Hybrid transformer rapid grid connection method for guaranteeing uninterruptible power supply of load

Abstract

The grid connection method is suitable for the field of connection of a low-voltage load independent power supply system into a medium-voltage power grid, and is an independent power supply system grid connection method which can give consideration to important load uninterrupted power supply and transformer starting inrush current suppression at the same time. Considering that the capacity of an energy storage battery is limited and power supply of all loads is difficult to support, the loads are divided into sensitive loads and general loads, and when a main network loses power, the energy storage battery supplies power to important loads through a hybrid transformer; in the reclosing grid connection process, the starting inrush current and time of the transformer are effectively reduced through voltage and current multi-control mode switching of a converter in the hybrid transformer device, and meanwhile uninterrupted power supply of an important load is guaranteed; and after the grid-connected starting of the passive transformer is completed, the medium-voltage power grid is switched to supply power, and a general load at a low-voltage side is put into use. According to the method, the problem that the sensitive load needs secondary power failure after the power grid loses power in a traditional power supply mode is solved, the service life of the passive transformer is effectively prolonged, and the working efficiency of the low-voltage important load is effectively improved.

Description

Technical Field

[0001] The invention of the present application is applicable to the field of stable power supply and rapid grid connection of low-voltage loads, and can be applied to rapid start-up and grid connection of transformers under independent power supply systems. It is a grid connection method for independent power supply systems that can simultaneously take into account uninterrupted power supply to important loads and transformer startup inrush current suppression. Background Art

[0002] The medium-voltage power grid supplies power to low-voltage loads through passive industrial frequency transformers. When the power grid is interrupted, the low-voltage loads often need to be powered off again. When the power grid is restored, the traditional passive transformer will directly start up, which will generate large inrush current and voltage fluctuations, affecting the stable power supply of the low-voltage loads.

[0003] In recent years, by deploying UPS uninterruptible power supplies on the low-voltage side, uninterruptible power supply to important low-voltage loads can be achieved when the power grid loses power. However, when the power grid is restored, direct excitation of the transformer by the UPS uninterruptible power supply will bring a large excitation surge current. Excessive current shock may cause the UPS power supply to trigger overcurrent protection. Therefore, under the traditional power supply method, when the power grid is restored, the UPS power supply needs to be bypassed and shut down, resulting in a secondary power outage of sensitive loads, affecting the stable power supply of important loads.

[0004] With the widespread application of new power electronic converter devices in traditional distribution networks, hybrid transformers composed of traditional passive transformers and active power electronic converters play an important role in ensuring stable power supply of low-voltage systems. The present invention is applied to the rapid grid-connection process of low-voltage loads being connected to the medium-voltage power grid through hybrid transformers. When the main grid loses power, the energy storage battery supplies power to important loads through the hybrid transformer; during the grid-connection process of reclosing, the transformer startup inrush current and time are effectively reduced by switching the voltage and current control modes of the converter in the hybrid transformer device, while ensuring uninterrupted power supply to important loads; after the passive transformer grid-connection startup is completed, it is switched to the medium-voltage power grid for power supply, and general loads on the low-voltage side are put into operation. The full grid-connection process is short, the transformer startup excitation inrush current is suppressed, and the stable power supply of important loads is guaranteed during the whole process, overcoming the problem that sensitive loads need to be shut down for a second time after the power grid loses power under the traditional power supply mode, and effectively improving the life of the passive transformer and the working efficiency of the low-voltage important loads. Summary of the invention

[0005] This application proposes a hybrid transformer grid - connection method that can simultaneously take into account the uninterrupted power supply for important loads and the suppression of transformer inrush current. Considering the limited capacity of the energy storage battery, which is difficult to support the power supply of all loads, the loads are divided into sensitive loads and general loads. When the main grid loses power, the energy storage battery supplies power to important loads through the hybrid transformer; during the reclosing grid - connection process, through the multi - control - mode switching of the voltage and current in the converter device of the hybrid transformer, while reducing the transformer inrush current, it ensures the uninterrupted power supply for important loads; after the passive transformer grid - connection is started and completed, it switches to the medium - voltage grid power supply and connects the general loads on the low - voltage side to achieve the uninterrupted power supply for low - voltage important loads throughout the process of grid power loss and restoration.

[0006] The object of the present invention is achieved by the following technical solutions: According to the voltage sensor described in claim 1, the grid voltage on the medium - voltage grid side is measured , the primary voltage of the transformer , the secondary voltage of the transformer , and the output voltage of the series converter ; according to the current sensor described in claim 1, the output current of the shunt converter is measured , and the output current of the series converter ; The controller is used to receive the voltage and current information measured by the above - mentioned sensors and accept the grid - connection instruction for the independent power supply system issued by the grid dispatching center. If the grid - connection instruction is not received, the independent power supply system operates in island mode, and the controller operates in Mode 1; when the grid - connection instruction is received, the transformer switch is closed, and the controller switches to Mode 2; when it is monitored that the primary voltage of the transformer reaches , the controller switches to Mode 3; when it is monitored that the primary voltage of the transformer meets the grid - connection conditions, the grid - side switch is closed to complete the grid - connection operation of the independent power supply system; The Mode 1 controller obtains the voltage reference required to support the low - voltage load through the load voltage generator; the shunt converter obtains the modulation voltage of the shunt converter through the voltage - current double - loop controller; the controller determines whether the grid - connection instruction is received. If so, the passive transformer start switch is closed, and the controller switches to Mode 2. If not, the controller still operates in Mode 1; The Mode 2 controller calculates the difference between the output current of the shunt converter and the output current of the series converter as the transformer - side current , obtains the secondary - side voltage reference in Mode 2 through the exciting - current outer - loop controller, and obtains the modulation voltage of the parallel power - conversion circuit in Mode 2 through the voltage - current double - loop controller described in Mode 1; The series converter calculates the amplitude of the secondary side voltage during startup The deviation from the reference value, and according to the voltage-current double-loop controller, the modulation voltage of the series converter is obtained to suppress the load voltage fluctuation caused by the direct startup of the transformer in Mode 2; The controller monitors the amplitude of the primary side voltage of the transformer through a phase-locked loop of to judge whether the excitation of the transformer is completed, and judge whether the amplitude of the primary side voltage is greater than ? If so, the controller switches from Mode 2 to Mode 3. If not, the controller still operates in Mode 2; The Mode 3 controller monitors the amplitude of the grid voltage through a phase-locked loop and phase , as well as the amplitude of the grid-connected point voltage on the primary side of the transformer and phase , and adjusts the amplitude reference value of the secondary side voltage of the transformer through closed-loop control and phase reference value ; Based on the phase reference after pre-synchronization control adjustment, the controller performs d-axis orientation on the current of the parallel converter and the secondary side voltage of the transformer, and adjusts the secondary side voltage of the transformer through the voltage-current double closed-loop controller in Mode 1 to obtain the modulation voltage of the parallel converter; The controller calculates the amplitude difference and phase difference between the grid voltage and the primary side voltage of the transformer, and judges whether both meet the grid connection conditions? If so, it issues a closing instruction for the grid-side switch , and issues a closing instruction for the general load switch . If not, it continues to execute the Mode 3 controller; Based on the d-axis components of the modulation wave of the parallel converter and the modulation wave of the series converter obtained by the controller , based on the reference phase, perform inverse transformation to obtain the modulation wave voltage of the series and parallel power circuits of the hybrid transformer, and through the sine pulse width modulator, obtain the control signals of the series and parallel power circuits.

[0007] Compared with the prior art, the beneficial effects brought by the technical solution of the present invention are: 1. By applying the technical solution proposed by the present invention, it is possible to realize the uninterrupted power supply support for important low-voltage loads during the process of integrating a low-voltage independent power supply system into a medium-voltage power grid, and there is no need to use a large-capacity energy storage battery, which reduces the equipment cost, and there is no voltage fluctuation on the low-voltage load side during the whole process; 2. Applying the technical solution proposed by the present invention can significantly reduce the inrush current brought by the direct start of a traditional power frequency transformer, reduce the transformer startup time, and improve the service life and power supply efficiency of the transformer.

[0008] 3. For the method for rapid grid connection of an independent power supply system supported by a hybrid transformer proposed by the present invention, voltage closed-loop control is adopted during the island operation of the low-voltage power supply system, and excitation current-voltage three-loop control is switched to when starting the transformer. On the premise of ensuring that the low-voltage system does not lose power, the excitation starting ability for the passive transformer is enhanced. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Legend 1 is the electrical connection structure of the hybrid transformer device for ensuring uninterrupted power supply to low-voltage loads provided by an embodiment of the present invention; Legend 2 is a schematic diagram of the implementation process of the hybrid transformer for ensuring uninterrupted power supply to loads from island operation to grid connection provided by an embodiment of the present invention; Legend 3 is the block diagram of the series and parallel converter controllers of the hybrid transformer provided by an embodiment of the present invention; Legend 4 is the timing diagram of the whole process of the hybrid transformer for ensuring uninterrupted power supply to loads from island operation to grid connection provided by an embodiment of the present invention; Legend 5 is the simulation operation effect diagram of directly closing the switch to start the passive transformer during the island operation of low-voltage loads provided by an embodiment of the present invention; Legend 6 is the simulation operation effect diagram of the whole process of grid connection of the independent power supply system supported by the hybrid transformer provided by an embodiment of the present invention; Legend 7 is the schematic diagram of the module of the embodiment of the method for grid connection of the independent power supply system supported by the hybrid transformer provided by an embodiment of the present invention; Legend 8 is the schematic diagram of the distribution network hybrid transformer device provided by an embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0010] To make the objectives, technical solutions, and advantages of this application clearer, the following will further describe this application in detail with reference to the accompanying drawings. The specific operation methods in the method embodiments can also be applied to the device embodiments or system embodiments. It should be noted that in the description of this application, "at least one" means one or more, where multiple means two or more. In view of this, in the embodiments of this application, "multiple" can also be understood as "at least two". "And / or" describes the association relationship of associated objects and indicates that there can be three relationships. For example, A and / or B can represent: A exists alone, A and B exist simultaneously, and B exists alone. In addition, the character " / ", unless otherwise specified, generally represents an "or" relationship between the associated objects before and after. In addition, it should be understood that in the description of this application, terms such as "first" and "second" are only used for the purpose of distinguishing descriptions and cannot be understood as indicating or implying relative importance, nor can they be understood as indicating or implying an order. The following further describes the present invention in detail with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0011] A reactive power and harmonic hybrid compensation system device and resonance suppression method for a distribution network proposed by the present invention include the following steps: Please refer to FIGURE 1. An electrical connection structure of a hybrid transformer device for ensuring uninterrupted power supply to a low-voltage load, characterized by including: a grid-connected switch, a power-frequency passive transformer, a transformer switch, a parallel converter, an energy storage battery, a series converter, a series coupling transformer, a filter bank, a current sensor, a voltage sensor, and a controller; The primary coil of the power-frequency passive transformer is connected to the medium-voltage grid through the grid-connected switch, and the secondary coil is connected to the converter end through the transformer start switch. One end of the parallel converter and the series converter is connected to the controller, and the other end is connected to the filter bank through the current sensor. The other ends of the filters are all connected to the secondary coil of the transformer. One end of the primary coil of the series transformer is connected to the power-frequency transformer, and the other end is connected to the load-side switch. At the same time, voltage sensors are installed on the grid side, the primary and secondary sides of the power-frequency transformer, and the output side of the series converter.

[0012] Please refer to FIGURE 2. A fast grid connection method for a hybrid transformer to ensure uninterrupted power supply to a load, including: Step S201: Measure the grid voltage on the medium-voltage grid side, the primary voltage of the transformer, the secondary voltage of the transformer, and the output voltage of the series converter according to the voltage sensor described in claim 1; measure the output current of the parallel converter according to the current sensor described in claim 1. 、the primary voltage of the transformer 、the secondary voltage of the transformer and the output voltage of the series converter ; measure the output current of the parallel converter according to the current sensor described in claim 1. , and the output current of the series converter ; Please refer to FIG. 3. The block diagram of the series and parallel converter controller of the hybrid transformer for a distribution network provided by an embodiment of the present invention includes: Step S202: The controller receives the voltage and current information measured by the above sensors. When no grid connection command is received, the independent power supply system operates in island mode, and the controller operates in Mode 1. The voltage amplitude reference of the parallel converter is the required reference voltage on the load side , and the phase reference is obtained by integrating the reference frequency , where . According to the obtained reference phase of the parallel converter, the secondary side voltage and the output current of the parallel converter are subjected to coordinate transformation to obtain the corresponding axis components; The parallel converter obtains the current inner loop axis reference and through the secondary side voltage outer loop controller, as shown in the following formula: (1) where are the proportional and integral coefficients of the secondary side voltage outer loop controller, are the d-axis and q-axis components of the transformer secondary side voltage respectively; After that, through the current inner loop controller, the modulation voltage axis reference and when the parallel converter operates independently for power supply are obtained, as shown in the following formula: (2) where is the proportional coefficient of the current inner loop controller, is the active damping coefficient to reduce the risk of system oscillation.

[0013] Step S203: The controller determines whether a grid connection command is received. If so, it issues a closing command for the closing switch , and the controller switches to Mode 2. If not, the controller still operates in Mode 1; Step S204: The Mode 2 controller calculates the difference between the output current of the parallel converter and the local load current as the exciting current of the transformer. According to the reference phase of the parallel converter, the exciting current of the transformer is subjected to coordinate transformation to obtain the corresponding Axis component; By enabling the excitation current outer-loop controller, the reference value of the output voltage of the parallel converter when the transformer is directly connected is obtained, as shown in the following formula: (3) Wherein, are the proportional and integral coefficients of the excitation current outer-loop controller, is the reference value of the excitation current required for the direct connection of the power frequency transformer, which is positively correlated with the transformer capacity, is the rated capacity of the transformer, is the effective value of the reference voltage of the medium-voltage power grid, is the d-axis component of the excitation current, is the reference voltage of the independent power supply system; then, through the voltage-current double-loop controller described in Mode 1, the modulation voltage in Mode 2 of the parallel power conversion circuit is obtained.

[0014] Step S205: According to the reference phase of the secondary-side voltage, perform coordinate transformation on the output voltage and the output current of the series converter to obtain the corresponding axis component. The series converter calculates the difference between the secondary-side voltage and the reference voltage as the voltage reference that the series converter needs to compensate, as shown in the following formula: (4) Wherein, is the reference of the output voltage of the series converter; After that, through the voltage outer-loop controller, the d-axis reference and q-axis reference of the current inner-loop of the series converter are obtained, as shown in the following formula: (5) Wherein, are the proportional and integral coefficients of the voltage outer-loop of the series converter, are the d-axis and q-axis components of the output voltage of the series converter respectively; After that, through the current inner-loop controller, the modulation wave d-axis reference and q-axis reference (5) Wherein, is the proportional coefficient of the current inner-loop, are the d-axis and q-axis components of the output current of the series converter respectively.

[0015] Step S206: The controller monitors the amplitude of the primary voltage of the transformer through a phase-locked loop of the transformer to determine whether the excitation of the transformer is completed, and to determine whether the amplitude of the primary voltage is greater than ? If so, the controller switches from Mode 2 to Mode 3; if not, the controller remains operating in Mode 2; Step S207: The Mode 3 controller monitors the amplitude and phase of the grid voltage through a phase-locked loop, as well as the amplitude and phase of the voltage at the primary grid connection point of the transformer, and adjusts the amplitude reference value and phase reference value of the secondary voltage of the transformer through closed-loop control; (6) wherein, are the proportional and integral coefficients of the phase regulator, are the proportional and integral coefficients of the amplitude regulator, is the cut-off frequency of the low-pass filter; According to the deviation obtained in the pre-synchronization link, adjust the amplitude reference and phase reference of the secondary voltage of the transformer, as shown in the following formula: (7).

[0016] Step S208: Based on the phase reference adjusted by the pre-synchronization control, perform d-q axis orientation on the current of the parallel converter and the secondary voltage of the transformer, and adjust the secondary voltage of the transformer through the voltage-current double closed-loop controller in Mode 1 to obtain the modulation voltage in Mode 3 of the parallel converter.

[0017] Step S209: The controller calculates the amplitude difference and phase difference between the grid voltage and the primary voltage of the transformer, and determines whether both meet the grid connection conditions? If so, issue a closing instruction for the grid-side switch , and issue a closing instruction for the general load switch ; if not, continue to execute the Mode 3 controller.

[0018] Step S210: According to a hybrid transformer flexible reclosing grid connection method described in claim 2, characterized in that it includes the following steps: The controller is based on the modulation wave of the parallel power conversion circuit and the modulation wave of the series power conversion circuit obtained The axial component, based on the reference phase of the secondary side voltage of the transformer, obtains the modulated wave voltage of the series and parallel power circuits of the hybrid transformer. Through the sine pulse width modulator, the control signal of the series and parallel power circuits of the hybrid transformer is obtained.

[0019] Figure 5 is the simulation operation effect diagram of the direct switching-on start of the passive transformer during the island operation of the low-voltage load provided by the embodiment of the present invention; it can be seen that When directly switching on at a certain moment and putting the transformer into operation, the voltage of the low-voltage load fluctuates greatly, and it takes a certain time to recover stability, and the inrush current reaches close to which will cause the power supply to stop due to overcurrent protection and will also affect the life of the transformer at the same time.

[0020] Figures 6(a) and 6(b) are the simulation operation effect diagrams of the whole process of grid connection of the independent power supply system supported by the hybrid transformer provided by the embodiment of the present invention. From Figure 6 (a), it can be seen that: Before the transformer is put into operation, the low-voltage system operates in island mode. The secondary side voltage of the transformer is the reference value. The load current is the same as the output current of the parallel converter, and the important load is powered by the energy storage battery; When the transformer is put into operation at a certain moment, the secondary side voltage fluctuates, and it returns to the reference value around a certain time, completing the pre-synchronization adjustment. At the same time, the current of the important load is while the exciting current is only effectively suppressing the inrush current during the direct start of the transformer; After completing the grid connection startup process, close the grid side switch and the load is powered by the medium-voltage power grid.

[0021] From Figure 6 (b), it can be seen that during the whole process of grid connection, the voltage on the low-voltage load side always remains stable. When closing the general load switch at a certain moment, the supply voltage still has no obvious fluctuation, verifying the effectiveness of the method for rapid grid connection of the hybrid transformer for ensuring uninterrupted power supply to the load proposed by the present invention. The whole grid connection process takes a short time, the inrush current during the start of the transformer is suppressed, and at the same time, the stable power supply of the important load is ensured throughout the process.

[0022] The present invention is not limited to the embodiments described above. The above description of the specific embodiments is intended to describe and illustrate the technical solutions of the present invention. The above specific embodiments are merely illustrative and not restrictive. Without departing from the spirit of the present invention and the scope protected by the claims, those of ordinary skill in the art can make many specific transformations in various forms under the inspiration of the present invention, and these all fall within the protection scope of the present invention.

[0023] It should be understood that the sequence numbers of the steps in the above embodiments do not indicate the order of execution, and the execution order of each process should be determined according to its function and internal logic, and should not constitute any limitation to the implementation process of the embodiments of the present invention.

[0024] As shown in Example 8, a method for rapid grid connection of a hybrid transformer for ensuring uninterrupted power supply to a load in the middle includes: A first acquisition module 701, according to the voltage sensor, acquires the grid voltage, the primary voltage of the transformer, the secondary voltage, and the output voltage of the series converter, and according to the current sensor, acquires the output currents of the parallel converter and the series converter, and receives a grid connection instruction issued by the grid dispatching center; A second acquisition module 702, when the hybrid transformer operates in the island mode, according to the reference voltage reference, through the voltage-current double closed-loop controller, obtains the modulation voltage of the parallel converter in mode 1; A second determination module 703, according to whether a grid connection instruction is received, determines whether the parallel converter of the hybrid transformer changes its operating mode; A third determination module 704, according to the difference between the output currents of the parallel converter and the series converter, determines the starting current of the transformer, corrects the voltage reference of the parallel converter in mode 2 through the excitation current outer-loop controller, and obtains the modulation voltage of the parallel converter in mode 2 through the controller in mode 1; A third acquisition module 705, according to the amplitude difference between the secondary voltage and the reference voltage when the transformer is put into operation, as the voltage reference of the series converter, obtains the modulation voltage of the series converter in mode 2 through the voltage controller; A fourth determination module 706, according to whether the primary voltage amplitude is greater than 0.8 p.u., determines whether the converter switches to mode 3; A fourth acquisition module 707, for according to the monitored grid voltage, the amplitude difference and phase difference of the primary voltage of the transformer, through the pre-synchronization controller, obtains the voltage amplitude reference and phase reference of the parallel converter in mode 3; A fifth determination module 708, according to whether the amplitude difference and phase difference between the grid and the primary voltage are less than the threshold value, determines whether the grid connection condition is satisfied; A fifth acquisition module 709, if the grid connection condition is satisfied, then obtains the closing instructions of the grid-side switch and the load switch, closes the grid-side switch and the general load switch, and completes the grid connection of the hybrid transformer and the stable power supply to the low-voltage load.

[0025] Example 8 is a schematic diagram of a method for rapid grid connection of a hybrid transformer for ensuring uninterrupted power supply to a load in the middle provided by an embodiment of the present invention.

[0026] The schematic diagram of the hybrid transformer device with an energy storage system is shown in Example 8, including: a converter 801, a controller 802, a memory 803, and a computer program 804 stored in the memory 803 and executable on the controller 802. When the controller 802 executes the computer program 804, it implements the steps in the embodiment of the above resonant suppression method, such as Figure 2 the steps S201 to S208 shown. Alternatively, when the controller 802 executes the computer program 804, it implements the power of each module / unit in the above embodiment, such as the functions of modules 701 to 708 shown in Example 7.

[0027] Exemplarily, the computer program 804 can be divided into one or more modules / units. The one or more modules / units are stored in the memory 803 and executed by the controller 802 to complete the embodiment of the present invention. The one or more modules / units can be a series of computer program instruction segments capable of performing specific functions, and these instruction segments are used to describe the execution process of the computer program 804 in the reactive power and harmonic hybrid compensation system device. For example, the computer program 804 can be divided into a first acquisition module, a first determination module, a second determination module, a second acquisition module, a third determination module, a fourth determination module, a fifth determination module, and a third acquisition module. The functions of each module are as follows: The first acquisition module obtains the grid voltage, the primary side voltage of the transformer, the secondary side voltage, and the output voltage of the series converter according to the voltage sensor, obtains the output currents of the shunt converter and the series converter according to the current sensor, and receives the grid connection instruction issued by the grid dispatching center; The second acquisition module is used to obtain the modulation voltage of the shunt converter in mode 1 according to the reference voltage reference; The second determination module is used to determine the operating mode of the shunt converter of the hybrid transformer according to whether the grid connection instruction is received; The third determination module is used to determine the starting current of the transformer according to the difference between the output currents of the shunt converter and the series converter, and correct the voltage reference of the shunt converter in mode 2 through the excitation current outer loop controller; The third acquisition module is used to use the amplitude difference between the secondary side voltage and the reference voltage when the transformer is put into operation as the voltage reference of the series converter, and obtain the modulation voltage of the series converter in mode 2 through the voltage controller; The fourth determination module is used to determine whether the converter switches to mode 3 according to whether the primary side voltage amplitude is greater than 0.8 p.u; The fourth acquisition module is used to obtain the voltage amplitude reference and phase reference of the shunt converter in mode 3 through the pre-synchronization controller according to the monitored grid voltage, the amplitude difference and phase difference of the primary side voltage of the transformer; A fifth determination module, configured to determine whether the grid connection condition is satisfied according to whether the amplitude difference and phase difference between the power grid and the primary side voltage are less than a threshold value; A fifth acquisition module, if the grid connection condition is satisfied, acquires closing instructions for the grid-side switch and the load switch, closes the grid-side switch and the general load switch, and completes the grid connection of the hybrid transformer and the stable power supply for the low-voltage load.

[0028] The method for fast grid connection of a hybrid transformer for ensuring uninterrupted power supply to a load may include, but is not limited to, a converter 801, a controller 802, and a memory 803. Those skilled in the art can understand that the legend 8 is only an example of a hybrid transformer device with an energy storage system, and does not constitute a limitation on the hybrid transformer device with an energy storage system. It may include more or fewer components than shown in the figure, or combine certain components, or different components. For example, the life evaluation terminal device of the power transformer may further include input / output devices, network access devices, a bus, etc.

[0029] The so-called controller 802 may be a central processing unit (CPU), or may also be other general-purpose processors, digital signal processors (DSPs), application specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. The general-purpose processor may be a microprocessor or the processor may also be any conventional processor, etc.

[0030] The memory 803 may be an internal storage unit of the hybrid transformer device with an energy storage system, such as an external memory circuit of the hybrid transformer device with an energy storage system. For example, a plug-in hard disk, a smart media card (SMC), a secure digital (SD) card, a flash card, etc. equipped on the hybrid transformer device. Further, the memory 803 may also include both the internal storage unit of the hybrid compensation system device and an external storage device. The memory 803 is used to store the computer program and other programs and data required by the hybrid transformer device with an energy storage system. The memory 803 may be used to temporarily store data that has been output or is to be output.

[0031] Those skilled in the art can clearly understand that, for the convenience and conciseness of description, only the above-mentioned division of each functional unit and module is used as an example. In actual applications, the above functions can be allocated to different functional units and modules as needed, that is, the internal structure of the device can be divided into different functional units or modules to complete all or part of the functions described above. Each functional unit and module in the embodiments can be integrated into a processing unit, or each unit can exist physically alone, or two or more units can be integrated into one unit. The above integrated unit can be implemented in the form of hardware or in the form of a software functional unit. In addition, the specific names of each functional unit and module are only for the convenience of mutual distinction and do not limit the protection scope of this application. The specific working processes of the units and modules in the above system can refer to the corresponding processes in the foregoing method embodiments and will not be elaborated herein.

[0032] In the above embodiments, the descriptions of the respective embodiments have their own emphases. For the parts not described in detail or recorded in a certain embodiment, reference can be made to the relevant descriptions of other embodiments.

[0033] Those of ordinary skill in the art can realize that the units and algorithm steps of each example described in combination with the embodiments disclosed herein can be implemented by electronic hardware, or by a combination of computer software and electronic hardware. Whether these functions are executed in the form of hardware or software depends on the specific application and design constraints of the technical solution. Professionals can use different methods to implement the described functions for each specific application, but such implementation should not be considered to exceed the scope of the present invention.

[0034] In the embodiments provided by the present invention, it should be understood that the disclosed device / terminal device and method can be implemented in other ways. For example, the device / terminal device embodiments described above are merely illustrative. For example, the division of the modules or units is only a logical function division, and there can be other division methods in actual implementation. For example, multiple units or components can be combined or integrated into another system, or some features can be ignored or not executed. Another point is that the displayed or discussed couplings or direct couplings or communication connections to each other can be through some interfaces. The indirect couplings or communication connections of the devices or units can be in electrical, mechanical or other forms.

[0035] The units described as separate components may or may not be physically separated, and the components displayed as units may or may not be physical units, that is, they can be located in one place or distributed to multiple network units. Some of the units can be selected according to actual needs to achieve the purpose of the solution of this embodiment.

[0036] In addition, in each embodiment of the present invention, each functional unit may be integrated into one processing unit, or each unit may exist physically alone, or two or more units may be integrated into one unit. The above integrated unit may be implemented in the form of hardware or in the form of a software functional unit.

[0037] If the integrated module / unit is implemented in the form of a software functional unit and sold or used as an independent product, it may be stored in a computer-readable storage medium. Based on such an understanding, all or part of the processes in the above-described embodiment methods of the present invention may also be completed by instructing relevant hardware through a computer program. The computer program may be stored in a computer-readable storage medium. When the computer program is executed by a processor, the steps of the above-described method embodiments may be implemented. Among them, the computer program includes computer program code, and the computer program code may be in the form of source code, object code, executable file, or some intermediate form, etc. The computer-readable medium may include: any entity or device capable of carrying the computer program code, recording medium, USB flash drive, mobile hard disk, magnetic disk, optical disc, computer memory, read-only memory (ROM), random access memory (RAM), electrical carrier signal, telecommunication signal, and software distribution medium, etc. It should be noted that the content included in the computer-readable medium may be appropriately increased or decreased according to the requirements of legislation and patent practice in the jurisdiction. For example, in some jurisdictions, according to legislation and patent practice, the computer-readable medium does not include electrical carrier signals and telecommunication signals.

[0038] The above-described embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements for some of the technical features. These modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention and should all be included in the protection scope of the present invention.

Claims

1. A hybrid transformer device composed of a passive transformer and a power electronic power converter, characterized in that, Comprising: A reclosing switch, a traditional passive transformer, a parallel converter, an energy storage battery, a series converter, a series coupling transformer, a filter bank, a current sensor, a voltage sensor and a controller; The first end of the first voltage sensor is connected to the medium-voltage power grid, and the other end is connected to the grid-side switch , one end of the second voltage sensor is connected to the grid-side switch , the other end is connected to the primary coil of the traditional passive transformer, and the secondary coil is connected to the starting switch , the other end is connected to the third voltage sensor; the first end of the parallel converter is connected to the energy storage battery, the second end is connected to the first end of the current sensor, the second end of the current sensor is connected to the first end of the filter bank, and the second end of the filter is connected to the secondary coil of the power frequency transformer; the first end of the series converter is connected to the energy storage battery, the second end is connected to the first end of the current sensor, the second end of the current sensor is connected to the first end of the filter bank, and the second end of the filter is connected to the primary coil of the series transformer; the parallel converter, the series converter are connected to the output end of the controller; one end of the series coupling transformer is connected to the third voltage sensor, the other end is connected to the important load, and is connected to the general load through the load switch ​ 2. A rapid grid connection method for a hybrid transformer to ensure uninterrupted power supply to important loads, characterized in that, Comprising: The voltage sensor according to claim 1 measures the grid voltage on the medium-voltage grid side , the primary voltage of the transformer , the secondary voltage of the transformer and the output voltage of the series converter ; The current sensor according to claim 1 measures the output current of the parallel converter , and the output current of the series converter ; The controller is used to receive the voltage and current information measured by the above sensors, and accept the grid connection instruction of the independent power supply system issued by the grid dispatching center. If the grid connection instruction is not received, the independent power supply system operates in island mode, and the controller operates in mode 1; when the grid connection instruction is received, the transformer switch is closed, and the controller switches to mode 2; when it is monitored that the primary voltage of the transformer reaches , the controller switches to mode 3; when it is monitored that the primary voltage of the transformer meets the grid connection conditions, the grid side switch is closed to complete the grid connection operation of the independent power supply system; The modal 1 controller obtains a voltage reference required to support a low-voltage load through a load voltage generator; the parallel converter obtains a modulation voltage of the parallel converter through the voltage-current double-loop controller; the controller determines whether a grid connection command is received. If so, the passive transformer starting switch is closed. , the controller switches to modal 2. If not, the controller still operates in modal 1; The modal 2 controller calculates the output current of the parallel converter and the output current of the series converter The difference is used as the transformer-side current , and through the exciting current outer-loop controller, the secondary-side voltage reference under mode 2 is obtained. Through the voltage-current double-loop controller described in mode 1, the modulation voltage of the parallel power conversion circuit under mode 2 is obtained; The amplitude of the secondary side voltage during the startup calculation of the series converter The deviation from the reference value is obtained according to the voltage-current double-loop controller, and the modulation voltage of the series converter is obtained to suppress the load voltage fluctuation caused by the direct startup of the transformer in Mode 2; The controller monitors the voltage of the primary side of the transformer through a phase-locked loop amplitude to determine whether the excitation of the transformer is completed and to determine whether the amplitude of the primary side voltage is greater than ? If so, the controller switches from Mode 2 to Mode 3; if not, the controller still operates in Mode 2; The modal 3 controller monitors the amplitude of the grid voltage through a phase-locked loop and the phase , as well as the amplitude of the voltage at the grid connection point on the primary side of the transformer and the phase , and adjusts the amplitude reference value of the secondary side voltage of the transformer through closed-loop control and the phase reference value ; Based on the phase reference after pre-synchronization control adjustment, the controller performs d-q axis orientation, adjusts the secondary side voltage of the transformer through the voltage-current double closed-loop controller described in Mode 1, and obtains the modulation voltage of the parallel converter; The controller calculates the amplitude difference and phase difference between the grid voltage and the primary side voltage of the transformer, and determines whether both meet the grid connection conditions. If so, it issues a closing instruction for the grid side switch and a closing instruction for the general load switch . If not, it continues to execute the mode 3 controller; The controller, based on the obtained modulation waves of the parallel converter and the modulation waves of the series converter axis components, based on the reference phase, performs inverse transformation to obtain the modulation wave voltages of the series and parallel power circuits of the hybrid transformer, and through the sine pulse width modulator, obtains the control signals of the series and parallel power circuits.

3. A method for rapid grid connection of a hybrid transformer to ensure uninterrupted power supply to important loads according to claim 2, characterized in that, The controller does not receive a grid-connection command, and the independent power supply system operates in island mode. The controller operates in Mode 1, and the voltage amplitude reference of the parallel converter is the required reference voltage on the load side , and the phase reference is obtained by integrating the reference frequency , where . According to the obtained reference phase of the parallel converter, coordinate transformation is performed on the secondary side voltage and the output current of the parallel converter to obtain the corresponding axis component; The parallel converter obtains the current inner loop of the parallel converter through the secondary side voltage outer loop controller Axis reference and , as shown in the following formula: (1) Among them, are the proportional and integral coefficients of the secondary side voltage outer loop controller, are the d-axis and q-axis components of the secondary side voltage of the transformer respectively; After that, through the current inner loop controller, the modulation voltage during the independent power supply operation of the parallel converter is obtained Axis reference and , as shown in the following formula: (2) Among them, is the proportional coefficient of the current inner-loop controller, is the active damping coefficient, reducing the risk of system oscillation.

4. A method for rapid grid connection of a hybrid transformer for ensuring uninterrupted power supply to important loads during power outages, according to claim 2, characterized in that The controller determines whether a grid connection command is received. If so, the passive transformer starting switch is closed. , the controller switches to Mode 2. If not, the controller still operates in Mode 1. The modal 2 controller calculates the output current of the parallel converter and the local load current difference as the transformer excitation current , and performs a coordinate transformation on the transformer excitation current according to the reference phase of the parallel converter to obtain the corresponding axis component; By enabling the excitation current outer loop controller, the output voltage reference value of the parallel converter when the transformer is directly connected is obtained, as shown in the following formula: (3) Among them, are the proportional and integral coefficients of the excitation current outer-loop controller, is the reference value of the excitation current required for the direct input of the power-frequency transformer, which is positively correlated with the transformer capacity, is the rated capacity of the transformer, is the effective value of the reference voltage of the medium-voltage power grid, is the d-axis component of the excitation current, is the reference voltage of the independent power supply system; After that, through the voltage-current double loop controller described in Mode 1, the modulation voltage in Mode 2 of the parallel power conversion circuit is obtained.

5. A method for quickly connecting a hybrid transformer-supported independent power supply system to the grid according to claim 2, characterized in that, According to the reference phase of the secondary side voltage, the output voltage and output current of the series converter are subjected to coordinate transformation to obtain the corresponding axis components. The series converter calculates the difference between the secondary side voltage and the reference voltage as the voltage reference to be compensated by the series converter, as shown in the following formula: (4) wherein, is the output voltage reference of the series converter; After that, through the voltage outer loop controller, the current inner loop of the series converter is obtained axis reference and , as shown in the following formula: (5) Among them, are the proportional and integral coefficients of the voltage outer loop of the series converter, are the d-axis and q-axis components of the output voltage of the series converter, respectively; After that, through the current inner-loop controller, the modulation wave of the series converter when the transformer is directly connected is obtained Axis reference and , as shown in the following formula: (5) Among them, is the proportional coefficient of the current inner loop, are the d-axis and q-axis components of the output current of the series converter, respectively.

6. The controller monitors the voltage of the primary side of the transformer through a phase-locked loop for its amplitude to determine whether the excitation of the transformer is completed, and to determine whether the amplitude of the primary side voltage is greater than ? If so, the controller switches from Mode 2 to Mode 3; if not, the controller remains operating in Mode 2; The modal 3 controller monitors the amplitude of the grid voltage through a phase-locked loop and the phase , as well as the amplitude of the voltage at the grid connection point on the primary side of the transformer and the phase , and adjusts the amplitude reference value of the secondary side voltage of the transformer and the phase reference value through closed-loop control; (6) Among them, are the proportional and integral coefficients of the phase regulator, are the proportional and integral coefficients of the amplitude regulator, is the cut-off frequency of the low-pass filter; Adjust the amplitude reference and phase reference of the secondary side voltage of the transformer according to the deviation obtained in the pre-synchronization link, as shown in the following formula: and the phase reference , as shown in the following formula: (7)。 7. The controller performs d-axis orientation on the parallel converter current and the secondary side voltage of the transformer based on the phase reference after pre-synchronization control adjustment , and adjusts the secondary side voltage of the transformer through the voltage-current double closed-loop controller described in Mode 1 to obtain the modulation voltage of the parallel converter in Mode 3. ​ 8. The controller calculates the amplitude difference and phase difference between the grid voltage and the primary side voltage of the transformer, and determines whether both meet the grid connection conditions. If so, it issues a closing instruction for the grid side switch and a closing instruction for the general load switch . If not, it continues to execute the mode 3 controller.

9. A flexible reclosing grid connection method for a hybrid transformer according to claim 2, characterized in that Comprising the following steps: The controller, based on the modulation waves of the parallel power conversion circuit and the modulation waves of the series power conversion circuit obtained, for the axis components, based on the reference phase of the secondary side voltage of the transformer, obtains the modulation wave voltages of the series and parallel power circuits of the hybrid transformer, and through the sine pulse width modulator, obtains the control signals of the series and parallel power circuits of the hybrid transformer.

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