A method for autonomous load restoration of feeder lines with assistance of electric vehicles

Abstract

The present invention discloses an autonomous load recovery method for feeder lines with electric vehicle assistance, the method comprising: firstly modeling the corresponding elements on the feeder line, including feeder circuit breaker units, sectionalizer units, load units, renewable energy units, electric vehicle aggregation units, and power supply recovery service units; then determining strategies for fault recovery services of electric vehicles and distributed energy assisted feeder lines, and reducing the power outage time of non-fault section power users on the faulty feeder line. The present invention improves the resilience of the feeder level, realizes agile response and recovery; through real-time self-reconstruction strategies, it is possible to cope with single and subsequent cascading events, and obtain higher recovery capabilities before and during faults.

Description

Technical Field

[0001] The present invention relates to the field of medium and low voltage power grid resilience enhancement, and in particular to a feeder line autonomous load recovery method assisted by electric vehicles (EVs). Background Art

[0002] Strong grid resilience is reflected in enhancing grid resilience to reduce losses caused by faults, limiting faults within the grid, and quickly restoring normal operations after interruptions. High Impact and Low Probability (HILP) events may cause significant technical and economic losses throughout the energy sector. Therefore, power companies should pay more attention to HILP events and use effective strategies to maximize the comprehensive use of modern grid resources and flexible services before, during, and after HILP disasters to reduce power outages for end customers.

[0003] Distribution network resilience research and corresponding solutions can be categorized as single-node improvements or collective (feeder) level improvements; measures to enhance network resilience can be taken in three different time periods:

[0004] (1) Pre-event system planning: This includes preventive measures before an event occurs, such as strengthening the grid and infrastructure by installing new equipment. These actions enhance the resilience of the infrastructure.

[0005] (2) System operation during the event: Corrective measures are triggered to avoid large-scale power outages. Corrective measures are designed to suppress possible cascading accidents and reduce the scope of the fault impact through rapid response and rapid isolation of the fault area.

[0006] (3) Post-event power supply service restoration (SR): After the fault is isolated, all modern power resources in the power grid are dispatched in a unified manner to restore power to the non-faulty areas as soon as possible, thereby reducing the power outage time for users and potential economic losses.

[0007] The current technologies used to enhance grid resilience have the following problems: they can only be used to deal with contingencies that are certain to be self-healing, rather than extreme HILP events; during grid restoration, only dispatching power from adjacent feeders is considered, while the positive impact of other modern power resources (such as electric vehicles) on recovery capabilities is not properly considered; current grid restoration algorithms are mostly applicable to passive distributed grids with unidirectional current flow, which only rely on the spare capacity provided by adjacent feeders, so the cost is higher than using the local grid. In general, most of the existing distribution network resilience restoration technologies do not effectively utilize the internal resources located in the healthy section of the fault feeder. Summary of the invention

[0008] The object of the present invention is to provide a feeder line autonomous load recovery method with electric vehicle assistance in view of the deficiencies in the prior art.

[0009] The object of the present invention is achieved through the following technical solution: A method for autonomous load recovery of a feeder line with electric vehicle assistance, comprising the following steps:

[0010] (1) Analyze and model the operating characteristics of active radial feeder line equipment, including feeder breaker unit (FBU), segment unit (SU), load unit (LU), distributed renewable energy unit (DERU), electric vehicle aggregation unit (EVAU), and power supply service recovery unit (SRU);

[0011] (2) When a feeder line fails, the feeder circuit breaker unit FBU and the power restoration service unit SRU dispatch the renewable energy units DERU and electric vehicle aggregation units EVAU connected to the normal bus of the line to reduce the power outage time of users and assist in the autonomous recovery of loads.

[0012] Furthermore, the step (1) specifically includes:

[0013] The feeder circuit breaker unit FBU is located in the substation, and includes a reclosing overcurrent relay, a current transformer, a measurement and calculation module, and a communication module; the measurement and calculation module is used to measure and calculate the reserve current capacity RCC of the feeder transformer TR in real time, and the communication module is used to send the calculated reserve current capacity RCC to the fault recovery service unit in real time and publish "fault processing" information to the renewable energy unit DERU and the electric vehicle aggregation unit EVAU; the feeder circuit breaker unit FBU is used to calculate and report the reserve current capacity RCC of the feeder; in the calculation of the reserve current capacity RCC, the model of the feeder transformer capacity FTC and the secondary side current of the feeder transformer TR is:

[0014]

[0015] Among them, RCC i,t represents the reserve current capacity of feeder i at time t, FTC i represents the transformer capacity on feeder i, represents the rated voltage of the secondary side of the transformer on feeder i, It represents the rated current of the secondary side of the transformer on feeder i at time t, and the subscript s represents the rated value.

[0016] The sectionalizer unit SU is composed of a current relay, a current transformer and a communication module; the communication module is used to issue "discovery" and "isolation" information to the feeder circuit breaker unit FBU and receive the "fault handling" instruction issued by the feeder circuit breaker unit FBU, and transmit the line overcurrent situation to the feeder circuit breaker unit FBU; the sectionalizer unit SU is used to detect the line overcurrent situation and transmit the information, and isolate the detected fault through remote control; the current in the active radial feeder line flows bidirectionally, and the sectionalizer unit SU is installed at both ends of each section of the line. When the line current is overcurrent or reverse, the relay is disconnected and the fault information is uploaded to the feeder circuit breaker unit FBU. The model is:

[0017] or

[0018] in, and They represent the amplitude and phase angle of the current at the location of the kth sectionalizer unit SU in the feeder i during time period t, r is the ratio of the primary to the secondary side of the current transformer, and r>1; represents the setting current of the current relay in the kth sectionalizer unit SU in feeder i, and N represents the rated setting current.

[0019] The busbar connected to the load unit LU covers the entire smart community, and the ZIP load model is used to describe the active and reactive power of the load. The ZIP load model is:

[0020]

[0021]

[0022] Among them, P b,t and They represent the active power and initial value of each bus at time t, Q b,t and Respectively represent the reactive power and initial value of each bus at time t, V b,t and They represent the voltage and initial value of each busbar at time t, and the subscript b represents the electrical parameters of the load unit; (Z p , I p , P p ) and (Z q , I q , P q ) represent the active load factor and reactive load factor of the ZIP model respectively.

[0023] The renewable energy unit DERU refers to a wind and solar power generation unit, which is equipped with a remote automatic circuit breaker. After receiving a feeder fault signal, it is responsible for disconnecting the renewable energy unit DERU from the feeder, and reconnecting the renewable energy unit DERU to the grid after receiving a "reconnect" signal. The grid-connected power has the following model constraints:

[0024]

[0025] in, and They represent the upper and lower limits of the grid-connected power of the renewable energy unit DERU, P DER,t It represents the grid-connected power of renewable energy unit DERU during period t.

[0026] The electric vehicle aggregation unit EVAU is a physical facility responsible for controlling the aggregation of electric vehicles, including charging piles, a communication remote control module and a data processing center; wherein the communication remote control module is used to receive instructions from the feeder circuit breaker unit FBU and control the electric vehicles connected to the charging piles to supply power to the power grid, and send the available capacity of the electric vehicle aggregation unit EVAU to the fault recovery service unit in real time; the data processing center is used to calculate the available capacity of the electric vehicle aggregation unit in real time, and send the calculation results to the fault recovery service unit through the communication remote control module; the electric vehicle aggregation unit EVAU communicates with other smart devices in the power grid to remotely control the electric vehicle charging piles in the area, and by changing the aggregation coefficient of the electric vehicle, the aggregated electric vehicle load distribution is reflected in the ZIP load model, which has two states: "normal" and "dispatching"; after a fault recovery service is completed, the model for corresponding economic compensation based on the recovery capacity provided by each electric vehicle is:

[0027]

[0028] Among them, EC i The service revenue obtained by the i-th electric vehicle participating in the fault recovery service, Q i The recovery capacity provided for the participating failure recovery services, Q Tot The total restoration capacity provided by the electric vehicle aggregation unit EVAU in the fault restoration service, EC Tot The total revenue obtained by the Electric Vehicle Aggregation Unit (EVAU) from participating in the fault recovery service.

[0029] The power supply restoration service unit SRU is composed of a circuit breaker connecting two radial feeders, a communication module and a data processing module; the communication module is used to receive information sent by all other units, and publish the data processing results to the corresponding units for reception and execution; after the communication module receives the "fault handling" instruction issued by the feeder circuit breaker unit, the data processing module executes the power supply service restoration SR algorithm after the fault event through the real-time measurement data of the electric vehicle aggregation unit, the renewable energy aggregation unit, the feeder circuit breaker unit and the sectionalizer unit; the power supply restoration service unit SRU has two states of "normal" and "restored", and restores the non-fault load by utilizing all available resources within a certain time interval after the event occurs; whether to close the circuit breaker in the power supply restoration service unit SRU is determined by the standard of the following model:

[0030]

[0031] in, Represents the total fault recovery demand current, RCC i,t represents the reserve current capacity of feeder i at time t, It represents the recovery current that the renewable energy unit DERU can provide, represents the restoration current that can be provided by the electric vehicle aggregation unit EVAU; α, β and γ represent the contribution factors of the restoration current provided by the adjacent feeders, the renewable energy unit DERU and the electric vehicle aggregation unit EVAU in the normal section of the faulty line to the restoration of the faulty section.

[0032] Furthermore, step (2) includes the following sub-steps:

[0033] (2.1) When a fault occurs, the feeder breaker unit FBU and the renewable energy unit DERU sense that the line is overcurrent; the renewable energy unit DERU automatically disconnects from the grid and waits for instructions to reconnect to the grid;

[0034] (2.2) The feeder circuit breaker unit FBU changes from the "ready" state to the "fault" state, and issues a "fault handling" command, triggering the downstream algorithm to determine which section of the line the fault is located in by sensing the overcurrent direction of the line through the sectionalizer unit SU, and report the fault location information to the power supply restoration service unit;

[0035] (2.3) The sectionalizer unit SU that senses the reverse overcurrent changes its state to the rear-end fault state, and publishes a message to the sectionalizer unit SU upstream of the same section, changing it to the "discovery" state, and at the same time publishes an "isolation" message to the power restoration service unit SRU, and the faulty line section is isolated;

[0036] (2.4) After receiving the "isolated" information, the service recovery unit starts to initiate the service recovery plan. Based on the pre-fault measurement data, the power supply recovery service unit SRU checks whether the following standards are met:

[0037]

[0038] in, represents the total required current for fault recovery, RCC is the reserve current margin of the adjacent feeder transformer, It represents the recovery current that the renewable energy unit DERU can provide, represents the restoration current that can be provided by the electric vehicle aggregation unit EVAU; α, β and γ represent their respective weight proportions in grid restoration, and their weight proportions depend on the capacity of the adjacent feeding lines, renewable energy units DERU and electric vehicle aggregation units EVAU;

[0039] The first power restoration service unit SRU that meets the requirements closes its normally open connection circuit breaker with the faulty feeder, and at the same time publishes a "completed" message to other power restoration service units SRU to ensure that only one power restoration service unit SRU executes the plan;

[0040] (2.5) The power restoration service unit SRU issues "reconnect", "dispatch" and "close" commands to the renewable energy unit DERU, the electric vehicle aggregation unit EVAU and the feeder circuit breaker unit FBU; the adjacent feeder lines, the distributed energy units in the non-fault area of ​​the faulty feeder line and the electric vehicle aggregation unit EVAU jointly supply power to the downstream non-fault area; the feeder circuit breaker unit FBU of the faulty feeder line closes and turns to the "normal" state, and power supply is restored upstream of the faulty section.

[0041] The beneficial effects of the present invention are as follows: this application reduces dependence on external feeder lines and grid restoration costs, and enhances the resilience of the grid by constructing a grid power supply service restoration plan that takes into account renewable energy resources and electric vehicle aggregated resources in healthy areas within the faulty feeder lines; compared with traditional grid power supply restoration plans, it makes full use of the internal resources of the grid and reduces the overall margin reserve pressure of the grid. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 A distribution network elastic recovery model diagram of a feeder line autonomous load recovery method including electric vehicle assistance provided by the present invention. DETAILED DESCRIPTION

[0043] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the embodiments and the drawings in the embodiments. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0044] In order to make the purpose and features of the present invention more obvious and easy to understand, the present invention is further described below in conjunction with the accompanying drawings and specific implementation methods.

[0045] like Figure 1 As shown, a method for autonomous load recovery of a feeder line with assistance of an electric vehicle, the recovery method comprising:

[0046] (1) Analyze and model the operating characteristics of active radial feeder line equipment, including feeder breaker unit (FBU), segment unit (SU), load unit (LU), distributed renewable energy unit (DERU), electric vehicle aggregation unit (EVAU), and power supply service recovery unit (SRU).

[0047] The feeder circuit breaker unit FBU is located in the substation, and includes a reclosing overcurrent relay, a current transformer, a measurement and calculation module, and a communication module; the measurement and calculation module is used to measure and calculate the reserve current capacity RCC of the feeder transformer TR in real time, and the communication module is used to send the calculated reserve current capacity RCC to the fault recovery service unit in real time and publish "fault processing" information to the renewable energy unit DERU and the electric vehicle aggregation unit EVAU; the feeder circuit breaker unit FBU is used to calculate and report the reserve current capacity RCC of the feeder; in the calculation of the reserve current capacity RCC, the model of the feeder transformer capacity FTC and the secondary side current of the feeder transformer TR is:

[0048]

[0049] Among them, RCC i,t represents the reserve current capacity of feeder i at time t, FTC i represents the transformer capacity on feeder i, represents the rated voltage of the secondary side of the transformer on feeder i, It represents the rated current of the secondary side of the transformer on feeder i at time t, and the subscript s represents the rated value.

[0050] The sectionalizer unit SU is composed of a current relay, a current transformer and a communication module; the communication module is used to issue "discovery" and "isolation" information to the feeder circuit breaker unit FBU and receive the "fault handling" instruction issued by the feeder circuit breaker unit FBU, and transmit the line overcurrent situation to the feeder circuit breaker unit FBU; the sectionalizer unit SU is used to detect the line overcurrent situation and transmit the information, and isolate the detected fault through remote control; the current in the active radial feeder line flows bidirectionally, and the sectionalizer unit SU is installed at both ends of each section of the line. When the line current is overcurrent or reverse, the relay is disconnected and the fault information is uploaded to the feeder circuit breaker unit FBU. The model is:

[0051] or

[0052] in, and They represent the amplitude and phase angle of the current at the location of the kth sectionalizer unit SU in the feeder i during time period t, r is the ratio of the primary to the secondary side of the current transformer, and r>1; represents the setting current of the current relay in the kth sectionalizer unit SU in feeder i, and N represents the rated setting current.

[0053] The busbar connected to the load unit LU covers the entire smart community, and the ZIP load model is used to describe the active and reactive power of the load. The ZIP load model is:

[0054]

[0055]

[0056] Among them, P b,t and They represent the active power and initial value of each bus at time t, Q b,t and Respectively represent the reactive power and initial value of each bus at time t, V b,t and They represent the voltage and initial value of each busbar at time t, and the subscript b represents the electrical parameters of the load unit; (Z p , I p , P p ) and (Z q , I q ,I q ) represent the active load factor and reactive load factor of the ZIP model respectively.

[0057] The renewable energy unit DERU refers to a wind and solar power generation unit, which is equipped with a remote automatic circuit breaker. After receiving a feeder fault signal, it is responsible for disconnecting the renewable energy unit DERU from the feeder, and reconnecting the renewable energy unit DERU to the grid after receiving a "reconnect" signal. The grid-connected power has the following model constraints:

[0058]

[0059] in, and They represent the upper and lower limits of the grid-connected power of the renewable energy unit DERU, P DER,t It represents the grid-connected power of renewable energy unit DERU during period t.

[0060] The electric vehicle aggregation unit EVAU is a physical facility responsible for controlling the aggregation of electric vehicles, including charging piles, a communication remote control module and a data processing center; wherein the communication remote control module is used to receive instructions from the feeder circuit breaker unit FBU and control the electric vehicles connected to the charging piles to supply power to the power grid, and send the available capacity of the electric vehicle aggregation unit EVAU to the fault recovery service unit in real time; the data processing center is used to calculate the available capacity of the electric vehicle aggregation unit in real time, and send the calculation results to the fault recovery service unit through the communication remote control module; the electric vehicle aggregation unit EVAU communicates with other smart devices in the power grid to remotely control the electric vehicle charging piles in the area, and by changing the aggregation coefficient of the electric vehicle, the aggregated electric vehicle load distribution is reflected in the ZIP load model, which has two states: "normal" and "dispatching"; after a fault recovery service is completed, the model for corresponding economic compensation based on the recovery capacity provided by each electric vehicle is:

[0061]

[0062] Among them, EC i The service revenue obtained by the i-th electric vehicle participating in the fault recovery service, Q i The recovery capacity provided for the participating failure recovery services, Q Tot The total restoration capacity provided by the electric vehicle aggregation unit EVAU in the fault restoration service, EC Tot The total revenue obtained by the Electric Vehicle Aggregation Unit (EVAU) from participating in the fault recovery service.

[0063] The power supply restoration service unit SRU is composed of a circuit breaker connecting two radial feeders, a communication module and a data processing module; the communication module is used to receive information sent by all other units, and publish the data processing results to the corresponding units for reception and execution; after the communication module receives the "fault handling" instruction issued by the feeder circuit breaker unit, the data processing module executes the power supply service restoration SR algorithm after the fault event through the real-time measurement data of the electric vehicle aggregation unit, the renewable energy aggregation unit, the feeder circuit breaker unit and the sectionalizer unit; the power supply restoration service unit SRU has two states of "normal" and "restored", and restores the non-fault load by utilizing all available resources within a certain time interval after the event occurs; whether to close the circuit breaker in the power supply restoration service unit SRU is determined by the standard of the following model:

[0064]

[0065] in, Represents the total fault recovery demand current, RCC i,t represents the reserve current capacity of feeder i at time t, It represents the recovery current that the renewable energy unit DERU can provide, represents the restoration current that can be provided by the electric vehicle aggregation unit EVAU; α, β and γ represent the contribution factors of the restoration current provided by the adjacent feeders, the renewable energy unit DERU and the electric vehicle aggregation unit EVAU in the normal section of the faulty line to the restoration of the faulty section.

[0066] (2) When a feeder line fails, the feeder circuit breaker unit FBU and the power restoration service unit SRU dispatch the renewable energy units DERU and electric vehicle aggregation units EVAU connected to the normal bus of the line to reduce the power outage time of users and assist in the autonomous recovery of loads.

[0067] (2.1) Determine the communication information that needs to be transmitted between the corresponding components, including the information name, publisher and receiver of the information, and the information type, as summarized in the following table:

[0068]

[0069] (2.2) Before the fault occurs, the current relay detection status in the sectionalizer unit on each line segment of the feeder line is normal, and the relay remains in the closed state, that is:

[0070] and

[0071] Wherein, K = {1, 2, 3 ...} is the set of labels of the segmenter units on feeder i = {1, 2, 3 ...}, and represent the amplitude and phase angle of the current detected by the current relay in the kth sectionalizer unit in feeder i during time period t, represents the setting current value of the current relay in the kth sectionalizer unit in feeder i;

[0072] (2.3) Assuming that a fault occurs in the mth section line, each sectionalizer unit SU on the feeder line detects a forward overcurrent in the line, that is:

[0073]

[0074] in, represents the amplitude of the feeder current at the location of the mth sectionalizer unit in feeder i during period t, r is the ratio of the primary and secondary coils of the current transformer, is the setting value of the current relay in the mth sectionalizer unit in feeder i; at this time, the communication module in the mth sectionalizer unit reports the fault information to the feeder circuit breaker unit;

[0075] (2.4) The feeder circuit breaker unit changes from the "ready" state to the "fault" state and issues a "fault handling" command, triggering the downstream algorithm;

[0076] (2.5) Each renewable energy unit receives a "fault handling" message from the feeder circuit breaker unit, and after disconnecting, switches from the grid-connected operation mode to the off-grid operation mode; the renewable energy unit receives the line overcurrent information, and its internal feeder circuit breaker is disconnected, causing the wind and solar power generation units to be disconnected from the grid and wait for the command to reconnect to the grid;

[0077] (2.6) Downstream sectionalizer unit SU of the faulty line section in the feeder line m+1 The current relay inside the circuit first detects the reverse overcurrent of the line, that is:

[0078]

[0079] Segmenter Unit SU m+1 The current relay in the feeder is automatically disconnected, and the communication module reports this information to the feeder circuit breaker unit of the feeder. Then, the fault location is determined, which is the mth segment line;

[0080] (2.7) The sectionalizer unit SU detects the reverse overcurrent of the line m+1 and the upstream sectionalizer unit SU of the line segment where it is located m The mth section of the line is isolated together. After the faulty line section is successfully isolated, the current relays in the upstream section units are no longer triggered by the line overcurrent, the internal spring pieces are reset, the upstream feeder line continues to be powered, and the downstream feeder line stops powering;

[0081] (2.8) Then, the sectionalizer units SU at both ends of the faulty line segment m and SU m+1 The "fault state" is changed to the "discovery" state, and the "isolated" information is sent to all fault recovery service units connected to the faulty feeder i. The SRU satisfies the following formula:

[0082] SRU i,j ,∈ψ i

[0083] Among them, SRU i,j represents the fault recovery service unit located between feeder i and feeder j, ψ i represents the set of all feeders connected to feeder i through fault recovery service units; the power supply recovery service unit SRU located between feeder line i and the end bus of feeder line j i,j After receiving the "isolated" message, the "normal" state is changed to the "restored" state. The power supply service restoration plan is implemented;

[0084] (2.9) Then, each power supply restoration service unit SRU starts to check whether other normal feeder lines connected to the faulty feeder line meet the support conditions based on the measurement data before the fault occurs, as shown in the following formula:

[0085]

[0086]

[0087]

[0088]

[0089] in, Indicates the total current required during the fault recovery period, demand indicates the demand, and RCC i,t It represents the reserve current capacity of the adjacent feeder connected to the faulty feeder i in time period t, which is affected by the transformer power margin FTC on feeder i. i , Rated voltage of transformer secondary side on feeder i and the transformer secondary current on feeder i The subscript s indicates the rated electrical parameters of the transformer. represents the total current that can be supplied by renewable energy units in the normal area of ​​the faulty feeder, is the adjustable output of the renewable energy unit immediately before the fault. The subscript DER refers to the renewable energy unit. represents the total current available from the EV aggregation units in the normal area of ​​the fault feeder, is the adjustable total output of the electric vehicle aggregation unit immediately before the fault. The subscript V2G represents the electric vehicle aggregation unit. V i is the voltage level of feeder i.

[0090] (2.10) Let the first power restoration service unit that meets the requirements be SRU i,n , which controls the closing of the normally open connecting circuit breaker (located in the fault restoration service unit) connecting feeder n and the fault feeder i, and at the same time restores power to all other power supply service units SRU i,j ,∈ψ i \Publish the "Complete" message to ensure that only one power restoration service unit SRU executes the restoration plan, where ψ i \ represents the set of all feeders connected to the fault feeder i except the first feeder that meets the power supply restoration service requirements;

[0091] (2.11) Further, the power restoration service unit SRU i,n The feeder breaker unit FBU of the faulty feeder line i is respectively connected to the feeder breaker unit FBU i , all available renewable energy units DERU and electric vehicle aggregation units EVAU in the normal downstream section of the faulty section of feeder i issue “reclose”, “reconnect” and “dispatch” commands;

[0092] (2.12) Furthermore, the power support transmitted by the electric vehicle aggregation unit EVAU to the power grid is related to the number of electric vehicles connected to the electric vehicle aggregation unit EVAU, the charging and discharging status of the electric vehicles, and the charging and discharging efficiency. The following modeling is used:

[0093]

[0094]

[0095]

[0096]

[0097]

[0098]

[0099] in, represents the energy that the jth electric vehicle aggregation unit EVAU can deliver to the grid in time period t, which is affected by the cumulative number of grid-connected electric vehicles at historical moments; ζ t It represents the number of electric vehicles connected to the grid through the jth electric vehicle charging station in time period t, which is a quantity that changes with time t; and They represent the charging power and discharging power of the i-th electric vehicle in time period t, Δt represents the scheduling unit time, which is 1 hour. represents the charging power of the i-th electric vehicle in time period t, It represents the discharge power of the ith electric vehicle in the t period, and the unit of power is kilowatt (kw); represents the charging efficiency of the i-th electric vehicle, represents the discharge efficiency of the i-th electric vehicle, They are all constants greater than 0 and less than 1; represents the charging status of the i-th electric vehicle in time period t, When , it means that the i-th electric car has no action in time period t. When indicates that the i-th electric vehicle is charging in time period t; represents the discharge state of the i-th electric vehicle in time period t, When , it means that the i-th electric car has no action in time period t. When , it means that the i-th electric car discharges in time period t, let This is to prevent electric vehicles from charging and discharging at the same time. represents the total power that the electric vehicle aggregation unit can deliver to the grid in time period t;

[0100] (2.13) Subsequently, the power support delivered by the electric vehicle aggregation unit to the grid is also subject to the constraints of the electric vehicle's initial state of charge, the minimum allowable state of charge, and the charging power limit, which is reflected as follows:

[0101]

[0102]

[0103]

[0104] represents the initial state of charge of the i-th electric vehicle, represents the minimum allowable state of charge of the ith electric vehicle to meet the owner's bottom-line travel needs, and They represent the maximum allowable charging power and discharging power of electric vehicles respectively;

[0105] (2.14) The grid-connected power of renewable energy units is subject to upper and lower limits, expressed as:

[0106]

[0107] in, and It represents the minimum and maximum output range of renewable energy at time t, which varies with the environment and time;

[0108] (2.15) Further, the normally open circuit breaker on the power restoration service unit SRU is closed, and the adjacent feeders, the electric vehicle aggregation unit and the renewable energy unit located downstream of the fault area jointly supply power to the normal area downstream of the fault area;

[0109] (2.16)Finally, the feeder circuit breaker units, the sectionalizer units in the normal area, and the renewable energy units are all turned back to the “ready” state to deal with the next fault.

Claims

1. A method for autonomous load recovery of feeder lines with electric vehicle assistance, characterized in that: The method comprises the following steps: (1) Analyze and model active radial feeder line elements with electric vehicle assistance, wherein the active radial feeder line elements include feeder breaker unit FBU, sectionalizer unit SU, load unit LU, renewable energy unit DERU, electric vehicle aggregation unit EVAU and power restoration service unit SRU; (2) When a feeder line fails, the feeder circuit breaker unit FBU and the power restoration service unit SRU dispatch the renewable energy unit DERU and the electric vehicle aggregation unit EVAU connected to the busbar of the normal part of the line to reduce the power outage time of users and assist in the autonomous recovery of loads; (2.1) When a fault occurs, the feeder breaker unit FBU and the renewable energy unit DERU sense that the line is overcurrent; the renewable energy unit DERU automatically disconnects from the grid and waits for instructions to reconnect to the grid; (2.2) The feeder circuit breaker unit FBU changes from the "ready" state to the "fault" state, and issues a "fault handling" command, triggering the downstream algorithm to determine which section of the line the fault is located in by sensing the overcurrent direction of the line through the sectionalizer unit SU, and report the fault location information to the power supply restoration service unit SRU; (2.3) The sectionalizer unit SU that senses the reverse overcurrent changes its state to the rear-end fault state, and sends a message to the sectionalizer unit SU upstream of the same section, changing it to the "discovery" state. At the same time, it sends an "isolation" message to the power restoration service unit SRU, and the faulty line section is isolated; (2.4) After receiving the "isolated" information, the power restoration service unit SRU starts to initiate the service restoration plan. Based on the pre-fault measurement data, the power restoration service unit SRU checks whether the following standards are met: in, represents the total required current for fault recovery, RCC is the reserve current margin of the adjacent feeder transformer, It represents the recovery current that the renewable energy unit DERU can provide, represents the restoration current that can be provided by the electric vehicle aggregation unit EVAU; α1, β1 and γ1 represent their respective weight proportions in grid restoration, and their weight proportions depend on the capacity of the adjacent feeding lines, renewable energy units DERU and electric vehicle aggregation units EVAU; The first power restoration service unit SRU that meets the requirements closes its normally open connection circuit breaker with the faulty feeder, and simultaneously sends a "completed" message to other power restoration service units SRU to ensure that only one power restoration service unit SRU executes the plan; (2.5) The power restoration service unit SRU issues "reconnect", "dispatch" and "close" commands to the renewable energy unit DERU, the electric vehicle aggregation unit EVAU and the feeder circuit breaker unit FBU; the adjacent feeder lines, the distributed energy units in the non-fault area of ​​the faulty feeder line and the electric vehicle aggregation unit EVAU jointly supply power to the downstream non-fault area; the feeder circuit breaker unit FBU of the faulty feeder line closes and turns to the "normal" state, and power supply is restored upstream of the faulty area.

2. The method for autonomous load recovery of feeder lines with electric vehicle assistance according to claim 1, characterized in that: The analysis and modeling of the feeder breaker unit FBU in step (1) specifically includes: The feeder circuit breaker unit FBU is located in the substation, and includes a reclosing overcurrent relay, a current transformer, a measurement and calculation module, and a communication module; the measurement and calculation module is used to measure and calculate the reserve current capacity RCC of the feeder transformer TR in real time, and the communication module is used to send the calculated reserve current capacity RCC to the fault recovery service unit in real time and publish "fault processing" information to the renewable energy unit DERU and the electric vehicle aggregation unit EVAU; the feeder circuit breaker unit FBU is used to calculate and report the reserve current capacity RCC of the feeder; in the calculation of the reserve current capacity RCC, the model of the feeder transformer capacity FTC and the secondary side current of the feeder transformer TR is: Among them, RCC i,t represents the reserve current capacity of feeder i at time t, FTC i represents the transformer capacity on feeder i, represents the rated voltage of the secondary side of the transformer on feeder i, It represents the rated current of the secondary side of the transformer on feeder i at time t, and the subscript s represents the rated value.

3. The method for autonomous load recovery of feeder lines with electric vehicle assistance according to claim 1, characterized in that: The analysis and modeling for the segmenter unit SU in step (1) specifically includes: The sectionalizer unit SU is composed of a current relay, a current transformer and a communication module; the communication module is used to issue "discovery" and "isolation" information to the feeder circuit breaker unit FBU and receive the "fault handling" instruction issued by the feeder circuit breaker unit FBU, and transmit the line overcurrent situation to the feeder circuit breaker unit FBU; the sectionalizer unit SU is used to detect the line overcurrent situation and transmit the information, and isolate the detected fault through remote control; the current in the active radial feeder line flows bidirectionally, and the sectionalizer unit SU is installed at both ends of each section of the line. When the line current is overcurrent or reverse, the relay is disconnected and the fault information is uploaded to the feeder circuit breaker unit FBU. The model is: or in, and They represent the amplitude and phase angle of the current at the location of the kth sectionalizer unit SU in the feeder i during time period t, r is the ratio of the primary to the secondary side of the current transformer, and r>1; represents the setting current of the current relay in the kth sectionalizer unit SU in feeder i, and N represents the rated setting current.

4. The method for autonomous load recovery of feeder lines with electric vehicle assistance according to claim 1, characterized in that: The analysis and modeling for the load unit LU in step (1) specifically includes: The busbar connected to the load unit LU covers the entire smart community, and the ZIP load model is used to describe the active and reactive power of the load. The ZIP load model is: Among them, P b,t and They represent the active power and initial value of each bus at time t, Q b,t and Respectively represent the reactive power and initial value of each bus at time t, V b,t and They represent the voltage and initial value of each busbar at time t, and the subscript b represents the electrical parameters of the load unit; (Z p , I p , P p ) and (Z q , I q , P q ) represent the active load factor and reactive load factor of the ZIP model respectively.

5. The method for autonomous load recovery of feeder lines with electric vehicle assistance according to claim 1, characterized in that: The analysis and modeling for the renewable energy unit DERU in step (1) specifically includes: The renewable energy unit DERU refers to a wind and solar power generation unit, which is equipped with a remote automatic circuit breaker. After receiving a feeder fault signal, it is responsible for disconnecting the renewable energy unit DERU from the feeder, and reconnecting the renewable energy unit DERU to the grid after receiving a "reconnect" signal. The grid-connected power has the following model constraints: in, and They represent the upper and lower limits of the grid-connected power of the renewable energy unit DERU, P DER,t It represents the grid-connected power of renewable energy unit DERU during period t.

6. The method for autonomous load recovery of feeder lines with electric vehicle assistance according to claim 1, characterized in that: The analysis and modeling for the electric vehicle aggregation unit EVAU in step (1) specifically includes: The electric vehicle aggregation unit EVAU is a physical facility responsible for controlling the aggregation of electric vehicles, including charging piles, a communication remote control module and a data processing center; wherein the communication remote control module is used to receive instructions from the feeder circuit breaker unit FBU and control the electric vehicles connected to the charging piles to supply power to the power grid, and send the available capacity of the electric vehicle aggregation unit EVAU to the fault recovery service unit in real time; the data processing center is used to calculate the available capacity of the electric vehicle aggregation unit in real time, and send the calculation results to the fault recovery service unit through the communication remote control module; the electric vehicle aggregation unit EVAU communicates with other intelligent devices in the power grid to remotely control the electric vehicle charging piles in the area, and by changing the aggregation coefficient of the electric vehicle, the aggregated electric vehicle load distribution is reflected in the ZIP load model, which has two states of "normal" and "dispatching"; after a fault recovery service is completed, the model for corresponding economic compensation based on the recovery capacity provided by each electric vehicle is: Among them, EC i The service revenue obtained by the i-th electric vehicle participating in the fault recovery service, Q i The recovery capacity provided for the participating failure recovery services, Q Tot The total restoration capacity provided by the electric vehicle aggregation unit EVAU in the fault restoration service, EC Tot The total revenue obtained by the Electric Vehicle Aggregation Unit (EVAU) from participating in the fault recovery service.

7. The method for autonomous load recovery of feeder lines with electric vehicle assistance according to claim 1, characterized in that: The analysis and modeling for the power restoration service unit SRU in step (1) specifically includes: The power supply restoration service unit SRU is composed of a circuit breaker connecting two radial feeders, a communication module and a data processing module; the communication module is used to receive information sent by all other units, and publish the data processing results to the corresponding units for reception and execution; after the communication module receives the "fault handling" instruction issued by the feeder circuit breaker unit, the data processing module executes the power supply service restoration SR algorithm after the fault event through the real-time received measurement data of the electric vehicle aggregation unit, the renewable energy aggregation unit, the feeder circuit breaker unit and the sectionalizer unit; the power supply restoration service unit SRU has two states of "normal" and "restored", and restores non-fault loads by using all available resources within a certain time interval after the event occurs; whether to close the circuit breaker in the power supply restoration service unit SRU is determined by the standard of the following model: in, Represents the total fault recovery demand current, RCC i,t represents the reserve current capacity of feeder i at time t, It represents the recovery current that the renewable energy unit DERU can provide, represents the restoration current that can be provided by the electric vehicle aggregation unit EVAU; α, β and γ represent the contribution factors of the restoration current provided by the adjacent feeders, the renewable energy unit DERU and the electric vehicle aggregation unit EVAU in the normal section of the faulty line to the restoration of the faulty section.

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