Excitation inrush current control method and equipment based on phase-shifting transformer

Abstract

The invention relates to an excitation inrush current control method and equipment based on a phase-shifting transformer, and belongs to the field of power systems. According to the voltage and current of any phase primary side of a series transformer in the phase-shifting transformer, a primary side winding flux linkage is calculated; if the flux linkage of the primary winding is decomposed to obtain a direct-current flux linkage component, determining that the phase-shifting transformer generates an excitation inrush current fault; according to the winding structure and the direct-current flux linkage component of the series transformer, a specific voltage for offsetting the direct-current flux linkage component is generated, the excitation surge current fault is judged ingeniously through the flux linkage change of the winding, and the direct-current flux linkage component is offset through the specific voltage in combination with the winding structure, so that the excitation surge current is suppressed accurately and efficiently, and the excitation surge current fault is eliminated. The protection device effectively protects the phase-shifting transformer, and is suitable for various phase-shifting transformers.

Description

Technical Field

[0001] The invention relates to a method and device for controlling magnetizing inrush current based on a phase-shifting transformer, and belongs to the field of power systems. Background Art

[0002] Currently, no practical power flow regulators can simultaneously achieve the advantages of flexible regulation and low cost. A hybrid power flow control system based on a phase-shifting transformer and a voltage source converter, proposed by some scholars, effectively combines the advantages of traditional electromagnetic mechanical devices with power electronics. On the one hand, it utilizes the passive electromagnetic device of the phase shifter to achieve large-scale discontinuous regulation, low cost, and high reliability, leveraging the inherent regulation capabilities of the phase shifter. On the other hand, it utilizes the voltage source converter to achieve precise, rapid, and broadband continuous regulation, minimizing the configuration capacity of the voltage source device. This achieves technological breakthroughs in the overall insulation, volume, and cost of the hybrid power flow control equipment, and the system has significant technical and economic advantages.

[0003] However, the excitation inrush current generated when the phase-shifting transformer fails will directly affect the control effect of the hybrid power flow controller, and the excitation inrush current will cause a composite differential malfunction. In the existing technology, the second harmonic braking method is used to eliminate the excitation inrush current for the phase-shifting transformer differential protection, but it does not suppress the excitation inrush current, and there is still a risk of device malfunction, which cannot protect the phase-shifting transformer and cannot accurately realize the power flow control of the hybrid power flow controller. Summary of the Invention

[0004] The object of the present invention is to provide a method and device for controlling the excitation inrush current based on a phase-shifting transformer, so as to solve the problem that the excitation inrush current generated when the phase-shifting transformer fails cannot be offset.

[0005] To achieve the above objectives, the present invention proposes a method for controlling magnetizing inrush current based on a phase-shifting transformer, comprising:

[0006] Calculate the primary winding flux based on the voltage and current of any phase of the series transformer in the phase-shifting transformer. If the primary winding flux is decomposed to obtain a DC flux component, it is determined that the phase-shifting transformer has an excitation inrush current fault.

[0007] Based on the winding structure and DC flux component of the series transformer, a specific voltage is generated to offset the DC flux component.

[0008] Furthermore, the primary winding flux is decomposed by the following method: performing a filtering operation on the primary winding flux; and determining whether the filtered primary winding flux is decomposed to obtain a DC flux component.

[0009] Furthermore, the primary winding flux is calculated using the following formula:

[0010]

[0011] in, is the magnetic linkage; U STa1 is the primary voltage of the series transformer; L STa1 is the primary current of the series transformer; R STa1 is the series transformer resistance; L STa1 is the series transformer inductance; s is the Laplace operator.

[0012] Furthermore, when the winding structure of the series transformer is a star-delta structure, a specific voltage is inputted to the three-phase circuit of the series transformer on average to cancel out the DC magnetic flux component.

[0013] Furthermore, the specific voltage is generated by a voltage source converter connected in series with a phase-shifting transformer.

[0014] On the other hand, the present invention provides a control device for an excitation inrush current based on a phase-shifting transformer, comprising a processor, wherein the processor is configured to execute the following method:

[0015] Calculate the primary winding flux based on the voltage and current of any phase of the series transformer in the phase-shifting transformer. If the primary winding flux is decomposed to obtain a DC flux component, it is determined that the phase-shifting transformer has an excitation inrush current fault.

[0016] Based on the winding structure and DC flux component of the series transformer, a specific voltage is generated to offset the DC flux component.

[0017] Furthermore, the primary winding flux is decomposed by executing the following method: performing a filtering operation on the primary winding flux; and determining whether the filtered primary winding flux is decomposed to obtain a DC flux component.

[0018] Furthermore, the primary winding flux is calculated using the following formula:

[0019]

[0020] in, is the magnetic linkage; U STa1 is the primary voltage of the series transformer; I STa1 is the primary current of the series transformer; R STa1 is the series transformer resistance; L STa1 is the series transformer inductance; s is the Laplace operator.

[0021] Furthermore, when the winding structure of the series transformer is a star-delta structure, a specific voltage is inputted to the three-phase circuit of the series transformer on average to cancel out the DC magnetic flux component.

[0022] Furthermore, the specific voltage is generated by a voltage source converter connected in series with a phase-shifting transformer.

[0023] The beneficial effects of the present invention are as follows: the primary winding flux is calculated based on the voltage and current of the primary side of any phase of the series transformer in the phase-shifting transformer; if the primary winding flux is decomposed to obtain a DC flux component, it is determined that the phase-shifting transformer has an excitation inrush current fault; according to the winding structure and DC flux component of the series transformer, a specific voltage is generated to offset the DC flux component, and the excitation inrush current fault is cleverly judged through the flux change of the winding, and combined with the winding structure, the DC flux component is offset by a specific voltage, thereby achieving accurate and efficient suppression of the excitation inrush current and effectively protecting the phase-shifting transformer, and is applicable to a variety of phase-shifting transformers. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a topological diagram of a hybrid power flow controller in an actual application scenario of a control method for magnetizing inrush current based on a phase-shifting transformer proposed in the present invention;

[0025] Figure 2 Schematic diagram of a method for controlling magnetizing inrush current based on a phase-shifting transformer proposed in the present invention in an actual application scenario of an HPFC fault;

[0026] Figure 3 This is a diagram showing the characteristics of the inrush current of a series transformer in an actual application scenario using a method for controlling inrush current of a phase-shifting transformer proposed in the present invention;

[0027] Figure 4 This is a diagram showing the internal structure of a series transformer in a practical application scenario of a method for controlling magnetizing inrush current based on a phase-shifting transformer proposed in the present invention;

[0028] Figure 5 This is a schematic diagram of the excitation inrush current waveform and corresponding flux linkage in an actual application scenario of a control method for excitation inrush current based on a phase-shifting transformer proposed in the present invention;

[0029] Figure 6 This is a schematic diagram of a circuit for suppressing the magnetizing inrush current of a star-delta series transformer in an actual application scenario using a method for controlling the magnetizing inrush current based on a phase-shifting transformer proposed in the present invention;

[0030] Figure 7 This is a structural diagram of a control method for excitation inrush current based on a phase-shifting transformer proposed in the present invention after suppressing the excitation inrush current in an actual application scenario. DETAILED DESCRIPTION

[0031] In order to make the objectives, technical solutions and advantages of the present invention more clear, the present invention is further described in detail below with reference to the accompanying drawings and embodiments.

[0032] The inventive concept of the present invention is to monitor the primary winding flux in real time and filter the primary winding flux, and determine that a phase-shifting transformer has failed in response to the DC flux component generated after filtering; then combine the winding structure to generate a specific voltage for offsetting the DC flux component, effectively judge and process the excitation inrush current, and protect the phase-shifting transformer while also protecting the hybrid power flow controller.

[0033] Method Specific Implementation 1:

[0034] The present invention provides a method for controlling an excitation inrush current based on a phase-shifting transformer, wherein the phase-shifting transformer includes a series transformer. The method includes steps S11 and S12, specifically:

[0035] Step S11, calculate the primary winding flux according to the voltage and current of any phase of the series transformer of the phase-shifting transformer; if the primary winding flux is decomposed to obtain a DC flux component, it is determined that the phase-shifting transformer has an excitation inrush current fault; it should be noted that the primary winding flux is decomposed by the following method: perform a filtering operation on the primary winding flux; and judge whether the primary winding flux is decomposed to obtain a DC flux component after filtering. If the primary winding flux is only decomposed to obtain an AC flux after filtering, it means that the line has not failed, that is, the phase-shifting transformer has not generated an excitation inrush current fault, and the fault is judged by observing the flux change of the series transformer, breaking through the traditional idea of ​​excitation inrush current fault detection, and providing a signal basis for the subsequent generation of a specific voltage for offsetting the DC flux component. When calculating the primary winding flux, based on Kirchhoff's law, the primary winding flux is calculated by the following formula:

[0036]

[0037] in, is the magnetic linkage; U STa1 is the primary voltage of the series transformer; I STa1 is the primary current of the series transformer; R STa1 is the series transformer resistance; L STa1 is the series transformer inductance; s is the Laplace operator.

[0038] At the same time, in actual application scenarios, the voltage and current of the primary side of any phase of the series transformer will be monitored in real time, the primary winding flux will be quickly calculated, and it will be quickly determined whether an excitation inrush current fault occurs.

[0039] Step S12, generating a specific voltage for offsetting the DC flux component based on the winding structure and DC flux component of the series transformer; here, the winding structure of the series transformer refers to the winding structure of the series transformer in the phase-shifting transformer, which includes but is not limited to a star-delta structure, a star connection structure, a delta connection structure, etc., to achieve voltage generation that integrates the characteristics of the series transformer winding and can offset the DC flux component, so that the characteristic voltage is consistent with the excitation inrush current while balancing the voltage stability in various lines, and has great application prospects.

[0040] Through the above-mentioned steps S11 and S12, the flux changes of the series transformer are observed in real time, and the flux changes are analyzed in combination with the filtering operation. In response to the DC flux component obtained after filtering, it is determined that the phase-shifting transformer has generated an excitation inrush current fault. Then, based on the DC flux component and the winding structure of the series transformer, a specific voltage is generated that can not only offset the DC flux component but also meet the winding structure of the series transformer.

[0041] Method Specific Implementation Method 2:

[0042] Continuing with the above-described specific embodiment of the present invention, in step S12, when the winding structure of the series transformer is a star-delta configuration, a specific voltage is inputted to the three-phase circuit of the series transformer on average to cancel out the DC flux component. This takes into account the structural characteristic of the star-delta configuration, where changing the voltage value of one phase also changes the voltage values ​​of the other two phases, and forms a cancellation strategy that conforms to the characteristics of the star-delta configuration. In actual application scenarios, the characteristic voltage output will be adjusted according to different winding structures to suppress the excitation inrush current while not affecting the stability of the circuit.

[0043] At the same time, in actual application scenarios, combined with the situation where the excitation inrush current fault of the phase-shifting transformer has a greater impact on the hybrid power flow controller, the specific voltage is generated by a voltage source converter connected in series with the phase-shifting transformer. It should be noted that the voltage source converter connected in series with the phase-shifting transformer and the phase-shifting transformer constitute a hybrid power flow controller. Specifically, Figure 1As shown in the figure, a topological structure diagram of a hybrid power flow controller in an actual application scenario of a control method for excitation inrush current based on a phase-shifting transformer proposed in the present invention is shown, wherein a phase-shifting transformer (PST) and a cascaded H-bridge converter (CHBC) form a hybrid power flow controller (HPFC), wherein the PST includes an excitation transformer (ET) and a series transformer (ST), and the CHBC is connected in series on the low-voltage side of the ET to control its output voltage amplitude to assist the PST in regulating the power flow, realizing the special structure of the hybrid power flow control and the sensitive and fast characteristics of the voltage source converter to suppress the DC flux of the phase shifter, thereby reducing the excitation inrush current and effectively protecting the hybrid power flow controller.

[0044] Method Specific Implementation 3:

[0045] like Figure 2 FIG2 is a schematic diagram of an HPFC fault in an actual application scenario of a method for controlling magnetizing inrush current based on a phase-shifting transformer proposed in the present invention. When a ring network fault occurs, the voltage across the PST winding in the HPFC changes suddenly, and the fault can be confirmed by the voltage change and magnetic flux of the transformer winding. Specifically:

[0046] When a fault occurs, the transformer winding voltage change is calculated using the following formula:

[0047] u=U m sin(ωt+θ)

[0048] Where, u is the voltage; U m is the voltage amplitude after the fault; θ is the initial phase.

[0049] The flux equation is as follows:

[0050]

[0051] Where N is the number of turns of the primary winding; is the total magnetic flux that interlinks it.

[0052]

[0053] in, is the residual flux, From the above formula we can get When θ=0, the fault occurs and the magnetic flux of the winding reaches the maximum

[0054] like Figure 3As shown in FIG, a control method for excitation inrush current based on a phase-shifting transformer proposed by the present invention is used to connect the transformer in series in an actual application scenario, wherein: is the steady-state magnetic flux; is the saturation flux; is the DC component; the red curve is the total magnetic flux The purple dotted line is the magnetizing inrush current I f ; The blue curve is voltage, refer to Figure 3 It can be seen that the magnetic flux is slightly larger than the steady-state flux Ordinary transformers designed with a nominal current are prone to magnetic saturation. When a transformer generates a magnetizing inrush current, it can reach several to dozens of times the rated current and then decay after several to dozens of power frequency cycles before reaching stability, threatening the transformer's safe operation. Due to the design of phase shifter parameters, the rated capacity of a series transformer is relatively small, making it more susceptible to large magnetizing inrush currents. This paper analyzes the transient characteristics of a series transformer during a fault.

[0055] like Figure 4 As shown in the figure, the internal structure diagram of the series transformer in the actual application scenario of the control method of the excitation inrush current based on the phase shifting transformer proposed by the present invention is shown. Taking the A phase of the phase shifter as an example, U STa1 is the primary voltage of the series transformer; L STa1 is the primary current of the series transformer; R STa1 is the series transformer parameter; L STa1 To obtain the series transformer parameters, the current and voltage parameters are detected in real time, and the magnetic flux of the series transformer winding is solved.

[0056] like Figure 5 As shown in the figure, a control method for excitation inrush current based on a phase-shifting transformer proposed in the present invention is used to control the excitation inrush current in an actual application scenario, and a schematic diagram of the corresponding magnetic flux. Figure (a) is a schematic diagram of the excitation inrush current of a series transformer; Figure (b) is a DC magnetic flux component of a series transformer. Specifically, after a fault occurs in phase A, the winding magnetic flux generates a large amount of DC components, the series transformer becomes magnetically saturated, and a large excitation inrush current is generated. The main reason is that the magnetic flux contains a large amount of DC components. The voltages UB and UC at both ends of the series transformer can be changed through CHBC, thereby offsetting the DC component generated by the fault, thereby suppressing the excitation inrush current.

[0057] like Figure 6 As shown, a schematic diagram of a circuit for suppressing the excitation inrush current of a star-delta series transformer in an actual application scenario of a control method for excitation inrush current based on a phase-shifting transformer proposed in the present invention is shown. Since the connection mode of the primary side of the series transformer is a star-delta structure, changing the voltage value of one phase will also change the other two phases. Therefore, it is necessary to suppress the flux of the three phases at the same time, and distribute the flux command evenly to each phase.

[0058] like Figure 7 Figure 2 shows a schematic diagram of the structure of a phase-shifting transformer-based magnetizing inrush current control method proposed in this invention after suppressing the magnetizing inrush current in an actual application scenario. Figure (c) shows the DC flux suppression effect, and Figure (d) shows the magnetizing inrush current suppression effect. It can be seen that after a fault occurs, the CHBC significantly reduces the DC component of the flux by changing the voltage across the transformer. During and after the system fault occurs, the DC component remains near zero. After the suppression strategy is implemented, the magnetizing inrush current is significantly reduced, demonstrating the effectiveness of the control strategy.

[0059] Method Specific Implementation Method 4:

[0060] For example, in practical applications, first, when a system fault occurs, the transient characteristics of the phase shifter are analyzed, and a flux observer is designed to observe the flux changes of the series transformer in real time. It is clear that the main reason for the phase shifter to generate excitation inrush current is that the series transformer generates a large DC component of the flux. Secondly, based on the reason for the phase shifter to generate excitation inrush current, a strategy is designed to utilize the fast and sensitive characteristics of the voltage source converter to suppress the DC flux generated by the phase shifter during a fault, thereby effectively reducing the excitation inrush current of the transformer. A flux distribution strategy is designed for the star-delta structure of the phase shifter series transformer, which can effectively reduce the impact on non-fault phases, identify multiple short-circuit faults, and quickly and effectively suppress them. Finally, an application scenario is built in PSCAD and verified under different short-circuit fault conditions, proving the effectiveness of the suppression strategy.

[0061] Specific implementation of the equipment:

[0062] On the other hand, the present invention further provides a control device for an excitation inrush current based on a phase-shifting transformer, comprising a processor, wherein the processor is configured to execute the following method:

[0063] The primary winding flux is calculated based on the voltage and current of any primary phase of the series transformer in the phase-shifting transformer. If the primary winding flux is decomposed to obtain a DC flux component, it is determined that the phase-shifting transformer has an excitation inrush current fault. The primary winding flux is decomposed by performing the following method: filtering the primary winding flux; and determining whether the filtered primary winding flux is decomposed to obtain a DC flux component. The primary winding flux is calculated using the following formula:

[0064]

[0065] in, is the magnetic linkage; U STa1 is the primary voltage of the series transformer; I STa1 is the primary current of the series transformer; R STa1 is the series transformer resistance; L STa1is the series transformer inductance; s is the Laplace operator.

[0066] Based on the winding structure and DC flux components of the series transformer, a specific voltage is generated to offset the DC flux components. When the series transformer has a star-delta winding structure, the specific voltage is inputted evenly into the three-phase circuit of the series transformer to offset the DC flux components. Simultaneously, the specific voltage is generated by a voltage source converter connected in series with the phase-shifting transformer.

[0067] For this purpose, please refer to the specific implementation methods of the device 1-4 of the control method of the excitation inrush current based on the phase-shifting transformer, which will not be repeated here.

[0068] The present invention addresses the needs of power grid power flow control by combining the advantages of phase-shifting transformers and cascaded H-bridge converters. This approach retains the high reliability and low-cost advantages of electromagnetic mechanical equipment while also offering the flexibility of power electronics. This approach is of great significance for promoting the practical application of power grid power flow control projects, facilitating the high-level integration of new energy sources, and enhancing the flexible regulation capabilities of new power systems. Specifically, when a system fault occurs, the phase shifter, due to its inherent transformer magnetizing inrush current characteristics, is prone to generating a large magnetizing inrush current. To address this issue, a detailed analysis of the phase shifter's structure and operating principle is conducted. A flux observer is used to observe the real-time flux changes of the transformer. The primary cause of magnetizing inrush current within the phase shifter is the large DC flux component generated by the series transformer, leading to transformer flux saturation and, consequently, a large magnetizing inrush current. This large DC flux component leads to magnetizing inrush current. A magnetizing inrush current suppression strategy is designed. By leveraging the fast and sensitive characteristics of a voltage source converter, the voltage across the series transformer is altered, thereby offsetting the large DC flux component generated during a fault. Simultaneously, the three-phase voltages are controlled based on the star-delta configuration of the series transformer, effectively protecting the non-faulty phases while suppressing the faulty phase.

[0069] In summary, the present invention mainly includes two parts: 1. The causes and characteristics of the excitation inrush current of the phase-shifting transformer; 2. The excitation inrush current suppression strategy. (1) The causes and characteristics of the excitation inrush current of the phase-shifting transformer: When a line fault occurs, the voltage at both ends of the phase shifter suddenly changes, but the magnetic flux cannot change suddenly, which easily accumulates a large magnetic flux. According to the characteristics of the transformer, when the transformer is saturated with magnetic flux, the magnetic permeability of the core drops sharply, resulting in the core being unable to continue to increase the magnetic flux effectively, causing the excitation inrush current to reach a peak near the core saturation point, which may cause the transformer to be prone to a large current shock when a fault occurs. For the multi-winding structure of the phase shifter, the causes of the excitation inrush current are relatively complex, and it is necessary to analyze the main reasons for its generation. For this purpose, a magnetic flux observer is designed to observe the changes in the magnetic flux of the transformer winding after a fault occurs in the phase shifter winding. (2) Excitation inrush current suppression strategy: The main cause of the excitation inrush current generated by the phase shifter is identified. By utilizing the output voltage controllable characteristics of the voltage source converter, a specific voltage is output, which changes the voltage of the transformer windings at both ends, thereby offsetting the excitation DC component generated by the phase shifter due to the fault, thereby achieving the purpose of suppressing the excitation inrush current. With the purpose of suppressing the DC component of the flux linkage, and based on the special winding structure of the phase shifter, a magnetizing inrush current suppression strategy suitable for the phase shifter is proposed. It can suppress the excitation inrush current caused by various short-circuit faults and achieves good results. The above-mentioned excitation inrush current suppression strategy designed based on the special structure of the HPFC can effectively suppress the excitation inrush current generated by the phase shifter during faults.

Claims

1. A method for controlling magnetizing inrush current based on a phase-shifting transformer, characterized in that: include: Calculate the primary winding flux linkage based on the voltage and current of any phase of the series transformer in the phase-shifting transformer; If the primary winding flux is decomposed to obtain the DC flux component, it is determined that the phase-shifting transformer has an excitation inrush current fault; Based on the winding structure and DC flux component of the series transformer, a specific voltage is generated to offset the DC flux component.

2. The method for controlling magnetizing inrush current based on a phase-shifting transformer according to claim 1, characterized in that: The primary winding flux is decomposed by the following method: performing a filtering operation on the primary winding flux; and determining whether the primary winding flux is decomposed to obtain a DC flux component after filtering.

3. The method for controlling magnetizing inrush current based on a phase-shifting transformer according to claim 1, characterized in that: The primary winding flux is calculated using the following formula: in, is the magnetic linkage; U STa1 is the primary voltage of the series transformer; U STa1 is the primary current of the series transformer; R STa1 is the series transformer resistance; L STa1 is the series transformer inductance; s is the Laplace operator.

4. The method for controlling magnetizing inrush current based on a phase-shifting transformer according to claim 1, characterized in that: When the winding structure of the series transformer is a star-delta structure, a specific voltage is inputted to the three-phase circuit of the series transformer on average so as to cancel out the DC magnetic flux component.

5. The method for controlling magnetizing inrush current based on a phase-shifting transformer according to claim 1, characterized in that: The specific voltage is generated by a voltage source converter connected in series with a phase-shifting transformer.

6. A control device for magnetizing inrush current based on a phase-shifting transformer, characterized in that: The invention comprises a processor configured to execute the following method: Calculate the primary winding flux based on the voltage and current of any phase of the series transformer in the phase-shifting transformer. If the primary winding flux is decomposed to obtain a DC flux component, it is determined that the phase-shifting transformer has an excitation inrush current fault. Based on the winding structure and DC flux component of the series transformer, a specific voltage is generated to offset the DC flux component.

7. The control device for magnetizing inrush current based on a phase-shifting transformer according to claim 6, characterized in that: The primary winding flux is decomposed by executing the following method: performing a filtering operation on the primary winding flux; and determining whether the primary winding flux is decomposed to obtain a DC flux component after filtering.

8. The control device for magnetizing inrush current based on a phase-shifting transformer according to claim 6, characterized in that: The primary winding flux is calculated using the following formula: in, is the magnetic linkage; U STa1 is the primary voltage of the series transformer; I STa1 is the primary current of the series transformer; R STa1 is the series transformer resistance; L STa1 is the series transformer inductance; s is the Laplace operator.

9. The control device for magnetizing inrush current based on a phase-shifting transformer according to claim 6, characterized in that: When the winding structure of the series transformer is a star-delta structure, a specific voltage is inputted to the three-phase circuit of the series transformer on average so as to cancel out the DC magnetic flux component.

10. The control device for magnetizing inrush current based on a phase-shifting transformer according to claim 6, characterized in that: The specific voltage is generated by a voltage source converter connected in series with a phase-shifting transformer.

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