Distributed resource participation in grid stability control and cutting coordination control method and system

Abstract

A kind of distributed resource participates in the method and system of regulating and cutting coordination control of power grid emergency control, method includes: step 1, the distributed resource data of terminal is gathered to the stable control terminal;Step 2, the distributed resource data is sent to control substation by stable control terminal;Step 3, control substation statistics distributed resource data;Step 4, control substation receives cut load instruction P ref Afterwards, P ref Compare with all charging piles modulated total amount, if modulated charging pile, if then, except modulated charging pile, according to load level, select cut-off part interruptible load;Step 5, when microgrid is in parallel grid mode, establish multi-objective optimization model;When microgrid is in island mode, there is unbalanced power P unb , if P unb >0, calculate the modulation command of distributed photovoltaic, if P unb <0, establish optimization model;Step 6, solve optimization model using genetic algorithm;Step 7, implement control to load and unit.The present application reduces the influence on important load power supply, improves system power supply reliability.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of power system safety and stability control, and more particularly relates to a method and system for coordinated control of distributed resources participating in grid stability control. BACKGROUND

[0002] Load shedding is one of the main measures for power system safety and stability control. When a serious accident occurs or a large amount of power supply is suddenly lost, quickly removing part of the load can reduce the power imbalance of the system, thereby ensuring the stability of the system.

[0003] Due to the impact of global energy crisis, electric vehicles use electric energy as a power source, breaking away from the dependence on traditional fossil fuels, and have developed rapidly in recent years. The number of charging piles is also increasing. However, disordered charging behavior can increase the peak-valley difference of the load of the power grid, posing a challenge to the safe and stable operation of the power grid. Distributed photovoltaic power generation can fully utilize local solar energy resources, replace part of fossil energy consumption, and gradually expand the scale of grid connection. Distributed photovoltaic output is influenced by light and environmental temperature, showing randomness and intermittency. A large number of distributed photovoltaic grid connections can 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 experiences out-of-step oscillation, frequency abnormalities, voltage abnormalities, and other accidents, measures such as generator tripping and load shedding are taken, affecting the power supply to normal users and important loads, and causing serious economic losses.

[0004] Prior art document 1 (CN 106856330 A) discloses a method for adjusting active power imbalance in a flexible load control system. This document only addresses the field of power system preventive control and cannot adapt to emergency control. It does not provide a specific solution for engineering implementation and only considers bidirectional controllable energy storage power stations without considering specific distributed resources such as charging piles and photovoltaic inverters, and without considering specific allocation principles for distributed resources.

[0005] Prior art document 2 (CN 118281943 A) discloses a source-grid-load-storage coordination control method, device, and electronic equipment for an island microgrid. This document only considers island microgrids and establishes a unified target function for solving within the island microgrid. It also considers a single-objective function of minimum power cost for the island microgrid. The number of nodes within a single microgrid is limited. If this technology is used in emergency control of a large power grid, the computational load will greatly increase with a large number of node (distributed resource) access, which cannot meet the demand of power system emergency control. SUMMARY

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

[0007] To solve the problems in the prior art, the present application provides a transformer area distributed resource fast stability control system and method, which can optimize the load shedding control strategy, quickly and accurately shed part of the load, and ensure the stability of the power system.

[0008] The first aspect of the application provides a coordinated control strategy for distributed resources participating in grid stability control, comprising:

[0009] Step 1: The collection terminal calculates the adjustable load amount and the interruptible load amount of each charging pile and distributed photovoltaic, and sends them to the stability control terminal;

[0010] Step 2: According to the data sent by the collection terminal, the stability control terminal calculates the total amount of cuttable load, the total amount of charging pile modulation and the total amount of distributed photovoltaic modulation, and sends them to the control substation;

[0011] Step 3: According to the data sent by the stability control terminal, the total amount of charging pile modulation of all control substation access and the total amount of interruptible load of each level are calculated, and the calculated data are sent 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 ref from the upper level, compares P ref with the total amount of charging pile modulation calculated in step 3, and if P is greater than the total amount of charging pile modulation, the control substation sends a charging pile modulation command to the stability control terminal, and if P is less than the total amount of charging pile modulation, the control substation sends a charging pile modulation command to the stability control terminal.

[0013] Step 5: The operation mode of the microgrid has grid-connected mode and island mode. For the grid-connected mode, a multi-objective optimization model is established for the adjustable load capacity command of the stability control terminal. When the microgrid operates in island mode, there is an unbalanced power P unb , if P unb > 0, the modulation command of the distributed photovoltaic is calculated, if P unb < 0, a multi-objective optimization model considering the charging and discharging mode conversion of the charging pile is established.

[0014] ​Step 6, the multi-objective optimization model established in step 5 is solved by using a genetic algorithm to obtain the modulation command of each charging pile and distributed photovoltaic;

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

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

[0017] The aggregation terminal calculates the amount of adjustable load according to the collected charging pile and distributed photovoltaic information, and the calculation formula is as follows:

[0018]

[0019] 1≤i1+i2≤N (3)

[0020] In the formula, and are the adjustable load amounts of the i1th charging pile and the i2th distributed photovoltaic, respectively; and are the current powers 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 aggregation terminal.

[0022] Preferably, the total amount of cuttable load, the total amount of modulatable charging pile and the total amount of modulatable distributed photovoltaic in step 2 can be calculated 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] In the formula, P i is the power of the i-th interruptible load; S i is the hierarchical value of the interruptible load; Tys i is the load type attribute, Tys iTys i = 0 represents that the load type is interruptible load; Tys i = 1 represents that the load type is charging pile; Tys i = 2 represents that the load type is distributed power supply; M is the number of collection terminals accessed by a stability control terminal; K is the total number of interruptible loads, charging piles and distributed power supplies accessed in the stability control terminal; N is the total number of interruptible loads, charging piles and distributed power supplies collected by each collection terminal; F j (P i , S i , Tys i ) is the set of all interruptible loads of the jth level under the stability control terminal; P cut,j is the total amount of interruptible loads of the jth level;

[0027] is the set of adjustable load amounts of all charging piles under the collection terminal, is the adjustable load amount of the i1th charging pile, is the total amount of adjustable regulation of all charging piles of the collection terminal;

[0028] is the adjustable load amount of the i2th distributed photovoltaic, is the set of adjustable load amounts of all distributed photovoltaics under the collection terminal, is the total amount of adjustable regulation of all distributed photovoltaics of the collection terminal.

[0029] Preferably, the total amount of adjustable regulation of charging piles, the total amount of adjustable regulation of distributed photovoltaics and the total amount of cuttable loads of the access control substation in step 3 can be calculated and expressed by the following formula:

[0030]

[0031] In the formula: j is the level of interruptible load, 0≤j≤3; Q is the number of control substation access stability control terminal; P cut,j,k is the total amount of jth level cuttable load of the kth collection terminal; P substation_cut,j is the total amount of jth level cuttable load of all control substations;

[0032] is the total amount of adjustable regulation of charging piles of the kth stability control terminal; is the total amount of adjustable regulation of all charging piles of the control substation.

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

[0034]

[0035]

[0036] f1 is a modulation command target function; is a modulation command; N1 is the number of first type charging piles, N2 is the number of second type charging piles; is the charging power of the first type charging pile j1; is the control mode of the first type charging pile j1, represents cutting off, represents not cutting off; ΔP c2,k is the modulation power of the second type charging pile k; Y k is the control mode of the second type charging pile, Y k = 1 represents modulation power, Y k = 0 represents no modulation power;

[0037] f2 is a charging loss target function; C1 and C2 are the electricity prices in cutting off period and normal operation period of the power grid respectively; T is the cutting off duration;

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

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

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

[0041] In the formula, P PV is the distributed photovoltaic output of the microgrid, P C is the charging power of the charging pile, and P l is the interruptible load of the household.

[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] In the formula:

[0046] f4 is a power balance target 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; 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 discharging 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 indicates the discharging mode, Y k1 = 0 indicates the charging mode; P l,m is the power of the interruptible load m; Z m is the control mode of the interruptible load, Z m = 1 indicates the removal, Z m = 0 indicates no removal; is the upper limit of the charging power, is the upper limit of the discharging power;

[0047] f5 is the charging loss target function; C1, C2 are the electricity prices of the removal period and the normal operation period respectively; T is the removal duration; t k is the discharging duration of the second type of charging pile k, E k0 is the remaining battery capacity;

[0048] f6 is the load shedding priority target function; L c1,j is 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 pile; N3 is the number of interruptible loads in the microgrid; Z m is the control mode of the interruptible load, pri1, pri2 are the upper and lower limits of the priority respectively.

[0049] Preferably, the specific steps of solving the model in step 6 by the genetic algorithm 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 command; take the optimization model established in step 5 as the fitness function, and substitute the value of each individual into the fitness function to obtain the initial fitness value;

[0051] (2) Cross, select the parents and mothers for crossing by the tournament selection method, and complete the gene recombination between two individuals by single-point crossing;

[0052] (3) Mutation, a single-point mutation is used to modify the gene value of a random position, and a small mutation rate is set;

[0053] (4) selection, the new population generated after cross variation is combined with the original population, the fitness value corresponding to each variable is sorted from small to large, and a new population is screened out;

[0054] (5) repeat steps (2)-(4), if the termination iteration condition is met or the maximum iteration number is reached, the calculation is ended.

[0055] The second aspect of the application provides a distributed resource participation grid stability control coordinated control system, which runs the distributed resource participation grid stability control coordinated control strategy.

[0056] The stability control system layer is used to issue a generator tripping or load shedding command through an offline strategy table when a grid fault or disturbance occurs.

[0057] The stability control terminal layer and the stability control system use 2M communication or wireless communication of SDH to receive the load shedding or generator tripping instructions of the stability control system, and transmit the operation data received by the fiber collection terminal through the optical fiber.

[0058] The collection terminal layer is connected to the charging pile, the inverter and the intelligent air switch through the RS485 communication mode, receives the operation data communicated by the intelligent air switch, the inverter and the charging pile, simultaneously, the collection terminal detects the state information of the charging pile, the load and the distributed photovoltaic in real time, and uploads the state information and the operation data to the stability control terminal in the form of optical fiber communication.

[0059] The intelligent air switch layer has the function of breaking the circuit, and is used to control the input or removal of the charging pile and the distributed photovoltaic, and control the breaking of the interruptible load.

[0060] The operation mode of the microgrid has a grid-connected operation mode and an island operation mode, when the grid fault or the power quality does not meet the requirements, the microgrid will be disconnected from the grid in time to operate in the island mode.

[0061] Preferably, according to the coordinated control method, after receiving the load shedding instruction, the stability control terminal calculates the power adjustment instruction of the charging pile and sends it to the collection terminal; after receiving the generator tripping instruction, the distributed photovoltaic reduces the output power or exits the operation.

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

[0063] The beneficial effects of the application are as follows: when the power district receives a load shedding instruction, the application prioritizes load shedding of the charging pile, reduces the impact on important load power supply, improves the stability of the power system, and reduces economic losses; in order to quantify the impact of load shedding on charging pile operation and power grid benefits, an economic cost evaluation index is established, with the optimization goal of responding to load shedding instructions and minimizing economic cost, and a fast and stable control strategy is designed; when the microgrid is in island operation mode, the charging pile and distributed photovoltaic are cooperatively controlled to maintain the voltage and frequency stability of the microgrid and improve the reliability of the system. It can be used for the second line of defense of the power system, and when the power system is disturbed, the stability and integrity of the system are maintained; in the emergency control process, part of the adjustable load is used to replace the interruptible load to reduce the impact on people's livelihood; the hierarchical and zoned control system architecture meets the timeliness requirements of emergency control; the controllable resources reach the 380V voltage level, and the control is more precise. BRIEF DESCRIPTION OF DRAWINGS

[0064] Figure 1 Primary connection diagram of the distributed resource fast and stable control system;

[0065] Figure 2 Secondary system architecture diagram of the distributed resource fast and stable control;

[0066] Figure 3 Distributed resource load and cut coordination control strategy schematic diagram. DETAILED DESCRIPTION

[0067] In order to make the purpose, technical scheme and advantages of the present application clearer, the technical scheme of the present application will be described clearly and completely below in combination with the drawings in the embodiments of the present application. The embodiments described in the present application are only a part of the embodiments of the present application, not all the embodiments. Based on the spirit of the present application, other embodiments obtained by those skilled in the art without creative labor are within the protection scope of the present application.

[0068] The first embodiment of the present application discloses a method for coordinated control of distributed resource participation in stability control. The method can optimize the load shedding control strategy through the coordinated work between the collection terminal, the stability control terminal, the intelligent air switch and the control substation, quickly and accurately shed part of the load, and ensure the stability of the power system. The charging frequency of the charging pile is controllable, and reducing the charging power is equivalent to shedding part of the load for the power grid, reducing the active power shortage of the power system, and not affecting the power supply of important loads. When the power grid needs to perform low-frequency load shedding or low-voltage load shedding control, the charging power of the charging pile can be adjusted or the charging pile can be disconnected for charging, and the charging task can be completed after the power system returns to normal state. The distributed photovoltaic system is relatively independent and controllable, and has fast start-stop speed, and participation in stability control can make up for the lack of stability of the large power grid. When the power grid needs to perform frequency modulation control, the distributed photovoltaic power source can be selected to be put into operation or cut off, and participate in power grid dispatching according to the need of balancing load. The following will be described in detail in combination with Figure 3 .

[0069] Step 1: The collection terminal uploads the distributed resource operation data;

[0070] The intelligent air switch collects the current of the load, the charging pile collects the current power value, the minimum charging power and the state information of the charging pile, the state information includes the real-time power, the charging time, the power range in 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, calculates the power value of the interruptible load according to the received load current information; the collection terminal calculates the adjustable load amount and the interruptible load amount of each charging pile and each distributed photovoltaic, and the collection terminal will consider the allowable cutting state and abnormal state of the interruptible load to calculate the actual cuttable amount of the load, and send it to the stability control terminal.

[0071] The collection terminal calculates the adjustable load amount according to the collected charging pile and distributed photovoltaic information, and the calculation formula is as follows:

[0072]

[0073] 1≤i1+i2≤N (3)

[0074] In the formula, and are the adjustable load amounts of the i1th charging pile and the i2th distributed photovoltaic respectively; and are the current powers 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,i2Pmin(i2) is the minimum output power of the ith2distributed photovoltaic; N is the total number of interruptible loads, charging piles and distributed power sources collected by each collection terminal, in the present application, N is 8 due to the limit of the communication protocol of the collection terminal. The communication protocol between the collection terminal and the stability control terminal is shown in Table 4-11.

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

[0077] According to the load level setting value and load attribute uploaded by the collection terminal, the total amount of interruptible loads 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] In the formula, P i is the power of the ithinterruptible load; S i is the level setting value of the interruptible load, in engineering practice, according to the communication protocol between the stability control terminal and the control substation, 0≤S i ≤3, the protocol is shown in Table 4-10; Tys i is the load type attribute, the value of Tys i is 0, 1, 2, Tys i = 0 represents that the load type is an interruptible load; Tys i = 1 represents that the load type is a charging pile; Tys i = 2 represents that the load type is a distributed power source; M is the number of collection terminals connected to one stability control terminal; K is the total number of interruptible loads, charging piles and distributed power sources connected to the stability control terminal, and N is the total number of interruptible loads, charging piles and distributed power sources collected by each collection terminal; F j (P i ,S i ,Tys i ) is the set of all interruptible loads of the jthlevel under the jurisdiction of the present stability control terminal; P cut,j is the total amount of interruptible loads at the jthlevel.

[0082] According to the load type attribute uploaded by the collection terminal, the total amount of charging piles that can be modulated is calculated, and the calculation formula is as follows:

[0083]

[0084] In the formula, is the set of adjustable load amounts of all charging piles under the jurisdiction of the current collection terminal, is the adjustable load amount of the i1th charging pile, is the total adjustable amount of all charging piles under the jurisdiction of the collection terminal.

[0085] According to the load type attribute uploaded by the collection terminal, the total adjustable amount of distributed photovoltaic is calculated:

[0086]

[0087] In the formula, is the adjustable load amount of the i2th distributed photovoltaic, is the set of adjustable load amounts of all distributed photovoltaics under the jurisdiction of the current collection terminal, is the total adjustable amount of all distributed photovoltaics under the jurisdiction of the collection terminal.

[0088] Step 3: The control substation counts all distributed resource data;

[0089] According to the data calculated in step 2, the total adjustable amount of charging piles and the total amount of interruptible loads of each level accessed by the control substation 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 aforementioned indicators.

[0090] The calculation formula of the total amount of interruptible loads of 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 accessed by the control substation; P cut,j,k is the total amount of j-level interruptible loads of the kth stable control terminal; P substation_cut,j is the total amount of j-level interruptible loads accessed by all control substations;

[0093] Calculate the total adjustable amount of charging piles

[0094]

[0095] Where: is the total adjustable amount of charging piles of the kth stable control terminal; is the total adjustable amount of all charging piles accessed by the control substation.

[0096] As one of the outstanding substantial features of the present application and the significant progress brought to the prior art, the present application considers that the distributed charging piles, photovoltaics, and controllable resources in the distribution network station area reach the 380V voltage level, and the control is more fine.

[0097] Step 4: The control substation issues a control command to the stability control terminal;

[0098] The control substation receives the load shedding instruction P ref Then, P ref is compared with the total modulatable amount of all charging piles of the access control substation calculated in step 3 , and the charging pile or the interruptible load is selected according to the comparison result, and the specific process is as follows:

[0099] When P , the charging pile is preferentially selected, the modulatable capacity of each stability control terminal is proportionally distributed according to the charging pile modulatable capacity of each stability control terminal, and the specific proportion can be calculated by formula (14):

[0100]

[0101] Wherein: is the modulatable load capacity instruction issued by the control substation to the kth stability control terminal; is the total modulatable amount of the charging pile of the kth stability control terminal, P ref is the load shedding instruction of the upper level of the control substation.

[0102] When P , the control substation issues a charging pile modulatable capacity command to the stability control terminal, the charging pile modulatable capacity is insufficient, the charging pile modulatable capacity is maximized, and part of the interruptible load is selected and cut off according to the total amount of the cuttable load of each level, and the total amount of the charging pile modulatable capacity is The charging pile modulatable amount of each stability control terminal is The total amount of the cuttable load is

[0103] The total amount of the cuttable load is compared with the total amount of the interruptible load P substation_cut,j of each level, when P , the cuttable load capacity of each level is proportionally distributed according to the charging pile modulatable capacity of each stability control terminal, and the calculation formula is as follows:

[0104]

[0105] Wherein, is the cut-off jth level load capacity instruction issued by the control substation to the kth stability control terminal; is the modulatable load capacity instruction issued by the control substation to the kth stability control terminal.

[0106] As one of the prominent substantial features of the present application and the significant progress brought to the prior art, the present application is a coordinated control strategy of conventional load and distributed resources when active power shortage caused by power grid failure needs emergency load shedding in the context of a networked system (large power grid).

[0107] Step 5: Establishing a fast and stable control model of distributed resources in the transformer area;

[0108] The operation mode of the microgrid has a grid-connected operation mode and an island operation mode. For the grid-connected operation mode, a multi-objective optimization model including a modulation command target function, a charging loss target function and a load shedding priority target function is established for the adjustable load capacity command of the stability control terminal, thereby realizing fast and stable control of the distributed resources in the transformer area. For the island mode, the value of the unbalanced power P unb is used to determine the calculation of the photovoltaic modulation command or to establish a multi-objective optimization model including the power balance, charging loss and load shedding priority target function. The cuttable load under the stability control terminal is divided into three categories, and is cut off in the order of category 1, category 2 and category 3 according to the minimum overcut principle.

[0109] Step 5.1, the adjustable load under the stability control terminal calculates the modulation command according to the multi-objective optimization model and sends it to the corresponding collection terminal for execution. The charging piles connected to the stability control terminal are divided into two categories: the first category of charging piles cannot be modulated power and can only be cut off; the second category 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 target function

[0111] Part of the charging piles are cut off, and part of the charging piles modulate the charging power to meet the modulation command.

[0112]

[0113] In the formula: is the modulation command issued; N1 is the number of the first category of charging piles, and N2 is the number of the second category of charging piles; is the charging power of the first category of charging piles j1; is the control mode of the first category of charging piles j1 (“1” represents cutting off, and “0” represents not cutting off); ΔP c2,k is the modulation power of the second category of charging piles k; Y k is the control mode of the second category of charging piles (“1” represents modulating power, and “0” represents not modulating power).

[0114] b. Charging loss target function

[0115] ​The power grid uses a time-of-use pricing system (TPS) C(t). For the first type of charging pile, the charging task that should have been completed during the off-peak hours was delayed until after the power grid resumed normal operation, resulting in charging losses due to the TPS. Similarly, for the second type of charging pile, the originally scheduled charging task also needed to be completed, thus incurring charging losses. The total charging losses are calculated as follows:

[0116]

[0117] In the formula, C1 and C2 are the electricity prices during the cut-off period and the normal operation period of the power grid, respectively; T is the cut-off duration.

[0118] c. Load shedding priority objective function

[0119] Different load shelving priorities are assigned to loads within the microgrid, with lower priority loads receiving higher priority. The priority is calculated as follows:

[0120]

[0121] In the formula, pri1 and pri2 are the upper and lower limits of priority, respectively; Priority is given to Class I charging piles; L c2,k It is given priority for the second type of charging pile.

[0122] Step 5.2: For islanded operation mode, if there is excess active power, calculate the modulation command for distributed photovoltaic; if there is excessive load, establish a multi-objective optimization model to achieve power balance of the microgrid.

[0123] After the microgrid is disconnected from the main grid, there is an imbalance power P. unb Its expression is:

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

[0125] In the formula, P PV P contributes to the distributed photovoltaic power generation of microgrids. C P represents the charging power of the charging station. l This is an interruptible load.

[0126] If P unb If the value is greater than 0, then the microgrid has excess active power, and distributed photovoltaic power needs to operate at reduced load to eliminate unbalanced power. At that time, the distributed photovoltaic offload rate σ = 100%

[0127] When the distributed photovoltaic offload rate σ is reached, the expression is:

[0128]

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

[0130]

[0131] In the formula, is the real-time power of the distributed photovoltaic under the gathering terminal.

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

[0133] a. Power balance objective function

[0134] After cutting off part of the load and converting the second category of charging piles to the discharging mode, the new unbalanced power is calculated, and the absolute value of the new unbalanced power is taken as the objective function, which can be expressed by the following formula:

[0135]

[0136] In the formula,

[0137] P unb0 is the initial unbalanced power;

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

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

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

[0141] Pj1 is the charging power of the first category of charging piles j1;

[0142] is the control mode of the first category of charging piles (“1” represents cutting off, and “0” represents not cutting off);

[0143] P c2,k is the charging power of the second category of charging piles k;

[0144] P f,k is the discharging power of the second category of charging piles k;

[0145] Y kControl mode of the second type of charging pile (“1” represents discharging mode, and “0” represents charging mode);

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

[0147] Z m Control mode of the interruptible load (“1” represents disconnection, and “0” represents no disconnection);

[0148] Upper limit of the charging power, Upper limit of the discharging power.

[0149] b. Charging loss objective function

[0150] For the first type of charging pile, the charging task that should be completed during the disconnection period is delayed until the power grid returns to normal operation, and charging loss is generated due to the time-of-use electricity price C(t). For the second type of charging pile, a part of the income is obtained in the discharging mode, and the discharged power is charged back after the power grid returns to normal operation; at the same time, the second type of charging pile also needs to complete the originally set charging task, and charging loss is generated.

[0151] The total charging loss function f5 can be expressed by the following formula:

[0152]

[0153] In the formula, C1 and C2 are the electricity prices of the disconnection period and the normal operation period respectively; T is the disconnection duration; t k Discharging duration of the second type of charging pile k, E k0 Remaining battery capacity.

[0154] c. Load shedding priority objective function

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

[0156]

[0157] In the formula, L c1,j Priority of the first type of charging pile; L l,m Priority of the interruptible load; N1 is the number of the first type of charging pile; N3 is the number of the interruptible load in the microgrid; Z m Control mode of the interruptible load (“1” represents disconnection, and “0” represents no disconnection), pri1 and pri2 are the upper and lower limits of the priority respectively.

[0158] As one of the prominent substantial features of the present application and the significant progress brought to the prior art, the present application establishes a multi-objective optimization model of adjustable load for grid-connected operation and island operation mode respectively, considering modulation command, load priority, charging loss, maintaining the stability and integrity of the system when the power system is subjected to large disturbance; maintaining the dynamic balance of the microgrid after island splitting.

[0159] Step 6: solve the fast and stable control model of the distribution resource of the transformer 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 charging pile modulation power and the control mode. 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 command of the distributed photovoltaic and charging pile; the multi-objective optimization model established in step 5 is used as the fitness function, and the value of each individual is substituted into the fitness function to obtain the initial fitness value;

[0162] (2) crossover, the tournament selection method is used to select the father and mother for crossover, and the gene recombination between two individuals is completed through single-point crossover;

[0163] (3) mutation, a single-point mutation is used to modify the gene value of a random position, and a small mutation rate is set;

[0164] (4) selection, the new population generated after crossover and mutation is combined with the original population, and the fitness values of each variable are sorted from small to large to select a new population;

[0165] (5) repeat steps (2) to (4), if the termination iteration condition is met or the maximum iteration number is reached, the calculation is ended.

[0166] As one of the prominent substantial features of the present application and the significant progress brought to the prior art, the present application establishes a multi-objective effective model of adjustable load for grid-connected operation and island operation mode, and uses a genetic algorithm to solve the model.

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

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

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

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

[0171] bit0: cut off load 1; bit1: cut off load 2; bit2-7: cut off load 3-8 in turn.

[0172] As one of the outstanding substantial features of the present application and the significant progress brought to the prior art, the present application stipulates the control mode of the cuttable load, charging pile and photovoltaic inverter, 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 are maintained, and in the emergency control process, a part of the adjustable load is used to replace the interruptible load, thereby reducing the impact on people's livelihood.

[0173] Table 4-9 illustrates the load shedding command code of the gathering terminal n. If multiple types of loads need to be cut off at the same time, the corresponding bit positions need to be set to 1 respectively.

[0174] Table 4-9: Load shedding hierarchical command code of the nearest station to the net load interaction terminal

[0175] Terminal cut load level command Cut load level command code Cut load 1 command 0XFE01 (11111110 00000001) Cut load 2 command 0xFD02 (11111101 00000010)

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

[0177]

[0178]

[0179] Table 4-11: Communication protocol between the stability control terminal and the gathering terminal

[0180]

[0181] Example 2

[0182] Referring to Figure 2 The second embodiment of the present application provides a substation distributed resource rapid stability control system, which includes a stability control system layer, a stability control terminal layer, a gathering terminal layer and an intelligent air switch layer. The microgrid is an integrated part of the substation, and its control and management functions are distributed in the above four layers. Distributed resources are connected to the substation to participate in stability control in a certain way, and the distributed resources include charging piles and distributed photovoltaics.

[0183] Preferably, in the power distribution network, the 10kV power distribution room serves as a stability control terminal, and communicates with the meter box through optical fiber in a ring network or star connection mode; the meter box serves as a collection terminal, and connects the charging pile and the intelligent air switch of the distributed photovoltaic through RS485 communication mode. The collection terminal can detect the state information of the charging pile, load and distributed photovoltaic in real time, receive the operation data of the intelligent air switch, inverter and charging pile, and send the state information and operation data to the stability control terminal through optical fiber communication. Taking the charging pile as an example, the state information includes real-time charging power, voltage, current, set charging time, control mode and allowed power range in the charging state.

[0184] When the power grid fails or is disturbed, the stability control system issues a generator trip / load shedding command through an offline strategy table, generally in milliseconds, while the command issued by the dispatching system is 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 state information, calculates the power adjustment command of the charging pile according to the control strategy, and generates a control signal for controlling the intelligent air switch of the collection terminal to control the charging pile to reduce the charging power or exit operation. When receiving the generator trip command, the stability control terminal controls the distributed photovoltaic to reduce the output power or exit operation to maintain the balance between supply and demand of the power grid. Through load shedding or generator trip control, the active power balance in the microgrid is achieved, and voltage or frequency collapse caused by power grid splitting is avoided.

[0185] When the power grid fails or the power quality does not meet the requirements, the microgrid will be disconnected from the power grid and run independently, including distributed power supply, energy storage devices and loads, which is called island mode. When the microgrid runs in island mode, the distributed photovoltaic is responsible for power generation, the electric vehicle plays a role in energy storage, and the microgrid load is powered, so that the microgrid realizes internal power supply and demand balance, thereby maintaining the stability of voltage and frequency.

[0186] Preferably, the intelligent air switch has the function of opening and closing the circuit, and the closing or opening of the intelligent air switch corresponds to the access or disconnection of the control equipment to the power grid. Specifically, the charging pile and the distributed photovoltaic can be controlled to be put into operation or cut off; the opening and closing of the interruptible load can also be controlled; the load parameters including current can be monitored in real time; the RS485 communication mode is supported, and information can be transmitted with the collection terminal;

[0187] Preferably, the collection terminal communicates with the intelligent air switch, inverter and charging pile, and receives the operation data monitored by each device. The collection terminal receives the state information of the charging pile, including real-time power, charging time, and power range in the charging state; and receives the state information of the distributed photovoltaic, including real-time power and output power range.

[0188] Preferably, the stable control terminal and the stable control system adopt 2M communication or wireless communication of SDH to receive load / unit control instructions of the stable control system; and adopt optical fiber network communication or wireless communication with the dispatching system to receive load / unit control instructions of the dispatching system, receive monitoring and management of the dispatching system, and receive operation data transmitted by the collection terminal through optical fiber.

[0189] As one of the prominent substantial features of the present application and the significant progress brought to the prior art, the present application provides an engineering embodiment of a distributed resource participating in a power grid stability control system, including: distributed resource data statistics and command distribution and issuance, system device information interaction communication protocol, etc., and the present application can be used in the field of stability control, a hierarchical and partitioned control system architecture, meeting the timeliness requirement of emergency control, generally ms level, using a part of adjustable load to replace interruptible load in the emergency control process, reducing the impact on people's livelihood.

Claims

1. A method for distributed resources participating in grid stability control, characterized in that: Step 1: Collecting the adjustable load and interruptible load of each charging pile and distributed photovoltaic connected to the terminal and sending them to the stability control terminal; Step 2: According to the data sent by the collection terminal, the stability control terminal calculates the total interruptible load, the total adjustable load of charging piles and the total adjustable load of distributed photovoltaic, and sends them to the control substation; Step 3: According to the data sent by the stability control terminal, the total adjustable load of charging piles and the total interruptible load of each level connected to the control substation are calculated, and the calculated data is sent 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 is compared with the total amount of modulatable load of all charging piles calculated in step 3 If the control substation issues a modulatable capacity command to the stabilizing terminal, if the control substation issues a modulatable capacity command to the stabilizing terminal, and according to the total amount of interruptible load calculated in step 3, the interruptible load is selected for shedding according to the load level. Step 5, the operation mode of the microgrid has a grid-connected mode and an island mode, for the grid-connected mode, a multi-objective optimization model is established for the adjustable load capacity command of the stability control terminal, when the microgrid operates in the island mode, there is an unbalanced power P unb , if P unb >0, the modulation command of the distributed photovoltaic is calculated, if P unb <0, a multi-objective optimization model considering the charging pile charging and discharging mode conversion needs to be established; The multi-objective optimization model established in the grid-connected mode can be expressed by the following formula: In the formula: f1 is a modulation command target function; is a modulation command; N1 is the number of first type charging piles, N2 is the number of second type charging piles; is the charging power of the first type charging pile j1; is the control mode of the first type charging pile j1, represents cutting off, represents not cutting off; ΔP c2,k is the modulation power of the second type charging pile k; Y k is the control mode of the second type charging pile, Y k =1 represents modulation power, Y k =0 represents no modulation power; f2 is a charging loss target function; C1, C2 are the electricity prices in the cutting-off period and the normal operation period of the power grid respectively; T is the cutting-off duration; f3 is a cutting load priority target function; pri1, pri2 are the upper and lower limits of the priority respectively; is the priority of the first type charging pile; L c2,k is the priority of the second type charging pile; The multi-objective optimization model established when the load is too high in island mode can be expressed by the following formula: wherein: f4 is a power balance objective function; P unb0 is the initial unbalanced power; N3 is the number of interruptible loads in the microgrid; P c2,k is the charging power of the second type of charging pile k; P f,k is the discharging 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 indicates a discharging mode, Y k1 = 0 indicates a charging mode; P l,m Pm is the power of interruptible load; Z m Z is the control mode of interruptible load, m =1 indicates shedding, Z m =0 indicates not shedding; Pmax is the upper limit of charging power, Pmin is the upper limit of discharging power; f5 is the charging loss objective function; t k E is the discharging duration of the second type of charging pile k, k0 E is the remaining battery capacity; f6 is the load shedding priority objective function; L l,m N3 is the number of interruptible loads in the microgrid; Step 6: Solving the multi-objective optimization model established in step 5 by genetic algorithm to obtain the modulation command of 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 removes the interruptible load according to the specified load shedding instruction issued by the stability control terminal. 2.A method for distributed resources participating in grid stability control according to claim 1, characterized in that: The formula for calculating the adjustable load in step 1 is as follows: The formula for calculating the adjustable load by the collection terminal according to the charging pile and distributed photovoltaic information is as follows: 1≤i1+i2≤N (9) in which, and are the adjustable load amount of the ith1 charging pile and the ith2 distributed photovoltaic, respectively; and are the current power of the ith1 charging pile and the ith2 distributed photovoltaic, respectively. Pmin(i1) is the minimum charging power of the ith1 charging pile; P min_DPV,i2 Pmin(i2) is the minimum output power of the ith2 distributed photovoltaic; N is the total number of interruptible loads, charging piles and distributed photovoltaics collected by each collection terminal. 3.A method for distributed resources participating in grid stability control according to claim 2, characterized in that: The formula for calculating the total interruptible load, the total adjustable load of charging piles and the total adjustable load of distributed photovoltaic by the stability control terminal in step 2 is as follows: F j (P i ,S i ,Tys i )={P i |S i =j,Tys i =0,1≤i≤K} (10) K=M*N (11) In the formula, P i is the power of the ith interruptible load; S i is the hierarchical value of the interruptible load; Tys i is the load type attribute, Tys i takes the value of 0, 1, 2, Tys i = 0 represents that the load type is an interruptible load; Tys i = 1 represents that the load type is a charging pile; Tys i = 2 represents that the load type is a distributed photovoltaic; M is the number of collection terminals accessed by a stability control terminal; K is the total number of interruptible loads, charging piles and distributed photovoltaics accessed in the stability control terminal; N is the total number of interruptible loads, charging piles and distributed photovoltaics collected by each collection terminal; F j (P i , S i , Tys i ) is the collection of all interruptible loads of the jth level under the stability control terminal; P cut,j is the total amount of interruptible loads of the jth level; a collection of adjustable load amounts for all charging piles under the jurisdiction of the terminal, an adjustable load amount for the i1th charging pile, an adjustable total amount for all charging piles under the jurisdiction of the terminal is the adjustable load amount of the ith distributed photovoltaic, is the set of adjustable load amounts of all distributed photovoltaics under the jurisdiction of the current aggregation terminal, is the total amount of adjustable load of all distributed photovoltaics under the jurisdiction of all aggregation terminals. 4.A method for distributed resources participating in grid stability control according to claim 3, characterized in that: The formula for calculating the total interruptible load and the total adjustable load of charging piles connected to the control substation in step 3 is as follows: In the formula: j is the level of interruptible load, 0≤j≤3; Q is the number of control sub-stations accessing the stability control terminal; P cut,j,g is the total amount of the jth level of interruptible load of the gth stability control terminal; P substation_cut,j is the total amount of the jth level of interruptible load accessing all control sub-stations; is the total amount of the gth stability control terminal of the charging pile The total amount of all charging piles of the access control substation can be modulated. 5.A method for distributed resources participating in grid stability control according to claim 1, characterized in that: The unbalanced power P in step 5 unb This can be expressed by the equation: P unb = P PV - P C - P l (19) where P PV is the distributed photovoltaic power of the microgrid, P C is the charging power of the charging pile, P l is the interruptible load power. 6.A method for distributed resources participating in grid stability control according to claim 1, characterized in that: The specific steps of solving the model by genetic algorithm in step 6 are as follows: (1) Initialize the population, randomly generate a group of individuals as the initial population, and obtain the initial modulation command of distributed photovoltaic and charging pile; Take the optimization model established in step 5 as the fitness function, and substitute the value of each individual into the fitness function to obtain the initial fitness value; (2) Cross, select the father and mother for crossing by tournament selection method, and complete the gene recombination between two individuals by single-point crossing; (3) Mutation, modify the gene value of a random position by single-point mutation, and set a small mutation rate at the same time; (4) Selection, combine the new population generated after crossing and mutation with the original population, sort the fitness values of each variable from small to large, and select a new population; (5) Repeat steps (2)-(4), if the termination iteration condition is met or the maximum number of iterations is reached, end the calculation.

7. A distributed resource participating in grid stability control coordinated control system, which runs a distributed resource participating in grid stability control coordinated control method as claimed in any one of claims 1 to 6, characterized in that, Comprise: The stability control system layer is used for issuing the tripping or load shedding command through the off-line strategy table when the power grid fails or is disturbed; The stability control terminal layer and the stability control system adopt 2M communication or wireless communication of SDH to receive the load shedding or tripping instruction of the stability control system and transmit the operation data received by the fiber receiving and collecting terminal; The collecting terminal layer is connected with the charging pile, the inverter and the intelligent air switch through the RS485 communication mode, receives the operation data communicated by the intelligent air switch, the inverter and the charging pile, simultaneously, the collecting terminal layer detects the state information of the charging pile, the load and the distributed photovoltaic in real time and uploads the state information and the operation data to the stability control terminal in the form of optical fiber communication; The intelligent air switch layer has the function of breaking the circuit and is used for controlling the input or cut-off of the charging pile and the distributed photovoltaic and controlling the breaking of the interruptible load; The operation mode of the micro-grid has the grid-connected mode and the island mode, when the grid failure or the power quality does not meet the requirement is detected, the micro-grid will be disconnected from the grid and operates in the island mode.

8. The coordinated control system of claim 7, wherein: According to the coordinated control method, the stability control terminal calculates the power adjustment instruction of the charging pile after receiving the load shedding instruction and sends the instruction to the collecting terminal; and controls the distributed photovoltaic to reduce the output power or exit operation after receiving the tripping instruction.

9. The coordinated control system of claim 7, wherein: The collecting terminal receives the power adjustment instruction of the charging pile and controls the charging pile to reduce the charging power or exit operation.

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