CN112039048A - Bipolar direct current micro-grid system - Google Patents
Bipolar direct current micro-grid system 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
- 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
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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
- H02J1/10—Parallel operation of dc sources
- H02J1/102—Parallel operation of dc sources being switching converters
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
- H02J3/36—Arrangements for transfer of electric power between ac networks via a high-tension dc link
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/60—Arrangements for transfer of electric power between AC networks or generators via a high voltage DC link [HVCD]
Abstract
The invention relates to the technical field of bipolar direct current micro-grids, and discloses a bipolar direct current micro-grid system, which comprises a power grid topological structure, a communication system and an unbalanced voltage control system; the distributed direct-current power supply is connected to a bus by adopting a DC/DC direct-current converter, and the distributed direct-current power supply participates in unbalanced voltage regulation and control by controlling the DC/DC direct-current converter; the unbalanced voltage control system completes the adjustment and control of the unbalanced voltage through the coordination and the coordination of the primary control system and the secondary control system, and the primary control system directly acts on the direct current converter to adjust the output voltage of the direct current converter; the secondary control system provides a correction reference voltage for the primary control and adjusts the deviation generated by the primary control, such as voltage and power deviation; the sparse communication network based on the direct current converter enables information interaction between adjacent nodes, so that distributed coordination control is formed, unbalanced voltages of multiple nodes between a positive electrode and a negative electrode in a bipolar direct current micro-grid are coordinated and controlled, and the reliability and stability of grid operation are improved.
Description
Technical Field
The invention relates to the technical field of bipolar direct current micro-grids.
Background
Compared with a unipolar direct-current microgrid, the bipolar direct-current microgrid provides more voltage class interfaces, the voltage class can be flexibly converted, and meanwhile, the utilization rate of the bipolar direct-current microgrid to an AC/DC converter is high. In addition, when one pole fails, the other pole can continue to operate, and the system has higher reliability and safety. However, unbalanced power, load, line parameters and the like of the positive electrode and the negative electrode can generate unbalanced current in a neutral line, so that line loss is increased, and the voltage of the positive electrode bus and the voltage of the negative electrode bus deviate from a rated value. When the load of a certain node is seriously unbalanced, the unbalance degree can exceed the standard, and even unbalanced voltage protection of a neutral line is triggered. In order to flexibly adjust the voltage unbalance degree of the bipolar direct-current microgrid and simultaneously ensure that the bus voltage operates in a reasonable range, an unbalanced voltage control system needs to be designed to ensure the normal operation of a direct-current load
The suppression of unbalanced voltage of a bipolar direct-current micro-grid at the present stage can be started from a source side and a grid side, line loss and voltage deviation caused by unbalanced current are reduced by adding an unbalanced compensation control link, the method that an AC/DC converter capable of suppressing the unbalanced voltage, a voltage balancer and the like are mainly adopted at an outlet of the AC/DC converter is adopted, the suppression of the unbalanced voltage of a single converter is only considered, the coordination capability of a distributed power supply between converters of different nodes participating in unbalance degree adjustment is not considered, a mature design scheme does not exist at the present stage aiming at the unbalanced voltage coordination control among multiple nodes in the bipolar direct-current micro-grid, and the development of the bipolar direct-current micro-grid is prevented.
Disclosure of Invention
Aiming at the technical defects, the invention provides a bipolar direct current micro-grid system, which solves the technical problem of improving the unbalanced voltage regulation capability of the bipolar direct current micro-grid.
In order to solve the technical problem, the invention provides a bipolar direct-current micro-grid, which comprises a grid topological structure, a communication system and an unbalanced voltage control system;
the power grid topological structure comprises three direct current buses: the positive direct current bus, the zero line and the negative direct current bus; the positive end and the negative end of the low-voltage direct-current load are respectively connected to the positive direct-current bus and the negative direct-current bus to form a positive node and a negative node, and the neutral point of the low-voltage direct-current load is connected to a zero line to form a neutral node; each low-voltage direct-current load is supplied with power by a corresponding pair of positive and negative distributed direct-current power supplies; the positive distributed direct-current power supply is connected with the positive node through a positive direct-current converter, the negative distributed direct-current power supply is connected with the negative node through a negative direct-current converter, and the positive direct-current converter and the negative direct-current converter both return through a neutral node, so that power supply to a low-voltage direct-current load is realized;
the communication system comprises a sparse communication network consisting of all direct current converters in a power grid topological structure, so that electric energy data can be interacted between every two adjacent direct current converters; the electric energy data comprise positive bus voltage of a positive node, negative bus voltage of a negative node, load current of the positive node and load current of the negative node;
the unbalanced voltage control system comprises a primary control system and a secondary control system for providing a corrected reference voltage for the primary control system; the primary control system can generate a control signal for controlling the direct current converter, which enables the bus voltage to meet the corrected reference voltage, so that the bus voltage is adjusted by adjusting the output voltage of the direct current converter;
the secondary control system comprises a voltage unbalance controller; the voltage unbalance controller comprises a voltage unbalance calculation unit, an expected voltage calculation unit, an unbalance correction term calculation unit and a correction reference voltage calculation unit;
the voltage unbalance calculation unit is used for calculating the voltage unbalance of the unit node according to the positive and negative bus voltages of the same unit node; the same unit node consists of a positive electrode node and a negative electrode node corresponding to the same low-voltage direct-current load; the expected voltage unbalance calculation unit is used for calculating the expected voltage unbalance of the unit node when the voltage unbalance of the unit node and the adjacent unit node is consistent based on a consistency algorithm according to the voltage unbalance of the unit node and the adjacent unit node; the expected voltage calculation unit is used for calculating the expected positive and negative bus voltages of the positive and negative nodes in the unit node according to the expected voltage unbalance degree; the unbalance correction term calculation unit is used for calculating positive and negative unbalance correction terms which enable positive and negative bus voltages of the positive and negative nodes to respectively meet positive and negative expected bus voltages; the corrected reference voltage calculating unit comprises a positive corrected reference voltage calculating unit and a negative corrected reference voltage calculating unit, and is respectively used for adding corresponding correction terms comprising a positive unbalance degree correction term and a negative unbalance degree correction term on the basis of the rated reference voltages of the positive bus and the negative bus so as to generate the positive corrected reference voltage and the negative corrected reference voltage.
Further, the secondary control system further comprises an unbalanced voltage observer; the unbalanced voltage observer comprises a positive electrode unbalanced voltage observer and a negative electrode unbalanced voltage observer; the unbalanced voltage observer comprises a positive bus average voltage prediction unit and a positive voltage stabilization correction term calculation unit; the positive bus average voltage prediction unit is used for calculating the positive bus average voltage of the positive node at the next moment based on a consistency algorithm according to the positive bus voltages of the positive node and the adjacent positive node; the positive pole voltage stabilization correction term calculation unit is used for calculating a positive pole voltage stabilization correction term which enables the positive pole average bus voltage to meet the positive pole bus rated reference voltage;
the negative bus average voltage prediction unit is used for calculating the negative bus average voltage of the negative node at the next moment based on a consistency algorithm according to the negative bus voltages of the negative node and the adjacent negative node; the negative voltage stabilization correction term calculation unit is used for calculating a negative voltage stabilization correction term which enables the negative average bus voltage to meet the negative bus rated reference voltage;
the positive correction reference voltage calculation unit is used for adding a corresponding positive unbalance correction term and a positive voltage stabilization correction term on the basis of the positive bus rated reference voltage to generate a positive correction reference voltage; the negative pole correction reference voltage calculation unit is used for adding a corresponding negative pole unbalance degree correction term and a negative pole voltage stabilization correction term on the basis of the negative pole bus rated reference voltage to generate a negative pole correction reference voltage.
Compared with the prior art, the invention has the advantages that:
1. in the power grid topological structure, the DC/DC direct-current converter is adopted to connect the distributed direct-current power supply to the bus, and the distributed direct-current power supply can participate in unbalanced voltage regulation and control by controlling the DC/DC direct-current converter. Different from the prior art that only an AC/DC converter can be adopted for carrying out unbalanced voltage suppression, the distributed direct-current power supply can carry out bidirectional regulation on unbalanced voltage through the DC/DC converter, and is not limited to unidirectional suppression.
2. The sparse communication network based on the direct current converter enables information interaction between adjacent nodes, so that distributed coordination control is formed, unbalanced voltages of multiple nodes between a positive electrode and a negative electrode in a bipolar direct current micro-grid are coordinated and controlled, and the defect of poor consistency caused by single node isolated control in the prior art is overcome.
3. The unbalanced voltage control system completes the unbalanced voltage regulation and control through the coordination and the coordination of the primary control system and the secondary control system, and the primary control system directly acts on the direct current converter to regulate the output voltage of the direct current converter; the secondary control system provides a reference (correction reference voltage) for the primary control, and is also equivalent to adjusting the deviation generated by the primary control, such as voltage and power deviation.
4. The invention adjusts the bus voltage of the positive and negative electrode nodes in the unit node by the unbalancing degree correction term, thereby adjusting the voltage unbalancing degree of the unit node, and meanwhile, the unbalancing degree correction term is based on the expected voltage unbalancing degree of the unit node when the voltage unbalancing degree tends to be consistent, thereby the voltage unbalancing degree between the adjacent unit nodes tends to be consistent, and the reliability of the power grid operation is improved.
5. The invention adjusts the average bus voltage of the positive and negative electrode nodes through the voltage stabilization correction term, so that the average bus voltage of the adjacent nodes tends to be consistent, the bus rated reference voltage is met, and the operation stability of the power grid is improved.
Drawings
Fig. 1 is a schematic diagram of a network structure of a bipolar dc microgrid in the present embodiment;
FIG. 2 is a simplified model of a bipolar DC microgrid in accordance with the present embodiment;
fig. 3 is an overall architecture diagram of the unbalanced voltage control system.
FIG. 4 is a functional block diagram of a primary control system;
FIG. 5 is a functional block diagram of a secondary control system;
Detailed Description
A bipolar direct current micro grid is established, and as shown in fig. 1, the micro grid comprises a grid topology (physical layer), a communication system (network layer) and an unbalanced voltage control system. The power grid topological structure comprises three direct current buses: the positive direct current bus, the zero line and the negative direct current bus; the positive end and the negative end of the low-voltage direct-current load are respectively connected to the positive direct-current bus and the negative direct-current bus to form a positive node and a negative node, and the neutral point of the low-voltage direct-current load is connected to a zero line to form a neutral node; each low-voltage direct-current load is supplied with power by a corresponding pair of positive and negative distributed direct-current power supplies; the positive distributed direct-current power supply is connected with the positive node through the positive direct-current converter, the negative distributed direct-current power supply is connected with the negative node through the negative direct-current converter, and the positive direct-current converter and the negative direct-current converter both return through the neutral node, so that power supply to a low-voltage direct-current load is realized.
The communication system comprises a sparse communication network consisting of all direct current converters in a power grid topological structure, so that electric energy data can be interacted between every two adjacent direct current converters; the electric energy data comprise positive bus voltage of the positive node, negative bus voltage of the negative node, load current of the positive node and load current of the negative node.
The system comprises three direct current buses, namely a Distributed Generation (DG), a direct current converter (DC/DC), a low-voltage direct current load, a positive line (P line), a zero line (O line) and a negative line (N line). The DG is connected to a direct current bus through a DC/DC converter, and the low-voltage direct current load is connected between the PO and the NO. The network layer can facilitate information exchange of a plurality of direct current converters, in the voltage unbalance degree consistency control, the direct current converters corresponding to the positive pole and the negative pole are regarded as the same node, and in the bus average voltage control, the direct current converters of the positive pole and the negative pole are regarded as different nodes. The nodes are connected through a sparse communication network, exchange information of control variables with adjacent nodes, update self control information and achieve global consistency of the control variables.
On the basis of a voltage unbalance degree definition formula, a bipolar direct current micro-grid simplified model is utilized to calculate and obtain a functional relation between the voltage unbalance degree and the load, the neutral line resistance and the positive and negative power supply voltages.
The degree of unbalance is an index for evaluating the voltage unbalance of the bipolar direct-current microgrid, and the degree of unbalance of the voltage of the ith node is defined as:
wherein v ishbiIs the voltage unbalance degree, v, of the ith unit node in the bipolar direct current micro-gridpi、vniRespectively, the positive and negative bus voltages of the ith cell node, and the subscripts p and n respectively indicate the positive and negative polarities.
The simplified model of the bipolar direct current microgrid is shown in fig. 2, wherein the node voltage and current satisfy:
wherein R isp、RnRespectively positive and negative electrode load, RLp、RLn、RmRespectively, positive, negative and neutral line resistances ip、in、imRespectively, positive, negative, neutral current, vsp、vsnPositive and negative output voltages, respectively, the positive and negative line impedances being equal in the invention, i.e. RLp＝RLn＝RL。
The relationship between the unbalance and the load, the neutral line resistance and the positive and negative power supply voltages is solved as follows:
it can be seen that the voltage imbalance of the bipolar direct current microgrid varies with the variation of the positive and negative output voltages. Therefore, the voltage unbalance degree can be adjusted by regulating the positive and negative output voltages.
Referring to fig. 3, the unbalanced voltage control system includes a secondary control system for the primary control system and for providing a modified reference voltage to the primary control system; the primary control system is capable of generating a control signal for controlling the dc converter so that the bus voltage satisfies the modified reference voltage, thereby adjusting the bus voltage by adjusting the output voltage of the dc converter.
Referring to fig. 4, the primary control system includes a voltage droop controller and a virtual impedance loop, where the virtual impedance loop is used to obtain a load current of a node and generate a corresponding virtual impedance output voltage to the voltage droop controller; the voltage droop controller is used for generating a control signal (controlling the duty ratio of a switch of the direct current converter) for meeting the corrected reference voltage according to the corrected reference voltage, the virtual impedance output voltage and the bus voltage of the node, which are provided by the secondary control system, so as to adjust the output voltage of the direct current converter; corresponding positive and negative voltage droop controllers and positive and negative virtual impedance rings are arranged corresponding to the positive and negative nodes;
the virtual impedance output voltage comprises a positive virtual impedance output voltage and a negative virtual impedance output voltage, and the calculation formula is as follows:
wherein v isdpiRepresenting the positive virtual impedance output voltage, vdniRepresenting the negative virtual impedance output voltage, RdpiRepresents the positive virtual impedance, RdniRepresents the negative virtual impedance, ipiRepresenting the positive load current, iniRepresenting the negative load current.
Referring to fig. 5, the secondary control system includes a voltage unbalance controller; the voltage unbalance controller includes a voltage unbalance calculation unit, an expected voltage calculation unit, an unbalance correction term calculation unit, and a correction reference voltage calculation unit.
The voltage unbalance degree calculation unit is used for calculating the voltage unbalance degree of the unit node according to the positive and negative bus voltages of the same unit node; the same unit node consists of a positive electrode node and a negative electrode node corresponding to the same low-voltage direct-current load; the expected voltage unbalance calculation unit is used for calculating the expected voltage unbalance of the unit node when the voltage unbalance of the unit node and the adjacent unit node is consistent based on a consistency algorithm according to the voltage unbalance of the unit node and the adjacent unit node; the expected voltage calculation unit is used for calculating the expected positive and negative bus voltages of the positive and negative nodes in the unit node according to the expected voltage unbalance degree; the unbalance correction term calculation unit is used for calculating positive and negative unbalance correction terms which enable positive and negative bus voltages of the positive and negative nodes to respectively meet positive and negative expected bus voltages; the corrected reference voltage calculating unit comprises a positive corrected reference voltage calculating unit and a negative corrected reference voltage calculating unit, and is respectively used for adding corresponding correction terms comprising a positive unbalance degree correction term and a negative unbalance degree correction term on the basis of the rated reference voltages of the positive bus and the negative bus so as to generate the positive corrected reference voltage and the negative corrected reference voltage.
The desired voltage imbalance is calculated as follows:
wherein, v'hbiThe expected voltage unbalance degree of the ith unit node in the bipolar direct current micro-grid is obtained; j represents a jth neighboring cell node among neighboring cell nodes of the ith cell node; a isijRepresenting the communication weight between the ith unit node and the jth adjacent unit node, wherein j belongs to { 1., N }, and N represents the total number of adjacent unit nodes of the ith unit node; v. ofhbiAnd vhbjAre respectively the ith and jth unit nodesVoltage imbalance of (2).
The desired bus voltage is calculated as follows:
wherein, v'piAnd v'niThe positive electrode expected bus voltage and the negative electrode expected bus voltage of the ith unit node are respectively.
The unbalance correction term is calculated as follows:
wherein, Δ v ″)piCorrection term for positive pole imbalance of i-th unit node, Δ v ″)niFor the negative imbalance correction term, k, of the ith cell nodePhbpi、kPhbniRespectively representing the proportional coefficients, k, of positive and negative PI controls of a voltage imbalance controllerIhbpi、kIhbniRespectively representing the integral coefficients of the positive and negative PI controls of the voltage unbalance controller.
Referring to fig. 5, the secondary control system further includes an unbalanced voltage observer; the unbalanced voltage observer comprises a positive electrode unbalanced voltage observer and a negative electrode unbalanced voltage observer; the unbalanced voltage observer comprises a positive bus average voltage prediction unit and a positive voltage stabilization correction term calculation unit.
The positive bus average voltage prediction unit is used for calculating the positive bus average voltage of the positive node at the next moment based on a consistency algorithm according to the positive bus voltages of the positive node and the adjacent positive node; and the positive voltage stabilization correction term calculation unit is used for calculating a positive voltage stabilization correction term which enables the average bus voltage of the positive electrode to meet the rated reference voltage of the positive electrode bus.
The negative bus average voltage prediction unit is used for calculating the negative bus average voltage of the negative node at the next moment based on a consistency algorithm according to the negative bus voltages of the negative node and the adjacent negative node; and the negative voltage stabilization correction term calculation unit is used for calculating a negative voltage stabilization correction term which enables the negative average bus voltage to meet the negative bus rated reference voltage.
The bus average voltage is calculated as follows:
wherein v ispi、vniRespectively represent positive and negative bus voltages of the ith cell node, j represents the jth adjacent cell node in the adjacent cell nodes of the ith cell node, aijRepresents the weight between the ith node and its jth neighbor unit node, vavgpiRepresents the average voltage of the positive bus of the ith unit node, vavgniRepresents the average voltage of the negative bus of the ith unit node, vavgpjRepresents the average voltage of the positive bus of the j-th adjacent unit node, vavgnjRepresenting the negative bus average voltage of the jth adjacent cell node.
The formula of the voltage stabilization correction term is as follows:
wherein v isrefIs the bus nominal reference voltage, Δ v'piA positive electrode stabilization correction term, Δ v ', representing the ith unit node'niNegative voltage stabilization correction term, k, representing the ith cell nodePVpi、kPVniRespectively representing positive and negative PI control proportionality coefficients, k, of the unbalanced voltage observerIVpi、kIVniRespectively representing positive and negative PI control integral coefficients of the unbalanced voltage observer.
The positive correction reference voltage calculation unit is used for adding a corresponding positive unbalance correction term and a positive voltage stabilization correction term on the basis of the positive bus rated reference voltage to generate a positive correction reference voltage; the negative pole correction reference voltage calculation unit is used for adding a corresponding negative pole unbalance degree correction term and a negative pole voltage stabilization correction term on the basis of the negative pole bus rated reference voltage to generate a negative pole correction reference voltage.
The corrected reference voltage calculation formula is as follows:
wherein the content of the first and second substances,
and
respectively representing a positive modified reference voltage, a negative modified reference voltage, vrefIs the bus nominal reference voltage, Δ v'piDenotes a positive electrode stabilization correction term,. DELTA.v'niDenotes a negative electrode voltage stabilization correction term, Δ v ″piTABLE Positive electrode imbalance correction term, Δ v ″)niTo represent the negative pole imbalance correction term.
The bipolar direct-current micro-grid has good reliability and stability, multi-node unbalanced voltage between the positive electrode and the negative electrode in the bipolar direct-current micro-grid can be effectively adjusted, and further development of the bipolar direct-current micro-grid is promoted.
Claims (10)
1. A bipolar dc microgrid system characterized by: the system comprises a power grid topological structure, a communication system and an unbalanced voltage control system;
the power grid topological structure comprises three direct current buses: the positive direct current bus, the zero line and the negative direct current bus; the positive end and the negative end of the low-voltage direct-current load are respectively connected to the positive direct-current bus and the negative direct-current bus to form a positive node and a negative node, and the neutral point of the low-voltage direct-current load is connected to a zero line to form a neutral node; each low-voltage direct-current load is supplied with power by a corresponding pair of positive and negative distributed direct-current power supplies; the positive distributed direct-current power supply is connected with the positive node through a positive direct-current converter, the negative distributed direct-current power supply is connected with the negative node through a negative direct-current converter, and the positive direct-current converter and the negative direct-current converter both return through a neutral node, so that power supply to a low-voltage direct-current load is realized;
the communication system comprises a sparse communication network consisting of all direct current converters in a power grid topological structure, so that electric energy data can be interacted between every two adjacent direct current converters; the electric energy data comprise positive bus voltage of a positive node, negative bus voltage of a negative node, load current of the positive node and load current of the negative node;
the unbalanced voltage control system comprises a primary control system and a secondary control system for providing a corrected reference voltage for the primary control system; the primary control system can generate a control signal for controlling the direct current converter, which enables the bus voltage to meet the corrected reference voltage, so that the bus voltage is adjusted by adjusting the output voltage of the direct current converter;
the secondary control system comprises a voltage unbalance controller; the voltage unbalance controller comprises a voltage unbalance calculation unit, an expected voltage calculation unit, an unbalance correction term calculation unit and a correction reference voltage calculation unit;
the voltage unbalance calculation unit is used for calculating the voltage unbalance of the unit node according to the positive and negative bus voltages of the same unit node; the same unit node consists of a positive electrode node and a negative electrode node corresponding to the same low-voltage direct-current load; the expected voltage unbalance calculation unit is used for calculating the expected voltage unbalance of the unit node when the voltage unbalance of the unit node and the adjacent unit node is consistent based on a consistency algorithm according to the voltage unbalance of the unit node and the adjacent unit node; the expected voltage calculation unit is used for calculating the expected positive and negative bus voltages of the positive and negative nodes in the unit node according to the expected voltage unbalance degree; the unbalance correction term calculation unit is used for calculating positive and negative unbalance correction terms which enable positive and negative bus voltages of the positive and negative nodes to respectively meet positive and negative expected bus voltages; the corrected reference voltage calculating unit comprises a positive corrected reference voltage calculating unit and a negative corrected reference voltage calculating unit, and is respectively used for adding corresponding correction terms comprising a positive unbalance degree correction term and a negative unbalance degree correction term on the basis of the rated reference voltages of the positive bus and the negative bus so as to generate the positive corrected reference voltage and the negative corrected reference voltage.
2. The bipolar direct current microgrid system of claim 1, wherein: the primary control system comprises a voltage droop controller and a virtual impedance ring, wherein the virtual impedance ring is used for acquiring the load current of a node and generating corresponding virtual impedance output voltage to the voltage droop controller; the voltage droop controller is used for generating a control signal meeting the corrected reference voltage according to the corrected reference voltage, the virtual impedance output voltage and the bus voltage of the node, which are provided by the secondary control system, so as to adjust the output voltage of the direct current converter; corresponding positive and negative voltage droop controllers and positive and negative virtual impedance rings are arranged corresponding to the positive and negative nodes;
the virtual impedance output voltage comprises a positive virtual impedance output voltage and a negative virtual impedance output voltage, and the calculation formula is as follows:
wherein v isdpiRepresenting the positive virtual impedance output voltage, vdniRepresenting the negative virtual impedance output voltage, RdpiRepresents the positive virtual impedance, RdniRepresents the negative virtual impedance, ipiRepresenting the positive load current, iniRepresenting the negative load current.
3. The bipolar direct current microgrid system of claim 1, wherein: the secondary control system further comprises an unbalanced voltage observer; the unbalanced voltage observer comprises a positive electrode unbalanced voltage observer and a negative electrode unbalanced voltage observer; the unbalanced voltage observer comprises a positive bus average voltage prediction unit and a positive voltage stabilization correction term calculation unit;
the positive bus average voltage prediction unit is used for calculating the positive bus average voltage of the positive node at the next moment based on a consistency algorithm according to the positive bus voltages of the positive node and the adjacent positive node; the positive pole voltage stabilization correction term calculation unit is used for calculating a positive pole voltage stabilization correction term which enables the positive pole average bus voltage to meet the positive pole bus rated reference voltage;
the negative bus average voltage prediction unit is used for calculating the negative bus average voltage of the negative node at the next moment based on a consistency algorithm according to the negative bus voltages of the negative node and the adjacent negative node; the negative voltage stabilization correction term calculation unit is used for calculating a negative voltage stabilization correction term which enables the negative average bus voltage to meet the negative bus rated reference voltage;
the positive correction reference voltage calculation unit is used for adding a corresponding positive unbalance correction term and a positive voltage stabilization correction term on the basis of the positive bus rated reference voltage to generate a positive correction reference voltage; the negative pole correction reference voltage calculation unit is used for adding a corresponding negative pole unbalance degree correction term and a negative pole voltage stabilization correction term on the basis of the negative pole bus rated reference voltage to generate a negative pole correction reference voltage.
4. The bipolar direct current microgrid system of claim 1, wherein: the calculation formula of the voltage unbalance degree of the cell node is as follows:
wherein v ishbiIs the voltage unbalance degree, v, of the ith unit node in the bipolar direct current micro-gridpi、vniRespectively, the positive and negative bus voltages of the ith cell node, and the subscripts p and n respectively indicate the positive and negative polarities.
5. The bipolar direct current microgrid system of claim 1, wherein: the desired voltage imbalance is calculated as follows:
wherein, v'hbiThe expected voltage unbalance degree of the ith unit node in the bipolar direct current micro-grid is obtained; j represents a jth neighboring cell node among neighboring cell nodes of the ith cell node; a isijRepresenting the communication weight between the ith unit node and the jth adjacent unit node, wherein j belongs to { 1., N }, and N represents the total number of adjacent unit nodes of the ith unit node; v. ofhbiAnd vhbjThe voltage unbalances of the ith and jth cell nodes, respectively.
6. The bipolar direct current microgrid system of claim 1, wherein: the desired bus voltage is calculated as follows:
wherein, v'piAnd v'niThe positive electrode expected bus voltage and the negative electrode expected bus voltage of the ith unit node are respectively.
7. The bipolar direct current microgrid system of claim 1, wherein: the unbalance correction term is calculated as follows:
wherein, Δ v ″)piCorrection term for positive pole imbalance of i-th unit node, Δ v ″)niFor the negative imbalance correction term, k, of the ith cell nodePhbpi、kPhbniRespectively representing the proportional coefficients, k, of positive and negative PI controls of a voltage imbalance controllerIhbpi、kIhbniRespectively representing the integral coefficients of the positive and negative PI controls of the voltage unbalance controller.
8. The bipolar direct current microgrid system of claim 3, wherein: the bus average voltage is calculated as follows:
wherein v ispi、vniRespectively represent positive and negative bus voltages of the ith cell node, j represents the jth adjacent cell node in the adjacent cell nodes of the ith cell node, aijRepresents the weight between the ith node and its jth neighbor unit node, vavgpiRepresents the average voltage of the positive bus of the ith unit node, vavgniRepresents the average voltage of the negative bus of the ith unit node, vavgpjRepresents the average voltage of the positive bus of the j-th adjacent unit node, vavgnjRepresenting the negative bus average voltage of the jth adjacent cell node.
9. The bipolar direct current microgrid system of claim 3, wherein: the formula of the voltage stabilization correction term is as follows:
wherein v isrefIs the bus nominal reference voltage, Δ v'piA positive electrode stabilization correction term, Δ v ', representing the ith unit node'niNegative voltage stabilization correction term, k, representing the ith cell nodePVpi、kPVniRespectively representing positive and negative PI control proportionality coefficients, k, of the unbalanced voltage observerIVpi、kIVniRespectively representing positive and negative PI control integral coefficients of the unbalanced voltage observer.
10. The bipolar direct current microgrid system of claim 3, wherein: the corrected reference voltage calculation formula is as follows:
wherein the content of the first and second substances,
and
respectively representing a positive modified reference voltage, a negative modified reference voltage, vrefIs the bus nominal reference voltage, Δ v'piDenotes a positive electrode stabilization correction term,. DELTA.v'niDenotes a negative electrode voltage stabilization correction term, Δ v ″piTABLE Positive electrode imbalance correction term, Δ v ″)niTo represent the negative pole imbalance correction term.
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