CN110474354B - Micro-grid island operation mode coordination control method for lithium-containing battery and super capacitor - Google Patents
Micro-grid island operation mode coordination control method for lithium-containing battery and super capacitor Download PDFInfo
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- WHXSMMKQMYFTQS-UHFFFAOYSA-N Lithium Chemical compound [Li] WHXSMMKQMYFTQS-UHFFFAOYSA-N 0.000 title claims abstract description 142
- 229910052744 lithium Inorganic materials 0.000 title claims abstract description 142
- 239000003990 capacitor Substances 0.000 title claims abstract description 120
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- 238000004146 energy storage Methods 0.000 claims abstract description 111
- 238000010248 power generation Methods 0.000 claims abstract description 74
- 238000007599 discharging Methods 0.000 claims abstract description 32
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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
- 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
- H02J7/345—Parallel operation in networks using both storage and other dc sources, e.g. providing buffering using capacitors as storage or buffering devices
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- 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
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- 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
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- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
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Abstract
The invention discloses a coordination control method for an island operation mode of a micro-grid containing a lithium battery and a super capacitor. And the micro-grid coordination controller determines a coordination control instruction and issues the coordination control instruction to the photovoltaic power generation local controller and the combined energy storage system local controller for power tracking control, so that coordination control of the photovoltaic power generation system and the combined energy storage system is realized. The super capacitor has the advantages of high power density, high response speed and almost unlimited charging and discharging times, so that high-frequency and small-amplitude fluctuation of power is balanced, and voltage and frequency references of a micro-grid system are provided; the characteristics of large energy density and limited charging and discharging times of the lithium battery are utilized, and the low-frequency power can be effectively balanced.
Description
Technical Field
The invention relates to a coordination control method for a micro-grid island operation mode of a lithium-containing battery and a super capacitor, belonging to the technical field of new energy power generation.
Background
The primary task of a coordination control strategy of the micro-grid operating in an island mode is to ensure the stability of the micro-grid and the power supply quality and reliability of important loads and avoid the influence of new energy power fluctuation on the micro-grid; when the microgrid isolated island operation adopting single energy storage is operated, the phenomenon of overcharge and overdischarge is easily caused by the unbalanced influence of new energy power generation and load supply and demand relationship, and the limitation of a single energy storage system cannot meet the diversified electric energy requirements. After the hybrid energy storage is adopted, particularly for a micro-grid containing a lithium battery and a super capacitor, the advantages of different energy storages need to be fully exerted, so that the advantages of different energy storages can be greatly exerted, the overcharge and overdischarge are avoided, and the stability of the system and the service life of the energy storage are greatly prolonged; and thirdly, on the premise of ensuring safety and preventing the energy storage element from being damaged, the island operation time of the micro-grid is ensured to be prolonged as much as possible so as to reserve sufficient time for grid recovery.
Therefore, how to reasonably distribute various requirements such as power change, load fluctuation and micro-grid voltage frequency establishment under different time scales in an island operation mode better by means of different energy storage characteristics is a problem to be solved.
Disclosure of Invention
The invention aims to solve the problems that the advantages of a lithium battery and a super capacitor are not fully exerted and the stability of a microgrid is difficult to guarantee in a microgrid isolated island operation mode coordination control method of the lithium battery and the super capacitor in the prior art, and provides the microgrid isolated island operation mode coordination control method of the lithium battery and the super capacitor.
The super capacitor has the advantages of high power density, high response speed and almost unlimited charging and discharging times, decomposition control is carried out on the compensation power of the combined energy storage system, the super capacitor is used for balancing high-frequency and small-amplitude fluctuation of the power, and voltage and frequency reference of the micro-grid system is provided. The lithium battery has the characteristics of high energy density and limited charging and discharging times, and is mainly used for balancing low-frequency power in a micro-grid.
In order to achieve the technical purpose, the invention adopts the following technical scheme:
in one aspect, the invention provides a coordination control method for an island operation mode of a micro-grid containing a lithium battery and a super capacitor, wherein the micro-grid comprises a photovoltaic power generation system, a combined energy storage system, loads (including important loads and common loads), a micro-grid coordination controller, a photovoltaic power generation local controller, a combined energy storage system local controller, a plurality of switches and the like. The combined energy storage system consists of a lithium battery energy storage unit and a super capacitor energy storage unit. The lithium battery energy storage unit consists of a lithium battery, a bidirectional DC/DC converter 1 and a bidirectional DC/AC converter 1; the lithium battery is connected with the bidirectional DC/DC converter 1, the bidirectional DC/DC converter 1 is connected with the bidirectional DC/AC converter 1, and the bidirectional DC/DC converter 1 is connected to a public alternating current bus in series through a switch K1; the super capacitor energy storage unit consists of a super capacitor, a bidirectional DC/DC converter 2 and a bidirectional DC/AC converter 2; the super capacitor is connected with the bidirectional DC/DC converter 2, the bidirectional DC/DC converter 2 is connected with the bidirectional DC/AC converter 2, and the super capacitor is connected to a public alternating current bus in series through a switch K2; the photovoltaic power generation system is connected with the photovoltaic grid-connected inverter and is connected to the public alternating current bus in series through a switch K3; the important loads are connected in series to the public alternating current bus through a switch K4, and the common loads are connected in series to the public alternating current bus through a switch K5.
SOCbFor the charging and discharging depth and the electric quantity of the lithium battery, a state of charge, UdscThe charge-discharge depth of the super capacitor is represented by terminal voltage, and the difference active power delta P is an actual output power signal P of the micro-grid loadloadOutput power P of photovoltaic power generation systemVThe difference, i.e. (Δ P ═ P)load-PV)，SOCbIs the state of charge, SOC, of the lithium batteryb_maxIs the maximum value of the charge, SOC, of the lithium batteryb_minIs the minimum value of the state of charge, P, of the lithium batteryb_refIs the active power reference value, P, of the lithium batteryb_discIs the discharge power of a lithium battery, Pb_cFor charging power of lithium batteries, Udsc_maxMaximum value of terminal voltage for charging and discharging depth of super capacitor, Udsc_minMinimum value of terminal voltage for charging and discharging depth of super capacitor, PscFor power compensation values, P, of supercapacitors in energy storage control systemssc_highCompensating the reference value of the power component, P, for the high frequency requirement of the supercapacitorsc_discIs the discharge power of the supercapacitor, Psc_cCharging power for the super capacitor, Psc_refAnd the reference value of the active power of the super capacitor is obtained.
The photovoltaic power generation system is controlled by photovoltaic power generationAn electrical local controller, the combined energy storage system being controlled by the combined energy storage system local controller; the microgrid coordinated controller outputs a power signal P according to the actual load output power of the microgridloadLoad reactive power QloadOutput power P of photovoltaic power generation systemVAnd state of charge SOC of the lithium batterybAnd the charging and discharging depth U of the super capacitordscDetermining a coordination control instruction of the photovoltaic power generation system and the combined energy storage system, and respectively issuing the control instruction to a photovoltaic power generation local controller and a combined energy storage system local controller;
the photovoltaic power generation local controller and the combined energy storage system local controller respectively control the converters of the respective systems to perform power tracking control according to the received control instruction, so that coordinated control of the photovoltaic power generation system and the combined energy storage system is realized.
Further, the method for determining the coordination control instruction of the photovoltaic power generation system and the combined energy storage system by the micro-grid coordination controller is as follows:
1) determining actual output power signal P of micro-grid loadloadOutput power P of photovoltaic power generation systemVThe difference active power difference value delta P; and the combined energy storage system judges whether the absorption or the emission power is generated according to the difference active power delta P so as to ensure the power balance of the micro-grid system.
2) For difference active power difference value delta P and load reactive power QloadAnd decomposing to obtain compensation power components of the lithium battery and the super capacitor, distributing high-frequency power to the super capacitor, and distributing low-frequency power to the lithium battery so as to give full play to the advantages of the super capacitor and realize accurate power tracking.
3) Judging the state of charge SOC of a lithium batterybAnd the charging and discharging depth U of the super capacitordscAnd controlling the operation states of the lithium battery and the super capacitor by combining the sign of the delta P.
On the basis of the above technical solution, further, the method of step 2) includes:
the method comprises the following steps: decomposing the difference value delta P by using a low-pass filter to obtain a reference value P of the low-frequency compensation power component of the lithium batteryb_lowThen the difference Δ P is subtractedRemoving Pb_lowObtaining the reference value P of the high-frequency compensation power component of the super capacitorsc_highAs shown in the following formula;
step two: since the photovoltaic power generation system does not generate reactive power, the reactive power required by the load is all provided by the combined energy storage system. Using a low-pass filter to convert the reactive power Q of the loadloadDecomposing to obtain the reference value Q of the low-frequency compensation reactive power component of the lithium batteryb_lowReuse of the reactive power Q of the loadloadSubtracting the reference value Q of the low-frequency compensation reactive power component of the lithium batteryb_lowObtaining a reference value Q of a high-frequency reactive power component to be compensated of the super capacitorsc_highAs shown in the following formula;
where s integral function, T time step, here denotes the integral function and the time compensation of the filtering order 1 low-pass filter.
Further, the method for determining the parameters of the low-pass filter is as follows: the maximum service life N years and the maximum allowable charging and discharging times M of the lithium batterymaxThen, the allowable charging and discharging times of the lithium battery per day are
When the working time of the photovoltaic power generation system is from T1 to T2, the lithium battery is used for balancing the frequency of photovoltaic power fluctuation
Therefore, the power compensation frequency critical value of the lithium battery and the super capacitor is set. The frequency f determined here is finally the time step T, which is 1/f, so as to design the parameters of the low-pass filter to ensure the maximum service life and the optimal number of charges of the lithium battery.
Further, the step 3) comprises judging the SOC of the lithium batterybAnd U of super capacitordscThe operating states of the lithium battery and the super capacitor are controlled by combining the delta P symbol, the occurrence of the energy storage deep charging and discharging condition is avoided, a larger charging margin is kept, the energy storage loss is reduced, and the service life of the super capacitor is prolonged.
(1) When the delta P is less than 0, the photovoltaic power generation power is greater than the load power, the energy storage device is required to absorb redundant power, and the charge state of the energy storage device is judged:
1-1) when SOCb<SOCb_maxAnd U isdsc<Udsc_maxWhen it is, order Psc＝Psc_high，Pb_ref＝Pb_low。
1-2) when SOCb<SOCb_maxAnd U isdsc≥Udsc_maxAnd setting the super capacitor to charge the lithium battery when the state of the super capacitor exceeds the upper limit value, and enabling P to charge the lithium battery at the momentsc＝Psc_high-Psc_disc，Pb_ref＝Pb_low+Psc_disc。
1-3) when SOCb≥SOCb_maxAnd U isdsc<Udsc_maxAnd when the state of the lithium battery exceeds the upper limit value, the lithium battery is set to charge the super capacitor, and P is made at the momentsc＝Psc_high+Pb_disc，Pb_ref＝Pb_low-Pb_disc。
1-4) SOC asb≥SOCb_maxAnd U isdsc≥Udsc_maxAt the moment, the MPPT mode of the photovoltaic power generation system is switched to the AGC mode to limit the power generation amount of the photovoltaic power generation system, so that the delta P>0, the load power is preferentially selected from lithium battery and super powerProvided, go to step 2-5).
1-5) when SOCb≤SOCb_minAnd U isdsc≤Udsc_minWhen is, Psc＝Psc_high+Psc_c，Pb_ref＝Pb_low+Pb_c。
(2) When the delta P is greater than 0, the load power is greater than the photovoltaic power, the energy storage device is required to discharge to compensate the difference of active power, and the state of charge of the energy storage device is judged:
2-1) when SOCb>SOCb_minAnd U isdsc>Udsc_minWhen it is, order Psc＝Psc_high；Pb_ref＝Pb_low。
2-2) when SOCb>SOCb_minAnd U isdsc≤Udsc_minAnd setting the lithium battery to charge the super capacitor when the state of the super capacitor is at the lower limit value, and enabling P to be charged at the momentsc＝Psc_high+Psc_c，Pb_ref＝Pb_low-Psc_c。
2-3) when SOCb≤SOCb_minAnd U isdsc>Udsc_minAnd setting the super capacitor to charge the lithium battery when the lithium battery is at the lower limit value, and enabling P to be charged at the momentsc＝Psc_high-Pb_c，Pb_ref＝Pb_low+Pb_c。
2-4) SOC asb≤SOCb_minAnd U isdsc≤Udsc_minAt this time, the ordinary load needs to be cut off step by step to make Δ P<And 0, preferentially charging the combined energy storage system through the photovoltaic power generation system, so that the energy storage system is not damaged due to too low charge, and turning to the step 1-5).
2-5) SOC asb≥SOCb_maxAnd U isdsc≥Udsc_maxWhen is, Psc＝Psc_high-Psc_disc，Pb_ref＝Pb_low-Pb_disc。
(3) When Δ P is equal to 0, the photovoltaic power is equal to the load power, the energy storage system and the microgrid have no power exchange, but the energy storage devices can exchange power:
3-1) when U is presentdsc>Udsc_maxAnd SOCb<SOCb_maxWhen, or Udsc>Udsc_minAnd SOCb<SOCb_minSetting super capacitor to charge lithium battery, i.e. order Psc＝-Psc_disc，Pb_ref＝Psc_disc；
3-2) when U is presentdsc<Udsc_maxAnd SOCb>SOCb_maxWhen, or Udsc<Udsc_minAnd SOCb>SOCb_minWhen the lithium battery is set to charge the super capacitor, the P is orderedsc＝Pb_disc，Pb_ref＝-Pb_disc
3-3) when U is presentdsc≥Udsc_maxAnd SOCb≥SOCb_maxAt the moment, the MPPT mode of the photovoltaic power generation system is switched to the AGC mode to limit the power generation amount of the photovoltaic power generation system, so that the delta P>0, the load power is preferentially provided by a lithium battery and a super capacitor, and the process is switched to the step 2-5).
3-4) when U is presentdsc≤Udsc_minAnd SOCb≤SOCb_minAt this time, the ordinary load needs to be cut off step by step to make Δ P<And 0, preferentially charging the combined energy storage system through the photovoltaic power generation system, so that the energy storage system is not damaged due to too low charge, and turning to the step 1-5).
3-5) if the state of charge of the energy storage device does not meet the conditions of 3-1), 3-2), 3-3) and 3-4), the energy storage device is not charged and not discharged.
Further, the photovoltaic power generation local controller operates the MPPT state or the AGC state according to the working state issued by the micro-grid coordination controller, and the photovoltaic inverter realizes different power tracking control according to different states.
Further, the joint energy storage local controller comprises two parts of control of the bidirectional DC/DC converters 1 and 2 and control of the bidirectional DC/AC converters 1 and 2. The main objective of the control for DC/DC is to ensure that the DC side voltage is stable. And a double-loop control method of a power outer loop and a current inner loop is adopted for controlling the DC/AC converter 1, so that the low-frequency power tracking control of the lithium battery power reference value issued by the micro-grid coordination controller is realized. The DC/AC converter 2 is controlled by adopting three-loop control of tracking power grid voltage frequency control, power outer loop and current inner loop, on one hand, voltage support of an island operation micro-grid is provided, and on the other hand, high-frequency power tracking control of a super-capacitor power reference value issued by a micro-grid coordination controller is realized.
Further, the bidirectional DC/DC converter 1 and the bidirectional DC/DC converter 2 are controlled by the following method:
will give a given DC voltage UdcAnd measured DC voltage UdcSubtracting, and obtaining a direct current reference value I by the obtained difference through a PI controllerdc*；
Reference value I of direct currentdc *And subtracting the measured direct current I, forming a reference voltage signal after the obtained difference passes through a PI controller, and finally obtaining control signals of S1 and S2 in the bidirectional DC/DC converter 1 after PWM modulation.
The switching control signal in the bidirectional DC/DC converter 2 corresponds to the above-described control method.
Still further, the bidirectional DC/AC converter 1 adopts the following control steps:
the active power P of the lithium battery generated according to the control method of power decompositionb_lowAnd low-frequency reactive power Q of lithium batteryb_lowLithium battery active power reference value P as bidirectional DC/AC converter 1b_refAnd the reference value Q of the reactive power of the lithium batteryb_refReference value P of active power of lithium batteryb_refAnd the reference value Q of the reactive power of the lithium batteryb_refDecoupling to obtain a reference value I of the current inner ring 1drefAnd IqrefReference value IdrefAnd IqrefCompared with the actually measured inductive current, the obtained error signal is used as a modulation voltage signal U of the bidirectional DC/AC converter 1 through the instantaneous current loop PI controllerabc。
Still further, the bidirectional DC/AC converter 2 adopts the following control steps:
control of tracking grid voltage and frequency: real-time sampling voltage U of power gridgridGenerating the output voltage U of a bidirectional DC/AC converter by means of a three-phase-locked loop and an amplitude valuescReference value f (i.e. the support voltage of an islanded microgrid)nomSum frequency UnomComparing the two signals, and generating active power P required for maintaining the voltage and frequency stability of the microgrid by passing the obtained difference value through a PI controllermAnd reactive power Qm；
The current inner ring 2 controls: will control the generation of PmAnd the power superposition value P of the super capacitor in the energy storage control system generated by controlscAdded as a reference value P of the total bidirectional DC/AC converter 2sc_refThe generated output reactive power Q of the bidirectional DC/AC converter 2 is to be controlledmHigh-frequency compensation power component reference value Q of super capacitor for controlling productionsc_highAdding the reference value Q of the reactive power as a super-capacitor of the total bidirectional DC/AC converter 2sc_refWill have active power Psc_refAnd reactive power Qsc_refAnd decoupling to obtain a reference value of the current inner ring 2, comparing the reference value with the actually measured inductive current, and taking the obtained error signal as a modulation voltage signal of the bidirectional DC/AC converter 2 through the instantaneous current ring PI controller. The invention achieves the following beneficial technical effects:
the invention judges the SOC of the lithium batterybAnd U of super capacitordscCombined with the actual output power signal P of the load of the microgridloadOutput power P of photovoltaic power generation systemVThe running states of the lithium battery and the super capacitor are controlled by the sign of the differential active power delta P, so that the condition of deep charge and discharge of energy storage is avoided, a larger charge margin is kept, the energy storage loss is reduced, and the service life of the super capacitor is prolonged;
the differential active power delta P is decomposed, high-frequency power is distributed to the super capacitor, low-frequency power is distributed to the lithium battery, so that the advantages of the super capacitor and the lithium battery are fully exerted, and accurate power tracking is realized;
the invention utilizes the advantages that the super capacitor has high power density, high response speed and almost unlimited charging and discharging times to decompose and control the power, uses the super capacitor to balance the high frequency and small amplitude fluctuation of the power and provides the voltage and frequency reference of the micro-grid system; the characteristics of large energy density and limited charging and discharging times of the lithium battery are utilized, the power balance in the micro-grid is mainly controlled, and low-frequency power is absorbed; finally, the interference of new energy power fluctuation on the microgrid is avoided, the electric energy quality and the power supply reliability of important loads in the microgrid are realized, and the safe and stable operation of the microgrid is realized;
the invention determines a low-pass filter according to the allowable charging and discharging times of the lithium battery every day and the frequency of balancing photovoltaic power fluctuation by the lithium battery, and decomposes the actual output power signal P of the micro-grid load according to the low-pass filterloadThe difference active power delta P between the output power of the photovoltaic power generation system and the output power of the photovoltaic power generation system ensures the maximum service life and the optimal charging times of the lithium battery.
Drawings
FIG. 1 is a schematic diagram of a typical microgrid and a topology of a multi-component energy storage system in the microgrid according to the present invention;
FIG. 2 is a diagram of a topology of a DC/DC converter according to an embodiment of the present invention;
FIG. 3 is a control block diagram of a DC/DC converter in an embodiment of the present invention;
FIG. 4 is a schematic block diagram of power resolution control in an embodiment of the present invention;
FIG. 5 is a topology structure diagram of a DC/AC bidirectional converter 1 in the embodiment of the present invention;
FIG. 6 is a schematic diagram of a control of the bidirectional DC/AC converter 1 according to the embodiment of the present invention;
FIG. 7 is a topology structure diagram of a DC/AC bidirectional converter 2 in the embodiment of the present invention;
fig. 8 is a block diagram illustrating the control principle of the bidirectional DC/AC converter 2 according to the embodiment of the present invention.
Detailed Description
The invention is further described below with reference to the accompanying drawings. The following examples are only for illustrating the technical solutions of the present invention more clearly, and the protection scope of the present invention is not limited thereby.
In this embodiment, the microgrid comprises a photovoltaic power generation system, a combined energy storage system, an important load, a common load, a microgrid coordinated controller, a photovoltaic power generation local controller, a combined energy storage system local controller, a plurality of switches, and the like. The combined energy storage system consists of a lithium battery energy storage unit and a super capacitor energy storage unit. As shown in fig. 1, the lithium battery energy storage module is composed of a lithium battery, a bidirectional DC/DC converter 1, and a bidirectional DC/AC converter 1; the super capacitor energy storage module is composed of a super capacitor, a bidirectional DC/DC converter 2 and a bidirectional DC/AC converter 2. The lithium battery is converted by the bidirectional DC/DC converter 1 and the bidirectional DC/AC converter 1, the super capacitor is converted by the bidirectional DC/DC converter 2 and the bidirectional DC/AC converter 2, and a combined energy storage system formed by the two is collected to an alternating current bus and finally supplies power to the outside uniformly. The combined energy storage system uses the DC/DC converter to reduce the influence of different voltage levels on the DC side voltage input of the DC/AC converter, reduce the current ripple caused by the voltage change of the terminal in the discharging process of the stored energy, and simultaneously easily control the charging and discharging modes of the energy storage unit. The method is characterized in that: the bidirectional DC/DC converter mainly realizes the bidirectional flow of energy of the energy storage equipment and maintains the constant voltage of the direct current side; the bidirectional DC/AC converter is mainly used for realizing the source-load power balance in an island mode and the stability of the voltage and the frequency of a microgrid.
To facilitate understanding of the following, definitions of the parameters involved are given here:
SOCbfor the charging and discharging depth and the electric quantity of the lithium battery, a state of charge, UdscThe charge-discharge depth of the super capacitor is represented by terminal voltage, and the difference active power delta P is an actual output power signal P of the micro-grid loadloadOutput power P of photovoltaic power generation systemVThe difference, i.e. (Δ P ═ P)load-PV)，SOCb_maxIs the maximum value of the charge, SOC, of the lithium batteryb_minIs the minimum value of the state of charge, P, of the lithium batteryb_refIs the active power reference value, P, of the lithium batteryb_discIs the discharge power of a lithium battery, Pb_cFor charging power of lithium batteries, Udsc_maxMaximum value of terminal voltage for charging and discharging depth of super capacitor, Udsc_minMinimum value of terminal voltage for charging and discharging depth of super capacitor, PscFor power compensation values, P, of supercapacitors in energy storage control systemssc_highCompensating the reference value of the power component, P, for the high frequency requirement of the supercapacitorsc_discIs the discharge power of the supercapacitor, Psc_cCharging power for the super capacitor, Psc_refAnd the reference value of the active power of the super capacitor is obtained.
The microgrid coordinated controller is used for realizing coordinated control of the photovoltaic power generation system and the combined energy storage system, and the control process is as follows:
1) the photovoltaic power generation system preferentially operates in a Maximum Power Point Tracking (MPPT) state so as to ensure the maximum utilization rate of illumination and adjust the photovoltaic power generation power; and the combined energy storage system judges whether the absorption or the emission power is generated according to the difference active power delta P so as to ensure the power balance of the micro-grid system.
2) For difference active power delta P and load reactive power QloadAnd decomposing to obtain compensation power components of the lithium battery and the super capacitor, distributing high-frequency power to the super capacitor, and distributing low-frequency power to the lithium battery so as to give full play to the advantages of the super capacitor and realize accurate power tracking.
3) As shown in fig. 4, the decomposition control method includes:
the method comprises the following steps: low pass filter parameters are determined. Preferably, in order to ensure the maximum service life and the optimal charging times of the lithium battery, the maximum service life N years and the maximum allowable charging and discharging times M of the lithium battery are usedmaxThen, the allowable charging and discharging times of the lithium battery per day are
When the working time of the photovoltaic power generation system is from 8 hours to 18 hours, the lithium battery is used for balancing the frequency of photovoltaic power fluctuation
Therefore, the power compensation frequency critical value of the lithium battery and the super capacitor is set.
Step two: using a low-pass filter to sum the differenceDecomposing the value delta P to obtain a reference value P of the low-frequency compensation power component of the lithium batteryb_lowThen subtracting P from the difference Δ Pb_lowObtaining the reference value P of the high-frequency compensation power component of the super capacitorsc_highAs shown in the following formula;
step three: since the photovoltaic power generation system does not generate reactive power, the reactive power required by the load is all provided by the combined energy storage system. Using a low-pass filter to convert the reactive power Q of the loadloadDecomposing to obtain the reference value Q of the low-frequency compensation reactive power component of the lithium batteryb_lowReuse of the reactive power Q of the loadloadSubtracting the reference value Q of the low-frequency compensation reactive power component of the lithium batteryb_lowObtaining a reference value Q of a high-frequency reactive power component to be compensated of the super capacitorsc_highAs shown in the following formula;
4) judging SOC of lithium batterybAnd U of super capacitordscThe operating states of the lithium battery and the super capacitor are controlled by combining the delta P symbol, the occurrence of the energy storage deep charging and discharging condition is avoided, a larger charging margin is kept, the energy storage loss is reduced, and the service life of the super capacitor is prolonged.
(1) When the delta P is less than 0, the photovoltaic power generation power is greater than the load power, the energy storage device is required to absorb redundant power, and the charge state of the energy storage device is judged:
1-1) when SOCb<SOCb_maxAnd U isdsc<Udsc_maxWhen it is, order Psc＝Psc_high，Pb_ref＝Pb_low。
1-2) when SOCb<SOCb_maxAnd U isdsc≥Udsc_maxAnd setting the super capacitor to charge the lithium battery when the state of the super capacitor exceeds the upper limit value, and enabling P to charge the lithium battery at the momentsc＝Psc_high-Psc_disc，Pb_ref＝Pb_low+Psc_disc。
1-3) when SOCb≥SOCb_maxAnd U isdsc<Udsc_maxAnd when the state of the lithium battery exceeds the upper limit value, the lithium battery is set to charge the super capacitor, and P is made at the momentsc＝Psc_high+Pb_disc，Pb_ref＝Pb_low-Pb_disc。
1-4) SOC asb≥SOCb_maxAnd U isdsc≥Udsc_maxAt the moment, the MPPT mode of the photovoltaic power generation system is switched to the AGC mode to limit the power generation amount of the photovoltaic power generation system, so that the delta P>0, the load power is preferentially provided by a lithium battery and a super capacitor, and the process is switched to the step 2-5).
1-5) when SOCb≤SOCb_minAnd U isdsc≤Udsc_minWhen is, Psc＝Psc_high+Psc_c，Pb_ref＝Pb_low+Pb_c。
(2) When the delta P is greater than 0, the load power is greater than the photovoltaic power, the energy storage device is required to discharge to compensate the difference of active power, and the state of charge of the energy storage device is judged:
2-1) when SOCb>SOCb_minAnd U isdsc>Udsc_minWhen it is, order Psc＝Psc_high；Pb_ref＝Pb_low。
2-2) when SOCb>SOCb_minAnd U isdsc≤Udsc_minAnd setting the lithium battery to charge the super capacitor when the state of the super capacitor is at the lower limit value, and enabling the lithium battery to charge the super capacitorPsc＝Psc_high+Psc_c，Pb_ref＝Pb_low-Psc_c。
2-3) when SOCb≤SOCb_minAnd U isdsc>Udsc_minAnd setting the super capacitor to charge the lithium battery when the lithium battery is at the lower limit value, and enabling P to be charged at the momentsc＝Psc_high-Pb_c，Pb_ref＝Pb_low+Pb_c。
2-4) SOC asb≤SOCb_minAnd U isdsc≤Udsc_minAt this time, the ordinary load needs to be cut off step by step to make Δ P<And 0, preferentially charging the combined energy storage system through the photovoltaic power generation system, so that the energy storage system is not damaged due to too low charge, and turning to the step 1-5).
2-5) SOC asb≥SOCb_maxAnd U isdsc≥Udsc_maxWhen is, Psc＝Psc_high-Psc_disc，Pb_ref＝Pb_low-Pb_disc。
(3) When Δ P is equal to 0, the photovoltaic power is equal to the load power, the energy storage system and the microgrid have no power exchange, but the energy storage devices can exchange power:
3-1) when U is presentdsc>Udsc_maxAnd SOCb<SOCb_maxWhen, or Udsc>Udsc_minAnd SOCb<SOCb_minSetting super capacitor to charge lithium battery, i.e. order Psc＝-Psc_disc，Pb_ref＝Psc_disc；
3-2) when U is presentdsc<Udsc_maxAnd SOCb>SOCb_maxWhen, or Udsc<Udsc_minAnd SOCb>SOCb_minWhen the lithium battery is set to charge the super capacitor, the P is orderedsc＝Pb_disc，Pb_ref＝-Pb_disc
3-3) when U is presentdsc≥Udsc_maxAnd SOCb≥SOCb_maxAt the moment, the MPPT mode of the photovoltaic power generation system is switched to the AGC mode to limit the power generation amount of the photovoltaic power generation system, so that the delta P>0, the load power is preferentially provided by a lithium battery and a super capacitor, and the process is switched to the step 2-5).
3-4) when U is presentdsc≤Udsc_minAnd SOCb≤SOCb_minAt this time, the ordinary load needs to be cut off step by step to make Δ P<And 0, preferentially charging the combined energy storage system through the photovoltaic power generation system, so that the energy storage system is not damaged due to too low charge, and turning to the step 1-5).
3-5) if the state of charge of the energy storage device does not meet the conditions of 3-1), 3-2), 3-3) and 3-4), the energy storage device is not charged and not discharged.
The photovoltaic power generation local controller operates in an MPPT state or an AGC state according to the working state issued by the microgrid coordinated controller, and the photovoltaic inverter realizes different power tracking control according to different states.
The joint energy storage local controller comprises two parts of control of the bidirectional DC/DC converters 1 and 2 and control of the bidirectional DC/AC converters 1 and 2. The main objective of the control of the DC/DC is to ensure that the DC side voltage is stable. And a double-loop control method of a power outer loop and a current inner loop is adopted for controlling the DC/AC converter 1, so that the low-frequency power tracking control of the lithium battery power reference value issued by the micro-grid coordination controller is realized. The DC/AC converter 1 is controlled by adopting three-loop control including tracking power grid voltage frequency control, power outer loop and current inner loop, on one hand, voltage support of an island operation micro-grid is provided, and on the other hand, high-frequency power tracking control is performed on a super-capacitor power reference value issued by a micro-grid coordination controller.
When the micro-grid operates in an island working mode, the bidirectional DC/DC converter 1 in the lithium battery energy storage module and the bidirectional DC/DC converter 2 in the super capacitor energy storage module operate in two working modes: a charge mode and a discharge mode. In a charging mode, the converter is used as a Buck circuit and absorbs external energy to charge the stored energy; in the discharging mode, the converter is used as a Boost circuit, and the energy storage device releases energy to the outside. The topology of the DC/DC converter is shown in FIG. 2.
Fig. 3 shows a control block diagram of the bidirectional DC/DC converters 1 and 2, which employs dual-loop control of a DC voltage outer loop and a DC current inner loop.
Will give a given DC voltage UdcAnd measured DC voltage UdcSubtracting, and obtaining a direct current reference value I by the obtained difference through a PI controllerdcA first step of; reference value I of direct currentdc *And subtracting the measured direct current I, forming a reference voltage signal after the obtained difference passes through a PI controller, and finally obtaining control signals of S1 and S2 in the bidirectional DC/DC converter 1 after PWM modulation.
The switching control signal in the bidirectional DC/DC converter 2 corresponds to the above-described control method.
The voltage frequency support of the micro-grid operated in an isolated island mode is achieved through the control method of the converter, and high-frequency power tracking control is conducted according to the super-capacitor power reference value issued by the micro-grid coordination controller.
Fig. 5 shows a topology structure of the bidirectional DC/AC converter 1:
reference value P of low-frequency compensation power component of lithium battery generated by power decomposition controlb_lowAnd the reference value Q of the low-frequency compensation reactive power component of the lithium batteryb_lowLithium battery active power reference value P as bidirectional DC/AC converter 1b_refAnd the reference value Q of the reactive power of the lithium batteryb_refA 1 is to Pb_refAnd Qb_refDecoupling to obtain a reference value I of the current inner ring 1drefAnd Iqref(see I in the figure)dAnd Iq) Comparing with the actually measured inductive current, the obtained error signal is used as a modulation voltage signal U of the bidirectional DC/AC converter 1 through an instantaneous current loop PI controllerabc. The control artwork is shown in fig. 6.
Fig. 7 is a topology structure diagram of the bidirectional DC/AC converter 2, and fig. 8 is a control schematic diagram of the bidirectional DC/AC converter 2, and the control steps are as follows:
control of tracking grid voltage and frequency: real-time sampling voltage U of power gridgridGenerating the output voltage U of a bidirectional DC/AC converter by means of a three-phase-locked loop and an amplitude valuesc(alsoI.e. the support voltage of an islanded microgrid) is determinednomSum frequency UnomComparing the two signals, and generating active power P required for maintaining the voltage and frequency stability of the microgrid by passing the obtained difference value through a PI controllermAnd reactive power Qm。
The current inner ring 2 controls: will control the generation of PmAnd the power superposition value P of the super capacitor in the energy storage control system generated by controlscAdded as a reference value P of the total bidirectional DC/AC converter 2sc_refThe generated output reactive power Q of the bidirectional DC/AC converter 2 is to be controlledmHigh-frequency compensation power component reference value Q of super capacitor for controlling productionsc_highAdding the reference value Q of the reactive power as a super-capacitor of the total bidirectional DC/AC converter 2sc_refWill have active power Psc_refAnd reactive power Qsc_refAnd decoupling to obtain a reference value of the current inner ring 2, comparing the reference value with the actually measured inductive current, and taking the obtained error signal as a modulation voltage signal of the bidirectional DC/AC converter 2 through the instantaneous current ring PI controller.
The invention utilizes the advantages that the super capacitor has high power density, high response speed and almost unlimited charging and discharging times to decompose and control the power, uses the super capacitor to balance the high frequency and small amplitude fluctuation of the power and provides the voltage and frequency reference of the micro-grid system; the characteristics of large energy density and limited charging and discharging times of the lithium battery are utilized, the power balance in the micro-grid is mainly controlled, and low-frequency power is absorbed; finally, the stability of the micro-grid and the safe continuous power supply to the load are realized, the interference of new energy power fluctuation to the micro-grid is avoided, the electric energy quality and the power supply reliability of important loads in the micro-grid are finally realized, and the safe and stable operation of the micro-grid is realized.
As will be appreciated by one skilled in the art, embodiments of the present application may be provided as a method, system, or computer program product. Accordingly, the present application may take the form of an entirely hardware embodiment, an entirely software embodiment or an embodiment combining software and hardware aspects. Furthermore, the present application may take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, and the like) having computer-usable program code embodied therein.
The present application is described with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the application. It will be understood that each flow and/or block of the flow diagrams and/or block diagrams, and combinations of flows and/or blocks in the flow diagrams and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer, special purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be stored in a computer-readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer-readable memory produce an article of manufacture including instruction means which implement the function specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
While the present invention has been described with reference to the embodiments shown in the drawings, the present invention is not limited to the embodiments, which are illustrative and not restrictive, and it will be apparent to those skilled in the art that various changes and modifications can be made therein without departing from the spirit and scope of the invention as defined in the appended claims.
Claims (5)
1. The coordination control method for the micro-grid island operation mode of the lithium-containing battery and the super capacitor is characterized in that the micro-grid comprises a photovoltaic power generation system, a combined energy storage system, a load and a micro-grid coordination controller; the photovoltaic power generation system, the combined energy storage system and the load are respectively connected to a public alternating current bus through switches;
the combined energy storage system comprises a lithium battery energy storage unit and a super capacitor energy storage unit;
the lithium battery energy storage unit comprises a lithium battery, a bidirectional DC/DC converter 1 and a bidirectional DC/AC converter 1; the lithium battery is connected with the bidirectional DC/DC converter 1, and the bidirectional DC/DC converter 1 is connected with the bidirectional DC/AC converter 1;
the super capacitor energy storage unit comprises a super capacitor, a bidirectional DC/DC converter 2 and a bidirectional DC/AC converter 2; the super capacitor is connected with the bidirectional DC/DC converter 2, and the bidirectional DC/DC converter 2 is connected with the bidirectional DC/AC converter 2;
the photovoltaic power generation system is controlled by a photovoltaic power generation local controller, and the combined energy storage system is controlled by a combined energy storage system local controller; the microgrid coordinated controller outputs an active power signal P according to the actual load of the microgridloadLoad reactive power QloadOutput power P of photovoltaic power generation systemVAnd state of charge SOC of the lithium batterybAnd the charging and discharging depth U of the super capacitordscDetermining a coordination control instruction of the photovoltaic power generation system and the combined energy storage system, and respectively issuing the control instruction to a photovoltaic power generation local controller and a combined energy storage system local controller;
the photovoltaic power generation local controller and the joint energy storage system local controller respectively control the converters of the respective systems to carry out power tracking control according to the received control instructions so as to realize the coordination control of the photovoltaic power generation system and the joint energy storage system,
the method for determining the coordination control instruction of the photovoltaic power generation system and the combined energy storage system by the microgrid coordination controller comprises the following steps:
determining actual output power signal P of micro-grid loadloadOutput power P of photovoltaic power generation systemVThe expression of the difference active power Δ P is: Δ P ═ Pload-PV；
Respectively aiming at the difference active power value delta P and the load reactive power QloadDecomposing to obtain the compensation power components of the lithium battery and the super capacitor;
judging the state of charge SOC of a lithium batterybAnd the charging and discharging depth U of the super capacitordscControlling the operation states of the lithium battery and the super capacitor by combining the symbol of the delta P, specifically comprising the following steps:
(1) when the delta P is less than 0, the photovoltaic power generation power is greater than the load power, the energy storage device is required to absorb redundant power, and the charge state of the energy storage device is judged:
1-1) when SOCb<SOCb_maxAnd U isdsc<Udsc_maxWhen it is, order Psc＝Psc_high，Pb_ref＝Pb_low；
1-2) when SOCb<SOCb_maxAnd U isdsc≥Udsc_maxAnd setting the super capacitor to charge the lithium battery when the state of the super capacitor exceeds the upper limit value, and enabling P to charge the lithium battery at the momentsc＝Psc_high-Psc_disc，Pb_ref＝Pb_low+Psc_disc；
1-3) when SOCb≥SOCb_maxAnd U isdsc<Udsc_maxAnd when the state of the lithium battery exceeds the upper limit value, the lithium battery is set to charge the super capacitor, and P is made at the momentsc＝Psc_high+Pb_disc，Pb_ref＝Pb_low-Pb_disc；
1-4) SOC asb≥SOCb_maxAnd U isdsc≥Udsc_maxAt the moment, the MPPT mode of the photovoltaic power generation system is switched to the AGC mode to limit the power generation amount of the photovoltaic power generation system, so that the delta P>0, the load power is preferentially provided by a lithium battery and a super capacitor, and the step 2-5) is changed;
1-5) when SOCb≤SOCb_minAnd U isdsc≤Udsc_minWhen is, Psc＝Psc_high+Psc_c，Pb_ref＝Pb_low+Pb_c；
(2) When the delta P is greater than 0, the load power is greater than the photovoltaic power, the energy storage device is required to discharge to compensate the difference of active power, and the state of charge of the energy storage device is judged:
2-1) when SOCb>SOCb_minAnd U isdsc>Udsc_minWhen it is, order Psc＝Psc_high；Pb_ref＝Pb_low；
2-2) when SOCb>SOCb_minAnd U isdsc≤Udsc_minAnd setting the lithium battery to charge the super capacitor when the state of the super capacitor is at the lower limit value, and enabling P to be charged at the momentsc＝Psc_high+Psc_c，Pb_ref＝Pb_low-Psc_c；
2-3) when SOCb≤SOCb_minAnd U isdsc>Udsc_minAnd setting the super capacitor to charge the lithium battery when the lithium battery is at the lower limit value, and enabling P to be charged at the momentsc＝Psc_high-Pb_c，Pb_ref＝Pb_low+Pb_c；
2-4) SOC asb≤SOCb_minAnd U isdsc≤Udsc_minAt this time, the ordinary load needs to be cut off step by step to make Δ P<0, charging the combined energy storage system by the photovoltaic power generation system preferentially to prevent the energy storage system from being damaged due to too low charge, and turning to the step 1-5);
2-5) SOC asb≥SOCb_maxAnd U isdsc≥Udsc_maxWhen is, Psc＝Psc_high-Psc_disc，Pb_ref＝Pb_low-Pb_disc；
(3) When Δ P is equal to 0, the photovoltaic power is equal to the load power, the energy storage system and the microgrid have no power exchange, but the energy storage devices can exchange power:
3-1) when U is presentdsc>Udsc_maxAnd SOCb<SOCb_maxWhen, or Udsc>Udsc_minAnd SOCb<SOCb_minSetting super capacitor to charge lithium battery, i.e. order Psc＝-Psc_disc，Pb_ref＝Psc_disc；
3-2) when U is presentdsc<Udsc_maxAnd SOCb>SOCb_maxWhen, or Udsc<Udsc_minAnd SOCb>SOCb_minWhen the lithium battery is set to charge the super capacitor, the P is orderedsc＝Pb_disc，Pb_ref＝-Pb_disc
3-3) when U is presentdsc≥Udsc_maxAnd SOCb≥SOCb_maxAt the moment, the MPPT mode of the photovoltaic power generation system is switched to the AGC mode to limit the power generation amount of the photovoltaic power generation system, so that the delta P>0, the load power is preferentially provided by a lithium battery and a super capacitor, and the step 2-5) is changed;
3-4) when U is presentdsc≤Udsc_minAnd SOCb≤SOCb_minAt this time, the ordinary load needs to be cut off step by step to make Δ P<0, charging the combined energy storage system by the photovoltaic power generation system preferentially to prevent the energy storage system from being damaged due to too low charge, and turning to the step 1-5);
3-5) if the state of charge of the energy storage device does not meet the conditions of 3-1), 3-2), 3-3) and 3-4), the energy storage device is not charged or discharged;
wherein the SOCb_maxIs the maximum value of the charge, SOC, of the lithium batteryb_minIs the minimum value of the state of charge, P, of the lithium batteryb_refIs the active power reference value, P, of the lithium batteryb_discIs the discharge power of a lithium battery, Pb_cFor charging power of lithium batteries, Udsc_maxMaximum value of terminal voltage for charging and discharging depth of super capacitor, Udsc_minMinimum value of terminal voltage for charging and discharging depth of super capacitor, PscFor power compensation values, P, of supercapacitors in energy storage control systemssc_highIs superHigh frequency capacitance compensation power component reference, Psc_discIs the discharge power of the supercapacitor, Psc_cCharging power for the super capacitor, Psc_refIs the reference value of active power, P, of the super capacitorb_lowAnd compensating the reference value of the active power component for the low frequency of the lithium battery.
2. The method for coordinated control of the micro-grid island operation mode of the lithium-containing battery and the super capacitor as claimed in claim 1, wherein the specific method for decomposing the difference active power Δ P to obtain the compensation active power component of the lithium battery and the super capacitor is as follows:
the method comprises the following steps: decomposing the difference active power value delta P by using a predetermined low-pass filter to obtain a reference value P of the low-frequency compensation active power component of the lithium batteryb_lowThen subtracting P from the difference Δ Pb_lowObtaining the reference value P of the high-frequency active power component to be compensated of the super capacitorsc_highAs shown in the following formula;
step two: using a predetermined low-pass filter to convert the reactive power Q of the loadloadDecomposing to obtain the reference value Q of the low-frequency compensation reactive power component of the lithium batteryb_lowReuse of the reactive power Q of the loadloadSubtracting the reference value Q of the low-frequency compensation reactive power component of the lithium batteryb_lowObtaining a reference value Q of a high-frequency reactive power component to be compensated of the super capacitorsc_highAs shown in the following formula;
where S integral function, T time step.
3. The coordination control method for the micro-grid island operation mode of the lithium-containing battery and the super capacitor as claimed in claim 2, wherein the parameter determination method of the low-pass filter is as follows:
the maximum service life N years and the maximum allowable charging and discharging times M of the lithium batterymaxSecondly, determining the allowable charging and discharging times of the lithium battery every day as
When the working time of the photovoltaic power generation system is from T1 to T2, the lithium battery is used for balancing the frequency of photovoltaic power fluctuation
Therefore, the power compensation frequency critical value of the lithium battery and the super capacitor is set.
4. The coordination control method for the micro-grid island operation mode of the lithium-containing battery and the super capacitor as claimed in claim 1, wherein the control of the converter of the combined energy storage system by the combined energy storage system local controller comprises two parts of control of the bidirectional DC/DC converters 1 and 2 and control of the bidirectional DC/AC converters 1 and 2, and the main control aim for the DC/DC is to ensure the voltage on the direct current side to be stable; the control of the DC/AC converter 1 adopts a double-loop control method of a power outer loop and a current inner loop; the control of the DC/AC converter 2 adopts tracking network voltage frequency control, power outer loop and current inner loop three-loop control.
5. The microgrid island operation mode coordinated control method of a lithium-containing battery and a supercapacitor as claimed in claim 1, characterized in that a photovoltaic power generation system is operated in a maximum power generation state preferentially and in an automatic power generation control state secondarily to regulate photovoltaic power generation power;
and the combined energy storage system judges whether the absorption or the emission power is generated according to the difference active power delta P so as to ensure the power balance of the micro-grid system.
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| CN109904866B (en) * | 2019-02-22 | 2021-07-02 | 国电南瑞科技股份有限公司 | Multi-energy-storage microgrid grid-connected coordination control method and system |
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