CN115276092A - Microgrid self-adaptive dual-mode operation control strategy based on virtual synchronous generator - Google Patents

Microgrid self-adaptive dual-mode operation control strategy based on virtual synchronous generator Download PDF

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CN115276092A
CN115276092A CN202210962843.4A CN202210962843A CN115276092A CN 115276092 A CN115276092 A CN 115276092A CN 202210962843 A CN202210962843 A CN 202210962843A CN 115276092 A CN115276092 A CN 115276092A
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voltage
power
synchronous generator
virtual synchronous
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屈艾文
赵文波
周扬忠
朱泓晖
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Fuzhou 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
    • H02J3/38—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
    • H02J3/28—Arrangements for balancing of the load in a network by storage of energy
    • H02J3/32—Arrangements for balancing of the load in a network by storage of energy using batteries with converting means
    • 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
    • H02J3/40—Synchronising a generator for connection to a network or to another generator
    • 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
    • H02J7/00—Circuit arrangements for charging or depolarising batteries or for supplying loads from batteries
    • H02J7/34—Parallel operation in networks using both storage and other dc sources, e.g. providing buffering
    • H02J7/35—Parallel operation in networks using both storage and other dc sources, e.g. providing buffering with light sensitive cells
    • 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
    • H02J2300/00—Systems for supplying or distributing electric power characterised by decentralized, dispersed, or local generation
    • H02J2300/20—The dispersed energy generation being of renewable origin
    • H02J2300/22—The renewable source being solar energy
    • H02J2300/24—The renewable source being solar energy of photovoltaic origin
    • H02J2300/26—The renewable source being solar energy of photovoltaic origin involving maximum power point tracking control for photovoltaic sources
    • 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
    • Y02E10/00—Energy generation through renewable energy sources
    • Y02E10/50—Photovoltaic [PV] energy
    • Y02E10/56—Power conversion systems, e.g. maximum power point trackers

Abstract

The invention provides a microgrid self-adaptive dual-mode operation control strategy based on a virtual synchronous generator, which comprises an island operation voltage control type virtual synchronous generator control strategy, a grid-connected operation self-adaptive droop damping coefficient and a current control type virtual synchronous generator control strategy of a reactive droop coefficient and smooth switching between island/grid-connected modes; the island/grid-connected dual-mode operation control strategy adopts the same electromagnetic equation, a voltage and current dual-loop control module, a filter capacitor current feedback active damping control module and a pulse width modulation module, and realizes seamless switching between modes by adopting a power reference slow start control method in the grid-connected/island switching process and a presynchronization control method in the island/grid-connected switching process; the invention can maintain the voltage stability of the power grid, solve the problem of power overload of the inverter caused by larger rated value difference between the voltage of the power grid and the output voltage of the virtual synchronous generator, and ensure the reliability and stability of the power grid and the reliable operation of the inverter.

Description

Microgrid self-adaptive dual-mode operation control strategy based on virtual synchronous generator
Technical Field
The invention relates to the technical field of new energy power generation, in particular to a microgrid self-adaptive dual-mode operation control strategy based on a virtual synchronous generator.
Background
With the aggravation of the problems of environmental pollution and energy shortage, distributed energy is rapidly developed, a large amount of photovoltaic power generation and wind power generation are connected into a low-voltage distribution network, the permeability of a power grid is continuously improved, and an electric power system is lack of inertia and damping. In view of stable operation of the power grid, the distributed power supply needs to have good autonomous capability and plug-and-play characteristics. When the grid is connected, the distributed power supply has the characteristics of maintaining the voltage stability of the power grid and guaranteeing the reliability and stability of the power grid. When off-grid, the distributed power supply should be able to operate independently to provide power to local loads. The microgrid in which the distributed power supply is located runs in an island and grid-connected dual-mode state, and seamless switching between the two modes needs to be considered.
In order to improve the characteristics of the distributed power supply in the power system, a Virtual Synchronous Generator (VSG) control strategy is adopted, so that the grid-connected inverter has the external characteristics of a Synchronous Generator, inertia and damping are provided for a power grid, and the stability of the voltage of the power grid is improved. The current virtual synchronous generator dual-mode operation control adopts a voltage control type virtual synchronous generator technology. In order to solve the problem of active power and reactive power overload caused by large difference between rated values of grid voltage and output voltage of a virtual synchronous generator during grid-connected operation, the voltage control type virtual synchronous generator is adopted for controlling and converting to constant power control, and stable output of grid-connected power of an inverter is realized.
Although effective seamless switching can be realized by adopting a dual-mode operation control strategy of the voltage control type virtual synchronous generator, when grid-connected operation is switched from the control of the voltage control type virtual synchronous generator to the control of constant power, the constant power control cannot provide inertia and damping for a power grid. The island/grid-connected operation is controlled by a voltage control type virtual synchronous generator, an inverter is equivalent to a voltage source, and the parallel operation requirement of the plug-and-play characteristic of a distributed power supply can not be well met during grid connection.
Disclosure of Invention
The invention provides a virtual synchronous generator-based microgrid self-adaptive dual-mode operation control strategy, which is applied to a low-voltage distribution network power system with a large number of distributed power supplies connected, and can maintain the voltage stability of a power grid, guarantee the reliability and stability of the power grid and the reliable operation of an inverter.
The invention adopts the following technical scheme:
a microgrid self-adaptive dual-mode operation control strategy based on a virtual synchronous generator is applied to a low-voltage distribution network power system with a large number of connected distributed power supplies, and the control strategy comprises an island operation voltage control type virtual synchronous generator control strategy, a grid-connected operation self-adaptive current control type virtual synchronous generator control strategy and smooth switching between island/grid-connected modes; when the distributed power supply is connected to the power grid, the island/grid-connected dual-mode operation control strategy adopts the same electromagnetic equation, a voltage and current double-loop control module, a filter capacitor current feedback active damping control module and a pulse width modulation module; virtual inductors are introduced into an electromagnetic equation to optimize the impedance-inductance ratio of the microgrid circuit to realize power decoupling, so that a low-voltage distribution network with the resistive power grid impedance can meet the control requirements of active-frequency and reactive-voltage virtual synchronous generators.
The micro-grid system comprises a photovoltaic power generation unit, an energy storage unit, a local load and a low-voltage alternating-current power grid; the photovoltaic power generation unit and the energy storage unit are connected with a system consisting of a photovoltaic array and an energy storage battery through a three-port quasi-Z-source inverter; the photovoltaic array is connected with the input end of the quasi-Z source inverter and outputs the maximum photovoltaic power under the control of the photovoltaic power control module; the energy storage battery is connected in parallel to an energy storage capacitor of the quasi-Z source inverter impedance network to balance the difference between the output power of the inverter and the output power of the photovoltaic inverter; the quasi-Z source inverter consists of an input filter capacitor, an impedance network, a three-phase inverter bridge and a three-phase LCL filter; the impedance network consists of a diode, an energy storage capacitor and an energy storage inductor.
The island operation voltage control type virtual synchronous generator control strategy adopts the following method:
step S1, based on the voltage at two ends of the local load of the output end of the inverter, namely the voltage sampling signal u at the output end of the virtual synchronous generator oa 、u ob 、u oc And inverter side filter inductor current sampling signal i a 、i b 、i c Obtaining the alpha-beta axis component u by abc/alpha-beta coordinate transformation oα 、u oβ And i α 、i β And then obtaining a dq axis component u through alpha beta/dq coordinate transformation od 、u oq And i d 、i q And by the power calculation formula P out ＝1.5(u od i d +u oq i q )、Q out ＝1.5(u od i q -u oq i d ) Obtaining the output active power P of the inverter out And reactive power Q out ；
S2, outputting active power P by the inverter obtained in the S1 out And reactive power Q out Obtaining an output power angle theta and an output voltage amplitude E of the virtual synchronous generator through a voltage control type virtual synchronous generator control model m And by the formula
Figure BDA0003793532990000031
Obtaining the output three-phase reference voltage E of the virtual synchronous generator a 、E b 、E c And obtaining a dq axis component E of the output reference voltage of the virtual synchronous generator through abc/dq coordinate transformation d 、E q ；
Wherein the voltage control type virtual synchronous generator control model is
Figure BDA0003793532990000032
In the formula, P ref A reference active power set for the virtual synchronous generator control; p out Outputting active power for the inverter; j is the rotational inertia of the virtual synchronous generator; d ω And K Q Respectively representing droop damping coefficients and reactive droop coefficients of the stable operation of the virtual synchronous generator; omega 0 And ω is the nominal angular velocity and the output angular velocity of the virtual synchronous generator, respectively; e 0 The rated voltage value is a virtual synchronous generator rated voltage value; e m Outputting a voltage amplitude for the virtual synchronous generator; q ref Controlling the set reference reactive power for the virtual synchronous generator; q out Outputting reactive power for the inverter;
step S3, utilizing the dq axis component E of the output reference voltage of the virtual synchronous generator obtained in the step S2 d 、E q Obtaining voltage reference dq axis component u of output end of virtual synchronous generator of voltage and current double-loop control module through electromagnetic equation od * And u oq * Wherein the electromagnetic equation is
Figure BDA0003793532990000033
In the formula, L s Is a virtual inductor;
step S4, utilizing the voltage and current double-loop control module obtained in the step S3 to obtain the voltage reference dq axis component u of the output end of the virtual synchronous generator od * And u oq * D is compared with the output end voltage dq axis component u of the virtual synchronous generator od And u oq Subtraction-pass voltage outer loop Proportional Integral (PI) regulator G u (s) obtaining an inverter output current reference signal i d *、i q * Obtaining the alpha-beta axis component i of the inverter output current reference signal through dq/alpha-beta coordinate transformation α *、i β * Then with the inverter-side filter inductor current alpha beta axis component i α 、i β By subtraction via current inner loop proportional resonance(PR) regulator G i (s) obtaining an output signal u Lα * And u Lβ *；
Wherein, the voltage outer loop PI regulator G u The transfer function of(s) is:
Figure BDA0003793532990000041
in the formula, k pu Is a voltage regulator G u Proportionality coefficient of(s), k iu Is a voltage regulator G u (s) an integral coefficient;
wherein the current inner ring PR regulator G i The transfer function of(s) is:
Figure BDA0003793532990000042
in the formula, k pi For the current regulator G i Proportionality coefficient of(s), ω c As a current regulator G i Bandwidth of(s), ω 1 Is the angular frequency of the fundamental wave, k r For the current regulator G i (s) a resonance coefficient, h being the harmonic number corresponding to the resonance characteristic frequency;
step S5, filtering the capacitor current sampling signal i cfa 、i cfb 、i cfc Obtaining the alpha-beta axis component i thereof by abc/alpha-beta coordinate transformation cfα 、i cfβ And is connected with the output end voltage alpha beta axis component u of the virtual synchronous generator oα 、u oβ And the current inner loop output signal u obtained in the step S4 Lα * And u Lβ * The inverter bridge output voltage modulation signal u is obtained by a filter capacitor current feedback active damping control module α *、u β * The control equation of the filter capacitor current feedback active damping control module is as follows;
Figure BDA0003793532990000043
s6, utilizing the inverter bridge output voltage modulation signal obtained in the S5u α *、u β * Direct duty ratio signal D output by photovoltaic power control module 0 And the voltage sampling signal u of the energy storage capacitor c1 Inputting the signals into a pulse width modulation module, and modulating to obtain 6 switching tubes S for controlling a three-phase inverter bridge 1 ～S 6 The drive signal of (a); the voltage control type virtual synchronous generator control strategy controls the output voltage of the virtual synchronous generator according to the active power and the reactive power output by the inverter, and provides power for a local load.
The photovoltaic power control module comprises a photovoltaic Maximum Power Point Tracking (MPPT) algorithm unit and a photovoltaic voltage regulator; sampled photovoltaic voltage U PV And photovoltaic current i PV Sending the photovoltaic power into an MPPT algorithm unit to obtain a photovoltaic maximum power point voltage U PV *，U PV * To photovoltaic voltage U PV Generating a pass-through duty cycle D by a photovoltaic voltage PI regulator 0 To achieve photovoltaic power output control; transfer function G of photovoltaic voltage regulator PV (s) is
Figure BDA0003793532990000044
In the formula k p For photovoltaic voltage regulators G PV Proportionality coefficient of(s), k i For photovoltaic voltage regulators G PV (s) coefficient of integration.
The control strategy of the grid-connected operation self-adaptive current control type virtual synchronous generator adopts the following modes:
a1, based on a PCC voltage sampling signal u of a public connection point of a power grid pcca 、u pccb 、u pccc Obtaining the angular frequency omega of the power grid through a double generalized second-order integral phase-locked loop (DSOGI-PLL) g And the filtered PCC point voltage alpha beta axis component u pccα 、u pccβ Or dq axis component u pccd 、u pccq According to the formula
Figure BDA0003793532990000051
Or formula
Figure BDA0003793532990000052
To obtain PCC voltage amplitude E pcc I.e. the amplitude of the voltage at the output of the virtual synchronous generator, omega g And E pcc Sending the power reference P into a self-adaptive current control type virtual synchronous generator control model, and estimating the output active power reference P of the inverter according to the current control type virtual synchronous generator control model out * And reactive power reference Q out * Is derived from adaptively adjusting the droop damping coefficient D in the current control model virtual synchronous generator control model ω And reactive sag factor K Q And substituting the obtained new droop damping coefficient and the obtained reactive droop coefficient into the current control type virtual synchronous generator control model again to obtain the final inverter output active power reference P out * And reactive power reference Q out *；
Wherein the current control type virtual synchronous generator control model is
Figure BDA0003793532990000053
In the formula, P ref 、Q ref Respectively controlling set reference active power and reference reactive power for the virtual synchronous generator; p out * And Q out * Respectively outputting an active power reference and a reactive power reference for the inverter; omega g The angular frequency of the power grid is also the actual angular speed of the virtual synchronous generator; theta.theta. g The phase is a PCC voltage phase and is also a virtual synchronous generator output power angle; omega 0 Rated angular velocity for the virtual synchronous generator; d ω And K Q Respectively serving as a virtual synchronous generator self-adaptive droop damping coefficient and a self-adaptive reactive droop coefficient during grid-connected operation; e 0 For a given PCC voltage amplitude reference, also the virtual synchronous generator rated voltage value; e pcc The amplitude of the PCC voltage is also the amplitude of the voltage at the output end of the virtual synchronous generator;
the calculation method of the self-adaptive droop damping coefficient and the reactive droop coefficient comprises the following steps: in order to prevent the droop damping coefficient and the reactive droop coefficient from changing too frequently at the critical point, the values of the droop damping coefficient and the reactive droop coefficient are determined by adopting a hysteresis comparison method;
droop damping coefficient D ω Is calculated by
Figure BDA0003793532990000061
In the formula, P max And P min Respectively for setting the maximum and minimum values, P, of the active power output by the inverter ref Reference active power, P, set for virtual synchronous generator control out * Outputting an active power reference for the inverter, wherein delta P is an active power hysteresis comparison interval, omega g_min And omega g_max For setting the minimum and maximum values, ω, of the grid angular frequency 0 Rated angular speed for the virtual synchronous generator, D ω0 Droop damping coefficient for stable operation;
reactive sag coefficient K Q Is calculated by
Figure BDA0003793532990000062
In the formula, Q max And Q min For setting maximum and minimum values, Q, of the output reactive power of the inverter, respectively ref Reference reactive power, Q, set for virtual synchronous generator control out * For the inverter to output a reactive power reference, Δ Q is the reactive power hysteresis comparison interval, E m_max And E m_min To set the maximum and minimum values, ω, of the PCC voltage amplitude 0 For a virtual synchronous generator rated angular speed, K Q0 The reactive droop coefficient is stable in operation;
step A2, the inverter output active power reference P obtained in the step A1 out * And reactive power reference Q out * Sending into an additional power loop and respectively outputting active power P with the inverter out And reactive power Q out PI regulator G with subtraction and additional power loop P (s) obtaining the dq axis component E of the output reference voltage of the virtual synchronous generator d 、E q ；
Power loop PI regulator G P (s) a transfer function of
Figure BDA0003793532990000071
In the formula, k pp As a power loop PI regulator G P Proportionality coefficient of(s), k ip As a power loop PI regulator G P (s) an integral coefficient;
step A3, utilizing the dq axis component E of the output reference voltage of the virtual synchronous generator obtained in the step A2 d 、E q By introducing a virtual inductance L s Obtaining the voltage reference dq axis component u of the output end of the virtual synchronous generator of the voltage and current double-loop control module by the electromagnetic equation od * And u oq * . Wherein the electromagnetic equation is shown in formula three;
step A4, utilizing the voltage and current double-loop control module obtained in the step A3 to obtain a voltage reference dq axis component u of the output end of the virtual synchronous generator od * And u oq * Of the output voltage dq axis component u of the virtual synchronous generator od And u oq Subtracting to obtain an inverter output current reference signal i through a voltage outer ring PI regulator d *、i q * Obtaining the alpha-beta axis component i of the inverter output current reference signal through dq/alpha-beta coordinate transformation α *、i β * Then with the inverter-side filter inductor current alpha beta axis component i α 、i β Subtracting, and obtaining an output signal u through a current inner loop PR regulator Lα * And u Lβ * (ii) a The transfer function of the voltage outer ring PI regulator is shown as a formula IV, and the transfer function of the current inner ring PR regulator is shown as a formula V;
step A5, filtering the capacitor current sampling signal i cfa 、i cfb 、i cfc Obtaining an alpha-beta axis component i thereof through abc/alpha-beta coordinate transformation cfα 、i cfβ And is connected with the output end voltage alpha beta axis component u of the virtual synchronous generator oα 、u oβ And the current inner loop output signal u obtained in the step A4 Lα * And u Lβ * Through a filter capacitor current feedback active damping control moduleOutput voltage modulation signal u to inverter bridge α *、u β * The control equation of the filter capacitor current feedback active damping control module is shown as a formula six;
step A6, utilizing the inverter bridge output voltage modulation signal u obtained in the step A5 α *、u β * Direct duty ratio signal D output by photovoltaic power control module 0 And a storage capacitor voltage sampling signal u c1 Inputting the signals into a pulse width modulation module, and modulating to obtain 6 switching tubes S for controlling a three-phase inverter bridge 1 ～S 6 The drive signal of (1); the control strategy of the current control type virtual synchronous generator adjusts the output active power and reactive power of the inverter according to the angular frequency and amplitude of the voltage of the power grid, so that the voltage of the power grid is maintained to be stable, and the reliability and stability of the power grid are guaranteed; meanwhile, the droop damping coefficient and the reactive droop coefficient in the self-adaptive control type virtual synchronous generator control model are adjusted to prevent the output power of the inverter from being overloaded during grid connection so as to ensure the reliable operation of the inverter.
The seamless switching operation method from the island mode to the grid-connected mode comprises the following steps:
step B1, when the inverter receives a grid-connected instruction during the isolated island operation, closing the pre-synchronous control switch S syn Enabling the phase and amplitude of the output voltage of the virtual synchronous generator to continuously approach the phase and amplitude of the voltage of the power grid through a pre-synchronous control module with phase synchronization and amplitude synchronization functions;
and step B2, when the phase and amplitude of the output voltage of the virtual synchronous generator are consistent with those of the grid voltage, the system is switched to a current control type virtual synchronous generator control strategy, the PCC switch is closed, and the system is seamlessly switched to a grid-connected operation mode.
The operation method for seamless switching from the grid-connected mode to the island mode comprises the following steps:
step C1, in a grid-connected mode, when a power grid fails or an active off-grid signal is received, detecting the output active power and reactive power of an inverter during grid connection and using the output active power and reactive power as an initial active power value P of a power reference slow starter ref0 And initial value of reactive power Q ref0 (ii) a Detect andthe active power and the reactive power which are output to the local load in network time are taken as the active power final value P of the power reference slow starter ref1 And a reactive power end value Q ref1 ；
Step C2, according to the initial value and the final value of the power obtained in the step C1, the active power is referred to P through a power reference slow start equation ref And reactive power reference Q ref Gradually transitioning from the initial value to the final value, switching the system into a voltage control type virtual synchronous generator control strategy after transitioning to the final value, disconnecting the PCC switch, and seamlessly switching the system into an island operation mode.
The power reference slow start equation is as follows:
Figure BDA0003793532990000081
in the formula, T is the execution time of the slow start.
According to the invention, the voltage control type virtual synchronous generator is adopted to control when the distributed power supply island operates to provide electric power for a local load, and the current control type virtual synchronous generator with the self-adaptive droop damping coefficient and the reactive droop coefficient is adopted to control when the distributed power supply is connected to the power grid, so that the problem of active power and reactive power overload caused by large difference between the angular frequency and amplitude of the grid voltage and the rated value of the output voltage of the inverter during the grid-connected operation is effectively solved, and the distributed power supply is easy to operate in parallel, so that the distributed power supply has good autonomous capability and plug-and-play characteristic.
The island/grid-connected dual-mode operation control strategy adopts the same electromagnetic equation, a voltage and current dual-loop control module, a filter capacitor current feedback active damping control module and a pulse width modulation module, adopts a power reference slow start control method in the grid-connected/off-grid switching process, adopts a pre-synchronization control method in the off-grid/grid-connected switching process, effectively reduces impact current during switching, and realizes seamless switching between the two modes.
Compared with the prior art, the invention has the following advantages:
(1) Aiming at the problem of active power and reactive power overload caused by large difference between the angular frequency and amplitude of the grid voltage and the rated value of the output voltage of the inverter during grid-connected operation, the invention adopts the self-adaptive current control type virtual synchronous generator for control during grid-connected operation, thereby not only realizing the stable output of the grid-connected power of the inverter and ensuring the safe and reliable operation of the inverter, but also solving the problem that the prior art can not provide inertia and damping for the grid.
(2) The invention adopts the current control type virtual synchronous generator to control during grid connection, and solves the problem that the prior art can not well meet the parallel operation requirement of the plug and play characteristic of the distributed power supply during grid connection.
Drawings
The invention is described in further detail below with reference to the following figures and detailed description:
fig. 1 is a schematic structural diagram of an equivalent circuit of an optical storage inverter system under a low-voltage distribution network in an embodiment of the invention; wherein, Z g As the impedance of the grid, u g Is the grid voltage;
fig. 2 is a schematic diagram of a three-port quasi-Z source inverter system with a photovoltaic power generation unit and an energy storage unit according to an embodiment of the present invention;
fig. 3 is a schematic diagram of an adaptive dual-mode operation control structure based on a virtual synchronous generator according to an embodiment of the invention.
Detailed Description
As shown in the figure, the microgrid self-adaptive dual-mode operation control strategy based on the virtual synchronous generator is applied to a low-voltage distribution network power system with a large number of connected distributed power supplies, and the control strategy comprises an island operation voltage control type virtual synchronous generator control strategy, a grid-connected operation self-adaptive current control type virtual synchronous generator control strategy and smooth switching between island/grid-connected modes; when the distributed power supply is connected to the power grid, the island/grid-connected dual-mode operation control strategy adopts the same electromagnetic equation, a voltage and current double-loop control module, a filter capacitor current feedback active damping control module and a pulse width modulation module; virtual inductors are introduced into an electromagnetic equation to optimize the impedance-inductance ratio of the microgrid circuit to achieve power decoupling, so that a low-voltage distribution network with the resistive power grid impedance can meet the control requirements of active-frequency and reactive-voltage virtual synchronous generators.
The micro-grid system comprises a photovoltaic power generation unit, an energy storage unit, a local load and a low-voltage alternating-current power grid; the photovoltaic power generation unit and the energy storage unit are connected with a system consisting of a photovoltaic array and an energy storage battery through a three-port quasi-Z-source inverter; the photovoltaic array is connected with the input end of the quasi-Z source inverter and outputs the maximum photovoltaic power under the control of the photovoltaic power control module; the energy storage battery is connected in parallel to an energy storage capacitor of the quasi-Z source inverter impedance network to balance the difference between the output power of the inverter and the output power of the photovoltaic inverter; the quasi-Z-source inverter consists of an input filter capacitor, an impedance network, a three-phase inverter bridge and a three-phase LCL filter; the impedance network consists of a diode, an energy storage capacitor and an energy storage inductor.
The control strategy of the island operation voltage control type virtual synchronous generator adopts the following method:
step S1, sampling signal u of voltage at two ends of local load, namely voltage at output end of virtual synchronous generator, based on output end of inverter oa 、u ob 、u oc And inverter side filter inductor current sampling signal i a 、i b 、i c Obtaining an alpha-beta axis component u by abc/alpha-beta coordinate transformation oα 、u oβ And i α 、i β And then obtaining a dq axis component u through alpha beta/dq coordinate transformation od 、u oq And i d 、i q And by the power calculation formula P out ＝1.5(u od i d +u oq i q )、Q out ＝1.5(u od i q -u oq i d ) Obtaining the output active power P of the inverter out And reactive power Q out ；
Step S2, outputting active power P by using the inverter obtained in the step S1 out And reactive power Q out Obtaining a virtual through a voltage control type virtual synchronous generator control modelOutput power angle theta and output voltage amplitude E of synchronous generator m And by the formula
Figure BDA0003793532990000101
Obtaining the output three-phase reference voltage E of the virtual synchronous generator a 、E b 、E c And a dq axis component E of the output reference voltage of the virtual synchronous generator is obtained through abc/dq coordinate transformation d 、E q ；
Wherein the voltage control type virtual synchronous generator control model is
Figure BDA0003793532990000102
In the formula, P ref A reference active power set for the virtual synchronous generator control; p is out Outputting active power for the inverter; j is the rotational inertia of the virtual synchronous generator; d ω And K Q Respectively representing the droop damping coefficient and the reactive droop coefficient of the stable operation of the virtual synchronous generator; omega 0 And ω is the nominal angular velocity and the output angular velocity of the virtual synchronous generator, respectively; e 0 A rated voltage value of the virtual synchronous generator; e m Outputting a voltage amplitude for the virtual synchronous generator; q ref Controlling the set reference reactive power for the virtual synchronous generator; q out Outputting reactive power for the inverter;
step S3, utilizing the dq axis component E of the output reference voltage of the virtual synchronous generator obtained in the step S2 d 、E q Obtaining voltage reference dq axis component u of output end of virtual synchronous generator of voltage and current double-loop control module through electromagnetic equation od * And u oq * Wherein the electromagnetic equation is
Figure BDA0003793532990000111
In the formula, L s Is a virtual inductor;
step S4, utilizing the voltage and current double-loop control module obtained in the step S3 to obtain the voltage reference dq axis component u of the output end of the virtual synchronous generator od * And u oq * D is compared with the output end voltage dq axis component u of the virtual synchronous generator od And u oq Subtraction-pass voltage outer loop Proportional Integral (PI) regulator G u (s) obtaining an inverter output current reference signal i d *、i q * Obtaining an alpha-beta axis component i of an inverter output current reference signal through dq/alpha-beta coordinate transformation α *、i β * Then with the inverter-side filter inductor current alpha beta axis component i α 、i β Subtracted, passed through a current inner loop Proportional Resonant (PR) regulator G i (s) obtaining an output signal u Lα * And u Lβ *；
Wherein, the voltage outer loop PI regulator G u The transfer function of(s) is:
Figure BDA0003793532990000112
in the formula, k pu Is a voltage regulator G u Proportionality coefficient of(s), k iu Is a voltage regulator G u (s) an integral coefficient;
wherein the current inner ring PR regulator G i The transfer function of(s) is:
Figure BDA0003793532990000113
in the formula, k pi For the current regulator G i Coefficient of proportionality of(s), ω c As a current regulator G i Bandwidth of(s), ω 1 Is the angular frequency of the fundamental wave, k r For the current regulator G i (s) the resonance coefficient, h is the harmonic frequency corresponding to the resonance characteristic frequency;
step S5, filtering the capacitor current sampling signal i cfa 、i cfb 、i cfc Obtaining an alpha-beta axis component i thereof through abc/alpha-beta coordinate transformation cfα 、i cfβ And synchronizing with the virtualMotor output terminal voltage alpha beta axis component u oα 、u oβ And the current inner loop output signal u obtained in step S4 Lα * And u Lβ * Obtaining an inverter bridge output voltage modulation signal u through a filter capacitor current feedback active damping control module α *、u β * The control equation of the filter capacitor current feedback active damping control module is as follows;
Figure BDA0003793532990000121
s6, utilizing the inverter bridge output voltage modulation signal u obtained in the S5 α *、u β * Direct duty ratio signal D output by photovoltaic power control module 0 And the voltage sampling signal u of the energy storage capacitor c1 The signals are input to a pulse width modulation module together, and 6 switching tubes S for controlling the three-phase inverter bridge are obtained through modulation 1 ～S 6 The drive signal of (1); the voltage control type virtual synchronous generator control strategy controls the output voltage of the virtual synchronous generator according to the active power and the reactive power output by the inverter, and provides power for a local load.
The photovoltaic power control module comprises a photovoltaic Maximum Power Point Tracking (MPPT) algorithm unit and a photovoltaic voltage regulator; sampled photovoltaic voltage U PV And photovoltaic current i PV Sending the voltage into an MPPT algorithm unit to obtain a photovoltaic maximum power point voltage U PV *，U PV * To photovoltaic voltage U PV Generating a pass-through duty cycle D by a photovoltaic voltage PI regulator 0 To achieve photovoltaic power output control; transfer function G of photovoltaic voltage regulator PV (s) is
Figure BDA0003793532990000122
In the formula k p For photovoltaic voltage regulators G PV Proportionality coefficient of(s), k i For photovoltaic voltage regulators G PV (s) coefficient of integration.
The control strategy of the grid-connected operation self-adaptive current control type virtual synchronous generator adopts the following modes:
a1, based on a PCC voltage sampling signal u of a public connection point of a power grid pcca 、u pccb 、u pccc Obtaining the angular frequency omega of the power grid through a double generalized second-order integral phase-locked loop (DSOGI-PLL) g And the filtered PCC point voltage alpha beta axis component u pccα 、u pccβ Or dq axis component u pccd 、u pccq According to the formula
Figure BDA0003793532990000123
Or formula
Figure BDA0003793532990000124
Obtaining the PCC voltage amplitude E pcc I.e. the amplitude of the voltage at the output of the virtual synchronous generator, omega g And E pcc Sending the power to a self-adaptive current control type virtual synchronous generator control model, and estimating an inverter output active power reference P according to the current control type virtual synchronous generator control model out * And reactive power reference Q out * Is derived from adaptively adjusting the droop damping coefficient D in the current control model virtual synchronous generator control model ω And reactive sag factor K Q And substituting the obtained new droop damping coefficient and the obtained reactive droop coefficient into the current control type virtual synchronous generator control model again to obtain the final inverter output active power reference P out * And reactive power reference Q out *；
Wherein the current control type virtual synchronous generator control model is
Figure BDA0003793532990000131
In the formula, P ref 、Q ref Respectively controlling set reference active power and reference reactive power for the virtual synchronous generator; p is out * And Q out * Respectively outputting an active power reference and a reactive power reference for the inverter; omega g The angular frequency of the power grid is also the actual angular speed of the virtual synchronous generator; theta.theta. g The phase is a PCC voltage phase and is also a virtual synchronous generator output power angle; omega 0 Rated angular velocity for the virtual synchronous generator; d ω And K Q Respectively serving as a virtual synchronous generator self-adaptive droop damping coefficient and a self-adaptive reactive droop coefficient during grid-connected operation; e 0 For a given PCC voltage amplitude reference, also the virtual synchronous generator rated voltage value; e pcc The amplitude of the PCC voltage is also the amplitude of the voltage at the output end of the virtual synchronous generator;
the calculation method of the self-adaptive droop damping coefficient and the reactive droop coefficient comprises the following steps: in order to prevent the droop damping coefficient and the reactive droop coefficient from changing too frequently at the critical point, the values of the droop damping coefficient and the reactive droop coefficient are determined by adopting a hysteresis comparison method;
sag damping coefficient D ω Is calculated by
Figure BDA0003793532990000132
In the formula, P max And P min Respectively for setting the maximum and minimum values, P, of the active power output by the inverter ref Reference active power, P, set for virtual synchronous generator control out * Outputting an active power reference for the inverter, wherein delta P is an active power hysteresis comparison interval, omega g_min And ω g_max For setting the minimum and maximum values, ω, of the grid angular frequency 0 Rated angular speed for the virtual synchronous generator, D ω0 Droop damping coefficient for stable operation;
reactive sag coefficient K Q Is calculated by
Figure BDA0003793532990000141
In the formula, Q max And Q min For setting maximum and minimum values, Q, of the output reactive power of the inverter, respectively ref Reference reactive power, Q, set for virtual synchronous generator control out * For the inverter to output a reactive power reference, Δ Q is the reactive power hysteresis comparison interval, E m_max And E m_min To set the maximum and minimum values, ω, of the PCC voltage amplitude 0 For a virtual synchronous generator rated angular speed, K Q0 The reactive droop coefficient is stable in operation;
step A2, the inverter output active power reference P obtained in the step A1 out * And reactive power reference Q out * Sending into an additional power loop and respectively outputting active power P with the inverter out And reactive power Q out PI regulator G with subtraction and additional power loop P (s) obtaining the dq axis component E of the output reference voltage of the virtual synchronous generator d 、E q ；
Power loop PI regulator G P (s) a transfer function of
Figure BDA0003793532990000142
In the formula, k pp As a power loop PI regulator G P Proportionality coefficient of(s), k ip As a power loop PI regulator G P (s) an integral coefficient;
step A3, utilizing the dq axis component E of the output reference voltage of the virtual synchronous generator obtained in the step A2 d 、E q By introducing a virtual inductance L s The electromagnetic equation obtains a voltage reference dq axis component u of the output end of the virtual synchronous generator of the voltage and current double-loop control module od * And u oq * . Wherein the electromagnetic equation is shown in formula three;
step A4, utilizing the voltage and current double-loop control module obtained in the step A3 to obtain a voltage reference dq axis component u of the output end of the virtual synchronous generator od * And u oq * D is compared with the output end voltage dq axis component u of the virtual synchronous generator od And u oq Subtracting to obtain an inverter output current reference signal i through a voltage outer ring PI regulator d *、i q * Obtaining the alpha-beta axis component i of the inverter output current reference signal through dq/alpha-beta coordinate transformation α *、i β * Then with the inverter-side filter inductor current alpha beta axis component i α 、i β Are subtracted from each other byCurrent inner loop PR regulator obtaining output signal u Lα * And u Lβ * (ii) a The transfer function of the voltage outer ring PI regulator is shown as a formula IV, and the transfer function of the current inner ring PR regulator is shown as a formula V;
step A5, filtering the current sampling signal i of the capacitor cfa 、i cfb 、i cfc Obtaining the alpha-beta axis component i thereof by abc/alpha-beta coordinate transformation cfα 、i cfβ And is connected with the output end voltage alpha beta axis component u of the virtual synchronous generator oα 、u oβ And the current inner loop output signal u obtained in the step A4 Lα * And u Lβ * Obtaining an inverter bridge output voltage modulation signal u through a filter capacitor current feedback active damping control module α *、u β * The control equation of the filter capacitor current feedback active damping control module is shown as a formula six;
step A6, utilizing the inverter bridge output voltage modulation signal u obtained in the step A5 α *、u β * Direct duty ratio signal D output by photovoltaic power control module 0 And the voltage sampling signal u of the energy storage capacitor c1 Inputting the signals into a pulse width modulation module, and modulating to obtain 6 switching tubes S for controlling a three-phase inverter bridge 1 ～S 6 The drive signal of (1); the control strategy of the current control type virtual synchronous generator adjusts the output active power and reactive power of the inverter according to the angular frequency and amplitude of the voltage of the power grid, so that the voltage of the power grid is maintained to be stable, and the reliability and stability of the power grid are guaranteed; meanwhile, the droop damping coefficient and the reactive droop coefficient in the self-adaptive control type virtual synchronous generator control model are adjusted to prevent the output power of the inverter from being overloaded during grid connection so as to ensure the reliable operation of the inverter.
The seamless switching operation method from the island mode to the grid-connected mode comprises the following steps:
step B1, when the inverter receives a grid-connected instruction during island operation, closing the pre-synchronous control switch S syn Enabling the phase and the amplitude of the output voltage of the virtual synchronous generator to continuously approach the phase and the amplitude of the voltage of the power grid through a pre-synchronous control module with phase synchronization and amplitude synchronization functions;
and step B2, when the phase and amplitude of the output voltage of the virtual synchronous generator are consistent with the phase and amplitude of the voltage of the power grid, the system is switched to a current control type virtual synchronous generator control strategy, the PCC point switch is closed, and the system is seamlessly switched to a grid-connected operation mode.
The operation method for seamless switching from the grid-connected mode to the island mode comprises the following steps:
step C1, in a grid-connected mode, when a power grid fails or an active off-grid signal is received, detecting the output active power and reactive power of an inverter during grid connection and using the output active power and reactive power as an initial active power value P of a power reference slow starter ref0 And initial value of reactive power Q ref0 (ii) a Detecting active power and reactive power output to a local load during grid connection, and taking the active power and reactive power as an active power final value P of a power reference slow starter ref1 And a reactive power end value Q ref1 ；
Step C2, according to the initial value and the final value of the power obtained in the step C1, the active power is referred to P through a power reference slow start equation ref And reactive power reference Q ref And gradually transitioning from the initial value to the final value, switching the system into a voltage control type virtual synchronous generator control strategy after transitioning to the final value, disconnecting the PCC switch, and seamlessly switching the system into an island operation mode.
The power reference slow start equation is as follows:
Figure BDA0003793532990000161
in the formula, T is the execution time of the slow start.
The foregoing is directed to preferred embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow. However, any simple modification, equivalent change and modification of the above embodiments according to the technical essence of the present invention will still fall within the protection scope of the technical solution of the present invention.

Claims (7)

1. Microgrid self-adaptation dual mode operation control strategy based on virtual synchronous generator is applied to the low pressure of a large amount of accesses of distributed generator and joins in marriage net power system, its characterized in that: the control strategy comprises an island operation voltage control type virtual synchronous generator control strategy, a grid-connected operation self-adaptive current control type virtual synchronous generator control strategy and smooth switching between island/grid-connected modes; the island/grid-connected dual-mode operation control strategy of the distributed power supply adopts the same electromagnetic equation, a voltage and current dual-loop control module, a filter capacitor current feedback active damping control module and a pulse width modulation module; virtual inductors are introduced into an electromagnetic equation to optimize the impedance-inductance ratio of the microgrid circuit to realize power decoupling, so that a low-voltage distribution network with the resistive power grid impedance can meet the control requirements of active-frequency and reactive-voltage virtual synchronous generators.
2. The virtual synchronous generator-based microgrid adaptive dual-mode operation control strategy according to claim 1, characterized in that: the micro-grid system comprises a photovoltaic power generation unit, an energy storage unit, a local load and a low-voltage alternating-current power grid; the photovoltaic power generation unit and the energy storage unit are connected with a system consisting of a photovoltaic array and an energy storage battery through a three-port quasi-Z-source inverter; the photovoltaic array is connected with the input end of the quasi-Z source inverter and outputs the maximum photovoltaic power under the control of the photovoltaic power control module; the energy storage battery is connected in parallel to an energy storage capacitor of the quasi-Z source inverter impedance network to balance the difference between the output power of the inverter and the output power of the photovoltaic inverter; the quasi-Z source inverter consists of an input filter capacitor, an impedance network, a three-phase inverter bridge and a three-phase LCL filter; the impedance network consists of a diode, an energy storage capacitor and an energy storage inductor.
3. The virtual synchronous generator-based microgrid adaptive dual-mode operation control strategy according to claim 1, characterized in that: the control strategy of the island operation voltage control type virtual synchronous generator adopts the following method:
step S1, sampling signal u of voltage at two ends of local load, namely voltage at output end of virtual synchronous generator, based on output end of inverter oa 、u ob 、u oc And inverter side filter inductor current sampling signal i a 、i b 、i c Obtaining the alpha-beta axis component u by abc/alpha-beta coordinate transformation oα 、u oβ And i α 、i β And then obtaining a dq axis component u through alpha beta/dq coordinate transformation od 、u oq And i d 、i q And through a power calculation formula P out ＝1.5(u od i d +u oq i q )、Q out ＝1.5(u od i q -u oq i d ) Obtaining the output active power P of the inverter out And reactive power Q out ；
Step S2, outputting active power P by using the inverter obtained in the step S1 out And reactive power Q out Obtaining an output power angle theta and an output voltage amplitude E of the virtual synchronous generator through a voltage control type virtual synchronous generator control model m And by the formula
Figure FDA0003793532980000021
Obtaining the output three-phase reference voltage E of the virtual synchronous generator a 、E b 、E c And obtaining a dq axis component E of the output reference voltage of the virtual synchronous generator through abc/dq coordinate transformation d 、E q ；
Wherein the voltage control type virtual synchronous generator control model is
Figure FDA0003793532980000022
In the formula, P ref Parameters set for virtual synchronous generator controlExamining active power; p is out Outputting active power to the inverter; j is the rotational inertia of the virtual synchronous generator; d ω And K Q Respectively representing the droop damping coefficient and the reactive droop coefficient of the stable operation of the virtual synchronous generator; omega 0 And ω is the rated angular velocity and the output angular velocity of the virtual synchronous generator, respectively; e 0 The rated voltage value is a virtual synchronous generator rated voltage value; e m Outputting a voltage amplitude for the virtual synchronous generator; q ref Controlling the set reference reactive power for the virtual synchronous generator; q out Outputting reactive power for the inverter;
step S3, utilizing the dq axis component E of the output reference voltage of the virtual synchronous generator obtained in the step S2 d 、E q Obtaining voltage reference dq axis component u of output end of virtual synchronous generator of voltage and current double-loop control module through electromagnetic equation od * And u oq * Wherein the electromagnetic equation is
Figure FDA0003793532980000023
In the formula, L s Is a virtual inductor;
step S4, utilizing the voltage and current double-loop control module obtained in the step S3 to obtain a voltage reference dq axis component u of the output end of the virtual synchronous generator od * And u oq * Of the output voltage dq axis component u of the virtual synchronous generator od And u oq Subtracting passing voltage outer loop proportional integral PI regulator G u (s) obtaining an inverter output current reference signal i d *、i q * Obtaining the alpha-beta axis component i of the inverter output current reference signal through dq/alpha-beta coordinate transformation α *、i β * Then the current is compared with the inverter side filter inductance current alpha beta axis component i α 、i β Subtracted, passed through a current inner loop proportional resonant PR regulator G i (s) obtaining an output signal u Lα * And u Lβ *；
Wherein, the voltage outer loop PI regulator G u The transfer function of(s) is:
Figure FDA0003793532980000031
in the formula, k pu Is a voltage regulator G u Proportionality coefficient of(s), k iu Is a voltage regulator G u (s) an integral coefficient; wherein the current inner ring PR regulator G i The transfer function of(s) is:
Figure FDA0003793532980000032
in the formula, k pi As a current regulator G i Coefficient of proportionality of(s), ω c As a current regulator G i Bandwidth of(s), ω 1 Is the angular frequency, k, of the fundamental wave r As a current regulator G i (s) a resonance coefficient, h being the harmonic number corresponding to the resonance characteristic frequency;
step S5, filtering the capacitor current sampling signal i cfa 、i cfb 、i cfc Obtaining the alpha-beta axis component i thereof by abc/alpha-beta coordinate transformation cfα 、i cfβ And is connected with the output end voltage alpha beta axis component u of the virtual synchronous generator oα 、u oβ And the current inner loop output signal u obtained in step S4 Lα * And u Lβ * The inverter bridge output voltage modulation signal u is obtained by a filter capacitor current feedback active damping control module α *、u β * The control equation of the filter capacitor current feedback active damping control module is as follows;
Figure FDA0003793532980000033
s6, utilizing the inverter bridge output voltage modulation signal u obtained in the S5 α *、u β * Direct duty ratio signal D output by photovoltaic power control module 0 And a storage capacitor voltage sampling signal u c1 The signals are input to a pulse width modulation module together, and 6 switching tubes S for controlling the three-phase inverter bridge are obtained through modulation 1 ～S 6 The drive signal of (a); the voltage control type virtual synchronous generator control strategy controls the output voltage of the virtual synchronous generator according to the active power and the reactive power output by the inverter, and provides power for a local load.
4. The virtual synchronous generator-based microgrid adaptive dual mode operation control strategy of claim 2, characterized in that: the photovoltaic power control module comprises a photovoltaic Maximum Power Point Tracking (MPPT) algorithm unit and a photovoltaic voltage regulator; sampled photovoltaic voltage U PV And photovoltaic current i PV Sending the voltage into an MPPT algorithm unit to obtain a photovoltaic maximum power point voltage U PV *，U PV * To photovoltaic voltage U PV Generating a pass-through duty cycle D by a photovoltaic voltage PI regulator 0 To achieve photovoltaic power output control; transfer function G of photovoltaic voltage regulator PV (s) is
Figure FDA0003793532980000041
In the formula k p For photovoltaic voltage regulators G PV Proportionality coefficient of(s), k i For photovoltaic voltage regulators G PV (s) coefficient of integration.
5. The virtual synchronous generator-based microgrid adaptive dual-mode operation control strategy according to claim 1, characterized in that: the control strategy of the grid-connected operation self-adaptive current control type virtual synchronous generator adopts the following mode;
a1, based on a PCC voltage sampling signal u of a public connection point of a power grid pcca 、u pccb 、u pccc Obtaining the angular frequency omega of the power grid through a double generalized second-order integral phase-locked loop DSOGI-PLL g And the filtered PCC point voltage alpha beta axis component u pccα 、u pccβ Or dq axis component u pccd 、u pccq According to the formula
Figure FDA0003793532980000042
Or formula
Figure FDA0003793532980000043
Obtaining the PCC voltage amplitude E pcc I.e. the amplitude of the voltage at the output of the virtual synchronous generator, omega g And E pcc Sending the power reference P into a self-adaptive current control type virtual synchronous generator control model, and estimating the output active power reference P of the inverter according to the current control type virtual synchronous generator control model out * And reactive power reference Q out * Is derived from adaptively adjusting the droop damping coefficient D in the current control model virtual synchronous generator control model ω And reactive sag factor K Q And substituting the obtained new droop damping coefficient and the obtained reactive droop coefficient into the current control type virtual synchronous generator control model again to obtain the final inverter output active power reference P out * And reactive power reference Q out *；
Wherein the current control type virtual synchronous generator control model is
Figure FDA0003793532980000044
In the formula, P ref 、Q ref Respectively controlling set reference active power and reference reactive power for the virtual synchronous generator; p out * And Q out * Respectively outputting an active power reference and a reactive power reference for the inverter; omega g The actual angular speed is the grid angular frequency and also the virtual synchronous generator actual angular speed; theta g The phase is a PCC voltage phase and is also an output power angle of the virtual synchronous generator; omega 0 Rated angular velocity for the virtual synchronous generator; d ω And K Q Respectively serving as a virtual synchronous generator self-adaptive droop damping coefficient and a self-adaptive reactive droop coefficient during grid-connected operation; e 0 For a given PCC voltage amplitude reference, also the virtual synchronous generator rated voltage value; e pcc The amplitude of the PCC voltage is also the amplitude of the voltage at the output end of the virtual synchronous generator;
the calculation method of the self-adaptive droop damping coefficient and the reactive droop coefficient comprises the following steps: in order to prevent the droop damping coefficient and the reactive droop coefficient from changing too frequently at the critical point, the values of the droop damping coefficient and the reactive droop coefficient are determined by adopting a hysteresis comparison method;
sag damping coefficient D ω Is calculated by
Figure FDA0003793532980000051
In the formula, P max And P min Respectively for setting the maximum and minimum values, P, of the active power output by the inverter ref Reference active power, P, set for virtual synchronous generator control out * Outputting active power reference for the inverter, wherein delta P is an active power hysteresis comparison interval, omega g_min And ω g_max For setting minimum and maximum values, ω, of angular frequency of the grid 0 Rated angular speed for the virtual synchronous generator, D ω0 Droop damping coefficient for stable operation;
reactive sag coefficient K Q Is calculated by
Figure FDA0003793532980000052
A formula ten;
in the formula, Q max And Q min For setting maximum and minimum values, Q, of the output reactive power of the inverter, respectively ref Reference reactive power, Q, set for virtual synchronous generator control out * For the inverter to output a reactive power reference, Δ Q is the reactive power hysteresis comparison interval, E m_max And E m_min To set the maximum and minimum values, ω, of the PCC voltage amplitude 0 For a virtual synchronous generator rated angular speed, K Q0 The reactive droop coefficient is the reactive droop coefficient in stable operation;
step A2, the inverter output active power reference P obtained in the step A1 out * And reactive power reference Q out * Feeding into an additional power loop and dividingOutput active power P of inverter out And reactive power Q out PI regulator G with subtraction and additional power loop P (s) obtaining the dq axis component E of the output reference voltage of the virtual synchronous generator d 、E q ；
Power loop PI regulator G P (s) a transfer function of
Figure FDA0003793532980000061
In the formula, k pp As a power loop PI regulator G P Proportionality coefficient of(s), k ip As a power loop PI regulator G P (s) an integral coefficient;
step A3, utilizing the dq axis component E of the output reference voltage of the virtual synchronous generator obtained in the step A2 d 、E q By introducing a virtual inductance L s Obtaining the voltage reference dq axis component u of the output end of the virtual synchronous generator of the voltage and current double-loop control module by the electromagnetic equation od * And u oq * . Wherein the electromagnetic equation is shown in formula three;
step A4, utilizing the voltage and current double-loop control module obtained in the step A3 to obtain a voltage reference dq axis component u of the output end of the virtual synchronous generator od * And u oq * Of the output voltage dq axis component u of the virtual synchronous generator od And u oq Subtracting to obtain an inverter output current reference signal i through a voltage outer ring PI regulator d *、i q * Obtaining the alpha-beta axis component i of the inverter output current reference signal through dq/alpha-beta coordinate transformation α *、i β * Then with the inverter-side filter inductor current alpha beta axis component i α 、i β Subtracting, and obtaining an output signal u through a current inner loop PR regulator Lα * And u Lβ * (ii) a The transfer function of the voltage outer ring PI regulator is shown as a formula IV, and the transfer function of the current inner ring PR regulator is shown as a formula V;
step A5, filtering the capacitor current sampling signal i cfa 、i cfb 、i cfc Obtaining the alpha-beta axis thereof by abc/alpha-beta coordinate transformationComponent i cfα 、i cfβ And is connected with the output end voltage alpha beta axis component u of the virtual synchronous generator oα 、u oβ And the current inner loop output signal u obtained in the step A4 Lα * And u Lβ * Obtaining an inverter bridge output voltage modulation signal u through a filter capacitor current feedback active damping control module α *、u β * The control equation of the filter capacitor current feedback active damping control module is shown as a formula six;
step A6, utilizing the inverter bridge output voltage modulation signal u obtained in the step A5 α *、u β * Direct duty ratio signal D output by photovoltaic power control module 0 And the voltage sampling signal u of the energy storage capacitor c1 The signals are input to a pulse width modulation module together, and 6 switching tubes S for controlling the three-phase inverter bridge are obtained through modulation 1 ～S 6 The drive signal of (1); the control strategy of the current control type virtual synchronous generator adjusts the output active power and reactive power of the inverter according to the angular frequency and amplitude of the voltage of the power grid, so that the voltage of the power grid is maintained to be stable, and the reliability and stability of the power grid are guaranteed; meanwhile, the droop damping coefficient and the reactive droop coefficient in the self-adaptive control type virtual synchronous generator control model are adjusted to prevent the output power of the inverter from being overloaded during grid connection so as to ensure the reliable operation of the inverter.
6. The virtual synchronous generator-based microgrid adaptive dual mode operation control strategy of claim 1, characterized in that: the seamless switching operation method from the island mode to the grid-connected mode comprises the following steps:
step B1, when the inverter receives a grid-connected instruction during the isolated island operation, closing the pre-synchronous control switch S syn Enabling the phase and amplitude of the output voltage of the virtual synchronous generator to continuously approach the phase and amplitude of the voltage of the power grid through a pre-synchronous control module with phase synchronization and amplitude synchronization functions;
and step B2, when the phase and amplitude of the output voltage of the virtual synchronous generator are consistent with the phase and amplitude of the voltage of the power grid, the system is switched to a current control type virtual synchronous generator control strategy, the PCC point switch is closed, and the system is seamlessly switched to a grid-connected operation mode.
7. The virtual synchronous generator-based microgrid adaptive dual mode operation control strategy of claim 1, characterized in that: the seamless switching operation method from the grid-connected mode to the island mode comprises the following steps:
step C1, in a grid-connected mode, when a power grid fails or an active off-grid signal is received, detecting the output active power and reactive power of an inverter during grid connection, and taking the output active power and reactive power as the initial value P of the active power of a power reference slow starter ref0 And initial value of reactive power Q ref0 (ii) a Detecting active power and reactive power output to a local load during grid connection, and taking the active power and reactive power as an active power final value P of a power reference slow starter ref1 And a final value of reactive power Q ref1 ；
Step C2, according to the initial value and the final value of the power obtained in the step C1, the active power is referred to P through a power reference slow start equation ref And reactive power reference Q ref And gradually transitioning from the initial value to the final value, switching the system into a voltage control type virtual synchronous generator control strategy after transitioning to the final value, disconnecting the PCC switch, and seamlessly switching the system into an island operation mode.
The power reference slow start equation is as follows:
Figure FDA0003793532980000071
wherein, T is the execution time of the slow start.
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CN115995813A (en) * 2023-02-21 2023-04-21 广东工业大学 Grid-connected inverter oscillation suppression strategy based on hybrid damping
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* Cited by examiner, † Cited by third party
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CN115995813A (en) * 2023-02-21 2023-04-21 广东工业大学 Grid-connected inverter oscillation suppression strategy based on hybrid damping
CN117096960A (en) * 2023-08-25 2023-11-21 山东大学 Virtual synchronous machine amplitude limiting operation control method and system considering electric quantity constraint
CN117096960B (en) * 2023-08-25 2024-03-05 山东大学 Virtual synchronous machine amplitude limiting operation control method and system considering electric quantity constraint

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