Adjusting and switching cooperative control method and system for distributed resources to participate in power grid stability control

Abstract

The invention discloses an adjusting and switching cooperative control method and system for distributed resources to participate in power grid emergency control. The method comprises the steps that 1, a collection terminal uploads distributed resource data to a stability control terminal; 2, the stability control terminal uploads the distributed resource data to the control substation; step 3, the control substation counts distributed resource data; 4, after the control substation receives the load shedding instruction Pref, the Pref is compared with the modulation total amount # imgabs0 # of all the charging piles, if # imgabs1 # is adopted, the charging piles are modulated, and if # imgabs2 # is adopted, part of interruptible loads are selectively cut off according to the load level except for the modulation charging piles; step 5, when the micro-grid operates in a grid-connected mode, establishing a multi-objective optimization model; when the micro-grid operates in the island mode, unbalanced power Punb exists, if the Punb is larger than 0, a distributed photovoltaic modulation command is calculated, and if the Punb is smaller than 0, an optimization model is established; 6, solving the optimization model by adopting a genetic algorithm; and 7, controlling the load and the unit. The influence on important load power supply is reduced, and the power supply reliability of the system is improved.

Description

Technical Field

[0001] The present invention belongs to the field of safe and stable control of power systems, and more specifically, to a coordinated control method and system for distributed resources participating in power grid stability control. Background Art

[0002] Load shedding is one of the main measures for safe and stable control of power systems. When a serious accident occurs in the system or a large amount of power is suddenly lost, quickly shedding part of the load can reduce the power imbalance of the system and thus ensure the stability of the system.

[0003] Due to the impact of the global energy crisis, electric vehicles use electricity as a power source, getting rid of dependence on traditional fossil fuels, and have developed rapidly in recent years. The number of charging piles has also increased. However, disordered charging behavior will lead to an increase in the peak-to-valley difference of the power grid load, which poses a challenge to the safe and stable operation of the power grid. Distributed photovoltaic power generation can make full use of local solar energy resources and replace part of the fossil energy consumption, and the scale of grid connection has gradually expanded. Distributed photovoltaic output is affected by light and ambient temperature and presents randomness and intermittent characteristics. A large number of distributed photovoltaic grid connection will impact the active power balance of the power grid, increasing the difficulty of stabilizing the power grid. In the third line of defense, when the power system has out-of-step oscillation, frequency abnormality, voltage abnormality and other accidents, it will take measures such as cutting the machine and cutting the load, affecting the power supply of normal users and important loads, causing serious economic losses.

[0004] Prior art document 1 (CN 106856330 A) discloses a method for regulating active power imbalance in a flexible load control system. This document only addresses the field of preventive control of power systems and cannot adapt to emergency control. It does not propose a specific solution for engineering implementation and only considers bidirectional controllable energy storage power stations. It does not consider specific distributed resources such as charging piles and photovoltaic inverters, and does not consider the specific allocation principles of distributed resources.

[0005] Prior art document 2 (CN 118281943 A) discloses a source-grid-load-storage coordinated control method, device and electronic equipment for an isolated microgrid. This document only considers the isolated microgrid, establishes a unified objective function solution within the isolated microgrid, and considers a single objective function of the minimum power cost of the isolated microgrid. The number of nodes in a single microgrid is limited. If this technology is used for emergency control of a large power grid, as a large number of nodes (distributed resources) are connected, the amount of calculation will increase greatly, and it will be unable to meet the emergency control needs of the power system. Summary of the invention

[0006] In the above context, charging piles and distributed photovoltaics, as distributed resources in the substation, need to participate in the grid stability control, respond to the power instructions issued by the system, and support the stable operation of the grid. Therefore, it is necessary to design a fast and stable control system for distributed resources in the substation.

[0007] In order to solve the deficiencies in the prior art, the present invention proposes a rapid and stable control system and method for distributed resources in an area, which can optimize the load shedding control strategy, quickly and accurately cut off part of the load, and ensure the stability of the power system.

[0008] A first aspect of the present invention provides a coordinated control strategy for distributed resources participating in power grid stability control, including:

[0009] Step 1: The aggregation terminal calculates the adjustable load and interruptible load of each charging pile and distributed photovoltaic, and sends it to the stabilization terminal;

[0010] Step 2: According to the data sent by the aggregation terminal, the stabilization terminal calculates the total amount of load that can be cut, the total amount of charging piles that can be modulated, and the total amount of distributed photovoltaics that can be modulated, and sends them to the control substation;

[0011] Step 3: Calculate the total modulatable amount of charging piles connected to the control substation and the total interruptible load at each level according to the data sent by the stabilization and control terminal, and send the calculated data to the control master station or the dispatching system through the control substation;

[0012] Step 4: The control substation receives the load shedding instruction P from the upper level. ref After that, P ref The total amount of all charging piles in the control substation that can be modulated calculated in step 3 For comparison, if The control substation sends the charging pile adjustable capacity command to the stabilization control terminal. The control substation sends the charging pile adjustable capacity command to the stabilization control terminal, and at the same time, according to the total amount of cuttable load at each level calculated in step 3, the interruptible load is selected to be cut off according to the load level;

[0013] Step 5: The operation modes of the microgrid include grid-connected operation mode and island operation mode. For the grid-connected mode, a multi-objective optimization model is established for the adjustable load capacity command of the stable control terminal. When the microgrid is operated in the island mode, there is an unbalanced power P unb , if P unb > 0, calculate the modulation command of distributed photovoltaic, if P unb <0, it is necessary to establish a multi-objective optimization model that takes into account the charging and discharging mode conversion of the charging pile;

[0014] Step 6, using a genetic algorithm to solve the multi-objective optimization model established in step 5 to obtain modulation commands for each charging pile and distributed photovoltaic;

[0015] Step 7: The collection terminal modulates the charging pile and distributed photovoltaic according to the modulation command obtained in step 6, and cuts off the interruptible load according to the specified load cutting instruction issued by the stabilization control terminal.

[0016] Preferably, the adjustable load amount calculated in step 1 can be expressed by the following formula:

[0017] The collection terminal calculates the adjustable load based on the collected charging pile and distributed photovoltaic information. The calculation formula is as follows:

[0018]

[0019] 1≤i1+i2≤N (3)

[0020] In the formula, and are the adjustable loads of the i1th charging pile and the i2th distributed photovoltaic respectively; and are the current power of the i1th charging pile and the i2th distributed photovoltaic respectively;

[0021] is the minimum charging power of the i1th charging pile; P min_DPV,i2 is the minimum output power of the i2th distributed photovoltaic; N is the total number of interruptible loads, charging piles and distributed power sources collected by each collection terminal.

[0022] Preferably, in step 2, the stabilization terminal calculates the total amount of load that can be cut, the total amount of charging pile that can be modulated, and the total amount of distributed photovoltaic that can be modulated, which can be expressed by the following formula:

[0023] F j (P i ,S i ,Tys i )={P i |S i =j,Tys i =0, 1≤i≤K} (3)

[0024] K=M*N (4)

[0025]

[0026] Where P i is the power of the i-th interruptible load; S i Tys is the level setting for interruptible loads; i is the load type attribute, Tys iThe value of Tys is 0, 1, 2, i =0 means the load type is interruptible load; Tys i =1 means the load type is charging pile; Tys i =2 represents that the load type is distributed power supply; M is the number of aggregation terminals connected to a stabilization terminal; K is the total number of interruptible loads, charging piles and distributed power supplies connected to the stabilization terminal; N is the total number of interruptible loads, charging piles and distributed power supplies collected by each aggregation terminal; F j (P i ,S i ,Tys i ) is the set of all interruptible loads of the jth level under the jurisdiction of this stabilization control terminal; P cut,j is the total interruptible load of the jth level;

[0027] It is the set of adjustable loads of all charging piles under the control of this collection terminal. is the adjustable load of the i1th charging pile, The total amount of charging piles that can be adjusted for all the terminals under its jurisdiction;

[0028] is the adjustable load of the i2th distributed photovoltaic system, It is the aggregate of the adjustable loads of all distributed photovoltaics under the jurisdiction of this collection terminal. It is the total modulatable amount of distributed photovoltaic power generation with all the collection terminals under its jurisdiction.

[0029] Preferably, the total amount of modulatable charging piles connected to the control substation, the total amount of modulatable distributed photovoltaics and the total amount of load that can be cut in step 3 can be expressed by the following formula:

[0030]

[0031] Where: j is the level of interruptible load, 0≤j≤3; Q is the number of stable control terminals connected to the control substation; P cut,j,k is the total load shedding capacity of the jth level of the kth aggregation terminal; P substation_cut,j is the total amount of shelvable load at the jth level connected to all control substations;

[0032] is the total amount of charging pile that can be modulated for the kth stable control terminal; The total amount can be adjusted for all charging piles connected to the control substation.

[0033] Preferably, the multi-objective optimization model established in the grid-connected mode in step 5 can be expressed by the following formula:

[0034]

[0035]

[0036] Where: f1 is the modulation command objective function; is the modulation command issued; N1 is the number of the first type of charging piles, and N2 is the number of the second type of charging piles; is the charging power of the first type of charging pile j1; is the control mode of the first type of charging pile j1, Indicates removal, Indicates no excision; ΔP c2,k is the modulation power of the second type of charging pile k; Y k is the control mode of the second type of charging pile, Y k =1 indicates modulation power, Y k =0 means no power modulation;

[0037] f2 is the charging loss objective function; C1 and C2 are the electricity prices during the removal period and the normal operation period of the power grid respectively; T is the removal duration;

[0038] f3 is the load shedding priority objective function; pri1 and pri2 are the upper and lower limits of the priority, respectively; The priority of the first type of charging pile; L c2,k The priority of the second type of charging pile.

[0039] Preferably, in step 5, the unbalanced power P unb The calculation formula is as follows:

[0040] P unb =P PV -P C -P l (18)

[0041] Where P PV is the distributed photovoltaic output of the microgrid, P C is the charging power of the charging pile, P l For households, loads can be interrupted.

[0042] Preferably, the multi-objective optimization model established in the island mode in step 5 can be expressed by the following formula:

[0043]

[0044]

[0045] Where:

[0046] f4 is the power balance objective function; P unb0is the initial unbalanced power; N1 is the number of the first type of charging piles; N2 is the number of the second type of charging piles; N3 is the number of interruptible loads in the microgrid; is the charging power of the first type of charging pile j1; It is the control mode of the first type of charging pile; P c2,k is the charging power of the second type of charging pile k; P f,k is the discharge power of the second type of charging pile k; Y k1 is the control mode of the second type of charging pile, Y k1 =1 means discharge mode, Y k1 =0 means charging mode; P l,m is the power of interruptible load m; Z m For the control mode of interruptible load, Z m =1 means resection, Z m =0 means no resection; is the upper limit of charging power, is the upper limit of the discharge power;

[0047] f5 is the charging loss objective function; C1 and C2 are the electricity prices during the removal period and the normal operation period respectively; T is the removal time; t k is the discharge time of the second type of charging pile k, E k0 The remaining battery power;

[0048] f6 is the load shedding priority objective function; L c1,j The priority of the first type of charging pile; L l,m is the priority of the interruptible load; N1 is the number of the first type of charging piles; N3 is the number of interruptible loads in the microgrid; Z m It is the control mode of interruptible load, pri1 and pri2 are the upper and lower limits of priority respectively.

[0049] Preferably, the specific steps of solving the model by genetic algorithm in step 6 are as follows:

[0050] (1) Initialize the population, randomly generate a group of individuals as the initial population, and obtain the initial charging pile and distributed photovoltaic modulation commands; use the optimization model established in step 5 as the fitness function, substitute the value of each individual into the fitness function, and obtain the initialized fitness value;

[0051] (2) Crossover: The sire and dam for the crossover are selected using the tournament selection method, and genetic recombination between the two individuals is completed through single-point crossover;

[0052] (3) Mutation: using single-point mutation to modify the gene value at a random position while setting a smaller mutation rate;

[0053] (4) Selection: merge the new population generated after crossover mutation with the original population, sort the fitness values ​​corresponding to each variable from small to large, and screen out the new population;

[0054] (5) Repeat steps (2) to (4). If the termination condition is met or the maximum number of iterations is reached, the calculation ends.

[0055] A second aspect of the present invention provides a coordinated control system for distributed resources participating in power grid stability control, and runs the above-mentioned coordinated control strategy for distributed resources participating in power grid stability control, including:

[0056] The stabilization control system layer is used to issue a generator or load shedding command through an offline strategy table when a fault or disturbance occurs in the power grid;

[0057] The stabilization control terminal layer uses SDH 2M communication or wireless communication with the stabilization control system to receive load shedding or machine shedding instructions from the stabilization control system, and receive the operating data transmitted by the aggregation terminal through optical fiber;

[0058] The collection terminal layer connects the charging pile, inverter and intelligent circuit breaker through RS485 communication, receives the operation data of the intelligent circuit breaker, inverter and charging pile communication, and at the same time, the collection terminal detects the status information of the charging pile, load and distributed photovoltaic in real time, and sends the status information and operation data to the stabilization control terminal through optical fiber communication;

[0059] The intelligent circuit breaker layer has the function of breaking the circuit, which is used to control the input or removal of charging piles and distributed photovoltaics, and control the disconnection of interruptible loads;

[0060] The microgrid has two operating modes: grid-connected mode and island mode. When a grid fault is detected or the power quality does not meet the requirements, the microgrid will be disconnected from the grid in time and operate in island mode.

[0061] Preferably, according to the coordinated control method, after receiving the load shedding instruction, the stabilization terminal calculates the power adjustment instruction of the charging pile and sends it to the collection terminal; after receiving the machine shedding instruction, the distributed photovoltaic is controlled to reduce the output power or exit operation.

[0062] Preferably, the collection terminal receives a charging pile power adjustment instruction, generates a control signal for controlling the intelligent circuit breaker, and controls the charging pile to reduce the charging power or exit operation.

[0063] The beneficial effects of the present invention are as follows: when the station receives a load shedding instruction, the present invention gives priority to cutting off the load of the charging pile, reducing the impact on the power supply of important loads, improving the stability of the power system and reducing economic losses; in order to quantify the impact of load shedding on the operation of the charging pile and the benefits of the power grid, an economic cost evaluation index is established, and a fast and stable control strategy is designed with the response to the load shedding instruction and the minimum economic cost as the optimization goal; when the microgrid is in the island operation mode, the charging pile and the distributed photovoltaic are coordinated to maintain the voltage and frequency stability of the microgrid and improve the reliability of the system. It can be used as the second line of defense of the power system to maintain the stability and integrity of the system when a large disturbance occurs in the power system; a part of the modulatable load is used to replace the interruptible load during the emergency control process to reduce the impact on people's livelihood; the hierarchical and partitioned control system architecture meets the timeliness requirements of emergency control; the controllable resources reach a voltage level of 380V, and the control is more refined. BRIEF DESCRIPTION OF THE DRAWINGS

[0064] Figure 1 A connection diagram of a distributed resource rapid and stable control system;

[0065] Figure 2 Distributed resource rapid and stable control secondary system architecture diagram;

[0066] Figure 3 Schematic diagram of the coordinated control strategy for distributed resource scheduling. DETAILED DESCRIPTION

[0067] In order to make the purpose, technical scheme and advantages of the present invention clearer, the technical scheme of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. The embodiments described in this application are only part of the embodiments of the present invention, not all of them. Based on the spirit of the present invention, other embodiments obtained by ordinary technicians in this field without creative work are all within the scope of protection of the present invention.

[0068] The first embodiment of the present invention discloses a coordinated control method for the regulation and switching of distributed resources participating in stable control. The load shedding control strategy can be optimized through the coordinated work between the aggregation terminal, the stable control terminal, the intelligent circuit breaker and the control substation, and part of the load can be quickly and accurately cut off to ensure the stability of the power system. The charging frequency of the charging pile is controllable. Reducing the charging power is equivalent to cutting off part of the load for the power grid, reducing the active power shortage of the power system, and does not affect the power supply of important loads. When the power grid needs to perform low-frequency load reduction or low-voltage load reduction control, you can choose to adjust the charging power of the charging pile or disconnect the charging pile to complete the charging task after the power system returns to normal. The distributed photovoltaic system is relatively independent and controllable, and has a fast start and stop speed. Participating in stable control can make up for the lack of stability of the large power grid. When the power grid needs to perform frequency modulation control, you can choose to put in or cut off the distributed photovoltaic power source to participate in the grid dispatch according to the need to balance the load. The following is combined with Figure 3 Provide detailed explanation.

[0069] Step 1: The terminal collects and sends distributed resource operation data;

[0070] The intelligent circuit breaker collects the current of the load, the charging pile collects the current power value, the minimum charging power and the status information of the charging pile, including the real-time power, charging time and the power range under the charging state. The inverter collects the current power value and the minimum output power of the distributed photovoltaic and sends them to the collection terminal respectively. The collection terminal collects the line voltage and calculates the power value of the interruptible load based on the received load current information; the collection terminal calculates the adjustable load and interruptible load of each connected charging pile and each distributed photovoltaic. The collection terminal will consider the allowable cutting state and abnormal state of the interruptible load, etc., to calculate the actual load that can be cut and send it to the stabilization terminal.

[0071] The collection terminal calculates the adjustable load based on the collected charging pile and distributed photovoltaic information. The calculation formula is as follows:

[0072]

[0073] 1≤i1+i2≤N (3)

[0074] In the formula, and are the adjustable loads of the i1th charging pile and the i2th distributed photovoltaic respectively; and are the current power of the i1th charging pile and the i2th distributed photovoltaic respectively;

[0075] is the minimum charging power of the i1th charging pile; P min_DPV,i2is the minimum output power of the i2th distributed photovoltaic; N is the total number of interruptible loads, charging piles and distributed power sources collected by each collection terminal. In the present invention, due to the limitation of the collection terminal sending protocol, N is 8. The communication protocol between the collection terminal and the stabilization terminal is detailed in Table 4-11.

[0076] Step 2: The stabilization control terminal collects and uploads system operation data;

[0077] According to the load level setting value and load attributes sent by the aggregation terminal, the total amount of interruptible load at each level is calculated:

[0078] F j (P i ,S i ,Tys i )={P i |S i =j,Tys i =0, 1≤i≤K} (4)

[0079] K=M*N (5)

[0080]

[0081] Where P i is the power of the i-th interruptible load; S i is the level setting value of the interruptible load. In actual engineering, according to the communication protocol between the stabilization control terminal and the control substation, 0≤S i ≤3, see Table 4-10 for details; Tys i is the load type attribute, Tys i The value of Tys is 0, 1, 2, i =0 means the load type is interruptible load; Tys i =1 means the load type is charging pile; Tys i =2 represents that the load type is distributed power supply; M is the number of aggregation terminals connected to a stabilization terminal; K is the total number of interruptible loads, charging piles and distributed power supplies connected to the stabilization terminal, and N is the total number of interruptible loads, charging piles and distributed power supplies collected by each aggregation terminal; F j (P i ,S i ,Tys i ) is the set of all interruptible loads of the jth level under the jurisdiction of this stabilization control terminal; P cut,j is the total interruptible load of the jth level.

[0082] According to the load type attribute of the aggregation terminal, the total amount of charging pile that can be modulated is calculated. The calculation formula is as follows:

[0083]

[0084] In the formula, It is the set of adjustable loads of all charging piles under the control of this collection terminal. is the adjustable load of the i1th charging pile, It is the total amount that can be modulated for all charging piles in the collection terminals under its jurisdiction.

[0085] According to the load type attribute of the aggregation terminal, the total amount of distributed photovoltaic power that can be modulated is calculated:

[0086]

[0087] In the formula, is the adjustable load of the i2th distributed photovoltaic system, It is the aggregate of the adjustable loads of all distributed photovoltaics under the jurisdiction of this collection terminal. It is the total modulatable amount of distributed photovoltaic power generation with all the collection terminals under its jurisdiction.

[0088] Step 3: Control the substation to collect statistics of all distributed resource data;

[0089] According to the data calculated in step 2, the total amount of modulatable charging piles and the total amount of interruptible loads at each level of all connected control substations are calculated, and the calculated data is sent to the control master station or the dispatching system through the control substation. The following is the calculation method of the above indicators.

[0090] The calculation formula for the total amount of load that can be cut at each level in the control substation is as follows:

[0091]

[0092] Where: j is the level of interruptible load (0≤j≤3); Q is the number of stable control terminals connected to the control substation; P cut,j,k is the total interruptible load of the jth level of the kth stabilization terminal; P substation_cut,j is the total amount of shelvable load at the jth level connected to all control substations;

[0093] Calculate the total amount of charging pile that can be modulated

[0094]

[0095] in: is the total amount of charging pile that can be modulated for the kth stable control terminal; The total amount can be adjusted for all charging piles connected to the control substation.

[0096] As a prominent substantive feature of the present invention and one of the significant advances it brings to the prior art, the present invention takes into account distributed charging piles and photovoltaics in the distribution network area, and the controllable resources reach a voltage level of 380V, with more precise control.

[0097] Step 4: The control substation sends a control command to the stabilization control terminal;

[0098] The control substation receives the load shedding instruction P from the upper level. ref After that, P ref The total amount of charging piles that can be modulated by the access control substation calculated in step 3 Compare and select the modulation charging pile or cut off the interruptible load according to the comparison result. The specific process is as follows:

[0099] when When the modulated charging pile is selected, the adjustable capacity of each stable control terminal is allocated in proportion according to the modulated capacity of each stable control terminal charging pile. The specific proportion can be calculated using formula (14):

[0100]

[0101] in: To control the adjustable load capacity command sent from the substation to the kth stabilization terminal; is the total amount of charging pile that can be modulated by the kth stable control terminal, P ref To control the load shedding instruction of the upper level of the substation.

[0102] when When the control substation sends the charging pile adjustable capacity command to the stabilization terminal, the charging pile modulation capacity is insufficient. After the charging pile modulates the maximum capacity, according to the total amount of load that can be cut at each level, some interruptible loads are selected according to the load level. The total amount of charging pile that can be modulated is The modulation amount of each stable control terminal charging pile is The total load that can be cut is

[0103] The total load that can be cut The total interruptible load P of each level substation_cut,j For comparison, At this time, according to the modulatable capacity of each stable control terminal charging pile, the load shedding capacity of each level is allocated proportionally. The calculation formula is as follows:

[0104]

[0105] in, The instruction to remove the j-th level load capacity is sent from the substation to the k-th stabilization control terminal; The adjustable load capacity instruction sent from the substation to the kth stabilization terminal.

[0106] As a prominent substantive feature of the present invention and one of the significant advances it brings to the prior art, the present invention is a conventional load and distributed resource collaborative control strategy adopted when a power grid failure in the context of a networked system (large power grid) causes a shortage of active power and requires emergency load shedding.

[0107] Step 5: Establish a fast and stable control model for distributed resources in the substation area;

[0108] The operation modes of the microgrid include grid-connected operation mode and island operation mode. For the grid-connected operation mode, a multi-objective optimization model including modulation command objective function, charging loss objective function and load shedding priority objective function is established for the adjustable load capacity command of the stable control terminal, thereby realizing rapid and stable control of the distributed resources in the substation area. For the island mode, the unbalanced power P is used to optimize the load capacity of the microgrid. unb The value of determines the calculation of photovoltaic modulation command or establishes a multi-objective optimization model including power balance, charging loss and load shedding priority objective function. The shedding load under the stable control terminal is divided into three categories. The tumors are removed in the order of Class 1, Class 2, and Class 3 according to the principle of minimum overcutting.

[0109] Step 5.1, the adjustable load under the stabilization terminal calculates the modulation command according to the multi-objective optimization model and sends it to the corresponding aggregation terminal for execution. The charging piles connected to the stabilization terminal are divided into two categories: the first type of charging piles cannot modulate power and can only be cut off; the second type of charging piles can modulate power and can also be cut off. The multi-objective optimization model formula for calculating the modulation command is as follows:

[0110] a. Modulation command objective function

[0111] Cut off some charging piles, and some charging piles modulate the charging power to meet the modulation command.

[0112]

[0113] Where: is the modulation command issued; N1 is the number of the first type of charging piles, and N2 is the number of the second type of charging piles; is the charging power of the first type of charging pile j1; is the control mode of the first type of charging pile j1 (“1” means cut-off, “0” means not cut-off); ΔP c2,k is the modulation power of the second type of charging pile k; Y k This is the control mode for the second type of charging pile (“1” means modulated power, and “0” means non-modulated power).

[0114] b. Charging loss objective function

[0115] The power grid uses a time-of-use electricity price C(t). For the first type of charging pile, the charging task that should have been completed during the cut-off period is delayed until the power grid resumes normal operation, resulting in charging losses due to the time-of-use electricity price. Similarly, for the second type of charging pile, the originally set charging task must also be completed, resulting in charging losses. The total charging loss is calculated as follows:

[0116]

[0117] Where C1 and C2 are the electricity prices during the shedding period and the normal operation period of the power grid respectively; T is the shedding duration.

[0118] c. Load shedding priority objective function

[0119] Different removal priorities are set for the loads in the microgrid. The lower the importance of the load, the higher the removal priority. The priority is calculated as follows:

[0120]

[0121] In the formula, pri1 and pri2 are the upper and lower limits of the priority respectively; The priority of the first type of charging pile; L c2,k The priority of the second type of charging pile.

[0122] Step 5.2: For the island operation mode, if there is excess active power, the modulation command of the distributed photovoltaic is calculated; if the load is too high, a multi-objective optimization model is established to achieve power balance of the microgrid.

[0123] After the microgrid is disconnected from the large grid, there is an unbalanced power P unb , whose expression is:

[0124] P unb =P PV -P C -P l (18)

[0125] Where P PV is the distributed photovoltaic output of the microgrid, P C is the charging power of the charging pile, P l Interruptible load.

[0126] If P unb >0, the microgrid has excess active power and distributed photovoltaics need to reduce load to eliminate unbalanced power. When the distributed photovoltaic load reduction rate σ=100%

[0127] When , the expression of distributed photovoltaic load reduction rate σ is:

[0128]

[0129] Modulation command P of distributed photovoltaic PV The expression is:

[0130]

[0131] In the formula, To collect the real-time power of distributed photovoltaics under the terminal.

[0132] If P unb <0, the load of the microgrid is too high and the active power provided is insufficient. Charging piles are divided into two categories. The first type of charging piles only have charging mode, and the second type of charging piles can adjust the power, switch the charging and discharging mode, and support the operation of the power grid when necessary. In the case of excessive load, part of the load needs to be removed, and the second type of charging piles need to be switched to the discharging mode to achieve the power balance of the microgrid. A multi-objective optimization model considering the conversion of charging and discharging modes of charging piles is established. The model can be expressed by the following formula:

[0133] a. Power balance objective function

[0134] After removing part of the load and switching the second type of charging pile to the discharge mode, the new unbalanced power is calculated, and the minimum absolute value is taken as the objective function, which can be expressed by the following formula:

[0135]

[0136] Where:

[0137] P unb0 is the initial unbalanced power;

[0138] N1 is the number of the first type of charging piles;

[0139] N2 is the number of the second type of charging piles;

[0140] N3 is the number of interruptible loads in the microgrid;

[0141] is the charging power of the first type of charging pile j1;

[0142] It is the control mode of the first type of charging pile ("1" means cutting off, "0" means not cutting off);

[0143] P c2,k is the charging power of the second type of charging pile k;

[0144] P f,k is the discharge power of the second type of charging pile k;

[0145] Y kThe control mode of the second type of charging pile (“1” indicates discharge mode, “0” indicates charge mode);

[0146] P l,m is the power of interruptible load m;

[0147] Z m It is the control mode of interruptible load ("1" means cut-off, "0" means not cut-off);

[0148] is the upper limit of charging power, is the upper limit of the discharge power.

[0149] b. Charging loss objective function

[0150] For the first type of charging piles, the charging task that should have been completed during the cut-off period is delayed until after the grid resumes normal operation, resulting in charging losses due to the grid's use of time-of-use electricity prices C(t). For the second type of charging piles, there is a portion of revenue in the discharge mode, and the discharged electricity is recharged after the grid is operating normally; at the same time, the second type of charging piles also need to complete the originally set charging task, resulting in charging losses.

[0151] The total charging loss function f5 can be expressed as follows:

[0152]

[0153] Where C1 and C2 are the electricity prices during the removal period and normal operation period respectively; T is the removal time; t k is the discharge time of the second type of charging pile k, E k0 Remaining battery power.

[0154] c. Load shedding priority objective function

[0155] Different removal priorities are set for the loads in the microgrid. The lower the importance of the load, the higher the removal priority. The priority objective function f6 is calculated as follows:

[0156]

[0157] Where, L c1,j The priority of the first type of charging pile; L l,m is the priority of the interruptible load; N1 is the number of the first type of charging piles; N3 is the number of interruptible loads in the microgrid; Z m is the control mode of the interruptible load ("1" means disconnection, "0" means non-disconnection), pri1 and pri2 are the upper and lower limits of the priority respectively.

[0158] As a prominent substantive feature of the present invention and one of the significant advances it brings to the prior art, the present invention considers modulation commands, load priority, and charging losses for both grid-connected and isolated grid operation modes, establishes a multi-objective optimization model for adjustable loads, and maintains the stability and integrity of the system when a large disturbance occurs in the power system; and maintains the dynamic balance of the microgrid after the isolated grid is disconnected.

[0159] Step 6: Solve the rapid stability control model of distributed resources in the substation area.

[0160] The control model established in step 5 is solved using a genetic algorithm to obtain the modulation command values ​​of each distributed photovoltaic and charging pile. The modulation command of the charging pile is the modulation power and control mode of the charging pile. The specific steps are as follows:

[0161] (1) Initialize the population, randomly generate a group of individuals as the initial population, and obtain the initial modulation commands of distributed photovoltaics and charging piles; use the multi-objective optimization model established in step 5 as the fitness function, substitute the value of each individual into the fitness function, and obtain the initialized fitness value;

[0162] (2) Crossover: The sire and dam for the crossover are selected using the tournament selection method, and genetic recombination between the two individuals is completed through single-point crossover;

[0163] (3) Mutation: using single-point mutation to modify the gene value at a random position while setting a smaller mutation rate;

[0164] (4) Selection: merge the new population generated after crossover mutation with the original population, sort the fitness values ​​corresponding to each variable from small to large, and screen out the new population;

[0165] (5) Repeat steps (2) to (4). If the termination condition is met or the maximum number of iterations is reached, the calculation ends.

[0166] As a prominent substantive feature of the present invention and one of the remarkable advances brought to the prior art, the present invention establishes a multi-objective effective model of adjustable load for grid-connected operation and isolated grid operation modes respectively, and uses a genetic algorithm to solve the model.

[0167] Step 7: Implement load and unit control.

[0168] (1) The aggregation terminal sends the modulation command value of each charging pile calculated in step 6 to the charging pile control module through RS485 communication for modulation;

[0169] (2) The aggregation terminal sends the modulation command value of each distributed photovoltaic calculated in the island operation mode in step 6 to each distributed photovoltaic for modulation through RS485 communication;

[0170] (3) The collection terminal cuts off the interruptible load according to the specified load shedding instruction issued by the stabilization and control terminal, and the intelligent switch is responsible for disconnecting the load.

[0171] Among them, the first word of the command sent from the stabilization terminal to the aggregation terminal is defined as the load shedding level command from the stabilization terminal to the aggregation terminal, in which the lower eight bits are positive codes and the upper eight bits are inverse codes, that is, the positive code is inverted bit by bit. For the positive code, bit0: shedding load 1; bit1: shedding load 2; bits 2 to 7: shedding loads 3 to 8, respectively.

[0172] As a prominent substantive feature of the present invention and one of the significant advances it brings to the prior art, the present invention stipulates a control method for cuttable loads, charging piles, and photovoltaic inverters, which can be used for the second line of defense of the power system. When a large disturbance occurs in the power system, the stability and integrity of the system can be maintained. During emergency control, a part of the modulatable load is used to replace the interruptible load to reduce the impact on people's livelihood.

[0173] Table 4-9 gives an example of the command code for shedding loads at the aggregation terminal n. If multiple types of loads need to be shelved at the same time, the corresponding bits need to be set to 1 respectively.

[0174] Table 4-9 Load shedding level command codes from the nearest station to the grid-load interactive terminal

[0175] Terminal load shedding level command Load shedding level command code Load shedding 1 command 0XFE01(1111111000000001) Load shedding 2 command 0xFD02(1111110100000010)

[0176] Table 4-10 Communication protocol between the stability control terminal and the control substation

[0177]

[0178]

[0179] Table 4-11 Communication protocol between stabilization terminal and aggregation terminal

[0180]

[0181] Example 2

[0182] Reference Figure 2 The second embodiment of the present invention provides a rapid and stable control system for distributed resources in a substation, including a stable control system layer, a stable control terminal layer, a collection terminal layer, and an intelligent circuit breaker layer. As an integrated part of the substation, the control and management functions of the microgrid are distributed in the above four layers. Distributed resources are connected to the substation in a certain way to participate in stable control, and distributed resources include charging piles and distributed photovoltaics.

[0183] Preferably, in the distribution network, the 10kV distribution room serves as a stabilization and control terminal, communicating with the meter box through optical fiber in a ring network or star connection mode; the meter box serves as a collection terminal, connecting the charging pile and the intelligent circuit breaker of distributed photovoltaics through RS485 communication. The collection terminal can detect the status information of the charging pile, load and distributed photovoltaics in real time, and at the same time receive the operating data of the intelligent circuit breaker, inverter and charging pile communication, and send the status information and operating data to the stabilization and control terminal by optical fiber communication. Taking the charging pile as an example, the status information includes parameters such as real-time charging power, voltage, current, set charging time, control mode and the allowable power range under charging state.

[0184] When a fault or disturbance occurs in the power grid, the stability control system issues a machine / load shedding command through the offline strategy table, which is generally in milliseconds, while the instructions issued by the dispatching system are generally in seconds. After receiving the load shedding command from the stability control system or the dispatching system, the stability control terminal evaluates the economic indicators of the charging pile in combination with the status information, and calculates the power adjustment command of the charging pile according to the control strategy; the collection terminal generates a control signal for controlling the intelligent circuit breaker to control the charging pile to reduce the charging power or exit operation; when the stability control terminal receives the machine shedding command, it controls the distributed photovoltaic to reduce the output power or exit operation to maintain the supply and demand balance of the power grid. Through load shedding or machine shedding control, the active power in the microgrid is balanced to avoid voltage or frequency collapse causing the power grid to be disconnected.

[0185] When a grid fault is detected or the power quality does not meet the requirements, the microgrid will be disconnected from the grid in time and operate independently, including distributed power sources, energy storage devices and loads, which is called island mode. When the microgrid is operating in an island mode, distributed photovoltaics are responsible for power generation, and electric vehicles play the role of energy storage, supplying power to the microgrid load, so that the microgrid can achieve internal power supply and demand balance, thereby maintaining voltage and frequency stability.

[0186] Preferably, the intelligent circuit breaker has the function of breaking the circuit. The closing or opening of the intelligent circuit breaker corresponds to the control device connecting to or disconnecting from the power grid. Specifically, it can control the input or removal of charging piles and distributed photovoltaics; it can also control the disconnection of interruptible loads; it can monitor load parameters including current in real time; it supports RS485 communication mode and can transmit information with the aggregation terminal;

[0187] Preferably, the aggregation terminal communicates with the intelligent circuit breaker, inverter, and charging pile to receive the operating data monitored by each device. The aggregation terminal receives the status information of the charging pile, including real-time power, charging time, and power range under charging state; and receives the status information of distributed photovoltaic, including real-time power and output power range.

[0188] Preferably, SDH 2M communication or wireless communication is used between the stabilization and control terminal and the stabilization and control system to receive the load / unit control instructions of the stabilization and control system; optical fiber network communication or wireless communication is used between the terminal and the dispatching system to receive the load / unit control instructions of the dispatching system and accept monitoring and management by the dispatching system; and the operation data transmitted by the aggregation terminal is received via optical fiber.

[0189] As one of the outstanding substantial features of the present invention and the significant progress it brings to the prior art, the present invention provides a specific engineering implementation plan for the participation of distributed resources in the power grid stability control system, including: distributed resource data statistics and command allocation and issuance, information interaction and communication protocols for devices at all levels of the system, etc., and the present invention can be used in the field of stability control, hierarchical and partitioned control system architecture, to meet the timeliness requirements of emergency control, generally at the ms level, and during the emergency control process, a part of the modulatable load is used to replace the interruptible load to reduce the impact on people's livelihood.

Claims

1. A coordinated control method for distributed resources participating in power grid stability control, characterized in that: Step 1: The aggregation terminal calculates the adjustable load and interruptible load of each connected charging pile and distributed photovoltaic, and sends it to the stabilization control terminal; Step 2: According to the data sent by the aggregation terminal, the stabilization terminal calculates the total amount of interruptible load, the total amount of modulatable charging piles and the total amount of modulatable distributed photovoltaics, and sends them to the control substation; Step 3: Calculate the total modulatable amount of charging piles connected to the control substation and the total interruptible load at each level according to the data sent by the stabilization control terminal, and send the calculated data to the control master station or the dispatching system through the control substation; Step 4: The control substation receives the load shedding instruction P from the upper level. ref After that, P ref The total amount of all charging piles in the control substation that can be modulated calculated in step 3 For comparison, if The control substation sends the charging pile adjustable capacity command to the stabilization control terminal. The control substation sends the charging pile adjustable capacity command to the stabilization control terminal, and at the same time, according to the total amount of cuttable load at each level calculated in step 3, the interruptible load is selected to be cut off according to the load level; Step 5: The operation modes of the microgrid include grid-connected operation mode and island operation mode. For the grid-connected mode, a multi-objective optimization model is established for the adjustable load capacity command of the stable control terminal. When the microgrid is operated in the island mode, there is an unbalanced power P unb , if P unb > 0, calculate the modulation command of distributed photovoltaic, if P unb <0, it is necessary to establish a multi-objective optimization model that considers the conversion of charging and discharging modes of charging piles; Step 6, using a genetic algorithm to solve the multi-objective optimization model established in step 5 to obtain modulation commands for each charging pile and distributed photovoltaic; Step 7: The collection terminal modulates the charging pile and distributed photovoltaic according to the modulation command obtained in step 6, and cuts off the interruptible load according to the specified load cutting instruction issued by the stabilization control terminal.

2. A coordinated control method for distributed resources participating in power grid stability control according to claim 1, characterized in that: The adjustable load calculated in step 1 can be expressed by the following formula: The collection terminal calculates the adjustable load based on the collected charging pile and distributed photovoltaic information. The calculation formula is as follows: 1≤i1+i2≤N (3) In the formula, and are the adjustable loads of the i1th charging pile and the i2th distributed photovoltaic respectively; and are the current power of the i1th charging pile and the i2th distributed photovoltaic respectively; is the minimum charging power of the i1th charging pile; P min_DPV,i2 is the minimum output power of the i2th distributed photovoltaic; N is the total number of interruptible loads, charging piles and distributed power sources collected by each collection terminal.

3. A coordinated control method for distributed resources participating in power grid stability control according to claim 2, characterized in that: In step 2, the stabilization terminal calculates the total amount of load that can be cut, the total amount of charging piles that can be modulated, and the total amount of distributed photovoltaics that can be modulated, which can be expressed by the following formula: F j (P i ,WITH i ,You i )={P i |S i =j,You i =0,1≤i≤K} (3) K=M*N (4) Where P i is the power of the i-th interruptible load; S i Tys is the level setting for interruptible loads; i is the load type attribute, Tys i The value of Tys is 0, 1, 2, i =0 means the load type is interruptible load; Tys i =1 means the load type is charging pile; Tys i =2 represents that the load type is distributed power source; M is the number of aggregation terminals connected to a stabilization terminal; K is the total number of interruptible loads, charging piles and distributed power sources connected to the stabilization terminal; N is the total number of interruptible loads, charging piles and distributed power sources collected by each aggregation terminal; F j (P i ,S i ,Tys i ) is the set of all interruptible loads of the jth level under the jurisdiction of this stabilization control terminal; P cut,j is the total interruptible load of the jth level; It is the set of adjustable loads of all charging piles under the control of this collection terminal. is the adjustable load of the i1th charging pile, The total amount of charging piles that can be adjusted for all the terminals under its jurisdiction; is the adjustable load of the i2th distributed photovoltaic system, It is the aggregate of the adjustable loads of all distributed photovoltaics under the jurisdiction of this collection terminal. It is the total modulatable amount of distributed photovoltaic power generation with all the collection terminals under its jurisdiction.

4. A coordinated control method for distributed resources participating in power grid stability control as claimed in claim 3, characterized in that: The total amount of modulatable and shelvable loads of the charging piles connected to the control substation in step 3 can be expressed by the following formula: Where: j is the level of interruptible load, 0≤j≤3; Q is the number of stable control terminals connected to the control substation; P cut,j,k is the total load shedding capacity of the jth level of the kth aggregation terminal; P substation_cut,j is the total amount of shelvable load at the jth level connected to all control substations; is the total amount of charging pile that can be modulated for the kth stable control terminal; The total amount can be adjusted for all charging piles connected to the control substation.

5. The method for coordinated control of distributed resources participating in power grid stability control according to claim 1, characterized in that: The multi-objective optimization model established in the grid-connected mode in step 5 can be expressed by the following formula: Where: f1 is the modulation command objective function; is the modulation command issued; N1 is the number of the first type of charging piles, and N2 is the number of the second type of charging piles; is the charging power of the first type of charging pile j1; is the control mode of the first type of charging pile j1, Indicates removal, Indicates no excision; ΔP c2,k is the modulation power of the second type of charging pile k; Y k is the control mode of the second type of charging pile, Y k =1 indicates modulation power, Y k =0 means no power modulation; f2 is the charging loss objective function; C1 and C2 are the electricity prices during the removal period and the normal operation period of the power grid respectively; T is the removal duration; f3 is the load shedding priority objective function; pri1 and pri2 are the upper and lower limits of the priority, respectively; The priority of the first type of charging pile; L c2,k The priority of the second type of charging pile.

6. A coordinated control method for distributed resources participating in power grid stability control according to claim 5, characterized in that: Unbalanced power P in step 5 unb , which can be expressed by the following formula: P unb =P PV -P C -P l (18) Where P PV is the distributed photovoltaic output of the microgrid, P C is the charging power of the charging pile, P l Interruptible load.

7. A coordinated control method for distributed resources participating in power grid stability control according to claim 6, characterized in that: The multi-objective optimization model established in step 5 when the load is too high in the island mode can be expressed by the following formula: Where: f4 is the power balance objective function; P unb0 is the initial unbalanced power; N1 is the number of the first type of charging piles; N2 is the number of the second type of charging piles; N3 is the number of interruptible loads in the microgrid; is the charging power of the first type of charging pile j1; It is the control mode of the first type of charging pile; P c2,k is the charging power of the second type of charging pile k; P f,k is the discharge power of the second type of charging pile k; Y k1 is the control mode of the second type of charging pile, Y k1 =1 means discharge mode, Y k1 =0 means charging mode; P l,m is the power of interruptible load m; Z m For the control mode of interruptible load, Z m =1 means resection, Z m =0 means no resection; is the upper limit of charging power, is the upper limit of the discharge power; f5 is the charging loss objective function; C1 and C2 are the electricity prices during the removal period and the normal operation period respectively; T is the removal time; t k is the discharge time of the second type of charging pile k, E k0 The remaining battery power; f6 is the load shedding priority objective function; L c1,j The priority of the first type of charging pile; L l,m is the priority of the interruptible load; N1 is the number of the first type of charging piles; N3 is the number of interruptible loads in the microgrid; Z m It is the control mode of interruptible load, pri1 and pri2 are the upper and lower limits of priority respectively.

8. A coordinated control method for distributed resources participating in power grid stability control according to claim 7, characterized in that: The specific steps of the genetic algorithm to solve the model in step 6 are as follows: (1) Initialize the population, randomly generate a group of individuals as the initial population, and obtain the initial distributed photovoltaic and charging pile modulation commands; use the optimization model established in step 5 as the fitness function, substitute the value of each individual into the fitness function, and obtain the initialized fitness value; (2) Crossover: The sire and dam for the crossover are selected using the tournament selection method, and genetic recombination between the two individuals is completed through single-point crossover; (3) Mutation: using single-point mutation to modify the gene value at a random position while setting a smaller mutation rate; (4) Selection: merge the new population generated after crossover mutation with the original population, sort the fitness values ​​corresponding to each variable from small to large, and screen out the new population; (5) Repeat steps (2) to (4). If the termination condition is met or the maximum number of iterations is reached, the calculation ends.

9. A coordinated control system for distributed resources participating in power grid stability control, running a coordinated control method for distributed resources participating in power grid stability control as described in claims 1 to 7, characterized in that: include: The stabilization control system layer is used to issue a generator or load shedding command through an offline strategy table when a fault or disturbance occurs in the power grid; The stabilization control terminal layer uses SDH 2M communication or wireless communication with the stabilization control system to receive load shedding or machine shedding instructions from the stabilization control system, and receive the operating data transmitted by the aggregation terminal through optical fiber; The collection terminal layer connects the charging pile, inverter and intelligent circuit breaker through RS485 communication, receives the operation data of the intelligent circuit breaker, inverter and charging pile communication, and at the same time, the collection terminal detects the status information of the charging pile, load and distributed photovoltaic in real time, and sends the status information and operation data to the stabilization control terminal through optical fiber communication; The intelligent circuit breaker layer has the function of breaking the circuit, which is used to control the input or removal of charging piles and distributed photovoltaics, and control the disconnection of interruptible loads; The microgrid has two operating modes: grid-connected mode and island mode. When a grid fault is detected or the power quality does not meet the requirements, the microgrid will be disconnected from the grid in time and operate in island mode.

10. A coordinated control system for distributed resources participating in power grid stability control according to claim 8, characterized in that: According to the coordinated control method of load shedding, after receiving the load shedding command, the stabilization control terminal calculates the power adjustment command of the charging pile and sends it to the collection terminal; after receiving the machine shedding command, the distributed photovoltaic is controlled to reduce the output power or exit operation.

11. A coordinated control system for distributed resources participating in power grid stability control according to claim 8, characterized in that: The collection terminal receives the charging pile power adjustment instruction and controls the charging pile to reduce the charging power or exit operation.

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