A current-limiting phase-shifting transformer topology and control method thereof

Abstract

The present invention provides a current-limiting phase-shifting transformer topology structure and a control method thereof, relating to the technical field of power system power flow control and short-circuit current protection. The current-limiting phase-shifting transformer topology structure includes an excitation transformer and a series transformer, wherein the excitation transformer includes an excitation transformer primary winding and an excitation transformer secondary winding, and 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 circuit and obtains the excitation voltage from the circuit; 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 circuit. The present invention can solve the problems of unreasonable power flow distribution and excessive short-circuit current faced by the power system, has the advantages of low cost and high economy, and has a wide range of applications.

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 continued construction of new power systems, grid structures are becoming increasingly complex. Interconnected large power grids can better optimize energy distribution and enhance the system's economy, safety, and stability. However, the complex grid structure and dense power distribution also reduce the system's equivalent impedance. With the further increase in load and substation locations, a large number of lines in the system face the problem of excessive short-circuit currents, significantly reducing the system's safety and stability. At the same time, due to the complex configuration of network structures and network parameters in new power systems, the natural flow of the power grid cannot effectively respond to changes in power supply and load, and uneven flow distribution is prone to occur, severely limiting the power supply capacity of regional ring networks. Problems such as unreasonable flow distribution and excessive short-circuit currents have become the biggest obstacles to the development of new power systems, challenging the efficient and stable operation of power grids. Therefore, there is an urgent need for effective flow limiting and regulation equipment to cost-effectively solve this problem.

[0003] Currently, the main power flow regulation technologies include FACTS (Flexible Alternative Current Transmission Systems) and phase-shifting transformers (PSTs). FACTS devices, based on power electronic equipment, suffer from disadvantages such as high cost, high losses, heavy maintenance, and damage to system waveform quality. FACTS devices include series compensation devices and unified power flow controllers (UPFCs). The series compensation device has limited power flow regulation capabilities and is mainly used for voltage stabilization and reactive power compensation, making it difficult to apply to optimize regional power flow distribution in power grids. The UPFC has strong power flow regulation capabilities but is too expensive. Currently, power grids do not have the conditions to widely promote UPFC for power flow regulation. PSTs, on the other hand, are more widely used due to their large power flow regulation capacity, high flexibility, low cost, low losses, and waveform quality. However, PSTs currently lack short-circuit current limiting and cannot fully meet the needs of power grids.

[0004] Currently, the main current-limiting technologies include changing the grid structure or operating mode, using series-compensated high-impedance transformers and reactors, and superconducting fault current limiters (SFCLs). Current-limiting measures for grid reconstruction and operational changes primarily include ring network splitting and busbar segmentation. These measures have a significant impact on the grid and are difficult to implement in existing, fully constructed grids. SFCLs and reactors increase line reactance, impacting the system's dynamic performance and voltage stability. Superconducting fault current limiters, however, are currently limited in practical application due to their high cost and limited current-limiting capacity. Furthermore, current mainstream current-limiting devices and measures lack power flow control capabilities, failing to fully meet grid requirements. Summary of the Invention

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

[0006] In order to achieve the above-mentioned objectives, in a first aspect, the present invention provides a current-limiting phase-shifting transformer topology structure, including an excitation transformer and a series transformer, the excitation transformer including an excitation transformer primary winding and an excitation transformer secondary winding, the series transformer including a series transformer primary winding and a series transformer secondary winding; the excitation transformer primary winding is connected in parallel in the circuit to obtain the excitation voltage from the circuit; the excitation transformer secondary winding is connected to the series transformer primary winding; the series transformer secondary winding is three independent windings that are not connected to each other, and are directly connected in series to the three phases of the circuit respectively.

[0007] According to a current-limiting phase-shifting transformer topology structure provided by the present invention, 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 the phase. .

[0008] According to a current-limiting phase-shifting transformer topology structure provided by the present invention, the excitation transformer is a three-phase double-winding on-load tap-changing transformer, including an on-load tap-changing switch; the on-load tap-changing switch includes multiple adjustment gears for adjusting the amplitude of the excitation voltage.

[0009] According to a current-limiting phase-shifting transformer topology provided by the present invention, a fast switch is provided on the secondary winding of the excitation transformer, and the fast switch is connected to the on-load tap-changer; when the line is in a steady state, the fast switch is closed, thereby generating compensation voltages of different sizes for the series transformer.

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

[0011] According to a current-limiting phase-shifting transformer topology provided by the present invention, the secondary winding of the excitation transformer is provided with a current-limiting gear, which is connected to the switch connector of the on-load tap-changer. A current-limiting impedance and an anti-parallel thyristor are installed on the current-limiting gear; when a line fault occurs, the anti-parallel thyristor is triggered, the fast switch is disconnected, and the current-limiting impedance is connected to the line.

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

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

[0014] In a second aspect, the present invention provides a control method for the current-limiting phase-shifting transformer topology structure according to the first aspect, comprising:

[0015] When the line is in a steady state, the fast switch is closed, and the amplitude of the excitation voltage is adjusted by adjusting the adjustment gear of the on-load tap changer, thereby generating different compensation voltages for the series transformer;

[0016] When a line fault occurs, the anti-parallel thyristor is triggered, the fast switch is disconnected, and the current limiting impedance is connected to the line to limit the line current when a fault occurs.

[0017] According to the present invention, a control method for a current-limiting phase-shifting transformer topology structure further includes: performing an inverting operation on the compensation voltage by toggling a polarity switch, thereby achieving leading and lagging regulation of the line voltage phase.

[0018] The present invention provides a current-limiting phase-shifting transformer topology structure and a control method thereof, which have at least the following technical effects:

[0019] 1. Introducing current-limiting impedance into the current-limiting phase-shifting transformer gives it 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, better economy, high integration and small footprint, and can be widely used in power system control and protection operations.

[0020] 2. Through the unique topological structure design, the current limiting impedance is connected in star on the excitation winding, while the primary winding of the series transformer is connected in triangle. According to Kirchhoff's law, the impedance will become three times the original when the star connection is equivalent to the triangle connection. Therefore, when the current limiting phase-shifting transformer is connected to the line through the series transformer, the current limiting impedance displayed to the outside is much larger than the actual current limiting impedance. A better current limiting effect can be achieved with a smaller current limiting device. It has the advantages of low cost and high economy, and can be widely used in short-circuit current limiting operations in power systems. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the technical solutions in the present invention or the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0022] In the attached figure:

[0023] Figure 1 Schematic diagram of the topological structure of the current-limiting phase-shifting transformer of the present invention;

[0024] Figure 2 is a steady-state equivalent circuit diagram of the current-limiting phase-shifting transformer of the present invention;

[0025] Figure 3 This is a fault equivalent circuit diagram of the current-limiting phase-shifting transformer of the present invention;

[0026] Figure 4 This is a simulated power flow control waveform diagram of the current-limiting phase-shifting transformer of the present invention;

[0027] Figure 5 This is a simulated limited short-circuit current waveform diagram of the current-limiting phase-shifting transformer of the present invention. DETAILED DESCRIPTION

[0028] To make the objectives, technical solutions, and advantages of the present invention more clear, the technical solutions of the present invention will be clearly and completely described below in conjunction with the accompanying drawings. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts shall fall within the scope of protection of the present invention.

[0029] The following will describe some embodiments of the present invention in detail with reference to the accompanying drawings. In the absence of conflict, the following embodiments and features in the embodiments may be combined with each other.

[0030] See also Figure 1 , Figure 1 This is a schematic diagram of a current-limiting phase-shifting transformer topology. An embodiment of the present invention provides a current-limiting phase-shifting transformer topology, including 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 primary winding of the excitation transformer is connected in parallel in the circuit to obtain the excitation voltage from the circuit. The secondary winding of the excitation transformer is connected to the primary winding of the series transformer. The secondary winding of the series transformer is three independent windings that are not connected to each other and are directly connected in series to the three phases A, B, and C of the circuit respectively.

[0031] Specifically, the excitation transformer is a three-phase, dual-winding, on-load tap-changing transformer, including an on-load tap-changing switch (OLT). The OLT has multiple adjustment positions for adjusting the excitation voltage amplitude. Both the primary and secondary windings are star-connected, with the primary winding connected in parallel to the line, drawing its excitation voltage from the line. The secondary winding of the excitation transformer is equipped with a fast-acting switch connected to the OLT. When the line is in steady state, the fast-acting switch closes, generating compensation voltages of varying magnitudes for the series transformer.

[0032] The series transformer is a three-phase double-winding transformer with a primary winding connected in delta. A tap is provided in the middle of the secondary winding of the series transformer. The connection between the excitation transformer and the series transformer realizes the transformation from star connection to delta connection. The voltage on the primary winding of the series transformer leads or lags the excitation voltage of the same phase. , and then, through the electromagnetic induction of the series transformer, this voltage is injected into the line, which can adjust the phase of the system line voltage and thus control the line power flow. The excitation voltage is taken from the tap in the middle of the secondary winding of the series transformer. This tap is the excitation point. The number of turns of the windings on both sides of the tap is equal, half of the secondary winding of the series transformer. The adjusted compensation voltage is perpendicular to the excitation voltage. Therefore, the voltages of the windings on both sides of the excitation point are equal and perpendicular to the excitation voltage, forming an isosceles triangle. The voltages before and after adjustment are symmetrical about the excitation voltage, and the amplitude remains unchanged.

[0033] The secondary winding of the excitation transformer is connected to a polarity switch. By flipping the polarity switch, the series transformer's compensation voltage can be reversed, thereby enabling lead and lag adjustment of the line voltage phase. The secondary winding of the excitation transformer is equipped with a current-limiting position, which is connected to the switch connector of the on-load tap changer. A current-limiting resistor and an anti-parallel thyristor are installed on the current-limiting position. This current-limiting position is always connected to the switch connector via a wire. However, when the line is in a steady state, the anti-parallel thyristor is not triggered, and the current-limiting resistor is not connected to the line. When a line fault occurs (such as a short circuit), the anti-parallel thyristor is triggered, and the rapid switch is disconnected. The excitation transformer switches to no-load operation and exits the line, and the current-limiting resistor is connected to the line. After being amplified three times by the star-to-delta transformation between the excitation transformer and the series transformer, the current-limiting resistor is effectively connected to the line through the transformation ratio of the series transformer, thus limiting the short-circuit current. Therefore, the current-limiting phase-shifting transformer of the present invention injects a compensation voltage into the line in a steady state and injects a current-limiting impedance into the line in a fault state, thereby achieving the functions of power flow regulation and short-circuit current suppression.

[0034] It should be noted that when a line fault occurs, such as a line short circuit, the relay protection device of the power system detects the short circuit and sends a signal to the control device of the anti-parallel thyristor and the fast switch to activate the anti-parallel thyristor and the fast switch.

[0035] Furthermore, by combining the topological structure of the current-limiting phase-shifting transformer and the T-type equivalent circuit diagram of the transformer, the A-phase equivalent circuit diagram of the current-limiting phase-shifting transformer in steady state can be obtained, as shown in FIG. Figure 2 As shown, U SA 、 U LA 、 I SA 、 I LA They are the system voltage and system current before and after adjustment, U AL 、 U aL 、 U AC and U aC They are the voltages generated on the primary winding of the excitation transformer, the secondary winding of the excitation transformer, the primary winding of the series transformer and the secondary winding of the series transformer. I AL 、 I aL 、I AC 、 I aCThey are the currents in the primary winding of the excitation transformer, the secondary winding of the excitation transformer, the primary winding of the series transformer and the secondary winding of the series transformer, Z AL 、 Z aL 、 Z AC and Z aC They are the impedances of the primary winding of the excitation transformer, the secondary winding of the excitation transformer, the primary winding of the series transformer and the secondary winding of the series transformer, U is the voltage obtained from the system line by the current-limiting phase-shifting transformer, K is the transformation ratio of the excitation transformer. The transformation ratio of the series transformer is 1. The corresponding relationship is as follows: Figure 2 shown.

[0036] For the voltage phasor at the first terminal before compensation U SA and the terminal voltage phasor after compensation U LA They are:

[0037] (1.1)

[0038] (1.2)

[0039] (1.3)

[0040] (1.4)

[0041] According to the transformation ratio of the series transformer, the voltage and current relationship of each winding of the series transformer can be obtained as follows:

[0042] (1.5)

[0043] (1.6)

[0044] According to the ratio of the excitation transformer, the voltage and current relationship of each winding of the excitation transformer can be obtained as follows:

[0045] (1.7)

[0046] (1.8)

[0047] Considering that the current-limiting phase-shifting transformer only has positive sequence components during normal operation, under positive sequence conditions, the electrical connection between the primary winding of the series transformer and the secondary winding of the excitation transformer yields:

[0048] (1.9)

[0049] (1.10)

[0050] Therefore, 10 equations containing 8 variables have been established. By simplifying Equations 1.1 to 1.10, the electrical quantities on the power supply side and the load side can be obtained. U SA 、 I SA 、 U LA The relationship is as follows:

[0051] (1.11)

[0052] Rearranging Equation 1.11 yields:

[0053] (1.12)

[0054] (1.13)

[0055] is the phase shift angle of the current-limiting phase-shifting transformer, for which:

[0056] (1.14)

[0057] (1.15)

[0058] Z equ is the overall internal impedance of the current-limiting phase-shifting transformer, which is generated by the internal impedance of all windings:

[0059] (1.16)

[0060] in, A 、 B 、 C 、 D They are the effect coefficients of each winding impedance in the total internal impedance, and they are related to the transformation ratio K related:

[0061] (1.17)

[0062] (1.18)

[0063] (1.19)

[0064] (1.20)

[0065] From Equation 1.12, the input-output characteristic equation of the current-limiting phase-shifting transformer, it can be seen that the current-limiting phase-shifting transformer has the ability to adjust the voltage phase of the system node. According to the active power flow formula in the line, it can be known that:

[0066] (1.21)

[0067] Where, P is the active power flow on the line, U S is the voltage amplitude at the line head end, U L is the voltage amplitude at the end of the line, is the voltage phase difference between the beginning and the end of the line.

[0068] In steady state, the ratio is adjusted by adjusting the gear of the excitation transformer K Adjustable phase shift angle , thereby effectively regulating the line flow.

[0069] 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 is disconnected, the anti-parallel thyristor is turned on, and the current-limiting phase-shifting transformer structure is reconstructed to work in the current-limiting mode. Combining the topological structure of the current-limiting phase-shifting transformer and the T-type equivalent circuit diagram of the transformer, the equivalent circuit diagram of the current-limiting phase-shifting transformer during the fault can be obtained, as shown in FIG. Figure 3 As shown. I A 、 I B and I C is the three-phase current of the line, I AC 、 I BC and I CC is the three-phase current of the primary winding of the series transformer, I aL 、 I bL and I cL is the three-phase current on the switch connection line of the secondary winding of the excitation transformer, Z BC 、 Z bC and Z CC 、 Z cC They are the B-phase and C-phase impedances of the primary winding of the series transformer and the secondary winding of the series transformer, Z Lis the current limiting impedance. Taking the parameters of phase A as an example, based on the electrical connection of the primary winding of the series transformer and the secondary winding of the excitation transformer, we can obtain:

[0070] (1.22)

[0071] (1.23)

[0072] (1.24)

[0073] According to the transformation ratio of the series transformer, the voltage and current relationship of each winding of the series transformer can be obtained as follows:

[0074] (1.25)

[0075] (1.26)

[0076] For the voltage phasor at the first terminal before compensation U SA and the terminal voltage phasor after compensation U LA They are:

[0077] (1.27)

[0078] By simplifying Equation 1.22 to Equation 1.27, the electrical quantities on the power supply side and the load side can be obtained U SA 、 I A 、 U LA The relationship is as follows:

[0079] (1.28)

[0080] As can be seen from Equation 1.28, when the current-limiting phase-shifting transformer operates in current-limiting mode, three times the current-limiting impedance is equivalently connected in series on each phase line. Through the unique topological structure design, three sets of current-limiting impedances achieve the effect of nine sets of current-limiting impedances, realizing the high efficiency and economy of the current-limiting function.

[0081] Based on the same inventive concept, another embodiment of the present invention provides a control method for the current-limiting phase-shifting transformer topology structure of the aforementioned embodiment, comprising:

[0082] When the line is in a steady state, the fast switch is closed, and the amplitude of the excitation voltage is adjusted by adjusting the adjustment gear of the on-load tap changer, thereby generating different compensation voltages for the series transformer;

[0083] When a line fault occurs, the anti-parallel thyristor is triggered, the fast switch is disconnected, and the current limiting impedance is connected to the line to limit the line current when a fault occurs.

[0084] Specifically, the method further includes: implementing an inverting operation on the compensation voltage by toggling a polarity switch, thereby achieving leading and lagging adjustment of the line voltage phase.

[0085] The following is a specific embodiment of the present invention.

[0086] This example uses the multi-winding transformer module in MATLAB / Simulink to build an equivalent model of a current-limiting phase-shifting transformer. The excitation transformer is configured with eight adjustment levels, and the simulation model and system parameters are set as shown in the following table:

[0087]

[0088] In steady-state operation, the adjustment gear of the excitation transformer is gradually increased, and the phase shift angle of the current-limiting phase-shifting transformer and the line power flow change with the adjustment gear. Figure 4 As shown, Figure 4 In the figure, the horizontal axis represents time, with the level increasing every 2 seconds. It can be seen that the line active power flow increases with the adjustment level of the excitation transformer, and the power flow regulation effect is significant. The line load increases by 300%, effectively shifting the power flow and improving the line's light load condition, fully verifying the power flow regulation capability of the current-limiting, phase-shifting transformer.

[0089] A short-circuit fault is applied to the model line. The short-circuit current waveforms with and without the infinite current phase-shifting transformer are as follows: Figure 5 As shown, it can be seen that after the multifunctional current limiting phase-shifting transformer is connected in series, the circuit peak value is reduced by 40% during short circuit, which effectively suppresses the short circuit current and fully proves the current limiting capability of the current limiting phase-shifting transformer.

[0090] In summary, the present invention proposes a current-limiting phase-shifting transformer topology structure and its control method, introduces a current-limiting impedance into the current-limiting phase-shifting transformer, and gives the current-limiting phase-shifting transformer the ability to limit short-circuit current, which can simultaneously solve the problems of unreasonable current 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 footprint. At the same time, through the unique topological structure design, the current-limiting impedance is star-connected on the excitation winding, while the primary winding of the series transformer is triangle-connected. According to Kirchhoff's law, when the star connection is equivalent to the triangle 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 current-limiting impedance displayed to the outside is much larger than the actual current-limiting impedance. A better current-limiting effect can be achieved with a smaller current-limiting device. It has the advantages of low cost and high economy and can be widely used in the operation of power system regulation and protection.

[0091] Those skilled in the art will readily appreciate other embodiments of the present invention after considering the specification and practicing the embodiments disclosed herein. The present invention is intended to cover any variations, uses, or adaptations of the present invention that follow the general principles of the present invention and include common knowledge or customary techniques in the art not disclosed herein. It should be understood that the present invention is not limited to the precise structure described above and shown in the accompanying drawings, and various modifications and variations can be made without departing from the scope thereof. The scope of the present invention is limited only 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, wherein the excitation transformer includes an excitation transformer primary winding and an excitation transformer secondary winding, and 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 circuit and obtains the excitation voltage from the circuit; the excitation transformer secondary winding is connected to the series transformer primary winding; the series transformer secondary winding is three independent windings that are not connected to each other and are directly connected in series to the three phases of the circuit respectively; 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 the same phase. ; The excitation transformer is a three-phase double-winding on-load tap-changing transformer, including an on-load tap-changing switch; the on-load tap-changing switch includes multiple adjustment gears for adjusting the amplitude of the excitation voltage; The secondary winding of the excitation transformer is provided with a fast switch, which is connected to the on-load tap changer; when the circuit is in a steady state, the fast switch is closed, thereby generating compensation voltages of different magnitudes for the series transformer; The secondary winding of the excitation transformer is provided with a current limiting gear, which is connected to the switch connector of the on-load tap changer. A current limiting impedance and an anti-parallel thyristor are installed on the current limiting gear; when a fault occurs in the line, the anti-parallel thyristor is triggered, and at the same time the fast switch is disconnected, and the current limiting impedance is connected to the line.

2. The current-limiting phase-shifting transformer topology structure according to claim 1, characterized in that: The secondary winding of the excitation transformer is connected to a polarity switch, and the inverting operation of the compensation voltage is achieved by toggling the polarity switch.

3. The current-limiting phase-shifting transformer topology structure according to claim 1, characterized in that: The fault includes a short circuit.

4. The current-limiting phase-shifting transformer topology structure according to claim 1, characterized in that: A tap is provided in the middle of the secondary winding of the series transformer, and 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 secondary winding of the series transformer.

5. A control method for a current-limiting phase-shifting transformer topology structure according to claim 2, characterized in that: include: When the line is in a steady state, the fast switch is closed, and the amplitude of the excitation voltage is adjusted by adjusting the adjustment gear of the on-load tap changer, thereby generating different compensation voltages for the series transformer; When a line fault occurs, the anti-parallel thyristor is triggered, the fast switch is disconnected, and the current limiting impedance is connected to the line to limit the line current when a fault occurs.

6. The control method of the current-limiting phase-shifting transformer topology structure according to claim 5, characterized in that: Also includes: By toggling the polarity switch, the compensation voltage is subjected to an inverted phase operation, thereby achieving leading and lagging adjustment of the line voltage phase.

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