A closed-loop transformer based on a single-core hexagonal phase-shifting transformer and its control method.

Abstract

This invention discloses a loop-closing transformer based on a single-core hexagonal phase-shifting transformer and its control method, belonging to the field of 10kV distribution network loop-closing power supply technology. The loop-closing transformer includes a single-core hexagonal phase-shifting transformer bank and a voltage-regulating transformer bank. The six windings of the single-core hexagonal phase-shifting transformer are connected sequentially, and the output of the three-phase power supply and the single-core hexagonal phase-shifting transformer are symmetrical according to the middle tap of the primary winding. The first terminal of the primary winding of the voltage-regulating transformer is connected to the output terminal of the single-core hexagonal phase-shifting transformer, and the other end is grounded; one end of the secondary winding of the voltage-regulating transformer is directly led out as the output terminal of the loop-closing transformer, and the other end is grounded. This invention achieves physical isolation between phase angle adjustment and amplitude compensation, effectively avoiding harmonic superposition problems caused by phase-amplitude coupling. It is suitable for the dynamic stability requirements of the power grid under high phase angle difference scenarios, simplifies the transformation ratio adjustment process of the voltage-regulating transformer, and is suitable for scenarios requiring rapid response.

Description

Technical Field

[0001] This invention belongs to the field of 10KV distribution network loop switching technology, and more specifically, relates to a loop transformer based on a single-core hexagonal phase-shifting transformer and its control method. Background Technology

[0002] With the rapid development of the national economy, electricity users have increasingly higher requirements for power supply reliability. In the power system, the distribution network is the part most closely related to electricity users, and its power supply reliability is a major concern for both power grid companies and electricity users. When certain lines in the distribution network need maintenance or faults requiring load switching, loop closing operations can be used to avoid short-term power outages for electricity users and ensure power supply reliability. However, loop closing operations may also affect the safe and stable operation of the power system because large steady-state currents and inrush currents may be generated during this process.

[0003] Therefore, when a distribution network performs a loop-closing operation, it may cause overload of distribution lines, which in severe cases could even burn out electrical equipment. It may also trigger relay protection devices to malfunction, leading to power outages in larger areas. In the most serious cases, it could even endanger the lives of power workers, posing a significant threat to the economic and safe operation of the power grid. Therefore, it is necessary to design a device that can decouple the amplitude and phase of the voltage phasor difference on both sides of the loop-closing point to solve the above problems.

[0004] Prior art document 1 (CN119109338A) discloses a closed-loop transformer based on a single-core asymmetrical phase-shifting transformer and its control method. Its shortcoming is that the amplitude of the output voltage of the single-core asymmetrical phase-shifting transformer is changed compared with the input voltage due to the existence of the phase shift angle. When adjusting the turns ratio of the voltage regulating transformer, this change in voltage amplitude caused by the phase shift must be considered and compensated. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a closed-loop transformer based on a single-core hexagonal phase-shifting transformer and its control method. Specifically, it provides a closed-loop transformer consisting of a voltage-regulating transformer and a single-core hexagonal phase-shifting transformer connected in series and its control method, in order to solve the problem of phasor difference in voltage on both sides of the closed-loop point mentioned in the background technology.

[0006] The present invention adopts the following technical solution.

[0007] A first aspect of the present invention provides a closed-loop transformer based on a single-core hexagonal phase-shifting transformer, the closed-loop transformer comprising a single-core hexagonal phase-shifting transformer bank and a voltage regulating transformer bank, characterized in that:

[0008] The six windings of a single-core hexagonal phase-shifting transformer are connected in sequence. The primary winding of the single-core hexagonal phase-shifting transformer group is connected to the three-phase power supply. The output of the three-phase power supply and the single-core hexagonal phase-shifting transformer are symmetrical according to the middle tap of the primary winding of the single-core hexagonal phase-shifting transformer.

[0009] The single-core hexagonal phase-shifting transformer bank includes a phase of single-core hexagonal phase-shifting transformer, a phase of single-core hexagonal phase-shifting transformer, and a phase of single-core hexagonal phase-shifting transformer. The secondary winding of each phase of the single-core hexagonal phase-shifting transformer outputs a compensation voltage phasor that is perpendicular to the voltage of the intermediate tap of the primary winding of that phase.

[0010] The voltage regulating transformer group includes voltage regulating transformer phase a, voltage regulating transformer phase b and voltage regulating transformer phase c. The first terminal of the primary winding of each phase of the voltage regulating transformer is connected to the output terminal of the corresponding phase of the single-core hexagonal phase-shifting transformer, and the other terminal is grounded, which is used to change the voltage amplitude.

[0011] One end of the secondary winding of each phase of the voltage regulating transformer is directly led out as the output terminal of the closed-loop transformer, and the other end is grounded.

[0012] Preferably, the second terminal of the primary winding of each phase of the voltage regulating transformer is grounded;

[0013] The first terminal of the secondary winding of each phase of the voltage regulating transformer is unconnected, and the wire is directly led out to be the output terminal of the corresponding phase of the closed-loop transformer. The second terminal is grounded.

[0014] Preferably, the first terminal of the primary winding of the first phase of the single-core hexagonal phase-shifting transformer is connected to the first terminal of the secondary winding of the second phase of the single-core hexagonal phase-shifting transformer; the second terminal serves as the output terminal of the first phase of the single-core hexagonal phase-shifting transformer and is connected to the first terminal of the primary winding of the first phase of the voltage regulating transformer; the third terminal is directly connected to the power supply of the first phase; and the fourth terminal is connected to the second terminal of the secondary winding of the third phase of the single-core hexagonal phase-shifting transformer.

[0015] The first terminal of the secondary winding of the first phase of the single-core hexagonal phase-shifting transformer is connected to the first terminal of the primary winding of the third phase of the single-core hexagonal phase-shifting transformer, and the second terminal of the secondary winding of the first phase of the single-core hexagonal phase-shifting transformer is connected to the fourth terminal of the primary winding of the second phase of the single-core hexagonal phase-shifting transformer.

[0016] A second aspect of the present invention provides a control method for a closed-loop transformer based on a single-core hexagonal phase-shifting transformer, operating on the closed-loop transformer based on a single-core hexagonal phase-shifting transformer described in the first aspect of the present invention, comprising the following steps:

[0017] By adjusting the connection sequence and direction of the primary side terminals and the secondary side terminals of the single-core hexagonal phase-shifting transformer, the connection method of the single-core hexagonal phase-shifting transformer can be obtained.

[0018] Based on the connection method of the single-core hexagonal phase-shifting transformer, a constraint relationship between the phase of the compensation voltage and the actual number of turns connected to the secondary winding in the single-core hexagonal phase-shifting transformer is constructed to obtain the output voltage of each phase of the closed-loop transformer.

[0019] Based on the output voltage of each phase of the closed-loop transformer, the actual number of turns connected to the secondary coil of the single-core hexagonal phase-shifting transformer is dynamically adjusted by means of a lookup table or by a controller.

[0020] Based on the actual number of turns connected to the secondary coil, the voltage phasor difference on both sides of the loop closing point is compensated to realize the control of the loop closing transformer based on a single-core hexagonal phase-shifting transformer.

[0021] Preferably, the connection sequence and direction of adjusting the primary side terminals and the secondary side terminals of the single-core hexagonal phase-shifting transformer, specifically include the following:

[0022] The second terminal of the primary winding of each phase of the single-core hexagonal phase-shifting transformer is directly connected to the power supply of that phase, and the third terminal, as the output terminal of that phase of the single-core hexagonal phase-shifting transformer, is connected to the first terminal of the primary winding of that phase of the voltage regulating transformer.

[0023] Preferably, the connection sequence and direction of adjusting the primary side terminals and the secondary side terminals of the single-core hexagonal phase-shifting transformer, specifically include the following:

[0024] The first terminal of the primary winding of the first phase of the single-core hexagonal phase-shifting transformer is connected to the first terminal of the secondary winding of the third phase of the single-core hexagonal phase-shifting transformer.

[0025] The fourth terminal of the primary winding of the first phase of the single-core hexagonal phase-shifting transformer is connected to the second terminal of the secondary winding of the second phase of the single-core hexagonal phase-shifting transformer.

[0026] The first terminal of the secondary winding of the first phase of the single-core hexagonal phase-shifting transformer is connected to the first terminal of the primary winding of the second phase of the single-core hexagonal phase-shifting transformer.

[0027] The second terminal of the secondary winding of the first phase of the single-core hexagonal phase-shifting transformer is connected to the fourth terminal of the primary winding of the third phase of the single-core hexagonal phase-shifting transformer.

[0028] The fourth terminal of the primary winding of the second phase of the single-core hexagonal phase-shifting transformer is connected to the second terminal of the secondary winding of the third phase of the single-core hexagonal phase-shifting transformer.

[0029] The first terminal of the secondary winding of the second phase of the single-core hexagonal phase-shifting transformer is connected to the first terminal of the primary winding of the third phase of the single-core hexagonal phase-shifting transformer.

[0030] Preferably, the actual number of turns connected to the secondary coil in the single-core hexagonal phase-shifting transformer is the same as the actual number of turns connected to the secondary coil in the single-core hexagonal phase-shifting transformer when the loop transformer is adjusted in the forward amplitude phase.

[0031] Preferably, the connection method based on the single-core hexagonal phase-shifting transformer establishes a constraint relationship between the phase of the compensation voltage and the actual number of turns connected to the secondary winding in the single-core hexagonal phase-shifting transformer, thereby obtaining the output voltage of each phase of the closed-loop transformer. Based on the three-phase symmetrical operation of the closed-loop transformer, the process of solving for the output voltage of each phase of the closed-loop transformer includes:

[0032] The output voltage of each phase of the closed-loop transformer can be calculated by multiplying the primary and secondary turns ratios of each phase of the voltage regulating transformer with the output voltage of the corresponding phase of the single-core hexagonal phase-shifting transformer.

[0033] The output voltage of the corresponding phase of the single-core hexagonal phase-shifting transformer can be calculated by summing the power supply voltage of each phase and the compensation voltage of the corresponding phase.

[0034] Preferably, the step of dynamically adjusting the actual number of turns connected to the secondary winding of the single-core hexagonal phase-shifting transformer by using a lookup table method based on the output voltage of each phase of the closed-loop transformer specifically includes:

[0035] Solve for the turns ratio iteration values ​​of each phase secondary winding coil in a single-core hexagonal phase-shifting transformer;

[0036] A simulation model of a closed-loop transformer based on a single-core hexagonal phase-shifting transformer is constructed. Different voltage phasor differences on both sides of the closed-loop point are set according to the output voltage of each phase of the closed-loop transformer. The turns ratio iteration value is used as the simulation parameter value. The simulation waveform or simulation data is observed, and the L2 norm of the difference between the simulated output voltage phasor and the theoretically calculated output voltage phasor is compared to see if it is within the allowable error range. If it is, the theoretical derivation value is correct. If not, the equation set is wrong or the iterative solution value is incorrect. The derivation or solution should be repeated.

[0037] If the theoretical derivation is correct, the corresponding simulation data will be recorded in the table. When the loop transformer based on the single-core hexagonal phase-shifting transformer is actually put into operation, the turns ratio data of each phase secondary winding of the single-core hexagonal phase-shifting transformer will be selected by looking up the table according to the real-time detected voltage phasor difference on both sides of the loop point, and the actual number of turns connected to each phase secondary winding of the single-core hexagonal phase-shifting transformer will be dynamically adjusted.

[0038] Preferably, the step of dynamically adjusting the actual number of turns connected to the secondary winding of the single-core hexagonal phase-shifting transformer by controlling the controller based on the output voltage of each phase of the closed-loop transformer specifically includes:

[0039] When the loop-connected transformer based on the single-core hexagonal phase-shifting transformer is actually put into operation, the voltage phasor difference between the two sides of the loop-connection point is obtained by the voltage of each phase output terminal of the loop-connected transformer. This phasor difference is used as a parameter input to the controller. The controller calculates and outputs control commands in real time according to the pre-set closed-loop control algorithm, thereby dynamically adjusting the actual number of turns connected to the secondary coil of each phase of the single-core hexagonal phase-shifting transformer in real time.

[0040] Compared with the prior art, the beneficial effects of the present invention include at least the following:

[0041] 1. The closed-loop transformer designed in this invention is based on a single-core hexagonal phase-shifting transformer. Specifically, it is a closed-loop transformer consisting of a voltage regulating transformer and a single-core hexagonal phase-shifting transformer connected in series. The six windings of the single-core hexagonal phase-shifting transformer are connected sequentially. The output of the three-phase power supply and the single-core hexagonal phase-shifting transformer are symmetrical according to the center tap of the primary winding, thereby changing the voltage phase angle. Then, the voltage amplitude is changed through the voltage regulating transformer group, achieving amplitude-phase decoupling compensation adjustment of the voltage phasors on both sides of the closed-loop point. The compensation method is more flexible and precise, resulting in a more ideal actual closed-loop effect.

[0042] 2. The compensation voltage phasor output by this invention is a compensation voltage phasor perpendicular to the voltage of the middle tap of the primary winding of each phase of the single-core hexagonal phase-shifting transformer. A segment of the compensation voltage phasor is perpendicular to the voltage of the corresponding phase power supply in the three-phase power supply. The topology and electrical connection relationship between the windings are relatively simple.

[0043] 3. By designing a suitable single-core hexagonal phase-shifting transformer and a voltage regulating transformer with appropriate primary and secondary turns ratio, this invention can inject a compensation voltage phasor with controllable phase angle and amplitude under no-load and load conditions. By dynamically adjusting the actual number of turns connected to the secondary coil of the single-core hexagonal phase-shifting transformer and the primary and secondary turns ratio of the voltage regulating transformer, the desired compensation voltage phasor can be output. This can achieve decoupling compensation adjustment of the voltage phasor difference amplitude on both sides of the loop point. The control law and control method are simple, the adjustment method is flexible, the adjustment range is large, and the adjustment accuracy is high.

[0044] 4. This invention achieves physical isolation between phase angle adjustment and amplitude compensation through the symmetrical winding design of a single-core hexagonal phase-shifting transformer. Compared to a single-core asymmetrical phase-shifting transformer, the input and output voltages of the single-core hexagonal phase-shifting transformer have the same amplitude characteristics, differing only in phase angle. Therefore, when adjusting the turns ratio of the subsequent voltage regulating transformer, there is no need to compensate for amplitude changes caused by this type of phase shift. The hexagonal winding layout eliminates the need to consider amplitude fluctuations during phase angle difference adjustment. The inherent amplitude stability of the single-core hexagonal phase-shifting transformer eliminates the amplitude compensation required by the single-core asymmetrical phase-shifting transformer, effectively avoiding harmonic superposition problems caused by amplitude-phase coupling. This design significantly improves the independence and accuracy of voltage regulation during loop-closing operations, making it particularly suitable for the dynamic stability requirements of the power grid in high phase angle difference scenarios. It simplifies the turns ratio adjustment process of the voltage regulating transformer and is suitable for scenarios requiring rapid response. Attached Figure Description

[0045] Figure 1 This is a schematic diagram of the topology of a closed-loop transformer based on a single-core hexagonal phase-shifting transformer provided in accordance with an embodiment of the present invention;

[0046] Figure 2 This is a schematic diagram of the input and output voltage vector relationship during forward amplitude-phase adjustment of a single-core hexagonal phase-shifting transformer according to an embodiment of the present invention;

[0047] Figure 3 This is a schematic diagram of the input and output voltage vector relationship during negative amplitude phase adjustment of a single-core hexagonal phase-shifting transformer according to an embodiment of the present invention;

[0048] Figure 4 This is a schematic diagram of PSCAD simulation of a closed-loop transformer based on a single-core hexagonal phase-shifting transformer according to an embodiment of the present invention;

[0049] Figure 5 This is a schematic diagram of the simulated waveform of the output voltage amplitude of phase a of a closed-loop transformer based on a single-core hexagonal phase-shifting transformer, according to an embodiment of the present invention.

[0050] Figure 6 This is a schematic diagram of the simulated phase angle waveform of the output voltage of phase a of a closed-loop transformer based on a single-core hexagonal phase-shifting transformer, according to an embodiment of the present invention.

[0051] Figure 7 This is a schematic diagram of the simulated waveform of the a-phase line current of a closed-loop transformer based on a single-core hexagonal phase-shifting transformer, provided according to an embodiment of the present invention. Detailed Implementation

[0052] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of this invention. The described embodiments are merely some embodiments of this invention, and not all embodiments. Based on the spirit of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of this invention.

[0053] like Figure 1 As shown, Embodiment 1 of the present invention provides a closed-loop transformer based on a single-core hexagonal phase-shifting transformer. The closed-loop transformer includes a single-core hexagonal phase-shifting transformer group and a voltage regulating transformer group. The six windings of the single-core hexagonal phase-shifting transformer are connected in sequence. The primary winding of the single-core hexagonal phase-shifting transformer group is connected to a three-phase power supply. The output of the three-phase power supply and the single-core hexagonal phase-shifting transformer are symmetrical according to the middle tap of the primary winding of the single-core hexagonal phase-shifting transformer.

[0054] The single-core hexagonal phase-shifting transformer group includes: single-core hexagonal phase-shifting transformer phase a, single-core hexagonal phase-shifting transformer phase b and single-core hexagonal phase-shifting transformer phase c. The secondary winding of each phase of the single-core hexagonal phase-shifting transformer outputs a compensation voltage phasor perpendicular to the intermediate tap voltage of the primary winding of that phase.

[0055] The voltage regulating transformer group includes: voltage regulating transformer phase a, voltage regulating transformer phase b, and voltage regulating transformer phase c. The output terminals of single-core hexagonal phase-shifting transformer phases a, b, and c are connected to the first terminals of the primary windings of voltage regulating transformer phases a, b, and c, respectively. That is, the first terminal of the primary winding of each phase of the voltage regulating transformer is connected to the output terminal of the corresponding phase of the single-core hexagonal phase-shifting transformer, and the other end is grounded. The voltage regulating transformer group is connected in series with the single-core hexagonal phase-shifting transformer group to change the voltage amplitude.

[0056] One end of the secondary winding of the voltage regulating transformer is directly led out as the output terminal of the closed-loop transformer, and the other end is grounded.

[0057] It is worth noting that, compared to existing technologies that "form a fixed magnetic flux path through a secondary side-delta connection, and the compensation voltage can only be constrained to a fixed 90° phase difference, which cannot adapt to power grid conditions where the phase difference is not equal to 90°", this invention constructs a hexagonal closed-loop magnetic circuit by "connecting six windings in sequence". Each phase winding is connected end-to-end to form a rotating magnetic flux path, breaking through the orthogonal constraint of the existing triangular connection. Referring to Formula 1 of this invention, the hexagonal closed-loop magnetic circuit can generate an adjustable compensation angle, that is, the phase of the compensation voltage in this invention, such as... Figure 2 and Figure 3 As shown, the phase range of the compensation voltage is [-120°, 120°], breaking the limitation of existing technology that locks the compensation angle to a fixed 90° due to its secondary side delta connection;

[0058] Compared to the existing technology of "secondary side delta connection" which fixes the compensation angle at 90°, this invention, combined with "symmetrical center taps of the primary side winding," provides a physical basis for dynamic phase adjustment. Figure 1 As can be seen, the tap can move on different terminals to achieve dynamic adjustment of the phase of the compensation voltage by ±120°. More preferably, the connection relationship of the voltage regulating transformer includes:

[0059] The second terminal of the primary winding of each phase of the voltage regulating transformer is grounded;

[0060] The first terminal of the secondary winding of each phase of the voltage regulating transformer is unconnected, and the wire is directly led out as the output terminal of the corresponding phase of the closed-loop transformer. The second terminal is grounded.

[0061] More preferably, the second terminal of the primary winding of phase a of the voltage regulating transformer is grounded; the first terminal of the secondary winding of phase a of the voltage regulating transformer is unconnected, and the conductor is directly led out as the output terminal of phase a of the closed-loop transformer. The second terminal is grounded;

[0062] The second terminal of the primary winding of phase B of the voltage regulating transformer is grounded; the first terminal of the secondary winding of phase B of the voltage regulating transformer is unconnected, and the conductor is directly led out as the output terminal of phase B of the closed-loop transformer. The second terminal is grounded;

[0063] The second terminal of the primary winding of phase C of the voltage regulating transformer is grounded; the first terminal of the secondary winding of phase C of the voltage regulating transformer is unconnected, and the conductor is directly led out as the output terminal of phase C of the closed-loop transformer. The second terminal is grounded.

[0064] It is worth noting that in the existing technology, the first terminal of the secondary winding of phase a of a single-core asymmetrical phase-shifting transformer is connected to the second terminal of the secondary winding of phase b of the single-core asymmetrical phase-shifting transformer; the second terminal of the secondary winding of phase a of the single-core asymmetrical phase-shifting transformer is connected to the first terminal of the secondary winding of phase c of the single-core asymmetrical phase-shifting transformer. By connecting the windings into a conductive closed loop with wires, any disturbance in the power grid can easily induce current in this loop and amplify it cyclically, resulting in limited anti-interference capability. Even if it is grounded, it is only for safety grounding and cannot eliminate or block the circulating current generated inside the triangular loop. In contrast, the present invention… Figure 1It is clearly evident that the six windings are not directly connected by wires, but are coupled through magnetic flux in the iron core. Each winding is electrically independent, and the coupling is magnetic rather than electrical. Because no conductive closed loop is formed, there are no physical conditions for generating circulating current. Grid interference can be confined to a single winding and will not circulate and amplify among multiple windings. Furthermore, because there is no circulating current, this invention further provides a discharge path for unavoidable common-mode interference by specifying that "the first terminal of each phase secondary winding of the voltage regulating transformer is unconnected, the wire is directly led out as the output terminal of the corresponding phase of the loop transformer, and the second terminal is grounded." Compared to the wire connections of existing technologies, this invention avoids circulating current through magnetic connections, thus improving anti-interference capability.

[0065] In a preferred but non-limiting embodiment of the present invention, the first terminal of the primary winding of the first phase of the single-core hexagonal phase-shifting transformer is connected to the first terminal of the secondary winding of the second phase of the single-core hexagonal phase-shifting transformer; the second terminal, as the output terminal of the first phase of the single-core hexagonal phase-shifting transformer, is connected to the first terminal of the primary winding of the first phase of the voltage regulating transformer; the third terminal is directly connected to the power supply of the first phase; and the fourth terminal is connected to the second terminal of the secondary winding of the third phase of the single-core hexagonal phase-shifting transformer. The first terminal of the secondary winding of the first phase of the single-core hexagonal phase-shifting transformer is connected to the first terminal of the primary winding of the third phase of the single-core hexagonal phase-shifting transformer; and the second terminal of the secondary winding of the first phase of the single-core hexagonal phase-shifting transformer is connected to the fourth terminal of the primary winding of the second phase of the single-core hexagonal phase-shifting transformer.

[0066] It is worth noting that the existing secondary delta connection fixes the compensation angle at 90°. Although there are two connection sequences, they are limited by the delta structure. The first structure outputs a compensation vector that lags the power supply voltage by 90°, while the second structure can only output a compensation vector that leads the power supply voltage by 90°. This fails to achieve non-orthogonal compensation, resulting in a narrow compensation range. This invention chooses to switch different terminal connections for tap offset. In the first connection sequence and direction, "the second terminal of the primary winding of each phase of the single-core hexagonal phase-shifting transformer is directly connected to the power supply of that phase, and the third terminal..." When the output terminal is connected to the voltage regulating transformer, the magnetic field is symmetrically distributed and the output has a fixed 90° compensation as in the existing technology. In the second connection sequence and direction, "the first terminal of the primary winding of phase a of the single-core hexagonal phase-shifting transformer is connected to the first terminal of the secondary winding of phase c, and its fourth terminal is connected to the second terminal of the secondary winding of phase b", the output breaks through the orthogonality constraint, dynamically changes the current path and magnetic field distribution of the cross-phase coupling, generates a non-orthogonal horizontal compensation voltage component, realizes dynamic adjustment of the compensation voltage phase within the range of ±120°, and improves the phase compensation range of the compensation voltage.

[0067] More preferably, the first terminal of the primary winding of phase a of the single-core hexagonal phase-shifting transformer is connected to the first terminal of the secondary winding of phase b of the single-core hexagonal phase-shifting transformer, and the second terminal serves as the output terminal of phase a of the single-core hexagonal phase-shifting transformer. The first terminal of the primary winding of phase a of the voltage regulating transformer is connected, and the third terminal is connected to the power supply of phase a. Directly connected, the fourth terminal is connected to the second terminal of the secondary winding of phase c of the single-core hexagonal phase-shifting transformer; the first terminal of the secondary winding of phase a of the single-core hexagonal phase-shifting transformer is connected to the first terminal of the primary winding of phase c of the single-core hexagonal phase-shifting transformer; the second terminal of the secondary winding of phase a of the single-core hexagonal phase-shifting transformer is connected to the fourth terminal of the primary winding of phase b of the single-core hexagonal phase-shifting transformer.

[0068] The first terminal of the primary winding of phase B of the single-core hexagonal phase-shifting transformer is connected to the first terminal of the secondary winding of phase C of the single-core hexagonal phase-shifting transformer, and the second terminal serves as the output terminal of phase B of the single-core hexagonal phase-shifting transformer. The first terminal of the primary winding of phase b of the voltage regulating transformer is connected, and the third terminal is connected to the phase b power supply. Directly connected, the fourth terminal is connected to the second terminal of the secondary winding of phase a of the single-core hexagonal phase-shifting transformer; the first terminal of the secondary winding of phase b of the single-core hexagonal phase-shifting transformer is connected to the first terminal of the primary winding of phase a of the single-core hexagonal phase-shifting transformer; the second terminal of the secondary winding of phase b of the single-core hexagonal phase-shifting transformer is connected to the fourth terminal of the primary winding of phase c of the single-core hexagonal phase-shifting transformer.

[0069] The first terminal of the primary winding of phase C of the single-core hexagonal phase-shifting transformer is connected to the first terminal of the secondary winding of phase A of the single-core hexagonal phase-shifting transformer, and the second terminal serves as the output terminal of phase C of the single-core hexagonal phase-shifting transformer. The first terminal of the primary winding of phase C of the voltage regulating transformer is connected, and the third terminal is connected to the phase C power supply. The fourth terminal is directly connected to the second terminal of the secondary winding of phase b of the single-core hexagonal phase-shifting transformer; the first terminal of the secondary winding of phase c of the single-core hexagonal phase-shifting transformer is connected to the first terminal of the primary winding of phase b of the single-core hexagonal phase-shifting transformer; and the second terminal of the secondary winding of phase c of the single-core hexagonal phase-shifting transformer is connected to the fourth terminal of the primary winding of phase a of the single-core hexagonal phase-shifting transformer.

[0070] Each phase of the single-core hexagonal phase-shifting transformer outputs a voltage compensation phasor perpendicular to the voltage at the center tap of the primary winding. Through the primary-to-secondary turns ratio of the single-core hexagonal phase-shifting transformer, the voltage compensation phasor is connected to the voltage regulating transformer as the output of the single-core hexagonal phase-shifting transformer. Then, the voltage regulating transformer performs amplitude transformation on the voltage compensation phasor of the single-core hexagonal phase-shifting transformer, thereby realizing the adjustment of the voltage amplitude and phase value at the output terminals of each phase of the closed-loop transformer.

[0071] In three-phase symmetry, the vector relationship between the compensation voltage phasors of each phase and the input and output voltage phasors of each phase is as follows: Figure 2 and Figure 3 As shown, in this embodiment, the closed-loop transformer is in positive amplitude-phase regulation. Taking phase a as an example, the output of phase a of the single-core hexagonal phase-shifting transformer is a voltage compensation phasor perpendicular to the voltage of the intermediate tap of the primary winding of phase a of the single-core hexagonal phase-shifting transformer. Through the primary-secondary turns ratio of the single-core hexagonal phase-shifting transformer, the voltage compensation phasor is connected as the output of the single-core hexagonal phase-shifting transformer to the voltage regulating transformer. Then, the voltage regulating transformer performs amplitude transformation on the voltage compensation phasor of the single-core hexagonal phase-shifting transformer, thereby realizing the voltage regulation of phase a output of the closed-loop transformer based on the single-core hexagonal phase-shifting transformer. Adjustment of amplitude and phase values.

[0072] In a loop transformer consisting of a voltage regulating transformer and a single-core hexagonal phase-shifting transformer connected in series, the single-core hexagonal phase-shifting transformer outputs a compensation voltage phasor for each phase, and the voltage regulating transformer then adjusts the amplitude. This phase adjustment followed by amplitude adjustment enables phase-amplitude decoupling compensation, and the compensation for voltage phasor differences on both sides of various loop closing points is more flexible and precise, resulting in a more ideal actual loop closing effect.

[0073] Embodiment 2 of the present invention provides a control method for a closed-loop transformer based on a single-core hexagonal phase-shifting transformer, comprising the following steps:

[0074] S1. Adjust the connection sequence and direction of the primary side terminals and the secondary side terminals of the single-core hexagonal phase-shifting transformer to realize the commutation of the closed-loop phase-shifting transformer and obtain the connection method of the single-core hexagonal phase-shifting transformer.

[0075] In a preferred but non-limiting embodiment of the present invention, step S1 includes:

[0076] Step S1.1: Construct the first connection order and connection direction.

[0077] More preferably, step S1.1 includes:

[0078] The second terminal of the primary winding of each phase of the single-core hexagonal phase-shifting transformer is directly connected to the power supply of that phase, and the third terminal, as the output terminal of that phase of the single-core hexagonal phase-shifting transformer, is connected to the first terminal of the primary winding of that phase of the voltage regulating transformer.

[0079] More preferably, the second terminal of the primary winding of phase a of the single-core hexagonal phase-shifting transformer is connected to the phase a power supply. Directly connected, the third terminal serves as the output terminal of phase a of the single-core hexagonal phase-shifting transformer. It is connected to the first terminal of the primary winding of phase a of the voltage regulating transformer;

[0080] The second terminal of the primary winding of phase b of a single-core hexagonal phase-shifting transformer is connected to the phase b power supply. Directly connected, the third terminal serves as the output terminal of phase b of the single-core hexagonal phase-shifting transformer. It is connected to the first terminal of the primary winding of phase b of the voltage regulating transformer;

[0081] The second terminal of the primary winding of the c-phase of a single-core hexagonal phase-shifting transformer is connected to the c-phase power supply. Directly connected, the third terminal serves as the output terminal of phase c of the single-core hexagonal phase-shifting transformer. It is connected to the first terminal of the primary winding of phase C of the voltage regulating transformer.

[0082] Step S1.2: Construct the second connection order and connection direction.

[0083] More preferably, step S1.2 includes:

[0084] The first terminal of the primary winding of the first phase of the single-core hexagonal phase-shifting transformer is connected to the first terminal of the secondary winding of the third phase of the single-core hexagonal phase-shifting transformer.

[0085] The fourth terminal of the primary winding of the first phase of the single-core hexagonal phase-shifting transformer is connected to the second terminal of the secondary winding of the second phase of the single-core hexagonal phase-shifting transformer.

[0086] The first terminal of the secondary winding of the first phase of the single-core hexagonal phase-shifting transformer is connected to the first terminal of the primary winding of the second phase of the single-core hexagonal phase-shifting transformer.

[0087] The second terminal of the secondary winding of the first phase of the single-core hexagonal phase-shifting transformer is connected to the fourth terminal of the primary winding of the third phase of the single-core hexagonal phase-shifting transformer.

[0088] The fourth terminal of the primary winding of the second phase of the single-core hexagonal phase-shifting transformer is connected to the second terminal of the secondary winding of the third phase of the single-core hexagonal phase-shifting transformer.

[0089] The first terminal of the secondary winding of the second phase of the single-core hexagonal phase-shifting transformer is connected to the first terminal of the primary winding of the third phase of the single-core hexagonal phase-shifting transformer.

[0090] More preferably, the first terminal of the primary winding of phase a of the single-core hexagonal phase-shifting transformer is connected to the first terminal of the secondary winding of phase c of the single-core hexagonal phase-shifting transformer;

[0091] The fourth terminal of the primary winding of phase a of the single-core hexagonal phase-shifting transformer is connected to the second terminal of the secondary winding of phase b of the single-core hexagonal phase-shifting transformer.

[0092] The first terminal of the secondary winding of phase a of the single-core hexagonal phase-shifting transformer is connected to the first terminal of the primary winding of phase b of the single-core hexagonal phase-shifting transformer.

[0093] The second terminal of the secondary winding of phase a of the single-core hexagonal phase-shifting transformer is connected to the fourth terminal of the primary winding of phase c of the single-core hexagonal phase-shifting transformer;

[0094] The fourth terminal of the primary winding of phase b of the single-core hexagonal phase-shifting transformer is connected to the second terminal of the secondary winding of phase c of the single-core hexagonal phase-shifting transformer.

[0095] The first terminal of the secondary winding of phase b of the single-core hexagonal phase-shifting transformer is connected to the first terminal of the primary winding of phase c of the single-core hexagonal phase-shifting transformer.

[0096] The physical wiring method of S1 through the phase-shifting transformer determines the adjustment range of the phase difference in the compensation voltage and the degree of freedom of voltage synthesis. If the first connection sequence and connection direction are selected, subsequent adjustments can only be carried out around the fixed phase difference, and only the amplitude of the compensation voltage can be adjusted. The compensation voltage is orthogonal to the power supply voltage, and only orthogonal compensation is provided. If the second connection sequence and connection direction are selected, the phase difference can be dynamically adjusted within the range of ±120°.

[0097] S2. Based on the connection method of the single-core hexagonal phase-shifting transformer in S1, a constraint relationship is constructed between the compensation voltage phasor output of the closed-loop transformer based on the single-core hexagonal phase-shifting transformer and the actual number of turns connected to the secondary coil in the single-core hexagonal phase-shifting transformer, so as to obtain the output voltage of each phase of the closed-loop transformer.

[0098] In a preferred but non-limiting embodiment of the present invention, step S2 includes:

[0099] The actual number of turns connected to the secondary winding in a single-core hexagonal phase-shifting transformer is the same as the actual number of turns connected to the secondary winding in a single-core hexagonal phase-shifting transformer during forward amplitude-phase adjustment of the closed-loop transformer. Since the closed-loop transformer operates symmetrically across three phases, only one phase needs to be analyzed. Taking phase a as an example, the relevant equations are as follows:

[0100]

[0101] in:

[0102] This represents the output terminal voltage of phase a of a single-core hexagonal phase-shifting transformer. This represents the output terminal voltage of phase b of a single-core hexagonal phase-shifting transformer. This represents the output voltage of phase c of a single-core hexagonal phase-shifting transformer.

[0103] This represents the voltage of phase a of the power supply.

[0104] This represents the compensation voltage for phase a.

[0105] This indicates the phase of the compensation voltage in phase a.

[0106] This represents the voltage at the center tap of the primary side of phase a of a single-core hexagonal phase-shifting transformer.

[0107] This represents the output voltage of phase a of the closed-loop transformer.

[0108] This indicates the primary and secondary turns ratio of phase a of the voltage regulating transformer.

[0109] It is worth noting that in existing technologies, the secondary side of phase a is not determined by phase a itself, but rather by the power supply voltages of phases b and c. Therefore, the output of phase a is strongly coupled with the states of phases b and c. To adjust phase a, the states of phases b and c must be monitored and calculated simultaneously, making independent control of phases b or c impossible. Any fluctuations in the power grid (harmonics, voltage sags) will directly interfere with the compensation effect of phase a. In contrast, the output voltage of phase a in this invention is determined only by the power supply voltage of phase a and the phase angle to be compensated. Adjusting phase a does not affect phases b and c at all. The control system can adjust each phase in parallel, independently, and quickly. Furthermore, because the structure of this invention completely decouples the three phases, power grid disturbances in phases b and c are completely isolated and will not propagate to phase a, thus improving the anti-interference capability of this invention.

[0110] S3. Based on the output voltage of each phase of the closed-loop transformer, the actual number of turns connected to the secondary coil of the single-core hexagonal phase-shifting transformer is dynamically adjusted by means of a lookup table or by a controller.

[0111] In a preferred but non-limiting embodiment of the present invention, S3 includes:

[0112] S3.1, based on the output voltage of each phase of the closed-loop transformer, the actual number of turns connected to the secondary coil of the single-core hexagonal phase-shifting transformer is dynamically adjusted by using a lookup table method.

[0113] More preferably, S3.1 specifically includes:

[0114] Solve for the turns ratio iteration values ​​of each phase secondary winding coil in a single-core hexagonal phase-shifting transformer;

[0115] A simulation model of a closed-loop transformer based on a single-core hexagonal phase-shifting transformer is constructed. Different voltage phasor differences on both sides of the closed-loop point are set according to the output voltage of each phase of the closed-loop transformer. The turns ratio iteration value is used as the simulation parameter value. The simulation waveform or simulation data is observed, and the L2 norm of the difference between the simulated output voltage phasor and the theoretically calculated output voltage phasor is compared to see if it is within the allowable error range. If it is, the theoretical derivation value is correct. If not, the equation set is wrong or the iterative solution value is incorrect. The derivation or solution should be repeated.

[0116] If the theoretical derivation is correct, the corresponding simulation data will be recorded in the table. When the loop transformer based on the single-core hexagonal phase-shifting transformer is actually put into operation, the turns ratio data of each phase secondary winding of the single-core hexagonal phase-shifting transformer will be selected by looking up the table according to the real-time detected voltage phasor difference on both sides of the loop point, and the actual number of turns connected to each phase secondary winding of the single-core hexagonal phase-shifting transformer will be dynamically adjusted.

[0117] S3.2, based on the output voltage of each phase of the closed-loop transformer, the controller dynamically adjusts the actual number of turns connected to the secondary coil of the single-core hexagonal phase-shifting transformer.

[0118] More preferably, S3.2 specifically includes:

[0119] When the loop-connected transformer based on the single-core hexagonal phase-shifting transformer is actually put into operation, the voltage phasor difference between the two sides of the loop-connection point is obtained by the voltage of each phase output terminal of the loop-connected transformer. This phasor difference is used as a parameter input to the controller. The controller calculates and outputs control commands in real time according to the pre-set closed-loop control algorithm, thereby dynamically adjusting the actual number of turns connected to the secondary coil of each phase of the single-core hexagonal phase-shifting transformer in real time.

[0120] S4. Based on the actual number of turns connected to the secondary coil, the voltage phasor difference on both sides of the loop closing point is compensated to realize the control of the loop closing transformer based on the single-core hexagonal phase-shifting transformer.

[0121] Embodiment 3 of this invention proposes a set of transformation ratio examples for verification: the closed-loop parameter settings and some theoretically calculated parameter values ​​are shown in columns 1 and 2 of Table 1:

[0122] Table 1. Parameter settings and simulation data for the flexible loop closing device.

[0123]

[0124] in,

[0125] , and These represent the primary and secondary turns ratios of phases a, b, and c of a single-core hexagonal phase-shifting transformer, respectively.

[0126] , and These represent the primary and secondary turns ratios of phases a, b, and c of the voltage regulating transformer, respectively.

[0127] , and These represent the effective values ​​of the output terminal voltages of phases a, b, and c of the closed-loop transformer, respectively.

[0128] This indicates the phase angle of the output voltage of the closed-loop transformer.

[0129] , and These represent the effective power values ​​for phases a, b, and c, respectively.

[0130] , and These represent the effective values ​​of the line current for phases a, b, and c, respectively.

[0131] Build such in PSCAD Figure 4 The transformer model shown, based on a single-core hexagonal phase-shifting transformer, simulates the output voltage amplitude of phase a of the closed-loop transformer as follows: Figure 5 As shown, the verification formula is:

[0132]

[0133] in,

[0134] This refers to the peak output voltage of phase a of a single-core hexagonal phase-shifting transformer.

[0135] The simulated waveform of the phase angle of the output voltage of phase a of the closed-loop transformer based on a single-core hexagonal phase-shifting transformer is shown below. Figure 6 As shown; the simulation waveform of the a-phase line current of the closed-loop transformer based on a single-core hexagonal phase-shifting transformer is as follows. Figure 7As shown, the errors between the simulation data and the theoretical derivation values ​​are all within the allowable range. Therefore, the theoretical calculation values ​​of a set of turns ratios of each phase secondary winding of the single-core hexagonal phase-shifting transformer are correct. The corresponding data are recorded in Table 1.

[0136] Compared with the prior art, the beneficial effects of the present invention include at least the following:

[0137] 1. The closed-loop transformer designed in this invention is based on a single-core hexagonal phase-shifting transformer. Specifically, it is a closed-loop transformer consisting of a voltage regulating transformer and a single-core hexagonal phase-shifting transformer connected in series. The six windings of the single-core hexagonal phase-shifting transformer are connected sequentially. The output of the three-phase power supply and the single-core hexagonal phase-shifting transformer are symmetrical according to the center tap of the primary winding, thereby changing the voltage phase angle. Then, the voltage amplitude is changed through the voltage regulating transformer group, achieving amplitude-phase decoupling compensation adjustment of the voltage phasors on both sides of the closed-loop point. The compensation method is more flexible and precise, resulting in a more ideal actual closed-loop effect.

[0138] 2. The compensation voltage phasor output by this invention is a compensation voltage phasor perpendicular to the voltage of the middle tap of the primary winding of each phase of the single-core hexagonal phase-shifting transformer. A segment of the compensation voltage phasor is perpendicular to the voltage of the corresponding phase power supply in the three-phase power supply. The topology and electrical connection relationship between the windings are relatively simple.

[0139] 3. By designing a suitable single-core hexagonal phase-shifting transformer and a voltage regulating transformer with appropriate primary and secondary turns ratio, this invention can inject a compensation voltage phasor with controllable phase angle and amplitude under no-load and load conditions. By dynamically adjusting the actual number of turns connected to the secondary coil of the single-core hexagonal phase-shifting transformer and the primary and secondary turns ratio of the voltage regulating transformer, the desired compensation voltage phasor can be output. This can achieve decoupling compensation adjustment of the voltage phasor difference amplitude on both sides of the loop point. The control law and control method are simple, the adjustment method is flexible, the adjustment range is large, and the adjustment accuracy is high.

[0140] 4. This invention achieves physical isolation between phase angle adjustment and amplitude compensation through the symmetrical winding design of a single-core hexagonal phase-shifting transformer. Compared to a single-core asymmetrical phase-shifting transformer, the input and output voltages of the single-core hexagonal phase-shifting transformer have the same amplitude characteristics, differing only in phase angle. Therefore, when adjusting the turns ratio of the subsequent voltage regulating transformer, there is no need to compensate for amplitude changes caused by this type of phase shift. The hexagonal winding layout eliminates the need to consider amplitude fluctuations during phase angle difference adjustment. The inherent amplitude stability of the single-core hexagonal phase-shifting transformer eliminates the amplitude compensation required by the single-core asymmetrical phase-shifting transformer, effectively avoiding harmonic superposition problems caused by amplitude-phase coupling. This design significantly improves the independence and accuracy of voltage regulation during loop-closing operations, making it particularly suitable for the dynamic stability requirements of the power grid in high phase angle difference scenarios. It simplifies the turns ratio adjustment process of the voltage regulating transformer and is suitable for scenarios requiring rapid response.

[0141] This disclosure can be a system, method, and / or computer program product. A computer program product may include a computer-readable storage medium having computer-readable program instructions loaded thereon for causing a processor to implement various aspects of this disclosure.

[0142] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the protection scope of the claims of the present invention.

Claims

1. A closed-loop transformer based on a single-core hexagonal phase-shifting transformer, the closed-loop transformer comprising a single-core hexagonal phase-shifting transformer bank and a voltage regulating transformer bank, characterized in that: The six windings of a single-core hexagonal phase-shifting transformer are connected in sequence. The primary winding of the single-core hexagonal phase-shifting transformer group is connected to the three-phase power supply. The output of the three-phase power supply and the single-core hexagonal phase-shifting transformer are symmetrical according to the middle tap of the primary winding of the single-core hexagonal phase-shifting transformer. The single-core hexagonal phase-shifting transformer bank includes a phase of single-core hexagonal phase-shifting transformer, a phase of single-core hexagonal phase-shifting transformer, and a phase of single-core hexagonal phase-shifting transformer. The secondary winding of each phase of the single-core hexagonal phase-shifting transformer outputs a compensation voltage phasor that is perpendicular to the voltage of the intermediate tap of the primary winding of that phase. The voltage regulating transformer group includes voltage regulating transformer phase a, voltage regulating transformer phase b and voltage regulating transformer phase c. The first terminal of the primary winding of each phase of the voltage regulating transformer is connected to the output terminal of the corresponding phase of the single-core hexagonal phase-shifting transformer, and the other terminal is grounded, which is used to change the voltage amplitude. One end of the secondary winding of each phase of the voltage regulating transformer is directly led out as the output terminal of the closed-loop transformer, and the other end is grounded. The first terminal of the primary winding of the first phase of the single-core hexagonal phase-shifting transformer is connected to the first terminal of the secondary winding of the second phase of the single-core hexagonal phase-shifting transformer; the second terminal, as the output terminal of the first phase of the single-core hexagonal phase-shifting transformer, is connected to the first terminal of the primary winding of the first phase of the voltage regulating transformer; the third terminal is directly connected to the power supply of the first phase; and the fourth terminal is connected to the second terminal of the secondary winding of the third phase of the single-core hexagonal phase-shifting transformer. The first terminal of the secondary winding of the first phase of the single-core hexagonal phase-shifting transformer is connected to the first terminal of the primary winding of the third phase of the single-core hexagonal phase-shifting transformer, and the second terminal of the secondary winding of the first phase of the single-core hexagonal phase-shifting transformer is connected to the fourth terminal of the primary winding of the second phase of the single-core hexagonal phase-shifting transformer.

2. A closed-loop transformer based on a single-core hexagonal phase-shifting transformer according to claim 1, characterized in that: The second terminal of the primary winding of each phase of the voltage regulating transformer is grounded; The first terminal of the secondary winding of each phase of the voltage regulating transformer is unconnected, and the wire is directly led out to be the output terminal of the corresponding phase of the closed-loop transformer. The second terminal is grounded.

3. A control method for a closed-loop transformer based on a single-core hexagonal phase-shifting transformer, operating on a closed-loop transformer based on a single-core hexagonal phase-shifting transformer as described in any one of claims 1 to 2, characterized in that, Includes the following steps: By adjusting the connection sequence and direction of the primary side terminals and the secondary side terminals of the single-core hexagonal phase-shifting transformer, the connection method of the single-core hexagonal phase-shifting transformer can be obtained. Based on the connection method of the single-core hexagonal phase-shifting transformer, a constraint relationship between the phase of the compensation voltage and the actual number of turns connected to the secondary winding in the single-core hexagonal phase-shifting transformer is constructed to obtain the output voltage of each phase of the closed-loop transformer. Based on the output voltage of each phase of the closed-loop transformer, the actual number of turns connected to the secondary coil of the single-core hexagonal phase-shifting transformer is dynamically adjusted by means of a lookup table or by a controller. Based on the actual number of turns connected to the secondary coil, the voltage phasor difference on both sides of the loop closing point is compensated to realize the control of the loop closing transformer based on a single-core hexagonal phase-shifting transformer.

4. The control method for a loop transformer based on a single-core hexagonal phase-shifting transformer according to claim 3, characterized in that: The adjustment of the connection sequence and direction of the primary side terminals and the secondary side terminals in the single-core hexagonal phase-shifting transformer, specifically includes the following: The second terminal of the primary winding of each phase of the single-core hexagonal phase-shifting transformer is directly connected to the power supply of that phase, and the third terminal, as the output terminal of that phase of the single-core hexagonal phase-shifting transformer, is connected to the first terminal of the primary winding of that phase of the voltage regulating transformer.

5. The control method for a loop transformer based on a single-core hexagonal phase-shifting transformer according to claim 3, characterized in that: The adjustment of the connection sequence and direction of the primary side terminals and the secondary side terminals in the single-core hexagonal phase-shifting transformer, specifically includes the following: The first terminal of the primary winding of the first phase of the single-core hexagonal phase-shifting transformer is connected to the first terminal of the secondary winding of the third phase of the single-core hexagonal phase-shifting transformer. The fourth terminal of the primary winding of the first phase of the single-core hexagonal phase-shifting transformer is connected to the second terminal of the secondary winding of the second phase of the single-core hexagonal phase-shifting transformer. The first terminal of the secondary winding of the first phase of the single-core hexagonal phase-shifting transformer is connected to the first terminal of the primary winding of the second phase of the single-core hexagonal phase-shifting transformer. The second terminal of the secondary winding of the first phase of the single-core hexagonal phase-shifting transformer is connected to the fourth terminal of the primary winding of the third phase of the single-core hexagonal phase-shifting transformer. The fourth terminal of the primary winding of the second phase of the single-core hexagonal phase-shifting transformer is connected to the second terminal of the secondary winding of the third phase of the single-core hexagonal phase-shifting transformer. The first terminal of the secondary winding of the second phase of the single-core hexagonal phase-shifting transformer is connected to the first terminal of the primary winding of the third phase of the single-core hexagonal phase-shifting transformer.

6. The control method for a loop transformer based on a single-core hexagonal phase-shifting transformer according to claim 3, characterized in that: The actual number of turns connected to the secondary coil of the single-core hexagonal phase-shifting transformer is the actual number of turns connected to the secondary coil of the single-core hexagonal phase-shifting transformer when the loop transformer is adjusted in the forward amplitude and phase.

7. A control method for a loop transformer based on a single-core hexagonal phase-shifting transformer according to claim 3 or 6, characterized in that: The connection method based on the single-core hexagonal phase-shifting transformer establishes a constraint relationship between the phase of the compensation voltage and the actual number of turns connected to the secondary winding in the single-core hexagonal phase-shifting transformer, thereby obtaining the output voltage of each phase of the closed-loop transformer. Based on the three-phase symmetrical operation of the closed-loop transformer, the solution process for the output voltage of each phase of the closed-loop transformer includes: The output voltage of each phase of the closed-loop transformer can be calculated by multiplying the primary and secondary turns ratios of each phase of the voltage regulating transformer with the output voltage of the corresponding phase of the single-core hexagonal phase-shifting transformer. The output voltage of the corresponding phase of the single-core hexagonal phase-shifting transformer can be calculated by summing the power supply voltage of each phase and the compensation voltage of the corresponding phase.

8. The control method for a loop transformer based on a single-core hexagonal phase-shifting transformer according to claim 3, characterized in that: The method of dynamically adjusting the actual number of turns connected to the secondary winding of the single-core hexagonal phase-shifting transformer by using a lookup table method based on the output voltage of each phase of the closed-loop transformer specifically includes: Solve for the turns ratio iteration values ​​of each phase secondary winding coil in a single-core hexagonal phase-shifting transformer; A simulation model of a closed-loop transformer based on a single-core hexagonal phase-shifting transformer is constructed. Different voltage phasor differences on both sides of the closed-loop point are set according to the output voltage of each phase of the closed-loop transformer. The turns ratio iteration value is used as the simulation parameter value. The simulation waveform or simulation data is observed, and the L2 norm of the difference between the simulated output voltage phasor and the theoretically calculated output voltage phasor is compared to see if it is within the allowable error range. If it is, the theoretical derivation value is correct. If not, the equation set is wrong or the iterative solution value is incorrect. The derivation or solution should be repeated. If the theoretical derivation is correct, the corresponding simulation data will be recorded in the table. When the loop transformer based on the single-core hexagonal phase-shifting transformer is actually put into operation, the turns ratio data of each phase secondary winding of the single-core hexagonal phase-shifting transformer will be selected by looking up the table according to the real-time detected voltage phasor difference on both sides of the loop point, and the actual number of turns connected to each phase secondary winding of the single-core hexagonal phase-shifting transformer will be dynamically adjusted.

9. The control method for a loop transformer based on a single-core hexagonal phase-shifting transformer according to claim 3, characterized in that: The method of dynamically adjusting the actual number of turns connected to the secondary winding of the single-core hexagonal phase-shifting transformer by controlling the controller based on the output voltage of each phase of the closed-loop transformer specifically includes: When the loop-connected transformer based on the single-core hexagonal phase-shifting transformer is actually put into operation, the voltage phasor difference between the two sides of the loop-connection point is obtained by the voltage of each phase output terminal of the loop-connected transformer. This phasor difference is used as a parameter input to the controller. The controller calculates and outputs control commands in real time according to the pre-set closed-loop control algorithm, thereby dynamically adjusting the actual number of turns connected to the secondary coil of each phase of the single-core hexagonal phase-shifting transformer in real time.

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