A voltage emergency control method and system for collaborative operation of multiple new energy power stations

Abstract

The present invention discloses a voltage emergency control method and system for collaborative operation of multiple new energy power stations. For a severe three-phase short circuit fault, the bus that is farther from the fault point among the buses connected to the fault branch is used as the bus to be supported, and the bus that is connected to this bus and has a smaller connection impedance is defined as the proximal bus, and the other buses in the power grid that are connected to new energy power stations are defined as distal buses. New energy power stations capable of providing transient voltage support are selected according to the disturbance degree of the distal buses, and the target power stations are sorted according to the adjustable capacity and regulation speed indicators; the reactive current required by the distal new energy power stations is estimated based on the reactive current required to improve the transient voltage, and the support current that each distal power station can provide is estimated in sequence until the sum of the support currents of each distal power station meets the reactive current demand, and an emergency control command is issued to the relevant power stations.

Description

Technical Field

[0001] The present invention belongs to the technical field of power system security and stability control, and particularly relates to a voltage emergency control method and system for coordinated operation of multiple new energy power stations. Background Art

[0002] The grid-connected scale of new energy sources such as wind power and photovoltaic power continues to increase, and the application of large-capacity UHVDC transmission is gradually increasing. These are two important trends and characteristics in the development of the current AC / DC hybrid large power grid, which deeply change the power source structure and the transmission grid structure. The impacts are mainly reflected in two aspects:

[0003] (1) The receiving-end power grid has concentrated loads, and new energy is closely coupled with the loads. The new energy power generation equipment has weak frequency and voltage withstand capabilities. After a serious fault occurs in the receiving-end power grid, it may enter low voltage ride-through or trigger low voltage protection actions, and then trip off the grid on a large scale, resulting in transient voltage instability of the receiving-end power grid.

[0004] (2) Due to the feeding-in of multiple DCs and the grid connection of large-scale new energy, synchronous generators of equal capacity are replaced and withdrawn from operation, and the characteristics of "hollowing out" of the load center are more obvious. The transient reactive power support capacity and equivalent inertia of the receiving-end power grid are reduced, and the problems of transient low voltage and low frequency are becoming increasingly prominent. In addition, after a voltage dip fault occurs in the DC receiving-end power grid, a large amount of reactive power will be absorbed from the system by the inverter station during the DC power recovery process. Coupled with the low power factor operation of heavy-load induction motor loads during the speed recovery process, the transient voltage problem of the system is further aggravated.

[0005] As the second line of defense for power system stability control, emergency control is aimed at pre-considered fault forms and operation modes. Triggered by fault events, it pre-determines control strategies, comprehensively coordinates the quantity and implementation locations of emergency control measures input in the whole system, and issues control commands to substations that need to take generator tripping or load shedding control. Usually, emergency control measures include fast valve closing, generator tripping / load shedding, braking resistors, etc. Since it does not require feedback signals such as system frequency to trigger, it can act quickly on the millisecond scale after detecting a fault, coordinate the available resources of the whole network, and enable the system to quickly reach a new equilibrium state after a serious fault.

[0006] The power system security and stability emergency control device has always been the focus of research in the industrial and academic fields. However, due to the uncertainty of actual system parameters and models, as well as the complexity of fault condition and stability boundary calculations, there is a possibility of misoperation of emergency control measures due to misjudgment of system stability. At the same time, the transient characteristic time constant of power electronic devices is small, and there is still much room for improvement in the current emergency control in utilizing the fast adjustment characteristics of power electronic devices. Summary of the Invention

[0007] Objective of the Invention: To solve the transient voltage safety problem of a power grid with a high proportion of new energy sources, the present invention proposes a voltage emergency control method and system for coordinated operation of multiple new energy power stations.

[0008] Technical Solution: The first solution is as follows: A voltage emergency control method for coordinated operation of multiple new energy power stations includes the following steps:

[0009] When a three-phase short-circuit fault occurs, determine the fault point and the bus connected to the branch where the fault point is located, and record this bus as the bus to be supported; define the bus directly connected to the bus to be supported and with a connection impedance less than the set threshold as the proximal bus, and define other buses connected to new energy power stations as the distal buses;

[0010] For any distal bus, the absolute value of the difference between its current voltage value and the voltage value at steady state is defined as the degree of disturbance. When a three-phase short-circuit fault occurs, the new energy power stations connected to the distal buses with a degree of disturbance exceeding the disturbance degree threshold are used as reserve adjustment resources, thereby forming a station set S1; calculate the adjustable capacity of each new energy power station in the station set S1, and sort the new energy power stations in the station set S1 in descending order according to the adjustable capacity to form a new station set S2; estimate the reactive current of the short-circuit branch required for transient voltage support according to the fault point and the bus connected to the branch where the fault point is located, and estimate the reactive current of the short-circuit branch that the proximal bus can provide and the reactive current of the short-circuit branch that the distal buses need to provide;

[0011] Estimate the reactive current of the short-circuit branch that the first new energy power station in the new station set S2 can provide; compare the reactive current of the short-circuit branch that the first new energy power station in the new station set S2 can provide with the reactive current of the short-circuit branch that the distal buses need to provide. If the demand is met, determine that the first new energy power station participates in the emergency control; if the demand is not met, estimate the reactive current of the short-circuit branch that the second new energy power station in the new station set S2 can provide, add it to the reactive current of the short-circuit branch that the first new energy power station can provide, and compare the added value with the reactive current of the short-circuit branch that the distal buses need to provide. If the demand is met, determine that the first new energy power station and the second new energy power station participate in the emergency control; if the demand is not met, continue to calculate the reactive current of the short-circuit branch that other new energy power stations in the new station set S2 can provide in sequence, and accumulate until the demand for the reactive current of the short-circuit branch that the distal buses need to provide is met, and obtain the new energy power stations determined to participate in the emergency control;

[0012] Issue voltage emergency control commands to the new energy power stations connected to the proximal bus and the new energy power stations determined to participate in the emergency control;

[0013] According to the voltage emergency control command, each new energy power station switches the control strategy to transient voltage emergency control to provide reactive power support for the bus to be supported; after the three-phase short-circuit fault is eliminated, each new energy power station releases the transient voltage emergency control and switches back to the control strategy.

[0014] Furthermore, the total current limit of the new energy power station is used as the adjustable capacity of the new energy power station; the total current limit of the new energy power station is calculated according to the following formula:

[0015] ;

[0016] In the formula, I Cmax is the total current limit of the new energy power station, N c is the number of converters in the new energy power station, I Cmaxi is the current limit of the i-th converter.

[0017] Furthermore, when the adjustable capacities of two new energy power stations are equal, the ranking is determined according to the adjustment speed;

[0018] The adjustment speed is calculated according to the following formula:

[0019] ;

[0020] In the formula, K pi , K ii are the proportional and integral coefficients of the i-th converter in the new energy power station respectively, N c is the number of converters in the new energy power station, K avr is the adjustment speed of the new energy power station.

[0021] Furthermore, based on the fault point and the bus connected to the branch where the fault point is located, the reactive current of the short-circuit branch required for transient voltage support is estimated. The specific calculation includes:

[0022] ;

[0023] In the formula, I s is the reactive current of the short-circuit branch required for transient voltage support, U tar is the target voltage value of the bus to be supported under the transient voltage condition, and z0 is the impedance of the branch where the fault point is located.

[0024] Furthermore, the reactive current of the short-circuit branch that the proximal bus can provide is estimated. The specific calculation includes:

[0025] According to the type of power source connected to the proximal bus, the reactive current of the short-circuit branch that can be provided is estimated; the types of the power sources include synchronous generators and new energy power stations;

[0026] For multiple proximal busbars, add up the reactive currents of the short-circuit branches that each proximal busbar can provide.

[0027] Furthermore, when the proximal busbar is connected to a synchronous generator, the reactive current of the short-circuit branch that the proximal busbar can provide is estimated according to the following formula:

[0028] ;

[0029] In the formula, I snG is the reactive current of the short-circuit branch that the synchronous generator connected to the proximal busbar can provide, E G is the internal electromotive force under the rated condition of the synchronous generator, z Gs is the impedance between the internal electromotive force of the synchronous generator and the busbar, and z0 is the impedance of the branch where the short-circuit fault point is located;

[0030] When the proximal busbar is connected to a new energy power station, use the output current limit value of the converter in the new energy power station as the calculation basis. At this time, the reactive current of the short-circuit branch that the proximal busbar can provide is estimated according to the following formula:

[0031] ;

[0032] Among them, I snC is the reactive current of the short-circuit branch that the new energy power station connected to the proximal busbar can provide, k c is the current coefficient, I Cmaxf is the output current limit value of the converter, and N Cf is the number of converters in the new energy power station.

[0033] Furthermore, the specific calculation of estimating the reactive current of the short-circuit branch that the distal busbar needs to provide includes:

[0034] ;

[0035] In the formula, I sf is the reactive current of the short-circuit branch that the distal busbar needs to provide, I s is the reactive current of the short-circuit branch required for transient voltage support, and I sn is the reactive current of the short-circuit branch that the proximal busbar can provide.

[0036] Furthermore, the specific calculation of estimating the reactive current of the short-circuit branch that the new energy power stations in the new station set S2 can provide includes:

[0037] ;

[0038] In the formula, U tar is the target voltage value of the busbar to be supported under the transient voltage condition, and I sfm$I_{mq}$ is the reactive current of the short - circuit branch that the $m$-th new - energy power station in the new power - station set $S2$ can provide; $I$ sn $I_{z}$ is the reactive current of the short - circuit branch that the proximal bus can provide; $z$ m0min $z_{m}$ is the sum of the impedance value of the shortest path from the bus to be supported to the bus where the $m$-th new - energy power station in the new power - station set $S2$ is located and the internal resistance; $z$ fs $z_{0m}$ is the connection impedance from the $m$-th new - energy power station in the new power - station set $S2$ to the bus it is connected to, and $z_{0}$ is the impedance of the branch where the short - circuit fault point is located.

[0039] Furthermore, each new - energy power station switches the control strategy to transient voltage emergency control according to the voltage emergency control command to provide reactive power support for the bus to be supported. The specific operations include:

[0040] For any new - energy power station, it includes an active - power control loop and a reactive - power control loop; in the active - power control loop, an active - outer - loop - current - inner - loop control structure is adopted. Under the control signal $EN$, a $d$-axis voltage for controlling the converter is generated U d ; in the reactive - power control loop, a reactive - outer - loop - current - inner - loop control structure is adopted. Under the control signal $EN$, a $q$-axis voltage for controlling the converter is generated U q ;

[0041] When any new - energy power station receives a voltage emergency control command, the control signal $EN = 1$, and the generated $d$-axis voltage for controlling the converter U d and the generated $q$-axis voltage for controlling the converter U q are transformed into three - phase voltage signals, and these three - phase voltage signals are used as the modulation - wave voltage to perform PWM control on the converter.

[0042] The second solution is: A voltage emergency control system for coordinated operation of multiple new - energy power stations, including:

[0043] A fault - point and bus confirmation module for the branch where the fault - point is located, which is used to determine the fault - point and the bus connected to the branch where the fault - point is located when a three - phase short - circuit fault occurs, and record this bus as the bus to be supported; define the bus directly connected to the bus to be supported and with a connection impedance less than the set threshold as the proximal bus, and define other buses connected to new - energy power stations as the distal buses;

[0044] The substation set formation module is used to define the degree of disturbance as the absolute value of the difference between the current voltage value and the voltage value at steady state for any remote bus. When a three-phase short-circuit fault occurs, the new energy substations connected to the remote buses with the degree of disturbance exceeding the disturbance degree threshold are used as the reserve adjustment resources, so as to form the substation set S1; calculate the adjustable capacity of each new energy substation in the substation set S1, and sort the new energy substations in the substation set S1 from large to small according to the adjustable capacity to form a new substation set S2;

[0045] The short-circuit branch reactive current estimation module is used to estimate the short-circuit branch reactive current required for transient voltage support according to the fault point and the bus connected to the branch where the fault point is located, and estimate the short-circuit branch reactive current that the proximal bus can provide and the short-circuit branch reactive current that the remote bus needs to provide;

[0046] The new energy substation determination module participating in emergency control is used to estimate the short-circuit branch reactive current that the first new energy substation in the new substation set S2 can provide; compare the short-circuit branch reactive current that the first new energy substation in the new substation set S2 can provide with the short-circuit branch reactive current that the remote bus needs to provide. If the demand is met, it is determined that the first new energy substation participates in emergency control; if the demand is not met, estimate the short-circuit branch reactive current that the second new energy substation in the new substation set S2 can provide, add it to the short-circuit branch reactive current that the first new energy substation can provide, and compare the added value with the short-circuit branch reactive current that the remote bus needs to provide. If the demand is met, it is determined that the first new energy substation and the second new energy substation participate in emergency control; if the demand is not met, continue to calculate the short-circuit branch reactive current that other new energy substations in the new substation set S2 can provide in sequence, and accumulate until the demand for the short-circuit branch reactive current that the remote bus needs to provide is met, and obtain the new energy substations determined to participate in emergency control;

[0047] The voltage emergency control command issuing module is used to issue voltage emergency control commands to the new energy substations connected to the proximal bus and the new energy substations determined to participate in emergency control;

[0048] The control switching module is used to switch the control strategy to transient voltage emergency control according to the voltage emergency control command to provide reactive power support for the bus to be supported; after the three-phase short-circuit fault is eliminated, each new energy substation releases the transient voltage emergency control and switches to the control strategy.

[0049] Furthermore, the total current limit of the new energy substation is used as the adjustable capacity of the new energy substation; the total current limit of the new energy substation is calculated according to the following formula:

[0050] ;

[0051] In the formula, I Cmax is the total current limit of the new energy power station, N c is the number of converters in the new energy power station, I Cmaxi is the current limit of the i-th converter.

[0052] Furthermore, when the adjustable capacities of two new energy power stations are equal, the ranking is determined according to the adjustment speed;

[0053] The adjustment speed is calculated according to the following formula:

[0054] ;

[0055] In the formula, K pi , K ii are respectively the proportional and integral coefficients of the i-th converter in the new energy power station, N c is the number of converters in the new energy power station, K avr is the adjustment speed of the new energy power station.

[0056] Furthermore, the reactive current of the short-circuit branch required for transient voltage support is estimated according to the fault point and the bus connected to the branch where the fault point is located. The specific calculation includes:

[0057] ;

[0058] In the formula, I s is the reactive current of the short-circuit branch required for transient voltage support, U tar is the target voltage value of the bus to be supported under transient voltage conditions, and z0 is the impedance of the branch where the fault point is located.

[0059] Furthermore, the reactive current of the short-circuit branch that the proximal bus can provide is estimated. The specific calculation includes:

[0060] Estimate the reactive current of the short-circuit branch that can be provided according to the type of power supply connected to the proximal bus; the types of the power supply include synchronous generators and new energy power stations;

[0061] For multiple proximal buses, add up the reactive currents of the short-circuit branches that each proximal bus can provide.

[0062] Furthermore, when the power supply connected to the proximal bus is a synchronous generator, the reactive current of the short-circuit branch that the proximal bus can provide is estimated according to the following formula:

[0063] ;

[0064] In the formula, I snG is the reactive current of the short-circuit branch that the synchronous generator connected to the proximal bus can provide, EG is the internal electromotive force of the synchronous generator under rated conditions, z Gs is the impedance between the internal electromotive force of the synchronous generator and the bus, and z0 is the impedance of the branch where the short-circuit fault point is located;

[0065] When the bus at the near end is connected to a new energy station, the output current limit value of the converter in the new energy station is used as the calculation basis. At this time, the reactive current of the short-circuit branch that the near-end bus can provide is estimated according to the following formula:

[0066] ;

[0067] Among them, I snC is the reactive current of the short-circuit branch that the new energy station connected to the near-end bus can provide, k c is the current coefficient, I Cmaxf is the output current limit value of the converter, N Cf is the number of converters in the new energy station.

[0068] Furthermore, the estimation of the reactive current of the short-circuit branch that the far-end bus needs to provide specifically includes:

[0069] ;

[0070] In the formula, I sf is the reactive current of the short-circuit branch that the far-end bus needs to provide, I s is the reactive current of the short-circuit branch required for transient voltage support, I sn is the reactive current of the short-circuit branch that the near-end bus can provide.

[0071] Furthermore, the estimation of the reactive current of the short-circuit branch that the new energy stations in the new station set S2 can provide specifically includes:

[0072] ;

[0073] In the formula, U tar is the target voltage value of the bus to be supported under transient voltage conditions, I sfm is the reactive current of the short-circuit branch that the m-th new energy station in the new station set S2 can provide; I sn is the reactive current of the short-circuit branch that the near-end bus can provide; z m0min is the sum of the impedance value and the internal resistance of the shortest path from the bus to be supported to the bus where the m-th new energy station in the new station set S2 is located; z fs is the connection impedance from the m-th new energy station in the new station set S2 to the bus it is connected to, and z0 is the impedance of the branch where the short-circuit fault point is located.

[0074] Further, each of the new energy power stations switches the control strategy to transient voltage emergency control according to the voltage emergency control command to provide reactive power support for the bus to be supported. The specific operations include:

[0075] For any new energy power station, it includes: an active power control loop and a reactive power control loop; in the active power control loop, an active outer loop - current inner loop control structure is adopted, and under the control signal EN, a d-axis voltage for controlling the converter is generated U d ; in the reactive power control loop, a reactive outer loop - current inner loop control structure is adopted, and under the control signal EN, a q-axis voltage for controlling the converter is generated U q ;

[0076] When any new energy power station receives a voltage emergency control command, the control signal EN = 1, and the generated d-axis voltage for controlling the converter U d and the q-axis voltage for controlling the converter U q are transformed into a three-phase voltage signal, and this three-phase voltage signal is used as the modulation wave voltage to perform PWM control on the converter.

[0077] Beneficial effects: Compared with the prior art, the present invention has the following advantages:

[0078] (1) The method of the present invention aims at a severe three-phase short-circuit fault with a long duration. The bus farther from the fault point among the buses connected to the fault branch is used as the bus to be supported, the bus connected to this bus with a smaller connection impedance is defined as the proximal bus, and the other buses in the power grid connected to new energy power stations are defined as the distal buses. The new energy power stations that can perform transient voltage support are screened according to the disturbance degree of the distal buses, and the target power stations are sorted according to the adjustable capacity and regulation speed indicators; the reactive current required by the distal new energy power stations is estimated based on the reactive current required to improve the transient voltage, and the support current that each distal power station can provide is estimated in sequence until the sum of the support currents of each distal power station meets the reactive current demand, and an emergency control command is issued to the relevant power stations; the converter of the selected power station starts emergency voltage control, changing from the original double-loop control of the power outer loop and current inner loop to a single-loop current control, quickly outputting reactive power for transient voltage support; after the fault ends, the converter resumes the original control; the method of the present invention quickly outputs reactive power to support the transient voltage through the converter power loop - current loop switching strategy, solves the two problems of response rapidity and control quantity accuracy in the current emergency voltage control, can effectively utilize the fast support characteristics of the new energy converter to support the transient voltage, ensure the safety of the power grid, and improve the anti-risk and anti-disturbance capabilities of the power grid;

[0079] (2) By improving the transient voltage control of new energy converters, the method of the present invention gives full play to their fast and accurate reactive power output capabilities, mobilizes the transient voltage support capabilities of remote new energy through emergency control, coordinates the available reactive power sources of the entire network to provide system support for the power grid, and combines appropriate transient voltage control strategies of converters with the emergency control of the power grid. It is an effective way to achieve fast transient voltage support in a power grid with a high proportion of new energy, which can ensure the safety and stability of the transient voltage of the new power system and improve the safe and stable operation level of the power grid.

[0080] (3) The method of the present invention gives play to the fast adjustment characteristics of new energy power stations to effectively support the transient voltage, and makes full use of the reactive power capacity under different working conditions through the transient voltage control strategy of the converter, so as to significantly improve the transient voltage support potential under faults and disturbances. BRIEF DESCRIPTION OF THE DRAWINGS

[0081] Figure 1 It is a flowchart of a voltage emergency control method based on the cooperation of multiple new energy power stations proposed by the present invention;

[0082] Figure 2 It is a block diagram of an improved transient voltage control strategy for a new energy power station;

[0083] Figure 3 It is the waveform of the target bus voltage under the emergency voltage support of a new energy power station. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0084] The technical solution of the present invention will be further described below in conjunction with the drawings and embodiments.

[0085] Now in combination with Figure 1 , a voltage emergency control method based on the cooperation of multiple new energy power stations proposed in this embodiment will be further described. The main steps are as follows:

[0086] Step 1: Through the wide-area monitoring system, monitor the transient voltage events. Generally, when the voltage drop at the short-circuit point and its vicinity exceeds 50%, it is considered that a severe three-phase short-circuit fault has occurred. However, depending on the local conditions, sometimes a voltage drop of 40% is also considered to have a severe three-phase short-circuit fault. When a severe three-phase short-circuit fault occurs, determine the fault point and the bus connected to its branch, and record this bus as the bus to be supported; define the bus directly connected to this bus and with a connection impedance less than the set threshold as the proximal bus, and define the other buses in the power grid connected to new energy power stations as the distal buses.

[0087] Step 2: After detecting a three-phase short-circuit fault, set the absolute value of the difference between the current bus voltage value and the steady-state voltage value as the degree of disturbance, and set a threshold for the degree of disturbance. Consider the new energy power stations connected to the remote buses whose degree of disturbance exceeds the set threshold after the fault occurs as the preliminary adjustment resources for transient voltage support, determine the scope of the transient voltage support power stations, and form a power station set S1 = {c1, c2, …, c N}, where N is the number of eligible new energy power stations, and c N is an eligible new energy power station.

[0088] Step 3: Characterize the reactive power output capacity of the new energy power stations in the power station set S1 according to formula (1), and sort them from large to small; when the reactive power output capacities of the new energy power stations are equal, determine the sorting according to formula (2) based on the adjustment speed; finally, form a new power station set S2 = {C1, C2, …, C N};

[0089] (1)

[0090] Where, I Cmax is the total current limit of the new energy power station, N c is the number of converters in the new energy power station, and I Cmaxi is the current limit of the i-th converter.

[0091] (2)

[0092] Where, G(s) is a PI controller, and K p , K i are the proportional and integral coefficients of the PI controller respectively; K pi , K ii are the proportional and integral coefficients of the i-th converter respectively; K avr is the adjustment speed of the new energy power station, and s represents the complex variable of the Laplace transform.

[0093] Step 4: Estimate the reactive current I s of the short-circuit branch required for transient voltage support according to formula (3);

[0094] (3)

[0095] Where, U tar is the target voltage value of the bus to be supported under the transient voltage condition, and z0 is the impedance of the branch where the fault point is located.

[0096] Estimate the reactive current of the short - circuit branch that can be provided according to the type of power source connected to the proximal bus; the types of this power source include synchronous generators and new - energy power stations; for multiple proximal buses, add up the reactive currents of the short - circuit branches that each proximal bus can provide.

[0097] When the power source connected to the proximal bus is a synchronous generator, estimate the reactive current of the short - circuit branch that the proximal bus can provide according to Equation (4): the internal resistance of this synchronous generator includes the impedance of the synchronous motor, transformer, and line impedance.

[0098] (4)

[0099] Among them, I snG is the reactive current of the short - circuit branch that the synchronous generator connected to the proximal bus can provide, E G is the internal electromotive force under the rated condition of the synchronous generator, z Gs is the impedance between the internal electromotive force of the synchronous generator and the bus.

[0100] When the power source connected to the proximal bus is a new - energy power station, considering the situation where one - side bus drops significantly due to a fault, use the output - current limit value of the converter in this new - energy power station as the calculation basis, then the reactive current that the proximal bus can provide is calculated as shown in Equation (5):

[0101] (5)

[0102] Among them, I snC is the reactive current of the short - circuit branch that the new - energy power station connected to the proximal bus can provide, k c is the current coefficient. If the converter adopts the LCL filtering form, k c is less than 1, I Cmaxf is the output - current limit value of the converter, N Cf is the number of converters in the new - energy power station.

[0103] Estimate the reactive current I sf of the short - circuit branch required to be provided by the distal bus according to Equation (6);

[0104] (6)

[0105] Among them, I sn is the reactive current provided by the generator or new - energy power station connected to the proximal bus.

[0106] Step 5: Estimate the reactive current of the short - circuit branch that the new - energy power stations in the new station set S2 can provide according to Equation (7):

[0107] (7)

[0108] Among them, I sfmThe reactive current of the short - circuit branch provided for the m - th remote new - energy substation in the new substation set S2; I sn The reactive current of the short - circuit branch that the proximal bus can provide; z m0min The sum of the impedance value of the shortest path from the bus to be supported to the bus where the m - th remote new - energy substation in the new substation set S2 is located and the internal resistance; z fs The connection impedance from the m - th new - energy substation in the new substation set S2 to the bus it is connected to, and z0 is the impedance of the branch where the short - circuit fault point is located.

[0109] Compare the reactive current of the short - circuit branch that the new - energy field C1 in the new substation set S2 can provide with the reactive current I of the short - circuit branch that the remote bus needs to provide sf If the demand can be met, it is determined that the new - energy field C1 participates in the emergency control for transient voltage support; if the demand cannot be met, calculate the reactive current of the short - circuit branch that the new - energy field C2 in the substation set S2 can provide, add it to the reactive current of the short - circuit branch that the new - energy field C1 can provide, and then compare it with the reactive current I of the short - circuit branch that the remote bus needs to provide sf If the demand is met, it is determined that the new - energy field C1 and the new - energy field C2 participate in the emergency control. If the demand cannot be met, continue to calculate the reactive current of the short - circuit branch that other new - energy fields can provide in sequence until the sum meets the demand of the reactive current I sf of the short - circuit branch that the remote bus needs to provide, and determine the remote new - energy substations participating in the emergency control.

[0110] Send voltage emergency control commands to the new - energy substations connected to the proximal bus and the new - energy substations determined to participate in the emergency control.

[0111] Step 6: Each new - energy substation switches the control strategy to transient voltage emergency control according to the voltage emergency control command to provide reactive power support for the bus to be supported. The specific operations include:

[0112] For any new - energy substation, it includes: an active - power control loop and a reactive - power control loop; in the active - power control loop, an inner - outer loop control structure is adopted, and under the control signal EN, a d - axis voltage for controlling the converter is generated U d ; in the reactive - power control loop, an inner - outer loop control structure is adopted, and under the control signal EN, a q - axis voltage for controlling the converter is generated U q ;

[0113] When any new - energy substation receives the voltage emergency control command, the control signal EN = 1, and the generated d - axis voltage for controlling the converter U dand the q-axis voltage for controlling the converter U q It is transformed into a three-phase voltage signal, and this three-phase voltage signal is used as the modulation wave voltage to perform PWM control on the converter.

[0114] There are various implementation methods for the inner and outer loop control. Now, in combination with Figure 2 , the inner and outer loop control adopted in this embodiment will be further described.

[0115] After receiving the emergency control command, the new energy power station switches the new energy converter to emergency voltage control. As Figure 2 shown, for any new energy power station, it includes: an active power control loop, a reactive power control loop, an abc / dq converter, a third PI controller, and a fourth PI controller.

[0116] In the active power control loop, the difference between the active power set value P ref and the actual active power P is calculated. The difference between the two is adjusted by the first proportional-integral controller to output the d-axis converter machine-side current; under the control signal EN, the d-axis converter machine-side current is limited to generate the d-axis current set value i gdref ; the difference between the d-axis current set value i gdref and the actual d-axis current value i gd is adjusted by the second proportional-integral controller to output the first intermediate voltage; the first intermediate voltage minus U cd , and added to the voltage L of the inductor 1 connected to the converter to generate the d-axis voltage U d for controlling the converter; where is the angular velocity.

[0117] In the reactive power control loop, the difference between the reactive power set value Q ref and the actual reactive power Q is calculated. The difference between the two is adjusted by the third proportional-integral controller to output the q-axis converter machine-side current; under the control signal EN, the q-axis converter machine-side current is limited to generate the q-axis current set value i gqref ; the difference between the q-axis current set value i gqref and the actual q-axis current value i gq is adjusted by the fourth proportional-integral controller to output the second intermediate voltage; the second intermediate voltage minus Ucq Inductor connected to the converter L Voltage of 1 , generating the q-axis voltage for controlling the converter U q .

[0118] Among them, the actual value of the d-axis current i gd and the actual value of the q-axis current i gq are obtained by inputting the converter machine-side current I g and the phase angle obtained by the phase-locked loop θ pll into the abc / dq converter for conversion. According to different dq transformation forms, there are also different representation methods of addition or subtraction.

[0119] After receiving the emergency voltage control command, the new energy power station will switch the control strategy to transient voltage emergency control. When the control signal EN = 1, the active-reactive outer loop-current inner loop control is switched to single-current control, i gdref is set to 0, i gqref is set to I gmax ; I gmax is the converter output current limit value. The given value of the active current control is compared with the actual value of the active current as the input of the active current control, and the given value of the reactive current control is compared with the actual value of the reactive current as the input of the reactive current control. The active and reactive control outputs are inverse dq-transformed into three-phase voltage signals and used as the modulation wave voltage to perform PWM control on the converter; the emergency voltage control has a high priority and does not respond to the control commands of other devices during the emergency voltage control; the support effect is as Figure 3 shown. The abscissa is time, the unit is second, and the ordinate is the bus voltage received by the power station, the unit is p.u.. Curves 1 and 2 are the voltage waveforms of the bus to be supported with only the near-end reactive source and with the reactive power support of the remote new energy power station respectively. 1 s is the fault occurrence time, and the fault duration is 1 s. It can be seen that the reactive power support of the remote new energy power station increases the voltage of the bus to be supported by 0.05 pu and reaches above the preset value of 0.8 pu, achieving a good support effect.

[0120] Step 7: After the three-phase short-circuit fault is eliminated, each new energy power station releases the transient voltage emergency control and switches to the control strategy.

Claims

1. A voltage emergency control method for collaborative operation of multiple new energy power stations, characterized in that: It includes the following steps: When a three-phase short-circuit fault occurs, determine the fault point and the bus connected to the branch where the fault point is located, and record this bus as the bus to be supported; define the bus directly connected to the bus to be supported and with a connection impedance less than the set threshold as the proximal bus, and define other buses accessing the new energy power station as the distal buses; For any one of the distal buses, the absolute value of the difference between its current voltage value and the voltage value at steady state is defined as the degree of disturbance. When a three-phase short-circuit fault occurs, take the new energy power stations connected to the distal buses with the degree of disturbance exceeding the disturbance degree threshold as the reserve adjustment resources, so as to form the power station set S1; calculate the adjustable capacity of each new energy power station in the power station set S1, and sort the new energy power stations in the power station set S1 from large to small according to the adjustable capacity to form a new power station set S2; according to the fault point and the bus connected to the branch where the fault point is located, estimate the reactive current of the short-circuit branch required for transient voltage support, and estimate the reactive current of the short-circuit branch that the proximal bus can provide and the reactive current of the short-circuit branch that the distal buses need to provide; Estimate the reactive current of the short-circuit branch that the first new energy power station in the new power station set S2 can provide; compare the reactive current of the short-circuit branch that the first new energy power station in the new power station set S2 can provide with the reactive current of the short-circuit branch that the distal buses need to provide. If the demand is met, determine that the first new energy power station participates in the emergency control; if the demand is not met, estimate the reactive current of the short-circuit branch that the second new energy power station in the new power station set S2 can provide, add it to the reactive current of the short-circuit branch that the first new energy power station can provide, and compare the added value with the reactive current of the short-circuit branch that the distal buses need to provide. If the demand is met, determine that the first new energy power station and the second new energy power station participate in the emergency control; if the demand is not met, continue to calculate in sequence the reactive current of the short-circuit branch that other new energy power stations in the new power station set S2 can provide, and accumulate until the demand for the reactive current of the short-circuit branch that the distal buses need to provide is met, and obtain the new energy power stations determined to participate in the emergency control; Issue a voltage emergency control command to the new energy power stations connected to the proximal bus and the new energy power stations determined to participate in the emergency control; According to the voltage emergency control command, each new energy power station switches the control strategy to transient voltage emergency control to provide reactive power support for the bus to be supported; After the three-phase short-circuit fault is eliminated, each new energy power station releases the transient voltage emergency control and switches to the control strategy.

2. The voltage emergency control method for collaborative operation of multiple new energy power stations according to claim 1, characterized in that: Use the total current limit of the new energy power station as the adjustable capacity of the new energy power station; the total current limit of the new energy power station is calculated according to the following formula: ； Wherein, I Cmax is the total current limit of the new energy power station, N c is the number of converters in the new energy power station, I Cmaxi is the current limit of the i-th converter.

3. A voltage emergency control method for coordinated operation of multiple new energy power stations according to claim 1, characterized in that: When the adjustable capacities of two new energy power stations are equal, the sorting is determined according to the adjustment speed; The adjustment speed is calculated according to the following formula: ； where K pi , K ii are the proportional and integral coefficients of the i-th converter in the new energy power station respectively, N c is the number of converters in the new energy power station, and K avr is the regulation speed of the new energy power station.

4. A voltage emergency control method for collaborative operation of multiple new energy power stations according to claim 1, characterized in that: The specific calculation of estimating the reactive current of the short-circuit branch required for transient voltage support according to the fault point and the bus connected to the branch where the fault point is located includes: ； Where, I s is the reactive current of the short-circuit branch required for transient voltage support, U tar is the target voltage value of the bus to be supported under transient voltage conditions, and z0 is the impedance of the branch where the fault point is located.

5. A voltage emergency control method for coordinated operation of multiple new energy power stations according to claim 1, characterized in that: The specific calculation of estimating the reactive current of the short-circuit branch that the proximal bus can provide includes: Estimate the reactive current of the short-circuit branch that can be provided according to the type of power source connected to the proximal bus; the types of the power sources include synchronous generators and new energy power stations; For multiple proximal buses, add up the reactive currents of the short-circuit branches that each proximal bus can provide.

6. The voltage emergency control method for collaborative operation of multiple new energy power stations according to claim 5, wherein: When the power source connected to the proximal bus is a synchronous generator, estimate the reactive current of the short-circuit branch that the proximal bus can provide according to the following formula: ； Where I snG is the reactive current of the short-circuit branch that the synchronous generator connected to the proximal bus can provide, and E G is the internal electromotive force of the synchronous generator under the rated condition, z Gs is the impedance between the internal electromotive force of the synchronous generator and the bus, and z0 is the impedance of the branch where the short-circuit fault point is located; When the power source connected to the proximal bus is a new energy power station, use the output current limit value of the converter in the new energy power station as the calculation basis. At this time, estimate the reactive current of the short-circuit branch that the proximal bus can provide according to the following formula: ； Among them, I snC is the reactive current of the short-circuit branch that can be provided by the new energy power station connected to the proximal bus, k c is the current coefficient, I Cmaxf is the output current limit value of the converter, N Cf is the number of converters in the new energy power station.

7. A voltage emergency control method for the coordination of multiple new energy power stations according to claim 1, characterized in that: The specific calculation of estimating the reactive current of the short-circuit branch required by the distal bus includes: ； Wherein, I sf is the reactive current of the short-circuit branch required to be provided by the remote bus, I s is the reactive current of the short-circuit branch required for transient voltage support, I sn is the reactive current of the short-circuit branch that can be provided by the proximal bus.

8. A voltage emergency control method for collaborative operation of multiple new energy power stations according to claim 1, characterized in that: Estimate the reactive current of the short-circuit branch that the new energy power stations in the new station set S2 can provide. The specific calculation includes: ； Where, U tar is the target voltage value of the bus to be supported under the transient voltage condition, and I sfm is the reactive current of the short-circuit branch that the m-th new energy power station in the new power station set S2 can provide; I sn is the reactive current of the short-circuit branch that the proximal bus can provide; z m0min is the sum of the impedance value of the shortest path from the bus to be supported to the bus where the m-th new energy power station in the new power station set S2 is located and the internal resistance; z fs is the connection impedance from the m-th new energy power station in the new power station set S2 to the bus it is connected to, and z0 is the impedance of the branch where the short-circuit fault point is located.

9. A voltage emergency control method for collaborative operation of multiple new energy power stations according to claim 1, characterized in that: According to the voltage emergency control command, each of the new energy power stations switches the control strategy to transient voltage emergency control to provide reactive power support for the bus to be supported. The specific operations include: For any new energy power station, it includes: an active power control loop and a reactive power control loop; in the active power control loop, an active outer loop - current inner loop control structure is adopted, and under the control signal EN, a d-axis voltage for controlling the converter is generated U d ; in the reactive power control loop, a reactive outer loop - current inner loop control structure is adopted, and under the control signal EN, a q-axis voltage for controlling the converter is generated U q ; When any new energy power station receives a voltage emergency control command, the control signal EN = 1, and the d-axis voltage for controlling the converter U d and the q-axis voltage for controlling the converter U q are transformed into three-phase voltage signals, and these three-phase voltage signals are used as the modulation wave voltage to perform PWM control on the converter.

10. A voltage emergency control system for the coordination of multiple new energy power stations, characterized in that: Include: A fault point and the bus connection confirmation module of the branch where the fault point is located, which is used to determine the fault point and the bus connected to the branch where the fault point is located when a three-phase short-circuit fault occurs, and record this bus as the bus to be supported; define the bus directly connected to the bus to be supported and with a connection impedance less than the set threshold as the proximal bus, and define the other buses connected to the new energy power stations as the distal buses; The station set formation module is used to define the absolute value of the difference between the current voltage value and the voltage value at steady state of any distal bus as the degree of disturbance. When a three-phase short-circuit fault occurs, use the new energy power stations connected to the distal buses with the degree of disturbance exceeding the disturbance degree threshold as the reserve adjustment resources, so as to form the station set S1; calculate the adjustable capacity of each new energy power station in the station set S1, and sort the new energy power stations in the station set S1 from largest to smallest according to the adjustable capacity to form a new station set S2; The short-circuit branch reactive current estimation module is used to estimate the reactive current of the short-circuit branch required for transient voltage support according to the fault point and the bus connected to the branch where the fault point is located, and estimate the reactive current of the short-circuit branch that the proximal bus can provide and the reactive current of the short-circuit branch required by the distal bus; The new energy power station determination module participating in emergency control is used to estimate the short - circuit branch reactive current that the first new energy power station in the new power station set S2 can provide; compare the short - circuit branch reactive current that the first new energy power station in the new power station set S2 can provide with the short - circuit branch reactive current required to be provided by the remote bus. If the requirement is met, determine that the first new energy power station participates in emergency control; if the requirement is not met, estimate the short - circuit branch reactive current that the second new energy power station in the new power station set S2 can provide, add it to the short - circuit branch reactive current that the first new energy power station can provide, and compare the added value with the short - circuit branch reactive current required to be provided by the remote bus. If the requirement is met, determine that the first and the second new energy power stations participate in emergency control; if the requirement is not met, continue to calculate in sequence the short - circuit branch reactive currents that other new energy power stations in the new power station set S2 can provide, and accumulate until the requirement of the short - circuit branch reactive current required to be provided by the remote bus is met, to obtain the new energy power stations determined to participate in emergency control. The voltage emergency control command issuing module is used to issue voltage emergency control commands to the new energy power stations connected to the proximal bus and the new energy power stations determined to participate in emergency control. The control switching module is used to switch the control strategy to transient voltage emergency control according to the voltage emergency control command to provide reactive power support for the bus to be supported. After the three - phase short - circuit fault is eliminated, each new energy power station releases the transient voltage emergency control and switches back to the control strategy.

11. A voltage emergency control system for collaborative operation of multiple new energy power stations according to claim 10, characterized in that: The total current limit of the new energy power station is used as the adjustable capacity of the new energy power station; the total current limit of the new energy power station is calculated according to the following formula: ； Wherein, I Cmax is the total current limit of the new energy power station, N c is the number of converters in the new energy power station, I Cmaxi is the current limit of the i-th converter.

12. A voltage emergency control system for the coordination of multiple new energy power stations according to claim 10, characterized in that: When the adjustable capacities of two new energy power stations are equal, the sorting is determined according to the speed of adjustment. The speed of adjustment is calculated according to the following formula: ； where K pi , K ii are the proportional and integral coefficients of the i-th converter in the new energy power station, respectively, N c is the number of converters in the new energy power station, and K avr is the regulation speed of the new energy power station.

13. A voltage emergency control system for the coordination of multiple new energy power stations according to claim 10, characterized in that: Estimating the short - circuit branch reactive current required for transient voltage support according to the fault point and the bus connected to the branch where the fault point is located, the specific calculation includes: ； Where, I s is the reactive current of the short-circuit branch required for transient voltage support, U tar is the target voltage value of the bus to be supported under transient voltage conditions, and z0 is the impedance of the branch where the fault point is located.

14. A voltage emergency control system for the coordination of multiple new energy power stations according to claim 10, characterized in that: Estimating the short - circuit branch reactive current that the proximal bus can provide, the specific calculation includes: Estimating the short - circuit branch reactive current that can be provided according to the type of power source connected to the proximal bus; the types of the power source include synchronous generators and new energy power stations. For multiple proximal buses, add the short - circuit branch reactive currents that each proximal bus can provide.

15. A voltage emergency control system for collaborative operation of multiple new energy power stations according to claim 14, characterized in that: When the power source connected to the proximal bus is a synchronous generator, the short - circuit branch reactive current that the proximal bus can provide is estimated according to the following formula: ； Where, I snG is the reactive current of the short - circuit branch that the synchronous generator connected to the proximal bus can provide, E G is the internal electromotive force of the synchronous generator under the rated condition, z Gs is the impedance between the internal electromotive force of the synchronous generator and the bus, and z0 is the impedance of the branch where the short - circuit fault point is located; When the power source connected to the proximal bus is a new energy power station, the output current limit value of the converter in the new energy power station is used as the calculation basis. At this time, the short - circuit branch reactive current that the proximal bus can provide is estimated according to the following formula: ； Among them, I snC is the reactive current of the short-circuit branch that can be provided by the new energy power station connected to the proximal bus, k c is the current coefficient, I Cmaxf is the output current limit value of the converter, N Cf is the number of converters in the new energy power station.

16. A voltage emergency control system for collaborative operation of multiple new energy power stations according to claim 10, characterized in that: Estimating the short - circuit branch reactive current required to be provided by the remote bus, the specific calculation includes: ； Where I sf is the reactive current of the short - circuit branch required to be provided by the remote bus, I s is the reactive current of the short - circuit branch required for transient voltage support, and I sn is the reactive current of the short - circuit branch that the proximal bus can provide.

17. A voltage emergency control system for the coordination of multiple new energy power stations according to claim 10, characterized in that: Estimating the short - circuit branch reactive current that the new energy power stations in the new power station set S2 can provide, the specific calculation includes: ； Wherein, U tar is the target voltage value of the bus to be supported under the transient voltage condition, and I sfm is the reactive current of the short-circuit branch that can be provided by the m-th new energy power station in the new power station set S2; I sn is the reactive current of the short-circuit branch that can be provided by the proximal bus; z m0min is the sum of the impedance value of the shortest path from the bus to be supported to the bus where the m-th new energy power station in the new power station set S2 is located and the internal resistance; z fs is the connection impedance from the m-th new energy power station in the new power station set S2 to the bus it is connected to, and z0 is the impedance of the branch where the short-circuit fault point is located.

18. A voltage emergency control system for collaborative operation of multiple new energy power stations according to claim 10, characterized in that: According to the voltage emergency control command, each new energy power station switches the control strategy to transient voltage emergency control to provide reactive power support for the bus to be supported. The specific operations include: For any new energy power station, it includes: an active power control loop and a reactive power control loop; in the active power control loop, an active outer loop - current inner loop control structure is adopted, and under the control signal EN, a d-axis voltage for controlling the converter is generated U d ; in the reactive power control loop, a reactive outer loop - current inner loop control structure is adopted, and under the control signal EN, a q-axis voltage for controlling the converter is generated U q ; When any new energy power station receives a voltage emergency control command, the control signal EN = 1, and the generated d-axis voltage for controlling the converter U d and the q-axis voltage for controlling the converter U q are transformed into three-phase voltage signals, and these three-phase voltage signals are used as the modulation wave voltage to perform PWM control on the converter.

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