Broadband oscillation suppression strategy for photovoltaic court supported by hybrid transformer

Abstract

According to the method, the difference of the impedance pairs of the series and parallel converters on different types of resonance suppression sensitivities is fully considered, the parallel damping coefficient of each frequency is adjusted through the load side voltage harmonic change rate, the parallel resonance suppression of the system is realized, and the harmonic overvoltage caused by the load side parallel oscillation is reduced; the series damping coefficient of each characteristic frequency is adjusted through the branch current flowing through the transformer, so that the series resonance suppression of the system is realized, and the harmonic overcurrent caused by the series oscillation of the line is reduced; meanwhile, by correcting the voltage and current reference of the converter, the hybrid transformer has the collaborative treatment of harmonic voltage and harmonic current, and has obvious advantages in the aspects of oscillation suppression effect and economy.

Description

Technical Field

[0001] The invention of this application is applicable to the field of power quality management of medium-voltage distribution networks, and can be used to suppress system broadband oscillations caused by large-scale access of distributed photovoltaics in distribution networks. It is a damping adjustment device and adaptive control method that can simultaneously take into account harmonic management and system oscillation suppression. Background Art

[0002] With the rapid development of distributed new energy, distributed photovoltaic clusters have become a typical scenario for new energy power generation through low-voltage access to the distribution network. At the same time, the increase in the proportion of rectifying power electronic equipment such as inverters and charging piles in the substation area has made the photovoltaic distribution substation area present a high proportion of power electronic characteristics of power generation equipment and loads. The interaction between source and load equipment makes the system exhibit weak damping, strong time variation, and multi-point distribution characteristics, which easily causes multi-type, wide-band oscillations in the distribution substation area.

[0003] Traditional oscillation damping equipment, such as medium-voltage SVGs and active filters, mostly utilizes parallel-type devices for control. These devices can inject reverse harmonic current to control harmonic currents caused by rectifying loads. However, when background harmonics are present in the medium-voltage grid, parallel-type filters lack the control capability and struggle to balance damping control, current, and voltage filtering. Currently, some filter devices utilize series-type filters, and series and parallel damping differ in their sensitivity to resonance suppression. Series-type devices provide harmonic isolation and can suppress overcurrents caused by broadband oscillations in the line. They are more sensitive to medium- and high-frequency series oscillations in the system. Parallel-type devices are more effective at suppressing low-frequency parallel oscillations in the system and can mitigate overvoltages caused by broadband oscillations.

[0004] With the widespread application of 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 harmonic control and oscillation suppression in photovoltaic areas. The present invention fully considers the differences in the sensitivity of series and parallel converter impedances to different types of resonance suppression. By adjusting the parallel damping coefficient of each frequency by the load-side voltage harmonic change rate, the system parallel resonance suppression is achieved, and the harmonic overvoltage caused by the load-side parallel oscillation is reduced; by adjusting the series damping coefficient of each characteristic frequency by the branch current flowing through the transformer, the system series resonance suppression is achieved, and the harmonic overcurrent caused by the line series oscillation is reduced; at the same time, by correcting the voltage and current reference of the converter, the hybrid transformer has the coordinated control of harmonic voltage and harmonic current, which has obvious advantages in oscillation suppression effect and economy. Summary of the Invention

[0005] The purpose of the present invention is achieved through the following technical solutions: According to the voltage sensor, the secondary voltage of the passive transformer is measured. and the load side voltage According to claim 1, the current sensor measures the output current of the series converter , the output current of the parallel converter , hybrid transformer branch current , and the local load current ; The controller obtains the load harmonic current through the characteristic subharmonic extraction link , series converter output harmonic current , parallel converter output harmonic current , branch harmonic current , and the load side harmonic voltage ; The controller obtains the phase reference of the parallel converter through the phase-locked loop , according to DC voltage control and coordinate transformation, the fundamental current reference of the parallel converter is obtained, and the load harmonic current obtained by the above extraction is superimposed , as the current reference of the parallel converter, and obtaining the compensation control modulation voltage of the parallel converter through the current controller; The controller obtains the harmonic current output by the parallel converter , through the parallel damping coefficient , obtain the parallel converter damping modulation voltage, and superimpose it with the above current compensation control voltage to obtain the parallel converter modulation signal; The controller is based on the load side fundamental voltage reference and coordinate transformation to obtain a load-side voltage reference, and obtain a compensation control modulation voltage of the series converter through the voltage closed-loop controller; The controller obtains the series converter output harmonic current , through the series damping coefficient , obtain the damping modulation voltage of the series converter, and superimpose it with the above voltage compensation control voltage to obtain the series converter modulation signal; The above parallel damping coefficient and series damping coefficient The controller obtains the load side harmonic voltage amplitude through the harmonic amplitude extractor. and branch harmonic voltage amplitude , calculate the load harmonic voltage amplitude change respectively and branch harmonic voltage amplitude change The controller determines whether the respective changes are greater than 0. If so, the respective adjustment factors are 1, and if not, the respective adjustment factors are 0. The optimal damping coefficients of the series converter and the parallel converter are obtained according to the respective damping coefficient integrators. The controller determines that when the series adjustment factor and the parallel adjustment factor are both 0, it means that the series resonance and parallel resonance of the system are completely suppressed, and the damping adjustment is terminated; The controller obtains control signals of the series and parallel power converters through the sinusoidal pulse width modulator based on the obtained modulation wave voltages of the series converter and the parallel converter.

[0006] Compared with the prior art, the technical solution of the present invention has the following beneficial effects: 1. The hybrid transformer-supported photovoltaic area broadband oscillation suppression strategy proposed in this invention can simultaneously compensate for nonlinear load harmonic currents and grid-side harmonic voltages when the distribution network contains background harmonic voltages, ensuring that the grid-connected current and load-side supply voltage are sinusoidal. 2. The present invention monitors the harmonic change rate of branch current and supply voltage in real time, and can effectively suppress resonances of different frequency bands and sizes in photovoltaic areas under different grid impedances and different photovoltaic capacities. There is no need to calculate parameters under different scenarios, which simplifies the system control parameter design process. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] Figure 1 The electrical connection structure of the photovoltaic distribution substation system supported by a hybrid transformer provided in an embodiment of the present invention; Figure 2 A schematic diagram of the implementation process of a broadband oscillation suppression strategy for a photovoltaic area supported by a hybrid transformer provided by an embodiment of the present invention; Figure 3 A block diagram of a broadband oscillation suppression control system for a photovoltaic station supported by a hybrid transformer according to an embodiment of the present invention; Figure 4 A control block diagram of the adaptive adjustment algorithm for series and parallel damping coefficients of hybrid transformers provided in an embodiment of the present invention; Figure 5 A flow chart of an adaptive adjustment algorithm for series and parallel damping coefficients of hybrid transformers provided in an embodiment of the present invention; Figure 6 This is a diagram showing the system simulation operation effect under the condition of photovoltaic capacity changes under the traditional method provided by an embodiment of the present invention; Figure 7 This is a diagram showing the system simulation operation effect under the condition of photovoltaic capacity changes under the support of the hybrid transformer provided by the embodiment of the present invention; Figure 8 This is a module diagram of an embodiment of broadband oscillation suppression in a photovoltaic area supported by a hybrid transformer provided by an embodiment of the present invention; Figure 9 It is a schematic diagram of a photovoltaic area broadband oscillation suppression device supported by a hybrid transformer provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0008] To further clarify the objectives, technical solutions, and advantages of this application, the present application will be described in further detail below with reference to the accompanying drawings. The specific operating 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" refers to one or more, while "multiple" refers to two or more. Therefore, in the embodiments of this application, "multiple" can also be understood as "at least two." "And / or" describes the relationship between associated objects, indicating that three possible relationships exist. For example, "A and / or B" can represent: A exists alone, A and B exist simultaneously, or B exists alone. Furthermore, the character " / ," unless otherwise specified, generally indicates that the associated objects are in an "or" relationship. Furthermore, it should be understood that in the description of this application, terms such as "first" and "second" are used solely for descriptive purposes and should not be construed to indicate or imply relative importance or order. The present invention will be further described below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the present invention and are not intended to limit it.

[0009] The present invention proposes a distribution network reactive power and harmonic hybrid compensation system device and a resonance suppression method, comprising the following steps: Referring to Figure 1, a medium-voltage photovoltaic distribution substation system supported by a hybrid transformer is characterized by comprising: a medium-voltage distribution network, a weak grid impedance, a passive transformer, a series coupling transformer, a series converter, a shunt converter, a current sensor, a voltage sensor, a controller, a substation load, and a photovoltaic cluster; The primary coil of the passive transformer is connected to the medium-voltage grid via a grid impedance. The secondary coil is connected to a first voltage sensor and the other end is connected to a series isolation transformer. The other end of the series transformer is connected to the load-side busbar via a first current sensor. The first end of the series converter is connected to the controller and the other end is connected to the series isolation transformer via a second current sensor. The first end of the shunt converter is connected to the controller and the other end is connected to the load-side busbar via a third current sensor. A second voltage sensor is installed on the load busbar. The load of the substation is connected to the load-side busbar via a fourth current sensor. At the same time, each photovoltaic cell forms a photovoltaic cluster through a converter and is connected to the load-side busbar. The number of photovoltaic units deployed can be determined based on the actual scenario.

[0010] Refer to Figure 2, which shows a resonance suppression strategy for a hybrid transformer-supported PV distribution station area, including: Step S201: Using the voltage sensor described in the claims, measure the secondary voltage of the passive transformer. and the load side voltage According to claim 1, the current sensor measures the output current of the series converter , the output current of the parallel converter , hybrid transformer branch current , and the local load current ; Referring to FIG. 3 , an embodiment of the present invention provides a hybrid transformer-supported photovoltaic distribution station resonance suppression strategy, including: Step S202: The controller obtains the parallel converter phase reference through the phase-locked loop, and obtains the parallel converter fundamental current reference according to the DC voltage control and coordinate transformation. , as shown below: (1) in, is the load side voltage phase reference obtained by the controller phase-locked loop, and are the proportional and integral coefficients of the DC voltage controller, is the DC bus voltage, is the reference voltage.

[0011] Step S203: The controller obtains the load harmonic current by superimposing the extraction link , as the current reference of the parallel converter, the compensation control modulation voltage of the parallel converter is obtained through the current controller, as shown in the following formula: (2) in, and are the proportional coefficient and resonant coefficient of the current controller, represents the bandwidth at the center frequency of the controller, represents the fundamental frequency, Indicates the number of characteristic subharmonics, which can be 5, 7, 11, or 13; The controller extracts the harmonic current output by the parallel converter , according to the parallel damping coefficient The damping modulation voltage of the parallel converter is obtained and superimposed with the compensation control modulation voltage to obtain the modulation signal of the parallel converter. , as shown below: (3) in, is the parallel damping coefficient, which is obtained from the output of the frequency-divided damping adaptive controller. Indicates the characteristic subharmonic order, which can be 5, 7, 11, or 13.

[0012] Step S204: The controller generates a voltage reference signal based on the fundamental voltage of the load side. and phase ,pass change Coordinate transformation to obtain the load side fundamental voltage reference , through the voltage closed-loop controller, the compensation control modulation voltage of the series converter is obtained, as shown in the following formula: (4) in, and are the proportional coefficient and resonance coefficient of the voltage controller respectively; The controller extracts the series converter output harmonic current , according to the series damping coefficient The damping modulation voltage of the series converter is obtained and superimposed with the above voltage compensation control voltage to obtain the modulation signal of the series converter. , as shown below: (5) in, is the parallel damping coefficient, which is obtained from the output of the frequency-divided damping adaptive controller. Indicates the characteristic subharmonic order, which can be 5, 7, 11, or 13.

[0013] Step S205: The controller obtains the load side harmonic voltage amplitude through the harmonic amplitude extractor and branch harmonic voltage amplitude , as shown below: (6) in, is the transfer function of the digital sliding average filter, and is the load side voltage The amplitude and phase angle of the subharmonics, and is the line current The amplitude and phase angle of the subharmonics, Representative interrupt cycle.

[0014] Step S206: The controller calculates the load harmonic voltage amplitude variation and branch harmonic voltage amplitude change The parallel regulation factor is determined by the magnitude of the change in the load harmonic voltage amplitude, and the series regulation factor is determined by the magnitude of the change in the line harmonic current amplitude, as shown in the following formula: (7) in, is the parallel damping adjustment factor, is the series damping adjustment factor, 1 represents resonance amplification, 0 represents resonance suppression, Represents the last interrupt cycle.

[0015] Step S207: According to the series and parallel damping coefficient integrators, the optimal damping coefficients of the series converter and the parallel converter are obtained, as shown in the following formula: (8) in, is the parallel damping integral coefficient, is the series damping integral coefficient, and are the initial values of parallel and series damping, respectively, both are set to 0.

[0016] Step S208: The controller determines that when the series adjustment factor and the parallel adjustment factor are both 0, it means that the series resonance and parallel resonance of the system are completely suppressed, and the frequency-divided damping adjustment is terminated.

[0017] Step S209: The controller obtains control signals of the series and parallel power converters through the sinusoidal pulse width modulator based on the obtained modulation wave voltages of the series converter and the parallel converter.

[0018] Figure 6 is a diagram of the system simulation operation effect under the condition of photovoltaic capacity change under the traditional method provided by an embodiment of the present invention; it can be seen that: under the traditional substation without damping equipment, no photovoltaic converter is put into operation, the system does not oscillate, and the branch current is sinusoidal; when 2 groups of photovoltaic converters are put into operation, the current THD is 26.83%, mainly the 13th harmonic component; when 4 groups of photovoltaic converters are put into operation, the current THD is 23.75%, the 11th component increases, the 13th component decreases, and the resonance shifts to the 11th; when 6 groups of photovoltaic converters are put into operation, the current THD is 40.31%, the 11th and 13th harmonic components are further reduced, the 7th component is amplified, and the 7th resonance occurs.

[0019] Figure 7 is a diagram showing the system simulation operation effect under the condition of photovoltaic capacity changes supported by the hybrid transformer provided by an embodiment of the present invention; it can be seen that: after adopting the broadband oscillation suppression strategy for the photovoltaic area supported by the proposed hybrid transformer, when the number of photovoltaic converter groups changes from 2 to 6, the current harmonic distortion rate in the steady state of each stage is maintained within 5%, and the resonance of each frequency is efficiently suppressed.

[0020] 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 scope of the present invention and the scope of protection of the claims, those skilled in the art may make various specific modifications based on the teachings of the present invention, all of which fall within the scope of protection of the present invention.

[0021] It should be understood that the order of execution of the steps in the above embodiments does not necessarily mean the order of execution. The order of execution of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present invention.

[0022] The embodiment module is shown in Figure 8, which is a broadband oscillation suppression strategy for a photovoltaic station supported by a hybrid transformer, including: The first obtaining module 801 obtains the secondary side voltage and the load side voltage of the passive transformer according to the voltage sensor; obtains the output current, branch current and load current of the series converter and the parallel converter according to the current sensor; The second obtaining module 802 obtains the load harmonic current, the series converter output harmonic current, the parallel converter output harmonic current, the branch harmonic current, and the load-side harmonic voltage according to the characteristic subharmonic extraction step; The second determination module 803 obtains the fundamental current reference of the parallel converter according to the DC voltage control, superimposes the load harmonic current obtained above, and determines the compensation control modulation voltage of the parallel converter through the current controller; The third obtaining module 804 determines the parallel converter damping modulation voltage according to the parallel converter output harmonic current and the parallel damping coefficient, and superimposes the voltage with the current compensation control voltage to obtain the parallel converter modulation signal; A fourth obtaining module 805 obtains a load side voltage reference according to the load side fundamental voltage reference, and obtains a compensation control modulation voltage of the series converter through the voltage closed-loop controller; The fourth determination module 806 determines the series damping coefficient according to the obtained series converter output harmonic current. R se,h , obtain the damping modulation voltage of the series converter, superimpose it with the compensation control voltage, and determine the modulation signal of the series converter; A fifth obtaining module 807 obtains the optimal damping coefficients of the series converter and the parallel converter according to the series and parallel damping coefficient adaptive regulators; The fifth determination module 808 determines whether the series adjustment factor and the parallel adjustment factor are both 0, and whether the series resonance and the parallel resonance of the system are completely suppressed. If so, the damping coefficient adjustment is terminated. In the sixth obtaining module 809 , the controller obtains control signals of the series and parallel power converters through the sinusoidal pulse width modulator based on the obtained modulation wave voltages of the series converter and the parallel converter.

[0023] Figure 9 is a schematic diagram of a photovoltaic area broadband oscillation suppression device supported by a hybrid transformer provided in an embodiment of the present invention.

[0024] The hybrid transformer device and control system schematic diagram is shown in Figure 9, including: a converter 901, a controller 902, a memory 903, and a computer program 904 stored in the memory 903 and executable on the controller 902. When the controller 902 executes the computer program 904, the steps in the above-mentioned resonance suppression method embodiment are implemented, such as Figure 2 Alternatively, when the controller 902 executes the computer program 904, the power of each module / unit in the above embodiment is realized, for example Figure 8 The functions of modules 801 to 809 are shown.

[0025] Exemplarily, the computer program 904 can be divided into one or more modules / units, which are stored in the memory 903 and executed by the controller 902 to implement the embodiments 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 the instruction segments are used to describe the execution process of the computer program 904 in the hybrid transformer device 9. For example, the computer program 904 can be divided into a first acquisition module, a second acquisition module, a second determination module, a third acquisition module, a fourth acquisition module, a fourth determination module, a fifth acquisition module, a fifth determination module, and a sixth acquisition module. The functions of each module are as follows: The first acquisition module obtains the secondary side voltage and the load side voltage of the passive transformer according to the voltage sensor; obtains the output current, branch current and load current of the series converter and the parallel converter according to the current sensor; The second obtaining module obtains the load harmonic current, the series converter output harmonic current, the parallel converter output harmonic current, the branch harmonic current, and the load side harmonic voltage according to the characteristic subharmonic extraction link; A second determination module obtains a fundamental current reference of the parallel converter according to DC voltage control, superimposes the load harmonic current obtained above, and determines the compensation control modulation voltage of the parallel converter through the current controller; The third obtaining module determines the parallel converter damping modulation voltage according to the parallel converter output harmonic current and the parallel damping coefficient, and superimposes the voltage with the current compensation control voltage to obtain the parallel converter modulation signal; a fourth obtaining module, which obtains a load-side voltage reference according to the load-side fundamental voltage reference, and obtains a compensation control modulation voltage of the series converter through the voltage closed-loop controller; The fourth determination module is to determine the harmonic current output by the series converter according to the series damping coefficient. R se,h , obtain the damping modulation voltage of the series converter, superimpose it with the compensation control voltage, and determine the modulation signal of the series converter; A fifth obtaining module obtains the optimal damping coefficients of the series converter and the parallel converter according to the series and parallel damping coefficient adaptive regulators; The fifth determination module determines whether the series resonance and parallel resonance of the system are completely suppressed according to whether the series adjustment factor and the parallel adjustment factor are both 0. If so, the damping coefficient adjustment is terminated; The sixth obtaining module, the controller obtains the control signals of the series and parallel power converters through the sinusoidal pulse width modulator based on the obtained modulation wave voltages of the series converter and the parallel converter.

[0026] The hybrid transformer-supported photovoltaic area broadband oscillation suppression strategy may include, but is not limited to, a converter 901, a controller 902, and a memory 903. Those skilled in the art will understand that Figure 9 It is only an example of the hybrid transformer device 9 and does not constitute a limitation on the hybrid transformer device. It can include more or fewer components than shown in the figure, or a combination of certain components, or different components. For example, the life assessment terminal device of the power transformer can also include input and output devices, network access equipment, buses, etc.

[0027] The controller 902 may be a central processing unit (CPU), or other general-purpose processors, digital signal processors (DSP), application-specific integrated circuits (ASIC), field-programmable gate arrays (FPGA), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. The general-purpose processor may be a microprocessor or any conventional processor.

[0028] The memory 903 can be an internal storage unit of the hybrid transformer device 9 with an energy storage system, such as an external memory circuit of the hybrid transformer device 9 with an energy storage system. Examples include a plug-in hard drive, a Smart Media Card (SMC), a Secure Digital (SD) card, a flash memory card, etc., equipped on the hybrid transformer device 9. Furthermore, the memory 803 can include both the internal storage unit of the hybrid compensation system device 9 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 can also be used to temporarily store data that has been output or is about to be output.

[0029] Those skilled in the art can clearly understand that, for the convenience and brevity of description, only the division of the above-mentioned functional units and modules is used as an example for illustration. In actual applications, the above-mentioned functions can be distributed and completed by 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. The functional units and modules in the embodiment can be integrated into one processing unit, or each unit can exist physically alone, or two or more units can be integrated into one unit. The above-mentioned integrated unit can be implemented in the form of hardware or in the form of software functional units. In addition, the specific names of the functional units and modules are only for the convenience of distinguishing each other, and are not used to limit the scope of protection of this application. The specific working process of the units and modules in the above-mentioned system can refer to the corresponding process in the aforementioned method embodiment, and will not be repeated here.

[0030] In the above embodiments, the description of each embodiment has its own focus. For parts that are not described or recorded in detail in a certain embodiment, reference can be made to the relevant description of other embodiments.

[0031] Those skilled in the art will appreciate that the units and algorithm steps of each example described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are performed in hardware or software depends on the specific application and design constraints of the technical solution. Professionals and technicians can use different methods to implement the described functions for each specific application, but such implementation should not be considered beyond the scope of the present invention.

[0032] In the embodiments provided by the present invention, it should be understood that the disclosed devices / terminal equipment and methods can be implemented in other ways. For example, the device / terminal equipment embodiments described above are merely illustrative. For example, the division of the modules or units is merely a logical function division. In actual implementation, there may be other division methods, such as 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 mutual coupling or direct coupling or communication connection shown or discussed can be through some interfaces, indirect coupling or communication connection of devices or units, which can be electrical, mechanical or other forms.

[0033] The units described as separate components may or may not be physically separate, and the components shown as units may or may not be physical units, that is, they may be located in one place or distributed across multiple network units. Some of these units may be selected according to actual needs to achieve the purpose of this embodiment.

[0034] In addition, the functional units in the various embodiments of the present invention may be integrated into a single processing unit, each unit may exist physically separately, or two or more units may be integrated into a single unit. The aforementioned integrated units may be implemented in the form of hardware or software functional units.

[0035] If the integrated module / unit is implemented as a software functional unit and sold or used as a standalone product, it can be stored in a computer-readable storage medium. Based on this understanding, the present invention can implement all or part of the process steps in the above-mentioned method embodiments by using a computer program to instruct the relevant hardware. The computer program can be stored in a computer-readable storage medium. When executed by a processor, the computer program can implement the steps of each of the above-mentioned method embodiments. The computer program includes computer program code, which can be in source code form, object code form, executable file, or some intermediate form. The computer-readable medium can include: any entity or device capable of carrying the computer program code, recording medium, USB flash drive, mobile hard drive, magnetic disk, optical disk, computer memory, read-only memory (ROM), random access memory (RAM), electric carrier signal, telecommunication signal, and software distribution medium. It should be noted that the content of the computer-readable medium can be appropriately increased or decreased based on the requirements of legislation and patent practice in a jurisdiction. For example, in some jurisdictions, based on legislation and patent practice, computer-readable media does not include electric carrier signals and telecommunication signals.

[0036] The embodiments described above are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present invention, and should all be included in the scope of protection of the present invention.

Claims

1. A medium voltage photovoltaic distribution substation system supported by a hybrid transformer, characterized in that: include: Medium voltage distribution network, weak grid impedance, passive transformer, series coupling transformer, series converter, shunt converter, current sensor, voltage sensor, controller, substation load and photovoltaic cluster; The passive transformer's primary coil is connected to the medium-voltage grid via grid impedance, while its secondary coil is connected to a first voltage sensor and a series isolation transformer. The series transformer's other end is connected to the load-side busbar via a first current sensor. The series converter's first end is connected to a controller, and its other end is connected to the series isolation transformer via a second current sensor. The parallel converter's first end is connected to the controller, and its other end is connected to the load-side busbar via a third current sensor. A second voltage sensor is installed on the load busbar. The substation load is connected to the load-side busbar via a fourth current sensor. Each photovoltaic cell forms a photovoltaic cluster via a converter and is connected to the load-side busbar. The number of photovoltaic units deployed can be tailored to the specific scenario.

2. A resonance suppression strategy for photovoltaic distribution stations supported by hybrid transformers, characterized in that: include: The voltage sensor according to claim 1 measures the secondary voltage of the passive transformer and the load side voltage ; The current sensor according to claim 1 measures the output current of the series converter , the output current of the parallel converter , hybrid transformer branch current , and the local load current ; The controller obtains the load harmonic current through the characteristic subharmonic extraction link , series converter output harmonic current , parallel converter output harmonic current , branch harmonic current , and the load side harmonic voltage ; The controller obtains the phase reference of the parallel converter through the phase-locked loop , according to DC voltage control and coordinate transformation, the fundamental current reference of the parallel converter is obtained, and the load harmonic current obtained by the above extraction is superimposed , as the current reference of the parallel converter, and obtaining the compensation control modulation voltage of the parallel converter through the current controller; The controller obtains the harmonic current output by the parallel converter , through the parallel damping coefficient , obtain the parallel converter damping modulation voltage, and superimpose it with the above current compensation control voltage to obtain the parallel converter modulation signal; The controller is based on the load side fundamental voltage reference and coordinate transformation to obtain a load-side voltage reference, and obtain a compensation control modulation voltage of the series converter through the voltage closed-loop controller; The controller obtains the series converter output harmonic current , through the series damping coefficient , obtain the damping modulation voltage of the series converter, and superimpose it with the above voltage compensation control voltage to obtain the series converter modulation signal; The above parallel damping coefficient and series damping coefficient The controller obtains the load side harmonic voltage amplitude through the harmonic amplitude extractor. and branch harmonic voltage amplitude , calculate the load harmonic voltage amplitude change respectively and branch harmonic voltage amplitude change The controller determines whether the respective changes are greater than 0. If so, the respective adjustment factors are 1, and if not, the respective adjustment factors are 0. The optimal damping coefficients of the series converter and the parallel converter are obtained according to the respective damping coefficient integrators. The controller determines that when the series adjustment factor and the parallel adjustment factor are both 0, it means that the series resonance and parallel resonance of the system are completely suppressed, and the damping adjustment is terminated; The controller obtains control signals of the series and parallel power converters through the sinusoidal pulse width modulator based on the obtained modulation wave voltages of the series converter and the parallel converter.

3. The resonance suppression strategy for photovoltaic power distribution stations supported by hybrid transformers according to claim 2 is characterized in that: The controller obtains the parallel converter phase reference through the phase-locked loop, and obtains the parallel converter fundamental current reference according to DC voltage control and coordinate transformation. , as shown below: (1) in, is the load side voltage phase reference obtained by the controller phase-locked loop, and are the proportional and integral coefficients of the DC voltage controller, is the DC bus voltage, is the reference voltage.

4. The resonance suppression strategy for photovoltaic power distribution stations supported by hybrid transformers according to claim 2 is characterized in that: The controller obtains the load harmonic current by superimposing the extraction link , as the current reference of the parallel converter, the compensation control modulation voltage of the parallel converter is obtained through the current controller, as shown in the following formula: (2) in, and are the proportional coefficient and resonant coefficient of the current controller, represents the bandwidth at the center frequency of the controller, represents the fundamental frequency, Indicates the number of characteristic subharmonics, which can be 5, 7, 11, or 13; The controller extracts the harmonic current output by the parallel converter , according to the parallel damping coefficient The damping modulation voltage of the parallel converter is obtained and superimposed with the compensation control modulation voltage to obtain the modulation signal of the parallel converter. , as shown below: (3) in, is the parallel damping coefficient, which is obtained from the output of the frequency-divided damping adaptive controller. Indicates the characteristic subharmonic order, which can be 5, 7, 11, or 13.

5. The resonance suppression strategy for photovoltaic power distribution stations supported by hybrid transformers according to claim 2 is characterized in that: The controller is based on the load side fundamental voltage reference and phase ,pass change Coordinate transformation to obtain the load side fundamental voltage reference , through the voltage closed-loop controller, the compensation control modulation voltage of the series converter is obtained, as shown in the following formula: (4) in, and are the proportional coefficient and resonance coefficient of the voltage controller respectively; The controller extracts the series converter output harmonic current , according to the series damping coefficient The damping modulation voltage of the series converter is obtained and superimposed with the above voltage compensation control voltage to obtain the modulation signal of the series converter. , as shown below: (5) in, is the parallel damping coefficient, which is obtained from the output of the frequency-divided damping adaptive controller. Indicates the characteristic subharmonic order, which can be 5, 7, 11, or 13.

6. The resonance suppression strategy for photovoltaic power distribution stations supported by hybrid transformers according to claim 2 is characterized in that: The controller obtains the load side harmonic voltage amplitude through the harmonic amplitude extractor and branch harmonic voltage amplitude , as shown below: (6) in, is the transfer function of the digital sliding average filter, and is the load side voltage The amplitude and phase angle of the subharmonics, and is the line current The amplitude and phase angle of the subharmonics, Representative Secondary interruption cycle; The controller calculates the load harmonic voltage amplitude change and branch harmonic voltage amplitude change The parallel regulation factor is determined by the magnitude of the change in the load harmonic voltage amplitude, and the series regulation factor is determined by the magnitude of the change in the line harmonic current amplitude, as shown in the following formula: (7) in, is the parallel damping adjustment factor, is the series damping adjustment factor, 1 represents resonance amplification, 0 represents resonance suppression, Represents the last interrupt cycle; According to the series and parallel damping coefficient integrators, the optimal damping coefficients of the series converter and the parallel converter are obtained, as shown in the following formula: (8) in, is the parallel damping integral coefficient, is the series damping integral coefficient, and are the initial values of parallel and series damping, respectively, both are set to 0.

7. The resonance suppression strategy for photovoltaic power distribution stations supported by hybrid transformers according to claim 2 is characterized in that: When the series adjustment factor and the parallel adjustment factor are both 0, it means that the series resonance and the parallel resonance of the system are completely suppressed, and the frequency-divided damping adjustment is ended.

8. The method for parallel operation of a passive transformer and a hybrid transformer according to claim 2, characterized in that: Based on the obtained modulation wave voltages of the series converter and the parallel converter, control signals of the series and parallel power converters are obtained through the sinusoidal pulse width modulator.

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