Cascade microgrid frequency control method, system, electronic device and storage medium

Abstract

This invention discloses a frequency control method, system, electronic device, and storage medium for cascaded microgrids. It includes: real-time acquisition of electrical parameters of the cascaded microgrid and each series inverter unit within it; determining the active and reactive power of each series inverter unit based on the electrical parameters; establishing a series inverter synchronization control logic; synchronizing the frequency and phase of each series inverter unit according to the series inverter synchronization control logic; establishing a distributed secondary frequency control logic based on the characteristic that all series inverter units in the cascaded microgrid have the same current; and performing secondary frequency recovery control on each series inverter unit according to the distributed secondary frequency control logic. This method enables frequency control without communication, reducing communication costs, avoiding communication delays, packet loss, and fault risks, and improving the reliability of the cascaded microgrid system.

Description

Technical Field

[0001] This invention relates to the field of microgrid frequency recovery control technology, and in particular to a cascaded microgrid frequency control method, device, electronic equipment, and storage medium. Background Technology

[0002] Microgrids have become a research hotspot due to their important role and status in the field of renewable energy. Depending on the configuration, microgrids can be divided into two types. The first type is the parallel microgrid, which has been studied for many years. Droop control and virtual synchronous generators are the most commonly used control strategies. The other type is the cascaded microgrid, a newer type compared to the former.

[0003] In recent years, the introduction of cascaded microgrids has driven the development of microgrids in high / medium voltage fields, especially in large-scale photovoltaic power generation and energy storage power stations. Traditional cascaded system control methods mostly rely on centralized control. In recent years, inspired by droop control, many decentralized control methods have been proposed to reduce communication burdens. Similarly, frequency synchronization and power balancing can be achieved automatically. Examples include inverse power factor droop control under RL loads, fP / Q droop control, and power factor angle droop control for different load characteristics. However, these methods neglect the frequency offset they cause.

[0004] Therefore, frequency recovery control is urgently needed for the operation of cascaded microgrids. The most classic method is the central control method. However, the central controller is highly dependent on communication and has a large computational load, which reduces the reliability of the system. To reduce communication dependence and localize the control algorithm, a distributed frequency control method based on local controllers and neighbor information is proposed. However, communication delays and faults still threaten the system's performance, stability, and reliability. Summary of the Invention

[0005] In order to at least partially solve the technical problems existing in the prior art, the inventors made this invention, which, through specific embodiments, provides a cascaded microgrid frequency control method, device, electronic device and storage medium.

[0006] In a first aspect, embodiments of the present invention provide a frequency control method for a cascaded microgrid, comprising the following steps:

[0007] Real-time acquisition of electrical parameters of the cascaded microgrid and each series inverter unit in the cascaded microgrid;

[0008] Based on the electrical parameters, determine the active power and reactive power of each of the series inverter units;

[0009] Based on the active and reactive power of each series inverter unit, a synchronous control logic for the series inverter is established.

[0010] According to the series inverter synchronization control logic, the frequency of each series inverter unit is synchronized;

[0011] Based on the electrical parameters, determine the desired output voltage phase angle model for each of the series inverter units;

[0012] The desired output voltage phase angle model is linearized using a small signal to obtain the output current frequency model of each series inverter unit.

[0013] Based on the output current frequency model, a frequency offset model for each of the series inverter units is constructed.

[0014] Based on the characteristic that all series inverter units in the cascaded microgrid have the same current, a distributed secondary frequency control logic is built based on the active power, reactive power and frequency offset model of each series inverter unit.

[0015] According to the distributed secondary frequency control logic, the frequency of each series inverter unit is subjected to secondary recovery control.

[0016] Specifically, before the real-time acquisition of electrical parameters of the cascaded microgrid and each series inverter unit in the cascaded microgrid, the following steps are included:

[0017] Determine the objective function for secondary frequency control, which specifically includes the following expression:

[0018]

[0019]

[0020] Where f ref f is the rated value for frequency recovery of a series-connected energy storage microgrid. i Let P be the frequency value of the i-th series inverter unit. i and m i P represents the output active power and droop control coefficient of the i-th series inverter unit, respectively. j and m j Let be the output power and droop control coefficient of the j-th series inverter unit, respectively; t represents time; i and j are the serial inverter unit numbers, which take values ​​from positive integers not exceeding n, and i is not equal to j; and n represents the total number of series inverter units.

[0021] Specifically, the real-time acquisition of electrical parameters of the cascaded microgrid and each series inverter unit in the cascaded microgrid includes the following steps:

[0022] Real-time acquisition of the overall power factor angle, steady-state load voltage phase angle, and output current frequency of the cascaded microgrid;

[0023] The output voltage, output current, output voltage phase angle, and output voltage angular frequency of each series inverter unit in the cascaded microgrid are collected in real time.

[0024] Specifically, the expression for the desired output voltage phase angle model is as follows:

[0025]

[0026] Where θ Ii Let be the desired output voltage phase angle of the i-th series inverter unit, and atan2 be the arctangent function. For the overall power factor angle of the series energy storage microgrid system, P * max_i For the upper limit constraint of the output power of the i-th series inverter unit, θ i Let θ' be the output voltage phase angle of the i-th series inverter unit. load is the phase angle of the load voltage in steady state, i is the number of the series inverter unit, i takes a value from positive integers not exceeding n, and n represents the total number of series inverter units.

[0027] Specifically, the desired output voltage phase angle model is linearized using small-signal methods to obtain the output current frequency model for each series inverter unit, including the following steps:

[0028] The desired output voltage phase angle model expression is linearized using small-signal methods.

[0029] Assuming the steady-state voltage angles are the same, let θ i =θ i0 +Δθ i Substitute the desired output voltage phase angle model expression after small-signal linearization and eliminate θ i0 The output current frequency model of each of the series inverter units is obtained, and the expression of the output current frequency model is as follows:

[0030]

[0031] Where f Ii Let be the frequency value of the output current of the i-th series inverter unit. For the overall power factor angle of the series energy storage microgrid system, P * max_i For the upper limit constraint of the output power of the i-th series inverter unit, ω iLet ω be the output voltage angular frequency of the i-th series inverter unit, where i is the serial inverter unit number and takes a value from a positive integer not exceeding n, where n represents the total number of series inverter units.

[0032] Specifically, the frequency offset model expression is as follows:

[0033]

[0034] Where Δf i k is the frequency offset of the i-th series inverter unit. Ii Here are the coefficients of the auxiliary controller, s is the Laplace operator, and f is the coefficient of the auxiliary controller. ref f is the rated value for frequency recovery of a series-connected energy storage microgrid. Ii Let i be the frequency value of the output current of the i-th series inverter unit, where i is the number of the series inverter unit, and i takes a value from a positive integer not exceeding n, where n represents the total number of series inverter units.

[0035] Specifically, based on the characteristic that all series inverter units in the cascaded microgrid have the same current, a distributed secondary frequency control logic is built based on the active power, reactive power, and frequency offset model of each series inverter unit, including the following steps:

[0036] Based on the characteristic that all series inverter units in the cascaded microgrid have the same current, the following expression is obtained.

[0037] f I1 =f I2 =…=f In =f I

[0038] Where f I1 f is the frequency value of the first series inverter unit. I2 f is the frequency value of the second series inverter unit. In f is the frequency value of the nth series inverter unit, where n represents the total number of series inverter units. I The frequency value of the output current;

[0039] Based on the active power, reactive power, and frequency offset model of each series inverter unit, a distributed secondary frequency control logic is constructed, and the expression of the distributed secondary frequency control logic is as follows:

[0040]

[0041] Where f i f is the frequency value of the i-th series inverter unit. * For the no-load frequency value of the series microgrid, sgn represents the sign function, and Q... iLet m be the output reactive power of the i-th series inverter unit. i P is the droop control factor. i Let k be the output active power of the i-th series inverter unit. Ii Let f be the integral coefficient of the i-th series inverter unit, s be the Laplace operator, and f be the integral coefficient of the i-th series inverter unit. ref f is the rated value for frequency recovery of a series-connected energy storage microgrid. I is the frequency value of the output current, i is the number of the series inverter unit, i takes a value from positive integers not exceeding n, and n represents the total number of series inverter units.

[0042] In a second aspect, embodiments of the present invention provide a cascaded microgrid frequency control system, comprising:

[0043] An electrical parameter acquisition module is used to acquire electrical parameters of the cascaded microgrid and each series inverter unit in the cascaded microgrid in real time.

[0044] A power determination module is used to determine the active power and reactive power of each of the series inverter units based on the electrical parameters.

[0045] The synchronization control module is used to build a series inverter synchronization control logic based on the active power and reactive power of each series inverter unit; and to synchronize the frequency of each series inverter unit according to the series inverter synchronization control logic.

[0046] The frequency control module is used to determine the desired output voltage phase angle model of each series inverter unit based on the electrical parameters; perform small-signal linearization on the desired output voltage phase angle model to obtain the output current frequency model of each series inverter unit; construct a frequency offset model for each series inverter unit based on the output current frequency model; based on the characteristic that all series inverter units in the cascaded microgrid have the same current, build a distributed secondary frequency control logic based on the active power, reactive power and frequency offset model of each series inverter unit; and perform secondary frequency recovery control on the frequency of each series inverter unit based on the distributed secondary frequency control logic.

[0047] Specifically, a cascaded microgrid frequency control system also includes:

[0048] The objective function determination module is used to determine the secondary frequency control objective function, which specifically includes the following expression:

[0049]

[0050]

[0051] Where f ref f is the rated value for frequency recovery of a series-connected energy storage microgrid. i Let P be the frequency value of the i-th series inverter unit. i and m i P represents the output active power and droop control coefficient of the i-th series inverter unit, respectively. j and m j Let be the output power and droop control coefficient of the j-th series inverter unit, respectively; t represents time; i and j are the serial inverter unit numbers, which take values ​​from positive integers not exceeding n, and i is not equal to j; and n represents the total number of series inverter units.

[0052] Specifically, the electrical parameter acquisition module is used for:

[0053] Real-time acquisition of the overall power factor angle, steady-state load voltage phase angle, and output current frequency of the cascaded microgrid;

[0054] The output voltage, output current, output voltage phase angle, and output voltage angular frequency of each series inverter unit in the cascaded microgrid are collected in real time.

[0055] Specifically, the frequency control module includes:

[0056] The desired output voltage phase angle determination submodule is used to determine the desired output voltage phase angle model for each of the series inverter units based on the electrical parameters. The expression for the desired output voltage phase angle model is as follows:

[0057]

[0058] Where θ Ii Let be the desired output voltage phase angle of the i-th series inverter unit, and atan2 be the arctangent function. For the overall power factor angle of the series energy storage microgrid system, P * max_i For the upper limit constraint of the output power of the i-th series inverter unit, θ i Let θ' be the output voltage phase angle of the i-th series inverter unit. load is the phase angle of the load voltage in steady state, i is the number of the series inverter unit, i takes a value from positive integers not exceeding n, and n represents the total number of series inverter units;

[0059] The output current frequency model determination submodule is used to perform small-signal linearization on the expression of the desired output voltage phase angle model.

[0060] Assuming the steady-state voltage angles are the same, let θ i =θ i0 +Δθ iSubstitute the desired output voltage phase angle model expression after small-signal linearization and eliminate θ i0 The output current frequency model of each of the series inverter units is obtained, and the expression of the output current frequency model is as follows:

[0061]

[0062] Where f Ii Let be the frequency value of the output current of the i-th series inverter unit. For the overall power factor angle of the series energy storage microgrid system, P * max_i For the upper limit constraint of the output power of the i-th series inverter unit, ω i Let be the angular frequency of the output voltage of the i-th series inverter unit;

[0063] The frequency offset determination submodule is used to construct a frequency offset model for each of the series inverter units based on the output current frequency model. The expression for the frequency offset model is:

[0064]

[0065] Where Δf i k is the frequency offset of the i-th series inverter unit. Ii Here are the coefficients of the auxiliary controller, s is the Laplace operator, and f is the coefficient of the auxiliary controller. ref f is the rated value for frequency recovery of a series-connected energy storage microgrid. Ii Let be the frequency value of the output current of the i-th series inverter unit;

[0066] The secondary frequency control logic submodule is used to derive the following expression based on the characteristic that all series inverter units in the cascaded microgrid have the same current.

[0067] f I1 =f I2 =…=f In =f I

[0068] Where f I1 f is the frequency value of the first series inverter unit. I2 f is the frequency value of the second series inverter unit. In f is the frequency value of the nth series inverter unit, where n represents the total number of series inverter units. I The frequency value of the output current;

[0069] Based on the active power, reactive power, and frequency offset model of each series inverter unit, a distributed secondary frequency control logic is constructed, and the expression of the distributed secondary frequency control logic is as follows:

[0070]

[0071] Where f i f is the frequency value of the i-th series inverter unit. * For the no-load frequency value of the series microgrid, sgn represents the sign function, and Q... i Let m be the output reactive power of the i-th series inverter unit. i P is the droop control factor. i Let k be the output active power of the i-th series inverter unit. Ii Let f be the integral coefficient of the i-th series inverter unit, s be the Laplace operator, and f be the integral coefficient of the i-th series inverter unit. ref f is the rated value for frequency recovery of a series-connected energy storage microgrid. I The frequency value of the output current;

[0072] The secondary frequency control submodule is used to perform secondary recovery control on the frequency of each of the series inverter units according to the distributed secondary frequency control logic.

[0073] Based on the same inventive concept, embodiments of the present invention also provide an electronic device, including: a memory, a processor, and a computer program stored in the memory and running on the processor, wherein the processor executes the computer program to implement the cascaded microgrid frequency control method as described above.

[0074] Based on the same inventive concept, embodiments of the present invention also provide a computer storage medium storing computer-executable instructions, which, when executed, implement the cascaded microgrid frequency control method as described above.

[0075] The beneficial effects of the above-described technical solutions provided in the embodiments of the present invention include at least the following:

[0076] The distributed frequency recovery control proposed in this invention relies solely on local information to restore the frequency of a cascaded microgrid system to its rated value. Frequency control requires no communication, reducing communication costs and avoiding communication delays, packet loss, and fault risks. Compared to centralized control schemes, this method employs communication-free distributed control, significantly enhancing the reliability of the cascaded microgrid system.

[0077] Other features and advantages of the invention will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing the invention. The objects and other advantages of the invention may be realized and obtained by means of the structures particularly pointed out in the written description, claims, and drawings.

[0078] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0079] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used in conjunction with embodiments of the invention to explain the invention and do not constitute a limitation thereof. In the drawings:

[0080] Figure 1 This is a flowchart of a cascaded microgrid frequency control method according to an embodiment of the present invention;

[0081] Figure 2 This is a schematic diagram of the cascaded microgrid system structure in an embodiment of the present invention;

[0082] Figure 3 This is a schematic diagram of frequency control for a cascaded microgrid system in an embodiment of the present invention;

[0083] Figure 4a This is a schematic diagram illustrating the frequency recovery principle when the resistive-inductive load changes in an embodiment of the present invention.

[0084] Figure 4b This is a schematic diagram illustrating the frequency recovery principle when the resistive-capacitive load changes in an embodiment of the present invention.

[0085] Figure 5a This is a schematic diagram illustrating the working performance of the frequency recovery control logic under resistive-inductive load in an embodiment of the present invention.

[0086] Figure 5b This is a schematic diagram illustrating the working performance of the frequency recovery control logic under resistive-capacitive load in an embodiment of the present invention.

[0087] Figure 6a This is a schematic diagram of the dynamic response of the control logic when the resistive-inductive load is switched to the resistive-capacitive load in an embodiment of the present invention;

[0088] Figure 6b This is a schematic diagram of the dynamic response of the control logic when the resistive-capacitive load is switched to the resistive-inductive load in an embodiment of the present invention;

[0089] Figure 7 This is a block diagram of a cascaded microgrid frequency control system according to an embodiment of the present invention;

[0090] Figure 8 This is a schematic diagram of the structure of an electronic device according to an embodiment of the present invention. Detailed Implementation

[0091] Exemplary embodiments of the present disclosure will now be described in more detail with reference to the accompanying drawings. While exemplary embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure may be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art.

[0092] To address the problems existing in the prior art, embodiments of the present invention provide a cascaded microgrid frequency control method, apparatus, electronic device, and storage medium.

[0093] Example 1

[0094] Embodiment 1 of the present invention provides a frequency control method for a cascaded microgrid, the process of which is as follows: Figure 1 As shown, it includes the following steps:

[0095] Step S1: Determine the secondary frequency control objective function, which specifically includes the following expression:

[0096]

[0097]

[0098] Where f ref f is the rated value for frequency recovery of a series-connected energy storage microgrid. i Let P be the frequency value of the i-th series inverter unit. i and m i P represents the output active power and droop control coefficient of the i-th series inverter unit, respectively. j and m j Let be the output power and droop control coefficient of the j-th series inverter unit, respectively; t represents time; i and j are the serial inverter unit numbers, which take values ​​from positive integers not exceeding n, and i is not equal to j; and n represents the total number of series inverter units.

[0099] Cascaded microgrid system structure as follows Figure 2 As shown, each series inverter unit includes a distributed micro-source, a series inverter, and a resonant circuit. Multiple series inverter units and loads constitute a cascaded microgrid system. Distributed micro-sources are also known as distributed power sources, or DGs for short. The Institute of Electrical and Electronics Engineers (IEEE) defines DGs as small-capacity generators that can be connected to the grid at any location within the power system, with a capacity range of less than 10MW. The grid connection voltage level is typically connected to the various voltage levels of the distribution system.

[0100] Step S2: Real-time acquisition of electrical parameters of the cascaded microgrid and each series inverter unit in the cascaded microgrid; determination of active power and reactive power of each series inverter unit based on the electrical parameters.

[0101] Specifically, the real-time acquisition of electrical parameters of the cascaded microgrid and each series inverter unit in the cascaded microgrid includes the following steps:

[0102] The system collects the overall power factor angle, steady-state load voltage phase angle, and output current frequency of the cascaded microgrid in real time; it also collects the output voltage, output current, output voltage phase angle, and output voltage angular frequency of each series inverter unit in the cascaded microgrid in real time.

[0103] Step S3: Based on the active power and reactive power of each series inverter unit, establish the series inverter synchronization control logic; according to the series inverter synchronization control logic, synchronize the frequency of each series inverter unit.

[0104] The synchronous control logic expression for the series inverter is as follows:

[0105] f i =f * +sgn(Q i )m i P i

[0106] Where f i f is the frequency value of the i-th series inverter unit. * For the no-load frequency value of the series microgrid, sgn represents the sign function, and Q... i Let m be the output reactive power of the i-th series inverter unit. i P is the droop control factor. i Let i be the output active power of the i-th series inverter unit, and let i be the number of the series inverter unit. i takes a value from a positive integer not exceeding n, where n represents the total number of series inverter units.

[0107] Step S4: Determine the desired output voltage phase angle model for each of the series inverter units based on the electrical parameters;

[0108] For cascaded microgrids, each distributed generation (DG) unit has the same load current, which is an inherently common characteristic. Specifically, the expression for the desired output voltage phase angle model is:

[0109]

[0110] Where θ IiLet be the desired output voltage phase angle of the i-th series inverter unit, and atan2 be the arctangent function. For the overall power factor angle of the series energy storage microgrid system, P * max_i For the upper limit constraint of the output power of the i-th series inverter unit, θ i Let θ' be the output voltage phase angle of the i-th series inverter unit. load is the phase angle of the load voltage in steady state, i is the number of the series inverter unit, i takes a value from positive integers not exceeding n, and n represents the total number of series inverter units.

[0111] Step S5: Perform small-signal linearization on the desired output voltage phase angle model to obtain the output current frequency model of each series inverter unit;

[0112] Specifically, the desired output voltage phase angle model is linearized using small-signal methods to obtain the output current frequency model for each series inverter unit, including the following steps:

[0113] The desired output voltage phase angle model expression is linearized using small-signal methods.

[0114] Assuming the steady-state voltage angles are the same, let θ i =θ i0 +Δθ i Substitute the desired output voltage phase angle model expression after small-signal linearization and eliminate θ i0 The output current frequency model of each of the series inverter units is obtained, and the expression of the output current frequency model is as follows:

[0115]

[0116] Where f Ii Let be the frequency value of the output current of the i-th series inverter unit. For the overall power factor angle of the series energy storage microgrid system, P * max_i For the upper limit constraint of the output power of the i-th series inverter unit, ω i Let ω be the output voltage angular frequency of the i-th series inverter unit, where i is the serial inverter unit number and takes a value from a positive integer not exceeding n, where n represents the total number of series inverter units.

[0117] As can be seen from the output current frequency model expression, the current frequency of the cascaded microgrid system represents the weighted average frequency of all units. Therefore, the inherent characteristics of the cascaded microgrid system can be utilized to adjust the frequency of the entire cascaded microgrid system by restoring the current frequency.

[0118] Step S6: Construct a frequency offset model for each of the series inverter units based on the output current frequency model;

[0119] Specifically, the frequency offset model expression is as follows:

[0120]

[0121] Where Δf i k is the frequency offset of the i-th series inverter unit. Ii Here are the coefficients of the auxiliary controller, s is the Laplace operator, and f is the coefficient of the auxiliary controller. ref f is the rated value for frequency recovery of a series-connected energy storage microgrid. Ii Let i be the frequency value of the output current of the i-th series inverter unit, where i is the number of the series inverter unit, and i takes a value from a positive integer not exceeding n, where n represents the total number of series inverter units.

[0122] Step S7: Based on the characteristic that all series inverter units in the cascaded microgrid have the same current, a distributed secondary frequency control logic is built based on the active power, reactive power and frequency offset model of each series inverter unit.

[0123] Specifically, based on the characteristic that all series inverter units in the cascaded microgrid have the same current, the following expression is obtained:

[0124] f I1 =f I2 =…=f In =f I

[0125] Where f I1 f is the frequency value of the first series inverter unit. I2 f is the frequency value of the second series inverter unit. In f is the frequency value of the nth series inverter unit, where n represents the total number of series inverter units. I The frequency value of the output current;

[0126] Based on the active power, reactive power, and frequency offset model of each series inverter unit, a distributed secondary frequency control logic is constructed, and the expression of the distributed secondary frequency control logic is as follows:

[0127]

[0128] Where f i f is the frequency value of the i-th series inverter unit. * For the no-load frequency value of the series microgrid, sgn represents the sign function, and Q... i Let m be the output reactive power of the i-th series inverter unit.i P is the droop control factor, inversely proportional to the DG capacity. i Let k be the output active power of the i-th series inverter unit. Ii Let f be the integral coefficient of the i-th series inverter unit, s be the Laplace operator, and f be the integral coefficient of the i-th series inverter unit. ref f is the rated value for frequency recovery of a series-connected energy storage microgrid. I k represents the frequency value of the output current, i is the unit number of the series inverter, i takes a value from a positive integer not exceeding n, and n represents the total number of series inverter units. Ii Used for secondary recovery control of frequency.

[0129] Step S8: Perform secondary recovery control on the frequency of each series inverter unit according to the distributed secondary frequency control logic.

[0130] Through PI control, the current frequency returns to its normal value, and the frequencies of each output gate (DG) converge to a value equal to the current frequency. PI control, or proportional integral controller, is a linear controller that uses the control deviation between the given value and the actual output value as a basis. The proportional and integral components of this deviation are then linearly combined to form the control quantity, which controls the controlled object.

[0131] Under steady-state conditions, the current frequency recovers to its normal value through PI control, and the frequencies of all series inverter units converge to a value equal to the current frequency. Then, the rated value f of the system frequency recovery to the series energy storage microgrid can be obtained. ref .

[0132] f1 = f2 = ... = f i =…=f n =f I =f ref

[0133] Where fi is the frequency value of the i-th series inverter unit, i is the series inverter unit number, i takes a value from a positive integer not exceeding n, and n represents the total number of series inverter units, f I This represents the frequency value of the output current.

[0134] At the same time, since all series inverter units share the same current,

[0135] Δf1=Δf2=…=Δf i =…=Δf n

[0136] m1ΔP1=m2ΔP2=…m i ΔP i =…=m nΔP n

[0137] Where Δfi is the frequency offset of the i-th series inverter unit, i is the series inverter unit number, i takes a value from a positive integer not exceeding n, n represents the total number of series inverter units, and m i ΔPi is the droop control coefficient, and ΔPi is the power offset of the i-th series inverter unit when the series microgrid is unloaded.

[0138] A schematic diagram of frequency control for a cascaded microgrid system is shown below. Figure 3 As shown, by real-time acquisition of electrical parameters of the cascaded microgrid and each series inverter unit within it, the active and reactive power data of each series inverter unit are determined based on these electrical parameters. According to the distributed secondary frequency control logic, PI control is performed within each series inverter unit to achieve secondary frequency recovery control. This enables the switching of resistive-capacitive or resistive-inductive loads during load switching. Figure 3 In this context, PLL stands for Phase-Locked Loop, a type of feedback control circuit. It is characterized by using an externally input reference signal to control the frequency and phase of the internal oscillation signal.

[0139] Frequency recovery principle as follows Figure 4a and Figure 4b As shown, when the resistive-inductive load or resistive-capacitive load increases, the frequency moves from point a to point b. The proposed control core is to change the offset of the fP curve, so that the operating point will move from point b to the desired point c.

[0140] To more clearly verify the effect of the SoC equalization achieved by the embodiments of the present invention, a comparative case simulation analysis is presented here. A cascaded microgrid consisting of four cascaded units is established in the simulation software. The overall control strategy diagram is as follows. Figure 3 As shown. The following is an analysis of cases A and B respectively:

[0141] In Case A, the simulation results are as follows: Figure 5a and Figure 5b As shown. Figure 5a and Figure 5b The performance of the proposed control logic under resistive-inductive loads and resistive-capacitive loads are respectively represented. Figure 5a and Figure 5b The four curves correspond to the four cascaded units in the established cascaded microgrid. As can be seen from the figure, the four curves can be restored to the desired position, realizing frequency recovery control without communication, thus verifying the effectiveness of the proposed frequency recovery control logic. Its stability is not affected by the load impedance characteristics.

[0142] In Case B, the simulation results are as follows: Figure 6a and Figure 6b As shown, the dynamic response of the proposed control logic during load characteristic changes is verified. Figure 6a In the cascaded microgrid system, the load initially operates under resistive-inductive load, and when t = 3s, the load switches to resistive-capacitive load. Figure 6a and Figure 6b The four curves in the simulation correspond to the four cascaded units in the established cascaded microgrid. The four curves can recover to the desired positions, achieving frequency recovery control without communication, maintaining system stability, and realizing frequency recovery and power sharing. The simulation results when the capacitive-resistive load is converted to an inductive-resistive load are similar to the above analysis results; the four curves can recover to the desired positions, achieving frequency recovery control without communication, maintaining system stability, and realizing frequency recovery and power sharing.

[0143] In the method described in this embodiment, the frequency of the cascaded microgrid system is restored to its rated value relying only on local information. Frequency control does not require any communication, reducing communication costs and avoiding communication delays, packet loss, and fault risks. Compared with centralized control schemes, this method employs communication-free distributed control, which greatly enhances the reliability of the cascaded microgrid system.

[0144] Those skilled in the art can change the above order without departing from the scope of protection of this disclosure.

[0145] Example 2

[0146] Embodiment 2 of the present invention provides a cascaded microgrid frequency control system, the structure of which is as follows: Figure 7 As shown, it includes:

[0147] The objective function determination module 100 is used to determine the secondary frequency control objective function, which specifically includes the following expression:

[0148]

[0149]

[0150] Where f ref f is the rated value for frequency recovery of a series-connected energy storage microgrid. i Let P be the frequency value of the i-th series inverter unit. i and m i P represents the output active power and droop control coefficient of the i-th series inverter unit, respectively. j and m jLet i and j represent the output power and droop control coefficient of the j-th series inverter unit, respectively; t represents time; i and j are the serial inverter unit numbers, which take values ​​from positive integers not exceeding n, and i is not equal to j; and n represents the total number of series inverter units.

[0151] The electrical parameter acquisition module 200 is used to acquire electrical parameters of the cascaded microgrid and each series inverter unit in the cascaded microgrid in real time.

[0152] The power determination module 300 is used to determine the active power and reactive power of each of the series inverter units based on the electrical parameters.

[0153] The synchronization control module 400 is used to build a series inverter synchronization control logic based on the active power and reactive power of each series inverter unit; and to synchronize the frequency of each series inverter unit according to the series inverter synchronization control logic.

[0154] The frequency control module 500 is used to determine the desired output voltage phase angle model of each series inverter unit based on the electrical parameters; perform small-signal linearization on the desired output voltage phase angle model to obtain the output current frequency model of each series inverter unit; construct a frequency offset model for each series inverter unit based on the output current frequency model; based on the characteristic that all series inverter units in the cascaded microgrid have the same current, build a distributed secondary frequency control logic based on the active power, reactive power and frequency offset model of each series inverter unit; and perform secondary frequency recovery control on the frequency of each series inverter unit based on the distributed secondary frequency control logic.

[0155] Specifically, the electrical parameter acquisition module 200 is used for:

[0156] The system collects the overall power factor angle, steady-state load voltage phase angle, and output current frequency of the cascaded microgrid in real time; it also collects the output voltage, output current, output voltage phase angle, and output voltage angular frequency of each series inverter unit in the cascaded microgrid in real time.

[0157] Specifically, the frequency control module 500 includes:

[0158] The desired output voltage phase angle determination submodule is used to determine the desired output voltage phase angle model for each of the series inverter units based on the electrical parameters. The expression for the desired output voltage phase angle model is as follows:

[0159]

[0160] Where θ IiLet be the desired output voltage phase angle of the i-th series inverter unit, and atan2 be the arctangent function. For the overall power factor angle of the series energy storage microgrid system, P * max_i For the upper limit constraint of the output power of the i-th series inverter unit, θ i Let θ' be the output voltage phase angle of the i-th series inverter unit. load is the phase angle of the load voltage in steady state, i is the number of the series inverter unit, i takes a value from positive integers not exceeding n, and n represents the total number of series inverter units;

[0161] The output current frequency model determination submodule is used to perform small-signal linearization on the expression of the desired output voltage phase angle model.

[0162] Assuming the steady-state voltage angles are the same, let θ i =θ i0 +Δθ i Substitute the desired output voltage phase angle model expression after small-signal linearization and eliminate θ i0 The output current frequency model of each of the series inverter units is obtained, and the expression of the output current frequency model is as follows:

[0163]

[0164] Where f Ii Let be the frequency value of the output current of the i-th series inverter unit. For the overall power factor angle of the series energy storage microgrid system, P * max_i For the upper limit constraint of the output power of the i-th series inverter unit, ω i Let be the angular frequency of the output voltage of the i-th series inverter unit;

[0165] The frequency offset determination submodule is used to construct a frequency offset model for each of the series inverter units based on the output current frequency model. The expression for the frequency offset model is:

[0166]

[0167] Where Δf i k is the frequency offset of the i-th series inverter unit. Ii Here are the coefficients of the auxiliary controller, s is the Laplace operator, and f is the coefficient of the auxiliary controller. ref f is the rated value for frequency recovery of a series-connected energy storage microgrid. Ii Let be the frequency value of the output current of the i-th series inverter unit;

[0168] The secondary frequency control logic submodule is used to derive the following expression based on the characteristic that all series inverter units in the cascaded microgrid have the same current.

[0169] f I1 =f I2 =…=f In =f I

[0170] Where f I1 f is the frequency value of the first series inverter unit. I2 f is the frequency value of the second series inverter unit. In f is the frequency value of the nth series inverter unit, where n represents the total number of series inverter units. I The frequency value of the output current;

[0171] Based on the active power, reactive power, and frequency offset model of each series inverter unit, a distributed secondary frequency control logic is constructed, and the expression of the distributed secondary frequency control logic is as follows:

[0172]

[0173] Where f i f is the frequency value of the i-th series inverter unit. * For the no-load frequency value of the series microgrid, sgn represents the sign function, and Q... i Let m be the output reactive power of the i-th series inverter unit. i P is the droop control factor. i Let k be the output active power of the i-th series inverter unit. Ii Let f be the integral coefficient of the i-th series inverter unit, s be the Laplace operator, and f be the integral coefficient of the i-th series inverter unit. ref f is the rated value for frequency recovery of a series-connected energy storage microgrid. I The frequency value of the output current;

[0174] The secondary frequency control submodule is used to perform secondary recovery control on the frequency of each of the series inverter units according to the distributed secondary frequency control logic.

[0175] Regarding the system in the above embodiments, the specific manner in which each module performs its operations has been described in detail in the embodiments related to the method, and will not be elaborated upon here.

[0176] In this embodiment, the frequency of the cascaded microgrid system is restored to its rated value relying only on local information. Frequency control requires no communication, reducing communication costs and avoiding communication delays, packet loss, and fault risks. Compared with centralized control schemes, this method employs communication-free distributed control, which significantly enhances the reliability of the cascaded microgrid system.

[0177] Based on the same inventive concept, embodiments of the present invention also provide an electronic device, including: a memory, a processor, and a computer program stored in the memory and running on the processor, wherein the processor executes the computer program to implement the cascaded microgrid frequency control method as described above.

[0178] Based on the same inventive concept, embodiments of the present invention also provide a computer storage medium storing computer-executable instructions, which, when executed, implement the cascaded microgrid frequency control method as described above.

[0179] Any modifications, additions, and equivalent substitutions made within the scope of the principles of this invention shall still fall within the patent coverage of this invention.

Claims

1. A frequency control method for a cascaded microgrid, characterized in that, Includes the following steps: Real-time acquisition of electrical parameters of the cascaded microgrid and each series inverter unit in the cascaded microgrid; Based on the electrical parameters, determine the active power and reactive power of each of the series inverter units; Based on the active and reactive power of each series inverter unit, a synchronous control logic for the series inverter is established. According to the series inverter synchronization control logic, the frequency of each series inverter unit is synchronized; Based on the electrical parameters, determine the desired output voltage phase angle model for each of the series inverter units; The desired output voltage phase angle model is linearized using a small signal to obtain the output current frequency model of each series inverter unit. Based on the output current frequency model, a frequency offset model for each of the series inverter units is constructed. Based on the characteristic that all series inverter units in the cascaded microgrid have the same current, a distributed secondary frequency control logic is built based on the active power, reactive power and frequency offset model of each series inverter unit. According to the distributed secondary frequency control logic, the frequency of each series inverter unit is subjected to secondary recovery control. The frequency offset model expression is: in This represents the frequency offset of the i-th series inverter unit. k Ii For the coefficients of the auxiliary controller, s For the Laplace operator, f ref This is the rated value for frequency recovery of a series-connected energy storage microgrid. f Ii Let be the frequency value of the output current of the i-th series inverter unit. i Numbering of series inverter units i within no more than n Take values ​​from positive integers, n This represents the total number of series inverter units; Based on the characteristic that all series inverter units in the cascaded microgrid have the same current, a distributed secondary frequency control logic is built based on the active power, reactive power, and frequency offset model of each series inverter unit, including the following steps: Based on the characteristic that all series inverter units in the cascaded microgrid have the same current, the following expression is obtained. f I1 = f I2 =…= f In = f I in f I1 This is the frequency value of the first series inverter unit. f I2 This is the frequency value of the second series inverter unit. f In For the first n Frequency values ​​of each series inverter unit n Represents the total number of series inverter units. f I The frequency value of the output current; Based on the active power, reactive power, and frequency offset model of each series inverter unit, a distributed secondary frequency control logic is constructed, and the expression of the distributed secondary frequency control logic is as follows: in f i Let i be the frequency value of the i-th series inverter unit. f sg represents the frequency value of a series microgrid under no-load conditions. n Represents a symbolic function. Q i For the first i The output reactive power of each series inverter unit m i This is the droop control coefficient. P i For the first i The output active power of each series inverter unit Let be the integral coefficient of the i-th series inverter unit. s For the Laplace operator, f ref This is the rated value for frequency recovery of a series-connected energy storage microgrid. f I The frequency value of the output current. i Numbering of series inverter units i within no more than n Take values ​​from positive integers, n This represents the total number of series inverter units.

2. The method as described in claim 1, characterized in that, Before the real-time acquisition of electrical parameters of the cascaded microgrid and each series inverter unit in the cascaded microgrid, the following steps are included: Determine the objective function for secondary frequency control, which specifically includes the following expression: in f ref This is the rated value for frequency recovery of a series-connected energy storage microgrid. f i For the first i Frequency values ​​of each series inverter unit P i and m i The first i Output active power and droop control coefficient of each series inverter unit P j and m j The first j Output power and droop control coefficient of a series inverter unit t Represents time, i and j Numbering of series inverter units i and j within no more than n Take values ​​from positive integers, and i Not equal to j , n This represents the total number of series inverter units.

3. The method as described in claim 1, characterized in that, The real-time acquisition of electrical parameters of the cascaded microgrid and each series inverter unit in the cascaded microgrid includes the following steps: Real-time acquisition of the overall power factor angle, steady-state load voltage phase angle, and output current frequency of the cascaded microgrid; The output voltage, output current, output voltage phase angle, and output voltage angular frequency of each series inverter unit in the cascaded microgrid are collected in real time.

4. The method according to any one of claims 1-3, characterized in that, The expression for the desired output voltage phase angle model is: in For the first i The desired output voltage phase angle of a series inverter unit, ata n 2 is the arctangent function. φ To determine the overall power factor angle of the series energy storage microgrid system, P max_i For the first i Output power upper limit constraint for each series inverter unit θ i For the first i The output voltage phase angle of a series inverter unit The phase angle of the load voltage in steady state. i Numbering of series inverter units i within no more than n Take values ​​from positive integers, n This represents the total number of series inverter units.

5. The method as described in claim 4, characterized in that, The desired output voltage phase angle model is linearized using a small-signal method to obtain the output current frequency model for each series inverter unit, including the following steps: The desired output voltage phase angle model expression is linearized using small-signal methods. Assuming the steady-state voltage angles are the same, θ i = θ i0 + θ i Substitute the expression for the desired output voltage phase angle after small-signal linearization and eliminate θ i0 The output current frequency model of each of the series inverter units is obtained, and the expression of the output current frequency model is as follows: in f Ii Let be the frequency value of the output current of the i-th series inverter unit. φ To determine the overall power factor angle of the series energy storage microgrid system, P max_i For the first i Output power upper limit constraint for each series inverter unit ω i Let be the output voltage angular frequency of the i-th series inverter unit. i Numbering of series inverter units i within no more than n Take values ​​from positive integers, n This represents the total number of series inverter units.

6. A cascaded microgrid frequency control system, characterized in that, include: An electrical parameter acquisition module is used to acquire electrical parameters of the cascaded microgrid and each series inverter unit in the cascaded microgrid in real time. A power determination module is used to determine the active power and reactive power of each of the series inverter units based on the electrical parameters. The synchronization control module is used to build a series inverter synchronization control logic based on the active power and reactive power of each series inverter unit; and to synchronize the frequency of each series inverter unit according to the series inverter synchronization control logic. The frequency control module is used to determine the desired output voltage phase angle model of each series inverter unit based on the electrical parameters; perform small-signal linearization on the desired output voltage phase angle model to obtain the output current frequency model of each series inverter unit; construct a frequency offset model for each series inverter unit based on the output current frequency model; based on the characteristic that all series inverter units in the cascaded microgrid have the same current, build a distributed secondary frequency control logic based on the active power, reactive power and frequency offset model of each series inverter unit; and perform secondary recovery control on the frequency of each series inverter unit based on the distributed secondary frequency control logic. The frequency offset model expression is: in This represents the frequency offset of the i-th series inverter unit. k Ii For the coefficients of the auxiliary controller, s For the Laplace operator, f ref This is the rated value for frequency recovery of a series-connected energy storage microgrid. f Ii Let be the frequency value of the output current of the i-th series inverter unit. i Numbering of series inverter units i within no more than n Take values ​​from positive integers, n This represents the total number of series inverter units; Based on the characteristic that all series inverter units in the cascaded microgrid have the same current, a distributed secondary frequency control logic is built based on the active power, reactive power, and frequency offset model of each series inverter unit, including the following steps: Based on the characteristic that all series inverter units in the cascaded microgrid have the same current, the following expression is obtained. f I1 = f I2 =…= f In = f I in f I1 This is the frequency value of the first series inverter unit. f I2 This is the frequency value of the second series inverter unit. f In For the first n Frequency values ​​of each series inverter unit n Represents the total number of series inverter units. f I The frequency value of the output current; Based on the active power, reactive power, and frequency offset model of each series inverter unit, a distributed secondary frequency control logic is constructed, and the expression of the distributed secondary frequency control logic is as follows: in f i Let i be the frequency value of the i-th series inverter unit. f sg represents the frequency value of a series microgrid under no-load conditions. n Represents a symbolic function. Q i For the first i The output reactive power of each series inverter unit m i This is the droop control coefficient. P i For the first i The output active power of each series inverter unit Let be the integral coefficient of the i-th series inverter unit. s For the Laplace operator, f ref This is the rated value for frequency recovery of a series-connected energy storage microgrid. f I The frequency value of the output current. i Numbering of series inverter units i within no more than n Take values ​​from positive integers, n This represents the total number of series inverter units.

7. The system as described in claim 6, characterized in that, Also includes: The objective function determination module is used to determine the secondary frequency control objective function, which specifically includes the following expression: in f ref This is the rated value for frequency recovery of a series-connected energy storage microgrid. f i For the first i Frequency values ​​of each series inverter unit P i and m i The first i Output active power and droop control coefficient of each series inverter unit P j and m j The first j Output power and droop control coefficient of a series inverter unit t Represents time, i and j Numbering of series inverter units i and j within no more than n Take values ​​from positive integers, and i Not equal to j , n This represents the total number of series inverter units.

8. The system as described in claim 6, characterized in that, The electrical parameter acquisition module is specifically used for: Real-time acquisition of the overall power factor angle, steady-state load voltage phase angle, and output current frequency of the cascaded microgrid; The output voltage, output current, output voltage phase angle, and output voltage angular frequency of each series inverter unit in the cascaded microgrid are collected in real time.

9. The system as described in claim 6, characterized in that, The frequency control module includes: The desired output voltage phase angle determination submodule is used to determine the desired output voltage phase angle model for each of the series inverter units based on the electrical parameters. The expression for the desired output voltage phase angle model is as follows: in For the first i The desired output voltage phase angle of a series inverter unit, ata n 2 is the arctangent function. φ To determine the overall power factor angle of the series energy storage microgrid system, P max_i For the first i Output power upper limit constraint for each series inverter unit θ i For the first i The output voltage phase angle of a series inverter unit The phase angle of the load voltage in steady state. i Numbering of series inverter units i within no more than n Take values ​​from positive integers, n This represents the total number of series inverter units; The output current frequency model determination submodule is used to perform small-signal linearization on the expression of the desired output voltage phase angle model. Assuming the steady-state voltage angles are the same, θ i = θ i0 + θ i Substitute the expression for the desired output voltage phase angle after small-signal linearization and eliminate θ i0 The output current frequency model of each of the series inverter units is obtained, and the expression of the output current frequency model is as follows: in f Ii Let be the frequency value of the output current of the i-th series inverter unit. φ To determine the overall power factor angle of the series energy storage microgrid system, P max_i For the first i Output power upper limit constraint for each series inverter unit ω i Let be the angular frequency of the output voltage of the i-th series inverter unit; The frequency offset determination submodule is used to construct a frequency offset model for each of the series inverter units based on the output current frequency model. The secondary frequency control submodule is used to perform secondary recovery control on the frequency of each of the series inverter units according to the distributed secondary frequency control logic.

10. An electronic device, characterized in that, include: A memory, a processor, and a computer program stored in the memory and running on the processor, wherein the processor, when executing the computer program, implements the cascaded microgrid frequency control method according to any one of claims 1-5.

11. A computer storage medium, characterized in that, The computer storage medium stores computer-executable instructions, which, when executed, implement the cascaded microgrid frequency control method according to any one of claims 1-5.

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