CN112331433A

CN112331433A - Metal oxide piezoresistor folding structure for near square wave generating circuit

Info

Publication number: CN112331433A
Application number: CN202011147281.5A
Authority: CN
Inventors: 杨汉武; 陆昊; 张慧博; 张自成; 高景明
Original assignee: National University of Defense Technology
Current assignee: National University of Defense Technology
Priority date: 2020-10-23
Filing date: 2020-10-23
Publication date: 2021-02-05
Anticipated expiration: 2040-10-23
Also published as: CN112331433B

Abstract

The invention discloses a metal oxide piezoresistor folding structure for a near square wave generating circuit, and aims to solve the problems that the output voltage level of the conventional MOV folding structure is low and partial area is easy to break down. The invention is composed of 7 MOV columns, an input electrode, a copper plate electrode and a load; the distances between the first to seventh MOV columns and the load are increased in sequence by taking the load as an axis and are distributed in an involute shape; the top of the load is connected with the top of the first MOV column through an input electrode; the MOV single bodies on each MOV column are coaxially stacked, and the low-voltage end of the upper MOV column is connected with the high-voltage end of the lower MOV column through a copper plate electrode; the potential difference between the load and the first to seventh MOV legs increases gradually and the potential difference between the outer barrel and the first to seventh MOV legs decreases gradually. The maximum output voltage of the invention reaches 500kV, the risk of breakdown caused by overhigh voltage can be effectively relieved, and the insulating capability of the whole folding structure is improved.

Description

Metal oxide piezoresistor folding structure for near square wave generating circuit

Technical Field

The invention relates to the technical field of pulse power, in particular to a Metal Oxide Varistor (MOV) folding structure for a near square wave high-voltage generating circuit.

Background

The metal oxide piezoresistor has nonlinear volt-ampere characteristics, is mainly used for limiting transient overvoltage in a circuit and absorbing surge energy, and can be applied to the generation of near square wave pulses in the technical field of pulse power based on the voltage stabilizing characteristic of MOV. Generally, a Marx generator generates high-voltage pulses, and the MOV stabilizes the overvoltage near the voltage-sensitive voltage value of the high-voltage pulses, so that pulse square wave output can be obtained on a load. In particular implementations, because of the limited voltage-dependent voltage of a single MOV, it is often necessary to stabilize higher voltages by connecting a large number of MOV cells in series. In the working process, under the condition that a plurality of MOV monomers are connected in series, the structure is adopted, the inductance can be reduced, and meanwhile, the insulation capacity of the whole structure is increased as much as possible, so that the method becomes a key engineering problem.

The researchers of the national defense science and technology university are the trekking course and the academic paper research on the high-voltage pulse forming technology based on the metal oxide piezoresistor introduces an MOV near square wave generating circuit and two different MOV folding structures, and the two MOV folding structures are respectively called as a structure 1 and a structure 2 below. The MOV near square wave generating circuit is shown in fig. 1 and comprises a Marx generator, an MOV assembly, an LC filter branch, an inductor L1 and a discharge switch S1, wherein the MOV assembly comprises an MOV folding structure and a fixed supporting structure. The metal oxide piezoresistors in the structure 1 are divided into two groups according to the number average, and MOV monomers in each group are tightly connected to form an MOV column. As shown in fig. 2, the two MOV posts rely on copper plate electrodes at the bottom for direction switching and electrical connection. There are horseshoe shaped copper electrodes on the top of each MOV post for connection to other wires. The structure folds the MOV to be connected in series, so that the directions of currents in the left MOV column and the right MOV column are opposite, the directions of generated induction magnetic fields are opposite to each other due to the opposite directions, and the total inductance is reduced. In the structure 1, each MOV column contains 7 metal oxide varistors at most, the whole folding structure contains 14 metal oxide varistors at most, each MOV is estimated according to the voltage-dependent voltage of 7.5kV, and the structure 1 can realize the voltage output of more than 100 kV. When the voltage output requirement is higher, the structure 1 is no longer satisfactory for use, and the structure 2 is provided on the basis of the trefoil. As shown in fig. 3, the circuit load in the structure 2 is placed in the center, 5 MOV columns are arranged at equal intervals by taking the load as an axis, the distance between each MOV column and the load is equal, and the included angle between the adjacent MOV columns and the connecting line of the load is equal. The load and the first MOV post between realize connecting through the input electrode, realize connecting through the copper electrode between the adjacent MOV post, whole structure carries out a large amount of MOV monomers in series. The folding structure 2 is fixedly supported through a supporting structure to jointly form an MOV assembly, and can be applied to engineering experiments. The supporting structure comprises a fixing plate, an upper cover, a lower bottom, an outer cylinder, a supporting nylon column and a screw rod. The fixed plate is provided with holes corresponding to the MOV column and the load, and the MOV column and the load pass through the fixed plate and are fixed on the fixed plate through a support nylon column and a screw rod. The upper cover is opened, the fixing plate is placed into the barrel and is attached to the outer barrel, and after the upper cover is covered, the whole assembly is assembled and fixed. Structure 2 accommodates a maximum of 10 metal oxide varistors per MOV column and a maximum of 50 metal oxide varistors per folded structure, and structure 2 is expected to achieve voltage outputs above 350 kV.

Through different designs, the two structures can respectively realize 100kV and 300kV magnitude voltage output in the near square wave generating circuit, can reasonably reduce MOV branch inductance and improve the insulating capability as much as possible. However, the following problems still remain: 1. one of the technical indexes pursued in the field of pulse power is higher output voltage, and the structure cannot meet the requirement of higher 500 kV-order output voltage. 2. When the output voltage is increased to 500kV magnitude, the coaxial and equidistant structure causes serious uneven voltage distribution in the structure, and the electric field of partial area is overlarge, thus being easy to generate breakdown.

Disclosure of Invention

The technical problem to be solved by the invention is as follows: aiming at the problems of low output voltage level and easy breakdown of partial areas of two existing MOV folding structures, a novel MOV folding structure for a near square wave generating circuit is provided, the problem that the existing MOV folding structure cannot meet the output voltage of higher 500kV magnitude is solved, and the problems that when the voltage is increased to the higher magnitude, the pressure distribution in the structure is seriously uneven due to the coaxial and equidistant structure, the electric field of partial areas is overlarge, and the breakdown is easy to occur are solved.

The technical scheme of the invention is as follows:

an MOV folding structure for a near square wave generating circuit is presented. The folding structure can support high voltage output above 500kV, and the problem that partial areas are prone to breakdown due to uneven pressure distribution can be effectively solved by adopting a coaxial gradually-opening arrangement mode, so that the insulating capability of the whole structure is improved.

The invention is an improvement on the basis of a folding structure 2 in the background technology, increases the number of MOV columns and changes the arrangement of the MOV columns from coaxial equal spacing to coaxial gradual-open type. The invention consists of 7 MOV columns, an input electrode, a copper plate electrode and a load. The coaxial involute is distributed in an involute shape by taking the load as an axis and sequentially increasing the distance from the first MOV column to the seventh MOV column to the load. The top of the load is a high-voltage input end of an MOV folding structure, and the top of the load is connected with the top of the first MOV column through an input electrode. The MOV monomer on every MOV post stacks neatly with the same axle, and the low voltage end of last MOV post realizes the electricity through the copper electrode with the high voltage end of next MOV post. In the experiment, the MOV folding structure needs to be fixed in an outer cylinder, the outer cylinder is grounded, the specific supporting device can see the background technology, and the openings in the fixing plate only need to correspond to the positions of the first MOV column to the seventh MOV column of the current folding structure and the load, and the rest of the structure is consistent with the original design. The design principle is as follows: according to the change of the potential difference between the load and different MOV columns, the distance between the load and different MOV columns is reasonably adjusted, the local field intensity is prevented from being too high, and the insulating capability is improved. Because the MOVs are connected in series in a folding mode, each MOV monomer generates voltage drop, the outer cylinder is grounded, the potential difference between the load and the first MOV column to the seventh MOV column is gradually increased, the potential difference between the outer cylinder and the first MOV column to the seventh MOV column is gradually reduced, and therefore the mode of gradually increasing the distance between the load and the MOV is adopted to avoid overhigh local field intensity.

The specific location of each MOV post can be represented in a two-dimensional plan view. For convenience of description, the parameters in the design scheme are uniformly introduced:wherein x₁，y₁The initial value is determined by the input voltage of the high-voltage end.

1. Defining a load center as an origin O, and establishing a plane rectangular coordinate system. The n-th MOV column has a center of P_nCorresponding to the coordinate is (x)_n，y_n)。

2. N-th MOV column center P_nA distance rn from the origin, where r₁For self-setting of initial values, taking into account the compactness and safety of the folding structure, r₁Generally controlled at 100-150 mm; n-th MOV column center P_nCenter P of MOV pillar of more than (n-1)_n-1Increase in distance from origin d_n(n is more than or equal to 2 and less than or equal to 7); the distance between two adjacent MOV columns is fixed to be L and is generally set to be 100-130 mm. (x)_n，y_n) The following two equations can be used simultaneously:

x_n ²+y_n ²＝(r_n-1+d_n)²(2≤n≤7)；

(x_n-x_n-1)²+(y_n-y_n-1)²＝L²(2≤n≤7)，

wherein x₁，y₁To satisfy

Any real number of (2).

3. The diameter of the MOV column is d, which is determined according to the actual size of the selected MOV monomer; the diameter of the load is D, and the diameter is determined according to the actual size of the selected load; the radius of the outer cylinder is R and is determined according to the miniaturization requirement of an experimental device; the thickness of the outer cylinder is h.

The MOV folding structure can contain 70 effective MOVs at most, and when an MOV monomer with the voltage-sensitive voltage of more than or equal to 7.5kV is selected, high-voltage output of more than 500kV can be realized.

The working process of the invention is as follows: the existing MOV near square wave generating circuit in the background art is adopted, and only the MOV folding structure is replaced and adjusted. In the experiment, the MOV folding structure is arranged on the supporting and fixing structure shown in the background technology figure 3 and is connected with a load in parallel, when the Marx generator generates an output pulse signal with higher magnitude, the MOV folding structure limits the voltage, and a near square wave high-voltage pulse signal with 500kV magnitude can be obtained on the load at most.

Compared with the prior art, the invention can achieve the following effects:

1. the MOV folding structure can contain more MOV monomers, can bear higher-level voltage output, and has the highest output voltage of more than 500 kV.

2. The MOV column adopts a coaxial gradually-opened arrangement design, the arrangement mode effectively relieves the risk of breakdown caused by overhigh voltage at a certain position in the original structure, and the insulating capability of the whole assembly is improved.

Drawings

FIG. 1 is a schematic diagram of an MOV near square wave pulse generating circuit introduced in the academic paper "research on high voltage pulse forming technology based on metal oxide piezoresistor" of the trekking equation in the background art;

FIG. 2 is a schematic diagram of a prior art MOV fold configuration;

FIG. 3 is a schematic diagram of a prior art MOV device;

figure 4 is the invention MOV folding structure diagram;

FIG. 5 is a schematic plan view of an MOV column arrangement of the present invention;

FIG. 6 shows the result of an inductance simulation of an MOV folded structure according to the present invention;

fig. 7 shows the simulation result of the electric field distribution when the input voltage of the MOV folding structure of the present invention is 1V, fig. 7(a) is the overall electric field distribution diagram, and fig. 7(b) is the planar two-dimensional electric field distribution diagram of the input terminal electrode.

Detailed Description

In order to make the objects, technical solutions, and the like of the present invention clearer, the present invention will be described below with reference to the accompanying drawings and specific embodiments. It should be understood that the description herein is only for the purpose of illustrating the present invention and is not intended to limit the present invention.

Fig. 1 is a schematic diagram of an MOV near square wave pulse generating circuit introduced by a trekking equation in the background art in the academic paper "research on high voltage pulse forming technology based on metal oxide piezoresistors". The circuit consists of a Marx generator, an MOV component, an LC filtering branch, an inductor L1 and a discharge switch S1. The LC filtering branch is formed by connecting an inductor L2 and a capacitor C2 in parallel, and the Marx generator, the inductor L1 and the LC filtering branch form a two-section pulse forming network. The LC filtering branch circuit is connected between the output end of the Marx generator and an inductor L1 in series, an inductor L1 is connected between the LC filtering branch circuit and the high-voltage end of the MOV assembly in series, and a discharge switch S1 is connected between the Marx generator and the LC filtering branch circuit. The load Z, MOV assembly and the Marx generator are connected in parallel. The Marx generator generates high-voltage pulses, and pulse square wave output is obtained on a load Z through the voltage clamping action of the MOV component.

Figure 2 is a background art MOV folded structure 1 diagram. As shown in fig. 2, the metal oxide varistors in the structure 1 are divided into two groups by number, and the MOV monomers in each group are tightly connected to form a first MOV column 1 and a second MOV column 2. The bottom of the first MOV column 1 and the bottom of the second MOV column 2 realize direction conversion and electrical connection by means of a copper plate electrode 11. The first MOV column 1 has a first horseshoe shaped copper electrode 31 on top and the second MOV column has a second horseshoe shaped copper electrode 32 on top for connection to other wires. The structure folds the MOV to be connected in series, the current directions in the first MOV column 1 and the second MOV column 2 are opposite, and the directions of the generated induction magnetic fields are opposite to each other due to the opposite directions, so that the total inductance is reduced. In the structure 1, each MOV column contains 7 metal oxide varistors at most, the whole folding structure contains 14 metal oxide varistors at most, each MOV is estimated according to the voltage-dependent voltage of 7.5kV, and the structure 1 can realize the voltage output of more than 100 kV.

Figure 3 is a background art MOV folded structure 2 diagram. As shown in fig. 3, the circuit load 8 in the structure 2 is arranged in the center, 5 MOV columns 1-5 (the first MOV column 1-the fifth MOV column 5) are arranged at equal intervals by taking the load 8 as a central axis, the distance between each MOV column and the load 8 is equal, and the included angle between the connecting lines of the adjacent MOV columns and the load 8 is equal. Load 8 and the first MOV post 1 between realize connecting through input electrode 10, realize connecting through copper electrode 11 ~ 14 (first copper electrode 11 ~ fourth copper electrode 14) between the adjacent MOV post, whole structure carries out a large amount of MOV monomers to establish ties folding connection. The folding structure 2 is fixedly supported through a supporting structure to jointly form an MOV assembly, and can be applied to engineering experiments. The supporting structure comprises a fixing plate 400, an upper cover 401, a lower base 402, an outer cylinder 9, 1 supporting

nylon column

403 and 6 screws 404. The fixing plate 400 is provided with holes corresponding to the positions of 5 MOV columns and the load 8, and the 5 MOV columns and the load 8 pass through the fixing plate 400 and are fixed on the fixing plate 400 through the supporting

nylon columns

403 and 6 screws 404. The upper cover 401 is opened, the fixing plate 400 is placed in the outer cylinder 9 and attached to the outer cylinder 9, and after the upper cover 401 is closed, the entire MOV assembly is assembled and fixed. Each MOV post holds 10 metal oxide piezo-resistors at most in the beta structure, and whole beta structure holds 50 metal oxide piezo-resistors at most, can realize the voltage output of 350kV above.

Figure 4 is the invention of MOV folding structure diagram. As shown in fig. 4, the present invention is composed of 7 MOV posts 1 to 7 (first to seventh MOV posts 1 to 7), an

input electrode

10, 6 copper plate electrodes 11 to 16 (first to sixth copper plate electrodes 11 to 16), and a load 8. The distance between the load 8 and the first MOV column 1 to the seventh MOV column 7 increases in sequence by taking the load 8 as a central axis, and the distances are distributed in an involute shape. The top of the load 8 is a high voltage input end of an MOV folding structure and is connected with the top of the first MOV column 1 through an input electrode 10. Each MOV column is formed by coaxially stacking 10 MOV monomers, the low-voltage end of the i (i is more than or equal to 1 and less than or equal to 6) MOV column i is electrically connected with the high-voltage end of the i +1 MOV column i +1 through a copper plate electrode (namely, the low-voltage end of the first MOV column 1 is electrically connected with the high-voltage end of the second MOV column 2 through a copper plate electrode 11, the low-voltage end of the second MOV column 2 is electrically connected with the high-voltage end of the third MOV column 3 through a copper plate electrode 12, the low-voltage end of the third MOV column 3 is electrically connected with the high-voltage end of the fourth MOV column 4 through a copper plate electrode 13, the low-voltage end of the fourth MOV column 4 is electrically connected with the high-voltage end of the fifth MOV column 5 through a copper plate electrode 14, the low-voltage end of the fifth MOV column 5 is electrically connected with the high-voltage end of the sixth MOV copper plate 6 through an electrode 15, and the low-voltage end of the sixth MOV column 6 is electrically. In the experiment, the MOV folding structure needs to be fixed in the outer cylinder 9, the outer cylinder 9 is grounded, the outer cylinder 9 belongs to a supporting structure, the supporting structure is completely the same as that in the figure 3, only the opening on the fixing plate 400 needs to correspond to 7 MOV columns and the load 8 of the folding structure, the number of the screw rods 404 is changed into 8, and the rest is consistent with that in the figure 3. The MOV folding structure can contain 70 effective MOVs at most, and the MOV monomer with the voltage-sensitive voltage more than or equal to 7.5kV is selected, so that the high-voltage output of more than 500kV can be realized.

Figure 5 is the MOV column arrangement position plan view diagram. As shown in fig. 5, a rectangular plane coordinate system is established by defining the center of the load 8 as the origin O. The 7 MOV columns from near to far away from the load 8 are numbered from 1 to 7 in sequence, and the first MOV column 1 is closest to the load 8 and farthest from the outer cylinder 9; the seventh MOV column 7 is furthest from the load 8 and closest to the outer cylinder 9. N center of n-th MOV column is P_n，P_nCorresponding coordinate is (x)_n，y_n). N center P of n-th MOV column_nAt a distance r from the origin O_n(ii) a N center P of n-th MOV column_nN-1 center P of MOV column (n-1)_n-1Increased distance d from origin O_n(when n is 2. ltoreq. n.ltoreq.7); the distance between two adjacent MOV posts is fixed as L, and L sets up at 100 ~ 130 mm. (x)_n，y_n) The following two equations can be used simultaneously:

x_n ²+y_n ²＝(r_n-1+d_n)²(2≤n≤7)；

when n is 1, corresponds to r₁Is P₁The distance from the origin O is a self-defined initial value, and the general r of the folding structure compactness and safety is considered₁Controlling the temperature at 100-150 mm; x is the number of₁，y₁To satisfy

Any real number of (2). The diameters of the first MOV column 1 to the seventh MOV column 7 are d, d is the diameter of an MOV monomer, MOV models with various specifications exist in the market, the folding structure can accommodate 70 effective MOVs at most, and in order to realize the voltage stabilizing function of 500kV, the voltage-dependent voltage of the MOV monomer is required to be controlled to be more than or equal to 7.5kV, the diameter d is 40-50 mm generally, and d is the diameter of the MOV monomer; the diameter of the load 8 is D, which is determined according to the actual size of the selected load, oneUnder the general condition, D is less than or equal to 60 mm; the radius of the outer cylinder 9 is R, which is determined according to the miniaturization requirement of the experimental device and ensures R>r₇R is generally controlled between 200mm and 300 mm; the thickness of the outer cylinder 9 is h, and is generally controlled to be 5-15 mm. The overall device has no special requirements for height as long as the load 8 is close to the height of the MOV column and the outer cylinder 9 is higher than the load 8 and the MOV column.

Fig. 6 shows the result of an inductance simulation of an embodiment of an MOV folded structure of the present invention. The outer cylinder is selected to be 360mm high, 240mm in outer radius and 10mm in thickness. The load diameter D is 30mm, and the height is 300 mm. The 7 MOV columns are all 21mm in diameter d, and 240mm in height. x is the number of₁＝0；y₁＝100mm，d₂～d₇15mm, 10mm, 15mm in sequence; l is 100 mm. Fig. 6 shows the result of the inductance matrix calculated by the CST static magnetic field, where the value of the abscissa 1 corresponding to the ordinate is the inductance value of the structure, and the inductance of the MOV folded structure is about 564nH, which is not much different from the inductance 365nH of the structure 2 in the background art, and this magnitude of inductance will not cause too much influence on the flat top, thereby satisfying the requirement of the device for reducing inductance.

FIG. 7 shows the simulation result of the electric field distribution of the embodiment of FIG. 6 under the condition that the input voltage is 1V. This corresponds to an input voltage of 1V and is chosen to show the maximum of the field strength, i.e. the field strength at any point in the figure is the maximum of the field strength at that point during the entire period of application of the excitation signal. The electric field distribution diagram is originally a color diagram (which is changed into pure black and white according to the requirements of patent laws), and the approximate electric field intensity of each position in the structure can be known corresponding to the color of the upper right scale (electric field intensity, unit: V/m) in the diagram. Figure 7(a) is the overall electric field distribution of the MOV module, where the field strength (darkest in colour) is significantly greater at the input end near the housing and at the axis than elsewhere in the module, with a maximum field strength of about 54.5V/m, much less than the maximum field strength of 118.9V/m for structure 2 of the prior art at the same input voltage. Fig. 7(b) is the two-dimensional electric field distribution of the input electrode plane, and it can be seen that the two ends of the input electrode are the maximum field intensity (deepest color) which is about 46.7V/m, and is also smaller than the maximum field intensity 62.24V/m of the structure 2 in the background art under the same input voltage condition. The invention really solves the problem of overlarge field intensity of partial areas and improves the insulating capability of the whole structure.

Claims

1. A metal oxide varistor folding structure for a near square wave generating circuit comprises MOV columns, input electrodes (10), copper plate electrodes and loads (8), wherein the MOV columns are arranged around the loads (8) serving as central axes, the top of each load (8) is a high-voltage input end of the MOV folding structure and is connected with the top of a first MOV column (1) through the input electrodes (10), and a plurality of MOV monomers are connected in series in the whole structure; the metal oxide piezoresistor folding structure for the near square wave generating circuit is fixed in the outer cylinder (9), and the outer cylinder (9) is grounded; the device is characterized in that the number of the MOV columns is 7, the MOV columns comprise a first MOV column (1) to a seventh MOV column (7), 6 copper plate electrodes comprise a first copper plate electrode (11) to a sixth copper plate electrode (16); the distances between the first MOV column (1) to the seventh MOV column (7) and the load (8) are sequentially increased and distributed in an involute shape, the potential difference between the load (8) and the first MOV column (1) to the seventh MOV column (7) is gradually increased, and the potential difference between the outer cylinder (9) and the first MOV column (1) to the seventh MOV column (7) is gradually reduced; the distance between two adjacent MOV columns is fixed to be L; each MOV column is formed by coaxially stacking 10 MOV monomers, the low-voltage end of the i-th MOV column (i) is electrically connected with the high-voltage end of the i + 1-th MOV column (i +1) through a copper plate electrode, i is more than or equal to 1 and less than or equal to 6, namely the low-voltage end of the first MOV column (1) is electrically connected with the high-voltage end of the second MOV column (2) through a copper plate electrode (11), the low-voltage end of the second MOV column (2) is electrically connected with the high-voltage end of the third MOV column (3) through a copper plate electrode (12), the low-voltage end of the third MOV column (3) is electrically connected with the high-voltage end of the fourth MOV column (4) through a copper plate electrode (13), the low-voltage end of the fourth MOV column (4) is electrically connected with the high-voltage end of the fifth MOV column (5) through a copper plate electrode (14), the low-voltage end of the fifth MOV column (5) is electrically connected with the high-voltage end of the sixth MOV column (6) through a copper plate electrode (15), and the high-voltage end of the seventh MOV column (7) is electrically connected with the high- And (6) electrically connecting.

2. The metal oxide varistor folding structure for the near square wave generating circuit of claim 1, characterized in that the voltage-dependent voltage of the MOV monomer in the first MOV column (1) to the seventh MOV column (7) is greater than or equal to 7.5kV, and the diameter of the MOV monomer is 40-50 mm.

3. A metal oxide varistor folded structure for use in a near square wave generating circuit according to claim 1, wherein said first to seventh MOV posts (1) to (7) have a diameter d equal to the diameter of a single MOV.

4. The metal oxide varistor folded structure for use in a near-square wave generating circuit of claim 1, wherein the distances between the first to seventh MOV posts (1 to 7) and the load (8) increase in sequence, and the involute profile is: the first MOV column (1) is closest to the load (8) and farthest from the outer cylinder (9); the seventh MOV column (7) is farthest from the load (8) and closest to the outer cylinder (9).

5. The metal oxide varistor folded structure for use in a near square wave generating circuit of claim 4, wherein the distances between the first to seventh MOV posts (1) to (7) and the load (8) increase in sequence, and the involute profile further means: establishing a plane rectangular coordinate system by taking the center of the load (8) as an origin O, and establishing the center P of the nth MOV column (n)_nCorresponding coordinate (x)_n，y_n) The following formula is used simultaneously to obtain:

x_n ²+y_n ²＝(r_n-1+d_n)²，2≤n≤7；

(x_n-x_n-1)²+(y_n-y_n-1)²＝D²，2≤n≤7；

r_nis P_nDistance from origin O, d_nIs P_nN-1 center P of MOV column (n-1)_n-1An increased distance from the origin O; when n is 1, r₁Is P₁Relative originThe distance of O; x is the number of₁，y₁To satisfy

Any real number of (d); d is the diameter of the load (8).

6. The folded metal oxide varistor structure of claim 5, wherein said r is a voltage dependent resistor₁Is 100-150mm, and the diameter D of the load (8) meets the requirement that D is less than or equal to 60 mm.

7. The folded metal oxide varistor structure of claim 1, wherein the distance between two adjacent MOV posts is 100-130 mm.

8. The folded structure of metal oxide piezoresistor for near-square wave generation circuit as claimed in claim 1, wherein the radius R of the outer cylinder (9) satisfies R > R₇，r₇Is the distance of the seventh MOV post (7) center P7 from the origin O, which is the load (8) center; the thickness h of the outer cylinder (9) is 5-15 mm.

9. The metal oxide varistor folded structure for use in a near-square wave generating circuit according to claim 8, wherein said outer cylinder (9) has a radius R of 200mm to 300 mm.