CN108808711B - Photovoltaic automatic phase-selecting parallel network used for three-phase load unbalance management system of low-voltage power network - Google Patents
Photovoltaic automatic phase-selecting parallel network used for three-phase load unbalance management system of low-voltage power network Download PDFInfo
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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
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- 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 relates to a photovoltaic automatic phase-selecting and networking system for a three-phase load unbalance management system of a power grid, which comprises the following components: the method comprises the steps that the electric energy output end of a first current transmitter is respectively connected with a second current transmitter, a third current transmitter and a fourth current transmitter through three normally open contacts of an alternating current contactor, the current value output by a photovoltaic power generation unit is detected in real time through the first current transmitter, the current value of a three-phase municipal power supply and a load connection side is detected in real time through the second current transmitter, the third current transmitter and the fourth current transmitter, detection signals are sent to an analog-to-digital converter in a logic control system, a programmable controller compares detection values of the current transmitters, the maximum load phase when three-phase power is unbalanced is analyzed, and an instruction is sent to a control coil of the alternating current contactor, so that the switching-on and switching-off of the normally open contacts of the corresponding alternating current contactor in a measuring and executing system are controlled, and the automatic phase selection of the photovoltaic power generation system is changed, and the corresponding phase in the mains supply is accessed.
Description
Technical Field
The invention relates to a photovoltaic automatic phase-selecting parallel network for a three-phase load unbalance management system of a power grid.
Background
The three-phase unbalance is an important quality index of the power grid operation, and although three-phase balance is striven for in the power grid design, the three-phase unbalance is very serious in actual operation because of the problem of user use, so that the three-phase unbalance greatly exceeds the national standard. The unbalanced three phases can bring serious harm to the power grid, the generated negative sequence voltage and negative sequence current can lead to heating and vibration of the rotating motor, the magnetic leakage of the transformer is increased, local overheat is caused, the line loss of the power grid is increased, various protection and automatic device misoperation are caused, the negative sequence voltage and negative sequence current of the power grid are caused, the power supply quality is influenced, the line loss is further increased, and the power supply reliability is reduced.
The existing common three-phase power balance regulator based on current regulation has the following working principles: the current of each phase of the system is detected in real time through an instrument, the detection value is sent to an internal controller for processing analysis so as to judge whether the system is in an unbalanced state or not, meanwhile, the current value required to be converted by each phase when the system reaches the balanced state is calculated, then signals are sent to an internal element and drive the internal element to act, unbalanced current is transferred from a phase sequence with large current to a phase sequence with small current, and finally the three-phase balanced state is achieved.
When the distributed photovoltaic power generation capacity is smaller, the distributed photovoltaic power generation unit is connected to a low-voltage power grid in a single-phase grid-connected mode, and at present, a single photovoltaic power generation unit is fixedly connected to a certain phase of the power grid and does not have an automatic phase selection function.
The traditional three-phase power balance regulator can meet the power balance requirement, but has complex equipment structure and higher cost; from the point of view of electric energy consumption, no economy can be said. Along with the high-density grid connection of the photovoltaic power generation units, the total capacity of the grid connection is continuously increased, and the instability of the photovoltaic power generation units can cause more serious three-phase unbalance conditions on the three-phase unbalanced power grid.
Disclosure of Invention
In order to solve the technical problems, the invention provides a photovoltaic automatic phase-selecting and grid-combining system for a three-phase load unbalance management system of a power grid, which is used for realizing power three-phase balance of the power distribution network and achieving the purposes of improving the quality of electric energy, reducing the consumption of electric energy, saving energy and protecting environment.
The invention discloses a photovoltaic automatic phase-selecting and networking system for a three-phase load unbalance management system of a power grid, which comprises the following components:
The monitoring execution unit, the logic control unit and the photovoltaic power generation unit;
The monitoring execution unit is used for obtaining the output current of the photovoltaic power generation system and the power supply current (load current) of the municipal power supply A, B, C phases and outputting the output current of the photovoltaic power generation unit and the power supply current of the municipal A, B, C phases to the logic control unit;
The logic control unit is used for judging whether the three-phase load of the municipal power supply is balanced according to the A, B, C-phase power supply current corresponding to the municipal power supply, and if so, the logic control unit controls the photovoltaic power generation unit to enter an energy storage state; if the load is unbalanced, determining a maximum load phase, and controlling the photovoltaic power generation unit to be connected with the maximum load phase by the logic control unit to perform three-phase balance adjustment.
Further, the monitoring execution unit comprises a first current transmitter which is respectively connected in series with a second current transmitter, a third current transmitter and a fourth current transmitter of municipal A, B, C three phases, wherein the second current transmitter, the third current transmitter and the fourth current transmitter are respectively connected with the first current transmitter through normally open contacts of an alternating current contactor, a neutral point of a A, B, C-phase load of a municipal power supply is connected with an alternating current input end of a photovoltaic power generation unit, and signal output ends of the first current transmitter, the second current transmitter, the third current transmitter and the fourth current transmitter are connected with a logic control unit;
The logic control unit comprises a central processor and a central processor, wherein the digital output point of the central processor is connected with the input end of the control coil of each alternating current contactor, and the output end of the control coil of each alternating current contactor is connected with a municipal power neutral line;
The first current transducer detects the current value output by the photovoltaic power generation unit in real time, the second current transducer, the third current transducer and the fourth current transducer detect the current value of each phase load of the municipal power supply in real time, detection signals are sent to the logic control system, the central processing unit compares the detection values of the current transducers, the maximum load phase when three-phase power is unbalanced is obtained through analysis, and an instruction is sent to the control coil of each alternating current contactor, so that the connection and disconnection of the normally open contact of the corresponding alternating current contactor in the measuring and executing system are controlled, and the corresponding phase of the photovoltaic power generation connected to the municipal power supply is changed.
Further, the photovoltaic power generation unit comprises a photovoltaic array, a single-phase grid-connected inverter, an energy storage system, a grid-connected control device, an energy storage control device, a first voltage transmitter and a fifth current transmitter, the collection and the processing of collection signals are carried out through a programmable controller, the photovoltaic array is controlled to receive solar energy and convert the solar energy into direct-current electric energy, the direct-current electric energy is provided for the single-phase grid-connected inverter, the single-phase grid-connected inverter is internally adjusted to obtain maximum power collection, and then the maximum power collection is converted into alternating-current electric energy meeting the standard of the mains supply of the low-voltage power network, or the alternating-current electric energy is provided for the energy storage system to store energy. Signals collected by the first voltage transmitter and the fifth current transmitter enter an analog-to-digital converter to control decision operation.
Further, signals output by the first current transducer, the second current transducer, the third current transducer, the fourth current transducer and the fifth current transducer are processed by the analog-to-digital converter and then input to the central processing unit.
Further, the central processing unit is connected with the display.
By means of the scheme, the photovoltaic automatic phase-selecting and networking system for the three-phase load unbalance management system of the low-voltage power grid has the following advantages:
When the three-phase power is unbalanced, the photovoltaic power generation unit automatically selects the phase, the photovoltaic power generation unit is connected to the highest load phase in the low-voltage network, the photovoltaic power supply is increased, the consumption of the electric energy of the low-voltage network is effectively reduced, the power compensation is carried out, the purpose that the power of the power distribution network is balanced is achieved, and the three-phase power distribution network has the advantages of improving the quality of the electric energy, reducing the consumption of the electric energy, saving energy and protecting the environment.
The conventional distributed photovoltaic grid connection is fixed phase grid connection, and in order to realize three-phase imbalance treatment, the system adopts an automatic phase selection mode to realize single-phase grid connection. Compared with the traditional three-phase unbalance treatment mode of the power distribution network, the method is not used, and the unbalance treatment is realized by adopting a photovoltaic power generation unit method. The device has the characteristics of improving the electric energy quality, reducing the electric energy consumption, saving energy and protecting environment.
The foregoing description is only an overview of the present invention, and is intended to provide a better understanding of the present invention, as it is embodied in the following description, with reference to the preferred embodiments of the present invention and the accompanying drawings.
Drawings
FIG. 1 is a circuit block diagram of the photovoltaic automatic phase-selecting and grid-connecting system for a three-phase load imbalance management system of a power grid according to the present invention;
In the figure, 1, a photovoltaic power generation system, 2, a monitoring execution system, 3, a logic control system, 4, a photovoltaic array, 5, a single-phase grid-connected inverter, 6, a first current transmitter, 7, an alternating-current contactor normally-open contact (for controlling grid-connected phase sequence selection), 8, an analog-to-digital converter, 9, a central processing unit 10, a display, 11, an alternating-current contactor control coil (for controlling grid-connected phase sequence selection), 12, a second current transmitter, 13, a third current transmitter, 14, a fourth current transmitter, 16, an energy storage system, 17, an alternating-current contactor normally-open contact (energy storage control device), 18, an alternating-current contactor normally-open contact (grid-connected control device), 19, an alternating-current contactor control coil (for controlling photovoltaic energy storage state), 20, an alternating-current contactor control coil (for controlling photovoltaic grid-connected state), 21, a fifth current transmitter, 22 and a first voltage transmitter; ( And (3) injection: A. b, C, N is a three-phase four-wire system power supply, 15, three-phase load system. )
Detailed Description
The following describes in further detail the embodiments of the present invention with reference to the drawings and examples. The following examples are illustrative of the invention and are not intended to limit the scope of the invention.
As shown in fig. 1, the photovoltaic automatic phase-selecting parallel network is used for the preferred implementation of a three-phase load unbalance management system of a power grid, and is used for realizing the three-phase unbalance management of the power grid by automatically selecting and connecting the phases. Comprising the following steps: the monitoring execution unit 2, the logic control unit 3 and the photovoltaic power generation unit 1;
The monitoring execution unit is used for obtaining the output current of the photovoltaic power generation unit and the power supply current (load current) of the municipal power supply A, B, C phase, and outputting the output current of the photovoltaic power generation unit and the power supply current of the municipal A, B, C phase to the logic control unit;
The logic control unit is used for judging whether the three-phase load of the municipal power supply is balanced according to the A, B, C-phase power supply current corresponding to the municipal power supply, and if so, the logic control unit controls the photovoltaic power generation unit to enter an energy storage state; if the load is unbalanced, determining a maximum load phase, and controlling the photovoltaic power generation unit to be connected with the maximum load phase by the logic control unit to perform three-phase balance adjustment. The automatic phase selection algorithm comprises the following steps:
i A is A phase power supply current, namely a second current transducer detection value, I B is B phase power supply current, namely a third current transducer detection value, I C is C phase power supply current, namely a fourth current transducer detection value, and I D is output current of the alternating-current side of the photovoltaic power generation unit, namely a first current transducer detection value;
Under the condition of not considering the three-phase load unbalance degree criterion, the algorithm before the photovoltaic grid connection,
I X is the maximum value of the three-phase supply current I A,IB,IC, i.e
IX＝MAX{IA,IB,IC}
When I X＝IA is carried out, the corresponding alternating current contactor of A acts to realize that the photovoltaic power supply system supplies power to the phase A parallel network;
when I X＝IB is carried out, the corresponding alternating current contactor of the B acts, so that the photovoltaic power supply system supplies power to the B-phase parallel network;
When I X＝IC is carried out, the corresponding alternating current contactor of the C acts, so that the photovoltaic power supply system supplies power to the C-phase parallel network;
the algorithm after photovoltaic grid connection under the condition of not considering the three-phase load unbalance degree criterion comprises the following steps:
Let I U be the maximum value of the three-phase load current, i.e
I X＝IA, I U＝MAX{IA+ID,IB,IC }
When I U＝IA+ID is carried out, the alternating-current contactor is kept in an original state, and the photovoltaic power supply system continues to supply power to the phase A parallel network;
When I U＝IB is carried out, the alternating current contactor acts, the phase A is opened, the phase B is closed, and the photovoltaic power supply system supplies power to the phase B in a parallel network manner;
When I U＝IC is carried out, the alternating current contactor acts, the phase A is opened, the phase C is closed, and the photovoltaic power supply system supplies power to the phase C in a parallel network manner;
I X＝IB, I U＝MAX{IA,IB+ID,IC }
When I U＝IA is carried out, the alternating current contactor acts, the phase B is opened, the phase A is closed, and the photovoltaic power supply system supplies power to the phase A in a parallel network manner;
When I U＝IB+ID is carried out, the alternating-current contactor is kept in an original state, and the photovoltaic power supply system continues to supply power to the phase B parallel network;
when I U＝IC is carried out, the alternating-current contactor acts (B phase is opened, C phase is closed) and the photovoltaic power supply system supplies power to the C phase in a parallel network manner;
I X＝IC, I U＝MAX{IA,IB,IC+ID }
When I U＝IA is carried out, the alternating-current contactor acts (C phase is opened, A phase is closed) and the photovoltaic power supply system supplies power to the A phase in a parallel network manner;
When I U＝IB is carried out, the alternating-current contactor acts (C phase is opened, B phase is closed), and the photovoltaic power supply system supplies power to the B phase in a parallel network manner;
When I U＝IC+ID is carried out, the alternating-current contactor is kept in an original state, and the photovoltaic power supply system continues to supply power to the phase C parallel network;
The three-phase load unbalance degree criterion specifically comprises:
Before grid connection of the photovoltaic power supply system, the output current formula of the inversion alternating current side after grid connection is calculated according to the direct current output by the photovoltaic panel is as follows:
V is light Fu Bangong as voltage (first voltage transmitter detection value), I E is direct-current side current (fifth current transmitter detection value) of the photovoltaic power generation unit, eta is working efficiency of the grid-connected inverter, V 1 is municipal power supply voltage grade of the pre-grid-connected side, and I F is current value injected into a power grid by the calculated photovoltaic power supply system
MAX{IA,IB,IC}＝IV
MIN{IA,IB,IC}＝IW
When I F≤(IV-IW) is carried out, the photovoltaic power supply system disconnects the energy storage alternating current contactor and enters a grid-connected power supply mode;
After the photovoltaic power supply system is connected with the grid, whether the photovoltaic is continuously supplied with power or not is judged according to the following calculation formula:
MIN{IA,IB,IC}＝IW
When I X is consistent with I W (which indicates that the power grid is in an overcompensated state), the photovoltaic power supply system stops grid-connected power supply and enters the working state of the energy storage system.
The actual automatic phase selection algorithm is completed under the condition of considering the three-phase load unbalance degree criterion.
The monitoring execution unit comprises a first current transmitter 6, and a second current transmitter 12, a third current transmitter 13 and a fourth current transmitter 14 which are respectively connected with the electric energy output end of the first current transmitter through three normally open contacts 7 of an alternating current contactor, wherein the electric energy input ends of the second current transmitter, the third current transmitter and the fourth current transmitter are respectively connected with A, B, C corresponding to municipal power sources in a one-to-one correspondence manner, the neutral point of a A, B, C-phase load corresponding to the municipal power sources is connected with the alternating current input end of the photovoltaic power generation unit, and the signal output ends of the first current transmitter, the second current transmitter, the third current transmitter and the fourth current transmitter are connected with the logic control unit;
The logic control unit comprises a central processor and a central processor connected with a display, wherein the digital output point of the central processor is connected with the input end of a control coil 11 of each alternating current contactor in a corresponding logic execution system, the output end of the control coil of each alternating current contactor is connected with a power neutral line, signals output by the first current transducer, the second current transducer, the third current transducer and the fourth current transducer are processed by an analog-to-digital converter 8 and then are input into the central processor 9, the current value output by the photovoltaic power generation unit is detected in real time through the first current transducer, the detection signal is sent into the logic control unit, the current value of the transformer and the load connection side is detected in real time through the second current transducer, the third current transducer and the fourth current transducer, the detection signal is sent into the analog-to-digital converter in the logic control system, the comparison of the detection values of the current transducers is analyzed to obtain the maximum load phase when three-phase power is unbalanced, and then the control coil of each alternating current contactor is controlled to be measured, and the normally-open state of the corresponding alternating current contactor in the execution system is switched on and off, so that the corresponding phase of the photovoltaic power generation system is automatically selected and connected to the mains supply is changed.
In this embodiment, the photovoltaic power generation unit includes a photovoltaic array 4, a single-phase grid-connected inverter 5, an energy storage system 16, an energy storage control device 17, a grid-connected control device 18, a first voltage transmitter 22, a fifth current transmitter 21, wherein the fifth current transmitter collects output current of the photovoltaic array, the first voltage transmitter collects output voltage of the photovoltaic array, the programmable controller processes collected signals of the fifth current transmitter and the first voltage transmitter, controls the photovoltaic array to receive solar energy and convert the solar energy into direct current electric energy, the direct current electric energy is provided for the single-phase grid-connected inverter, and the single-phase grid-connected inverter is internally adjusted to obtain maximum power collection and then converted into alternating current electric energy meeting the low-voltage grid mains supply standard, or provided for the energy storage system to store energy; the signals collected by the first voltage transmitter 22 and the fifth current transmitter 21 enter the analog-to-digital converter 8 to control the decision operation.
In this embodiment, the central processing unit is connected to the display.
The above description is only of the preferred embodiments of the present invention and is not intended to limit the present invention, and it should be noted that it is possible for those skilled in the art to make several improvements and modifications without departing from the technical principle of the present invention, and these improvements and modifications should also be regarded as the protection scope of the present invention.
Claims (5)
1. The photovoltaic automatic phase-selecting parallel network is used for a three-phase load unbalance management system of a low-voltage network and is characterized by comprising a monitoring execution unit, a logic control unit and a photovoltaic power generation unit;
The monitoring execution unit is used for obtaining the output current of the photovoltaic power generation unit and the power supply current of the municipal power supply A, B, C phase and outputting the output current of the photovoltaic power generation unit and the power supply current of the municipal A, B, C phase to the logic control unit;
The logic control unit is used for judging whether the three-phase load of the municipal power supply is balanced according to the A, B, C-phase power supply current corresponding to the municipal power supply before the photovoltaic grid connection, and if so, the photovoltaic power generation unit is used for storing energy and is not connected with the power grid; if the load is unbalanced, determining a maximum load phase, and controlling the photovoltaic power generation unit to be connected with the maximum load phase by the logic control unit so as to achieve the purpose of three-phase balance;
The three-phase load unbalance degree criterion of the photovoltaic power generation unit specifically comprises the following steps:
Before grid connection of the photovoltaic power supply system, the output current formula of the inversion alternating current side after grid connection is calculated according to the direct current output by the photovoltaic panel is as follows:
V is light Fu Bangong as voltage, i.e. a first voltage transmitter detection value, I E is direct-current side current of the photovoltaic power generation unit, i.e. a fifth current transmitter detection value, eta is working efficiency of the grid-connected inverter, V 1 is municipal power supply voltage grade at the pre-grid-connected side, and I F is current value injected into a power grid by the calculated photovoltaic power supply system
MAX{IA,IB,IC}＝IV
I A is A phase power supply current, I B is B phase power supply current, and I C is C phase power supply current.
MIN{IA,IB,IC}＝IW
When I F≤(IV-IW) is carried out, the photovoltaic power supply system disconnects the energy storage alternating current contactor and enters grid-connected power supply
A mode;
After the photovoltaic power supply system is connected with the grid, whether the photovoltaic is continuously supplied with power or not is judged according to the following calculation formula:
MIN{IA,IB,IC}＝IW
And I X is the maximum value of three-phase power supply current I A,IB,IC, and when I X is consistent with I W, the photovoltaic power supply system stops grid-connected power supply and enters the working state of the energy storage system.
2. The photovoltaic automatic phase-selecting parallel network for the three-phase load unbalance management system of the photovoltaic power generation network according to claim 1, wherein the monitoring execution unit comprises a first current transducer, a second current transducer, a third current transducer and a fourth current transducer which are respectively connected in series with municipal A, B, C three phases, the second current transducer, the third current transducer and the fourth current transducer are respectively connected with the first current transducer through normally open contacts of an alternating current contactor, the neutral point of a A, B, C-phase load of a municipal power supply is connected with an alternating current input end of a photovoltaic power generation unit, and signal output ends of the first current transducer, the second current transducer, the third current transducer and the fourth current transducer are connected with a logic control unit;
The logic control unit comprises a central processor, and the digital output point of the central processor is connected with the input end of the control coil of each alternating current contactor;
The first current transducer detects the current value output by the photovoltaic power generation unit in real time, the second current transducer, the third current transducer and the fourth current transducer detect the current value of each phase load of the municipal power supply in real time, detection signals are sent to the logic control system, the central processing unit compares the detection values of the current transducers, the maximum load phase when three-phase power is unbalanced is obtained through analysis, and an instruction is sent to the control coil of each alternating current contactor, so that the connection and disconnection of the normally open contact of the corresponding alternating current contactor are controlled, and the corresponding phase of the photovoltaic power generation connected to the municipal power supply is changed.
3. The photovoltaic automatic phase-selecting and grid-connecting system for the three-phase load unbalance management system of the low-voltage power grid according to claim 1, wherein the photovoltaic power generation unit comprises a photovoltaic array, a single-phase grid-connected inverter, an energy storage system, a grid-connected control device, an energy storage control device, a first voltage transmitter and a fifth current transmitter, the fifth current transmitter collects output current of the photovoltaic array, the first voltage transmitter collects output voltage of the photovoltaic array, a programmable controller processes collected signals of the fifth current transmitter and the first voltage transmitter, the photovoltaic array is controlled to receive solar energy and convert the solar energy into direct-current electric energy, the direct-current electric energy is provided for the single-phase grid-connected inverter, the single-phase grid-connected inverter is internally adjusted to obtain maximum power collection, and then the maximum power collection is converted into alternating-current electric energy meeting the low-voltage power grid standard, or the alternating-current electric energy is provided for the energy storage system to store energy.
4. The system for controlling three-phase load unbalance of a power grid according to claim 2, wherein signals output by the first current transducer, the second current transducer, the third current transducer, the fourth current transducer and the fifth current transducer are processed by the analog-to-digital converter and then input to the central processing unit.
5. The photovoltaic automatic phase-selecting and grid-connecting system for the three-phase load unbalance management system of the electric power grid according to claim 2, wherein the central processing unit is connected with a display.
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| CN110783936A (en) * | 2019-11-01 | 2020-02-11 | 国网河北省电力有限公司沧州供电分公司 | Distribution network three-phase load unbalance management method and system based on distributed photovoltaic |
| CN110912160B (en) * | 2019-11-19 | 2021-05-11 | 许继集团有限公司 | Distributed photovoltaic absorption method, system and computer readable medium |
| CN110957748A (en) * | 2019-12-17 | 2020-04-03 | 中国农业大学 | Three-phase voltage unbalance adjusting device and method |
| CN112895986B (en) * | 2021-03-15 | 2022-06-24 | 西南交通大学 | Traction power supply system connected with new energy power generation unit |
| CN113315159A (en) * | 2021-06-25 | 2021-08-27 | 山东中浩智能电气有限公司 | Energy optimization device applied to single-phase photovoltaic grid-connected power generation |
| CN114123255A (en) * | 2021-11-29 | 2022-03-01 | 珠海格力电器股份有限公司 | Light storage power utilization system and load three-phase power control method, device and equipment thereof |
| CN115296304B (en) * | 2022-09-30 | 2023-01-06 | 国网山西省电力公司营销服务中心 | Low-voltage line terminal voltage management method based on distributed photovoltaic power supply array |
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