Current-limiting phase-shifting transformer topological structure and control method thereof

Abstract

The invention provides a topological structure of a current-limiting phase-shifting transformer and a control method thereof, and relates to the technical field of power flow control and short-circuit current protection of a power system. The topological structure of the current-limiting phase-shifting transformer comprises an exciting transformer and a series transformer, the exciting transformer comprises an exciting transformer primary side winding and an exciting transformer secondary side winding, and the series transformer comprises a series transformer primary side winding and a series transformer secondary side winding; a primary side winding of the exciting transformer is connected in parallel in a line, and exciting voltage is obtained from the line; a secondary side winding of the exciting transformer is connected with a primary side winding of the series transformer; and the secondary side windings of the series transformer are three independent and disconnected windings which are respectively and directly connected in series into three phases of the line. The method can solve the problems that the power flow distribution is unreasonable and the short-circuit current exceeds the standard in the power system, has the advantages of low cost and high economy, and is wide in application range.

Description

Technical Field

[0001] The present invention relates to the technical field of power system power flow control and short-circuit current protection, and in particular to a current-limiting phase-shifting transformer topology structure and a control method thereof. Background Art

[0002] With the continuous construction of new power systems, the grid structure is becoming increasingly complex. The interconnected large power grid can better optimize energy distribution and enhance the economy, safety and stability of the system. However, the complex grid structure and dense power distribution also reduce the equivalent impedance of the system. With the further increase in loads and substations, a large number of lines in the system are facing the problem of excessive short-circuit current, which significantly reduces the safety and stability of the system. At the same time, due to the complex configuration of the network structure and network parameters in the new power system, the natural flow of the power grid cannot effectively respond to the changes in power supply and load, and it is very easy to have uneven flow distribution, which seriously limits the power supply capacity of the regional ring network. Problems such as unreasonable flow distribution and excessive short-circuit current have increasingly become the biggest obstacles to the development of new power systems, challenging the efficient and stable operation of the power grid. Therefore, effective flow limiting and current regulation equipment is urgently needed to solve this problem economically and efficiently.

[0003] At present, the main power flow regulation technologies include FACTS (Flexible Alternative Current Transmission Systems) equipment and phase shifting transformer (PST). FACTS equipment is based on power electronic equipment, which faces the disadvantages of high cost, high loss, high maintenance workload, and damage to system waveform quality. FACTS equipment includes series compensation devices and unified power flow controllers (UPFC). The power flow regulation capability of the series compensation device is limited, and it is mainly used for voltage stabilization and reactive power compensation, which is difficult to apply to optimize the regional power grid power distribution. UPFC has a strong power flow regulation capability, but the cost is too high. At present, the power grid does not have the conditions for large-scale promotion of UPFC for power flow regulation. PST is more widely used because of its large power flow regulation capacity, high flexibility, low cost, low loss and waveform quality advantages, but the current PST does not have the function of short-circuit current limitation and cannot fully meet the needs of the power grid.

[0004] At present, the main current-limiting technologies include changing the power grid structure or operation mode, series compensation high-impedance transformers and reactors, and superconducting fault current limiters. Among them, the current-limiting measures of power grid reconstruction and operation mode change mainly include measures such as loop network splitting and busbar hierarchical segmentation. These measures have a greater impact on the power grid, and it is difficult to implement for a fully built and complete power grid. For series compensation high-impedance transformers and reactors, such equipment will increase the line reactance and affect the dynamic performance and voltage stability of the system. The superconducting fault current limiter is limited by problems such as high cost and limited current-limiting capacity, and its current practical application is limited. Moreover, the current mainstream current-limiting equipment or measures lack the power flow regulation function and cannot fully meet the needs of the power grid. Summary of the Invention

[0005] The purpose of the present invention is to provide a current-limiting phase-shifting transformer topology structure and its control method, which are used to solve the problems that the existing current-limiting regulation equipment lacks the power flow regulation function, cannot limit the short-circuit current, and cannot fully meet the needs of the power grid, solve the problems of unreasonable power flow distribution and excessive short-circuit current in the power system, and have the advantages of low cost and high economy, and a wide range of applications.

[0006] To achieve the above purpose, in the first aspect, the present invention provides a current-limiting phase-shifting transformer topology structure, which includes an exciting transformer and a series transformer. The exciting transformer includes an exciting transformer primary side winding and an exciting transformer secondary side winding. The series transformer includes a series transformer primary side winding and a series transformer secondary side winding. The exciting transformer primary side winding is connected in parallel in the line to obtain the exciting voltage from the line. The exciting transformer secondary side winding is connected to the series transformer primary side winding. The series transformer secondary side winding is three independent and non-connected windings, which are directly connected in series to the three phases of the line respectively.

[0007] According to the current-limiting phase-shifting transformer topology structure provided by the present invention, both the exciting transformer primary side winding and the exciting transformer secondary side winding are star-connected, the series transformer primary side winding is delta-connected, and the voltage on the series transformer primary side winding leads or lags the exciting voltage of this phase .

[0008] According to the current-limiting phase-shifting transformer topology structure provided by the present invention, the exciting transformer is a three-phase double-winding on-load tap-changer transformer, which includes an on-load tap-changer switch. The on-load tap-changer switch includes multiple adjustment positions for adjusting the amplitude of the exciting voltage.

[0009] According to the current-limiting phase-shifting transformer topology structure provided by the present invention, a quick switch is provided on the exciting transformer secondary side winding, and the quick switch is connected to the on-load tap-changer switch. When the line is in a steady state, the quick switch is closed, so as to generate different magnitudes of compensation voltage for the series transformer.

[0010] According to a topology structure of a current-limiting phase-shifting transformer provided by the present invention, a polarity switch is connected to the secondary winding of the exciting transformer, and the reverse-phase operation of the compensation voltage is realized by toggling the polarity switch.

[0011] According to a topology structure of a current-limiting phase-shifting transformer provided by the present invention, a current-limiting gear is provided on the secondary winding of the exciting transformer. The current-limiting gear is connected to the switch contact of the on-load tap-changer, and a current-limiting impedance and an antiparallel thyristor are installed on the current-limiting gear; when a fault occurs in the line, the antiparallel thyristor is triggered, and at the same time, the fast switch is disconnected, and the current-limiting impedance is connected into the line.

[0012] According to a topology structure of a current-limiting phase-shifting transformer provided by the present invention, the fault includes a short circuit.

[0013] According to a topology structure of a current-limiting phase-shifting transformer provided by the present invention, a tap is provided in the middle of the secondary winding of the series transformer, and the exciting voltage is taken from the tap; the number of turns of the windings on both sides of the tap is equal, and each is half of the secondary winding of the series transformer.

[0014] In a second aspect, the present invention provides a control method for the topology structure of the current-limiting phase-shifting transformer in the first aspect, including: When the line is in a steady state, the fast switch is closed, and by adjusting the adjustment gear of the on-load tap-changer, the amplitude of the exciting voltage is adjusted, and then different magnitudes of compensation voltages are generated for the series transformer; When a fault occurs in the line, the antiparallel thyristor is triggered, the fast switch is disconnected, and the current-limiting impedance is connected into the line to realize the limitation of the line current when a fault occurs.

[0015] According to a control method for the topology structure of a current-limiting phase-shifting transformer provided by the present invention, it further includes: by toggling the polarity switch, the reverse-phase operation of the compensation voltage is realized, so as to realize the leading and lagging adjustment of the line voltage phase.

[0016] A topology structure of a current-limiting phase-shifting transformer and a control method thereof provided by the present invention at least have the following technical effects: 1. Introduce a current-limiting impedance to the current-limiting phase-shifting transformer, endowing the current-limiting phase-shifting transformer with the ability to limit short-circuit current, which can simultaneously solve the problems of unreasonable power flow distribution and excessive short-circuit current faced by the system. Compared with traditional phase-shifting transformers, it has more comprehensive functions, good economy, high integration and small floor area, and can be widely used in power system regulation and protection operations.

[0017] 2. Through a unique topological structure design, the current-limiting impedance is connected in a star configuration on the exciting winding, while the primary winding of the series transformer is in a delta connection. According to Kirchhoff's law, when the star connection is equivalently transformed into a delta connection, the impedance becomes three times the original. Therefore, when the current-limiting phase-shifting transformer is connected to the line through the series transformer, the externally presented current-limiting impedance is much larger than the actually set current-limiting impedance. A better current-limiting effect can be achieved with a smaller current-limiting device, which has the advantages of low cost and high economy and can be widely applied to the operation of limiting short-circuit current in the power system. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the technical solutions in the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0019] In the drawings: Figure 1 is a schematic diagram of the topological structure of the current-limiting phase-shifting transformer of the present invention; Figure 2 is the steady-state equivalent circuit diagram of the current-limiting phase-shifting transformer of the present invention; Figure 3 is the fault equivalent circuit diagram of the current-limiting phase-shifting transformer of the present invention; Figure 4 is the simulation power flow regulation waveform diagram of the current-limiting phase-shifting transformer of the present invention; Figure 5 is the simulation short-circuit current limiting waveform diagram of the current-limiting phase-shifting transformer of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0020] To make the objectives, technical solutions, and advantages of the present invention clearer, the following will clearly and completely describe the technical solutions in the present invention in conjunction with the drawings in the present invention. Obviously, the described embodiments are some but not all of the embodiments of the present invention. Based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the scope of protection of the present invention.

[0021] The following will describe in detail some embodiments of the present invention in conjunction with the drawings. Without conflict, the following embodiments and the features in the embodiments can be combined with each other.

[0022] Please refer to Figure 1 , Figure 1It is a schematic diagram of the topology structure of a current-limiting phase-shifting transformer. An embodiment of the present invention provides a topology structure of a current-limiting phase-shifting transformer, which includes an exciting transformer and a series transformer. The exciting transformer includes an exciting transformer primary-side winding and an exciting transformer secondary-side winding. The series transformer includes a series transformer primary-side winding and a series transformer secondary-side winding. The exciting transformer primary-side winding is connected in parallel in the line to obtain the exciting voltage from the line. The exciting transformer secondary-side winding is connected to the series transformer primary-side winding. The series transformer secondary-side winding is three independent and non-connected windings, which are directly connected in series to the three phases A, B, and C of the line respectively.

[0023] Specifically, the exciting transformer is a three-phase double-winding on-load tap-changing transformer, which includes an on-load tap-changer. The on-load tap-changer includes multiple adjustment positions for adjusting the amplitude of the exciting voltage. Both the primary-side winding and the secondary-side winding are star-connected. The primary-side winding is connected in parallel in the line to obtain the exciting voltage from the line. A quick switch is provided on the exciting transformer secondary-side winding, and the quick switch is connected to the on-load tap-changer. When the line is in a steady state, the quick switch is closed, so as to generate different magnitudes of compensation voltage for the series transformer.

[0024] The series transformer is a three-phase double-winding transformer, and the primary-side winding is delta-connected. A tap is provided in the middle of the series transformer secondary-side winding. The connection between the exciting transformer and the series transformer realizes the transformation from star connection to delta connection. The voltage on the series transformer primary-side winding leads or lags the exciting voltage of this phase , and then through the electromagnetic induction of the series transformer, this voltage is connected in series into the line, and the phase of the system line voltage can be adjusted, so as to control the line power flow. The exciting voltage is taken from the tap in the middle of the series transformer secondary-side winding. This tap is the exciting point. The number of turns of the windings on both sides of the tap is equal, both being half of the series transformer secondary-side winding. And the adjusted compensation voltage is perpendicular to the exciting voltage. Therefore, the voltages of the windings on both sides of the exciting point are equal in magnitude and perpendicular to the exciting voltage, forming an isosceles triangle. The voltages before and after adjustment are symmetric about the exciting voltage and the amplitude remains unchanged.

[0025] The secondary winding of the exciting transformer is connected with a polarity switch. By toggling the polarity switch, the reverse-phase operation of the compensated voltage of the series transformer can be realized, so that the leading and lagging adjustments of the line voltage phase can be achieved. A current-limiting gear is provided on the secondary winding of the exciting transformer. The current-limiting gear is connected with the switch contact of the on-load tap-changer. A current-limiting impedance and antiparallel thyristors are installed on the current-limiting gear. The current-limiting gear is always connected with the switch contact through a wire. However, when the line is in a steady state, the antiparallel thyristors are not triggered, and the current-limiting impedance will not be connected into the line. When a line fault (such as a short circuit) occurs, the antiparallel thyristors are triggered, and at the same time, the fast switch is disconnected. The exciting transformer is converted to no-load operation and withdrawn from the line. The current-limiting impedance is connected into the line. After the current-limiting impedance is amplified three times through the star-delta transformation between the exciting transformer and the series transformer, the current-limiting impedance is equivalently connected into the line through the transformation ratio effect of the series transformer to limit the short-circuit current. Therefore, the current-limiting phase-shifting transformer of the present invention injects compensated voltage into the line in a steady state and injects a current-limiting impedance into the line during a fault, realizing the functions of power flow regulation and short-circuit current suppression at the same time.

[0026] It should be noted that when a line fault occurs, such as a line short circuit, after the relay protection device of the power system detects the short circuit, it sends signals to the control devices of the antiparallel thyristors and the fast switch to make the antiparallel thyristors and the fast switch act.

[0027] Further, in combination with the topological structure of the current-limiting phase-shifting transformer and the T-equivalent circuit diagram of the transformer, the A-phase equivalent circuit diagram of the current-limiting phase-shifting transformer in a steady state can be obtained, as Figure 2 shown, where U SA 、 U LA 、 I SA 、 I LA are the system voltage and system current before and after adjustment respectively, U AL 、 U aL 、 U AC and U aC are the voltages generated on the primary winding of the exciting transformer, the secondary winding of the exciting transformer, the primary winding of the series transformer and the secondary winding of the series transformer respectively, I AL 、 I aL 、I AC 、 I aCare the currents in the primary winding of the exciting transformer, secondary winding of the exciting transformer, primary winding of the series transformer, and secondary winding of the series transformer, respectively, Z AL 、 Z aL 、 Z AC and Z aC are the impedances of the primary winding of the exciting transformer, secondary winding of the exciting transformer, primary winding of the series transformer, and secondary winding of the series transformer, respectively, U is the voltage obtained by the current-limiting phase-shifting transformer from the system line, K is the turns ratio of the exciting transformer. The turns ratio of the series transformer is 1, and their corresponding relationship is as Figure 2 shown.

[0028] For the pre-compensation leading-end voltage phasor U SA and the post-compensation trailing-end voltage phasor U LA are respectively: (1.1) (1.2) (1.3) (1.4) According to the turns ratio relationship of the series transformer, the voltage-current relationship of each winding of the series transformer can be obtained as: (1.5) (1.6) According to the turns ratio relationship of the exciting transformer, the voltage-current relationship of each winding of the exciting transformer can be obtained as: (1.7) (1.8) Considering that only positive-sequence components exist in the current-limiting phase-shifting transformer during normal operation, under positive-sequence conditions, from the electrical connection of the primary winding of the series transformer and the secondary winding of the exciting transformer, we can get: (1.9) (1.10) Therefore, 10 equations containing 8 variables have been established. By simplifying from Equation 1.1 to Equation 1.10, the electrical quantities on the power supply side and load side U SA 、 I SA 、U LA The relational expression is as follows: (1.11) After arranging Equation 1.11, we can obtain: (1.12) (1.13) is the phase shift angle of the current-limiting phase-shifting transformer, and for it, we have: (1.14) (1.15) Z equ is the overall internal impedance of the current-limiting phase-shifting transformer, which is jointly generated by the internal impedances of all windings: (1.16) Among them, A and B and C and D are the action coefficients of the impedances of each winding in the total internal impedance respectively, and they are related to the turns ratio K : (1.17) (1.18) (1.19) (1.20) It can be seen from Equation 1.12, that is, the input-output characteristic equation of the current-limiting phase-shifting transformer, that the current-limiting phase-shifting transformer has the ability to adjust the phase of the system node voltage. According to the active power flow formula in the line, we know: (1.21) In the formula, P is the active power flow on the line, U S is the amplitude of the voltage at the head end of the line, U L is the amplitude of the voltage at the end of the line, is the phase difference between the voltages at the head and end of the line.

[0029] In the steady state, by adjusting the turns ratio K of the excitation transformer through the regulating gear, the phase shift angle can be adjusted, thereby effectively adjusting the line power flow.

[0030] When a fault occurs, the relay protection device of the power system sends a signal to the current-limiting phase-shifting transformer. The fast switch of the excitation transformer of the current-limiting phase-shifting transformer disconnects, and the antiparallel thyristors conduct. The current-limiting phase-shifting transformer reconstructs its structure and operates in the current-limiting mode. Combining the topological structure of the current-limiting phase-shifting transformer and the T-equivalent circuit diagram of the transformer, the equivalent circuit diagram of the current-limiting phase-shifting transformer during a fault can be obtained, as shown in Figure 3 shown. Among them I A , I B and I C are the three-phase currents of the line, I AC , I BC and I CC are the three-phase currents of the primary winding of the series transformer, I aL , I bL and I cL are the three-phase currents on the switch connection line of the secondary winding of the excitation transformer, Z BC , Z bC and Z CC , Z cC are the impedances of the B-phase and C-phase of the primary winding of the series transformer and the secondary winding of the series transformer respectively, Z L is the current-limiting impedance. Taking the A-phase parameters as an example, according to the electrical connection of the primary winding of the series transformer and the secondary winding of the excitation transformer, we can get: (1.22) (1.23) (1.24) According to the turns ratio relationship of the series transformer, the voltage-current relationship of each winding of the series transformer can be obtained as: (1.25) (1.26) For the pre-compensation leading-end voltage phasor U SA and the post-compensation trailing-end voltage phasor U LA respectively, we have: (1.27) The electrical quantities on the power supply side and the load side can be obtained by simplifying from Equation 1.22 to Equation 1.27 U SA 、 I A 、 U LA The relational expressions are as follows: (1.28) It can be seen from Equation 1.28 that when the current-limiting phase-shifting transformer operates in the current-limiting mode, three times the current-limiting impedance is equivalently connected in series on each phase line. Through the unique topological structure design, the three groups of current-limiting impedances achieve the effect of nine groups of current-limiting impedances, realizing the high efficiency and economy of the current-limiting function.

[0031] Based on the same inventive concept, another embodiment of the present invention provides a control method for the topological structure of the current-limiting phase-shifting transformer described in the foregoing embodiment, including: When the line is in a steady state, the fast switch is closed, and by adjusting the adjustment position of the on-load tap-changer, the amplitude of the exciting voltage is adjusted, and then different magnitudes of compensation voltages are generated for the series transformer; When a line fault occurs, the antiparallel thyristors are triggered, the fast switch is disconnected, and the current-limiting impedance is connected into the line to limit the line current during the fault.

[0032] Specifically, the method further includes: by toggling the polarity switch, the inversion operation of the compensation voltage is realized, so as to realize the leading and lagging adjustment of the line voltage phase.

[0033] The following is a specific embodiment of the present invention.

[0034] In this embodiment, an equivalent model of the current-limiting phase-shifting transformer is built by using the multi-winding transformer module in MATLAB / Simulink. The structure of the exciting transformer has 8 adjustment positions, and the simulation model and system parameters are set as follows in the table:

[0035] During steady-state operation, the adjustment position of the exciting transformer is set to gradually increase. The waveforms of the phase-shifting angle and the line power flow of the current-limiting phase-shifting transformer changing with the adjustment position are as Figure 4 shown, Figure 4 in which the abscissa represents time, and one position is increased every 2 s. It can be seen that the active power flow of the line increases with the increase of the adjustment position of the exciting transformer, and the power flow adjustment effect is remarkable. The line load is increased by 300%, effectively transferring the power flow and improving the light-load state of the line, fully verifying the power flow regulation ability of the current-limiting phase-shifting transformer.

[0036] Apply a short-circuit fault to the model line, and the short-circuit current waveforms with and without the current-limiting phase-shifting transformer are asFigure 5 As shown, it can be seen that after the multi-functional current-limiting phase-shifting transformer is connected in series, the peak value of the circuit during short circuit is reduced by 40%, effectively suppressing the short-circuit current, which fully proves the current-limiting ability of the current-limiting phase-shifting transformer.

[0037] In summary, the present invention proposes a current-limiting phase-shifting transformer topology and its control method, introducing a current-limiting impedance to the current-limiting phase-shifting transformer, endowing the current-limiting phase-shifting transformer with the ability to limit short-circuit current, and can simultaneously solve the problems of unreasonable power flow distribution and excessive short-circuit current faced by the current system. Compared with traditional phase-shifting transformers, it has more comprehensive functions, good economy, high integration and small floor area. At the same time, through the unique topology design, the current-limiting impedance is star-connected on the exciting winding, while the primary winding of the series transformer presents a delta connection. According to Kirchhoff's law, when the star connection is equivalently converted to a delta connection, the impedance will become three times the original. Therefore, when the current-limiting phase-shifting transformer is connected to the line through the series transformer, the external current-limiting impedance shown is much larger than the actually set current-limiting impedance, and a better current-limiting effect can be achieved with a smaller current-limiting device, having the advantages of low cost and high economy, and can be widely applied to the operation of power system regulation and protection.

[0038] After considering the specification and the embodiments disclosed herein, those skilled in the art will easily think of other embodiments of the present invention. The present invention is intended to cover any variations, uses or adaptations of the present invention, which follow the general principles of the present invention and include the common general knowledge or conventional technical means in the technical field not disclosed in the present invention. It should be understood that the present invention is not limited to the exact structures described above and shown in the drawings, and various modifications and changes can be made without departing from its scope. The scope of the present invention is only limited by the appended claims.

Claims

1. A current-limiting phase-shifting transformer topology, characterized in that It includes an excitation transformer and a series transformer. The excitation transformer includes an excitation transformer primary winding and an excitation transformer secondary winding. The series transformer includes a series transformer primary winding and a series transformer secondary winding. The excitation transformer primary winding is connected in parallel in the line to obtain the excitation voltage from the line. The excitation transformer secondary winding is connected to the series transformer primary winding. The series transformer secondary winding is three independent and unconnected windings, which are directly connected in series to the three phases of the line respectively.

2. The current-limiting phase-shifting transformer topology according to claim 1, wherein The primary winding of the excitation transformer and the secondary winding of the excitation transformer are both star-connected, the primary winding of the series transformer is delta-connected, and the voltage on the primary winding of the series transformer leads or lags the excitation voltage of this phase .

3. The current-limiting phase-shifting transformer topology according to claim 1, characterized in that, The excitation transformer is a three-phase double-winding on-load tap-changer transformer, including an on-load tap-changer switch. The on-load tap-changer switch includes multiple adjustment positions for adjusting the amplitude of the excitation voltage.

4. The current-limiting phase-shifting transformer topology according to claim 3, wherein A quick switch is provided on the excitation transformer secondary winding. The quick switch is connected to the on-load tap-changer switch. When the line is in a steady state, the quick switch is closed, so as to generate different magnitudes of compensation voltage for the series transformer.

5. The current-limiting phase-shifting transformer topology according to claim 4, characterized in that, A polarity switch is connected to the excitation transformer secondary winding. The reverse-phase operation of the compensation voltage is realized by toggling the polarity switch.

6. The current-limiting phase-shifting transformer topology according to claim 5, wherein A current-limiting position is provided on the excitation transformer secondary winding. The current-limiting position is connected to the switch contact of the on-load tap-changer switch. A current-limiting impedance and an antiparallel thyristor are installed on the current-limiting position. When a fault occurs in the line, the antiparallel thyristor is triggered, and at the same time the quick switch is disconnected, and the current-limiting impedance is connected into the line.

7. The topology structure of the current-limiting phase-shifting transformer according to claim 6, characterized in that, The fault includes a short circuit.

8. The current-limiting phase-shifting transformer topology according to claim 1, characterized in that, A tap is provided in the middle of the series transformer secondary winding. The excitation voltage is taken from the tap. The number of turns of the windings on both sides of the tap is equal, and both are half of the series transformer secondary winding.

9. A control method for a current-limiting phase-shifting transformer topology as described in claim 6, characterized in that, It includes: When the line is in a steady state, the quick switch is closed. By adjusting the adjustment position of the on-load tap-changer switch, the amplitude of the excitation voltage is adjusted, and then different magnitudes of compensation voltage are generated for the series transformer. When a fault occurs in the line, the antiparallel thyristor is triggered, the quick switch is disconnected, and the current-limiting impedance is connected into the line to limit the line current when a fault occurs.

10. The control method of the current-limiting phase-shifting transformer topology according to claim 9, characterized in that, It also includes: By toggling the polarity switch, the reverse-phase operation of the compensation voltage is realized, so as to realize the leading and lagging adjustment of the line voltage phase.

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