CN111490558A - Microgrid grid-connected and off-grid safety control method for improved virtual synchronous generator - Google Patents

Microgrid grid-connected and off-grid safety control method for improved virtual synchronous generator Download PDF

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CN111490558A
CN111490558A CN202010245100.6A CN202010245100A CN111490558A CN 111490558 A CN111490558 A CN 111490558A CN 202010245100 A CN202010245100 A CN 202010245100A CN 111490558 A CN111490558 A CN 111490558A
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grid
synchronous generator
virtual
virtual synchronous
microgrid
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冯皓清
刘涛
张伟
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Hangzhou Hongsheng Electric Power Design Consulting Co ltd
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Hangzhou Hongsheng Electric Power Design Consulting Co ltd
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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
    • H02J3/38—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
    • H02J3/12—Circuit arrangements for ac mains or ac distribution networks for adjusting voltage in ac networks by changing a characteristic of the network load
    • H02J3/16—Circuit arrangements for ac mains or ac distribution networks for adjusting voltage in ac networks by changing a characteristic of the network load by adjustment of reactive power
    • 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
    • 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
    • H02J3/388—Islanding, i.e. disconnection of local power supply from the network
    • 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
    • H02J3/46—Controlling of the sharing of output between the generators, converters, or transformers
    • H02J3/50—Controlling the sharing of the out-of-phase component
    • 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]
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E40/00—Technologies for an efficient electrical power generation, transmission or distribution
    • Y02E40/30—Reactive power compensation

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Control Of Eletrric Generators (AREA)

Abstract

The invention discloses a microgrid grid-connected and off-grid safety control method for an improved virtual synchronous generator, which relates to the technical field of microgrid control and is used for solving the problem that the existing microgrid control scheme is lacked, and comprises the following steps: acquiring a pre-constructed virtual synchronous generator and virtual impedance; establishing an island operation model according to the virtual synchronous generator and the virtual impedance; and carrying out microgrid grid-connection and off-grid control through the island operation model, comprising the following steps: when the micro-grid is connected with or disconnected from the grid, the virtual synchronous generator sends a control signal to control the inverter to regulate the voltage and the frequency. The invention further completes the control of grid connection and disconnection by establishing the virtual synchronous generator and the virtual impedance.

Description

Microgrid grid-connected and off-grid safety control method for improved virtual synchronous generator
Technical Field
The invention relates to the technical field of microgrid control, in particular to a microgrid grid-connected and off-grid safety control method for an improved virtual synchronous generator.
Background
Energy and environmental benefits are often used as standards in consideration of engineering value, and it is becoming more and more important to find excellent renewable clean energy to meet the increasing demand for electricity.
Distributed generation (hereinafter referred to as DG) has the advantages of flexible position, no pollution, quick construction and the like, so that the distributed generation system can be well suitable for the imbalance of supply and demand caused by short-time peak load of a large power grid. However, DG also has its drawbacks; when the system side is in fault, the DG has to quit the operation in order to avoid the possible maintenance accident caused by continuous power supply; in addition, the DG side cannot control the quality of the power, thus causing scheduling difficulties.
In order to better utilize the advantages of the DGs, a novel realization form, namely a micro-grid is provided, namely a small-sized grid formed by combining modules such as the DGs, loads, energy storage devices and control devices under the definition mode of a transmission network and a distribution network. The micro-grid is equivalent to a small-sized network independent in a large power grid, the problem that a distributed power supply cannot be dispatched can be solved, the micro-grid can be operated as an independent unit isolated island and also can be interconnected with the large power grid, the controllability and the reliability are greatly improved, and resources can be better integrated.
Therefore, how to ensure reliable switching, fast transition process, good system economy and realize maximum efficiency utilization is the main direction of research.
Disclosure of Invention
In order to overcome the defects of the prior art, the invention aims to provide a microgrid grid-connected and off-grid safety control method, which realizes the safety control of grid-connected and off-grid by establishing a virtual synchronous generator and a virtual impedance.
The invention is realized by adopting the following technical scheme:
a microgrid grid-on and off-grid safety control method for an improved virtual synchronous generator comprises the following steps:
acquiring a pre-constructed virtual synchronous generator and virtual impedance; establishing an island operation model according to the virtual synchronous generator and the virtual impedance;
and carrying out microgrid grid-connection and off-grid control through the island operation model, comprising the following steps:
when the micro-grid is connected with or disconnected from the grid, the virtual synchronous generator sends a control signal to control the inverter to regulate the voltage and the frequency.
Further, the virtual synchronous generator comprises a main circuit part and a control part, wherein the main circuit part comprises a direct current voltage source, a grid-connected inverter, an L RC filter and a load, and the control part comprises a virtual synchronous generator body model, a virtual rotating speed regulator and a virtual excitation regulator.
Further, the active frequency control is adjusted by the virtual speed regulator, and the reactive voltage control is adjusted by the virtual excitation regulator.
Further, the mechanical equation of the virtual synchronous generator is as follows:
Figure BDA0002433794570000021
wherein J is the rotational inertia of the virtual synchronous generator; d is a rotor damping coefficient; omega, omega0Respectively an actual angular velocity and a rated angular velocity of the virtual synchronous generator; t ism、TeMechanical power and electromagnetic power of the virtual synchronous generator, respectively.
Further, the calculation formula of the difference between the actual angular speed and the rated angular speed of the virtual synchronous generator satisfies:
Figure BDA0002433794570000022
for the power angle of the virtual synchronous generator,
further, the calculation formula of the actual angular velocity ω of the virtual synchronous generator satisfies:
Figure BDA0002433794570000031
wherein, KpIs the coefficient of the virtual speed regulator, PeElectromagnetic power, omega, output for said virtual synchronous generator*Is the actual angular velocity per unit value, P, of the virtual synchronous generator0Being said virtual synchronous generatorNo load loss.
Further, when the excitation regulator regulates a reactive voltage, the voltage difference Δ U of the reactive voltage satisfies a formula:
Figure BDA0002433794570000032
wherein Q is0Is a reactive instruction of the inverter, Q is a reactive power value of the inverter, kqIs the coefficient of the excitation regulator.
Further, the virtual synchronous generator performs synchronous reactance of the inverter through the L RC filter and the virtual impedance, and the calculation formula of the virtual impedance is as follows:
Figure BDA0002433794570000033
wherein Z isvAs the virtual impedance, LvIs a virtual reactance, ωcFor angular frequencies, I and I, measured at a common junctionNThe actual current and the rated current of the branch circuit are respectively.
Further, the method for controlling the grid connection and disconnection of the microgrid through the island operation model further comprises the following steps:
judging a mode needing to be converted currently;
when grid connection is required to be switched to off-grid connection, mode switching is directly carried out;
when the off-grid conversion to the grid connection is required, the amplitude, the frequency and the phase of the micro-grid are controlled through the pre-synchronous controller.
Further, the presynchronization controller completes control of the amplitude, the frequency and the phase of the microgrid by adjusting q-axis components under the dq coordinate system to zero.
Compared with the prior art, the invention has the beneficial effects that:
the invention completes the reactive voltage control of active frequency control by establishing the virtual synchronous generator, thereby achieving the voltage and frequency regulation characteristics similar to those of the synchronous generator, being capable of adapting to the changes brought by large power grid switching or load increase and decrease, and the like, effectively simulating the reactance characteristics of the synchronous generator by introducing virtual impedance, and realizing the seamless conversion between isolated island and grid connection.
Drawings
Fig. 1 is a flowchart of a microgrid on-grid and off-grid safety control method for improving a virtual synchronous generator according to a first embodiment;
fig. 2 is a flowchart of microgrid grid-on and off-grid control of the second embodiment.
Detailed Description
The present invention will now be described in more detail with reference to the accompanying drawings, in which the description of the invention is given by way of illustration and not of limitation. The various embodiments may be combined with each other to form other embodiments not shown in the following description.
Example one
The embodiment I provides a microgrid grid-connected and off-grid safety control method for an improved virtual synchronous generator, and aims to simulate the synchronous generator in a mode of combining the virtual synchronous generator with virtual impedance so as to realize seamless switching between an island and grid connection.
At present, some grid-connected and grid-disconnected control methods based on a master-slave mode exist, in the mode, although constant power output can be ensured during grid connection and voltage and frequency can be maintained to be stable through a large power grid, when an island runs, a main power supply is automatically switched into a virtual F control mode to ensure the stability of system voltage and frequency. However, the method still has the problems of distortion of impact current and voltage which cannot be effectively solved, and the switching control mode is complex, so that misoperation is easily caused, and the plug and play requirement is difficult to meet.
At present, there is also a grid-connected and off-grid control method based on a peer-to-peer control mode, in which if one control strategy is operated, the other control strategy must be operated at the same time, so that the control strategies can be switched in time when grid-connected and off-grid operations occur, but the state quantities of the two strategies are often unequal, so that a large transient oscillation is generated in the process of switching the controller; therefore, the prior art starts to use a state follower which reduces the oscillation during the switching process by inputting the difference between the grid controller and the island controller into the island controller and introducing a closed loop feedback. However, the two sets of processors need to run simultaneously, so that a large amount of processor resources are occupied, and the switching process is slow.
In summary, there is a certain disadvantage in both the master-slave mode and the peer-to-peer control mode; therefore, the present embodiment implements grid-on and off-grid control by a virtual synchronous generator.
Referring to fig. 1, a method for improving microgrid grid-on and off-grid safety control of a virtual synchronous generator includes the following steps:
s110, acquiring a virtual synchronous generator and virtual impedance which are constructed in advance;
the method for constructing the virtual synchronous generator in S110 is a common prior art, and this embodiment is not described in detail, and the virtual synchronous generator is used to control an inverter, including an inverter in which power supplies such as a photovoltaic system, a wind turbine system, and a gas turbine system are connected to a power grid. Compared with the traditional safety control technology of the power grid, the fluctuation of the power grid is controlled by an active frequency modulator and an excitation regulator of the synchronous generator, and the virtual synchronous generator can improve the performance of island/grid connection switching by simulating the characteristics of the generator in the control of the inverter.
In the transition process of grid connection and grid disconnection, due to the introduction of the virtual synchronous generator, the inverter does not need to switch a control strategy, the virtual synchronous generator can be used for automatically adjusting the frequency and the voltage, the adjustment capability similar to that of the traditional large power grid is realized, and the problems of transient oscillation in the switching process and occupation of a large amount of processor resources are solved.
The virtual synchronous generator comprises a main circuit part and a control part, wherein the main circuit part comprises a direct current voltage source, a grid-connected inverter, an L RC filter and a load, the direct current voltage source takes an energy storage system as a power source in the embodiment, the direct current voltage source is equivalent to a prime motor in the synchronous generator, the voltage generated by the inverter is equivalent to the internal potential of the synchronous generator, and the capacitance voltage can be equivalent to the external voltage of the generator according to the circuit relation, so that an external voltage characteristic equation is established.
And equivalently replacing modules in the control flow, and introducing the modules into the control of the inverter to obtain a control part of the virtual synchronous generator, wherein the control part comprises a virtual synchronous generator body model, a virtual rotating speed regulator and a virtual excitation regulator.
In the transition process of grid connection and grid disconnection, the control strategy of the virtual synchronous generator is used, so that the inverter does not need to switch a control mode, the virtual synchronous generator can be used for automatically adjusting the frequency and the voltage, the adjustment capability similar to that of the traditional large power grid is realized, and the problems of transient oscillation in the switching process and occupation of a large amount of processor resources are solved.
In this embodiment, the active frequency control and the reactive voltage control are realized by a control part of the virtual synchronous generator, specifically, the active frequency control is adjusted by a virtual rotation speed adjuster, and the reactive voltage control is adjusted by a virtual excitation adjuster.
Notably, to reduce the complexity of subsequent microgrid analysis, virtual synchronous generators typically do not employ a high-order generator model.
Since the virtual synchronous generator has no mechanical device and no iron core, the input power P can be consideredmAll converted into electromagnetic power PeThe mechanical equation of the virtual synchronous generator can be obtained according to newton's second law:
Figure BDA0002433794570000061
wherein J is the rotational inertia of the virtual synchronous generator; d is a rotor damping coefficient; omega, omega0Respectively an actual angular velocity and a rated angular velocity of the virtual synchronous generator; t ism、TeMechanical power and electromagnetic power, omega-omega, respectively, of the virtual synchronous generator0The calculation formula of (2) is as follows:
Figure BDA0002433794570000062
for the power angle of the virtual synchronous generator, the calculation formula of the actual angular velocity ω of the virtual synchronous generator satisfies:
Figure BDA0002433794570000063
wherein, KpIs the coefficient of the virtual speed regulator, PeElectromagnetic power, omega, output for said virtual synchronous generator*Is the actual angular velocity per unit value, P, of the virtual synchronous generator0For the no-load loss of the virtual synchronous generator, when the number of pole pairs of a rotor in the virtual synchronous generator is 1, the actual angular velocity ω of the virtual synchronous generator is the electrical angular velocity.
During the operation of an actual synchronous generator, a part of the kinetic energy is stored in the rotor and is reflected in the form of the moment of inertia. The moment of inertia J buffers the transient process, slows down the energy loss of the system, delays the dynamic response of the system, can inhibit the rapid fluctuation of the frequency and can reduce the oscillation generated by parallel connection of the units.
When the load changes, TmAnd TeThere is a torque difference between them, especially in case the micro grid has a much smaller capacity than the large grid, a small disturbance may cause a large frequency deviation. If the value of J is large, it will decrease
Figure BDA0002433794570000071
I.e. the rate of change of omega decreases. In other words, the moment of inertia J mainly affects the transient process of the frequency change.
When the system is brought into a steady state,
Figure BDA0002433794570000072
is 0, and thus Δ T ═ ω Δ D, it can be seen that the damping coefficient D is a factor that mainly affects the amount of frequency change. The damping coefficient D can be adjusted to be larger, so that the frequency variation can be reduced, and the stable frequency can be kept in the allowable standard range.
When the load changes, the mechanical torque and the load torque have a difference, and the rotation speed changes. And amplifying and integrating the variable quantity delta omega of the angular frequency to obtain a control signal, and adjusting the opening degree of a steam valve or a water valve to realize negative feedback.
The control of the virtual synchronous generator on the frequency is different from that of the synchronous generator, and mechanical devices such as a speed regulator and the like are not arranged, so that the transition time from a control signal to the response of the mechanical devices does not exist, and the frequency is completely and automatically adjusted by the control of the inverter through an electric signal.
When the excitation regulator regulates to regulate the reactive voltage, the voltage difference delta U of the reactive voltage meets the formula:
Figure BDA0002433794570000073
wherein Q is0Is a reactive instruction of the inverter, Q is a reactive power value of the inverter, kqIs the coefficient of the excitation regulator.
The excitation regulator is used for regulating the reactive power at the generator end of the virtual synchronous generator so as to maintain the voltage stability.
The final purpose of introducing the virtual synchronous generator is to enable the inverter side to be equivalent to a port capable of adjusting frequency and voltage, so that inertia and damping are introduced, a relational equation of output end voltage and output current is similar to that of the synchronous generator, and the external characteristic can be considered to be fitted to the synchronous generator. Therefore, the virtual synchronous generator needs to have the property of synchronous reactance of the synchronous generator in output impedance.
The output side of the inverter in the microgrid is an L RC filter, but the inductance of the L RC filter is not enough to simulate the synchronous reactance, so the embodiment leads the inverter to show the characteristic of the synchronous reactance by introducing virtual impedance in the control of the inverter.
At present, two control algorithms of a direct virtual impedance method and an indirect virtual impedance method are used as algorithms of virtual impedance. The direct virtual impedance method is to multiply the output current of the inverter by virtual impedance after filtering. And subtracting the voltage drop on the virtual impedance from the open-circuit voltage output by the virtual synchronous generator body model to obtain the reference voltage. The indirect virtual impedance method is that on the basis of the direct virtual impedance method, the stator current is used as the output current reference, and the obtained reference voltage is sent to PWM modulation. The embodiment adopts a direct virtual impedance method to realize the synchronization of the virtual impedance and the virtual synchronous generator.
The specific calculation formula is as follows:
Figure BDA0002433794570000081
wherein Z isvAs the virtual impedance, LvIs a virtual reactance, ωcFor angular frequencies, I and I, measured at a common junctionNThe actual current and the rated current of the branch circuit are respectively.
S120, establishing an island operation model according to the virtual synchronous generator and the virtual impedance;
and carrying out microgrid grid-connection and off-grid control through the island operation model, comprising the following steps:
when the micro-grid is connected with or disconnected from the grid, the virtual synchronous generator sends a control signal to control the inverter to regulate the voltage and the frequency.
Example two
The second embodiment is performed on the basis of the first embodiment, and mainly explains and explains the grid-connected and off-grid strategy.
Referring to fig. 2, the method for controlling the microgrid during grid-on and grid-off through the islanding operation model includes the following steps:
s210, judging a mode needing to be converted currently;
s220, directly switching modes when grid connection is required to be switched to off-grid connection;
under the virtual synchronous generator control strategy model, when the PCC is suddenly disconnected, the virtual synchronous generator still keeps the grid-connected state before switching, the amplitude, the phase and the frequency of the voltage on the grid side are basically the same, and large transient impact current cannot be caused, so that in S220, mode switching can be directly carried out, and switching from grid-connected mode to island mode is realized.
And S230, when the off-grid to on-grid conversion is required, controlling the amplitude, the frequency and the phase of the microgrid through a pre-synchronization controller.
It should be noted that the process of S230 may be implemented by a simulation tool, such as simulink.
When the microgrid is operated in an island mode, the stability of voltage and frequency needs to be ensured. However, when the micro-grid is regulated once, the voltage and frequency are deviated from the grid voltage by the regulation action, and the deviation becomes a huge deviation of the phase under the accumulation action of time. At the moment, if the grid fault is repaired, a grid connection instruction is sent, and the micro-grid cannot be directly connected.
Usually the voltage of islanded operation does not differ much from the grid voltage magnitude, so both can be considered equal. Taking a phase analysis, uaFor terminal voltage, u, of a virtual synchronous generator in off-grid mode of operationgaFor the network voltage, the voltage expressions of the two are as follows:
Figure BDA0002433794570000091
the difference between the two formulas is:
Figure BDA0002433794570000092
it can be seen that the instantaneous value of the voltage across the switch in the case of non-synchronization has a magnitude of 2UmAnd the switch resistance is very small, which easily causes a large impact.
And performing park transformation by taking the power grid voltage as a reference, and transforming the three-phase abc voltage of the power grid into a voltage phasor under a dp rotation coordinate system.
Therefore, in order to prevent the problem that phase difference is large due to the fact that the amplitude of the microgrid is too large when the microgrid is converted into the grid-connected state from the island, the mode conversion of the microgrid into the grid-connected state is completed through the pre-synchronization controller, the pre-synchronization controller completes control over the amplitude, the frequency and the phase of the microgrid by adjusting the q-axis component under the dq coordinate system to be zero, specifically, grid voltage amplitude, frequency and phase information are obtained through a three-phase-locked loop P LL in a simulation tool, the reference angular frequency and the reference voltage are set to be the grid angular frequency and the grid voltage amplitude, and after the pre-synchronization controller is started, the q-axis component is adjusted to be close to zero.
Various other modifications and changes may be made by those skilled in the art based on the above-described technical solutions and concepts, and all such modifications and changes should fall within the scope of the claims of the present invention.

Claims (10)

1. A microgrid grid-connected and off-grid safety control method for an improved virtual synchronous generator is characterized by comprising the following steps:
acquiring a pre-constructed virtual synchronous generator and virtual impedance; establishing an island operation model according to the virtual synchronous generator and the virtual impedance;
and carrying out microgrid grid-connection and off-grid control through the island operation model, comprising the following steps:
when the micro-grid is connected with or disconnected from the grid, the virtual synchronous generator sends a control signal to control the inverter to regulate the voltage and the frequency.
2. The method for improving the microgrid grid-on and grid-off safety control of the virtual synchronous generator as claimed in claim 1, wherein the virtual synchronous generator comprises a main circuit part and a control part, the main circuit part comprises a direct current voltage source, a grid-connected inverter, an L RC filter and a load, and the control part comprises a virtual synchronous generator body model, a virtual rotating speed regulator and a virtual excitation regulator.
3. The method for improving microgrid grid-on and grid-off safety control of a virtual synchronous generator as claimed in claim 2, wherein an active frequency is controlled by said virtual speed regulator, and a reactive voltage is controlled by said virtual excitation regulator.
4. The method for improving the microgrid grid-on and off-grid safety control of the virtual synchronous generator as claimed in claim 3, wherein the mechanical equation of the virtual synchronous generator is as follows:
Figure FDA0002433794560000011
wherein J is the rotational inertia of the virtual synchronous generator; d is a rotor damping coefficient; omega, omega0Respectively an actual angular velocity and a rated angular velocity of the virtual synchronous generator; t ism、TeMechanical power and electromagnetic power of the virtual synchronous generator, respectively.
5. The method for improving the microgrid grid-on and off-grid safety control of the virtual synchronous generator as claimed in claim 4, wherein the calculation formula of the difference between the actual angular speed and the rated angular speed of the virtual synchronous generator satisfies the following requirements:
Figure FDA0002433794560000021
is the power angle of the virtual synchronous generator.
6. The method for improving the microgrid grid-on and off-grid safety control of the virtual synchronous generator as claimed in claim 4, wherein the actual angular speed ω calculation formula of the virtual synchronous generator satisfies:
Figure FDA0002433794560000022
wherein, KpIs the coefficient of the virtual speed regulator, PeElectromagnetic power, omega, output for said virtual synchronous generator*Is the actual angular velocity per unit value, P, of the virtual synchronous generator0Is the no-load loss of the virtual synchronous generator.
7. The method for improving the on-grid and off-grid safety control of the microgrid of a virtual synchronous generator as claimed in claim 3, wherein when the excitation regulator regulates reactive voltage regulation, the voltage difference Δ U of the reactive voltage satisfies the formula:
Figure FDA0002433794560000023
wherein the content of the first and second substances,Q0is a reactive instruction of the inverter, Q is a reactive power value of the inverter, kqIs the coefficient of the excitation regulator.
8. The method for improving the microgrid grid-on and off-grid safety control of a virtual synchronous generator as claimed in claim 3, wherein the virtual synchronous generator performs synchronous reactance of the inverter through the L RC filter and the virtual impedance, and the calculation formula of the virtual impedance is as follows:
Figure FDA0002433794560000024
wherein Z isvAs the virtual impedance, LvIs a virtual reactance, ωcFor angular frequencies, I and I, measured at a common junctionNThe actual current and the rated current of the branch circuit are respectively.
9. The method for improving the microgrid grid-connected and off-grid safety control of the virtual synchronous generator as claimed in claim 1, wherein the microgrid grid-connected and off-grid control is performed through the island operation model, further comprising the following steps:
judging a mode needing to be converted currently;
when grid connection is required to be switched to off-grid connection, mode switching is directly carried out;
when the off-grid conversion to the grid connection is required, the amplitude, the frequency and the phase of the micro-grid are controlled through the pre-synchronous controller.
10. The method for improving the microgrid on-grid and off-grid safety control of the virtual synchronous generator as claimed in claim 9, wherein the pre-synchronization controller completes the control of the amplitude, the frequency and the phase of the microgrid by adjusting q-axis components in a dq coordinate system to zero.
CN202010245100.6A 2020-03-31 2020-03-31 Microgrid grid-connected and off-grid safety control method for improved virtual synchronous generator Withdrawn CN111490558A (en)

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