Off-grid and grid-connected smooth switching method and system for self-tracking coefficient droop control

Abstract

The invention discloses an off-grid and grid-connected smooth switching method and system for self-tracking coefficient droop control, relates to the technical field of electrical engineering, and aims to respond to an off-grid and grid-connected switching instruction of a micro-grid, obtain micro-grid operation data of the micro-grid, and perform self-tracking coefficient droop control on the micro-grid according to the micro-grid operation data and a preset controller coefficient. Determining micro-grid adjustment data, the micro-grid adjustment data including micro-grid adjustment frequency and micro-grid adjustment voltage; performing off-grid and grid-connected switching on the micro-grid according to the micro-grid adjusting frequency and the micro-grid adjusting voltage; performing self-tracking coefficient droop control on the micro-grid to obtain the micro-grid adjusting frequency and the micro-grid adjusting voltage before smooth switching; quickly tracking the voltage and the frequency in the smooth switching process to numerical values before switching; therefore, stable switching of off-grid connection and grid connection of the micro-grid is realized, stable and reliable power supply in the micro-grid in the switching process is ensured, and excessive impact on the operation of the power grid and the micro-grid is avoided.

Description

Technical Field

[0001] The present invention relates to the field of electrical engineering technology, and in particular to a grid-connected and off-grid smooth switching method and system with self-tracking coefficient droop control. Background Art

[0002] At present, traditional power generation energy sources such as thermal power generation and hydropower generation are facing increasingly severe situations. As the demand for electricity consumption in various industries continues to increase, microgrids composed of clean energy such as photovoltaics and wind power have become the focus of research. Microgrids have two operating states, namely, grid-connected operation state and off-grid island operation state. When the microgrid is in the island operation state and uses traditional droop control, the inverter collects its own output power, provides voltage and frequency for the microgrid through the output power, and distributes active power and reactive power according to the load situation; when the microgrid is in the grid-connected operation state and uses traditional droop control, the inverter collects the grid-connected point voltage to provide corresponding power for power dispatching. Microgrids cannot maintain a state for a long time. When a microgrid fails or the microgrid dispatches for load allocation, the microgrid needs to switch between off-grid island and grid-connected operation. However, the two modes will produce large transient oscillations during the switching process. Summary of the invention

[0003] The present invention provides a method and system for off-grid and on-grid smooth switching with self-tracking coefficient droop control, which solves the technical problem of how to improve the power supply stability of a microgrid.

[0004] A first aspect of the present invention provides a method for smooth off-grid switching with self-tracking coefficient droop control, comprising:

[0005] Responding to a microgrid off-grid switching instruction, obtaining microgrid operation data of the microgrid;

[0006] Performing self-tracking coefficient droop control on the microgrid according to the microgrid operation data and the preset controller coefficient, and determining microgrid regulation data, wherein the microgrid regulation data includes a microgrid regulation frequency and a microgrid regulation voltage;

[0007] The microgrid is switched off and on to the grid according to the microgrid adjustment frequency and the microgrid adjustment voltage.

[0008] Optionally, the microgrid operation data includes power operation data, microgrid rated frequency, electrical characteristic data, voltage characteristic data and no-load electrical data, and the self-tracking coefficient droop control of the microgrid is performed according to the microgrid operation data and a preset controller coefficient to determine the microgrid regulation data, including:

[0009] Determine a frequency deviation using the power operation data, the microgrid rated frequency and a preset frequency modulation coefficient;

[0010] Determine a voltage deviation using the power operation data and the electrical characteristic data;

[0011] Determine a droop coefficient by using the voltage characteristic data and a preset controller coefficient, wherein the droop coefficient includes a frequency droop coefficient and a voltage droop coefficient;

[0012] Determine the microgrid adjustment frequency by using the frequency deviation, the power operation data, the no-load electrical data and the frequency droop coefficient;

[0013] The microgrid regulation voltage is determined by using the voltage deviation, the power operation data, the no-load electrical data and the voltage droop coefficient.

[0014] Optionally, the power operation data includes a load rated active power and an inverter output active power change, and the power operation data, the microgrid rated frequency and a preset frequency modulation coefficient are used to determine the frequency deviation, including:

[0015] A preset frequency modulation coefficient is used to perform a multiplication operation with the rated active power of the load to obtain a first multiplication value;

[0016] Performing a ratio operation on the first multiplication value and the microgrid rated frequency to obtain a first ratio;

[0017] The first ratio is multiplied by the change in the inverter output active power to obtain a frequency deviation.

[0018] Optionally, the power operation data further includes line transmission reactive power and line transmission active power, the electrical characteristic data includes line resistance value, line reactance value and microgrid rated voltage, and the use of the power operation data and the electrical characteristic data to determine the voltage deviation includes:

[0019] Performing a multiplication operation on the active power transmitted by the line and the line resistance value to obtain a second multiplication value;

[0020] Performing a multiplication operation on the reactive power transmitted by the line and the reactance value of the line to obtain a third multiplication value;

[0021] Performing a sum operation using the second product value and the third product value to obtain a first sum value;

[0022] The voltage deviation is obtained by performing a ratio operation between the first sum value and the microgrid rated voltage.

[0023] Optionally, the voltage characteristic data includes a grid voltage phase, a grid voltage amplitude, a microgrid voltage phase and a microgrid voltage amplitude, the preset controller coefficient includes a voltage phase proportional coefficient, a voltage phase integral coefficient, a voltage amplitude proportional coefficient and a voltage amplitude integral coefficient, and the voltage characteristic data and the preset controller coefficient are used to determine the droop coefficient, including:

[0024] Performing a difference operation using the grid voltage phase and the microgrid voltage phase to obtain a first difference;

[0025] Performing a ratio operation using the voltage phase integral coefficient and a preset complex frequency variable to obtain a second ratio;

[0026] Performing a sum operation using the second ratio and the voltage phase proportional coefficient to obtain a second sum;

[0027] Performing a multiplication operation on the second sum and the first difference to obtain the frequency droop coefficient;

[0028] Performing a difference operation on the grid voltage amplitude and the microgrid voltage amplitude to obtain a second difference;

[0029] Performing a ratio operation on the voltage amplitude integral coefficient and the preset complex frequency variable to obtain a third ratio;

[0030] Performing a sum operation using the third ratio and the voltage amplitude proportionality coefficient to obtain a third sum;

[0031] The voltage droop coefficient is obtained by performing a multiplication operation on the third sum and the second difference.

[0032] Optionally, the power operation data further includes inverter output active power and inverter rated active power, the no-load electrical data includes no-load frequency, and the frequency deviation, the power operation data, the no-load electrical data and the frequency droop coefficient are used to determine the microgrid adjustment frequency, including:

[0033] Performing a difference operation between the output active power of the inverter and the rated active power of the inverter to obtain a third difference;

[0034] Performing a multiplication operation on the third difference and the frequency droop coefficient to obtain a fourth multiplication value;

[0035] Performing a difference operation on the fourth product value and the no-load frequency to obtain a fourth difference;

[0036] The fourth difference value and the frequency deviation amount are used to perform a sum operation to obtain the microgrid adjustment frequency.

[0037] Optionally, the power operation data further includes inverter output reactive power and inverter rated reactive power, the no-load electrical data further includes no-load voltage amplitude, and the voltage deviation, the power operation data, the no-load electrical data and the voltage droop coefficient are used to determine the microgrid regulation voltage, including:

[0038] Performing a difference operation between the inverter output reactive power and the inverter rated reactive power to obtain a fifth difference;

[0039] Performing a multiplication operation using the fifth difference and the voltage droop coefficient to obtain a fifth multiplication value;

[0040] Performing a difference operation on the fifth product value and the no-load voltage amplitude to obtain a sixth difference value;

[0041] The microgrid regulated voltage is obtained by performing a sum operation on the sixth difference and the voltage deviation.

[0042] A second aspect of the present invention provides a grid-connected smooth switching system with self-tracking coefficient droop control, comprising:

[0043] A response module, used to respond to the off-grid switching instruction of the microgrid and obtain the microgrid operation data of the microgrid;

[0044] A droop control module, used for performing self-tracking coefficient droop control on the microgrid according to the microgrid operation data and the preset controller coefficient, and determining microgrid regulation data, wherein the microgrid regulation data includes a microgrid regulation frequency and a microgrid regulation voltage;

[0045] The off-grid switching module is used to switch the microgrid between off-grid and on-grid according to the microgrid adjustment frequency and the microgrid adjustment voltage.

[0046] A third aspect of the present invention provides an electronic device, comprising a memory and a processor, wherein a computer program is stored in the memory, and when the computer program is executed by the processor, the processor executes the steps of the off-grid smooth switching method with self-tracking coefficient droop control as described in any one of the above items.

[0047] A fourth aspect of the present invention provides a computer-readable storage medium having a computer program stored thereon, which, when executed, implements the off-grid and on-grid smooth switching method of self-tracking coefficient droop control as described in any one of the above items.

[0048] It can be seen from the above technical solutions that the present invention has the following advantages:

[0049] In the present invention, in response to the off-grid switching instruction of the microgrid, the microgrid operation data of the microgrid is obtained, the microgrid is subjected to self-tracking coefficient droop control according to the microgrid operation data and the preset controller coefficient, the microgrid regulation data is determined, the microgrid regulation data includes the microgrid regulation frequency and the microgrid regulation voltage, and the microgrid is switched off-grid according to the microgrid regulation frequency and the microgrid regulation voltage. The microgrid regulation frequency and the microgrid regulation voltage before the smooth switching are obtained by performing self-tracking coefficient droop control on the microgrid, and the voltage and frequency in the smooth switching process can be quickly tracked to the values ​​before the switching, so as to enable the microgrid to achieve smooth off-grid switching, and ensure that the power supply in the microgrid is stable and reliable during the switching process, and will not have excessive impact on the operation of the power grid and the microgrid itself. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0051] Figure 1 A flowchart of the steps of a method for off-grid and on-grid smooth switching with self-tracking coefficient droop control provided in Embodiment 1 of the present invention;

[0052] Figure 2 A flow chart of the steps of a method for smooth off-grid switching with self-tracking coefficient droop control provided in Embodiment 2 of the present invention;

[0053] Figure 3 Simplify the contour diagram for the system;

[0054] Figure 4 It is the control flow chart of self-tracking coefficient droop control;

[0055] Figure 5 It is the coordinate diagram of QU self-tracking coefficient droop control;

[0056] Figure 6 It is the Pf self-tracking coefficient droop control coordinate diagram;

[0057] Figure 7 It is the voltage simulation curve diagram;

[0058] Figure 8 It is the grid-connected instantaneous voltage simulation curve diagram;

[0059] Fig. 9 This is the off-grid instant voltage simulation curve;

[0060] Fig.10 It is the frequency simulation curve diagram;

[0061] Fig.11 It is the current simulation curve diagram;

[0062] Fig.12 A structural block diagram of a grid-connected smooth switching system with self-tracking coefficient droop control provided in Embodiment 3 of the present invention;

[0063] Fig.13 This is a structural block diagram of a computer device provided in Embodiment 4 of the present invention. DETAILED DESCRIPTION

[0064] The embodiments of the present invention provide a method and system for smooth off-grid and on-grid switching with self-tracking coefficient droop control, which are used to solve the technical problem of how to improve the power supply stability of a microgrid.

[0065] In order to make the purpose, features and advantages of the present invention more obvious and easy to understand, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the embodiments described below are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0066] In response to the problems mentioned in the background technology, researchers have proposed many improvement strategies. However, there are many shortcomings in the existing technology, mainly as follows: 1. The existing microgrid off-grid switching control strategy takes 0.6 seconds to complete synchronization, and the microgrid starts to be connected to the grid, but the smooth switching time response is long, resulting in the inability to quickly transition from the oscillation period to the stable period. 2. When the microgrid is off-grid and isolated, the voltage peak fluctuation range is about 5%, and the voltage waveform fluctuates significantly, and there is a problem of voltage waveform deviation. 3. The existing microgrid off-grid switching control strategy adopts the improved nonlinear droop curve of the grid-connected current. There are still current shocks and current distortion at the switching moment, resulting in current distortion and shock current. 4. After the existing microgrid off-grid switching control strategy adopts the improved control strategy, the maximum frequency fluctuation of the microgrid during switching is about 0.4Hz, regardless of whether the power shortage is large or small, and there is a problem of large frequency fluctuation.

[0067] In summary, the present invention provides a grid-connected smooth switching method with self-tracking coefficient droop control, which quickly tracks the voltage and frequency in the smooth switching process to the values ​​before switching through the droop control of two self-tracking droop coefficients (frequency droop coefficient and voltage droop coefficient), thereby reducing the smooth switching time, the voltage deviation value during switching, the current distortion and impact current during switching, and the frequency fluctuation deviation during switching.

[0068] Droop control is a method used to control synchronous generators and inverter-based resources in a power grid. It allows multiple generator sets to be connected in parallel to share the load in a certain proportion of their rated power. Under droop control, each generator set in the grid is assigned a frequency and voltage "droop" value. These droop values ​​indicate how much the frequency and voltage are allowed to deviate from their nominal values ​​when taking into account changes in power demand.

[0069] See also Figure 1 , Figure 1 A flowchart of the steps of a method for smooth off-grid switching with self-tracking coefficient droop control provided in Embodiment 1 of the present invention.

[0070] The present invention provides a method for smooth off-grid switching with self-tracking coefficient droop control, comprising:

[0071] Step 101: respond to a microgrid off-grid switching instruction and obtain microgrid operation data of the microgrid.

[0072] The off-grid switching command refers to a request command issued by the microgrid to instruct the microgrid to switch between the off-grid island operation mode and the grid-connected operation mode when the grid fails or the grid dispatcher performs load adjustment. The request command is intended to ensure that the microgrid can flexibly adjust its own operating status according to the real-time operating status of the grid, thereby ensuring the stability and reliability of power supply.

[0073] Microgrid operation data refers to a series of data sets that reflect the various operating states and characteristics of the microgrid system during its operation.

[0074] In an embodiment of the present invention, in response to a received request instruction instructing the microgrid to switch between an off-grid island operation mode and a grid-connected operation mode, microgrid operation data during the operation of the microgrid system is acquired.

[0075] Step 102: Perform self-tracking coefficient droop control on the microgrid according to the microgrid operation data and the preset controller coefficient, and determine the microgrid regulation data, where the microgrid regulation data includes the microgrid regulation frequency and the microgrid regulation voltage.

[0076] The preset controller coefficients refer to a set of preset parameters used to adjust and control the voltage phase and voltage amplitude in the microgrid.

[0077] Self-tracking coefficient droop control refers to a control strategy used in microgrid systems to achieve reasonable power distribution between distributed power sources (DG) and maintain stable system operation. The self-tracking coefficient is an adaptive mechanism introduced on the basis of traditional droop control. It can automatically adjust the droop coefficient of droop control according to various factors such as the operating status of the microgrid system, load changes, power supply characteristics, etc. These droop coefficients determine the proportional relationship between power changes and frequency and voltage changes. By tracking system changes in real time and dynamically adjusting the droop coefficient, the droop control is more flexible and accurate.

[0078] Microgrid regulation data refers to the key data obtained by performing self-tracking coefficient droop control on the microgrid based on the microgrid operation data and preset controller coefficients for achieving precise regulation and control of the microgrid frequency and voltage.

[0079] In an embodiment of the present invention, a self-tracking coefficient droop control is performed on a microgrid according to microgrid operation data and a preset controller coefficient to obtain microgrid regulation data, and the microgrid regulation data includes a microgrid regulation frequency and a microgrid regulation voltage.

[0080] Step 103: Switch the microgrid to and from the grid according to the microgrid adjustment frequency and the microgrid adjustment voltage.

[0081] In an embodiment of the present invention, before executing the off-grid switching action, the microgrid obtains the microgrid regulation frequency and microgrid regulation voltage before the smooth switching through the self-tracking coefficient droop control, and can quickly track the voltage and frequency during the smooth switching process to the values ​​before the switching, and then through the coordinated regulation of the distributed power source, energy storage device and related power electronic equipment, the microgrid is enabled to achieve a smooth switch from the current operating mode (grid-connected or off-grid) to the target operating mode (off-grid or grid-connected), ensuring that the power supply in the microgrid is stable and reliable during the switching process, and will not cause excessive impact on the operation of the power grid and the microgrid itself.

[0082] In the present invention, in response to the off-grid switching instruction of the microgrid, the microgrid operation data of the microgrid is obtained; the microgrid is subjected to self-tracking coefficient droop control according to the microgrid operation data and the preset controller coefficient, and the microgrid regulation data is determined, and the microgrid regulation data includes the microgrid regulation frequency and the microgrid regulation voltage; the microgrid is switched off-grid according to the microgrid regulation frequency and the microgrid regulation voltage, and the microgrid regulation frequency and the microgrid regulation voltage before the smooth switching are obtained by performing self-tracking coefficient droop control on the microgrid. The voltage and frequency in the smooth switching process can be quickly tracked to the values ​​before the switching, so as to enable the microgrid to achieve smooth switching off-grid and on-grid, and ensure that the power supply in the microgrid is stable and reliable during the switching process, and will not have excessive impact on the operation of the power grid and the microgrid itself.

[0083] See also Figure 2 , Figure 2 A flow chart of the steps of a method for smooth off-grid switching with self-tracking coefficient droop control provided in Embodiment 2 of the present invention.

[0084] Analysis of the mechanism of impact current and voltage generated when microgrids switch between off-grid and grid-connected modes:

[0085] The three phases of the microgrid inverter are symmetrical. Taking one phase as an example, the simplified equivalent circuit of one phase of the microgrid system is as follows: Figure 3 shown.

[0086] Figure 3 middle, and is the inverter output voltage and the inverter output current; and is the grid voltage and grid current; is the load impedance, and are the inverter output impedance and grid impedance; and are the load voltage and load current.

[0087] When the microgrid system is connected to the grid, Small, the voltage across the load Approximately equal to the grid voltage:

[0088] (1)

[0089] In formula (1), is the grid voltage amplitude; is the grid voltage angular frequency. The inverter output voltage is:

[0090] (2)

[0091] In formula (2), is the inverter voltage amplitude; is the inverter output voltage angular frequency; is the inverter output voltage phase angle.

[0092] Therefore, the voltage mutation amount during mode switching is:

[0093] (3)

[0094] The resulting current jump is:

[0095] (4)

[0096] because When the mode is switched, the inconsistency between the voltage amplitude, frequency and phase of the inverter and the grid will cause huge voltage and current shocks, long switching time and waveform distortion.

[0097] The traditional droop control theory formula is:

[0098] (5)

[0099] Among them, in formula (5) and The actual voltage amplitude of the inverter output and the voltage amplitude under no-load condition; and The actual frequency output by the inverter and the frequency under no-load condition; , are the active power droop coefficient and reactive power droop coefficient; , The active power and reactive power output by the inverter; , is the rated active power and rated reactive power of the inverter.

[0100] See also Figure 4 , Figure 4 This is the control flow diagram of the self-tracking coefficient droop control. According to the control flow of the self-tracking coefficient droop control, the self-tracking coefficient droop control formula is defined as:

[0101] (6)

[0102] The present invention provides a method for smooth off-grid switching with self-tracking coefficient droop control, comprising:

[0103] Step 201: respond to a microgrid off-grid switching instruction and obtain microgrid operation data of the microgrid.

[0104] In the embodiment of the present invention, the specific implementation process of step 201 is similar to step 101 and will not be repeated here.

[0105] Furthermore, the microgrid operation data includes power operation data, microgrid rated frequency, electrical characteristic data, voltage characteristic data and no-load electrical data.

[0106] Step 202: Determine the frequency deviation using power operation data, microgrid rated frequency and preset frequency modulation coefficient.

[0107] Furthermore, the power operation data includes the load rated active power and the inverter output active power change. Step 202 may include the following sub-steps:

[0108] S11. Perform multiplication operation on the preset frequency modulation coefficient and the rated active power of the load to obtain a first multiplication value.

[0109] S12. Perform a ratio operation on the first product value and the rated frequency of the microgrid to obtain a first ratio.

[0110] S13, performing a multiplication operation on the first ratio and the change in the inverter output active power to obtain a frequency deviation.

[0111] In the embodiment of the present invention, according to the power system comprehensive load frequency regulation effect coefficient Define frequency deviation .

[0112] In a specific implementation, in order to facilitate the implementation of the method, the above process can be converted into a formula encapsulation form, wherein the formula of the frequency deviation can be as follows:

[0113]

[0114] In the formula, Indicates the frequency deviation, Indicates the rated frequency of the microgrid, Indicates the preset frequency modulation coefficient. Indicates the rated active power of the load, specifically the rated value of the active power of the load. Indicates the change in inverter output active power.

[0115] It should be noted that the preset frequency modulation coefficient is obtained based on a large number of simulations, and the preset frequency modulation coefficient value range is 1~3, which has the best frequency regulation performance for the microgrid system.

[0116] Step 203: Determine the voltage deviation using the power operation data and the electrical characteristic data.

[0117] Furthermore, the power operation data also includes the line transmission reactive power and the line transmission active power, and the electrical characteristic data includes the line resistance value, the line reactance value and the microgrid rated voltage. Step 203 may include the following sub-steps:

[0118] S21. Perform a multiplication operation on the active power transmitted by the line and the line resistance value to obtain a second multiplication value.

[0119] S22. Perform a multiplication operation on the line transmission reactive power and the line reactance value to obtain a third product value.

[0120] S23. Perform a sum operation using the second product value and the third product value to obtain a first sum value.

[0121] S24. Perform a ratio operation between the first sum and the rated voltage of the microgrid to obtain a voltage deviation.

[0122] In the embodiment of the present invention, according to the line voltage drop formula Define voltage deviation .

[0123] In a specific implementation, in order to facilitate the implementation of the method, the above process can be converted into a formula encapsulation form, wherein the formula of the voltage deviation can be as follows:

[0124]

[0125] In the formula, Indicates the voltage deviation, Indicates the active power transmitted by the line. Indicates the line resistance value, Indicates the reactive power transmitted by the line. Indicates the line reactance value, Indicates the rated voltage of the microgrid.

[0126] Step 204: using the voltage characteristic data and the preset controller coefficient, determine the droop coefficient, where the droop coefficient includes a frequency droop coefficient and a voltage droop coefficient.

[0127] Further, the voltage characteristic data includes a grid voltage phase, a grid voltage amplitude, a microgrid voltage phase, and a microgrid voltage amplitude, and the preset controller coefficient includes a voltage phase proportional coefficient, a voltage phase integral coefficient, a voltage amplitude proportional coefficient, and a voltage amplitude integral coefficient. Step 204 may include the following sub-steps:

[0128] S31. Perform a difference operation on the grid voltage phase and the microgrid voltage phase to obtain a first difference.

[0129] S32. Perform a ratio operation on the voltage phase integral coefficient and the preset complex frequency variable to obtain a second ratio.

[0130] S33, performing a sum operation using the second ratio and the voltage phase proportional coefficient to obtain a second sum.

[0131] S34, performing a multiplication operation on the second sum and the first difference to obtain a frequency droop coefficient.

[0132] In a specific implementation, in order to facilitate the implementation of the method, the above process can be converted into a formula encapsulation form, wherein the formula of the frequency droop coefficient can be as follows:

[0133]

[0134] In the formula, represents the frequency droop coefficient, represents the voltage phase proportional coefficient, represents the voltage phase integral coefficient, represents the preset complex frequency variable, Indicates the grid voltage phase, Indicates the voltage phase of the microgrid.

[0135] S35. Perform a difference operation on the grid voltage amplitude and the microgrid voltage amplitude to obtain a second difference.

[0136] S36. Perform a ratio operation using the voltage amplitude integral coefficient and a preset complex frequency variable to obtain a third ratio.

[0137] S37. Perform a sum operation using the third ratio and the voltage amplitude proportionality coefficient to obtain a third sum.

[0138] S38. Perform a multiplication operation on the third sum and the second difference to obtain a voltage droop coefficient.

[0139] In a specific implementation, in order to facilitate the implementation of the method, the above process can be converted into a formula encapsulation form, wherein the formula of the voltage droop coefficient can be as follows:

[0140]

[0141] In the formula, represents the voltage droop coefficient, Represents the voltage amplitude proportionality coefficient, represents the voltage amplitude integral coefficient, represents the preset complex frequency variable, Indicates the grid voltage amplitude, Indicates the voltage amplitude of the microgrid.

[0142] Step 205: determine the microgrid regulation frequency using the frequency deviation, power operation data, no-load electrical data and frequency droop coefficient.

[0143] Furthermore, the power operation data also includes the inverter output active power and the inverter rated active power, and the no-load electrical data includes the no-load frequency. Step 205 may include the following sub-steps:

[0144] S41. Perform a difference operation between the inverter output active power and the inverter rated active power to obtain a third difference.

[0145] S42. Perform a multiplication operation on the third difference and the frequency droop coefficient to obtain a fourth multiplication value.

[0146] S43, performing a difference operation on the fourth product value and the no-load frequency to obtain a fourth difference.

[0147] S44. Perform a sum operation on the fourth difference and the frequency deviation to obtain the microgrid adjustment frequency.

[0148] In a specific implementation, in order to facilitate the implementation of the method, the above process can be converted into a formula encapsulation form, wherein the formula for adjusting the frequency of the microgrid can be as follows:

[0149]

[0150] In the formula, Indicates the microgrid regulation frequency, Indicates the no-load frequency, specifically the frequency of the inverter output under no-load conditions. Indicates the inverter output active power, Indicates the rated active power of the inverter.

[0151] Step 206: Determine the microgrid regulation voltage using the voltage deviation, power operation data, no-load electrical data, and voltage droop coefficient.

[0152] Furthermore, the power operation data also includes the inverter output reactive power and the inverter rated reactive power, and the no-load electrical data also includes the no-load voltage amplitude. Step 206 may include the following sub-steps:

[0153] S51. Perform a difference operation between the inverter output reactive power and the inverter rated reactive power to obtain a fifth difference.

[0154] S52: Perform a multiplication operation on the fifth difference and the voltage droop coefficient to obtain a fifth product.

[0155] S53, performing a difference operation on the fifth product value and the no-load voltage amplitude to obtain a sixth difference value.

[0156] S54, performing a sum operation on the sixth difference and the voltage deviation to obtain a microgrid regulated voltage.

[0157] In a specific implementation, in order to facilitate the implementation of the method, the above process can be converted into a formula encapsulation form, wherein the formula for regulating the voltage of the microgrid can be as follows:

[0158]

[0159] In the formula, Indicates the microgrid regulation voltage, Indicates the no-load voltage amplitude, specifically the voltage amplitude of the inverter output under no-load conditions. Indicates the inverter output reactive power, Indicates the rated reactive power of the inverter.

[0160] Step 207: Switch the microgrid to and from the grid according to the microgrid adjustment frequency and the microgrid adjustment voltage.

[0161] In an embodiment of the present invention, before executing the off-grid switching action, the microgrid obtains the microgrid regulation frequency and microgrid regulation voltage before the smooth switching through the self-tracking coefficient droop control, and can quickly track the voltage and frequency during the smooth switching process to the values ​​before the switching, and then through the coordinated regulation of the distributed power source, energy storage device and related power electronic equipment, the microgrid is enabled to achieve a smooth switch from the current operating mode (grid-connected or off-grid) to the target operating mode (off-grid or grid-connected), ensuring that the power supply in the microgrid is stable and reliable during the switching process, and will not cause excessive impact on the operation of the power grid and the microgrid itself.

[0162] In the present invention, in response to the off-grid switching instruction of the microgrid, the microgrid operation data of the microgrid is obtained; the microgrid is subjected to self-tracking coefficient droop control according to the microgrid operation data and the preset controller coefficient, and the microgrid regulation data is determined, and the microgrid regulation data includes the microgrid regulation frequency and the microgrid regulation voltage; the microgrid is switched off-grid according to the microgrid regulation frequency and the microgrid regulation voltage, and the microgrid regulation frequency and the microgrid regulation voltage before the smooth switching are obtained by performing self-tracking coefficient droop control on the microgrid. The voltage and frequency in the smooth switching process can be quickly tracked to the values ​​before the switching, so as to enable the microgrid to achieve smooth switching off-grid and on-grid, and ensure that the power supply in the microgrid is stable and reliable during the switching process, and will not have excessive impact on the operation of the power grid and the microgrid itself.

[0163] Through the two tracking parts, the voltage and frequency in the smooth switching process can be quickly tracked to the values ​​before the switching. The waveform distortion and current impact generated during the switching can also be effectively solved.

[0164] According to formula (6), the voltage and frequency is the vertical axis, active power and reactive power The control coordinates can be obtained by Figure 5 and Figure 6 .

[0165] according to Figure 5 As shown:

[0166] 1. If the microgrid system operates at point A, when the microgrid is connected to the main grid, the QU relationship curve is ①, and the voltage changes from Down to , reactive power from Rise to , the system operation mode changes from A to B. At this time, the quality of the voltage transmitted by the system to users has seriously declined and does not meet the requirements.

[0167] 2. According to formula (6), the system changes the slope of the curve through "self-tracking". At this time, the QU relationship curve is ②, and the voltage changes from Rise to , the system reactive power output remains unchanged, and the system operation mode changes from B to C. The system improves the voltage quality for users, but there is a deviation from the voltage at point A.

[0168] 3. According to formula (6), the system changes the height of the curve through "self-tracking". At this time, the QU relationship curve is ③, and the voltage changes from Rise to , the system reactive power output remains unchanged, and the system operation mode changes from B to D. At this point, the microgrid has completely completed smooth switching, and the voltage remains the same as the initial voltage.

[0169] according to Figure 6 As shown:

[0170] 4. If the microgrid system operates at point A, when the microgrid is connected to the main grid, the Pf relationship curve is ①, and the frequency changes from Rise to , the active power from Down to , the system operation mode changes from A to B. At this time, the system frequency deviation is serious and does not meet the requirements.

[0171] 5. According to formula (5), the system changes the slope of the curve after "self-tracking". At this time, the Pf relationship curve is ②, and the frequency changes from Down to , the system active power output remains unchanged, and the system operation mode changes from B to C. The system frequency is increased, but there is still a deviation from the frequency at point A.

[0172] 6. According to formula (5), the system changes the height of the curve through "self-tracking". At this time, the Pf relationship curve is ③, and the frequency changes from Down to , the system active power output remains unchanged, and the system operation mode changes from B to D. At this point, the microgrid has completely completed smooth switching, and the frequency is consistent with the initial voltage.

[0173] The following simulation diagram is obtained through simulation. The simulation process starts with grid-connected operation at 0.3s and starts with off-grid island operation at 1s.

[0174] Depend on Figure 7-Figure 11 It can be seen that:

[0175] 1. At the moment of grid connection, the voltage of the system dropped from 310V to 295V, a decrease of 3.2%; the frequency increased from 49.99Hz to 50.015Hz and ran stably, an increase of 0.025Hz, and it took 0.1s for the frequency to run stably. There was no sudden change in the current waveform and current shock.

[0176] 2. When the system is operating in an off-grid island, the voltage amplitude remains basically unchanged, and it only takes about 0.04s to restore the system to stable operation. The frequency drops from 50.015Hz to 49.985Hz, a decrease of 0.03Hz, and it takes about 0.05s for the system to operate stably, and there is no sudden change in current waveform or current shock.

[0177] Table 1. Comparison of various indicators between the present invention and the prior art

[0178]

[0179] See also Fig.12 , Fig.12 This is a structural block diagram of a grid-connected smooth switching system with self-tracking coefficient droop control provided in Embodiment 3 of the present invention.

[0180] The present invention provides a grid-connected smooth switching system with self-tracking coefficient droop control, comprising:

[0181] A response module 301 is used to respond to a microgrid off-grid switching instruction and obtain microgrid operation data of the microgrid;

[0182] The droop control module 302 is used to perform self-tracking coefficient droop control on the microgrid according to the microgrid operation data and the preset controller coefficient, and determine the microgrid regulation data, where the microgrid regulation data includes the microgrid regulation frequency and the microgrid regulation voltage;

[0183] The off-grid switching module 303 is used to switch the microgrid off-grid and on-grid according to the microgrid adjustment frequency and the microgrid adjustment voltage.

[0184] Further, the microgrid operation data includes power operation data, microgrid rated frequency, electrical characteristic data, voltage characteristic data and no-load electrical data, and the droop control module 302 includes:

[0185] The first processing submodule is used to determine the frequency deviation using power operation data, the rated frequency of the microgrid and a preset frequency modulation coefficient;

[0186] A second processing submodule is used to determine a voltage deviation using the power operation data and the electrical characteristic data;

[0187] A third processing submodule is used to determine a droop coefficient by using the voltage characteristic data and a preset controller coefficient, wherein the droop coefficient includes a frequency droop coefficient and a voltage droop coefficient;

[0188] The fourth processing submodule is used to determine the microgrid regulation frequency by using the frequency deviation, power operation data, no-load electrical data and frequency droop coefficient;

[0189] The fifth processing submodule is used to determine the microgrid regulation voltage by using the voltage deviation, power operation data, no-load electrical data and voltage droop coefficient.

[0190] Furthermore, the power operation data includes the load rated active power and the inverter output active power change, and the first processing submodule includes:

[0191] A first multiplication unit, used to perform a multiplication operation using a preset frequency modulation coefficient and a rated active power of the load to obtain a first multiplication value;

[0192] A first ratio unit, configured to perform a ratio operation using the first product value and the rated frequency of the microgrid to obtain a first ratio;

[0193] The frequency deviation unit is used to perform a multiplication operation on the first ratio and the change in the inverter output active power to obtain the frequency deviation.

[0194] Furthermore, the power operation data also includes the line transmission reactive power and the line transmission active power, the electrical characteristic data includes the line resistance value, the line reactance value and the microgrid rated voltage, and the second processing submodule includes:

[0195] A second multiplication unit is used to perform a multiplication operation using the line transmission active power and the line resistance value to obtain a second multiplication value;

[0196] A third multiplication unit is used to perform a multiplication operation using the line transmission reactive power and the line reactance value to obtain a third multiplication value;

[0197] A first sum value unit is used to perform a sum value operation using the second product value and the third product value to obtain a first sum value;

[0198] The voltage deviation unit is used to perform a ratio operation on the first sum value and the rated voltage of the microgrid to obtain the voltage deviation.

[0199] Further, the voltage characteristic data includes a grid voltage phase, a grid voltage amplitude, a microgrid voltage phase and a microgrid voltage amplitude, the preset controller coefficient includes a voltage phase proportional coefficient, a voltage phase integral coefficient, a voltage amplitude proportional coefficient and a voltage amplitude integral coefficient, and the third processing submodule includes:

[0200] A first difference unit, used to perform a difference operation using a grid voltage phase and a microgrid voltage phase to obtain a first difference;

[0201] A second ratio unit, used for performing a ratio operation using a voltage phase integral coefficient and a preset complex frequency variable to obtain a second ratio;

[0202] A second sum unit, used for performing a sum operation using the second ratio and the voltage phase proportional coefficient to obtain a second sum;

[0203] A frequency droop coefficient unit, used for performing a multiplication operation by the second sum and the first difference to obtain a frequency droop coefficient;

[0204] A second difference unit is used to perform a difference operation using the grid voltage amplitude and the microgrid voltage amplitude to obtain a second difference;

[0205] A third ratio unit, configured to perform a ratio operation using the voltage amplitude integral coefficient and a preset complex frequency variable to obtain a third ratio;

[0206] A third sum unit, used for performing a sum operation using the third ratio and the voltage amplitude proportionality coefficient to obtain a third sum;

[0207] The voltage droop coefficient unit is used to perform a multiplication operation on the third sum and the second difference to obtain the voltage droop coefficient.

[0208] Furthermore, the power operation data also includes the inverter output active power and the inverter rated active power, the no-load electrical data includes the no-load frequency, and the fourth processing submodule includes:

[0209] A third difference unit is used to perform a difference operation between the inverter output active power and the inverter rated active power to obtain a third difference;

[0210] a fourth multiplication unit, configured to perform a multiplication operation using the third difference value and the frequency droop coefficient to obtain a fourth multiplication value;

[0211] a fourth difference unit, configured to perform a difference operation on the fourth product value and the no-load frequency to obtain a fourth difference;

[0212] The microgrid frequency regulation unit is used to perform a sum operation using the fourth difference and the frequency deviation to obtain the microgrid regulation frequency.

[0213] Furthermore, the power operation data also includes the inverter output reactive power and the inverter rated reactive power, and the no-load electrical data also includes the no-load voltage amplitude. The fifth processing submodule includes:

[0214] A fifth difference unit, configured to perform a difference operation between the inverter output reactive power and the inverter rated reactive power to obtain a fifth difference;

[0215] a fifth multiplication unit, configured to perform a multiplication operation using the fifth difference and the voltage droop coefficient to obtain a fifth multiplication value;

[0216] a sixth difference unit, configured to perform a difference operation on the fifth product value and the no-load voltage amplitude to obtain a sixth difference value;

[0217] The microgrid voltage regulating unit is used to perform a sum operation using the sixth difference and the voltage deviation to obtain the microgrid regulating voltage.

[0218] In the present invention, in response to the off-grid switching instruction of the microgrid, the microgrid operation data of the microgrid is obtained; the microgrid is subjected to self-tracking coefficient droop control according to the microgrid operation data and the preset controller coefficient, and the microgrid regulation data is determined, and the microgrid regulation data includes the microgrid regulation frequency and the microgrid regulation voltage; the microgrid is switched off-grid according to the microgrid regulation frequency and the microgrid regulation voltage, and the microgrid regulation frequency and the microgrid regulation voltage before the smooth switching are obtained by performing self-tracking coefficient droop control on the microgrid. The voltage and frequency in the smooth switching process can be quickly tracked to the values ​​before the switching, so as to enable the microgrid to achieve smooth switching off-grid and on-grid, and ensure that the power supply in the microgrid is stable and reliable during the switching process, and will not have excessive impact on the operation of the power grid and the microgrid itself.

[0219] See also Fig.13 , Fig.13 This is a structural block diagram of a computer device provided in Embodiment 4 of the present invention.

[0220] An electronic device according to an embodiment of the present invention includes: a memory 401 and a processor 402, wherein the memory 402 stores a computer program; when the computer program is executed by the processor 402, the processor 402 executes a grid-connected smooth switching method with self-tracking coefficient droop control as in any of the above embodiments.

[0221] The memory 401 may be an electronic memory such as a flash memory, an EEPROM (electrically erasable programmable read-only memory), an EPROM, a hard disk or a ROM. The memory 401 has a storage space 403 for a program code 413 for executing any method step in the above method. For example, the storage space 403 for the program code may include individual program codes 413 for implementing the various steps in the above method, respectively. These program codes may be read from or written to one or more computer program products. These computer program products include program code carriers such as hard disks, compact disks (CDs), memory cards or floppy disks. The program code may be compressed, for example, in an appropriate form. When these codes are run by a computing and processing device, the computing and processing device performs the various steps in the method described above. These program codes may be read from or written to one or more computer program products. These computer program products include program code carriers such as hard disks, compact disks (CDs), memory cards or floppy disks. The program code may be compressed, for example, in an appropriate form. When these codes are executed by a computing and processing device, the computing and processing device is caused to execute each step of the above-described off-grid and on-grid smooth switching method of self-tracking coefficient droop control.

[0222] Embodiment 5 of the present invention further provides a computer-readable storage medium having a computer program stored thereon. When the computer program is executed by a processor, the method for off-grid and on-grid smooth switching with self-tracking coefficient droop control as in any of the above embodiments is implemented.

[0223] Those skilled in the art can clearly understand that, for the convenience and brevity of description, the specific working processes of the systems, devices and units described above can refer to the corresponding processes in the aforementioned method embodiments and will not be repeated here.

[0224] In the several embodiments provided in the present application, it should be understood that the disclosed systems, devices and methods can be implemented in other ways. For example, the device embodiments described above are only schematic. For example, the division of units is only a logical function division. There may be other division methods in actual implementation. For example, multiple units or components can be combined or integrated into another system, or some features can be ignored or not executed. Another point is that the mutual coupling or direct coupling or communication connection shown or discussed can be an indirect coupling or communication connection through some interfaces, devices or units, which can be electrical, mechanical or other forms.

[0225] The units described as separate components may or may not be physically separated, and the components shown as units may or may not be physical units, that is, they may be located in one place or distributed on multiple network units. Some or all of the units may be selected according to actual needs to achieve the purpose of the solution of this embodiment.

[0226] In addition, each functional unit in each embodiment of the present invention may be integrated into one processing unit, or each unit may exist physically separately, or two or more units may be integrated into one unit. The above-mentioned integrated unit may be implemented in the form of hardware or in the form of software functional units.

[0227] If the integrated unit is implemented in the form of a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present invention, in essence, or the part that contributes to the prior art, or all or part of the technical solution can be embodied in the form of a software product. The computer software product is stored in a storage medium, including several instructions for a computer device (which can be a personal computer, server, or network device, etc.) to perform all or part of the steps of the methods of each embodiment of the present invention. The aforementioned storage medium includes: U disk, mobile hard disk, read-only memory (ROM, Read-Only Memory), random access memory (RAM, Random Access Memory), disk or optical disk, etc. Various media that can store program codes.

[0228] The above embodiments 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 the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. However, 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 embodiments of the present invention.

Claims

1. A method for smooth off-grid switching with self-tracking coefficient droop control, characterized in that: include: Responding to a microgrid off-grid switching instruction, obtaining microgrid operation data of the microgrid; Performing self-tracking coefficient droop control on the microgrid according to the microgrid operation data and the preset controller coefficient, and determining microgrid regulation data, wherein the microgrid regulation data includes a microgrid regulation frequency and a microgrid regulation voltage; The microgrid is switched off and on to the grid according to the microgrid adjustment frequency and the microgrid adjustment voltage.

2. The method for smooth off-grid switching with self-tracking coefficient droop control according to claim 1, characterized in that: The microgrid operation data includes power operation data, microgrid rated frequency, electrical characteristic data, voltage characteristic data and no-load electrical data. The self-tracking coefficient droop control of the microgrid is performed according to the microgrid operation data and the preset controller coefficient to determine the microgrid regulation data, including: Determine a frequency deviation using the power operation data, the microgrid rated frequency and a preset frequency modulation coefficient; Determine a voltage deviation using the power operation data and the electrical characteristic data; Determine a droop coefficient by using the voltage characteristic data and a preset controller coefficient, wherein the droop coefficient includes a frequency droop coefficient and a voltage droop coefficient; Determine the microgrid adjustment frequency by using the frequency deviation, the power operation data, the no-load electrical data and the frequency droop coefficient; The microgrid regulation voltage is determined by using the voltage deviation, the power operation data, the no-load electrical data and the voltage droop coefficient.

3. The method for smooth off-grid switching with self-tracking coefficient droop control according to claim 2, characterized in that: The power operation data includes the load rated active power and the inverter output active power change, and the frequency deviation is determined by using the power operation data, the microgrid rated frequency and the preset frequency modulation coefficient, including: A preset frequency modulation coefficient is used to perform a multiplication operation with the rated active power of the load to obtain a first multiplication value; Performing a ratio operation on the first multiplication value and the microgrid rated frequency to obtain a first ratio; The first ratio is multiplied by the change in the inverter output active power to obtain a frequency deviation.

4. The method for smooth off-grid switching with self-tracking coefficient droop control according to claim 2, characterized in that: The power operation data also includes line transmission reactive power and line transmission active power, the electrical characteristic data includes line resistance value, line reactance value and microgrid rated voltage, and the voltage deviation is determined by using the power operation data and the electrical characteristic data, including: Performing a multiplication operation on the active power transmitted by the line and the line resistance value to obtain a second multiplication value; Performing a multiplication operation on the reactive power transmitted by the line and the reactance value of the line to obtain a third multiplication value; Performing a sum operation using the second product value and the third product value to obtain a first sum value; The voltage deviation is obtained by performing a ratio operation between the first sum value and the microgrid rated voltage.

5. The method for smooth off-grid switching with self-tracking coefficient droop control according to claim 2, characterized in that: The voltage characteristic data includes a grid voltage phase, a grid voltage amplitude, a microgrid voltage phase and a microgrid voltage amplitude, the preset controller coefficient includes a voltage phase proportional coefficient, a voltage phase integral coefficient, a voltage amplitude proportional coefficient and a voltage amplitude integral coefficient, and the voltage characteristic data and the preset controller coefficient are used to determine the droop coefficient, including: Performing a difference operation using the grid voltage phase and the microgrid voltage phase to obtain a first difference; Performing a ratio operation using the voltage phase integral coefficient and a preset complex frequency variable to obtain a second ratio; Performing a sum operation using the second ratio and the voltage phase proportional coefficient to obtain a second sum; Performing a multiplication operation on the second sum and the first difference to obtain the frequency droop coefficient; Performing a difference operation on the grid voltage amplitude and the microgrid voltage amplitude to obtain a second difference; Performing a ratio operation on the voltage amplitude integral coefficient and the preset complex frequency variable to obtain a third ratio; Performing a sum operation using the third ratio and the voltage amplitude proportionality coefficient to obtain a third sum; The voltage droop coefficient is obtained by performing a multiplication operation on the third sum and the second difference.

6. The method for smooth off-grid switching with self-tracking coefficient droop control according to claim 2, characterized in that: The power operation data also includes the inverter output active power and the inverter rated active power, the no-load electrical data includes the no-load frequency, and the frequency deviation, the power operation data, the no-load electrical data and the frequency droop coefficient are used to determine the microgrid adjustment frequency, including: Performing a difference operation between the output active power of the inverter and the rated active power of the inverter to obtain a third difference; Performing a multiplication operation on the third difference and the frequency droop coefficient to obtain a fourth multiplication value; Performing a difference operation on the fourth product value and the no-load frequency to obtain a fourth difference; The fourth difference value and the frequency deviation amount are used to perform a sum operation to obtain the microgrid adjustment frequency.

7. The method for smooth off-grid and on-grid switching with self-tracking coefficient droop control according to claim 2, characterized in that: The power operation data also includes inverter output reactive power and inverter rated reactive power, the no-load electrical data also includes no-load voltage amplitude, and the voltage deviation, the power operation data, the no-load electrical data and the voltage droop coefficient are used to determine the microgrid regulation voltage, including: Performing a difference operation between the inverter output reactive power and the inverter rated reactive power to obtain a fifth difference; Performing a multiplication operation using the fifth difference and the voltage droop coefficient to obtain a fifth multiplication value; Performing a difference operation on the fifth product value and the no-load voltage amplitude to obtain a sixth difference value; The microgrid regulated voltage is obtained by performing a sum operation on the sixth difference and the voltage deviation.

8. A grid-connected smooth switching system with self-tracking coefficient droop control, based on the grid-connected smooth switching method with self-tracking coefficient droop control according to any one of claims 1 to 7, characterized in that: include: A response module, used to respond to the off-grid switching instruction of the microgrid and obtain the microgrid operation data of the microgrid; A droop control module, used for performing self-tracking coefficient droop control on the microgrid according to the microgrid operation data and the preset controller coefficient, and determining microgrid regulation data, wherein the microgrid regulation data includes a microgrid regulation frequency and a microgrid regulation voltage; The off-grid switching module is used to switch the microgrid between off-grid and on-grid according to the microgrid adjustment frequency and the microgrid adjustment voltage.

9. An electronic device, characterized in that: It comprises a memory and a processor, wherein a computer program is stored in the memory, and when the computer program is executed by the processor, the processor executes the steps of the off-grid and on-grid smooth switching method of self-tracking coefficient droop control as described in any one of claims 1 to 7.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed, the off-grid and on-grid smooth switching method of the self-tracking coefficient droop control as described in any one of claims 1 to 7 is implemented.

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