CN115549144A - Microgrid and control method thereof - Google Patents
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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
- H02J3/28—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
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J3/00—Circuit arrangements for AC mains or AC distribution networks
- H02J3/24—Arrangements for preventing or reducing oscillations of power in networks
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J3/00—Circuit arrangements for AC mains or AC distribution networks
- H02J3/24—Arrangements for preventing or reducing oscillations of power in networks
- H02J3/241—The oscillation concerning frequency
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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
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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
- H02J3/388—Islanding, i.e. disconnection of local power supply from the network
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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
- H02J7/00—Circuit arrangements for charging or depolarising batteries or for supplying loads from batteries
- H02J7/0068—Battery or charger load switching, e.g. concurrent charging and load supply
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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
- H02J7/00—Circuit arrangements for charging or depolarising batteries or for supplying loads from batteries
- H02J7/007—Regulation of charging or discharging current or voltage
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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
- H02J7/00—Circuit arrangements for charging or depolarising batteries or for supplying loads from batteries
- H02J7/007—Regulation of charging or discharging current or voltage
- H02J7/00712—Regulation of charging or discharging current or voltage the cycle being controlled or terminated in response to electric parameters
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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
- H02J7/00—Circuit arrangements for charging or depolarising batteries or for supplying loads from batteries
- H02J7/02—Circuit arrangements for charging or depolarising batteries or for supplying loads from batteries for charging batteries from AC mains by converters
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Abstract
The present disclosure provides a microgrid and a control method thereof. The microgrid comprises: an energy storage system; and a controller configured to: and controlling the energy storage system to perform direct-current constant-voltage charging in response to the fact that the direct-current voltage of the energy storage system exceeds the upper-limit threshold voltage, and controlling the energy storage system to perform direct-current constant-voltage discharging in response to the fact that the direct-current voltage of the energy storage system is lower than the lower-limit threshold voltage.
Description
Technical Field
The disclosure relates to the field of micro-grids, in particular to a micro-grid energy storage system and a control method thereof.
Background
The micro-grid with the wind power generation system, the photovoltaic power generation system, the energy storage system and the load can work in a grid-connected mode and an island mode, and seamless switching between the grid-connected mode and the island mode needs to be realized. The direct current side of the virtual synchronous machine of little electric wire netting energy storage is connected to energy storage battery and the interchange side is connected to little electric wire netting generating line, can realize the voltage and the frequency support to little electric wire netting.
When the microgrid is in an islanded or off-grid state, voltage and frequency support is generally provided by parallel operation of a plurality of microgrid energy storage systems. In a microgrid energy storage system, the dc side of the energy storage converters are connected to the energy storage cells and the ac side is connected to the microgrid to achieve voltage and frequency support for the microgrid. When the power of the wind power generation system and the photovoltaic power generation system is larger than the load power, the energy storage battery is in a charging state; and when the power of the wind power generation system and the photovoltaic power generation system is less than the load power, the energy storage battery is in a discharging state. When a plurality of energy storage systems operate in parallel, power is distributed according to the droop coefficient of the micro-grid energy storage converter, because the SOC of a plurality of energy storages is different, the battery with the higher SOC is firstly close to a full-charge state, the battery with the lower SOC is firstly close to the lowest battery voltage, and if the power is continuously distributed according to the droop coefficient of the virtual synchronous machine, the energy storage battery can have the tripping or stopping condition with overhigh or overlow voltage. The existing technical scheme can adopt the shutdown measures of an energy storage system, but has low utilization efficiency on an energy storage battery and lags power response when an energy storage converter is restarted; or the upper control system schedules the generated power or the discharge power in the microgrid system to stop charging or discharging the energy storage battery, but the utilization efficiency of the energy storage battery is low, the generated power or the load power is sacrificed, and the autonomous operation capability of the microgrid system is reduced.
When the microgrid is in a grid-connected state, the energy storage system generally adopts constant power control. The existing microgrid energy storage virtual synchronous machine adopts an alternating voltage and frequency control mode instead of controlling direct voltage, and charging/discharging voltage is limited due to the characteristics of a battery. The microgrid energy storage virtual synchronous machine can also adopt a voltage and current switching double-loop control operation mode, adopt an alternating voltage phase locking tracking control mode when an island operates, and switch to a direct voltage control mode when a grid is connected, but has no supporting effect on the voltage and frequency of a power grid, and can not realize seamless switching.
In addition, when the microgrid is in a grid-connected state, the charging/discharging current of the battery is limited according to the characteristics of the battery under the constant power control of the energy storage system. When the battery voltage is low, the constant power may cause the battery current to exceed the peak charge/discharge current limit, which in turn causes the battery to trip or break. At present, a microgrid energy storage virtual synchronous machine can adopt an alternating voltage and frequency control mode, can work in a grid-connected mode and an off-grid mode, can realize seamless switching, but cannot realize control over direct current; the micro-grid energy storage virtual synchronous machine can also adopt a running mode of switching voltage and current double-loop control, adopts an alternating voltage control mode when in an isolated island running mode, adopts an alternating voltage phase-locked tracking and direct current limiting control mode when in a grid-connected running mode, has no supporting effect on the voltage and the frequency of a power grid, and can not realize seamless switching.
Disclosure of Invention
The utility model provides a little electric wire netting energy storage virtual synchrodyne is from net operation constant voltage control method, solves little electric wire netting isolated island operation energy storage system and does not shut down, can furthest's utilization energy storage battery to reduce upper control system's intervention and dispatch, the autonomous operation ability is stronger.
The invention provides a micro-grid energy storage virtual synchronous machine grid-connected operation constant voltage control method, which is used for controlling the alternating voltage and frequency of a micro-grid, has a supporting function on the micro-grid in a grid-connected mode and an isolated island mode, does not change the control mode of a voltage loop and a current loop, realizes constant voltage charging/discharging control on an energy storage battery in the grid-connected mode, and does not need mode switching in the grid-connected/off-grid switching process.
The utility model provides a little grid energy storage virtual synchrodyne current-limiting control method that is incorporated into the power networks, control little grid alternating voltage and frequency, have the supporting role under the mode of being incorporated into the power networks and the isolated island mode to little grid, when the energy storage battery direct current reaches the peak current of charging/discharging under the mode of being incorporated into the power networks simultaneously, can the current-limiting operation. And the switching of the voltage/current loop control mode is not required in the grid-connected/off-grid switching process.
An aspect of the present disclosure provides a microgrid comprising: an energy storage system; and a controller configured to: and controlling the energy storage system to perform direct-current constant-voltage charging in response to the direct-current voltage of the energy storage system exceeding an upper-limit threshold voltage, and controlling the energy storage system to perform direct-current constant-voltage discharging in response to the direct-current voltage of the energy storage system being lower than a lower-limit threshold voltage.
Where a microgrid is in islanding mode and the microgrid includes a plurality of energy storage systems, the controller is further configured to: when the direct-current voltage of the energy storage system is within a range between an upper threshold voltage and a lower threshold voltage, distributing power of the energy storage system according to a droop coefficient, performing direct-current constant-voltage charging by adjusting a voltage phase of at least one of the plurality of energy storage systems in response to the direct-current voltage of the at least one energy storage system exceeding the upper threshold voltage, and performing direct-current constant-voltage discharging by adjusting the voltage phase of the at least one energy storage system in response to the direct-current voltage of the at least one of the plurality of energy storage systems being lower than the lower threshold voltage.
In a case where the microgrid is in a grid-tie mode, the controller is further configured to: when the deviation between the direct current voltage of the energy storage system and the upper limit threshold voltage or the lower limit threshold voltage exceeds the reference power limit, the power of the energy storage system is limited according to the reference power of the energy storage system, the energy storage system is controlled to perform direct current constant voltage charging by adjusting the voltage phase of the energy storage system in response to the fact that the deviation between the direct current voltage of the energy storage system and the upper limit threshold voltage is smaller than the reference power limit, and the energy storage system is controlled to perform direct current constant voltage discharging by adjusting the voltage phase of the energy storage system in response to the fact that the deviation between the direct current voltage of the energy storage system and the lower limit threshold voltage is smaller than the reference power limit.
The reference power is determined by a product of a charging limiting current or a discharging limiting current of the energy storage system, which is constant, and a direct current voltage of the energy storage system, which varies according to a state of charge of the energy storage system.
The controller adjusts the operation of the microgrid through a virtual synchronous machine control strategy or a droop control strategy.
An aspect of the present disclosure provides a microgrid comprising: an energy storage system; and a controller configured to: and limiting the power of the energy storage system according to the reference power of the energy storage system, wherein the reference power is determined by the product of the charging limiting current or the discharging limiting current of the energy storage system and the direct current voltage of the energy storage system, the charging limiting current or the discharging limiting current is constant, and the direct current voltage is changed according to the state of charge of the energy storage system.
An aspect of the present disclosure provides a control method of a microgrid, the control method including: and controlling the energy storage system to perform direct-current constant-voltage charging in response to the fact that the direct-current voltage of the energy storage system of the microgrid exceeds an upper-limit threshold voltage, and controlling the energy storage system to perform direct-current constant-voltage discharging in response to the fact that the direct-current voltage of the energy storage system is lower than a lower-limit threshold voltage.
In a case where the microgrid is in an islanded mode and the microgrid comprises a plurality of energy storage systems, the control method further comprises: when the direct-current voltage of the energy storage system is within a range between an upper threshold voltage and a lower threshold voltage, distributing power of the energy storage system according to a droop coefficient, performing direct-current constant-voltage charging by adjusting a voltage phase of at least one of the plurality of energy storage systems in response to the direct-current voltage of the at least one energy storage system exceeding the upper threshold voltage, and performing direct-current constant-voltage discharging by adjusting the voltage phase of the at least one energy storage system in response to the direct-current voltage of the at least one of the plurality of energy storage systems being lower than the lower threshold voltage.
Under the condition that the microgrid is in a grid-connected mode, the control method further comprises the following steps: when the deviation between the direct current voltage of the energy storage system and the upper limit threshold voltage or the lower limit threshold voltage exceeds the reference power limit, the power of the energy storage system is limited according to the reference power of the energy storage system, the energy storage system is controlled to perform direct current constant voltage charging by adjusting the voltage phase of the energy storage system in response to the fact that the deviation between the direct current voltage of the energy storage system and the upper limit threshold voltage is smaller than the reference power limit, and the energy storage system is controlled to perform direct current constant voltage discharging by adjusting the voltage phase of the energy storage system in response to the fact that the deviation between the direct current voltage of the energy storage system and the lower limit threshold voltage is smaller than the reference power limit.
The reference power is determined by a product of a charging limiting current or a discharging limiting current of the energy storage system, which is constant, and a direct current voltage of the energy storage system, which varies according to a state of charge of the energy storage system.
And adjusting the operation of the microgrid through a virtual synchronous machine control strategy or a droop control strategy.
An aspect of the present disclosure provides a control method of a microgrid, the control method including: limiting the power of the energy storage system according to a reference power of the energy storage system of the microgrid, wherein the reference power is determined by the product of a charging limiting current or a discharging limiting current of the energy storage system and a direct current voltage of the energy storage system, wherein the charging limiting current or the discharging limiting current is constant, and the direct current voltage changes according to the state of charge of the energy storage system.
An aspect of the present disclosure provides a computer-readable storage medium storing a computer program, characterized in that the computer program, when executed by a processor, implements the control method of a microgrid as described above.
An aspect of the present disclosure provides a computer device, the computer device including: a processor; a memory storing a computer program which, when executed by the processor, implements the method of controlling a microgrid as described above.
Drawings
The above and other aspects, features and advantages of the present disclosure will be more clearly understood from the following description taken in conjunction with the accompanying drawings in which:
fig. 1 is a block diagram of a microgrid energy storage virtual synchronous machine control strategy according to an embodiment of the present disclosure;
FIG. 2 is a block diagram of off-grid constant voltage control of an energy storage battery control strategy according to an embodiment of the present disclosure;
FIG. 3 is a block diagram of grid-tied constant voltage control of an energy storage battery control strategy according to an embodiment of the present disclosure;
fig. 4 is a block diagram of grid-tied constant current control of an energy storage battery control strategy according to an embodiment of the disclosure;
fig. 5 is a block diagram of a microgrid droop control strategy according to an embodiment of the present disclosure; and
fig. 6 is a block diagram of a control method of a microgrid according to an embodiment of the present disclosure.
Detailed Description
The following detailed description is provided to help obtain a thorough understanding of the methods, devices, and/or systems described herein. However, various variations, modifications, and equivalents of the methods, apparatus, and/or systems described herein will be apparent to those skilled in the art upon reading the disclosure of this application. For example, the order of operations described herein is merely an example, which is not limited to the order set forth herein, but rather, may be changed in addition to operations that must occur in a particular order, as will be apparent upon an understanding of the present disclosure. Moreover, descriptions of features known in the art may be omitted for the sake of clarity and conciseness. In order that those skilled in the art will better understand the disclosure, specific embodiments thereof are described below in detail with reference to the accompanying drawings.
Definition of technical terms
Virtual synchronous machine: through simulating electromechanical transient characteristics such as inertia, internal potential and the like of the synchronous machine, the power and voltage operation external characteristics of the port are similar to those of a power electronic converter system or equipment of the synchronous machine.
Grid connection mode: the method refers to a mode that systems such as a power supply, a load and an energy storage system in a microgrid are connected with a large power grid for operation.
And (3) off-grid operation: the method is a mode that systems such as a power supply, a load and energy storage in a microgrid are disconnected from a large power grid to operate, and the microgrid provides voltage and frequency support.
And off-network seamless switching: the method refers to that the micro-grid is switched from a grid-connected mode to an off-grid mode or from the off-grid mode to the grid-connected mode, and the voltage and the frequency are kept stable and are not powered off in the switching process.
Constant voltage control of the energy storage battery: the energy storage battery controls charging/discharging of the battery at a constant direct current voltage when the battery SOC is high/low.
Energy storage battery current-limiting charge/discharge control: the energy storage battery limits the current of the battery or performs charge/discharge control in a constant direct current mode in the case where the direct current exceeds the charge/discharge limit current.
An embodiment in accordance with the present disclosure provides a microgrid comprising an energy storage system and a controller. The energy storage system may have an energy storage battery. The controller may be configured to control the energy storage system to perform dc constant voltage charging in response to a dc voltage of the energy storage system exceeding an upper threshold voltage, and to perform dc constant voltage discharging in response to the dc voltage of the energy storage system being lower than a lower threshold voltage. The controller may be implemented in the form of a DSP program or an analog circuit, etc., but is not limited thereto. The controller may implement various energy storage battery control strategies.
Fig. 1 is a block diagram of a microgrid energy storage virtual synchronous machine control strategy according to an embodiment of the present disclosure.
Feedback current i measured at output end of energy storage converter in energy storage system od And i oq And a voltage u od And u oq Obtaining active power P and reactive power Q, reactive power Q and reference reactive power Q through power calculation processing and filtering processing of a filter ref The voltage E is obtained after the deviation is applied with the reactive droop coefficient n Q Voltage E of Q And a reference voltage E 0 And superposing to obtain the voltage reference E. Frequency omega measured by output end of energy storage converter and reference frequency omega 0 After the deviation applies an active droop coefficient m, the active droop coefficient m is compared with an active power P and a reference active power P ref The offset is used as an input to the virtual synchronous machine, which outputs Δ ω. Δ ω and the frequency adjustment Δ ω' and the reference frequency ω 0 The deviation being integrated to obtain the networkThe voltage phase θ. The voltage phase theta and the voltage reference E are subjected to coordinate transformation to obtain a voltage E under a rotating coordinate system d And voltage E q For voltage current dual loop control. According to the embodiment of the disclosure, an energy storage battery control strategy based on a virtual synchronous machine is provided, and the output power of the energy storage battery is adjusted by providing a frequency adjustment amount Δ ω' through the energy storage battery control strategy. Embodiments of adding an energy storage battery control strategy based on microgrid energy storage virtual synchronous machine control will be described below.
The embodiment of the disclosure provides a constant voltage control method for a micro-grid energy storage virtual synchronous machine, which is characterized in that under the condition that a plurality of energy storage systems in a micro-grid operate in parallel, when a certain energy storage system reaches an upper limit threshold voltage/a lower limit threshold voltage, the energy storage system automatically reduces power to keep constant voltage charging/discharging operation of a battery so as to avoid shutdown. When the battery is switched from constant voltage charging to discharging (or from constant voltage discharging to charging), the battery automatically shifts to a normal operation state without shutdown in the middle.
Fig. 2 is a block diagram of off-grid constant voltage control of an energy storage battery control strategy according to an embodiment of the present disclosure.
In the case where the microgrid is operating off-grid and multiple energy storage systems are included in the microgrid, there may be differences in the states of charge (SOCs) of the multiple energy storage systems. Referring to FIG. 2, udc upLim For the upper voltage limit of the energy storage cell, udc downLim Is the lower limit voltage of the energy storage battery, udc is the real-time voltage of the energy storage battery, and P is the active power of the battery (P)<0 denotes charging of the energy storage battery, P>0 represents energy storage system discharge). When (Udc > Udc) downLim + Δ U) and (Udc < Udc) upLim - Δ U), the off-grid constant voltage control of the energy storage battery control strategy is not output, the charging/discharging power of the energy storage system is distributed according to the droop coefficient, and Δ ω' output is 0.Δ U is the set threshold voltage, udc downLim + Δ U may be referred to as the lower threshold voltage, udc upLim The- Δ U may be referred to as an upper threshold voltage. At this time, the energy storage system operates in a normal mode.
When at least one of the plurality of energy storage cells satisfies (Udc > Udc) upLim - Δ U) and P<0, i.e. the energy storage battery will chargeWhen the voltage reaches the upper limit voltage, the off-grid constant voltage control of the energy storage battery control strategy adjusts the frequency adjustment quantity delta omega ', and the frequency adjustment quantity delta omega' can realize the adjustment of the voltage phase so as to keep the energy storage battery in constant voltage charging operation. At this time, the charging power of the energy storage system is reduced to follow the frequency adjustment amount Δ ω ', and Δ ω' is the output of the dc voltage loop PI of the energy storage battery. At this time, the energy storage system operates in a direct current constant voltage charging mode.
When at least one of the plurality of energy storage cells satisfies (Udc < Udc) downLim + Δ U) and P>And 0, namely when the energy storage battery is discharged to the lower limit voltage, the off-grid constant voltage control of the energy storage battery control strategy adjusts the frequency adjustment quantity delta omega ', and the frequency adjustment quantity delta omega' can realize the adjustment of the voltage phase so as to keep the energy storage battery in constant voltage discharge operation. At this time, the discharge power of the energy storage system is reduced to follow the frequency adjustment amount Δ ω ', and Δ ω' is the output of the dc voltage loop PI of the energy storage battery. At this time, the energy storage system operates in a direct current constant voltage discharge mode.
According to the off-grid constant voltage control of the energy storage battery control strategy of the embodiment of the disclosure, the off-grid constant voltage control can automatically operate in a normal mode and a constant voltage charging/discharging mode according to the characteristics and state parameters of the battery in the operation process of the micro-grid, the overvoltage or undervoltage of the energy storage battery in the isolated island operation of the micro-grid can be avoided, and the adaptability of the isolated island operation of the micro-grid and the service efficiency of the battery are improved.
Fig. 3 is a block diagram of grid-tied constant voltage control of an energy storage battery control strategy according to an embodiment of the disclosure.
Referring to fig. 3, grid-tied constant voltage control of the energy storage battery control strategy involves constant voltage charge control, constant voltage discharge control, and power clipping, where P set Taking a negative value P for a set power limit value, also called reference power or reference power, in the charging state of the energy storage battery set Less than 0, the electric power flows from the micro-grid bus to the energy storage battery, and the positive value P is taken out when the energy storage battery is in a discharge state set And > 0, electric power flows from the energy storage battery to the microgrid bus. Udc upLim For the upper voltage limit of the energy storage cell, udc downLim Lower limit voltage of the energy storage battery, U dc Is the real-time voltage of the energy storage battery. While storingAnd when the deviation between the direct current voltage of the energy system and the upper limit threshold voltage or the lower limit threshold voltage is larger than the reference power limit, the power of the energy storage system is limited according to the reference power of the energy storage system.
In the charging state of the energy storage battery P set Is negative, udc upLim And U dc The difference is output through a direct current voltage loop PI regulator, the output result passes through a power amplitude limiting unit, the upper limit value of the power amplitude limiting unit is 0 (no charging), and the lower limit value is P set When the energy storage battery is low in electric quantity and does not enter a constant voltage charging mode, the output value of the direct current voltage loop PI regulator is smaller than the output value of the power amplitude limiting unit (the power is expressed as a negative value during charging and is finally limited by the power with a smaller absolute value), so that the charging power is mainly limited by the power amplitude limiting unit, and the charging power is limited to the upper limit charging power P set And at the moment, the micro-grid energy storage virtual synchronous machine operates in a constant power charging mode.
When the voltage of the energy storage battery rises and approaches the upper limit voltage, namely the deviation between the direct current voltage of the energy storage system and the upper limit threshold voltage is smaller than the reference power limit, the output of the direct current voltage loop PI regulator rises to be larger than P set And then, the charging power is limited by the output of the direct-current voltage loop PI regulator, and at the moment, the micro-grid energy storage virtual synchronous machine adjusts the frequency adjustment quantity delta omega ', and the frequency adjustment quantity delta omega' can realize the adjustment of the voltage phase so as to enable the energy storage system to operate in a direct-current constant-voltage charging mode.
P in the discharged state of the energy storage battery set Is positive, udc downLim And U dc The difference is output through a direct current voltage loop PI regulator, the output result passes through a power amplitude limiting unit, and the upper limit value of the power amplitude limiting unit is P set (upper limit discharge power), the lower limit is 0 (no discharge), when the energy storage battery has high electric quantity and does not enter the constant voltage discharge mode, the output of the direct current voltage loop PI regulator is larger than the output value P of the power amplitude limiting unit set (the power at discharge is shown as a positive value and is also limited by the power with a smaller absolute value), so the charging power is limited mainly by the power limiting unit and the discharging power is limited to discharge at the upper limitPower P set And at the moment, the micro-grid energy storage virtual synchronous machine operates in a constant power discharge mode.
As the voltage of the energy storage battery decreases, when the voltage approaches the lower limit voltage, that is, the deviation between the dc voltage of the energy storage system and the lower limit threshold voltage is smaller than the reference power limit, the output of the dc voltage loop PI regulator decreases to be smaller than P set And then, the discharge power is limited by the output of the direct-current voltage loop PI regulator, and at the moment, the micro-grid energy storage virtual synchronous machine adjusts the frequency adjustment quantity delta omega ', and the frequency adjustment quantity delta omega' can realize the adjustment of the voltage phase so that the energy storage system operates in a direct-current constant-voltage discharge mode.
The direct current voltage loop PI regulator outputs reference power through a selection switch after being regulated by a power amplitude limiting unit, the reference power is input into a power loop, the deviation delta P between the reference power and the actual power P is output through the power loop PI regulator, the output result of the power loop PI regulator obtains a frequency regulating quantity delta omega 'through the selection switch, and the frequency regulating quantity delta omega' is applied to virtual synchronous machine control.
According to the grid-connected constant voltage control of the energy storage battery control strategy of the embodiment of the disclosure, on the basis of the control of the virtual synchronous machine, the power loop and the direct current voltage loop are added, so that the indirect control of the power and the voltage of the battery can be realized, in the whole charging/discharging process, the constant power or constant voltage charging/discharging control can be automatically selected according to the characteristics and the operation parameters of the battery, and the working mode of the battery is not independently set. The voltage and current double-loop control and the virtual synchronous machine control can realize the on-grid and off-grid seamless switching without mode switching. The power is accurately controlled and the constant voltage of the energy storage battery is controlled under the grid-connected condition, and the two control modes can be automatically switched according to the battery state.
Fig. 4 is a block diagram of grid-tied constant current control of an energy storage battery control strategy according to an embodiment of the disclosure.
Referring to fig. 4, grid-tied current limiting control of the energy storage battery control strategy involves constant current charging control, constant current discharging control, and power control, where P set Is the set power limit value. Pdc (time dependent cell cycle) Chargelim Limiting power for charging an energy storage battery，Pdc Dishargelim For limiting the power for discharging the energy storage battery, see equations (1) and (2).
Pdc Dishargelim＝ Idc Dishargelim ×U dc (1)
Pdc Chargelim＝ Idc Chargelim ×U dc (2)
Wherein Idc Dishargelim For charging the limiting current or the charging current in the constant current mode, idc is set according to the characteristic parameters of the energy storage battery Dishargelim Is a positive value; idc Chargelim For limiting the current for discharging or for discharging the current in constant current mode, according to the characteristic parameter setting of the energy storage battery, idc Chargelim Is a negative value; u shape dc Is the real-time voltage of the energy storage battery. The charging limiting power and the discharging limiting power of the energy storage battery can be used as the reference power of grid-connected constant current control of the energy storage system.
Grid-connected constant current control is indirectly realized by limiting charging/discharging power, and the power limitation is changed along with the real-time change of direct current voltage. DC voltage U of energy storage battery dc When the set power P is reduced along with the discharge of the energy storage battery set ＞Pdc Dishargelim At the time, the discharge power of the energy storage battery is subjected to Pdc Dishargelim The restriction functions as current limiting or constant current control. DC voltage U of energy storage battery dc When the set power P is increased along with the charging of the energy storage battery set ＜Pdc Chargelim (the power is negative during charging and is limited by the power with small absolute value), the charging power of the energy storage battery is subjected to Pdc Chargelim The restriction functions as current limiting or constant current control.
Set power P set And after the regulation of the power amplitude limiting unit, outputting the reference power through a selection switch, inputting the reference power into a power loop, outputting the deviation delta P between the reference power and the actual power P through a power loop PI regulator, obtaining a frequency regulation quantity delta omega 'from the output result of the power loop PI regulator through the selection switch, and applying the frequency regulation quantity delta omega' to the virtual synchronous machine control.
According to the grid-connected constant current control of the energy storage battery control strategy of the embodiment of the disclosure, constant power or constant current charging/discharging control can be automatically selected according to the characteristic parameters of the battery, and the working mode of the energy storage battery can not be independently set in the whole charging/discharging process. The power is accurately controlled and the current-limiting control of the energy storage battery is realized under the grid-connected condition, and the two control modes can be automatically switched according to the battery state.
Fig. 5 is a block diagram of a microgrid droop control strategy according to an embodiment of the present disclosure.
Referring to fig. 5, a feedback current i measured at an output terminal of an energy storage converter in an energy storage system od And i oq And a voltage u od And u oq Obtaining active power P and reactive power Q through power calculation processing and filtering processing of a filter, and obtaining the reactive power Q and reference reactive power Q ref The voltage E is obtained after the reactive droop coefficient n is applied to the deviation Q Voltage E of Q And a reference voltage E 0 And superposing to obtain the voltage reference E. Active power P and reference active power P ref The frequency deviation Δ ω is obtained by applying the active droop coefficient m to the deviation Δ P. Frequency deviation delta omega, frequency adjustment quantity delta omega' and reference frequency omega 0 The voltage phase theta is obtained by integrating the superposition of (a) and (b). The voltage phase theta and the voltage reference E are subjected to coordinate transformation to obtain a voltage E under a rotating coordinate system d And voltage E q For voltage current dual loop control. An energy storage battery control strategy based on the droop control strategy is also provided according to the embodiment of the disclosure, and the output power of the energy storage battery is adjusted by providing the frequency adjustment amount delta omega' through the energy storage battery control strategy.
Fig. 6 is a block diagram of a control method of a microgrid according to an embodiment of the present disclosure.
Referring to fig. 6, in operation 601, a direct current voltage of an energy storage system is compared with an upper threshold voltage or a lower threshold voltage; in operation 602, in response to a direct current voltage of an energy storage system of a microgrid exceeding an upper threshold voltage, controlling the energy storage system to perform direct current constant voltage charging; in operation 603, the energy storage system is controlled to perform a direct current constant voltage discharge in response to the direct current voltage of the energy storage system being lower than a lower threshold voltage.
A control method of a microgrid according to a modified example of an embodiment of the present disclosure may include: limiting the power of the energy storage system according to a reference power of the energy storage system of the microgrid, wherein the reference power is determined by the product of a charging limiting current or a discharging limiting current of the energy storage system and a direct current voltage of the energy storage system, wherein the charging limiting current or the discharging limiting current is constant, and the direct current voltage changes according to the state of charge of the energy storage system. The control method of the microgrid according to a modified example of the embodiment of the present disclosure may be implemented in combination with the control method of the microgrid described with reference to fig. 6, or may be implemented separately.
There is also provided in accordance with an exemplary embodiment of the present disclosure a microgrid system. The microgrid system may include at least one of a wind power generator, a photovoltaic generator, a diesel generator, and an energy storage system, and may further include a harmonic detection and protection device for power electronics as described above. The control method of the microgrid, which is executed by the harmonic detection and protection device of the power electronic equipment, can avoid the damage of electrical elements caused by the voltage resonance output by the power electronic equipment in the microgrid.
There is also provided, in accordance with an exemplary embodiment of the present disclosure, a computer-readable storage medium storing a computer program. The computer readable storage medium stores a computer program that, when executed by a processor, causes the processor to execute a control method of a microgrid according to the present disclosure. The computer readable recording medium is any data storage device that can store data read by a computer system. Examples of the computer-readable recording medium include: read-only memory, random access memory, compact disc read-only memory, magnetic tape, floppy disk, optical data storage device, and carrier wave (such as data transmission through the internet via a wired or wireless transmission path).
A computer device is also provided according to an exemplary embodiment of the present disclosure. The computer device includes a processor and a memory. The memory is for storing a computer program. The computer program is executed by a processor, causing the processor to execute a computer program of a control method of a microgrid according to the present disclosure.
Although a few embodiments have been shown and described, it would be appreciated by those skilled in the art that changes may be made in these embodiments without departing from the principles and spirit of the disclosure, the scope of which is defined in the claims and their equivalents.
Claims (14)
1. A microgrid characterized in that it comprises:
an energy storage system; and
a controller configured to: and controlling the energy storage system to perform direct-current constant-voltage charging in response to the fact that the direct-current voltage of the energy storage system exceeds the upper-limit threshold voltage, and controlling the energy storage system to perform direct-current constant-voltage discharging in response to the fact that the direct-current voltage of the energy storage system is lower than the lower-limit threshold voltage.
2. The microgrid of claim 1, wherein in a case where the microgrid is in an islanded mode and the microgrid comprises a plurality of energy storage systems, the controller is further configured to:
when the direct-current voltage of the energy storage system is in the range between the upper limit threshold voltage and the lower limit threshold voltage, distributing the power of the energy storage system according to the droop coefficient;
performing a direct current constant voltage charging by adjusting a voltage phase of at least one energy storage system of the plurality of energy storage systems in response to a direct current voltage of the at least one energy storage system exceeding an upper threshold voltage; and is
Performing a direct current constant voltage discharge by adjusting a voltage phase of at least one of the plurality of energy storage systems in response to the direct current voltage of the at least one energy storage system being below a lower threshold voltage.
3. The microgrid of claim 1, wherein, with the microgrid in a grid-tie mode, the controller is further configured to:
when the deviation between the direct current voltage of the energy storage system and the upper limit threshold voltage or the lower limit threshold voltage exceeds the reference power limit, the power of the energy storage system is limited according to the reference power of the energy storage system,
controlling an energy storage system to perform DC constant voltage charging by adjusting a voltage phase of the energy storage system in response to a deviation between a DC voltage of the energy storage system and an upper limit threshold voltage being less than a reference power limit, and
and controlling the energy storage system to perform direct-current constant-voltage discharge by adjusting the voltage phase of the energy storage system in response to the deviation between the direct-current voltage of the energy storage system and the lower-limit threshold voltage being smaller than the reference power limit.
4. The microgrid of claim 3 wherein the reference power is determined by a product of a charge-limited current or a discharge-limited current of the energy storage system, which is constant, and a dc voltage of the energy storage system, which varies according to a state of charge of the energy storage system.
5. The microgrid of any of claims 1-4, wherein the controller regulates operation of the microgrid via a virtual synchronous machine control strategy or a droop control strategy.
6. A microgrid characterized in that it comprises:
an energy storage system; and
a controller configured to: the power of the energy storage system is limited according to the reference power of the energy storage system,
the reference power is determined by the product of a charging limiting current or a discharging limiting current of the energy storage system and a direct current voltage of the energy storage system, wherein the charging limiting current or the discharging limiting current is constant, and the direct current voltage changes according to the state of charge of the energy storage system.
7. A control method of a microgrid, characterized in that the control method comprises:
and controlling the energy storage system to execute direct current constant voltage charging in response to the fact that the direct current voltage of the energy storage system of the microgrid exceeds an upper limit threshold voltage, and controlling the energy storage system to execute direct current constant voltage discharging in response to the fact that the direct current voltage of the energy storage system is lower than a lower limit threshold voltage.
8. A control method according to claim 7, wherein in the case where the microgrid is in islanding mode and the microgrid comprises a plurality of energy storage systems, the control method further comprises:
when the direct-current voltage of the energy storage system is in the range between the upper limit threshold voltage and the lower limit threshold voltage, distributing the power of the energy storage system according to the droop coefficient;
performing a direct current constant voltage charging by adjusting a voltage phase of at least one energy storage system of the plurality of energy storage systems in response to a direct current voltage of the at least one energy storage system exceeding an upper threshold voltage; and is provided with
In response to the DC voltage of at least one of the plurality of energy storage systems being below a lower threshold voltage, performing a DC constant voltage discharge by adjusting a voltage phase of the at least one energy storage system.
9. The control method according to claim 7, wherein in a case where the microgrid is in a grid-connected mode, the control method further comprises:
when the deviation between the direct current voltage of the energy storage system and the upper limit threshold voltage or the lower limit threshold voltage exceeds the reference power limit, the power of the energy storage system is limited according to the reference power of the energy storage system,
controlling an energy storage system to perform DC constant voltage charging by adjusting a voltage phase of the energy storage system in response to a deviation between a DC voltage of the energy storage system and an upper limit threshold voltage being less than a reference power limit, and
and controlling the energy storage system to perform direct current constant voltage discharge by adjusting the voltage phase of the energy storage system in response to the deviation between the direct current voltage of the energy storage system and the lower limit threshold voltage being less than the reference power limit.
10. The control method according to claim 9, wherein the reference power is determined by a product of a charge-limited current or a discharge-limited current of the energy storage system, which is constant, and a direct-current voltage of the energy storage system, which varies according to a state of charge of the energy storage system.
11. The control method according to any one of claims 7-10, wherein the operation of the microgrid is regulated by a virtual synchronous machine control strategy or a droop control strategy.
12. A control method of a microgrid, characterized in that the control method comprises:
limiting the power of the energy storage system according to the reference power of the energy storage system of the microgrid,
the reference power is determined by the product of a charging limiting current or a discharging limiting current of the energy storage system and a direct current voltage of the energy storage system, wherein the charging limiting current or the discharging limiting current is constant, and the direct current voltage changes according to the state of charge of the energy storage system.
13. A computer-readable storage medium, in which a computer program is stored which, when being executed by a processor, carries out a method for controlling a microgrid according to any one of claims 7 to 12.
14. A computer device, characterized in that the computer device comprises:
a processor;
a memory storing a computer program which, when executed by the processor, implements the microgrid control method according to any one of claims 7 to 12.
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