CN115102183A - Cascaded microgrid frequency control circuit and design method - Google Patents

Cascaded microgrid frequency control circuit and design method Download PDF

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Publication number
CN115102183A
CN115102183A CN202210658978.1A CN202210658978A CN115102183A CN 115102183 A CN115102183 A CN 115102183A CN 202210658978 A CN202210658978 A CN 202210658978A CN 115102183 A CN115102183 A CN 115102183A
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frequency
inverter
inverter unit
circuit
series
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赵晋宇
孙宏印
张鹏林
马晨璨
邢宇
姜文旭
王皓
刘海洋
崔欣欣
刘雨佳
王含
王辉
余文杰
陈诗淼
施光泽
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Inner Mongolia Hmhj Aluminum Electricity Co ltd
Beijing Herui Energy Storage Technology Co ltd
Central South University
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Inner Mongolia Hmhj Aluminum Electricity Co ltd
Beijing Herui Energy Storage Technology Co ltd
Central South University
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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/24—Arrangements for preventing or reducing oscillations of power in networks
    • H02J3/241—The oscillation concerning frequency
    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06F—ELECTRIC DIGITAL DATA PROCESSING
    • G06F30/00—Computer-aided design [CAD]
    • G06F30/30—Circuit design
    • G06F30/32—Circuit design at the digital level
    • G06F30/327—Logic synthesis; Behaviour synthesis, e.g. mapping logic, HDL to netlist, high-level language to RTL or netlist
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
    • H02J3/381—Dispersed generators
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
    • H02J3/40—Synchronising a generator for connection to a network or to another generator
    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06F—ELECTRIC DIGITAL DATA PROCESSING
    • G06F2113/00—Details relating to the application field
    • G06F2113/04—Power grid distribution networks
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J2203/00—Indexing scheme relating to details of circuit arrangements for AC mains or AC distribution networks
    • H02J2203/20—Simulating, e g planning, reliability check, modelling or computer assisted design [CAD]

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Abstract

The invention discloses a cascade type microgrid frequency control circuit and a design method. The method comprises the following steps: the system comprises a public load and a plurality of inverter units, wherein the inverter units are connected in series, each inverter unit comprises a distributed power supply, a series inverter and a resonant circuit, and the inverter units further comprise an inner ring control circuit and are used for synchronizing the frequency of the inverter units according to the series inverter synchronous control logic; and performing secondary recovery control on the frequency of the inverter unit according to the distributed secondary frequency control logic. The frequency control can be realized under the condition of not carrying out communication, the communication cost is reduced, the communication delay, packet loss and fault risks are avoided, and the reliability of the cascaded micro-grid system is improved.

Description

Cascaded micro-grid frequency control circuit and design method
Technical Field
The invention relates to the technical field of microgrid circuit design, in particular to a cascade microgrid frequency control circuit and a design method thereof.
Background
The micro grid is a research hotspot due to the important role and position of the micro grid in the field of renewable energy sources. Micro-grids can be divided into two types, depending on the configuration. The first is a parallel microgrid, and research in this regard has been carried out for many years. Droop control and virtual synchronous generators are the most common control strategies. The other type is a cascade type microgrid, and compared with the former type, the cascade type microgrid is a novel microgrid.
In recent years, the development of the micro-grid in the high/medium voltage field is promoted by the introduction of the cascade micro-grid, particularly large-scale photovoltaic power generation, energy storage power stations and the like. The traditional cascade system control method mostly depends on centralized control. In recent years, many distributed control methods have been proposed in order to reduce communication load and inspire droop control. Also, frequency synchronization and power balancing may be automatically achieved. For example, reverse power factor droop control under RL load. f-P/Q droop control and power factor angle droop control for different load characteristics. However, these methods ignore the frequency offset they cause.
Therefore, frequency recovery control is also highly desirable for the operation of cascaded micro-grids. The most classical method is the central control method. However, the central controller has a high dependence on communication, and the amount of calculation is large, which may reduce the reliability of the system. In order to reduce communication dependence and localize control algorithm, a distributed frequency control method based on local controller and neighbor information is provided. Communication delays and failures can still threaten the operational performance, stability and reliability of the system.
Disclosure of Invention
The present invention has been made to solve at least part of the technical problems occurring in the prior art, and provides a cascaded microgrid frequency control circuit and a design method thereof.
In a first aspect, an embodiment of the present invention provides a cascaded microgrid frequency control circuit, including a common load and a plurality of inverter units, the plurality of inverter units being connected in series, each inverter unit including a distributed power source, a series inverter, and a resonant circuit, the inverter unit further including:
the data processing circuit is used for acquiring the integral power factor angle, the load voltage phase angle in a steady state and the output current frequency of the cascaded micro-grid system in real time; acquiring output voltage, output current, an output voltage phase angle and output voltage angular frequency of the inverter unit in real time;
the power calculation circuit is used for determining the active power and the reactive power of each inverter unit according to the electrical parameters;
an inner loop control circuit for synchronizing the frequency of the inverter units according to a series inverter synchronization control logic; performing secondary recovery control on the frequency of the inverter unit according to a distributed secondary frequency control logic;
and the phase-locked loop circuit is used for controlling the frequency and the phase of the internal loop oscillation signal of the inverter unit.
Specifically, the inner loop control circuit includes:
a synchronization control circuit for synchronizing the frequency of the inverter units according to a series inverter synchronization control logic, the series inverter synchronization control logic comprising:
f i ＝f * +sgn(Q i )m i P i
wherein f is i Frequency value of ith inverter unit, f * Is the no-load time-frequency value of the series micro-grid, sgn represents a symbolic function, Q i For the output reactive power of the i-th inverter unit, m i For droop control coefficient, P i The output active power i of the ith inverter unit is the serial number of the inverter unit, i takes the value in a positive integer not exceeding n, and n represents the total number of the inverter units;
a frequency secondary recovery circuit configured to perform secondary recovery control on the frequency of the inverter unit according to a distributed secondary frequency control logic, the distributed secondary frequency control logic being configured to:
Figure BDA0003686974220000021
wherein f is i Is the frequency value of the ith inverter unit, f * For the value of the no-load time frequency of the series micro-grid, sgn represents a sign function, Q i For the output reactive power of the ith inverter unit, m i For droop control coefficient, P i For the output active power, k, of the ith inverter unit Ii Is the integral coefficient of the ith inverter unit, s is the Laplace operator, f ref Rated value, f, for frequency recovery of series-connected energy-storage microgrid I And in the frequency value of the output current, i is the number of the inverter units, i takes a value in a positive integer not exceeding n, and n represents the total number of the inverter units.
Specifically, the inverter unit further includes:
a load switching circuit for switching between a resistive-inductive load and a resistive-capacitive load in the common load.
In a second aspect, an embodiment of the present invention provides a method for designing a cascaded microgrid frequency control circuit, including the following steps:
the method comprises the steps that a plurality of inverter units are arranged, wherein each inverter unit comprises a distributed power supply, a series inverter, a resonance circuit, a data processing circuit, a power calculation circuit, an inner ring control circuit and a phase-locked loop circuit; the inner ring control circuit comprises a synchronous control circuit and a frequency secondary recovery circuit;
connecting a common load and a plurality of inverter units in series;
wherein the inverter unit is provided, including the steps of:
setting a data processing circuit, and acquiring the electrical parameters of the cascaded micro-grid and each inverter unit in the cascaded micro-grid in real time;
setting a power calculation circuit, calculating the electrical parameters, and determining the active power and the reactive power of each inverter unit;
setting the synchronous control circuit according to the synchronous control logic of the series inverter to synchronize the frequency of the inverter units;
and according to a distributed secondary frequency control logic, the frequency secondary recovery circuit is arranged to perform secondary recovery control on the frequency of the inverter unit.
Specifically, the series inverter synchronous control logic is as follows:
f i ＝f * +sgn(Q i )m i P i
wherein f is i Frequency value of ith inverter unit, f * For the value of the no-load time frequency of the series micro-grid, sgn represents a sign function, Q i For the output reactive power of the ith inverter unit, m i For droop control coefficient, P i The output active power i of the ith inverter unit is the serial number of the inverter unit, i takes the value in a positive integer not exceeding n, and n represents the total number of the inverter units.
Specifically, the distributed secondary frequency control logic is as follows:
Figure BDA0003686974220000041
wherein f is i Is the frequency value of the ith inverter unit, f * Is the no-load time-frequency value of the series micro-grid, sgn represents a symbolic function, Q i For the output reactive power of the ith inverter unit, m i For droop control coefficient, P i For the output active power, k, of the ith inverter unit Ii Is the integral coefficient of the ith inverter unit, s is the Laplace operator, f ref Rated value, f, for frequency recovery of series-connected energy-storage microgrid I And i is the number of the inverter units, i is a value in a positive integer not exceeding n, and n represents the total number of the inverter units.
Specifically, the inverter unit is provided, and the method further includes the steps of:
setting a phase-locked loop circuit, and controlling the frequency and the phase of the internal loop oscillation signal of the inverter unit;
and a load switching circuit is arranged for switching the resistance-inductance load and the resistance-capacitance load in the common load.
The technical scheme provided by the embodiment of the invention has the beneficial effects that at least:
the distributed frequency recovery control provided by the embodiment of the invention only depends on local information to recover the frequency of the cascaded micro-grid system to a rated value, and the frequency control does not need any communication, thereby reducing the communication cost and avoiding the communication delay, packet loss and fault risk. Compared with a centralized control scheme, the method adopts communication-free distributed control, so that the reliability of the cascaded micro-grid system can be greatly enhanced.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by the practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
The technical solution of the present invention is further described in detail by the accompanying drawings and embodiments.
Drawings
The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention and not to limit the invention. In the drawings:
FIG. 1 is a schematic diagram of a cascaded microgrid frequency control circuit in an embodiment of the invention;
FIG. 2 is a schematic structural diagram of a cascaded micro-grid system in an embodiment of the invention;
FIG. 3a is a schematic diagram illustrating a frequency recovery principle when a resistive-inductive load changes according to an embodiment of the present invention;
FIG. 3b is a schematic diagram illustrating a frequency recovery principle when the RC load changes according to an embodiment of the present invention;
FIG. 4a is a schematic diagram illustrating the operation performance of the frequency recovery control logic under the resistive load according to the embodiment of the present invention;
FIG. 4b is a schematic diagram illustrating the operation performance of the frequency recovery control logic under RC load according to the embodiment of the present invention;
FIG. 5a is a schematic diagram illustrating the dynamic response of the control logic when the resistive-inductive load is switched to the resistive-capacitive load according to the embodiment of the present invention;
fig. 5b is a schematic diagram of the dynamic response of the control logic when the rc load is switched to the rc load according to the embodiment of the present invention.
Detailed Description
Exemplary embodiments of the present disclosure will be described in more detail below 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 embodied 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.
In order to solve the problems in the prior art, the embodiment of the invention provides a cascaded microgrid frequency control circuit and a design method.
Example one
The structure of the cascade microgrid frequency control circuit is shown in fig. 1, the electrical parameters of a cascade microgrid and each inverter unit in the cascade microgrid are collected in real time, data such as active power and reactive power of each inverter unit are determined according to the electrical parameters, and PI control is performed in each inverter unit according to distributed secondary frequency control logic to achieve secondary frequency recovery control. The switching of the resistance-capacitance load or the resistance-inductance load is realized in the load switching.
The structure of the cascaded micro-grid system is shown in fig. 2, each inverter unit comprises a distributed micro-source, a series inverter and a resonant circuit, and the plurality of inverter units and the load form the cascaded micro-grid system. Distributed micro sources are distributed power Supplies (DGs), the distributed power supplies are DGs (distributed generation for short), the DGs defined by the Institute of Electrical and Electronics Engineers (IEEE) are small-capacity generators which can be connected to the grid at any position of a power system, the capacity range is less than 10MW, and the grid-connected voltage class is generally connected to each voltage class of the power distribution system.
A cascaded microgrid frequency control circuit comprising a common load and a plurality of inverter units connected in series between the plurality of inverter units, the inverter units comprising a distributed power source, a series inverter and a resonant circuit, the inverter units further comprising:
the data processing circuit is used for acquiring the integral power factor angle, the load voltage phase angle in a steady state and the output current frequency of the cascaded micro-grid system in real time; acquiring output voltage, output current, an output voltage phase angle and output voltage angular frequency of the inverter unit in real time;
the power calculation circuit is used for determining the active power and the reactive power of each inverter unit according to the electrical parameters;
an inner loop control circuit for synchronizing the frequency of the inverter units according to a series inverter synchronization control logic; performing secondary recovery control on the frequency of the inverter unit according to a distributed secondary frequency control logic;
and the phase-locked loop circuit is used for controlling the frequency and the phase of the loop oscillation signal in the inverter unit. The PLL in fig. 2 represents a Phase-Locked Loop, and is a feedback control circuit, referred to as a Phase-Locked Loop (PLL), and is characterized in that: the frequency and phase of the oscillation signal inside the loop are controlled by an externally input reference signal.
Specifically, the inner loop control circuit includes:
a synchronization control circuit for synchronizing the frequency of the inverter units according to a series inverter synchronization control logic, the series inverter synchronization control logic comprising:
f i ＝f * +sgn(Q i )m i P i
wherein f is i Is the frequency value of the ith inverter unit, f * For the value of the no-load time frequency of the series micro-grid, sgn represents a sign function, Q i For the output reactive power of the i-th inverter unit, m i For droop control coefficient, P i For the ith inverter unitThe output active power i is the number of the inverter units, i takes a value in a positive integer not exceeding n, and n represents the total number of the inverter units;
a frequency secondary recovery circuit for performing secondary recovery control of the frequency of the inverter unit according to a distributed secondary frequency control logic, the distributed secondary frequency control logic being as follows:
Figure BDA0003686974220000071
wherein f is i Frequency value of ith inverter unit, f * For the value of the no-load time frequency of the series micro-grid, sgn represents a sign function, Q i For the output reactive power of the ith inverter unit, m i For droop control coefficient, P i For the output active power, k, of the i-th inverter unit Ii Is the integral coefficient of the ith inverter unit, s is the Laplace operator, f ref Rated value, f, for frequency recovery of series-connected energy-storage microgrid I And i is the number of the inverter units, i is a value in a positive integer not exceeding n, and n represents the total number of the inverter units.
Specifically, the inverter unit further includes:
a load switching circuit for switching between a resistive-inductive load and a resistive-capacitive load in the common load.
The detailed control process of the cascade type microgrid frequency control circuit in the embodiment is as follows:
determining a quadratic frequency control objective function, wherein the objective function specifically comprises the following expression:
Figure BDA0003686974220000072
Figure BDA0003686974220000073
wherein f is ref Rated value, f, for frequency recovery of series-connected energy-storage microgrid i Is the frequency value, P, of the ith inverter unit i And m i Respectively the output active power and droop control coefficient, P, of the ith inverter unit j And m j The output power and the droop control coefficient of the jth inverter unit are respectively shown, t represents time, i and j are inverter unit numbers, i and j take values in positive integers not exceeding n, i is not equal to j, and n represents the total number of the inverter units.
The method comprises the steps of collecting electrical parameters of a cascade type microgrid and each inverter unit in the cascade type microgrid in real time; and determining the active power and the reactive power of each inverter unit according to the electrical parameters.
Specifically, the real-time collection of the electrical parameters of the cascaded microgrid and each inverter unit in the cascaded microgrid comprises the following steps:
acquiring the integral power factor angle, the load voltage phase angle in a steady state and the output current frequency of a system of the cascaded micro-grid in real time; and acquiring the output voltage, the output current, the output voltage phase angle and the output voltage angular frequency of each inverter unit in the cascade type microgrid in real time.
Building a synchronous control logic of the series inverters based on the active power and the reactive power of each inverter unit; synchronizing the frequency of each inverter unit according to the series inverter synchronization control logic;
the synchronous control logic expression of the series inverter is as follows:
f i ＝f * +sgn(Q i )m i P i
wherein f is i Is the frequency value of the ith inverter unit, f * For the value of the no-load time frequency of the series micro-grid, sgn represents a sign function, Q i For the output reactive power of the ith inverter unit, m i For droop control coefficient, P i The output active power i of the ith inverter unit is the number of the inverter unit, i takes a value in a positive integer not exceeding n, and n represents the total number of the inverter units.
Determining a desired output voltage phase angle model for each of the inverter units based on the electrical parameters;
for the cascaded microgrid, the DG units have the same load current, which is an essential common information. Specifically, the expected output voltage phase angle model expression is as follows:
Figure BDA0003686974220000081
wherein theta is Ii For the desired output voltage phase angle of the ith inverter unit, atan2 is an arctangent function,
Figure BDA0003686974220000082
power factor angle, P, for the entire series energy storage microgrid system * max_i For the upper limit constraint of output power of the ith inverter unit, theta i Is the output voltage phase angle, theta' of the ith inverter unit load And (3) the phase angle of the load voltage in a steady state, i is the number of the inverter units, i is a value in a positive integer not exceeding n, and n represents the total number of the inverter units.
Carrying out small-signal linearization on the expected output voltage phase angle model to obtain an output current frequency model of each inverter unit;
specifically, the obtaining an output current frequency model of each inverter unit by performing small-signal linearization on the expected output voltage phase angle model includes the following steps:
carrying out small signal linearization on the expected output voltage phase angle model expression;
setting the steady state voltage angle to be the same, dividing theta i ＝θ i0 +Δθ i Substituting the linearized expected output voltage phase angle model expression of the small signal and eliminating theta i0 And obtaining an output current frequency model of each inverter unit, wherein the expression of the output current frequency model is as follows:
Figure BDA0003686974220000091
wherein f is Ii For the frequency value of the output current of the i-th inverter unit,
Figure BDA0003686974220000092
power factor angle, P, for the entire series energy storage microgrid system * max_i For the upper limit constraint of output power of the ith inverter unit, ω i And the angular frequency of the output voltage of the ith inverter unit is shown, i is the number of the inverter unit, i is a value in a positive integer not exceeding n, and n represents the total number of the inverter units.
According to the output current frequency model expression, the frequency of the current cascaded micro-grid system represents the weighted average frequency of all units. Therefore, the inherent characteristics of the cascaded micro-grid system can be utilized, and the frequency of the whole cascaded micro-grid system can be adjusted by recovering the current frequency.
Constructing a frequency offset model of each of the inverter units according to the output current frequency model;
specifically, the frequency offset model expression is as follows:
Figure BDA0003686974220000093
wherein Δ f i Offset of frequency value, k, for the ith inverter unit Ii For coefficients of the auxiliary controller, s is the Laplace operator, f ref Rating, f, for frequency recovery of series-connected energy-storage microgrid Ii And (3) the frequency value of the output current of the ith inverter unit is represented, i is the number of the inverter unit, i is a value in a positive integer not exceeding n, and n represents the total number of the inverter units.
According to the characteristic that currents of all inverter units in the cascade type microgrid are the same, building a distributed secondary frequency control logic based on active power, reactive power and the frequency deviation model of each inverter unit;
specifically, according to the characteristic that the currents of all inverter units in the cascade microgrid are the same, the following expression is obtained,
f I1 ＝f I2 ＝…＝f In ＝f I
wherein f is I1 Is the frequency value of the 1 st inverter unit, f I2 Is the frequency value of the 2 nd inverter unit, f In Is the frequency value of the nth inverter unit, n represents the total number of inverter units, f I Is the frequency value of the output current;
building a distributed secondary frequency control logic based on the active power, the reactive power and the frequency deviation model of each inverter unit, wherein the expression of the distributed secondary frequency control logic is as follows:
Figure BDA0003686974220000101
wherein f is i Is the frequency value of the ith inverter unit, f * For the value of the no-load time frequency of the series micro-grid, sgn represents a sign function, Q i Is the output reactive power of the ith inverter unit. m is i The droop control coefficient is inversely proportional to the DG capacity. P i The output active power of the ith inverter unit. k is a radical of Ii Is the integral coefficient of the ith inverter unit, s is the Laplace operator, f ref Rating, f, for frequency recovery of series-connected energy-storage microgrid I And i is the number of the inverter units, i is a value in a positive integer not exceeding n, and n represents the total number of the inverter units. k is a radical of Ii For the secondary recovery control of the frequency.
And performing secondary recovery control on the frequency of each inverter unit according to the distributed secondary frequency control logic.
By PI control, the current frequency is restored to a normal value, and each DG frequency converges to a value equal to the current frequency. PI control is a PI regulator (proportional integral controller), which is a linear controller, also called proportional integral controller, and forms a control deviation according to a given value and an actual output value, and linearly combines the proportion and the integral of the deviation to form a control quantity to control a controlled object.
In a steady state, the current frequency is restored to a normal value by the PI control, and all inverter unit frequencies converge to a value equal to the current frequency. The nominal value f of the frequency recovery of the system frequency, in fact recovered to the frequency of the series energy storage microgrid, can then be obtained ref 。
f 1 ＝f 2 ＝…＝f i ＝…＝f n ＝f I ＝f ref
Wherein fi is the frequency value of the ith series inverter unit, i is the serial number of the series inverter unit, i takes the value in a positive integer not exceeding n, n represents the total number of the series inverter units, f I Is the frequency value of the output current.
At the same time, since all inverter units share the same current, a result is obtained
Δf 1 ＝Δf 2 ＝…＝Δf i ＝…＝Δf n
m 1 ΔP 1 ＝m 2 ΔP 2 ＝…m i ΔP i ＝…＝m n ΔP n
Where Δ fi is a frequency offset of the ith series inverter unit, i is a serial number of the series inverter unit, i is a value in a positive integer not exceeding n, n represents a total number of the series inverter units, and m is a value of a frequency offset of the ith series inverter unit i And in order to obtain the droop control coefficient, delta Pi is the power offset of the ith series inverter unit when the series microgrid is in no-load state.
The principle of frequency recovery as shown in fig. 3a and 3b, when the resistance-inductance load or the resistance-capacitance load increases, the frequency reaches the point b from the point a, and the proposed control core is to change the offset of the f-P curve, so that the operating point moves from the point b to the desired point c.
In order to verify the effect of SoC equalization more clearly, a comparative case simulation analysis is shown. A cascaded microgrid consisting of four cascaded units is established in simulation software. The overall control strategy diagram is shown in fig. 2. The analysis of A, B two cases was performed separately as follows:
in case a, the simulation results are shown in fig. 4a and 4 b. Fig. 4a and 4b show the performance of the proposed control logic under resistive-inductive and resistive-capacitive loads, respectively. The four curves of fig. 4a and 4b correspond to four cascaded units in the established cascaded microgrid, and it can be seen from the diagrams that the four curves can be restored to desired positions, and frequency recovery control without communication is realized, so that the effectiveness of the proposed frequency recovery control logic is verified, and the stability is not affected by the load impedance characteristics.
In case B, the simulation results are shown in fig. 5a and 5B, which verify the dynamic response of the proposed control logic during load characteristic changes. In fig. 5a, the cascaded microgrid system is firstly operated under a resistive-inductive load, and when t is 3s, the load is switched to a resistive-capacitive load. The four curves in fig. 5a and fig. 5b respectively correspond to the four cascading units in the established cascading type microgrid, and the four curves can be restored to an expected position, so that frequency restoration control under no communication is realized, the system is kept stable, and frequency restoration and power sharing are realized. The simulation result of the capacitive resistive load converted into the inductive resistive load is similar to the analysis result, the four curves can be restored to the expected position, the frequency recovery control under the condition of no communication is realized, the system is kept stable, and the frequency recovery and the power sharing are realized.
In the circuit of the embodiment, the frequency of the cascaded micro-grid system is restored to a rated value only depending on local information, and frequency control does not need any communication, so that the communication cost is reduced, and communication delay, packet loss and fault risks are avoided. Compared with a centralized control scheme, the method adopts communication-free distributed control, so that the reliability of the cascaded micro-grid system can be greatly enhanced.
Example two
The embodiment of the invention provides a design method of a cascade type microgrid frequency control circuit, which comprises the following steps:
step S1: arranging a plurality of inverter units, wherein each inverter unit comprises a distributed power supply, a series inverter, a resonance circuit, a data processing circuit, a power calculation circuit, an inner ring control circuit and a phase-locked loop circuit; the inner ring control circuit comprises a synchronous control circuit and a frequency secondary recovery circuit;
step S2: connecting a common load and a plurality of inverter units in series;
wherein the inverter unit is provided, including the steps of:
step S11: setting a data processing circuit, and acquiring the electrical parameters of the cascaded micro-grid and each inverter unit in the cascaded micro-grid in real time;
step S12: setting a power calculation circuit, calculating the electrical parameters, and determining the active power and the reactive power of each inverter unit;
step S13: setting the synchronous control circuit according to the synchronous control logic of the series inverter to synchronize the frequency of the inverter unit;
step S14: and according to a distributed secondary frequency control logic, the frequency secondary recovery circuit is arranged to perform secondary recovery control on the frequency of the inverter unit.
Specifically, the series inverter synchronous control logic is as follows:
f i ＝f * +sgn(Q i )m i P i
wherein f is i Is the frequency value of the ith inverter unit, f * For the value of the no-load time frequency of the series micro-grid, sgn represents a sign function, Q i For the output reactive power of the i-th inverter unit, m i For droop control coefficient, P i The output active power i of the ith inverter unit is the number of the inverter unit, i takes a value in a positive integer not exceeding n, and n represents the total number of the inverter units.
Specifically, the distributed secondary frequency control logic is as follows:
Figure BDA0003686974220000131
wherein f is i Is the frequency value of the ith inverter unit, f * For the value of the no-load time frequency of the series micro-grid, sgn represents a sign function, Q i For the output reactive power of the i-th inverter unit, m i For droop control coefficient, P i For the output active power, k, of the i-th inverter unit Ii Is the integral coefficient of the ith inverter unit, s is the Laplace operator, f ref Rating, f, for frequency recovery of series-connected energy-storage microgrid I And i is the number of the inverter units, i is a value in a positive integer not exceeding n, and n represents the total number of the inverter units.
Specifically, the inverter unit is provided, and the method further includes the steps of:
setting a phase-locked loop circuit to control the frequency and the phase of the internal loop oscillation signal of the inverter unit;
and a load switching circuit is arranged for switching the resistance-inductance load and the resistance-capacitance load in the common load.
With regard to the method in the above-described embodiment, a detailed description has been made in the embodiment related to the circuit, and a detailed description will not be made here.
In the embodiment, the frequency of the cascaded micro-grid system is restored to the rated value only by depending on local information, and the frequency control does not need any communication, so that the communication cost is reduced, and the communication delay, packet loss and fault risk are avoided. Compared with a centralized control scheme, the method adopts communication-free distributed control, and the reliability of the cascaded micro-grid system can be greatly enhanced.
Any modification, addition, or equivalent may be made within the spirit and scope of the present invention and still fall within the scope of the present invention.

Claims (7)

1. A cascaded microgrid frequency control circuit comprising a common load and a plurality of inverter units connected in series between the inverter units, the inverter units comprising a distributed power source, a series inverter and a resonant circuit, characterized in that the inverter units further comprise:
the data processing circuit is used for acquiring the integral power factor angle, the load voltage phase angle in a steady state and the output current frequency of the system of the cascaded micro-grid in real time; acquiring output voltage, output current, an output voltage phase angle and output voltage angular frequency of the inverter unit in real time;
the power calculation circuit is used for determining the active power and the reactive power of each inverter unit according to the electrical parameters;
an inner loop control circuit for synchronizing the frequency of the inverter units according to a series inverter synchronization control logic; performing secondary recovery control on the frequency of the inverter unit according to a distributed secondary frequency control logic;
and the phase-locked loop circuit is used for controlling the frequency and the phase of the loop oscillation signal in the inverter unit.
2. The circuit of claim 1, wherein the inner loop control circuit comprises:
a synchronization control circuit for synchronizing the frequency of the inverter units according to a series inverter synchronization control logic, the series inverter synchronization control logic comprising:
f i ＝f * +sgn(Q i )m i P i
wherein f is i Is the frequency value of the ith inverter unit, f * For the value of the no-load time frequency of the series micro-grid, sgn represents a sign function, Q i For the output reactive power of the i-th inverter unit, m i For droop control coefficient, P i The output active power i of the ith inverter unit is the serial number of the inverter unit, i takes the value in a positive integer not exceeding n, and n represents the total number of the inverter units;
a frequency secondary recovery circuit for performing secondary recovery control of the frequency of the inverter unit according to a distributed secondary frequency control logic, the distributed secondary frequency control logic being as follows:
Figure FDA0003686974210000011
wherein f is i Is the frequency value of the ith inverter unit, f * For the value of the no-load time frequency of the series micro-grid, sgn represents a sign function, Q i For the output reactive power of the i-th inverter unit, m i For droop control coefficient, P i For the output active power, k, of the i-th inverter unit Ii Is the integral coefficient of the ith inverter unit, s is the Laplace operator, f ref Rated value, f, for frequency recovery of series-connected energy-storage microgrid I And i is the number of the inverter units, i is a value in a positive integer not exceeding n, and n represents the total number of the inverter units.
3. The circuit according to claim 1 or 2, wherein the inverter unit further comprises:
a load switching circuit for switching between a resistive-inductive load and a resistive-capacitive load in the common load.
4. A design method of a cascade type microgrid frequency control circuit is characterized by comprising the following steps:
the method comprises the steps that a plurality of inverter units are arranged, wherein each inverter unit comprises a distributed power supply, a series inverter, a resonance circuit, a data processing circuit, a power calculation circuit, an inner ring control circuit and a phase-locked loop circuit; the inner ring control circuit comprises a synchronous control circuit and a frequency secondary recovery circuit;
connecting a common load and a plurality of inverter units in series;
wherein the inverter unit is provided, including the steps of:
setting a data processing circuit, and acquiring the electrical parameters of the cascaded micro-grid and each inverter unit in the cascaded micro-grid in real time;
setting a power calculation circuit, calculating the electrical parameters, and determining the active power and the reactive power of each inverter unit;
setting the synchronous control circuit according to the synchronous control logic of the series inverter to synchronize the frequency of the inverter units;
and according to a distributed secondary frequency control logic, the frequency secondary recovery circuit is arranged to perform secondary recovery control on the frequency of the inverter unit.
5. The design method of the cascaded microgrid frequency control circuit according to claim 4, characterized in that the synchronous control logic of the series inverters is as follows:
f i ＝f * +sgn(Q i )m i P i
wherein f is i Is the frequency value of the ith inverter unit, f * For the value of the no-load time frequency of the series micro-grid, sgn represents a sign function, Q i For the output reactive power of the i-th inverter unit, m i For droop control coefficient, P i The output active power i of the ith inverter unit is the number of the inverter unit, i takes a value in a positive integer not exceeding n, and n represents the total number of the inverter units.
6. The method for designing the cascaded microgrid frequency control circuit according to claim 4, wherein the distributed secondary frequency control logic is as follows:
Figure FDA0003686974210000031
wherein f is i Is the frequency value of the ith inverter unit, f * For the value of the no-load time frequency of the series micro-grid, sgn represents a sign function, Q i For the output reactive power of the i-th inverter unit, m i For droop control coefficient, P i For the output active power, k, of the ith inverter unit Ii Is the integral coefficient of the ith inverter unit, s is the Laplace operator, f ref Rated value, f, for frequency recovery of series-connected energy-storage microgrid I As the frequency value of the output current,i is the number of the inverter units, i takes a value in a positive integer not exceeding n, and n represents the total number of the inverter units.
7. The design method of the cascade type microgrid frequency control circuit according to any one of claims 4 to 6, characterized in that the step of arranging the inverter unit further comprises the following steps:
setting a phase-locked loop circuit, and controlling the frequency and the phase of the internal loop oscillation signal of the inverter unit;
and a load switching circuit is arranged for switching the resistance-inductance load and the resistance-capacitance load in the common load.
CN202210658978.1A 2022-06-09 2022-06-09 Cascaded microgrid frequency control circuit and design method Pending CN115102183A (en)

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