown, it includes: the voltage balancing device 1 of Example 1, and multiple power devices 2, wherein each power device is connected in parallel with a voltage balancing device, and the power devices are connected in series.

[0053] The power devices in the embodiments of the present invention include, but are not limited to, power transistors GTRs, thyristors SCRs, and insulated gate bipolar thyristors IGBTs, and may also be other switching devices with the same functions and performances.

[0054] According to the voltage balancing device detailed in Example 1, the capacitance of the capacitor module 12 connected in parallel to each power device is not the same, but depends on the end surface voltage of the parallel composite body of each layer of power devices and metal oxide resistors, as well as the ground capacitance and mutual capacitance of each end surface.

[0055] Obviously, the above embodiments are merely examples for clarity of explanation and are not intended to limit the implementation methods. Those skilled in the art will appreciate that other variations or modifications can be made based on the above description. It is not necessary and impossible to enumerate all implementation methods here. Obvious variations or modifications arising therefrom remain within the scope of protection of the present invention.

Claims

1. A pressure equalizing device, characterized in that: include: Resistor module and capacitor module, wherein, The resistance module and the capacitance module are both connected in parallel with the power device; The resistance module operates in a low current region and is capacitive; The capacitance values ​​of the capacitor modules of the power devices are arranged differently according to the terminal voltage of the composite body formed by connecting the power devices of each layer in parallel with the resistance module, the capacitance of each terminal to ground, and the mutual capacitance between the terminal surfaces; The resistance module includes at least one resistor sheet; When the resistor module includes at least two resistor sheets, the resistor sheets are connected in any one of a series connection, a parallel connection, or a series-parallel connection; The continuous operating voltage of the resistance module is higher than the interlayer voltage of the power devices connected in series, and the sum of the maximum residual voltage values ​​of all the resistors in the resistance module is lower than the voltage tolerance value of the connected power devices.

2. The pressure equalizing device according to claim 1, characterized in that: The resistor is a metal oxide resistor.

3. The pressure equalizing device according to claim 1, characterized in that: The calculation formula of the capacitance of the capacitor module is: Among them, C ii C is the capacitance of each end face to ground from bottom to top. ij is the mutual capacitance between the end faces of each layer, U i is the voltage under the ideal potential distribution of each end surface, C i The capacitance values ​​of the capacitor modules installed in each layer of power modules starting from the second layer from bottom to top, i = 2, 3, ... n, j = 2, 3, ... n, n is the number of power modules.

4. The pressure equalizing device according to claim 3, characterized in that: When the capacitor module includes at least two capacitors, the capacitors are connected in series, in parallel, or in series and parallel.

5. A power electronic switch, characterized in that: include: The voltage balancing device and multiple power devices according to any one of claims 1 to 4, wherein each of the power devices is connected in parallel with a voltage balancing device, and the power devices are connected in series.

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