A method and device for suppressing inrush current of multiple parallel transformers

Abstract

The present disclosure relates to a kind of multi-parallel transformer excitation inrush suppression control method and device.Wherein, the method includes: according to the connection relationship of parallel transformer, current limiting resistor, main control gate, establish the topology of multi-parallel transformer excitation inrush suppression, and the equivalent impedance of each transformer high voltage side winding in the parallel transformer, line equivalent resistance is used to calculate the resistance value of the current limiting resistor;In the multi-parallel transformer excitation inrush suppression control system model, according to the preset opening voltage phase angle of the main control gate, the remanence induction intensity of each transformer in the parallel transformer is calculated;According to the remanence induction intensity of each transformer in the parallel transformer, the closing time is calculated, and the multi-parallel transformer excitation inrush suppression control is completed.The present disclosure analyzes the suppression excitation inrush of multi-parallel transformer topology, calculates the current limiting resistor in topology, determines the phase time of split-phase closing, reduces the closing impact, and prolongs the service life of transformer.

Description

Technical Field

[0001] This disclosure relates to the field of new energy, and more specifically, to a method and device for suppressing and controlling inrush current of multiple parallel transformers. Background Technology

[0002] Large-scale ground-mounted grid-connected photovoltaic (PV) power plants refer to solar PV power plants connected to the public power grid and sharing the power supply task. This represents a significant development direction for solar PV power generation, marking its entry into large-scale commercial power generation and its integration into the power industry. In existing application scenarios, the PV grid-connection model for large-scale ground-mounted grid-connected PV power plants involves first establishing a 1MWp power generation capacity using a PV array composed of multiple solar panels, then connecting multiple combiner boxes to a single PV inverter. Each PV inverter is connected to a dual-split grid-connected transformer, and the high-voltage side of every four grid-connected transformers is connected to the 10kV power grid via the same feeder. Please refer to the primary wiring diagram. Figure 1 .

[0003] At night, the photovoltaic inverters stop generating electricity, and the step-up grid-connected transformers and photovoltaic inverters of the photovoltaic power station are in an unloaded state. At this time, due to factors such as the transformer's no-load excitation current, the transformer is constantly consuming electricity at night. According to preliminary estimates, an 8MWp photovoltaic power station has a total nighttime no-load loss of 50,000 kWh of electricity per year, resulting in serious energy waste. Based on the above problems, it is necessary to disconnect the transformer at night. However, the inrush current generated when switching the unloaded transformer can easily cause relay protection devices to malfunction, increase the mechanical pressure on the windings, reduce the transformer's service life, and reduce power quality. When the unloaded transformer is running in steady state, the no-load current is about 0.35% to 10% of the rated current; however, when the transformer is connected to the grid under no-load conditions, due to the saturation of the transformer core flux, the presence of residual magnetism, and the nonlinear characteristics of the core material, a large inrush current may be generated at the moment of closing. Its amplitude can reach tens of times or more than that under steady state conditions, and can reach 6 to 8 times the rated current. If no measures are taken, it may lead to problems such as malfunction of the transformer differential protection device, increased mechanical stress in the windings, and reduced power quality, making it impossible for the transformer to be connected to the power grid.

[0004] In existing technologies, methods for suppressing the no-load closing excitation circuit of a transformer include:

[0005] (1) Series resistance method for closing circuit

[0006] A common approach is to connect a resistor in parallel with the circuit breaker to reduce the magnetizing current. However, this method does not allow for residual magnetic flux and increases investment costs and operational complexity.

[0007] (2) Transformer neutral point series resistance method

[0008] At the moment of closing, the main magnetic flux of the transformer core is the sum of the steady-state flux and the transient flux, where the transient flux is a decaying non-periodic component with a decay time constant of R / L. Based on this theory, connecting a suitable resistor in series at the transformer neutral point and increasing the value of R can accelerate the decay process of the magnetic flux. After closing, removing this resistor reduces the amplitude of the steady-state current and the transient duration of the excitation current at the moment of closing, thereby suppressing the current. Although this method can accelerate the decay of the core magnetic flux and reduce the transient duration of the excitation current, the excitation current is still very high at the moment of closing (t=0), and the suppression effect is not ideal.

[0009] (3) Parallel Capacitor Method: The excitation current is caused by the saturation of magnetic flux within the transformer. If measures are taken to limit the magnetic flux within the windings from reaching the saturation point, the excitation current can be weakened. Parallel capacitors on the low-voltage side of the transformer are proposed based on this idea. If a capacitor is connected in parallel on the low-voltage side, the magnetic flux generated on the low-voltage side will have the opposite polarity to the magnetic flux on the high-voltage side, thus eliminating the possibility of magnetic flux saturation within the windings. The advantage of this method is that it can weaken the excitation current to a certain extent regardless of the three-phase closing angle. The disadvantage lies in the selection of the capacitor value; a value that is too large or too small will not meet the requirements. If the capacitance value is too large, the resonant frequency of the system formed by the transformer and capacitor will decrease, making it difficult for the transformer to be excited; if the capacitance value is too small, it will not meet the need to weaken the excitation current.

[0010] Using this method, the peak value of the excitation current varies greatly depending on the capacitor value. Therefore, before adopting this method, the excitation characteristics of the transformer must be known in order to simulate the transient phenomenon during transformer no-load closing and to select an appropriate capacitor value. Moreover, connecting a suitable capacitor in parallel on the low-voltage side of the transformer requires accurate simulation of the transformer's excitation characteristics, which is quite difficult to obtain in actual engineering.

[0011] Therefore, one or more methods are needed to solve the above problems.

[0012] It should be noted that the information disclosed in the background section above is only used to enhance the understanding of the background of this disclosure, and therefore may include information that does not constitute prior art known to those skilled in the art. Summary of the Invention

[0013] The purpose of this disclosure is to provide a method and apparatus for suppressing and controlling inrush current of multiple transformers connected in parallel, thereby overcoming, at least to some extent, one or more problems caused by the limitations and defects of related technologies.

[0014] According to one aspect of this disclosure, a method for suppressing and controlling inrush current of multiple transformers connected in parallel is provided, comprising:

[0015] Based on the connection relationship between parallel transformers, current-limiting resistors, and main control gates, a topology for suppressing inrush current of multiple parallel transformers is established. The resistance value of the current-limiting resistor is calculated based on the equivalent impedance of the high-voltage winding of each transformer in the parallel transformers and the equivalent resistance of the line, thus completing the modeling of the inrush current suppression control system for multiple parallel transformers.

[0016] In the model of the inrush current suppression control system for multiple parallel transformers, the residual magnetic induction intensity of each transformer in the parallel transformers is calculated based on the preset opening voltage phase angle of the main control gate.

[0017] The closing time is calculated based on the residual magnetic induction intensity of each transformer in the parallel transformer, and the inrush current suppression control of multiple parallel transformers is completed.

[0018] In one exemplary embodiment of this disclosure, the method further includes:

[0019] A topology for suppressing inrush current of multiple parallel transformers is established based on the connection relationships of parallel transformers, current-limiting resistors, and main control gates. The resistance value of the current-limiting resistor is calculated based on the equivalent impedance of the high-voltage windings and the equivalent resistance of the line in each of the parallel transformers.

[0020]

[0021] Among them, R z R is the resistance value of the current-limiting resistor. s R is the equivalent resistance of the line. i ω is the equivalent impedance of the high-voltage winding of each transformer in the parallel transformer, ω is the grid frequency, and L is the equivalent inductance of the high-voltage winding of each transformer in the parallel transformer.

[0022] In one exemplary embodiment of this disclosure, the method further includes:

[0023] In the model of the inrush current suppression control system for multiple parallel transformers, based on the voltage phase angle during the pre-opening of the main control gate, and using... Calculate the residual magnetic induction intensity B of each transformer in the parallel transformers;

[0024] Among them, U s β represents the high-voltage side voltage of each transformer in the parallel transformer, β represents the voltage phase angle when the main control switch is opened in sequence, N represents the turns ratio of each transformer in the parallel transformer, and S represents the cross-sectional area of ​​the core of each transformer in the parallel transformer.

[0025] In one exemplary embodiment of this disclosure, the method further includes:

[0026] The closing time is calculated based on the residual magnetic induction intensity of each transformer in the parallel transformer system.

[0027]

[0028] Where, φ γ =BS is the remanent magnetic flux, φ m The induced magnetic flux at the moment of closing;

[0029] Phase A is closed at the specified closing time.

[0030] In one exemplary embodiment of this disclosure, the method further includes:

[0031] After closing phase A at the specified closing time, phases B and C are closed 1 / 4 of a grid frequency cycle after phase A is closed, thus completing the inrush current suppression control of multiple parallel transformers.

[0032] In one exemplary embodiment of this disclosure, the method further includes:

[0033] In the model of the inrush current suppression control system for multiple parallel transformers, the residual magnetic induction intensity of each transformer in the parallel transformers is calculated based on the preset opening voltage phase angle of the main control gate.

[0034] The high-precision fast phase-locked loop (PLL) technology based on dq coordinate transformation samples the three-phase phase voltage of the bus in the excitation inrush current suppression control system model of the multiple parallel transformers to obtain the phase of the three-phase voltage.

[0035] The closing time is calculated based on the residual magnetic induction intensity and three-phase voltage phase of each transformer in the parallel transformer, and the inrush current suppression control of multiple parallel transformers is completed.

[0036] In one exemplary embodiment of this disclosure, the method further includes:

[0037] In the model of the inrush current suppression control system for multiple parallel transformers, the residual magnetic induction intensity of each transformer in the parallel transformers is calculated based on the preset closing voltage phase angle of the main control gate.

[0038] The tripping time is calculated based on the residual magnetic induction intensity of each transformer in the parallel transformer, and the inrush current suppression control of multiple parallel transformers is completed.

[0039] In one aspect of this disclosure, a device for suppressing inrush current of multiple parallel transformers is provided, comprising:

[0040] The system modeling module is used to establish the inrush current suppression topology of multiple parallel transformers based on the connection relationship of parallel transformers, current limiting resistors, and main control gates, and to calculate the resistance value of the current limiting resistor based on the equivalent impedance of the high-voltage winding of each transformer in the parallel transformers and the equivalent resistance of the line, thereby completing the modeling of the inrush current suppression control system for multiple parallel transformers.

[0041] The residual magnetic induction intensity calculation module is used to calculate the residual magnetic induction intensity of each transformer in the parallel transformer in the excitation inrush current suppression control system model of multiple parallel transformers, based on the preset opening voltage phase angle of the main control gate.

[0042] The switching module is used to calculate the closing time based on the residual magnetic induction intensity of each transformer in the parallel transformer, and to complete the inrush current suppression control of multiple parallel transformers.

[0043] An exemplary embodiment of this disclosure provides a method for suppressing inrush current in multiple parallel transformers. The method includes: establishing an inrush current suppression topology for multiple parallel transformers based on the parallel transformers, current-limiting resistors, and the connection relationship of the main control gate; calculating the resistance value of the current-limiting resistors based on the equivalent impedance of the high-voltage windings and the equivalent resistance of the lines of each transformer in the parallel transformers; calculating the residual magnetic induction intensity of each transformer in the parallel transformers based on the preset opening voltage phase angle of the main control gate in the multi-parallel transformer inrush current suppression control system model; and calculating the closing time based on the residual magnetic induction intensity of each transformer in the parallel transformers, thereby completing the inrush current suppression control for multiple parallel transformers. This disclosure analyzes the suppression of inrush current through the topology of multiple parallel transformers, calculates the current-limiting resistors in the topology, determines the phase closing time of each phase, reduces closing impact, and extends transformer life.

[0044] It should be understood that the above general description and the following detailed description are exemplary and explanatory only, and are not intended to limit this disclosure. Attached Figure Description

[0045] The above and other features and advantages of this disclosure will become more apparent from the detailed description of exemplary embodiments thereof with reference to the accompanying drawings.

[0046] Figure 1 A flowchart is shown below for a method for suppressing inrush current of multiple transformers connected in parallel according to an exemplary embodiment of the present disclosure;

[0047] Figure 2 The diagram shows an overall wiring diagram for energy saving in a photovoltaic power plant, illustrating a method for suppressing inrush current of multiple parallel transformers according to an exemplary embodiment of this disclosure.

[0048] Figure 3 The diagram shows the main control circuit of a method for suppressing inrush current of multiple parallel transformers according to an exemplary embodiment of the present disclosure;

[0049] Figure 4 The diagram shows a circuit diagram of four transformers closing in a method for suppressing inrush current of multiple transformers in parallel, according to an exemplary embodiment of the present disclosure.

[0050] Figure 5 The diagram illustrates a logic diagram of a control strategy for switching on / off unloaded transformers based on phase selection and switching, according to an exemplary embodiment of the present disclosure, for a method for suppressing inrush current in multiple parallel transformers.

[0051] Figure 6 A schematic block diagram of a multi-parallel transformer inrush current suppression control device is shown according to an exemplary embodiment of the present disclosure. Detailed Implementation

[0052] Exemplary embodiments will now be described more fully with reference to the accompanying drawings. However, these exemplary embodiments can be implemented in many forms and should not be construed as limited to the embodiments set forth herein; rather, they are provided so that this disclosure will be thorough and complete, and will fully convey the concept of the exemplary embodiments to those skilled in the art. The same reference numerals in the drawings denote the same or similar parts, and therefore repeated descriptions of them will be omitted.

[0053] Furthermore, the described features, structures, or characteristics can be combined in any suitable manner in one or more embodiments. Numerous specific details are provided in the following description to give a thorough understanding of embodiments of this disclosure. However, those skilled in the art will recognize that the technical solutions of this disclosure can be practiced without one or more of the specific details described, or other methods, components, materials, apparatuses, steps, etc., can be employed. In other instances, well-known structures, methods, apparatuses, implementations, materials, or operations are not shown or described in detail to avoid obscuring various aspects of this disclosure.

[0054] The block diagrams shown in the accompanying drawings are merely functional entities and do not necessarily correspond to physically independent entities. That is, these functional entities can be implemented in software, or in one or more software-hardened modules, or in different network and / or processor devices and / or microcontroller devices.

[0055] In this example embodiment, a method for suppressing and controlling inrush current of multiple parallel transformers is first provided; refer to Figure 1 As shown, the method for suppressing and controlling inrush current of multiple transformers connected in parallel may include the following steps:

[0056] Step S110: Establish a topology for suppressing inrush current of multiple parallel transformers based on the connection relationship of parallel transformers, current limiting resistors, and main control gates; and calculate the resistance value of the current limiting resistor based on the equivalent impedance of the high-voltage winding of each transformer in the parallel transformers and the equivalent resistance of the line, thereby completing the modeling of the inrush current suppression control system for multiple parallel transformers.

[0057] Step S120: In the multi-parallel transformer inrush current suppression control system model, the residual magnetic induction intensity of each transformer in the parallel transformer is calculated according to the preset opening voltage phase angle of the main control gate.

[0058] Step S130: Calculate the closing time based on the residual magnetic induction intensity of each transformer in the parallel transformers, and complete the inrush current suppression control of multiple parallel transformers.

[0059] An exemplary embodiment of this disclosure provides a method for suppressing inrush current in multiple parallel transformers. The method includes: establishing an inrush current suppression topology for multiple parallel transformers based on the parallel transformers, current-limiting resistors, and the connection relationship of the main control gate; calculating the resistance value of the current-limiting resistors based on the equivalent impedance of the high-voltage windings and the equivalent resistance of the lines of each transformer in the parallel transformers; calculating the residual magnetic induction intensity of each transformer in the parallel transformers based on the preset opening voltage phase angle of the main control gate in the multi-parallel transformer inrush current suppression control system model; and calculating the closing time based on the residual magnetic induction intensity of each transformer in the parallel transformers, thereby completing the inrush current suppression control for multiple parallel transformers. This disclosure analyzes the suppression of inrush current through the topology of multiple parallel transformers, calculates the current-limiting resistors in the topology, determines the phase closing time of each phase, reduces closing impact, and extends transformer life.

[0060] The following will further explain a method for suppressing inrush current of multiple transformers in parallel in this example embodiment.

[0061] Example 1:

[0062] In step S110, a topology for suppressing inrush current of multiple parallel transformers can be established based on the connection relationship of parallel transformers, current-limiting resistors, and main control gates. The resistance value of the current-limiting resistor is calculated based on the equivalent impedance of the high-voltage winding of each transformer in the parallel transformers and the equivalent resistance of the line, thus completing the modeling of the inrush current suppression control system for multiple parallel transformers.

[0063] In this example embodiment, the method further includes:

[0064] A topology for suppressing inrush current of multiple parallel transformers is established based on the connection relationships of parallel transformers, current-limiting resistors, and main control gates. The resistance value of the current-limiting resistor is calculated based on the equivalent impedance of the high-voltage windings and the equivalent resistance of the line in each of the parallel transformers.

[0065]

[0066] Among them, R z R is the resistance value of the current-limiting resistor. s R is the equivalent resistance of the line. iω is the equivalent impedance of the high-voltage winding of each transformer in the parallel transformer, ω is the grid frequency, and L is the equivalent inductance of the high-voltage winding of each transformer in the parallel transformer.

[0067] In this example embodiment, the total installed capacity of the rooftop distributed photovoltaic power generation project is 8MWp, and the rooftop photovoltaic panels occupy an area of ​​360m*240m; there are a total of 8 dual-split grid-connected transformers, each with a capacity of 1000kVA, a transformation ratio of 10.5kV / 0.315kV / 0.315kV, and a structure of D / y11 / y11; each 1MWp photovoltaic panel is connected to one photovoltaic inverter through multiple combiner boxes, each photovoltaic inverter is connected to one dual-split grid-connected transformer, and the high-voltage side of every 4 grid-connected transformers is connected to the 10kV power grid via the same feeder.

[0068] In this example embodiment, phase-selective switching technology is employed. The control system optimizes the calculation of the pre-induced magnetic flux and residual magnetism in the iron core, and switches the transformer when both are equal, effectively reducing inrush current. Switching is performed when the load current is near zero, reducing the impact of induced voltage on load overvoltage, thus reducing electrical wear on the circuit breaker contacts and extending the maintenance cycle and service life of the circuit breaker equipment. The overall wiring diagram of the 10kV system for switching unloaded transformers based on phase-selective switching is shown below. Figure 2 The area within the dashed box represents the phase selection and switching structure, the control system, and the communication equipment between the control system and the host computer.

[0069] In step S120, the residual magnetic induction intensity of each transformer in the parallel transformers can be calculated in the multi-parallel transformer induction current suppression control system model according to the preset opening voltage phase angle of the main control gate.

[0070] In this example embodiment, the method further includes:

[0071] In the model of the inrush current suppression control system for multiple parallel transformers, based on the voltage phase angle during the pre-opening of the main control gate, and using... Calculate the residual magnetic induction intensity B of each transformer in the parallel transformers;

[0072] Among them, U s β represents the high-voltage side voltage of each transformer in the parallel transformer, β represents the voltage phase angle when the main control switch is opened in sequence, N represents the turns ratio of each transformer in the parallel transformer, and S represents the cross-sectional area of ​​the core of each transformer in the parallel transformer.

[0073] In this example embodiment, when a three-phase transformer group consisting of three single-phase transformers is used in the system modeling, since the secondary winding systems of each phase are independent of each other, the excitation current of each phase is numerically equal. A symmetrical single-phase excitation current will flow through the primary winding accordingly, generating a symmetrical three-phase main magnetic flux that varies according to the positive direction.

[0074]

[0075] Phase correlation strategy analysis

[0076] When a three-phase symmetrical voltage is applied to the primary winding, the three-phase magnetic flux is also symmetrical, therefore

[0077]

[0078] When the residual magnetism of all three phases of the transformer is 0, according to the closing principle, the optimal closing point for phase A is when the pre-induced magnetic flux is 0, which is also the peak voltage point of phase A. After phase A is closed, the change in magnetic flux in the core of phase A is:

[0079]

[0080] Therefore, the pre-induced magnetic flux of phases B and C is:

[0081]

[0082] In step S130, the closing time can be calculated based on the residual magnetic induction intensity of each transformer in the parallel transformers, thereby completing the inrush current suppression control of multiple parallel transformers.

[0083] In this example embodiment, the method further includes:

[0084] The closing time is calculated based on the residual magnetic induction intensity of each transformer in the parallel transformer system.

[0085]

[0086] Where, φ γ =BS is the remanent magnetic flux, φ m The induced magnetic flux at the moment of closing;

[0087] Phase A is closed at the specified closing time.

[0088] In this example embodiment, the method further includes:

[0089] After closing phase A at the specified closing time, phases B and C are closed 1 / 4 of a grid frequency cycle after phase A is closed, thus completing the inrush current suppression control of multiple parallel transformers.

[0090] In this example embodiment, the method further includes:

[0091] In the model of the inrush current suppression control system for multiple parallel transformers, the residual magnetic induction intensity of each transformer in the parallel transformers is calculated based on the preset opening voltage phase angle of the main control gate.

[0092] The high-precision fast phase-locked loop (PLL) technology based on dq coordinate transformation samples the three-phase phase voltage of the bus in the excitation inrush current suppression control system model of the multiple parallel transformers to obtain the phase of the three-phase voltage.

[0093] The closing time is calculated based on the residual magnetic induction intensity and three-phase voltage phase of each transformer in the parallel transformer, and the inrush current suppression control of multiple parallel transformers is completed.

[0094] In this example embodiment, the method further includes:

[0095] In the model of the inrush current suppression control system for multiple parallel transformers, the residual magnetic induction intensity of each transformer in the parallel transformers is calculated based on the preset closing voltage phase angle of the main control gate.

[0096] The tripping time is calculated based on the residual magnetic induction intensity of each transformer in the parallel transformer, and the inrush current suppression control of multiple parallel transformers is completed.

[0097] In this example embodiment, according to the phase selection closing principle, the circuit is closed at the moment when the pre-induced magnetic flux and the dynamic induced magnetic flux are equal. The magnetic fluxes of phases B and C will not undergo abrupt changes to generate transient magnetic flux. Therefore, after phase A is closed and brought to 1 / 4 of the power frequency cycle:

[0098]

[0099] At this point, the transient magnetic flux of phases B and C is zero. Therefore, phases B and C are switched off at 1 / 4 of the power frequency cycle after phase A is switched on. Based on the inductive magnetic flux, phases B and C can achieve a smooth, shock-free transition without the generation of transient magnetic flux. The magnetic flux of each phase then enters a steady state according to the system voltage change pattern, thus avoiding core flux saturation and achieving the goal of suppressing inrush current.

[0100] Example 2:

[0101] In this example embodiment, based on the on-site installation conditions of the photovoltaic power station, four GZB-12 / 0.315-1000 box-type transformers form one grid-connected feeder, for a total of two sets. Considering the complexity of construction during the project renovation and the power consumption of on-site equipment, phase-selective switching devices need to be installed on each of the two feeder sets. The bus voltage is 10kV, and each set consists of four Taikai GZB-12 / 0.315-1000 box-type transformers. Therefore, the total capacity of each feeder transformer is 1000kVA * 4 = 4MVA, and the rated current of the bus is approximately 230A. Considering both reliability and cost, and to highlight economic performance, the main control circuit diagram is as follows. Figure 3 As shown.

[0102] In this example embodiment, the parameter design includes: based on the calculated bus rated current of approximately 230A from the previous section, circuit breaker QS3 can be selected as the IR1 / XK-12 intelligent phase control system manufactured by Ruiyi Intelligent Control Equipment Wuxi Branch; QS3 can be selected as 10kV / 630A; the switch has sufficient margin; the inrush current during transformer no-load switching can reach 6 to 8 times the rated current (1380A to 1840A), and after 0.5 to 1 second, its value is usually 0.25 to 0.5 times the rated current. For large-capacity transformers, its total decay time may reach tens of seconds. The circuit diagram for the four transformers closing is shown below. Figure 4 As shown. Where R z R is a current-limiting resistor. s Let T1, T2, T3, and T4 be the equivalent resistance of the line, and T4 be the equivalent resistance of the high-voltage windings of the four transformers in the same feeder group. R1, L1, R2, L2, R3, L3, and R4, L4 are the equivalent impedances of the high-voltage windings of these four transformers. If the added resistance Rz is too large, it will lead to a large magnetic flux after K is closed, resulting in a large short-circuit current. Therefore, only when the magnetic flux after K is closed is it equal to the magnetic flux at the moment of closing the circuit breaker to obtain an optimal resistance that minimizes the current. Current-limiting resistor Rz z The optimal value can be obtained by the following formula.

[0103]

[0104] In this example embodiment, the system function and control strategy—the shockless phase selection opening and closing control strategy—includes that the transformer inrush current during no-load closing is mainly composed of the initial phase angle α of the voltage at the moment of closing and the residual magnetism φ at the time of the last opening. r The decision is made when there is no residual magnetism in the core of the transformer during no-load switching. The inrush current is only related to the initial phase angle α of the voltage at the time of switching. When the initial phase angle α = 90°, the induced magnetic flux in the core is 0, which is the optimal closing time when there is zero residual magnetism. When the residual magnetism of the transformer during no-load switching is not zero, it is necessary to first calculate the magnitude and direction of the residual magnetism through the sampled data, and then calculate the optimal closing time based on the residual magnetism. The residual magnetism of the transformer is related to the voltage phase angle β at the previous switching. Assuming that the cross-sectional area of ​​the transformer core is S, the residual magnetic induction intensity B can be obtained by formula (7).

[0105]

[0106] The optimal closing time when the residual magnetism is non-zero can be obtained from formula 7).

[0107]

[0108] φ m ω represents the induced magnetic flux at the moment of closing the circuit breaker, and ω is the power grid frequency.

[0109] Similarly, in order to achieve shock-free tripping, the optimal tripping time is first calculated, and then the tripping is completed according to the phase selection strategy.

[0110] In this example embodiment, a small-value current-limiting resistor is connected in series at the phase-selective trip switch position, such as... Figure 2 The "current-limiting resistor R" within the dashed box can avoid the influence of the dispersion of system opening and closing times. Another key to achieving phase-selective opening and closing lies in the extraction of voltage and current zero points. Conventional methods using hardware zero-crossing comparators are significantly affected by comparator offset voltage, harmonics, and white noise. To accurately calculate residual magnetism and the optimal closing time, this solution employs a high-precision fast phase-locked loop (PLL) technology based on dq coordinate transformation. The fast switching control strategy based on phase-selective opening and closing is as follows: Figure 5 As shown.

[0111] In this example embodiment, the system employs a host computer system controlled by RS-485 communication. It uses the Modbus communication protocol to communicate with the host computer (touchscreen), correctly receiving and processing commands sent by the host computer. It records in real-time electrical quantities such as bus voltage, line voltage, line current, closing signal timing, and switch action timing for analyzing closing phase and switch action delay. The host computer system records and corrects any problems that may occur during the closing process.

[0112] It should be noted that although the steps of the method in this disclosure are described in a specific order in the accompanying drawings, this does not require or imply that the steps must be performed in that specific order, or that all the steps shown must be performed to achieve the desired result. Additional or alternative steps may be omitted, multiple steps may be combined into one step, and / or a step may be broken down into multiple steps.

[0113] Furthermore, in this example embodiment, a device for suppressing inrush current of multiple parallel transformers is also provided. (Refer to...) Figure 6 As shown, the inrush current suppression control device 600 for multiple parallel transformers may include: a system modeling module 610, a residual magnetic induction intensity calculation module 620, and a switching module 630. Wherein:

[0114] The system modeling module 610 is used to establish the inrush current suppression topology of multiple parallel transformers based on the connection relationship of parallel transformers, current limiting resistors and main control gates, and to calculate the resistance value of the current limiting resistor based on the equivalent impedance of the high-voltage side winding of each transformer in the parallel transformers and the equivalent resistance of the line, so as to complete the modeling of the inrush current suppression control system of multiple parallel transformers.

[0115] The residual magnetic induction intensity calculation module 620 is used to calculate the residual magnetic induction intensity of each transformer in the parallel transformer in the excitation inrush current suppression control system model of multiple parallel transformers, based on the preset opening voltage phase angle of the main control gate.

[0116] The switching module 630 is used to calculate the closing time based on the residual magnetic induction intensity of each transformer in the parallel transformer, and to complete the inrush current suppression control of multiple parallel transformers.

[0117] The specific details of each of the above-mentioned multiple parallel transformer inrush current suppression control device modules have been described in detail in the corresponding multiple parallel transformer inrush current suppression control method, so they will not be repeated here.

[0118] It should be noted that although several modules or units of a multi-parallel transformer inrush current suppression control device 600 have been mentioned in the detailed description above, this division is not mandatory. In fact, according to embodiments of this disclosure, the features and functions of two or more modules or units described above can be embodied in one module or unit. Conversely, the features and functions of one module or unit described above can be further divided and embodied by multiple modules or units.

[0119] Furthermore, the above figures are merely illustrative of the processes included in the method according to exemplary embodiments of the present invention, and are not intended to be limiting. It is readily understood that the processes shown in the above figures do not indicate or limit the temporal order of these processes. Additionally, it is readily understood that these processes may be executed synchronously or asynchronously, for example, in multiple modules.

[0120] Other embodiments of this disclosure will readily occur to those skilled in the art upon consideration of the specification and practice of the invention disclosed herein. This application is intended to cover any variations, uses, or adaptations of this disclosure that follow the general principles of this disclosure and include common knowledge or customary techniques in the art not disclosed herein. The specification and embodiments are to be considered exemplary only, and the true scope and spirit of this disclosure are indicated by the claims.

[0121] It should be understood that this disclosure is not limited to the precise structures described above and shown in the accompanying drawings, and various modifications and changes can be made without departing from its scope. The scope of this disclosure is limited only by the appended claims.

Claims

1. A method for suppressing and controlling inrush current of multiple transformers connected in parallel, characterized in that, The method includes: A topology for suppressing inrush current in multiple parallel transformers is established based on the connection relationships of parallel transformers, current-limiting resistors, and main control switches. The resistance value of the current-limiting resistor is calculated based on the equivalent impedance of the high-voltage windings and the equivalent resistance of the line in each of the parallel transformers, thus completing the modeling of the inrush current suppression control system for multiple parallel transformers. ;in, R z The resistance value of the current-limiting resistor. R s The equivalent resistance of the line. R i The equivalent impedance of the high-voltage winding of each transformer in the parallel transformer is given. ω For the power grid frequency, L The equivalent inductance of the high-voltage winding of each transformer in the parallel transformer; In a multi-parallel transformer inrush current suppression control system model, the residual magnetic induction intensity of each transformer in the parallel transformers is calculated based on the preset opening voltage phase angle of the main control gate; in a multi-parallel transformer inrush current suppression control system model, the residual magnetic induction intensity of each transformer in the parallel transformers is calculated based on the voltage phase angle when the main control gate is opened in sequence. Calculate the residual magnetic induction intensity B of each transformer in the parallel transformer system; where, U s The voltage on the high-voltage side of each transformer in the parallel transformer system is given. β The voltage phase angle during the pre-operational tripping of the main control gate. N The turns ratio of each transformer in the parallel transformer system is given. S The cross-sectional area of ​​the core of each transformer in the parallel transformers; The closing time is calculated based on the residual magnetic induction intensity of each transformer in the parallel transformer system to achieve inrush current suppression control for multiple parallel transformers. in, =BS This is the remanent magnetic flux. The induced magnetic flux at the closing moment; the A phase is closed at the closing moment.

2. The method as described in claim 1, characterized in that, The method further includes: After closing phase A at the specified closing time, phases B and C are closed 1 / 4 of a grid frequency cycle after phase A is closed, thus completing the inrush current suppression control of multiple parallel transformers.

3. The method as described in claim 1, characterized in that, The method further includes: In the model of the inrush current suppression control system for multiple parallel transformers, the residual magnetic induction intensity of each transformer in the parallel transformers is calculated based on the preset opening voltage phase angle of the main control gate. The high-precision fast phase-locked loop (PLL) technology based on dq coordinate transformation samples the three-phase phase voltage of the bus in the excitation inrush current suppression control system model of the multiple parallel transformers to obtain the phase of the three-phase voltage. The closing time is calculated based on the residual magnetic induction intensity and three-phase voltage phase of each transformer in the parallel transformer, and the inrush current suppression control of multiple parallel transformers is completed.

4. The method as described in claim 1, characterized in that, The method further includes: In the model of the inrush current suppression control system for multiple parallel transformers, the residual magnetic induction intensity of each transformer in the parallel transformers is calculated based on the preset closing voltage phase angle of the main control gate. The tripping time is calculated based on the residual magnetic induction intensity of each transformer in the parallel transformer, and the inrush current suppression control of multiple parallel transformers is completed.

5. A device for suppressing and controlling inrush current of multiple transformers connected in parallel, characterized in that, The device includes: The system modeling module is used to establish a topology for suppressing inrush current in multiple parallel transformers based on the connection relationships of parallel transformers, current-limiting resistors, and main control gates. It also calculates the resistance value of the current-limiting resistors based on the equivalent impedance of the high-voltage windings and the equivalent resistance of the lines of each transformer in the parallel system, thus completing the modeling of the inrush current suppression control system for multiple parallel transformers. ;in, R z The resistance value of the current-limiting resistor. R s The equivalent resistance of the line. R i The equivalent impedance of the high-voltage winding of each transformer in the parallel transformer is given. ω For the power grid frequency, L The equivalent inductance of the high-voltage winding of each transformer in the parallel transformer; The residual magnetization intensity calculation module is used to calculate the residual magnetization intensity of each transformer in a multi-parallel transformer induction current suppression control system model, based on the preset opening voltage phase angle of the main control gate; and based on the voltage phase angle during the preceding opening of the main control gate, within the multi-parallel transformer induction current suppression control system model. Calculate the residual magnetic induction intensity B of each transformer in the parallel transformer system; where, U s The voltage on the high-voltage side of each transformer in the parallel transformer system is given. β The voltage phase angle during the pre-operational tripping of the main control gate. N The turns ratio of each transformer in the parallel transformer system is given. S The cross-sectional area of ​​the core of each transformer in the parallel transformers; The switching module is used to calculate the closing time based on the residual magnetic induction intensity of each transformer in the parallel transformer system, thereby completing the inrush current suppression control of multiple parallel transformers. in, =BS This is the remanent magnetic flux. The induced magnetic flux at the closing moment; the A phase is closed at the closing moment.

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