CN108828318A - A method of extracting cascade connection type isolating transformer parasitic capacitance - Google Patents
A method of extracting cascade connection type isolating transformer parasitic capacitance Download PDFInfo
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Abstract
The invention belongs to high frequency transformer modeling technique field more particularly to a kind of methods for extracting cascade connection type isolating transformer parasitic capacitance, including：Single isolating transformer equivalent-circuit model is constructed based on isolating transformer low frequency magnetic effect and high frequency capacitance effect；The cascade model of n isolating transformer is equivalent to link circuit and calculates cascade isolating transformer port Impedance function；The relational expression of cascade isolating transformer port Impedance resonance frequency and circuit parameter is constructed according to zero-pole analysis；Test to obtain the port open impedance resonance frequency of cascade isolating transformer, cascade isolating transformer output end open circuit and sending-end impedance in the case where short circuit in low frequency with impedance analyzer, and magnetizing inductance and leakage inductance are calculated separately, and calculate the parasitic capacitance of isolating transformer.The present invention can easily and effectively extract the parasitic capacitance of inside transformer without internal structure data, facilitate the broadband properties and parasitic parameter effect of studying cascade transformer two-port network.
Description
Technical Field
The invention belongs to the technical field of high-frequency transformer modeling, and particularly relates to a method for extracting parasitic capacitance of a cascade type isolation transformer.
Background
The energy supply system of the hybrid high-voltage direct-current circuit breaker is composed of a cascade isolation transformer and an energy taking magnetic ring. The high-voltage direct-current circuit breaker is directly connected with hundreds of kilovolts of high potential, an energy supply system of the high-voltage direct-current circuit breaker is tested in high voltage withstand to the ground, commercial power is cascaded to the high-potential direct-current circuit breaker through a plurality of isolation transformers due to the requirement of high potential isolation, and only an input port of a first isolation transformer and an output port of a last isolation transformer are connected with the outside after the cascade isolation transformers are subjected to insulation pouring and integrated packaging.
The distance between the energy supply loop cable and the main branch and the transfer branch of the circuit breaker is very close, mutual inductance between the loops cannot be ignored, and when the circuit breaker acts, the current of dozens of kiloamperes is cut off within a few ms according to the principle thatIt is known that a large overvoltage will be induced in the supply loop. And the load of the energy supply system is directly connected with the high-voltage direct-current overhead line, so that lightning overvoltage and various operation overvoltages are easily introduced into an energy supply loop. In order to analyze the reliability of an energy supply system under the condition of overvoltage, a model capable of accurately reflecting the broadband characteristic of the cascade isolation transformer needs to be established.
At present, a parasitic capacitance extraction method based on external measurement is mature for a single transformer, but no research is provided on external characteristic analysis and parasitic capacitance extraction methods of two-port networks cascaded by a plurality of transformers.
Disclosure of Invention
In view of the above technical problems, the present invention provides a method for extracting parasitic capacitance of a cascaded isolation transformer, comprising:
step 1, constructing an equivalent circuit model of a single isolation transformer based on a low-frequency magnetic effect and a high-frequency capacitance effect of the isolation transformer;
step 2, the model of the cascade connection of the n isolation transformers is equivalent to a chain circuit, and port impedance functions of the cascade isolation transformers are calculated according to a chain circuit transmission matrix;
step 3, constructing a relational expression of the port impedance resonant frequency of the cascade isolation transformer and the circuit parameters of the single isolation transformer according to the zero-pole analysis of the port impedance function of the cascade isolation transformer;
step 4, testing by using an impedance analyzer to obtain a port open-circuit impedance curve of the cascade isolation transformer, and obtaining the resonant frequency of the port open-circuit impedance;
step 5, testing by using an impedance analyzer to obtain input end impedance of the cascade isolation transformer under the conditions of open circuit and short circuit of the output end at low frequency, and respectively calculating to obtain excitation inductance and leakage inductance of the isolation transformer;
and 6, calculating the parasitic capacitance of the isolation transformer according to the port open-circuit impedance resonance frequency, the excitation inductance and the leakage inductance.
The single isolation transformer equivalent circuit model comprises: excitation inductance L of windingmLeakage inductance L of the windingsReduced to the winding resistance R of the primary sidesCore loss equivalent resistance R of isolation transformermSelf-capacitance C between winding turns1Mutual capacitance C between the primary winding and the secondary winding2。
The cascaded isolation transformer port impedance function comprises:
wherein Z isocFor the input impedance, Z, of the cascade isolation transformer when the output is opencFor the characteristic impedance, Z, of each isolating transformer0Is the open circuit impedance of a single isolating transformer, ZkThe short-circuit impedance of a single isolation transformer is N, the number of the single isolation transformers contained in the cascade isolation transformer is N, j is an imaginary number unit, and gamma is the propagation coefficient of each isolation transformer.
The relation between the port impedance resonance frequency of the cascade isolation transformer and the circuit parameter of the single isolation transformer comprises the following steps:
ωn＝2πfn
wherein, ω isn+1Angular velocity, ω, corresponding to the n +1 th parallel point frequencynFor the angular velocity corresponding to the nth series resonance point frequency, the intermediate variable L1＝2LmMiddle variable L2＝Ls，fnThe number is the nth parallel or series resonance point, N is the serial number of the isolation transformer, and N is the number of the single isolation transformers contained in the cascade isolation transformer.
Input end impedance Z under the condition that the output end is open circuit at low frequencyoThe expression is as follows:
input end impedance Z under the condition of short circuit of output end at low frequencysThe expression is as follows:
Zs＝N(jωLs+Rs)
ω is the angular frequency.
The invention has the beneficial effects that: the invention can conveniently and effectively extract the parasitic capacitance in the single isolation transformer without internal structure data only by external test of the two-port network of the n cascade transformers, and is beneficial to researching the broadband characteristic and parasitic parameter effect of the two-port network of the cascade transformer.
Drawings
FIG. 1 is an equivalent model schematic diagram of a single isolation transformer
FIG. 2 is a schematic diagram of an equivalent model of a cascaded isolation transformer
FIG. 3 is a graph of the impedance function of a two-port network of 5 cascaded transformers
Detailed Description
The embodiments are described in detail below with reference to the accompanying drawings.
The transformation ratio of the isolation transformer is 1: 1, the primary and secondary windings are uniformly and densely wound on the annular magnetic core, and a single transformer model can be regarded as an equivalent circuit which is symmetrical left and right, and up and down, as shown in fig. 1; in the cascade isolation transformer, the distance between the transformers is far enough, mutual inductance between the transformers can be ignored, therefore, the cascade models of the n transformers are directly connected with the models of the n figure 1 to form a chain circuit, as shown in figure 2, the parameter of the model is extracted, namely the parameter of a single isolation transformer of the model is required to be extracted.
Constructing an isolation transformer as shown in FIG. 1The device circuit model considers the low-frequency magnetic effect and the high-frequency capacitance effect of the isolation transformer and can reflect the broadband characteristic of the isolation transformer, wherein the meaning of each parameter is as follows: l ismExcitation inductance for the winding, LsIs the leakage inductance of the winding, RsTo be reduced to the winding resistance of the primary side. RmCore loss equivalent resistance, C, for isolating transformers1Is the self-capacitance between turns of the winding, C2Is the mutual capacitance between the primary winding and the secondary winding.
In this embodiment, the extraction of the capacitance of the single isolation transformer shown in fig. 1 is realized by testing the port impedance of the cascaded isolation transformer shown in fig. 2. The specific method comprises the following steps:
step 1, calculating the relation between the impedance resonance frequency of a port of a cascade isolation transformer and the circuit parameters of a single isolation transformer.
① the model of the cascade isolation transformer is equivalent to a chain circuit, and port impedance function of the cascade isolation transformer is calculated according to the transmission matrix of the chain circuit.
For a two-port chain circuit formed by cascading N identical symmetrical circuits, the impedance of an input end is equal to
Wherein,
Z0is the open circuit impedance of the subunit circuit, ZkIs the short circuit impedance of the subunit circuit.
② according to the zero-pole analysis of the port impedance function, the relation between the port impedance resonance frequency and the single isolation transformer circuit parameter is obtained.
The parallel resonance point of the open input impedance is the pole of the open impedance function,
the series resonance point of the open input impedance is the zero point of the open impedance function,
then
Considering that the resistance hardly affects the resonant frequency of the transformer, neglecting damping, the open-circuit impedance resonant frequency of the two-port network of fig. 2 has the following relationship with the individual transformer circuit parameters of fig. 1:
ωn＝2πfn
fnis the nth parallel/series resonance point frequency
Because only two capacitance parameters to be solved are arranged in the transformer, only the first two resonance points are needed, namely the first parallel resonance point and the first series resonance point.
According to formula (6), when N is 1 or N is N, there are
So when n is equal to 1, there are
ω1p 2L1C1-1＝0 (9)
According to formula (7), when n is 1, there are
ω1pIs the 1 st parallel resonance point, ω1sIs the 1 st series resonance point
The open-circuit and short-circuit impedance resonance conditions of the two-port network of the 5 cascaded isolation transformers are shown in fig. 3, wherein the peak value in the curve is a parallel resonance point, and the valley value is a series resonance point.
Step 2: and acquiring the port open-circuit impedance resonant frequency of the cascade isolation transformer.
And (3) opening the output end of the two-port network of the cascade isolation transformer, measuring the impedance of the input end by using an impedance analyzer, and setting the sweep frequency range as the lower limit and the upper limit of the impedance analyzer. The resonant point frequency thereof is acquired.
And step 3: calculating the excitation inductance LmAnd leakage inductance Ls。
① the output end of the cascade isolation transformer is opened, and the impedance Z of the input end under the condition of low frequency is tested by an impedance analyzeroThe range of the frequency sweep is set to be 50Hz-100 Hz. According to input terminal impedance ZoCalculating excitation inductance L of isolation transformerm. Input terminal impedance ZoThe expression of (a) is:
② the output end of the cascade isolation transformer is short-circuited, and the impedance Z of the input end under the condition of low frequency is tested by an impedance analyzersThe range of the frequency sweep is set to be 50Hz-100 Hz. According to input terminal impedance ZsCalculating leakage inductance L of isolation transformers. Input terminal impedance ZsThe expression of (a) is:
Zs＝N(jωLs+Rs) (12)
where n is the number of cascaded isolation transformers and ω is the angular frequency.
And 4, step 4: excitation inductance L according to open-circuit impedance resonance frequencymAnd leakage inductance LsAnd calculating the parasitic capacitance of the isolation transformer.
The parasitic capacitance in this embodiment comprises the self-capacitance C of the winding1And a mutual capacitance C between the primary winding and the secondary winding2The capacitance parameter is calculated according to the equations (9) and (10).
In this embodiment, a 5-stage cascade isolation transformer for a ± 500kV high-voltage dc circuit breaker energy supply system is described, and a 1 st parallel resonant frequency and a 1 st series resonant frequency are obtained by measurement with an impedance analyzer. The capacitance C can be obtained according to the formulas (8) and (9)1And C2The value of (c).
The present invention is not limited to the above embodiments, and any changes or substitutions that can be easily made by those skilled in the art within the technical scope of the present invention are also within the scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.
Claims (5)
1. A method for extracting parasitic capacitance of a cascade isolation transformer is characterized by comprising the following steps:
step 1, constructing an equivalent circuit model of a single isolation transformer based on a low-frequency magnetic effect and a high-frequency capacitance effect of the isolation transformer;
step 2, the model of the cascade connection of the n isolation transformers is equivalent to a chain circuit, and port impedance functions of the cascade isolation transformers are calculated according to a chain circuit transmission matrix;
step 3, constructing a relational expression of the port impedance resonant frequency of the cascade isolation transformer and the circuit parameters of the single isolation transformer according to the zero-pole analysis of the port impedance function of the cascade isolation transformer;
step 4, testing by using an impedance analyzer to obtain a port open-circuit impedance curve of the cascade isolation transformer, and obtaining the resonant frequency of the port open-circuit impedance;
step 5, testing by using an impedance analyzer to obtain input end impedance of the cascade isolation transformer under the conditions of open circuit and short circuit of the output end at low frequency, and respectively calculating to obtain excitation inductance and leakage inductance of the isolation transformer;
and 6, calculating the parasitic capacitance of the isolation transformer according to the port open-circuit impedance resonance frequency, the excitation inductance and the leakage inductance.
2. The method of claim 1, wherein the single isolation transformer equivalent circuit model comprises: excitation inductance L of windingmLeakage inductance L of the windingsReduced to the winding resistance R of the primary sidesCore loss equivalent resistance R of isolation transformermSelf-capacitance C between winding turns1Mutual capacitance C between the primary winding and the secondary winding2。
3. The method of claim 1, wherein the cascaded isolation transformer port impedance function comprises:
wherein Z isocFor the input impedance, Z, of the cascade isolation transformer when the output is opencFor the characteristic impedance, Z, of each isolating transformer0Is the open circuit impedance of a single isolating transformer, ZkIs the short-circuit impedance of a single isolation transformer, N is the number of single isolation transformers contained in the cascade isolation transformer, j is the unit of imaginary numberAnd Γ is the propagation coefficient of each isolation transformer.
4. The method of claim 1, wherein the relationship between the port impedance resonant frequency of the cascaded isolation transformer and the circuit parameter of the single isolation transformer comprises:
ωn＝2πfn
wherein, ω isn+1Angular velocity, ω, corresponding to the n +1 th parallel point frequencynFor the angular velocity corresponding to the nth series resonance point frequency, the intermediate variable L1＝2LmMiddle variable L2＝Ls，fnThe number is the nth parallel or series resonance point, N is the serial number of the isolation transformer, and N is the number of the single isolation transformers contained in the cascade isolation transformer.
5. Method according to claim 1, characterized in that the input impedance Z in the case of an open circuit at the output is the input impedanceoThe expression is as follows:
input impedance Z in case of short circuit of the outputsThe expression is as follows:
Zs＝N(jωLs+Rs)
ω is the angular frequency.
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Cited By (5)
| Publication number | Priority date | Publication date | Assignee | Title |
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| CN109977557A (en) * | 2019-03-28 | 2019-07-05 | 广东志成冠军集团有限公司 | A kind of modeling method suitable for electroacoustic longitudinal vibration transducer equivalent circuit |
| CN110174581A (en) * | 2019-04-28 | 2019-08-27 | 中国科学院宁波材料技术与工程研究所 | It is wirelessly transferred transformer leakage inductance measurement method and device |
| CN112711924A (en) * | 2020-12-11 | 2021-04-27 | 国网辽宁省电力有限公司葫芦岛供电公司 | High-frequency modeling method for high-capacity high-frequency transformer |
| CN113390932A (en) * | 2021-05-24 | 2021-09-14 | 南京航空航天大学 | Measuring method and system suitable for distribution parameters of high-frequency transformer |
| CN117010311A (en) * | 2023-06-28 | 2023-11-07 | 兰州交通大学 | Equivalent circuit of railway track circuit |
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Cited By (7)
| Publication number | Priority date | Publication date | Assignee | Title |
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| CN109977557A (en) * | 2019-03-28 | 2019-07-05 | 广东志成冠军集团有限公司 | A kind of modeling method suitable for electroacoustic longitudinal vibration transducer equivalent circuit |
| CN109977557B (en) * | 2019-03-28 | 2023-05-05 | 广东志成冠军集团有限公司 | Modeling method suitable for equivalent circuit of electroacoustic longitudinal vibration transducer |
| CN110174581A (en) * | 2019-04-28 | 2019-08-27 | 中国科学院宁波材料技术与工程研究所 | It is wirelessly transferred transformer leakage inductance measurement method and device |
| CN112711924A (en) * | 2020-12-11 | 2021-04-27 | 国网辽宁省电力有限公司葫芦岛供电公司 | High-frequency modeling method for high-capacity high-frequency transformer |
| CN113390932A (en) * | 2021-05-24 | 2021-09-14 | 南京航空航天大学 | Measuring method and system suitable for distribution parameters of high-frequency transformer |
| CN117010311A (en) * | 2023-06-28 | 2023-11-07 | 兰州交通大学 | Equivalent circuit of railway track circuit |
| CN117010311B (en) * | 2023-06-28 | 2024-05-17 | 兰州交通大学 | Equivalent circuit of railway track circuit |
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