CN111900710A - Grid-connected direct-current micro-grid coordination control method - Google Patents

Grid-connected direct-current micro-grid coordination control method Download PDF

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Publication number
CN111900710A
CN111900710A CN202010761826.5A CN202010761826A CN111900710A CN 111900710 A CN111900710 A CN 111900710A CN 202010761826 A CN202010761826 A CN 202010761826A CN 111900710 A CN111900710 A CN 111900710A
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voltage
grid
unit
current
direct current
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Inventor
舒恺
姚艳
郭高鹏
刘峰
黄炜
钱康
刘玉婷
张严
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Ningbo Electric Power Design Institute Co ltd
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Ningbo Electric Power Design Institute Co ltd
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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J1/00—Circuit arrangements for dc mains or dc distribution networks
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J1/00—Circuit arrangements for dc mains or dc distribution networks
    • H02J1/08—Three-wire systems; Systems having more than three wires
    • H02J1/082—Plural DC voltage, e.g. DC supply voltage with at least two different DC voltage levels
    • 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
    • H02J1/00—Circuit arrangements for dc mains or dc distribution networks
    • H02J1/10—Parallel operation of dc sources
    • 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
    • H02J1/00—Circuit arrangements for dc mains or dc distribution networks
    • H02J1/10—Parallel operation of dc sources
    • H02J1/106—Parallel operation of dc sources for load balancing, symmetrisation, or sharing
    • 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
    • H02J1/00—Circuit arrangements for dc mains or dc distribution networks
    • H02J1/14—Balancing the load in a network
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J7/00—Circuit arrangements for charging or depolarising batteries or for supplying loads from batteries
    • H02J7/34—Parallel operation in networks using both storage and other dc sources, e.g. providing buffering
    • H02J7/35—Parallel operation in networks using both storage and other dc sources, e.g. providing buffering with light sensitive cells
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J2300/00—Systems for supplying or distributing electric power characterised by decentralized, dispersed, or local generation
    • H02J2300/20—The dispersed energy generation being of renewable origin
    • H02J2300/22—The renewable source being solar energy
    • H02J2300/24—The renewable source being solar energy of photovoltaic origin
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J2300/00—Systems for supplying or distributing electric power characterised by decentralized, dispersed, or local generation
    • H02J2300/20—The dispersed energy generation being of renewable origin
    • H02J2300/22—The renewable source being solar energy
    • H02J2300/24—The renewable source being solar energy of photovoltaic origin
    • H02J2300/26—The renewable source being solar energy of photovoltaic origin involving maximum power point tracking control for photovoltaic sources
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E10/00—Energy generation through renewable energy sources
    • Y02E10/50—Photovoltaic [PV] energy
    • Y02E10/56—Power conversion systems, e.g. maximum power point trackers

Abstract

The invention relates to a grid-connected direct-current microgrid coordinated control method, wherein a direct-current microgrid comprises a photovoltaic power generation unit, a networking unit connected with an alternating-current main grid, an energy storage unit, an alternating-current and direct-current load unit and a working mode controller, the working mode controller is provided with a plurality of voltage levels to divide direct-current bus voltage into a plurality of voltage layers, the voltage layers execute corresponding working modes, the photovoltaic power generation unit, the networking unit, the energy storage unit and the alternating-current and direct-current load unit execute corresponding control modes in the working modes, the units are not interfered with each other, the working mode controller judges the voltage layers according to the voltage value of the locally acquired direct-current bus voltage and controls the photovoltaic power generation unit, the networking unit, the energy storage unit and the alternating-current and direct-current load unit to adjust to the corresponding control modes. Compared with the prior art, the method has the advantages of avoiding the influence of micro-source output fluctuation or load change on the bus voltage, having good system expansibility and the like.

Description

Grid-connected direct-current micro-grid coordination control method
Technical Field
The invention relates to the technical field of energy management and coordination control of a direct-current micro-grid, in particular to a grid-connected direct-current micro-grid coordination control method.
Background
Solar energy is used as a renewable energy source with wide distribution and no pollution, so that the photovoltaic becomes a power generation scheme favored by all countries in the world, but the photovoltaic has the characteristics of small inertia, large output randomness and easiness in being influenced by factors such as illumination intensity and temperature, and is not suitable for adopting a centralized power generation scheme, and the distributed power generation obviously can better utilize the clean energy source, so that the energy utilization rate of the distributed power generation is greatly improved. In this context, the concept of microgrid arises from the standpoints. Because the photovoltaic power generation unit outputs direct current, direct current loads of electric vehicles and the like are more and more, and the problems of frequency and phase do not need to be considered in the direct current micro-grid, the direct current micro-grid has unique application advantages compared with the alternating current micro-grid.
Because a large number of power electronic devices are connected into a microgrid, so that the system inertia is low, when the output of a micro source fluctuates or the load changes, the bus voltage may fluctuate seriously, and further the stable operation of the direct-current microgrid is influenced, so that the research on the energy coordination and the voltage control of the direct-current microgrid becomes a key technical drive influencing the development of the direct-current microgrid.
Disclosure of Invention
The invention aims to provide a coordinated control method of a grid-connected direct-current micro-grid, aiming at overcoming the defect of serious fluctuation of bus voltage caused by micro-source output fluctuation or load change in the prior art.
The purpose of the invention can be realized by the following technical scheme:
the utility model provides a grid-connected type direct current microgrid coordinated control method, direct current microgrid includes photovoltaic power generation unit, the networking unit of being connected with the interchange major network, energy storage unit, alternating current-direct current load unit and mode of operation controller, the mode of operation controller sets up a plurality of voltage levels and divides direct current busbar voltage into a plurality of voltage layers, corresponding mode of operation is carried out to the voltage layer, photovoltaic power generation unit, networking unit, energy storage unit and alternating current-direct current load unit carry out corresponding control mode under the mode of operation, mutual noninterference between the unit, and the mode of operation controller is according to the voltage value of the direct current busbar voltage of local collection and is judged the voltage layer of locating to control photovoltaic power generation unit, networking unit, energy storage unit and alternating current-direct current load unit adjust to corresponding control mode.
The number of the voltage grades is 6, and the voltage grades specifically comprise a third low voltage, a second low voltage, a first high voltage, a second high voltage and a third high voltage.
Further, the 6 voltage levels are sorted according to the voltage values, and are a third low voltage, a second low voltage, a first high voltage, a second high voltage and a third high voltage from small to large.
Further, the number of the working modes is 4, and the working modes specifically include a first working mode, a second working mode, a third working mode and a fourth working module.
Further, when the voltage value of the direct current bus voltage is between a first low voltage and a first high voltage, the corresponding working mode is the first working mode, the networking unit controls power fluctuation in the balance system and controls the bus voltage, the photovoltaic power generation unit operates in the maximum power point tracking control mode, the energy storage unit is in a charging state, if the energy storage unit is fully charged, the energy storage unit is kept in a full-power standby state, the storage battery is not discharged, and the alternating current/direct current load unit is in a normal operation state.
Further, when the voltage value of the direct current bus voltage is between a second low voltage and a first low voltage or between a first high voltage and a second high voltage, the corresponding working mode is the second working mode, the power transmission quantity of the networking unit reaches the limit capacity or is in a disconnection state, the photovoltaic power generation unit operates in a maximum power point tracking control mode, the energy storage unit regulates unbalanced power and controls the bus voltage, and the alternating current/direct current load unit is in a normal operation state.
Further, when the voltage value of the direct-current bus voltage is between the second high voltage and the third high voltage, the corresponding working mode is the third working mode, the networking unit absorbs electric energy from the direct-current micro-grid with the limit power capacity or is in a disconnection state, the photovoltaic power generation unit is switched to a voltage droop control mode, the energy storage unit is charged according to the maximum power, if the electric quantity of the energy storage unit is full, the full-electricity standby state is kept, the storage battery is not discharged, and the alternating-current/direct-current load unit is in a normal operation state.
Further, when the voltage value of the direct-current bus voltage is between the third low voltage and the second low voltage, the corresponding working mode is a fourth working mode, the networking unit transmits electric energy to the direct-current micro-grid with the limit power capacity or is in a disconnected state, the photovoltaic power generation unit operates in an MPPT control mode, the energy storage unit discharges with the maximum power, if the electric quantity of the energy storage unit is discharged, the energy storage unit keeps an empty power standby state, the storage battery is not charged, and the alternating-current/direct-current load unit cuts off internal loads according to the proportion.
The networking unit is internally provided with a bidirectional DC/AC converter, the bidirectional DC/AC converter adopts a double-closed-loop structure, the double-closed-loop structure specifically comprises a voltage outer loop and a current inner loop, the voltage outer loop maintains the voltage stability of a direct-current bus, and the current inner loop controls the current on the network side.
The photovoltaic power generation unit adopts a three-section maximum power point tracking control mode combined with a voltage droop control mode based on a working point, and the energy storage unit adopts a voltage droop control mode based on the self-correction of a droop coefficient of the SOC.
Compared with the prior art, the invention has the following beneficial effects:
the direct-current bus voltage is divided into a plurality of voltage layers by setting a plurality of voltage levels, the voltage layers execute corresponding working modes, the control of each micro source and load and the switching of the working modes are completed only by using the direct-current bus voltage as a unique signal, and simultaneously, the communication-free coordination of the photovoltaic power generation unit, the networking unit, the energy storage unit and the alternating-current/direct-current load unit is realized by selecting peer-to-peer control, so that the units are 'plug-and-play' and do not influence each other, and the system has good system expansibility.
Drawings
FIG. 1 is a schematic structural view of the present invention;
FIG. 2 is a graph of a piecewise plot of the output characteristic of a photovoltaic power generation unit in accordance with the present invention;
FIG. 3 is a schematic flow chart of three-stage MPPT control of the photovoltaic power generation unit according to the present invention;
FIG. 4 is a schematic illustration of an operating point stability analysis of a photovoltaic power generation unit of the present invention;
FIG. 5 is a schematic structural diagram of derating and voltage stabilizing control of a photovoltaic power generation unit according to the present invention;
FIG. 6 is a schematic diagram of a droop characteristic of an energy storage unit according to the present invention;
FIG. 7 is a schematic diagram of the networked converter control of the present invention;
FIG. 8 is a schematic diagram of DC bus voltage stratification in accordance with the present invention;
FIG. 9 is a graph showing the simulation effect of the networking regulation mode of the DC microgrid according to the present invention, wherein FIG. 9(a) is a graph showing the variation of the illumination intensity, FIG. 9(b) is a graph showing the variation of the output power of the networking unit, and FIG. 9(c) is a graph showing the variation of the DC bus voltage;
fig. 10 is a diagram of simulation effect of the energy storage regulation mode of the dc microgrid according to the present invention, wherein fig. 10(a) is a graph of variation of illumination intensity, fig. 10(b) is a graph of variation of discharge power of the storage battery of the energy storage unit, and fig. 10(c) is a graph of variation of dc bus voltage;
fig. 11 is a diagram of simulation effect of the photovoltaic derating operation mode of the direct current microgrid of the present invention, wherein fig. 11(a) is a graph of variation of illumination intensity, fig. 11(b) is a graph of variation of power of the photovoltaic power generation unit, and fig. 11(c) is a graph of variation of voltage of the direct current bus;
fig. 12 is a graph showing simulation effects of the active load shedding mode of the dc micro-grid according to the present invention, in which fig. 12(a) is a graph showing changes in illumination intensity, fig. 12(b) is a graph showing changes in power of the ac/dc load unit, and fig. 12(c) is a graph showing changes in voltage of the dc bus.
Detailed Description
The invention is described in detail below with reference to the figures and specific embodiments. The present embodiment is implemented on the premise of the technical solution of the present invention, and a detailed implementation manner and a specific operation process are given, but the scope of the present invention is not limited to the following embodiments.
As shown in fig. 1, a grid-connected dc microgrid coordinated control method includes a photovoltaic power generation unit, a networking unit connected to an ac main grid, an energy storage unit, an ac/dc load unit, and a working mode controller, where the working mode controller sets multiple voltage levels to divide a dc bus voltage into multiple voltage layers, the voltage layers execute corresponding working modes, and in the working modes, the photovoltaic power generation unit, the networking unit, the energy storage unit, and the ac/dc load unit execute corresponding control modes without mutual interference between the units, and the working mode controller determines the voltage layer according to a locally acquired voltage value of the dc bus voltage and controls the photovoltaic power generation unit, the networking unit, the energy storage unit, and the ac/dc load unit to adjust to the corresponding control mode.
DC bus voltage rated value Udc_nThe voltage change of the direct current bus is 380V, and delta U.
The number of the voltage grades is 6, and the voltage grades specifically comprise a third low voltage, a second low voltage, a first high voltage, a second high voltage and a third high voltage.
The 6 voltage grades are sorted according to the voltage values, and are a third low voltage, a second low voltage, a first high voltage, a second high voltage and a third high voltage from small to large.
The number of the working modes is 4, and the working modes specifically comprise a first working mode, a second working mode, a third working mode and a fourth working module.
When the fluctuation range of the voltage of the direct current bus is less than 7.6V, namely the voltage of the direct current bus meets the condition that U is satisfiedL1＜Udc＜UH1The corresponding working mode is a first working mode, the networking unit controls power fluctuation and control bus voltage in the balance system, the photovoltaic power generation unit operates in a maximum power point tracking control mode, the energy storage unit is in a charging state, if the energy storage unit is fully charged, the photovoltaic power generation unit is kept in a full-power standby state, the alternating current and direct current load unit is in a normal operation state, when the output of the microgrid and the main network not only meets load requirements but also has power surplus, the storage battery is charged preferentially and then is conveyed to the alternating current main network through the networking unit, the storage battery is only not charged, if the storage battery is fully charged, voltage is reduced, the storage battery also keeps in a non-discharging state, and therefore the adjusting capacity of the microgrid and the main network is guaranteed.
When the fluctuation range of the direct current bus voltage is less than 19V, namely the bus voltage meets the condition that UH1＜Udc＜UH2Or UL2＜Udc＜UL1And the corresponding working mode is a second working mode, the power transmission quantity of the networking unit reaches the limit capacity or is in a disconnection state, the photovoltaic power generation unit operates in a maximum power point tracking control mode, the energy storage unit regulates unbalanced power and controls bus voltage, and the alternating current/direct current load unit is in a normal operation state.
When the DC bus voltage satisfies Udc＞UH2And when the photovoltaic power generation unit is fully charged, the photovoltaic power generation unit is kept in a full-power standby state, the storage battery does not discharge, and the alternating current/direct current load unit is in a normal operation state.
When the voltage value of the direct current bus meets Udc＜UL2When the corresponding working mode is the fourth working mode, the networking unit transmits electric energy to the direct current micro-grid with the limit power capacity or is disconnectedAnd in the state, the photovoltaic power generation unit operates in an MPPT control mode, the energy storage unit discharges at the maximum power, if the electric quantity of the energy storage unit is discharged, the energy storage unit keeps an empty electricity standby state, the storage battery is not charged, and the internal load is cut off by the AC/DC load unit according to the proportion.
The photovoltaic power generation units are connected through a unidirectional DC/DC converter, the energy storage units for balancing power are connected through a bidirectional DC/DC converter when the system power fluctuates, and the alternating current/direct current load units are connected to the voltage of the direct current bus through corresponding unidirectional DC/AC or DC/DC.
As shown in fig. 2, the photovoltaic power generation unit adopts a three-stage Maximum Power Point Tracking (MPPT) control mode in combination with a voltage droop control mode based on a working point, and is divided into three sections, i.e., non-MPP, similar MPP, and MPP, according to a slope of an output characteristic curve of the photovoltaic power generation unit, and corresponding MPPT strategies are respectively adopted to accelerate tracking speed and improve optimization accuracy, and a flow of the MPPT strategy is shown in fig. 3.
The sections a-B and E-F of fig. 2 are non-MPP sections, the absolute value of the slope of the two curves is larger and is farther from the maximum power point, and the two sections are skipped by using a Constant Voltage Tracking (CVT) method to increase the tracking speed, wherein U is a Constant Voltage Tracking (CVT) methodn1、Un2Can be respectively taken as 0.65Uoc、0.9Uoc；
The sections B-C and D-E of fig. 2 are MPP-like sections, the absolute value of the slope of the two curves is small and is close to the maximum power point, a variable step disturbance Observation Method (P & O) is adopted to further approach the maximum power point, and disturbance oscillation is not easy to occur, and the determination condition is specifically:
Figure BDA0002613293380000051
wherein the content of the first and second substances,
Figure BDA0002613293380000052
the absolute value of the slope of the curve is the critical slope of the entering CD section;
the section C-D of FIG. 2 is the MPP section, the slope is close to 0, and the slope satisfies
Figure BDA0002613293380000053
The length is short, and the maximum power point is on the curve, so that the Particle Swarm Optimization (PSO) is adopted for Optimization, the tracking precision is improved, and oscillation around the maximum power point can not be generated like the traditional algorithm.
And based on the output characteristic curve of the photovoltaic power generation unit, adopting voltage droop control based on a stable working point. As can be seen from the P-U characteristic curve of the photovoltaic cell, when the photovoltaic power generation unit operates to reduce the generated power, there are two operating points that satisfy the power condition, which are located on the left side and the right side of the maximum power point, respectively, as shown in fig. 4, at points B and C.
If the photovoltaic cell currently works at the point B and keeps the voltage U of the photovoltaic power generation unitpvStable, when the illumination intensity is suddenly reduced, the current I of the photovoltaic power generation unit is causedpvThe instantaneous decrease is that the output power of the photovoltaic cell is less than the power required by the load, but UpvAnd then the output power of the photovoltaic cell is gradually increased to form negative feedback, so that the photovoltaic cell finally reaches a new stable working point. The point located in the region to the right of the maximum power point is therefore a stable operating point, whereas the point located in the region to the right of the maximum power point is due to UpvThe reduction of the voltage of the photovoltaic cell can further reduce the output power of the photovoltaic cell, and positive feedback is formed, so that the system cannot be stable, and therefore, the point C is an unstable working point.
The control block diagram of the photovoltaic power generation unit for stabilizing the direct current bus voltage is shown in fig. 5: double-loop control of a direct current bus voltage outer loop and an inductive current inner loop is adopted, and PI regulators are used for the inner loop and the outer loop. In order to meet the requirement that the photovoltaic cell works in the area on the right side of the maximum power point, an amplitude limiting link is added after the output of a PI regulator of an outer ring, and the inductive current is limited not to exceed the current I corresponding to the maximum power point of the photovoltaic cellmAnd the stability of the working point is ensured.
The droop control method is adopted to improve the voltage stabilization control of the photovoltaic power generation unit, and the droop control expression is as follows:
Figure BDA0002613293380000061
wherein the content of the first and second substances,
Figure BDA0002613293380000062
for reference value of DC bus voltage in closed-loop control, Kpv、Idc_pvIs the droop coefficient of the photovoltaic power generation unit and the bus side current of the converter, UH3A third high pressure.
And determining a reference value of the direct current bus voltage according to a droop control method, and performing closed-loop control on the direct current bus voltage by adopting a double-loop control system of a direct current bus voltage outer loop and an inductive current inner loop. The voltage outer ring is used for adjusting and stabilizing direct-current bus voltage, static error-free control is achieved by adopting the PI regulator, meanwhile, the current inner ring is introduced, on one hand, dynamic performance is improved, on the other hand, current is controlled without damaging power electronic devices, the PI regulator is also used for the current inner ring, and the specific control structure is shown in fig. 5.
As shown in fig. 6, the energy storage unit adopts a droop coefficient self-correcting voltage droop control mode based on the SOC, and controls the bidirectional energy storage converter by adopting a charge-discharge current-bus voltage droop control method, so as to achieve a current equalizing effect when multiple sets of equipment of the energy storage unit are operated in parallel.
As shown in fig. 6, UH1、UH2、UL1And UL2The critical voltage for switching the working mode is a first high voltage, a second high voltage, a first low voltage and a second low voltage, UdcnIs a DC bus reference voltage, IBFor charging and discharging current of the accumulator, IB>0 corresponds to the discharge of the accumulator, IB<0 corresponds to battery charging.
The droop control method of the following formula is applied to distribute the voltage regulation capacity of the storage battery, and specifically comprises the following steps:
Figure BDA0002613293380000071
wherein the content of the first and second substances,
Figure BDA0002613293380000072
is a reference value of the DC bus voltage to be controlled, KBi、Idc_BiIs a storage battery BiDroop coefficient and converter bus side current.
Usually, the droop control coefficient of the energy storage unit only considers the capacity of the energy storage equipment, the state of charge (SOC) of the storage battery is a key parameter for the working of the storage battery, and since the SOC of the storage battery is always changed during the working and the SOC values of the equipment are different, in the storage battery parallel energy storage system, the SOC of each storage battery tends to be consistent through a control strategy, and the consistency of the parallel working state is ensured. For this definition of alphaiThe ratio of the SOC of the battery to the average SOC of all devices is specifically as follows:
Figure BDA0002613293380000073
according to alphaiTo the original droop coefficient K of the storage batteryBiThe correction is carried out specifically as follows:
Figure BDA0002613293380000074
wherein, K'BiFor the corrected droop coefficient of the storage battery Bi, if the SOC of the storage battery Bi is higher than the average value, the application of the corrected droop coefficient will reduce the charging current, slow down the charging speed, or increase the discharging current, and accelerate the discharging speed. Therefore, the droop control is performed according to the correction coefficient, so that the final states of charge of the batteries are consistent.
The frequent overcharge and overdischarge of the storage battery during working are extremely unfavorable for the safe operation of the storage battery, the state of charge of the storage battery is required to meet the condition that the SOC is more than 40 percent and less than 90 percent in order to protect the storage battery, and the storage battery is in an idle standby state beyond the range.
As shown in fig. 7, a bidirectional DC/AC converter is arranged in the networking unit, the bidirectional DC/AC converter adopts a double closed-loop structure, the double closed-loop structure specifically includes a voltage outer loop and a current inner loop, wherein:
the voltage outer ring maintains the voltage stability of the direct current bus and introduces a feedback UdcAnd sending the result to a PI regulator, and setting the output of the PI regulator as a reference value i of an active current inner loopd *Realize to UdcNo-static-error control of (1);
the current inner loop controls the current on the network side, and a reference value i of the reactive current inner loop is setq *When the main grid three-phase current is equal to 0, the main grid three-phase current is converted into active current i through abc/dqdAnd a reactive current iqAs the corresponding feedback of the current inner loop, the adder result is sent to the PI regulator, and then u is outputdr *And uqr *And (4) combining the decoupling compensation quantity to obtain control quantities ud and uq, and generating PWM (pulse-width modulation) driving signals by the control quantities through SVPWM (space vector pulse-width modulation) to realize the control of the converter.
Example one
The little electric wire netting of direct current includes photovoltaic power generation unit, networking unit, energy storage unit and alternating current-direct current load unit, and third low-voltage, second low-voltage, first high pressure, second high pressure and third high pressure are shown as table 1 specifically:
TABLE 1 DC BUS VOLTAGE LAYER INTERVATION TABLE
Figure BDA0002613293380000081
As shown in fig. 8, the first operating mode is a networking regulation mode, the second operating mode is an energy storage regulation mode, the third operating mode is a photovoltaic derating mode, and the fourth operating mode is an active load shedding mode.
System simulation is performed according to the simulation conditions shown in table 2, the working condition of the system in the networked regulation mode is verified, the simulation result is shown in fig. 9, and table 2 specifically includes the following steps:
TABLE 2 networking Regulation mode simulation Condition Table
Figure BDA0002613293380000082
As shown in fig. 9(a), 9(b) and 9(c), in the networking regulation mode, as the environment and the load use condition change, the demand of the system for power changes, the demand of the system for power is met by the networking unit, and the dc bus voltage is stabilized between 0.98 and 1.02 per unit according to the droop control; the photovoltaic power generation unit operates an MPPT control mode, the AC/DC load unit is in a normal operation state, and if the electric quantity of the energy storage unit is not saturated and the networking converter has residual power, the energy storage equipment is charged.
Performing system simulation according to the simulation conditions shown in table 3, verifying the working condition of the system in the energy storage regulation mode, where the simulation result is shown in fig. 10, and table 3 specifically includes:
table 3 simulation condition table of energy storage adjusting mode
Figure BDA0002613293380000083
As shown in fig. 10(a), 10(b) and 10(c), when the power of the networked converter reaches the limit due to the failure of the ac main network, the networked unit loses the capability of balancing the system power, the dc bus voltage changes, and the energy storage unit assumes the power balancing node, so that the switching from the networked regulation mode to the energy storage regulation mode is realized. The energy storage unit is used as a power balance node, the voltage of the direct current bus is stabilized at a per unit value of 0.95 to 0.98 or a per unit value of 1.02 to 1.05 under the droop control, the energy storage unit discharges when the voltage is between 0.95 and 0.98, and the energy storage unit charges when the voltage is between 1.02 and 1.05.
Performing system simulation according to the simulation conditions shown in table 4, verifying the working condition of the system in the derating mode of the photovoltaic power generation unit, and obtaining the simulation result shown in fig. 11, where table 4 specifically includes the following steps:
TABLE 4 simulation Condition Table for photovoltaic derating mode
Figure BDA0002613293380000091
As shown in fig. 11(a), 11(b), and 11(c), when the power of the distributed power supply is greater than the load power, and the networking unit and the energy storage unit cannot absorb the remaining power, the voltage of the dc bus rises to enter a derating operation mode of the distributed power supply, so as to realize switching from the energy storage regulation mode to the photovoltaic derating mode. The photovoltaic power generation unit reduces the power generation power and meets the load requirement. Under the droop control of the photovoltaic power generation unit, the voltage of the direct-current bus is stabilized at a per unit value of 1.05-1.1. When the photovoltaic power generation power is smaller than the load power, the voltage of the direct-current bus changes, and the direct-current micro-grid system is switched to an energy storage regulation mode from a photovoltaic derating mode.
System simulation is performed according to the simulation conditions shown in table 5, the working condition of the system in the active load shedding mode is verified, the simulation result is shown in fig. 12, and table 5 specifically includes the following steps:
TABLE 5 initiative load shedding mode simulation condition table
Figure BDA0002613293380000092
As shown in fig. 12(a), 12(b) and 12(c), when the power of the power supply is smaller than the power of the load and the energy storage unit and the networking unit cannot provide the shortage power, the voltage of the dc bus is reduced, and when the voltage of the bus captured by the ac/dc load unit is reduced to below 0.95 per unit, the load with low priority is actively cut off, so as to ensure the reliable power supply of the load with high priority. After the bus voltage rises, the load control unit calculates that the cut load is automatically put into use again when the power which can be provided by the direct-current micro-grid system meets the cut load requirement.
In addition, it should be noted that the specific embodiments described in the present specification may have different names, and the above descriptions in the present specification are only illustrations of the structures of the present invention. All equivalent or simple changes in the structure, characteristics and principles of the invention are included in the protection scope of the invention. Various modifications or additions may be made to the described embodiments or methods may be similarly employed by those skilled in the art without departing from the scope of the invention as defined in the appending claims.

Claims (10)

1. The grid-connected type direct-current microgrid coordinated control method is characterized in that the direct-current microgrid comprises a photovoltaic power generation unit, a networking unit, an energy storage unit, an alternating-current and direct-current load unit and a working mode controller, wherein the networking unit, the energy storage unit, the alternating-current and direct-current load unit and the working mode controller are connected with an alternating-current main grid, the working mode controller is used for setting a plurality of voltage levels to divide direct-current bus voltage into a plurality of voltage layers, the voltage layers execute corresponding working modes, the photovoltaic power generation unit, the networking unit, the energy storage unit and the alternating-current and direct-current load unit execute corresponding control modes in the working modes, the units are not interfered with one another, the working mode controller judges the voltage layers according to the voltage values of the locally acquired direct-current bus voltage, and controls the photovoltaic power generation unit, the networking unit, the.
2. The grid-connected type direct current micro-grid coordination control method according to claim 1, wherein the number of the voltage classes is 6, and specifically includes a third low voltage, a second low voltage, a first high voltage, a second high voltage, and a third high voltage.
3. The grid-connected type direct current micro-grid coordination control method according to claim 2, characterized in that the 6 voltage levels are sorted according to the magnitude of the voltage values, and are a third low voltage, a second low voltage, a first high voltage, a second high voltage and a third high voltage from small to large.
4. The grid-connected type direct current micro-grid coordination control method according to claim 3, wherein the number of the operation modes is 4, and specifically includes a first operation mode, a second operation mode, a third operation mode and a fourth operation module.
5. The grid-connected direct current micro-grid coordination control method according to claim 4, wherein when a voltage value of the direct current bus voltage is between a first low voltage and a first high voltage, a corresponding working mode is a first working mode, the networking unit controls power fluctuation in the balancing system and controls the bus voltage, the photovoltaic power generation unit operates in a maximum power point tracking control mode, the energy storage unit is in a charging state, if the energy storage unit is fully charged, the photovoltaic power generation unit is kept in a full-charge standby state, the storage battery is not discharged, and the alternating current/direct current load unit is in a normal operating state.
6. The grid-connected type direct current micro-grid coordination control method according to claim 4, wherein when the voltage value of the direct current bus voltage is between the second low voltage and the first low voltage or between the first high voltage and the second high voltage, the corresponding working mode is the second working mode, the power transmission quantity of the grid-connected unit reaches a limit capacity or is in a disconnected state, the photovoltaic power generation unit operates in a maximum power point tracking control mode, the energy storage unit regulates unbalanced power and controls the bus voltage, and the alternating current/direct current load unit is in a normal operating state.
7. The grid-connected type direct current micro-grid coordination control method according to claim 4, wherein when the voltage value of the direct current bus voltage is between the second high voltage and the third high voltage, the corresponding working mode is the third working mode, the networking unit absorbs electric energy from the direct current micro-grid with a limit power capacity or is in a disconnected state, the photovoltaic power generation unit is switched to a voltage droop control mode, the energy storage unit is charged according to the maximum power, if the electric quantity of the energy storage unit is fully charged, a full-charge standby state is kept, the storage battery is not discharged, and the alternating current/direct current load unit is in a normal operation state.
8. The grid-connected type direct current micro-grid coordination control method according to claim 4, wherein when the voltage value of the direct current bus voltage is between the third low voltage and the second low voltage, the corresponding working mode is a fourth working mode, the networking unit transmits electric energy to the direct current micro-grid with a limit power capacity or is in a disconnected state, the photovoltaic power generation unit operates in the MPPT control mode, the energy storage unit discharges with maximum power, if the electric quantity of the energy storage unit is discharged, an empty power standby state is kept, the storage battery is not charged, and the internal load is cut off by the alternating current/direct current load unit according to a proportion.
9. The coordinated control method for the grid-connected type direct current micro-grid according to claim 1, wherein a bidirectional DC/AC converter is arranged in the networking unit, and the bidirectional DC/AC converter adopts a double closed-loop structure, and the double closed-loop structure is specifically a voltage outer loop and a current inner loop.
10. The grid-connected direct current micro-grid coordination control method according to claim 1, wherein the photovoltaic power generation unit adopts a three-stage maximum power point tracking control mode combined with a voltage droop control mode based on an operating point, and the energy storage unit adopts a self-correcting voltage droop control mode based on a droop coefficient of the SOC.
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