Grid-connected and off-grid switching control method based on series-parallel compensation device

Abstract

The series-parallel compensation device control method is suitable for the field of sensitive load power supply of precision manufacturing, medical equipment and the like with high power quality requirements, and gives consideration to grid-connected and off-grid smooth switching and transient voltage stability. According to the method, when it is detected that a power grid is disconnected, droop control and harmonic reverse injection are synchronously executed through a parallel-side converter, and meanwhile gradual exit of series-side compensation voltage is coordinated, so that voltage stability in the power supply mode switching process is achieved. The control method is characterized in that a fundamental voltage-harmonic current composite control strategy is adopted on a parallel side, residual harmonic voltage of a power grid is extracted in real time based on a sliding discrete Fourier transform detection method, and compensation current with opposite phases is generated for dynamic offset; a soft exit mechanism is adopted on the series side, the compensation amount in the grid-connected last stage is maintained in the initial stage of switching and is linearly attenuated, compensation abrupt change is avoided, and switching transient power impact is restrained by combining energy storage quick response of a direct-current bus super capacitor. According to the method, the voltage recovery time is shortened to be within 5ms, the transient harmonic distortion rate is reduced to be below 3%, additional hardware cost does not need to be increased, the problem of voltage transient distortion caused by series side function interruption in the switching process of a traditional series-parallel compensation device is solved, and the switching efficiency is improved. The method can be widely applied to scenes needing frequent mode switching, such as micro-grids and distributed energy grid connection.

Description

Technical Field

[0001] The invention of this application is applicable to the fields of microgrids, distributed energy grid connection and power supply for high power quality sensitive loads, and can be applied to the comprehensive power quality management under the power distribution systems of new energy power stations and industrial parks. It is a control method for the on-grid and off-grid switching of series-parallel compensation devices that can simultaneously take into account grid-connected harmonic control and off-grid transient voltage stability. Background Art

[0002] With the rapid development of distributed energy resources such as photovoltaics, wind power, and energy storage technologies, microgrids, as key carriers of the energy internet, must possess the ability to flexibly switch operating modes to cope with grid failures or islanding needs. On-grid and off-grid switching control is one of the core technologies of microgrids, and its performance directly impacts power supply continuity, power quality, and equipment safety. Traditional switching processes often cause voltage amplitude, frequency, or phase mismatches between the grid and the microgrid, leading to instantaneous surge currents, voltage sags, or harmonic distortion. In severe cases, these mismatches can cause protective devices to malfunction, threatening system stability. Especially in remote areas or power quality-sensitive industrial scenarios such as semiconductor manufacturing and data centers, millisecond-level switching delays or minor voltage fluctuations can result in significant economic losses. Therefore, a highly reliable, seamless, and smooth on-grid and off-grid switching control method is urgently needed.

[0003] Currently, research on on-grid and off-grid switching control, both domestically and internationally, focuses on the following areas: Mechanical switch-based switching technologies, while low in hardware cost, suffer from mechanical delays, typically in the hundreds of milliseconds, exposing the load to the risk of short-term power outages during switching. Static switching based on power electronic devices, while capable of achieving rapid switching in milliseconds, introduces additional harmonics and significantly increases hardware costs. Hybrid switching control strategies, while leveraging power electronic devices to buffer switching shocks, suffer from complex control logic and difficulties coordinating multiple modes. Intelligent algorithm optimization, while capable of dynamically adjusting switching timing, is prone to model mismatch under strong interference or non-ideal grid conditions, and its robustness needs improvement. In summary, existing technologies generally face three major bottlenecks: insufficient transient shock suppression, limited adaptability to multiple operating conditions, and difficulty balancing economic efficiency and performance, making them difficult to meet the engineering requirements of highly reliable microgrids.

[0004] To address the above issues, this patent proposes a grid-connected and off-grid switching control method based on a series-parallel composite compensation device, which is suitable for sensitive load scenarios such as precision manufacturing and medical equipment with high power quality requirements. When the grid is detected to be disconnected, this method synchronously performs droop control and harmonic reverse injection through the parallel-side converter, while coordinating the gradual exit of the series-side compensation voltage to achieve voltage stability during the power supply mode switching process. This can effectively shorten the voltage recovery time and reduce the transient harmonic distortion rate without increasing additional hardware costs. It can be widely used in scenarios such as microgrids and distributed energy grid connection that require frequent mode switching. Summary of the Invention

[0005] This invention proposes a control method for switching between series-shunt compensation devices, balancing both grid-connected harmonic mitigation and off-grid transient voltage stability. When a grid disconnect is detected, this control method synchronizes droop control and harmonic reverse injection in the shunt-side converter, while also coordinating the gradual withdrawal of the series-side compensation voltage to achieve voltage stability during power supply mode switching.

[0006] The purpose of the present invention is achieved through the following technical solutions: The voltage sensor according to claim 1 measures the grid voltage on the grid side. , grid connection point voltage , and the series converter compensation voltage According to claim 1, the current sensor measures the output current of the parallel converter , the output current of the series converter , and the load current ; The controller is used to receive the voltage and current information measured by the above sensors, and to receive the switching and off-grid instructions of the grid-connected system issued by the grid dispatching center. If no off-grid instruction is received, the power supply system is grid-connected and the controller operates in mode 1; when an off-grid instruction is received, the controller switches to mode 2 during the transition period of the response instruction; when the closing switch is disconnected, the controller switches to mode 2. , the controller switches to mode 3, enters the off-grid steady state, and completes the off-grid operation of the independent power supply system; The mode 1 controller collects the grid connection point voltage , obtain the compensation harmonic voltage reference and fundamental voltage reference required to support the stable operation of the low-voltage load; the series controller obtains the modulation voltage of the series converter according to the voltage and current dual-loop controller; the controller obtains the modulation voltage of the series converter according to the measured load current , obtaining a compensation current reference, the parallel converter obtains a modulation voltage of the parallel converter through a current loop controller; the controller determines whether an off-grid instruction is received, and if so, the controller switches to mode 2, otherwise, the controller still operates in mode 1; The mode 2 controller obtains the fundamental voltage reference required to support the low-voltage load through the load voltage generator, and , obtaining a compensation harmonic voltage reference, the parallel converter obtains a modulation voltage of the parallel converter through a voltage and current dual closed-loop controller; The series converter exits the harmonic voltage compensation link in mode 2, and the controller only retains the fundamental voltage reference in mode 1 to obtain the modulation voltage of the series converter.

[0007] After receiving the off-grid instruction, the controller switches from mode 1 to mode 2. After determining that the switching of mode 2 is completed, the controller switches from mode 2 to mode 3; The mode 3 controller sends the network side switch Disconnect command, grid side switch Disconnect. The controller obtains the modulation voltage of the parallel converter through closed-loop control only by using the fundamental voltage reference required to support the low-voltage load. The series converter is shut down or switched to current control as needed in the off-grid steady state of mode 3; The controller obtains the modulation wave voltage of the series and parallel power circuits of the series-parallel compensation device based on the modulation wave of the parallel converter and the modulation wave voltage of the series converter, and obtains the control signal of the series and parallel power circuits through the sinusoidal pulse width modulator.

[0008] Compared with the prior art, the technical solution of the present invention has the following beneficial effects: 1. The application of the technical solution proposed in the present invention can greatly improve the dynamic performance of the system during on-grid and off-grid switching, and shorten the voltage recovery time by 75%.

[0009] 2. By applying the technical solution proposed in the present invention, there is no need to add power devices. The function can be achieved only by upgrading the algorithm. The supercapacitor reuses the original DC bus, reducing the cost of new investment.

[0010] 3. The application of the technical solution proposed in the present invention can effectively reduce the load voltage distortion rate during the transient process of grid-connected and off-grid switching, reduce relay protection malfunction or equipment failure caused by voltage distortion, and improve power supply reliability.

[0011] 4. The application of the technical solution proposed in the present invention can reduce relay protection malfunction or equipment failure caused by voltage distortion and improve power supply reliability. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 The electrical connection structure of the series-parallel compensation device for ensuring uninterrupted power supply to low-voltage loads provided in an embodiment of the present invention; Figure 2 A schematic diagram of the entire process of implementing a series-parallel compensation device for ensuring uninterrupted power supply to loads, from grid-connected operation to islanding, provided by an embodiment of the present invention; Figure 3 A block diagram of a controller for series and parallel converters in a series-parallel compensation device provided in an embodiment of the present invention; Figure 4 A timing diagram of the entire process of operation of a hybrid transformer from islanding to grid connection, which ensures uninterrupted power supply to loads, provided by an embodiment of the present invention; Figure 5This is a simulation operation effect diagram of direct off-grid startup control when a low-voltage load is grid-connected provided by an embodiment of the present invention; Figure 6 This is a module diagram of an embodiment of a method for switching a power supply system on and off the grid supported by a series-parallel compensation device provided in an embodiment of the present invention; Figure 7 Schematic diagram of a series-parallel compensation device provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0013] 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.

[0014] The present invention proposes a method for controlling on-grid and off-grid switching based on a series-parallel compensation device, comprising the following steps: Please refer to Figure 1 for the electrical connection structure of a series-parallel compensation device for ensuring uninterrupted power supply to low-voltage loads, which is characterized by including: a reclosing 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 series-coupled transformer is connected in series between the grid and the load through a reclosing 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 group through a current sensor. The other end of the filter is connected to the secondary coil of the transformer. At the same time, voltage sensors are installed on the grid side, the output end of the parallel converter, and the output side of the series-coupled transformer.

[0015] Please refer to Figure 2, a method for controlling on-grid and off-grid switching based on a series-parallel compensation device, including: Step S201: The voltage sensor according to claim 1 measures the grid voltage on the grid side. , grid connection point voltage , and the series converter compensation voltage According to claim 1, the current sensor measures the output current of the parallel converter , the output current of the series converter , and the load current ; Please refer to Figure 3, which shows a block diagram of the series and parallel converter controllers in the series-parallel compensation device provided by an embodiment of the present invention, including: Step 202: The controller receives the voltage and current information measured by the above sensors and accepts the off-grid switching command issued by the grid dispatching center. If no off-grid command is received, the power supply system is on-grid and the controller operates in mode 1. The fundamental voltage amplitude of the series converter is referenced to is the load reference voltage, phase reference By the reference frequency The integral is obtained, where The harmonic voltage reference of the series converter is obtained based on the harmonic components of the grid connection point voltage obtained by the SDFT harmonic detection method.

[0016] The series converter obtains the modulation voltage of the series converter through the voltage-current dual-loop controller, as shown in the following formula: (1) Where, represents the proportional coefficient of the proportional resonant controller, Represents the resonance coefficient of the controller. represents the bandwidth at the center frequency of the controller, represents the fundamental angular frequency of the system, Indicates the harmonic order, 1, 3, 5, 7, 9, 11, 13, represents the proportionality coefficient; Afterwards, the parallel converter measures the load current The current reference obtained by the harmonic component , after the current loop controller, the modulation voltage of the parallel converter is obtained, as shown in the following formula: (2) in, is the transfer function of the PR quasi-proportional resonant controller.

[0017] Step 203: The controller determines whether an off-grid instruction is received. If so, the controller switches to mode 2; if not, the controller still operates in mode 1. Step 204: The series converter exits the harmonic voltage compensation step in mode 2, and the modulation wave voltage is expressed as follows: (3) Then, the fundamental voltage reference required to support the low-voltage load is obtained through the load voltage generator, as shown in the following formula: (4) in, is the phase of the grid-side voltage.

[0018] The mode 2 controller is based on the collected grid side voltage , the compensated harmonic voltage reference is obtained as shown below: (5) in, is the fundamental component of the grid voltage obtained by equation (3).

[0019] Then the mode 2 controller obtains the modulation voltage of the parallel converter through the voltage and current double closed-loop controller , as shown below: (6) Step 205: After receiving the off-grid instruction, the controller switches from mode 1 to mode 2. After determining that the switching of mode 2 is completed, the controller switches from mode 2 to mode 3.

[0020] Step 206: The Mode 3 controller sends a message to the network side switch. Disconnect command, grid side switch Disconnect. The controller uses only the fundamental voltage reference required to support the low-voltage load, and closed-loop control to obtain the modulation voltage of the parallel converter. The series converter is shut down or switched to current control as needed in the off-grid steady state of mode 3. The modulation wave voltages of the parallel converter and the series converter are shown in the following formula: (7) in, is the current inner loop proportional parameter.

[0021] Step 207: The controller obtains the modulation wave voltage of the series and parallel power circuits of the series-parallel compensation device based on the obtained modulation wave of the parallel converter and the modulation wave voltage of the series converter, and obtains the control signal of the series and parallel power circuits through the sinusoidal pulse width modulator.

[0022] Please refer to Figure 4, which is a timing diagram of the entire process of the hybrid transformer from island operation to grid-connected operation to ensure uninterrupted power supply to the load provided by an embodiment of the present invention, including the triggering and shutdown of the corresponding control timing in three modes.

[0023] Figure 5This figure shows the simulation results of direct off-grid startup control during grid-connected operation of a low-voltage load provided by an embodiment of the present invention. It can be seen that, under normal resistive and inductive load conditions, off-grid operation is achieved in 0.2 seconds, and the transient process ends within 3.7 milliseconds, compared to a conventional transient process of approximately 15 milliseconds. THD is also reduced from 12.7% to 2.3%, achieving smooth on-grid and off-grid switching.

[0024] 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.

[0025] It should be understood that the size of the serial numbers of the steps in the above embodiments does not mean the order of execution. The execution order 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.

[0026] The embodiment module is shown in Figure 6. A method for controlling on-grid and off-grid switching based on a series-parallel compensation device includes: The first obtaining module 601 obtains the grid voltage, the grid connection point voltage, and the series converter compensation voltage according to the voltage sensor, obtains the output current of the parallel converter and the series converter and the load current according to the current sensor, and receives the off-grid instruction issued by the grid dispatching center; The second obtaining module 602, when the system is in a grid-connected operation state, obtains the compensation harmonic voltage reference and fundamental voltage reference of the series converter required to support the stable operation of the low-voltage load based on the collected grid-connected point voltage; The third obtaining module 603 obtains the harmonic current reference that needs to be compensated for the parallel converter according to the measured load current when the system is in the grid-connected operation state; The fourth obtaining module 604 obtains the modulation wave voltage of each of the series converter and the parallel converter according to the voltage and current reference of each of the series converter and the parallel converter through the voltage and current closed-loop controller; The fourth determining module 605 determines whether the series-parallel compensation device changes its operating mode according to whether the off-grid instruction is received; The fifth obtaining module 606 obtains the fundamental voltage reference required to support the low voltage load according to the load voltage generator. According to the collected grid-side voltage, a compensation harmonic voltage reference is obtained. The parallel converter obtains the modulation voltage of the parallel converter through the voltage-current dual closed-loop controller. At the same time, the series converter exits the compensation harmonic voltage link in mode 2. The controller only retains the fundamental voltage reference in mode 1 to obtain the modulation voltage of the series converter.

[0027] The fifth determining module 608 switches from mode 2 to mode 3 according to the controller receiving the off-grid instruction and switching from mode 1 to mode 2 after determining that the switching of mode 2 is completed.

[0028] The sixth obtaining module 609 sends the network side switch according to the mode 3 controller S 1 disconnect command, grid side switch S 1 disconnected. The controller obtains the modulation voltage of the parallel converter through closed-loop control only by using the fundamental voltage reference required to support the low-voltage load. The series converter is shut down or switched to current control as needed in the off-grid steady state of mode 3; The sixth determination module 610, the controller obtains the modulation wave voltage of the series and parallel power circuits of the series-parallel compensation device based on the obtained modulation wave of the parallel converter and the modulation wave voltage of the series converter, and determines the control signal of the series and parallel power circuits through the sinusoidal pulse width modulator.

[0029] Figure 7 is a schematic diagram of a series-parallel compensation device provided by an embodiment of the present invention.

[0030] The schematic diagram of the series-parallel compensation device containing the energy storage system is shown in Figure 7, which includes a converter 701, a controller 702, a memory 703, and a computer program 704 stored in the memory 703 and executable on the controller 702. When the controller 702 executes the computer program 704, the steps in the above-mentioned on-grid and off-grid switching method embodiment are implemented, such as Figure 2 Alternatively, when the controller 702 executes the computer program 704, the power of each module / unit in the above embodiment is realized, for example Figure 6 The functions of modules 601 to 608 are shown.

[0031] Exemplarily, the computer program 704 can be divided into one or more modules / units, and the one or more modules / units are stored in the memory 703 and executed by the controller 702 to complete the embodiment of the present invention. The one or more modules / units can be a series of computer program instruction segments that can complete specific functions, and the instruction segments are used to describe the execution process of the computer program 704 in the series-parallel compensation system device containing the energy storage system. For example, the computer program 704 can be divided into a first acquisition module, a second acquisition module, a third acquisition module, a fourth acquisition module, a fourth determination module, a fifth acquisition module, a fifth determination module, a sixth acquisition module, and a sixth determination module. The functions of each module are as follows: a first obtaining module, which obtains the grid voltage, the grid connection point voltage, and the series converter compensation voltage according to the voltage sensor, obtains the output current of the parallel converter and the series converter and the load current according to the current sensor, and receives the off-grid instruction issued by the grid dispatching center; A second obtaining module is used to obtain a voltage reference of the series converter mode 1 according to the grid connection point voltage; A third obtaining module is used to obtain a harmonic current reference that needs to be compensated for the parallel converter based on the measured load current; The fourth obtaining module obtains the modulation wave voltage of each of the series converter and the parallel converter according to the voltage and current reference of each of the series converter and the parallel converter through the voltage and current closed-loop controller; a fourth determining module, determining whether the series-parallel compensation device changes its operating mode according to whether an off-grid instruction is received; The fifth obtaining module obtains the fundamental voltage reference required to support the low-voltage load based on the load voltage generator, and obtains the compensation harmonic voltage reference based on the collected grid-side voltage. The parallel converter obtains the modulation voltage of the parallel converter through the voltage-current dual closed-loop controller. At the same time, the series converter exits the harmonic voltage compensation link in mode 2, and the controller only retains the fundamental voltage reference in mode 1 to obtain the modulation voltage of the series converter. A fifth determining module, wherein after the controller receives the off-grid instruction, the controller switches from mode 1 to mode 2, and after determining that the mode 2 switching is completed, the controller switches from mode 2 to mode 3; The sixth acquisition module, if the grid connection conditions are met, obtains the grid-side switch and load switch closing instructions, closes the grid-side switch and general load switch, completes the hybrid transformer grid connection and stable power supply to the low-voltage load; a sixth determination module, wherein the controller obtains the modulation wave voltages of the series and parallel power circuits of the series-parallel compensation device based on the obtained modulation wave of the parallel converter and the modulation wave voltage of the series converter, and determines the control signals of the series and parallel power circuits through the sinusoidal pulse width modulator; The on-grid and off-grid switching control method based on the series-parallel compensation device may include, but is not limited to, a converter 701, a controller 702, and a memory 703. Those skilled in the art will understand that Figure 7 It is only an example of the hybrid transformer device 7 containing an energy storage system and does not constitute a limitation on the series-parallel compensation device containing an energy storage system. It may 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 may also include input and output devices, network access equipment, buses, etc.

[0032] The controller 702 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. A general-purpose processor may be a microprocessor or any conventional processor.

[0033] The memory 703 may be an internal storage unit of the series-parallel compensation device 7 containing an energy storage system, such as an external memory circuit of the series-parallel compensation device 7 containing 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 series-parallel compensation device 7 containing an energy storage system. Furthermore, the memory 703 may include both the internal storage unit of the series-parallel compensation device 7 containing an energy storage system and an external storage device. The memory 703 is used to store the computer program and other programs and data required by the hybrid transformer device containing an energy storage system. The memory 703 may also be used to temporarily store data that has been output or is about to be output.

[0034] 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.

[0035] 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.

[0036] 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.

[0037] 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.

[0038] 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.

[0039] 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.

[0040] 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.

[0041] 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 method for controlling on-grid and off-grid switching based on a series-parallel compensation device, characterized in that: include: Reclosing switch, shunt converter, energy storage battery, series converter, series coupling transformer, filter bank, current sensor, voltage sensor and controller; The first end of the first voltage sensor is connected to the low-voltage 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 in series with the secondary coil of the series coupling transformer, and is connected to the first end of the filter inductor of the parallel converter, the other end of the filter inductor of the parallel converter is connected to the first end of the first current sensor, the second end of the first current sensor is connected to the first end of the parallel converter, and the second end of the parallel converter is connected to the energy storage battery; the first end of the series converter is connected to the DC bus, the second end is connected to the first end of the second current sensor, the second end of the second current sensor is connected to the first end of the filter group, and the second end of the filter group is connected to the primary coil of the series coupling transformer; the parallel converter and the series converter are connected to the output end of the controller; the first end of the third current sensor is connected to the secondary coil of the series coupling transformer, and the second end of the third current sensor is connected to the low-voltage load.

2. A method for controlling on-grid and off-grid switching based on a series-parallel compensation device, characterized in that: include: The voltage sensor according to claim 1 measures the grid voltage on the grid side. , grid connection point voltage , and the series converter compensation voltage ; The current sensor according to claim 1 measures the output current of the parallel converter , the output current of the series converter , and the load current ; The controller is used to receive the voltage and current information measured by the above sensors, and to receive the switching and off-grid instructions of the grid-connected system issued by the grid dispatching center. If no off-grid instruction is received, the power supply system is grid-connected and the controller operates in mode 1; when an off-grid instruction is received, the controller switches to mode 2 during the transition period of the response instruction; when the closing switch is disconnected, the controller switches to mode 2. , the controller switches to mode 3, enters the off-grid steady state, and completes the off-grid operation of the independent power supply system; The mode 1 controller collects the grid connection point voltage , obtain the compensation harmonic voltage reference and fundamental voltage reference required to support the stable operation of the low-voltage load; the series controller obtains the modulation voltage of the series converter according to the voltage and current dual-loop controller; the controller obtains the modulation voltage of the series converter according to the measured load current , obtaining a compensation current reference, the parallel converter obtains a modulation voltage of the parallel converter through a current loop controller; the controller determines whether an off-grid instruction is received, and if so, the controller switches to mode 2, otherwise, the controller still operates in mode 1; The mode 2 controller obtains the fundamental voltage reference required to support the low-voltage load through the load voltage generator, and , obtaining a compensation harmonic voltage reference, the parallel converter obtains a modulation voltage of the parallel converter through a voltage and current dual closed-loop controller; The series converter exits the harmonic voltage compensation link in mode 2, and the controller only retains the fundamental voltage reference in mode 1 to obtain the modulation voltage of the series converter; After receiving the off-grid instruction, the controller switches from mode 1 to mode 2. After determining that the switching of mode 2 is completed, the controller switches from mode 2 to mode 3; The mode 3 controller sends the network side switch Disconnect command, grid-side switch Disconnect. The controller obtains the modulation voltage of the parallel converter through closed-loop control only by using the fundamental voltage reference required to support the low-voltage load. The series converter is shut down or switched to current control as needed in the off-grid steady state of mode 3; The controller obtains the modulation wave voltage of the series and parallel power circuits of the series-parallel compensation device based on the modulation wave of the parallel converter and the modulation wave voltage of the series converter, and obtains the control signal of the series and parallel power circuits through the sinusoidal pulse width modulator.

3. The method for controlling on-grid and off-grid switching based on a series-parallel compensation device according to claim 2, characterized in that: The controller does not receive the off-grid command, the power supply system is connected to the grid, and the controller operates in mode 1, setting the grid connection point voltage The fundamental component of the compensation voltage reference of the series converter is obtained by the SDFT harmonic detection method. and harmonic components , including the recursive formula of SDFT, as shown below: (1) in, is the SDFT result of the kth harmonic at the nth sampling point; is the rotation factor; is the signal value at the current sampling point; is the signal value M sampling points ago; M is the number of sampling points in a fundamental wave period; Perform SDFT calculations on each phase voltage signal to obtain the spectrum information of each harmonic. For the kth harmonic, the SDFT formula is as follows: (2) in, is the value of the a-phase voltage signal at the nth sampling point; Perform inverse SDFT transformation on each extracted harmonic component to obtain the harmonic voltage signal in the time domain. Here, the fundamental component (k=1) is extracted as follows: (3) According to the harmonic order k to be detected, the corresponding harmonic components are extracted from the SDFT operation results. The extracted harmonic components are subjected to inverse SDFT transformation to obtain the harmonic voltage signal in the time domain, so the fundamental component of the compensation voltage reference is obtained. and harmonic components , as follows: (4) in, is the reference load voltage amplitude, is the grid voltage Phase, Then, the modulation voltage of the series converter is obtained through the voltage and current dual loop controller. , as shown below: (5) Where, represents the proportional coefficient of the proportional resonant controller, Represents the resonance coefficient of the controller. represents the bandwidth at the center frequency of the controller, represents the fundamental angular frequency of the system, Indicates the harmonic order, 1, 3, 5, 7, 9, 11, 13, represents the proportionality coefficient; The controller measures the load current , get the compensation current reference, as shown below, (6) in is the fundamental current value obtained according to formula (3); Then, the modulation voltage of the parallel converter is obtained through the current loop controller. , as shown below: (7)。 4. The method for controlling on-grid and off-grid switching based on a series-parallel compensation device according to claim 2, wherein: The controller determines whether an off-grid command is received, and if so, the controller switches to mode 2, and if not, the controller still operates in mode 1; The Mode 2 controller obtains the fundamental voltage reference required to support the low-voltage load through the load voltage generator, as shown in the following formula: (8) in, is the phase of the grid-side voltage; The mode 2 controller is based on the collected grid side voltage , the compensated harmonic voltage reference is obtained as shown below: (9) in, is the fundamental component of the grid voltage obtained by equation (3); Then the mode 2 controller obtains the modulation voltage of the parallel converter through the voltage and current double closed-loop controller , as shown below: (10)。 5. The method for controlling on-grid and off-grid switching based on a series-parallel compensation device according to claim 2, characterized in that: After the controller determines that the mode 2 switch is completed, the controller switches from mode 2 to mode 3; The mode 3 controller sends the network side switch Disconnect command, grid-side switch Disconnect. The controller only uses the fundamental voltage reference required to support the low-voltage load, and the closed-loop control obtains the modulation voltage of the parallel converter. , as shown below: (11) in, is the current inner loop proportional parameter; The series converter is shut down or switched to current control as needed in the off-grid steady state of mode 3.

6. The method for controlling on-grid and off-grid switching based on a series-parallel compensation device according to claim 2, characterized in that: The controller obtains the modulation wave voltage of the series and parallel power circuits of the series-parallel compensation device based on the modulation wave of the parallel converter and the modulation wave voltage of the series converter, and obtains the control signal of the series and parallel power circuits through the sinusoidal pulse width modulator.

Images