CN111049181B - Micro-grid connection method, device and system based on joint control - Google Patents
Micro-grid connection method, device and system based on joint control Download PDFInfo
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- CN111049181B CN111049181B CN201911318220.8A CN201911318220A CN111049181B CN 111049181 B CN111049181 B CN 111049181B CN 201911318220 A CN201911318220 A CN 201911318220A CN 111049181 B CN111049181 B CN 111049181B
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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
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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
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Abstract
The invention relates to a microgrid grid-connected method, device and system based on joint control, which comprises the steps of acquiring a grid-connected signal of a direct-current microgrid in real time, sending a first closing instruction to a PCC switch according to the grid-connected signal, and sending a starting instruction to a grid-connected inverter after preset delay time; when the grid-connected inverter is started according to the starting instruction, the grid-connected inverter is set to be in a first control mode, and the direct-current energy storage is set to be in a second control mode; setting an active control instruction of the grid-connected inverter, and acquiring the exchange power and the direct-current voltage of the direct-current energy storage in real time according to the active control instruction; and judging whether the exchange power meets the exchange power criterion and judging whether the direct-current voltage meets the direct-current voltage criterion, and if so, switching the grid-connected inverter into a third control mode to complete grid connection. The invention realizes the flexible transition of the direct-current micro-grid to the normal operation state after the grid connection of the direct-current micro-grid is completed in an island mode based on the combined control of the grid-connected inverter and the direct-current energy storage.
Description
Technical Field
The invention relates to the field of microgrid grid connection and control, in particular to a microgrid grid connection method, device and system based on joint control.
Background
With the continuous increase of urban power generation, the traditional fossil energy is rapidly consumed, and the problems of energy shortage and environmental pollution are increasingly serious. The proportion of distributed power supplies mainly based on new energy power generation in a power grid is continuously improved. However, in the ac microgrid, the distributed power source needs to be synchronized with the phase angle and frequency of the large power grid through the inverter, wherein the control process is complicated, so the ac microgrid is not suitable for large-scale access to the distributed power source. Under the premise, the development of the direct-current micro-grid is the trend and direction of the future micro-grid.
However, the existing research on the dc microgrid mostly focuses on how to coordinate inverters in a grid-connected operation mode or an island operation mode of the dc microgrid, and how to avoid switching-on impact and other problems caused by power transient in the switching process of the two modes is not deeply researched. When the direct-current microgrid is converted from an island mode to a grid-connected mode, a Point of Common Coupling switch (PCC) is directly closed, so that current flowing through the PCC switch is increased rapidly, internal power of the direct-current microgrid vibrates seriously, protection misoperation is caused, and a direct-current microgrid grid-connected inverter is locked, namely grid-connected failure is caused.
Therefore, an excellent direct-current microgrid grid-connection method is needed, the direct-current microgrid can be flexibly transited to a normal operation state after grid connection is completed in an island mode, the problem of power impact caused by switching of a master station and a slave station in master-slave control is solved, and real zero impact of power in the grid-connection process of the direct-current microgrid is realized.
Disclosure of Invention
The technical problem to be solved by the invention is to provide a microgrid grid-connection method, device and system based on joint control aiming at the defects of the prior art, so that a direct-current microgrid can be flexibly transited to a normal operation state after grid connection is completed from an island mode, and the problem of power impact caused by switching of a master station and a slave station in master-slave control in the prior art is solved.
The technical scheme for solving the technical problems is as follows:
a micro-grid connection method based on joint control comprises the following steps:
step 1: acquiring a grid-connected signal for switching a direct-current micro-grid from an island mode to a grid-connected mode, sending a first closing instruction to a PCC switch according to the grid-connected signal, and sending a starting instruction to a grid-connected inverter after preset delay time;
step 2: when the grid-connected inverter is started according to the starting instruction, setting the grid-connected inverter to be in a first control mode, and setting the direct-current energy storage to be in a second control mode;
and step 3: in the first control mode, setting an active control instruction of the grid-connected inverter, and acquiring the exchange power and the direct-current voltage of the direct-current energy storage in real time in the second control mode according to the active control instruction;
and 4, step 4: judging whether the exchange power meets a preset exchange power criterion or not, judging whether the direct-current voltage meets a preset direct-current voltage criterion or not, and if so, switching the grid-connected inverter from the first control mode to a third control mode to complete grid connection; otherwise, returning to the step 3.
The invention has the beneficial effects that: the large alternating-current power grid is electrically connected with the direct-current microgrid through the PCC switch and the grid-connected inverter in sequence, the direct-current microgrid comprises direct-current energy storage and distributed power supplies such as direct-current loads and photovoltaic power supplies, therefore, when the direct-current microgrid is in an island operation mode, the grid-connected inverter is in a locked state, and direct-current voltage on a direct-current circuit is maintained to be stable and unchanged through the direct-current energy storage; when the alternating-current large power grid is in fault removal and normal recovery, a grid-connected signal switched from an island mode to a grid-connected mode is sent to the direct-current micro-grid, after the grid-connected signal is received, the PCC switch is turned off, the grid-connected inverter is turned on after a preset delay time, the grid-connected inverter is set to be in a first control mode, and the direct-current energy storage is set to be in a second control mode, so that capacitors and other devices in the grid-connected inverter can be charged, and subsequent grid-connected control is facilitated; after the grid-connected inverter is started and is set to be in a first control mode and the direct-current energy storage is set to be in a second control mode, an active control instruction of the grid-connected inverter is set, the exchange power of the direct-current energy storage meets a preset exchange power criterion and the direct-current voltage of the direct-current energy storage meets a preset direct-current voltage criterion under the active control instruction and the second control mode, then the control mode of the grid-connected inverter is switched to be in a third control mode, based on the combined control of the grid-connected inverter and the direct-current energy storage, the problem of switching-on impact caused by power transient caused by directly starting the grid-connected inverter is effectively avoided, the problem that the current flowing through a PCC switch is sharply increased due to directly closing the PCC switch, the micro-power oscillation in a direct-current network is caused, the protection misoperation and the locking problem of the grid-connected inverter are further is solved, and the flexible transition of a direct-current micro-grid from an, the problem of power impact caused by switching of the master station and the slave station in master-slave control is solved, and zero impact of power in the grid connection process of the direct-current micro-grid is really realized.
According to another aspect of the invention, a microgrid grid-connected device based on joint control is provided, which comprises a signal acquisition module, an instruction sending module, a mode setting module, a data acquisition module, a data analysis module and a mode switching module;
the signal acquisition module is used for acquiring a grid-connected signal for switching the direct-current micro-grid from an island mode to a grid-connected mode;
the command sending module is used for sending a first closing command to the PCC switch according to the grid-connected signal and sending a starting command to the grid-connected inverter after preset delay time;
the mode setting module is used for setting the grid-connected inverter into a first control mode and setting the direct-current energy storage into a second control mode after the grid-connected inverter is started according to the starting instruction; the active control instruction of the grid-connected inverter is set in the first control mode;
the data acquisition module is used for acquiring the exchange power and the direct-current voltage of the direct-current energy storage in real time in the second control mode according to the active control instruction;
the data analysis module is used for judging whether the exchange power meets a preset exchange power criterion or not and judging whether the direct current voltage meets a preset direct current voltage criterion or not;
and the mode switching module is used for switching the grid-connected inverter from the first control mode to a third control mode to complete grid connection when the data analysis module judges that the exchange power meets the exchange power criterion and the direct-current voltage meets the direct-current voltage criterion.
The invention has the beneficial effects that: when the alternating-current large power grid is in fault removal and normal recovery, a grid-connected signal switched from an island mode to a grid-connected mode is obtained through the signal obtaining module, after the grid-connected signal is received, the PCC switch is turned off, the grid-connected inverter is turned on after a preset delay time, and the grid-connected inverter is set to be in a first control mode and the direct-current energy storage is set to be in a second control mode through the mode setting module respectively, so that devices such as capacitors in the grid-connected inverter can be charged, and subsequent grid-connected control is facilitated; after the grid-connected inverter is started and is set to be in a first control mode and the direct-current energy storage is set to be in a second control mode, an active control instruction of the grid-connected inverter is set through the mode setting module, the exchange power of the direct-current energy storage meets a preset exchange power criterion and the direct-current voltage of the direct-current energy storage meets a preset direct-current voltage criterion under the active control instruction and the second control mode, then the control mode of the grid-connected inverter is switched to be in a third control mode through the mode switching module, and based on the combined control of the grid-connected inverter and the direct-current energy storage, the problem of switching-on impact caused by power transient caused by directly starting the grid-connected inverter is effectively avoided, the problem that the current flowing through the PCC switch is increased rapidly due to the fact that the PCC switch is directly closed, the direct-current micro-grid internal power oscillation is caused, and further the problems of protection, the direct-current micro-grid can be flexibly transited to a normal operation state after the direct-current micro-grid is connected to the grid from an island mode, the problem of power impact caused by switching of the master station and the slave station in master-slave control is solved, and zero impact of power in the direct-current micro-grid connection process is really realized.
According to another aspect of the invention, a micro-grid-connected system based on joint control is provided, which comprises the micro-grid-connected device based on joint control, a PCC switch, a grid-connected inverter and a direct-current energy storage;
the microgrid grid-connected device based on the joint control is respectively and electrically connected with the PCC switch, the grid-connected inverter and the direct current energy storage, the grid-connected inverter is electrically connected with the direct current energy storage, the grid-connected inverter is also electrically connected with a large alternating current power grid, and the PCC switch is arranged at a public connection point of the grid-connected inverter and the large alternating current power grid and is respectively and electrically connected with the grid-connected inverter and the large alternating current power grid.
The invention has the beneficial effects that: based on the combined control of the grid-connected inverter and the direct current energy storage, the problem of switching-on impact caused by power transient caused by directly starting the grid-connected inverter is effectively solved, and the problem that current flowing through a PCC switch is increased sharply due to directly closing the PCC switch, so that internal power oscillation of a direct current microgrid is caused, and further misoperation protection and grid-connected inverter locking are caused is solved.
Drawings
Fig. 1 is a schematic flow chart of a microgrid grid-connection method based on joint control according to an embodiment of the present invention;
fig. 2 is a schematic diagram illustrating a principle of a microgrid grid-connection method based on joint control according to an embodiment of the present invention;
fig. 3 is a schematic flow chart illustrating setting of the grid-connected inverter to the first control mode and setting of the dc storage to the second control mode according to the first embodiment of the present invention;
fig. 4 is a schematic flow chart illustrating the switching of the grid-connected inverter into the third control mode according to the first embodiment of the present invention;
fig. 5 is a schematic flow chart of turning off the dc energy storage when the grid-connected inverter is switched to the third control mode according to the first embodiment of the present invention;
FIG. 6 is a grid-connected waveform diagram obtained by performing grid-connection according to the conventional control method;
fig. 7 is a grid-connected waveform diagram obtained by a grid-connected method based on joint control according to a first embodiment of the present invention;
fig. 8 is a schematic view of a complete flow of a microgrid grid-connection method based on joint control according to a first embodiment of the present invention;
fig. 9 is a schematic structural diagram of an island detection device based on hybrid power feedback disturbance according to a second embodiment of the present invention;
fig. 10 is a simplified topology diagram of dc energy storage according to a third embodiment of the present invention;
fig. 11 is a schematic diagram of a simplified topology structure of a grid-connected inverter according to a third embodiment of the present invention.
Detailed Description
The principles and features of this invention are described below in conjunction with the following drawings, which are set forth by way of illustration only and are not intended to limit the scope of the invention.
The present invention will be described with reference to the accompanying drawings.
In an embodiment, as shown in fig. 1, a microgrid grid-connection method based on joint control includes the following steps:
s1: acquiring a grid-connected signal for switching a direct-current micro-grid from an island mode to a grid-connected mode, sending a first closing instruction to a PCC switch according to the grid-connected signal, and sending a starting instruction to a grid-connected inverter after preset delay time;
s2: when the grid-connected inverter is started according to the starting instruction, setting the grid-connected inverter to be in a first control mode, and setting the direct-current energy storage to be in a second control mode;
s3: in the first control mode, setting an active control instruction of the grid-connected inverter, and acquiring the exchange power and the direct-current voltage of the direct-current energy storage in real time in the second control mode according to the active control instruction;
s4: judging whether the exchange power meets a preset exchange power criterion or not, judging whether the direct-current voltage meets a preset direct-current voltage criterion or not, and if so, switching the grid-connected inverter from the first control mode to a third control mode to complete grid connection; otherwise, return to S3.
In the embodiment, when the large alternating-current power grid fails and is recovered to be normal, firstly, a grid-connected signal switched from an island mode to a grid-connected mode is sent to the direct-current micro-grid, after the grid-connected signal is received, the PCC switch is turned off, the grid-connected inverter is turned on after a preset delay time, the grid-connected inverter is set to be in a first control mode, the direct-current energy storage is set to be in a second control mode, and therefore devices such as capacitors in the grid-connected inverter can be charged, and subsequent grid-connected control is facilitated; after the grid-connected inverter is started and set as a first control mode and the direct-current energy storage is set as a second control mode, an active control instruction of the grid-connected inverter is set, the exchange power of the direct-current energy storage meets a preset exchange power criterion and the direct-current voltage of the direct-current energy storage meets a preset direct-current voltage criterion under the active control instruction and the second control mode, then the control mode of the grid-connected inverter is switched into a third control mode, based on the combined control of the grid-connected inverter and the direct-current energy storage, the problem of switching-on impact caused by power transient caused by directly starting the grid-connected inverter is effectively avoided, the problem that the direct-closing PCC switch causes the sharp increase of current flowing through the PCC switch, so that the internal power oscillation of the direct-current microgrid is caused, further the protection misoperation and the grid-connected inverter locking are caused is solved, and the direct-current microgrid can flexibly transit to a normal operation state after the grid connection is completed in an island mode, the problem of power impact caused by switching of the master station and the slave station in master-slave control is solved, and zero impact of power in the grid connection process of the direct-current micro-grid is really realized.
Specifically, a schematic diagram of a principle of a microgrid interconnection method based on joint control in this embodiment is shown in fig. 2, an ac large power grid is electrically connected to a dc microgrid through a PCC switch and an interconnection inverter in sequence, the dc microgrid includes a dc energy storage, and also includes a distributed power supply such as a dc load and a photovoltaic power supply, where the PCC switch is a switch connecting the ac large power grid and the dc microgrid; it should be noted that the present embodiment includes, but is not limited to, the operation structure shown in fig. 2.
Specifically, in this embodiment, when the direct-current microgrid in the island operation mode receives a grid-connected signal when t is 3s, first a first close command is sent to close the PCC switch, and after a delay of 0.1s, after charging of elements such as a voltage stabilizing capacitor in the grid-connected inverter is completed, a start command is sent to start the grid-connected inverter to start inversion control.
Preferably, as shown in fig. 3, the specific step of S2 includes:
s21: when the grid-connected inverter is started according to the starting instruction, acquiring the active power and the reactive power of the grid-connected inverter in real time;
s22: setting the grid-connected inverter to be in the first control mode according to the active power and the reactive power of the grid-connected inverter, wherein the first control mode is specifically an active power-reactive power control mode; and setting the direct-current energy storage to be in the second control mode, wherein the second control mode is specifically a constant direct-current voltage control mode.
When the direct-current micro-grid operates normally in a grid-connected mode, the grid-connected inverter is used as a main station for master-slave control to take charge of stable direct-current bus voltage (direct-current voltage for short) VdcAnd V in island mode of operationdcThe direct current energy storage is used for controlling, so that in order to enable the direct current micro-grid to flexibly transit to a normal operation state after the grid connection is completed in an island mode, the active power and the reactive power of a grid-connected inverter are firstly obtained, the grid-connected inverter is set to be in an active power-reactive power control mode, P/Q control mode for short, according to the active power and the reactive power of the grid-connected inverter, and the direct current energy storage is set to be in a constant direct current voltage control mode, namely the direct current energy storage is kept unchanged in the energy storage mode; through the P/Q control mode and the constant direct current voltage control mode, smooth transition of power can be realized, follow-up setting of active control instructions can be facilitated, the grid-connected inverter can be switched from the first control mode to the third control mode conveniently, flexible transition in master-slave control is guaranteed, internal power oscillation of a direct current microgrid caused by power transient is avoided, and therefore the problems of protection misoperation and grid-connected inverter locking are solved, and real power zero impact is realized.
Specifically, in this embodiment, the P/Q control mode refers to setting output values of active power and reactive power of a port of a certain element (specifically, in this embodiment, a grid-connected inverter) at the same time, so as to achieve the purpose of controlling the active power and the reactive power of the port at the same time.
Preferably, in S3, the active control command is specifically:
and gradually increasing the active power reference value of the grid-connected inverter corresponding to the grid-connected inverter.
The active power reference value of the grid-connected inverter is gradually increased, and the exchange power of the direct current energy storage can be gradually reduced to 0 based on the P/Q control mode, so that the P/Q control mode of the grid-connected inverter is conveniently switched, the flexible switching of a master station in master-slave control after grid connection is ensured, and the grid connection is smoothly completed.
Specifically, in this embodiment, when the grid-connected inverter active power reference value is increased step by step, the grid-connected inverter reactive power reference value is always 0.
Preferably, as shown in fig. 4, the specific step of S4 includes:
s41: in the process of gradually increasing the active power reference value of the grid-connected inverter, acquiring a final value of the exchange power of the direct-current energy storage, and judging whether the final value of the exchange power meets a preset exchange power criterion, if so, executing S42, and if not, returning to S3;
the switching power criterion is specifically:
wherein the content of the first and second substances,
is the final value of the exchange power;
s42: in the process of gradually increasing the active power reference value of the grid-connected inverter, judging whether the direct-current voltage of the direct-current energy storage meets a preset direct-current voltage criterion, if so, executing S43; if not, returning to S3;
the direct-current voltage criterion is specifically as follows:
0.95Vbase≤Vdc≤1.05Vbase；
wherein, VdcStoring energy for said direct currentSaid direct voltage, VbaseIs a DC voltage reference value;
s43: and switching the grid-connected inverter from the first control mode to a third control mode to complete grid connection, wherein the third control mode is a direct-current voltage-reactive power control mode.
Through the exchange power criterion and the direct-current voltage criterion, the port power of the grid-connected inverter can be continuously increased on the basis of setting the control mode of the grid-connected inverter to be the P/Q control mode, so that the power of the direct-current energy storage port is indirectly reduced, the flexible transfer of power is realized, the switching of the control mode of the grid-connected inverter is completed on the basis, and the zero-impact grid connection of the direct-current micro-grid is completed.
Specifically, in the present embodiment, the control mode of the grid-connected inverter is switched to the third control mode, i.e., the dc voltage-reactive power control mode, abbreviated as Vdca/Q control mode; wherein, Vdcthe/Q control mode is to set output values of the dc voltage and the reactive power of a port of a certain element (specifically, in this embodiment, a dc energy storage) at the same time, so as to achieve the purpose of controlling the dc voltage and the reactive power of the port at the same time.
In particular, VbaseThe voltage level of the dc voltage is 10kV, and when the dc voltage is within 0.95-1.05 per unit, that is, the dc voltage is between 9.5kV and 10.5 kV.
Preferably, as shown in fig. 5, after S43, the method further includes:
s44: and sending a second closing instruction to the direct-current energy storage, and closing the direct-current energy storage according to the second closing instruction.
Because the direct-current energy storage is required to be locked by default in the grid-connected operation process, if the direct-current energy storage is not closed, the ports of the direct-current energy storage are likely to be frequently charged and discharged, so that the service life of a battery in the direct-current energy storage is damaged, and therefore when the control mode of the grid-connected inverter is switched to VdcAfter the/Q control mode, the DC storage is closedThe energy can play a role in protecting direct current energy storage; it should be noted that, since both the mode switching and the dc energy storage blocking of the grid-connected inverter are instantly completed operations, and both the operations are short in time, the two operations can be considered to be performed synchronously when the dc energy storage is turned off after the mode switching of the grid-connected inverter.
Specifically, the traditional grid-connection method and the grid-connection method based on the joint control in the embodiment are respectively adopted to perform grid connection on the microgrid, and corresponding grid-connection waveform diagrams are obtained and compared, as shown in fig. 6 and 7, respectively, wherein performing grid connection by the traditional grid-connection method means that the direct-current energy storage is directly turned off at 3.1s, and the control mode of the grid-connected inverter is directly set to Vdca/Q control mode; as can be seen from fig. 6 and 7, in the microgrid grid-connection process based on the combined control of the direct-current energy storage and the grid-connected inverter in the embodiment, the power transition is smoother, the impact of the power is smaller, and the flexible switching of the master station in the master-slave control after grid connection is really realized.
Specifically, based on the above-mentioned complete steps of microgrid grid connection, a complete flow diagram of a preferred embodiment is obtained as shown in fig. 8. Based on the combined control of the grid-connected inverter and the direct-current energy storage, the problem of switching-on impact caused by power transient caused by directly starting the grid-connected inverter is effectively solved.
In a second embodiment, as shown in fig. 9, a microgrid grid-connected device based on joint control includes a signal acquisition module, an instruction sending module, a mode setting module, a data acquisition module, a data analysis module, and a mode switching module;
the signal acquisition module is used for acquiring a grid-connected signal for switching the direct-current micro-grid from an island mode to a grid-connected mode;
the command sending module is used for sending a first closing command to the PCC switch according to the grid-connected signal and sending a starting command to the grid-connected inverter after preset delay time;
the mode setting module is used for setting the grid-connected inverter into a first control mode and setting the direct-current energy storage into a second control mode after the grid-connected inverter is started according to the starting instruction; the active control instruction of the grid-connected inverter is set in the first control mode;
the data acquisition module is used for acquiring the exchange power and the direct-current voltage of the direct-current energy storage in real time in the second control mode according to the active control instruction;
the data analysis module is used for judging whether the exchange power meets a preset exchange power criterion or not and judging whether the direct current voltage meets a preset direct current voltage criterion or not;
and the mode switching module is used for switching the grid-connected inverter from the first control mode to a third control mode to complete grid connection when the data analysis module judges that the exchange power meets the exchange power criterion and the direct-current voltage meets the direct-current voltage criterion.
When the alternating-current large power grid is in fault removal and normal recovery, a grid-connected signal switched from an island mode to a grid-connected mode is obtained through the signal obtaining module, after the grid-connected signal is received, the PCC switch is turned off, the grid-connected inverter is turned on after a preset delay time, and the grid-connected inverter is set to be in a first control mode and the direct-current energy storage is set to be in a second control mode through the mode setting module respectively, so that devices such as capacitors in the grid-connected inverter can be charged, and subsequent grid-connected control is facilitated; after the grid-connected inverter is started and set as a first control mode and the direct-current energy storage is set as a second control mode, an active control instruction of the grid-connected inverter is set through the mode setting module, the exchange power of the direct-current energy storage meets a preset exchange power criterion and the direct-current voltage of the direct-current energy storage meets the preset direct-current voltage criterion under the active control instruction and the second control mode, then the control mode of the grid-connected inverter is switched into a third control mode through the mode switching module, and based on the combined control of the grid-connected inverter and the direct-current energy storage, the problem of switching-on impact caused by power transient caused by directly starting the grid-connected inverter is effectively avoided, and the problem that the current flowing through the PCC switch is sharply increased due to directly closing the PCC switch, so that the internal power of a direct-current microgrid vibrates, and further the problems of protection misoperation and grid-connected inverter locking are solved, the direct-current micro-grid can be flexibly transited to a normal operation state after the direct-current micro-grid is connected to the grid from an island mode, the problem of power impact caused by switching of the master station and the slave station in master-slave control is solved, and zero impact of power in the direct-current micro-grid connection process is really realized.
Preferably, the mode setting module is specifically configured to:
when the grid-connected inverter is started according to the starting instruction, acquiring the active power and the reactive power of the grid-connected inverter in real time;
setting the grid-connected inverter to be in the first control mode according to the active power and the reactive power of the grid-connected inverter, wherein the first control mode is specifically an active power-reactive power control mode; and setting the direct-current energy storage to be in the second control mode, wherein the second control mode is specifically a constant direct-current voltage control mode.
Preferably, the active control instruction specifically includes:
gradually increasing the grid-connected inverter active power reference value corresponding to the grid-connected inverter;
the data analysis module is specifically configured to:
in the process of gradually increasing the active power reference value of the grid-connected inverter, acquiring a final value of the exchange power of the direct-current energy storage, and judging whether the final value of the exchange power meets a preset exchange power criterion;
when the final value of the exchange power meets the exchange power criterion, judging whether the direct-current voltage of the direct-current energy storage meets a preset direct-current voltage criterion;
the mode switching module is specifically configured to:
and when the direct-current voltage meets the direct-current voltage criterion, switching the grid-connected inverter from the first control mode to a third control mode to complete grid connection, wherein the third control mode is a direct-current voltage-reactive power control mode.
Preferably, the instruction sending module is further specifically configured to:
and when the direct-current voltage meets the direct-current voltage criterion, sending a second closing instruction to the direct-current energy storage, and closing the direct-current energy storage according to the second closing instruction.
The microgrid grid-connected system based on the joint control comprises the microgrid grid-connected device based on the joint control, a PCC switch, a grid-connected inverter and direct-current energy storage;
the microgrid grid-connected device based on the joint control is respectively and electrically connected with the PCC switch, the grid-connected inverter and the direct current energy storage, the grid-connected inverter is electrically connected with the direct current energy storage, the grid-connected inverter is also electrically connected with a large alternating current power grid, and the PCC switch is arranged at a public connection point of the grid-connected inverter and the large alternating current power grid and is respectively and electrically connected with the grid-connected inverter and the large alternating current power grid.
Based on the combined control of the grid-connected inverter and the direct current energy storage, the problem of switching-on impact caused by power transient caused by directly starting the grid-connected inverter is effectively solved, and the problem that current flowing through a PCC switch is increased sharply due to directly closing the PCC switch, so that internal power oscillation of a direct current microgrid is caused, and further misoperation protection and grid-connected inverter locking are caused is solved.
Specifically, the microgrid grid-connected system based on joint control in the embodiment is shown in fig. 2, wherein a simplified topology structure diagram of direct-current energy storage is shown in fig. 10, and the simplified topology structure diagram includes a storage battery, a Boost circuit, a Buck circuit, an inductor and a capacitor; the simplified topology structure diagram of the grid-connected inverter is shown in fig. 11, and the grid-connected inverter is a three-phase full-bridge inverter and comprises 6 switching tubes, namely CG1, CG2, CG3, CG4, CG5 and CG 6.
For other details of the microgrid grid-connected system based on the joint control in this embodiment, reference is made to the detailed description of the first embodiment and the second embodiment, and details are not described here.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents, improvements and the like that fall within the spirit and principle of the present invention are intended to be included therein.
Claims (6)
1. A micro-grid connection method based on joint control is characterized by comprising the following steps:
step 1: acquiring a grid-connected signal for switching a direct-current micro-grid from an island mode to a grid-connected mode, sending a first closing instruction to a PCC switch according to the grid-connected signal, and sending a starting instruction to a grid-connected inverter after preset delay time;
step 2: when the grid-connected inverter is started according to the starting instruction, setting the grid-connected inverter to be in a first control mode, and setting the direct-current energy storage to be in a second control mode;
and step 3: in the first control mode, setting an active control instruction of the grid-connected inverter, and acquiring the exchange power and the direct-current voltage of the direct-current energy storage in real time in the second control mode according to the active control instruction;
and 4, step 4: judging whether the exchange power meets a preset exchange power criterion or not, judging whether the direct-current voltage meets a preset direct-current voltage criterion or not, and if so, switching the grid-connected inverter from the first control mode to a third control mode to complete grid connection; otherwise, returning to the step 3;
the specific steps of the step 2 comprise:
step 21: when the grid-connected inverter is started according to the starting instruction, acquiring the active power and the reactive power of the grid-connected inverter in real time;
step 22: setting the grid-connected inverter to be in the first control mode according to the active power and the reactive power of the grid-connected inverter, wherein the first control mode is specifically an active power-reactive power control mode; setting the direct-current energy storage to be in the second control mode, wherein the second control mode is specifically a constant direct-current voltage control mode;
in step 3, the active control instruction is specifically:
gradually increasing the grid-connected inverter active power reference value corresponding to the grid-connected inverter;
the specific steps of the step 4 comprise:
step 41: in the process of gradually increasing the active power reference value of the grid-connected inverter, acquiring a final value of the exchange power of the direct-current energy storage, and judging whether the final value of the exchange power meets a preset exchange power criterion, if so, executing a step 42, and if not, returning to the step 3;
step 42: in the process of gradually increasing the active power reference value of the grid-connected inverter, judging whether the direct-current voltage of the direct-current energy storage meets the preset direct-current voltage criterion, if so, executing a step 43; if not, returning to the step 3;
step 43: and switching the grid-connected inverter from the first control mode to a third control mode to complete grid connection, wherein the third control mode is a direct-current voltage-reactive power control mode.
2. The microgrid grid-connection method based on joint control of claim 1, characterized in that the exchange power criterion is specifically:
wherein the content of the first and second substances,
is the final value of the exchange power;
the direct-current voltage criterion is specifically as follows:
0.95Vbase≤Vdc≤1.05Vbase；
wherein, VdcSaid DC voltage, V, for storing said DC energybaseIs a DC voltage reference value.
3. The microgrid interconnection method based on joint control of claim 1, further comprising after the step 43:
step 44: and sending a second closing instruction to the direct-current energy storage, and closing the direct-current energy storage according to the second closing instruction.
4. A micro-grid connection device based on joint control is characterized by comprising a signal acquisition module, an instruction sending module, a mode setting module, a data acquisition module, a data analysis module and a mode switching module;
the signal acquisition module is used for acquiring a grid-connected signal for switching the direct-current micro-grid from an island mode to a grid-connected mode;
the command sending module is used for sending a first closing command to the PCC switch according to the grid-connected signal and sending a starting command to the grid-connected inverter after preset delay time;
the mode setting module is used for setting the grid-connected inverter into a first control mode and setting the direct-current energy storage into a second control mode after the grid-connected inverter is started according to the starting instruction; the active control instruction of the grid-connected inverter is set in the first control mode;
the data acquisition module is used for acquiring the exchange power and the direct-current voltage of the direct-current energy storage in real time in the second control mode according to the active control instruction;
the data analysis module is used for judging whether the exchange power meets a preset exchange power criterion or not and judging whether the direct current voltage meets a preset direct current voltage criterion or not;
the mode switching module is used for switching the grid-connected inverter from the first control mode to a third control mode to complete grid connection when the data analysis module judges that the exchange power meets the exchange power criterion and the direct-current voltage meets the direct-current voltage criterion;
the mode setting module is specifically configured to:
when the grid-connected inverter is started according to the starting instruction, acquiring the active power and the reactive power of the grid-connected inverter in real time;
setting the grid-connected inverter to be in the first control mode according to the active power and the reactive power of the grid-connected inverter, wherein the first control mode is specifically an active power-reactive power control mode; setting the direct-current energy storage to be in the second control mode, wherein the second control mode is specifically a constant direct-current voltage control mode;
the active control instruction specifically comprises:
gradually increasing the grid-connected inverter active power reference value corresponding to the grid-connected inverter;
the data analysis module is specifically configured to:
in the process of gradually increasing the active power reference value of the grid-connected inverter, acquiring a final value of the exchange power of the direct-current energy storage, and judging whether the final value of the exchange power meets a preset exchange power criterion;
when the final value of the exchange power meets the exchange power criterion, judging whether the direct-current voltage of the direct-current energy storage meets a preset direct-current voltage criterion;
the mode switching module is specifically configured to:
and when the direct-current voltage meets the direct-current voltage criterion, switching the grid-connected inverter from the first control mode to a third control mode to complete grid connection, wherein the third control mode is a direct-current voltage-reactive power control mode.
5. The microgrid interconnection apparatus based on joint control of claim 4, wherein the instruction sending module is further specifically configured to:
and when the direct-current voltage meets the direct-current voltage criterion, sending a second closing instruction to the direct-current energy storage, and closing the direct-current energy storage according to the second closing instruction.
6. A microgrid grid-connected system based on joint control is characterized by comprising the microgrid grid-connected device based on joint control of any one of claims 4 to 5, a PCC switch, a grid-connected inverter and a direct-current energy storage;
the microgrid grid-connected device based on the joint control is respectively and electrically connected with the PCC switch, the grid-connected inverter and the direct current energy storage, the grid-connected inverter is electrically connected with the direct current energy storage, the grid-connected inverter is also electrically connected with a large alternating current power grid, and the PCC switch is arranged at a public connection point of the grid-connected inverter and the large alternating current power grid and is respectively and electrically connected with the grid-connected inverter and the large alternating current power grid.
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