A micro-grid plug-and-play and multi-mode switching method based on edge cloud cooperation and facing flexible networking

Abstract

The application provides a micro-grid plug-and-play and multi-mode switching method based on edge cloud cooperation and facing flexible networking, which comprises the following steps: device modeling, data interaction and identity comparison and matching in a cloud platform and an edge device, so as to realize the plug-and-play function of the edge device; device modeling, data interaction and identity registration in the cloud platform and an end device, so as to realize the plug-and-play function of the end device; superimposing the output current feedback gain and the current reference quantity in the grid-connected mode, so as to realize the micro-grid control in the grid-connected mode; generating the current reference quantity in the compensation mode by using a predetermined sine wave detection strategy, so as to realize the micro-grid control in the compensation mode and the switching from the grid-connected mode to the compensation mode; obtaining the input voltage reference quantity by using the predetermined sine wave detection strategy, so as to realize the micro-grid control in the island mode and the switching from the compensation mode to the island mode. The application can alleviate the limitations of the existing plug-and-play technology, and solve the problems of mode conversion and unstable control.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of micro-grid control, and more specifically, a micro-grid plug-and-play and multi-mode switching method based on edge cloud cooperation and facing flexible networking. BACKGROUND

[0002] In recent years, micro-grids, as an important component of distributed energy systems, have received extensive attention. The core value lies in the integration of various renewable energy sources such as solar and wind energy, and seamless connection with energy storage systems, providing reliable, efficient and environmentally friendly power services for the region. However, the development and popularization of micro-grid technology still faces many technical challenges.

[0003] The deployment and operation of micro-grids are complex. The traditional device access and configuration process often requires professional technical knowledge and specific equipment, which is not user-friendly. In this context, the introduction of plug-and-play technology brings new ideas for the deployment and maintenance of micro-grids. This technology aims to simplify the deployment, operation and maintenance of micro-grid systems, reducing the need for professional technical personnel, and improving the popularity of the system. In addition, adaptive synchronous networking is also a key area of micro-grid research. How to achieve flexible switching of micro-grids between different operating modes and smooth transition between grid-connected and island modes is a problem that needs to be solved.

[0004] Traditionally, the deployment and integration of micro-grid devices require a lot of manual operation and complex technical configuration. To solve this problem, researchers have proposed a series of automatic detection and configuration algorithms, allowing new energy resources and management components to be automatically integrated into existing micro-grid systems. In addition, the development based on international standards such as IEC 61850 also promotes the interoperability and standardization between micro-grid components, providing a solid foundation for the widespread application of plug-and-play technology.

[0005] The multi-mode operation of micro-grids makes it possible for stable and flexible operation in different situations. The main research direction is how to achieve smooth switching of micro-grids from grid-connected mode to island mode, and how to respond quickly to ensure the safety and stability of micro-grids and the main grid when faults occur. Currently, multi-mode switching mainly relies on advanced control strategies, such as model predictive control, fuzzy control and neural network control. Researchers are also exploring how to complete the switching in the shortest time to reduce instability and faults that may occur during the switching process. In addition, how to ensure that the equipment is not damaged and the power supply quality of the grid is maintained during the switching process is also the focus of current research.

[0006] Current research on implementing micro-grid plug-and-play and multi-mode switching functions is of great significance, but still has defects, specifically:

[0007] First, the current plug-and-play technology is mainly based on the IEC 61850 international standard, which means that the method has limitations within a specific technical and regulatory framework. Especially in China, this limitation may limit its applicability in different energy infrastructure backgrounds.

[0008] Second, the existing effective value calculation method needs to process a large number of voltage samples during the power grid fault detection process when the practical power grid fails, which puts higher requirements on computing resources and processing capacity.

[0009] Third, when the grid-connected inverter switches from grid-connected mode to islanded mode, the conversion time often exceeds half a grid cycle due to the commutation current of the static switch. During this shutdown delay, the microgrid voltage may be affected by the grid fault. In addition, the current control method may cause voltage drop or spikes during switching, which has not been effectively solved. SUMMARY

[0010] In view of the above defects or improvement needs of the prior art, the present application aims to provide a microgrid plug-and-play and multi-mode switching method based on edge cloud collaboration and oriented to flexible networking, to alleviate the limitations of existing plug-and-play technology and solve the problem of unstable mode conversion and control.

[0011] In order to achieve the above-mentioned purpose, the present application discloses a microgrid plug-and-play and multi-mode switching method based on edge cloud collaboration and oriented to flexible networking, comprising the following steps:

[0012] 1) Device modeling, data interaction, identity comparison and matching steps are performed in the cloud platform and edge device to realize the plug-and-play function of the edge device;

[0013] 2) Device modeling, data interaction, identity registration steps are performed in the cloud platform and end device to realize the plug-and-play function of the end device;

[0014] 3) The output voltage of the inverter is collected as the input quantity of the microgrid controller in grid-connected mode, and the phase-locked loop generates the current reference quantity in grid-connected mode. At the same time, the output current of the inverter is collected, and the output current feedback gain is added to the current reference quantity in grid-connected mode to form the current superposition reference quantity in grid-connected mode. The current superposition reference quantity in grid-connected mode generates the inverter modulation signal through the current compensator to realize the microgrid control in grid-connected mode;

[0015] 4) Collecting the inverter output load current as the input quantity of the micro-grid controller in compensation mode, using the predetermined sinusoidal wave detection strategy to generate the current reference quantity in compensation mode, meanwhile, collecting the inverter output current, the output current after the output current feedback gain is superimposed with the current reference quantity in compensation mode to form the current superimposed reference quantity in compensation mode, the current superimposed reference quantity in compensation mode generates the inverter modulation signal through the current compensator, realizing the micro-grid control in compensation mode;

[0016] 5) Collecting the inverter output voltage as the input quantity of the micro-grid controller in island mode, using the input voltage reference quantity obtained by the predetermined sinusoidal wave detection strategy to superimpose the reference voltage to form the input voltage superimposed reference quantity, the voltage superimposed reference quantity outputs the current reference quantity in island mode through the voltage compensator, the current reference quantity in island mode is superimposed with the output current gain quantity to form the current superimposed reference quantity in island mode, after the current compensator, the inverter modulation signal is generated, realizing the micro-grid control in island mode.

[0017] Further, in the step 1), the device modeling, data interaction and identity comparison matching steps are performed in the cloud platform and the edge device, realizing the plug and play function of the edge device, specifically:

[0018] Step 1.1) In the cloud platform, a one-time information model and an encryption certificate are pre-set for the edge device;

[0019] Step 1.2) The cloud platform creates a product type according to the one-time information model file of the edge device;

[0020] Step 1.3) The cloud platform completes the secondary modeling of the edge device;

[0021] Step 1.4) The edge device uploads its identity information to the cloud platform through the Internet of Things application program;

[0022] Step 1.5) After receiving the identity information of the edge device, the cloud platform performs identity comparison and matching according to the already filed information, and gives the edge device access permission after successful matching;

[0023] Step 1.6) The edge device sends an online message to the cloud platform.

[0024] Further, in the step 2), the device modeling, data interaction and identity registration steps are performed in the cloud platform and the end device, realizing the plug and play function of the end device, specifically:

[0025] Step 2.1) The cloud platform pre-sets a one-time device model of the end device;

[0026] Step 2.2) The edge device installs an end device collection APP application program;

[0027] Step 2.3) After the end device is powered on, the identity information of the end device is uploaded to the edge device;

[0028] Step 2.4) The edge device completes the registration process between the end device and the edge device.

[0029] Step 2.5) After the end device is successfully registered, the edge device sends an end device identity registration message to the cloud platform.

[0030] Step 2.6) The cloud platform completes the filing of the end device.

[0031] Further, the step 3) specifically comprises:

[0032] Step 3.1) Collecting the inverter output voltage and inverter output current, denoted as v ac and i ac ;

[0033] Step 3.2) Designing the voltage feedback gain H v (s) of the microgrid controller in the grid-connected mode and the output current feedback gain H i1 of the microgrid controller.

[0034] Step 3.3) Generating a voltage gain quantity through the voltage feedback gain link, denoted as v ach .

[0035] Step 3.4) Generating a current gain quantity through the current feedback gain link, denoted as i ach .

[0036] Step 3.5) Setting a current command value I p .

[0037] Step 3.6) Recording the voltage gain quantity v ach and the phase angle information θ s after the phase-locked loop.

[0038] Step 3.7) Calculating the current reference quantity i ref_G under the joint action of the phase angle information and the current command value.

[0039] Step 3.8) Inputting the superimposed reference quantity of the current reference quantity and the current gain quantity, passing through the current compensator G c1 in the grid-connected mode, and outputting the inverter modulation signal in the grid-connected mode, wherein the proportional-resonant control method is adopted to design the current compensator G c1 (s) in the grid-connected mode, specifically,

[0040] through the admittance compensator G cv , the current compensator G c1 , and the DSP modulation gain F dspThe inverter modulation signal is obtained, and according to the superposition principle, the output current is affected by G id1 (s) and G iv (s), wherein G id1 (s) is the duty ratio of the output current transfer function, and G iv (s) is the output voltage to output current transfer function, and the expressions of the two transfer functions are respectively:

[0041]

[0042]

[0043] wherein V dc is the DC input voltage, r L and r C are the equivalent resistances of the output inductance L O and the output capacitance C O respectively;

[0044] The open-loop current loop transfer function T i (s) can be expressed as:

[0045] T i (s) = G c1 (s) F dsp G id1 (s) H i1 (s) (3)

[0046] wherein H i1 (s) is the inverter output current feedback gain;

[0047] The closed-loop transfer function of the inverter output voltage v ac and the inverter output current i ac can be expressed as:

[0048]

[0049] wherein H v (s) is the voltage feedback gain, and for eliminating the independent term of the duty ratio, the admittance compensator G cv (s) is designed as:

[0050]

[0051] For reducing the steady-state error, the current compensator G c1 (s) is designed as a proportional resonant type controller with a resonant frequency of 50Hz:

[0052]

[0053] wherein K p1 , Kr1 , ω c and ω1are proportional gain, resonant gain, equivalent bandwidth and resonant frequency in grid-connected mode respectively.

[0054] Further, the step 4) specifically comprises:

[0055] Step 4.1) collecting the load current of the inverter output and the inverter output current, denoted as i load and i ac ;

[0056] Step 4.2) designing the load current feedback gain H i2 of the micro-grid controller in compensation mode, the output current feedback gain H i1 of the micro-grid controller;

[0057] Step 4.3) generating the load current gain quantity through the load current feedback gain link, denoted as i loadh ;

[0058] Step 4.4) generating the current gain quantity through the current feedback gain link, denoted as i ach ;

[0059] Step 4.5) calculating the current reference quantity i ref_C in compensation mode by using the predetermined sinusoidal detection strategy;

[0060] Step 4.6) inputting the superimposed reference quantity of the current reference quantity and the current gain quantity, through the current compensator G c2 in compensation mode, and outputting the inverter modulation signal in compensation mode, wherein the current compensator G c2 in compensation mode is designed by using the commutation current compensation strategy, specifically,

[0061]

[0062] wherein K p4 and K r2 are proportional gain and resonant gain of the commutation current compensation strategy.

[0063] Further, the step 5) specifically comprises:

[0064] Step 5.1) collecting the inverter output voltage and the inverter output current, denoted as v ac and i ac ;

[0065] Step 5.2) designing the voltage feedback gain H v of the micro-grid controller in compensation mode, the output current feedback gain H i1 of the micro-grid controller;

[0066] Step 5.3) generating a voltage gain quantity through a voltage feedback gain link, denoted as v ach ;

[0067] Step 5.4) generating a current gain quantity through a current feedback gain link, denoted as i ach ;

[0068] Step 5.5) setting a voltage reference value V ref ;

[0069] Step 5.6) calculating an input voltage reference quantity v iref ;

[0070] Step 5.7) calculating a superimposed value of the voltage reference value and the input voltage reference quantity, through a voltage compensator G v , outputting a current reference quantity i ref_S in the island mode, wherein the voltage compensator G v is designed by using a proportional-resonant control method, specifically,

[0071]

[0072] wherein K p3 and K r3 are proportional gain and resonant gain in the island mode;

[0073] Step 5.8) inputting a superimposed reference quantity of the current reference quantity and the current gain quantity, through a current compensator G c3 in the island mode, outputting an inverter modulation signal in the island mode, wherein the current compensator G c1 (s) in the island mode is designed by using a proportional-resonant control method, specifically,

[0074] The inverter output current is affected by G id2 (s), and the double-loop controller is designed to suppress LC resonance and regulate the output voltage, and an open-loop voltage transfer function is represented as:

[0075]

[0076] wherein G id2 (s), G v (s), G c3 (s) and Z load (s) are duty ratio, voltage compensator in the island mode, current compensator in the island mode and output impedance of the output current transfer function;

[0077] G id2 (s) is obtained by the following way:

[0078]

[0079] Z load (s) is a parallel structure of output capacitance and equivalent output resistance, denoted as:

[0080]

[0081] where R O is the equivalent output resistance;

[0082] To compensate for the switching current, the controller G c3 (s) is designed as a proportional-resonant type controller and adopts a commutation current compensation strategy as follows:

[0083]

[0084] where K p2 and ω LC are the proportional gain of the current controller and the LC resonant frequency.

[0085] Further, step 1.1) pre-sets a one-time information model and encryption certificate for the edge device on the cloud platform, specifically:

[0086] a) the manufacturer defines a one-time information model for each device, which contains all the basic physical and electrical properties of the device, including the model, power level, rated current and voltage of the device;

[0087] b) the manufacturer converts the model into electronic format using a standard format;

[0088] c) the manufacturer contacts the certificate authority to apply for an encryption certificate;

[0089] d) the certificate authority verifies the identity and request of the manufacturer, and then issues a public key / private key pair and the corresponding certificate;

[0090] e) the manufacturer stores the one-time information model and private key / certificate in the firmware or internal memory of the device;

[0091] f) when the device is installed and connected to the microgrid, the device broadcasts its one-time information model;

[0092] g) after receiving the broadcasted information, the management system of the microgrid verifies the authenticity and integrity of the encryption certificate using the manufacturer's public key;

[0093] h) once the verification is successful, the device is considered a trusted device and is added to the microgrid.

[0094] Further, step 1.3) the cloud platform completes the edge device secondary model filing, specifically:

[0095] a) The first time the device connects to the microgrid, the central control system requests the operating parameters of the device, such as the control strategy of the device, communication interface and protection settings;

[0096] b) The device responds to the request and sends the above-mentioned parameters to the central control system;

[0097] c) The control system combines the received parameters with the primary information model to create a complete secondary information model of the device;

[0098] d) The secondary information model is verified using the operating specifications and standards of the microgrid (IEC-61850);

[0099] e) Once the model verification is successful, the central control system stores it in a database or other appropriate storage system;

[0100] f) In subsequent operation, when the device needs to be controlled or adjusted, its secondary information model is directly referenced.

[0101] Further, step 2.6) the cloud platform completes the end device filing, specifically:

[0102] a) According to the uploaded identity information, the cloud platform creates a new record for the device in its database, which stores all basic information, status, historical data and other related information of the device;

[0103] b) When the device filing is completed, the cloud platform will determine which secondary devices to associate with according to its identity information and pre-defined rules or algorithms;

[0104] c) Once the association is completed, the cloud platform can send a confirmation message to the end device, notifying it that it has been successfully filed and associated with the corresponding secondary device.

[0105] Further, the predetermined sine wave detection strategy is specifically:

[0106] 1) Calculate the RMS value of the grid voltage, which is commonly used for real-time monitoring of the grid voltage. The RMS calculation of the grid voltage is represented as:

[0107]

[0108] 2) Through an all-pass filter, a 90° phase delay signal with the same amplitude as the grid voltage is obtained. Using the trigonometric identity, the voltage amplitude V g (k) of the grid voltage v m is obtained as follows:

[0109]

[0110] 3) Use the grid angle θ scosine of the phase angle of the voltage v m (k+1) and the product of the amplitude V p (k+1) to detect a grid fault. g (k+1) and v p (k+1) to detect a grid fault.

[0111] 4) If the average error between v p (k+1) and v g (k+1) is greater than the threshold V th , the switch will be opened to disconnect from the grid.

[0112] Overall, the above technical solutions conceived by the present application have the following beneficial effects compared with the prior art:

[0113] (1) Real-time and high efficiency: Through the "edge-cloud" collaborative working mechanism, the present application can realize the immediate access and integration of microgrid devices, reducing the complex configuration and long waiting time required in traditional methods, thereby improving the response speed and working efficiency of the microgrid.

[0114] (2) Flexibility and stability: The multi-mode switching method adopted by the present application can quickly adapt to changes and emergencies of the external grid, ensuring the stable operation of the microgrid under various power environments. Whether it is normal operation, external grid fault not removed or fault removed, the present application can realize the fast and smooth switching of the microgrid.

[0115] (3) Overcome standard limitations: Although the current plug-and-play technology is mainly based on the IEC 61850 standard, the method of the present application does not completely rely on this standard, thereby expanding its applicability under different technical and regulatory frameworks, especially in the context of China's energy infrastructure. BRIEF DESCRIPTION OF DRAWINGS

[0116] Figure 1 is the microgrid plug-and-play function application framework based on "edge-cloud" collaboration of the embodiment of the present application;

[0117] Figure 2 is a data interaction schematic diagram between cloud and edge of the microgrid plug-and-play function application framework of the embodiment of the present application;

[0118] Figure 3 is a data interaction schematic diagram between cloud and edge of the microgrid plug-and-play function application framework of the embodiment of the present application;

[0119] Figure 4 is a schematic diagram of the inverter system architecture for multi-mode switching of the microgrid of the embodiment of the present application;

[0120] Figure 5 is a transfer function control block diagram of the inverter for micro-grid multi-mode switching in the grid-connected mode of an embodiment of the application;

[0121] Figure 6 is a transfer function control block diagram of the inverter for micro-grid multi-mode switching in the compensation mode of an embodiment of the application;

[0122] Figure 7 is a transfer function control block diagram of the inverter for micro-grid multi-mode switching in the island mode of an embodiment of the application;

[0123] Figure 8 is a calculation block diagram of the predetermined sinusoidal wave detection strategy of an embodiment of the application;

[0124] Figure 9 is a simulation result of mode conversion from the compensation mode to the island mode, wherein (a) the FCCC strategy is adopted, and (b) the FCCC strategy is not adopted;

[0125] Figure 10 is a flowchart of a micro-grid plug-and-play and multi-mode switching method based on edge cloud cooperation and oriented to flexible networking according to an embodiment of the application. DETAILED DESCRIPTION

[0126] The technical solutions in the application will be described clearly and completely below in combination with the drawings and specific embodiments in the application.

[0127] As shown in Figure 4 and Figure 10 , a micro-grid plug-and-play and multi-mode switching method based on edge cloud cooperation and oriented to flexible networking is provided according to an embodiment of the application, which includes the following steps:

[0128] 1) Device modeling, data interaction, identity comparison and matching steps are performed in the cloud platform and the edge device to realize the plug-and-play function of the edge device (as shown in Figure 1 and Figure 2 );

[0129] 2) Device modeling, data interaction, identity registration steps are performed in the cloud platform and the edge device to realize the plug-and-play function of the edge device (as shown in Figure 1 and Figure 3 );

[0130] 3) The output voltage of the inverter is collected as the input quantity of the micro-grid controller in the grid-connected mode, and the phase-locked loop (PLL) is used to generate the current reference quantity in the grid-connected mode. At the same time, the output current of the inverter is collected, which is superimposed with the current reference quantity in the grid-connected mode through the output current feedback gain to form the current superimposed reference quantity in the grid-connected mode. The current superimposed reference quantity is used to generate the inverter modulation signal through the current compensator to realize the micro-grid control in the grid-connected mode (as shown inFigure 5

[0131] 4) Collecting the inverter output load current as the input quantity of the micro-grid controller in compensation mode, generating the current reference quantity in compensation mode by using the predetermined sinusoidal detection strategy, collecting the inverter output current, superimposing the current reference quantity in compensation mode after the output current feedback gain to form the current superimposed reference quantity in compensation mode, generating the inverter modulation signal through the current compensator to realize the micro-grid control in compensation mode (as shown in Figure 6

[0132] 5) Collecting the inverter output voltage as the input quantity of the micro-grid controller in island mode, superimposing the input voltage reference quantity obtained by using the predetermined sinusoidal detection strategy and the reference voltage to form the input voltage superimposed reference quantity, outputting the current reference quantity in island mode through the voltage compensator, superimposing the output current gain quantity to form the current superimposed reference quantity in island mode, generating the inverter modulation signal through the current compensator to realize the micro-grid control in island mode (as shown in Figure 7

[0133] Specifically, in the step 1), the device modeling, data interaction and identity matching steps are performed in the cloud platform and the edge device to realize the plug-and-play function of the edge device, specifically:

[0134] Step 1.1) In the cloud platform, a one-time information model and an encryption certificate are pre-set for the edge device.

[0135] Step 1.2) The cloud platform creates a product type according to the one-time information model file of the edge device.

[0136] Step 1.3) The cloud platform completes the secondary modeling of the edge device.

[0137] Step 1.4) The edge device uploads its identity information to the cloud platform through the Internet of Things application program.

[0138] Step 1.5) After receiving the identity information of the edge device, the cloud platform performs identity matching according to the already filed information, and gives the edge device access permission after successful matching.

[0139] Step 1.6) The edge device sends an online message to the cloud platform.

[0140] Specifically, in the step 2), the device modeling, data interaction and identity registration steps are performed in the cloud platform and the end device to realize the plug-and-play function of the end device, specifically:

[0141] Step 2.1) The cloud platform pre-sets a one-time device model of the end device.

[0142] ​​​Step 2.2) Install the client device collection APP application on the edge device.

[0143] Step 2.3) After the end device is powered on, it uploads its identity information to the edge device.

[0144] Step 2.4) The edge device completes the registration process between the end device and the edge device.

[0145] Step 2.5) After the end device is successfully registered, the edge device sends an end device identity registration message to the cloud platform.

[0146] Step 2.6) The cloud platform completes the terminal device profile.

[0147] Specifically, in step 3), the inverter output voltage is collected as the input of the microgrid controller in the grid-connected mode, and the current reference in the grid-connected mode is generated through the phase-locked loop link. At the same time, the inverter output current is collected, and the current is superimposed with the current reference in the grid-connected mode through the output current feedback gain to form the current superposition reference in the grid-connected mode. The current superposition reference is passed through the current compensator to generate the inverter modulation signal to realize the microgrid control in the grid-connected mode. The control gear of the inverter is adjusted to the G gear, and the current reference is used. Figure 5 The control block diagram shown controls the inverter. Specifically:

[0148] Step 3.1) Collect the inverter output voltage and inverter output current, denoted as v ac and i ac .

[0149] Step 3.2) Design the voltage feedback gain H of the microgrid controller in grid-connected mode v (s), the output current feedback gain H of the microgrid controller i1 .

[0150] Step 3.3) Generate the voltage gain after the voltage feedback gain link, recorded as v ach .

[0151] Step 3.4) Generate the current gain after the current feedback gain link, recorded as i ach .

[0152] Step 3.5) Set the current command value I p .

[0153] Step 3.6) Record the voltage gain v ach Phase angle information θ after passing through the phase-locked loop s .

[0154] Step 3.7) Calculate the current reference i under the combined action of phase angle information and current command value ref_G .

[0155] Step 3.8) input the superimposed reference quantity of the current reference quantity and the current gain quantity, pass through the current compensator G c1 in grid-connected mode, output the inverter modulation signal in grid-connected mode. Wherein, the proportional-resonant control method is adopted to design the current compensator G c1 (s) in grid-connected mode, and specifically

[0156] obtain the inverter modulation signal through the admittance compensator G cv , the current compensator G c1 and the DSP modulation gain F dsp . According to the superposition principle, the output current is affected by G id1 (s) and G iv (s). Wherein, G id1 (s) is the duty ratio of the output current transfer function, and G iv (s) is the output voltage to output current transfer function. The expressions of the two transfer functions are respectively:

[0157]

[0158]

[0159] Wherein, V dc is the DC input voltage, r L and r C are the equivalent resistances of the output inductance L O and the output capacitance C O .

[0160] The open-loop current loop transfer function T i (s) can be expressed as:

[0161] T i (s) = G c1 (s) F dsp G id1 (s) H i1 (s) (3)

[0162] Wherein, H i1 (s) is the inverter output current feedback gain.

[0163] The closed-loop transfer function of the inverter output voltage v ac and the inverter output current i ac can be expressed as:

[0164]

[0165] Wherein, H v(s) is the voltage feedback gain. Since the given value is independent of the duty ratio, the resulting steady-state inverter output current will be affected. In order to eliminate the independent term of the duty ratio, the admittance compensator G cv (s) is designed as:

[0166]

[0167] Therefore, the independent term in the closed-loop transfer function of the inverter output current loop can be eliminated. In order to reduce the steady-state error, the current compensator G c1 (s) is designed as a proportional-resonant type controller with a resonant frequency of 50Hz:

[0168]

[0169] where K p1 , K r1 , ω c and ω1 are the proportional gain, the resonant gain, the equivalent bandwidth and the resonant frequency in the grid-connected mode, respectively.

[0170] Specifically, in step 4), the inverter output load current is collected as the input quantity of the microgrid controller in the compensation mode, and a predetermined sinusoidal detection strategy is used to generate the current reference quantity in the compensation mode. At the same time, the inverter output current is collected, which is superimposed with the current reference quantity in the compensation mode after passing through the output current feedback gain to form the current superimposed reference quantity in the compensation mode. The reference quantity generates the inverter modulation signal through the current compensator to realize the microgrid control in the compensation mode. The control range of the inverter is adjusted to the C range, and the control block diagram shown in the figure is used to control the inverter to realize the switching of the microgrid from the grid-connected mode to the compensation mode, specifically: Figure 6

[0171] Step 4.1) Collect the inverter output load current and the inverter output current, denoted as i load and i ac .

[0172] Step 4.2) Design the load current feedback gain H i2 of the microgrid controller in the compensation mode, the output current feedback gain H i1 of the microgrid controller.

[0173] Step 4.3) Generate the load current gain quantity through the load current feedback gain link, denoted as i loadh .

[0174] Step 4.4) Generate the current gain quantity through the current feedback gain link, denoted as i ach .

[0175] ​Step 4.5) Use the predetermined sine wave detection strategy to calculate the current reference i in the compensation mode ref_C .

[0176] Step 4.6) Input the current reference and the superposition reference of the current gain, and pass through the current compensator G in compensation mode. c2 , output the inverter modulation signal in compensation mode. Among them, the current compensator G in compensation mode is designed using the commutation current compensation strategy. c2 , specifically

[0177]

[0178] Among them, K p4 and K r2 are the proportional gain and resonant gain of the commutation current compensation strategy.

[0179] Specifically, in step 5), the inverter output voltage is collected as the input of the microgrid controller in the island mode. The input voltage reference obtained by the predetermined sine wave detection strategy is superimposed with the reference voltage to form an input voltage superposition reference. The voltage superposition reference passes through the voltage compensator to output the current reference in the island mode. The reference is superimposed with the output current gain to form the current superposition reference in the island mode. After passing through the current compensator, an inverter modulation signal is generated to realize the microgrid control in the island mode. The control gear of the inverter is adjusted to the S gear, and the current is superimposed. Figure 7 The control block diagram shown controls the inverter to switch the microgrid from compensation mode to island mode. Specifically:

[0180] Step 5.1) Collect the inverter output voltage and inverter output current, record as v ac and i ac

[0181] Step 5.2) Design the voltage feedback gain H of the microgrid controller in compensation mode v , the output current feedback gain H of the microgrid controller i1

[0182] Step 5.3) Generate the voltage gain after the voltage feedback gain link, denoted as v ach .

[0183] Step 5.4) Generate the current gain after the current feedback gain link, recorded as i ach .

[0184] Step 5.5) Set the voltage reference value V ref .

[0185] Step 5.6) Use the predetermined sine wave detection strategy to calculate the input voltage reference v iref.

[0186] Step 5.7) The superimposed value of the voltage reference value and the input voltage reference amount is calculated through the voltage compensator G v , and the current reference amount i ref_S in the island mode is output. Wherein the voltage compensator G v is designed by using the proportional-resonant control method, specifically

[0187]

[0188] Wherein, K p3 and K r3 are the proportional gain and the resonant gain in the island mode.

[0189] Step 5.8) The superimposed reference amount of the input current reference amount and the current gain amount is input through the current compensator G c3 in the island mode, and the inverter modulation signal in the island mode is output. Wherein the current compensator G c1 (s) in the island mode is designed by using the proportional-resonant control method, specifically

[0190] The inverter output current is affected by G id2 (s), and the double-loop controller is designed to suppress the LC resonance and adjust the output voltage. The open-loop voltage transfer function is represented as:

[0191]

[0192] Wherein, G id2 (s), G v (s), G c3 (s) and Z load (s) are the duty ratio, the voltage compensator in the island mode, the current compensator in the island mode and the output impedance of the output current transfer function.

[0193] G id2 (s) is obtained by the following way:

[0194]

[0195] Z load (s) is the parallel structure of the output capacitor and the equivalent output resistance, represented as:

[0196]

[0197] Wherein, R O is the equivalent output resistance.

[0198] Therefore, in order to compensate the switching current, the controller G c3(s) is designed as a proportional-resonant controller and adopts a commutation current compensation strategy as follows:

[0199]

[0200] where K p2 and ω LC are the proportional gain of the current controller and the LC resonant frequency.

[0201] Specifically, the modeling process of the edge device primary information model and encryption certificate is as follows:

[0202] a) The manufacturer defines a primary information model for each device, which contains all the basic physical and electrical properties of the device, such as the device model, power level, rated current and voltage, etc.

[0203] b) The manufacturer converts the model into an electronic format using a standard format such as XML, JSON, etc.

[0204] c) To ensure communication security, the manufacturer contacts an authoritative certificate authority (CA) to apply for an encryption certificate.

[0205] d) The certificate authority verifies the manufacturer's identity and request, and then issues a public key / private key pair and the corresponding certificate.

[0206] e) The manufacturer stores the primary information model and private key / certificate in the device's firmware or internal memory.

[0207] f) When the device is installed and connected to the microgrid, the device broadcasts its primary information model.

[0208] g) After receiving the broadcasted information, the microgrid's management system verifies the authenticity and integrity of the encryption certificate using the manufacturer's public key.

[0209] h) Once the verification is successful, the device is considered a trusted device and is added to the microgrid.

[0210] Specifically, the edge device secondary model filing process is as follows:

[0211] a) When the device is first connected to the microgrid, the central control system requests the device's operating parameters, such as the device's control strategy, communication interface, and protection settings.

[0212] b) The device responds to the request and sends the above parameters to the central control system.

[0213] c) The control system combines the received parameters with the primary information model to create a complete device secondary information model.

[0214] d) The secondary information model is verified using the microgrid operation specifications and standards (IEC-61850).

[0215] e) Once the model verification is successful, the central control system stores it in a database or other appropriate storage system.

[0216] f) In subsequent operation, when the device needs to be controlled or adjusted, its secondary information model can be directly referenced.

[0217] Specifically, the cloud platform completes the end device filing process, specifically:

[0218] a) According to the uploaded identity information, the cloud platform creates a new record for the device in its database. This record will store all basic information, status, historical data and other related information of the device.

[0219] b) After the device filing is completed, the cloud platform will determine which secondary devices to associate with according to its identity information and pre-defined rules or algorithms. For example, a generator (primary device) may need to be associated with a controller (secondary device) to ensure its normal operation. The cloud platform will update its database to associate the primary device with the corresponding secondary device.

[0220] c) Once the association is complete, the cloud platform can send a confirmation message to the end device, notifying it that it has been successfully filed and associated with the corresponding secondary device.

[0221] Specifically, the predetermined sinusoidal wave detection strategy is as follows: Figure 8 As shown, specifically:

[0222] 1) Calculate the RMS value of the grid voltage, which is commonly used for real-time monitoring of the grid voltage. The RMS calculation of the grid voltage can be expressed as:

[0223]

[0224] 2) Through the all-pass filter, a 90° phase delay signal with the same amplitude as the grid voltage can be obtained. Using the trigonometric identity, the voltage amplitude V g of the grid voltage v m (k) can be obtained as follows:

[0225]

[0226] 3) Using the cosine of the grid angle θ s and the amplitude V m , the next period of the predetermined grid voltage v p (k+1) is obtained. Then the actual grid voltage v g (k+1) of the next period is compared with vp (k+1) are compared to detect a grid fault.

[0227] 4) If v p (k+1) and v g (k+1) are compared to detect a grid fault. th (k+1) are compared to detect a grid fault.

[0228] Specifically, in the embodiment, the micro-grid plug-and-play and multi-mode switching method based on "edge cloud" collaboration considered by the application constructs a three-layer architecture of cloud layer, control layer and edge layer to realize the conceptualization of plug-and-play random power supply and realize seamless conversion from grid-connected mode to island mode, so as to alleviate the limitations of existing plug-and-play technology and solve the problem of unstable mode conversion and control.

[0229] To verify the performance of the proposed strategy, a prototype system is simplified and a simulation model of a 1kW prototype SGI is constructed, which has the specifications shown in Table 1. The experimental micro-grid system is composed of the same SGI, static switch and resistive load. The DC power supply of the SGI is a 110V AC output generated by grid connection, which can be a DC power supply or a battery pack. For this test, a 200-V, 2k-VA DC power supply with a parallel 1kW 6678 resistor is used as the power supply. The proposed strategy is verified by computer simulation.

[0230] Table 1 Specifications of SGI simulation model

[0231]

[0232] Figure 9 The simulation results of mode conversion from compensation mode to island mode with or without the proposed strategy are shown. The waveforms of the static switch state v ss , the static switch current i ss and the grid voltage v g with the proposed strategy are shown in (a) of FIG. Figure 9 , and the similar simulation waveforms without the proposed strategy are shown in (b) of FIG. Figure 9 . It can be seen that with the proposed strategy, the static switch current can reach zero and return to the blocking state immediately. In other words, the proposed strategy can immediately isolate the micro-grid from the grid fault.

[0233] The micro-grid plug-and-play and multi-mode switching method based on "edge cloud" collaboration proposed by the application constructs a three-layer architecture of cloud layer, control layer and edge layer, and adopts the proposed strategy, and finally realizes seamless conversion from grid-connected mode to island mode.

[0234] Those skilled in the art can easily understand that the above description is only the preferred embodiment of the present application, and is not intended to limit the present application. Any modification, equivalent replacement and improvement made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A microgrid plug-and-play and multi-mode switching method based on edge cloud cooperation and oriented to flexible networking, characterized in that The method comprises the following steps: 1) device modeling, data interaction, and identity comparison and matching in the cloud platform and the edge device to realize the plug-and-play function of the edge device; 2) device modeling, data interaction, and identity registration in the cloud platform and the end device to realize the plug-and-play function of the end device; 3) collecting the output voltage of the inverter as the input quantity of the micro-grid controller in the grid-connected mode, generating the current reference quantity in the grid-connected mode through a phase-locked loop, collecting the output current of the inverter at the same time, superimposing the output current feedback gain and the current reference quantity in the grid-connected mode to form the current superimposed reference quantity in the grid-connected mode, generating the inverter modulation signal through the current compensator to realize the micro-grid control in the grid-connected mode; 4) collecting the output load current of the inverter as the input quantity of the micro-grid controller in the compensation mode, generating the current reference quantity in the compensation mode by using a predetermined sinusoidal wave detection strategy, collecting the output current of the inverter at the same time, superimposing the output current feedback gain and the current reference quantity in the compensation mode to form the current superimposed reference quantity in the compensation mode, generating the inverter modulation signal through the current compensator to realize the micro-grid control in the compensation mode; 5) collecting the output voltage of the inverter as the input quantity of the micro-grid controller in the island mode, superimposing the input voltage reference quantity obtained by using the predetermined sinusoidal wave detection strategy and the reference voltage to form the input voltage superimposed reference quantity, outputting the current reference quantity in the island mode through the voltage compensator, superimposing the current reference quantity in the island mode and the output current gain to form the current superimposed reference quantity in the island mode, generating the inverter modulation signal through the current compensator to realize the micro-grid control in the island mode. 2.The microgrid plug and play and multi-mode switching method based on edge cloud cooperation and oriented to flexible networking according to claim 1, wherein, In the step 1), the device modeling, data interaction, and identity comparison and matching in the cloud platform and the edge device realize the plug-and-play function of the edge device, specifically: Step 1.1) setting a one-time information model and an encryption certificate for the edge device on the cloud platform; Step 1.2) creating a product type according to the one-time information model file of the edge device by the cloud platform; Step 1.3) completing the secondary modeling of the edge device by the cloud platform; Step 1.4) uploading the identity information of the edge device to the cloud platform through the Internet of Things application program; Step 1.5) comparing and matching the identity information according to the information in the archive after receiving the identity information of the edge device by the cloud platform, and giving the edge device access permission after the matching is successful; Step 1.6) sending the online message to the cloud platform by the edge device. 3.The microgrid plug and play and multi-mode switching method based on edge cloud cooperation and oriented to flexible networking according to claim 1, wherein, In the step 2), the device modeling, data interaction, and identity registration in the cloud platform and the end device realize the plug-and-play function of the end device, specifically: Step 2.1) pre-setting the one-time device model of the end device by the cloud platform; Step 2.2) installing the end device collection APP application program on the edge device; Step 2.3) uploading the identity information of the end device to the edge device after the end device is powered on; Step 2.4) completing the registration process between the end device and the edge device by the edge device. Step 2.5) After the end device successfully registers, the edge device sends an end device identity registration message to the cloud platform; Fees. 4.The microgrid plug and play and multi-mode switching method based on edge cloud cooperation and oriented to flexible networking according to claim 1, wherein, The step 3) specifically includes: Step 3.1) Collecting inverter output voltage and inverter output current, denoted as v ac and i ac ; Step 3.2) Design the voltage feedback gain H of the microgrid controller in grid-connected mode v (s), the output current feedback gain H of the microgrid controller i1 ; Step 3.3) generates a voltage gain quantity, denoted by v, through a voltage feedback gain block ach ; Step 3.4) generates a current gain quantity, denoted by i, through a current feedback gain block ach ; Step 3.5) Setting the current command value I p ; Step 3.6) Record the voltage gain amount v ach Phase angle information θ after the phase-locked loop s ; Step 3.7) Calculate the current reference quantity i under the joint action of the phase angle information and the current command value ref_G ; Step 3.8) input the superimposed reference quantity of the current reference quantity and the current gain quantity, pass through the current compensator G in the grid-connected mode c1 , and output the inverter modulation signal in the grid-connected mode, wherein the proportional-resonant control method is adopted to design the current compensator G in the grid-connected mode c1 (s), specifically, By means of the admittance compensator G cv , the current compensator G c1 and the DSP modulation gain F dsp , the inverter modulation signal is obtained, and according to the superposition principle, the output current is affected by G id1 (s) and G iv (s), wherein G id1 (s) is the duty ratio of the output current transfer function, and G iv (s) is the output voltage to output current transfer function, and the expressions of the two transfer functions are respectively: wherein V dc is the DC input voltage, r L and r C are the equivalent resistances of the output inductor L O and the output capacitor C O respectively; Open-circuit current loop transfer function T i (s) can be expressed as: T i (s) = G c1 (s) F dsp G id1 (s) H i1 (s) (3) where H i1 (s) is the inverter output current feedback gain; Inverter output voltage v ac The closed loop transfer function of the inverter output current i ac may be expressed as: where H v (s) is the voltage feedback gain, and G cv (s) is designed as: To reduce the steady state error, a current compensator G c1 (s) is designed as a proportional resonant controller with a resonant frequency of 50 Hz: where K p1 , K r1 , ω c , and ω1are the proportional gain, the resonant gain, the equivalent bandwidth, and the resonant frequency in grid-connected mode, respectively.

5. The microgrid plug-and-play and multi-mode switching method based on edge cloud cooperation and oriented to flexible networking according to claim 1, characterized in that, The step 4) specifically includes: Step 4.1) Collecting the inverter output load current and the inverter output current, denoted as i load and i ac ; Step 4.2) Design the load current feedback gain H of the microgrid controller in the compensation mode i2 , the output current feedback gain H of the microgrid controller i1 ; Step 4.3) generates a load current gain quantity, denoted by i loadh ; Step 4.4) generates a current gain quantity, denoted by i, through a current feedback gain block ach ; Step 4.5) The current reference quantity i is calculated in the compensated mode using the predetermined sinusoidal wave detection strategy ref_C ; Step 4.6) input the superimposed reference quantity of the current reference quantity and the current gain quantity, pass the current compensator G in the compensation mode c2 , output the inverter modulation signal in the compensation mode, wherein the current compensator G in the compensation mode is designed by using the commutation current compensation strategy c2 , specifically, where K p4 and K r2 are proportional and resonant gains of the commutation current compensation strategy. 6.The microgrid plug and play and multi-mode switching method based on edge cloud cooperation and oriented to flexible networking according to claim 1, wherein, The step 5) specifically includes: Step 5.1) Collecting the inverter output voltage and inverter output current, denoted as v ac and i ac ; Step 5.2) Design the voltage feedback gain H of the microgrid controller in the compensation mode v , the output current feedback gain H of the microgrid controller i1 ; Step 5.3) generates a voltage gain quantity, denoted by v, through a voltage feedback gain block ach ; Step 5.4) generates a current gain quantity, denoted by i, through a current feedback gain block ach ; Step 5.5) Setting the voltage reference value V ref ; Step 5.6) The input voltage reference quantity v is calculated using the predetermined sinusoidal detection strategy iref ; Step 5.7) Calculate the superimposed value of the voltage reference value and the input voltage reference amount, pass through the voltage compensator G v , output the current reference amount i ref_S in island mode v , specifically where K p3 and K r3 are proportional and resonant gains in island mode; Step 5.8) input the superimposed reference quantity of the current reference quantity and the current gain quantity, pass through the current compensator G in the island mode c3 , output the inverter modulation signal in the island mode, wherein the proportional-resonant control method is adopted to design the current compensator G in the island mode c1 (s), specifically, The inverter output current is affected by G id2 The dual-loop controller is designed to damp the LC resonance and regulate the output voltage, with the open-loop voltage transfer function represented as: wherein G id2 (s), G v (s), G c3 (s) and Z load (s) are the duty cycle of the output current transfer function, the voltage compensator in island mode, the current compensator in island mode and the output impedance, respectively. G id2 (s) is obtained by Z load (s) is a parallel structure of output capacitance and equivalent output resistance, denoted as: wherein R O is the equivalent output resistance; To compensate for the switching current, the controller G c3 (s) is designed as a proportional-resonant type controller and adopts a commutation current compensation strategy as follows: where K p2 and ω LC is the proportional gain of the current controller and the LC resonant frequency. 7.The microgrid plug and play and multi-mode switching method based on edge cloud cooperation and oriented to flexible networking according to claim 2, wherein, Step 1.1) On the cloud platform, pre-set the primary information model and encryption certificate for the edge device, specifically: a) The manufacturer defines a primary information model for each device, which contains all the basic physical and electrical properties of the device, including the model, power level, rated current and voltage of the device; b) The manufacturer converts the model into electronic format using a standard format; c) The manufacturer contacts the certificate authority to apply for an encryption certificate; d) The certificate authority verifies the identity and request of the manufacturer, and then issues a public key / private key pair and the corresponding certificate; e) The manufacturer stores the primary information model and private key / certificate in the firmware or internal memory of the device; f) When the device is installed and connected to the microgrid, the device will broadcast its primary information model; g) After receiving the broadcasted information, the management system of the microgrid verifies the authenticity and integrity of the encryption certificate using the manufacturer's public key; h) Once the verification is successful, the device is considered a trusted device and is added to the microgrid. 8.The microgrid plug and play and multi-mode switching method based on edge cloud cooperation and oriented to flexible networking according to claim 2, wherein, Step 1.3) The cloud platform completes the secondary model filing of the edge device, specifically: a) When the device is first connected to the microgrid, the central control system requests the operating parameters of the device, such as the control strategy, communication interface and protection settings of the device; b) The device responds to the request and sends the above parameters to the central control system; c) The control system combines the received parameters with the primary information model to create a complete secondary information model of the device; d) The secondary information model is verified using the operation specifications and standards (IEC-61850) of the microgrid; e) Once the model is verified successfully, the central control system stores it in a database or other appropriate storage system; f) In subsequent operation, when the device needs to be controlled or adjusted, its secondary information model is directly referenced. 9.The microgrid plug and play and multi-mode switching method based on edge cloud cooperation and oriented to flexible networking according to claim 3, wherein, Step 2.6) The cloud platform completes the filing of the end device, specifically: a) According to the uploaded identity information, the cloud platform creates a new record for the device in its database, which stores all the basic information, status, historical data and other related information of the device; b) After the device is filed, the cloud platform will determine which secondary devices to associate with according to its identity information and pre-defined rules or algorithms; c) Once the association is complete, the cloud platform can send a confirmation message to the end device, notifying it that it has been successfully filed and associated with the corresponding secondary device. 10.The microgrid plug and play and multi-mode switching method based on edge cloud cooperation and oriented to flexible networking according to claim 1 or 5, characterized in that, The predetermined sinusoidal wave detection strategy specifically includes: 1) Calculate the RMS value of the grid voltage, which is commonly used for real-time monitoring of the grid voltage, and the RMS calculation of the grid voltage is represented as: 2) By all-pass filter, obtain the same 90° phase delay signal as the grid voltage amplitude, using the identity of the triangle, obtain the grid voltage v g (k) voltage amplitude V m As follows: 3) using the product of the cosine of the grid angle θ s and the amplitude V m to obtain the predicted grid voltage v p (k+1) for the next cycle, and then comparing the actual grid voltage v g (k+1) for the next cycle with v p (k+1) to detect a grid fault; 4) if v p the average of the errors between v g (k+1) is greater than a threshold V th , the switch will be opened to cut the connection with the grid.

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