Voltage emergency control method and system for cooperation of multiple new energy stations

Abstract

The invention discloses a voltage emergency control method and system for cooperation of multiple new energy stations, and the method comprises the steps: taking a bus which is far away from a fault point in buses connected with a fault branch as a to-be-supported bus, and defining a bus which is connected with the bus and is smaller in connection impedance as a near-end bus for a severe three-phase short-circuit fault; other buses connected to the new energy stations in the power grid are defined as far-end buses, the new energy stations capable of carrying out transient voltage support are screened according to the disturbance degree of the far-end buses, and the target stations are sorted according to the adjustable capacity and the adjusting speed index; and estimating reactive current required to be provided by the far-end new energy station based on the reactive current required for increasing the transient voltage, estimating and calculating support current capable of being provided by each far-end station in sequence until the support current of each far-end station meets the reactive current requirement after being accumulated, and issuing an emergency control command to the related station.

Description

Technical Field

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

[0002] The grid connection scale of new energy sources such as wind power and photovoltaic power continues to increase, and the application of large-capacity UHV DC 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: (1) The receiving-end power grid has concentrated loads, and new energy sources are closely coupled with the loads. The frequency and voltage withstand capabilities of new energy power generation equipment are relatively weak. 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 a large area of disconnection may occur, leading to transient voltage instability in the receiving-end power grid.

[0003] (2) Due to the feeding-in of multiple DCs and the grid connection of large-scale new energy sources, synchronous generating units of equal capacity are replaced and withdrawn from operation, and the characteristics of "hollowing out" in 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, during the DC power recovery process, the inverter station will absorb a large amount of reactive power from the system. Coupled with the low power factor operation of heavy-load induction motor loads during the speed recovery process, both further exacerbate the transient voltage problem of the system.

[0004] As the second line of defense for power system stability control, emergency control is targeted at pre-considered fault forms and operating modes. Triggered by fault events, it pre-determines control strategies, comprehensively coordinates the quantity and implementation locations of emergency control measures invested in the whole system, and issues control commands to substations that need to take generator tripping or load shedding control. Usual 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 quickly act 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.

[0005] Power system security and stability emergency control devices have always been the focus of research in the industrial and academic fields. However, due to the uncertainties 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 relatively 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

[0006] Objective of the Invention: To solve the transient voltage security problem of a high-proportion new energy power grid, the present invention proposes a voltage emergency control method and system for collaborative operation of multiple new energy power stations.

[0007] Technical Solution: The first solution is as follows: A voltage emergency control method for collaborative operation of multiple new energy power stations, comprising 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 denote 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; 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, use the new energy power stations connected to the distal buses with a degree of disturbance exceeding the disturbance degree threshold as the reserve adjustment resources, thereby forming a power station set S 1 ; Calculate the adjustable capacity of each new energy power station in the power station set S 1 Arrange the new energy power stations in the power station set S 1 in descending order according to the adjustable capacity, forming a new power station set S 2 ; 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 S 2 can provide; Compare the reactive current of the short-circuit branch that the first new energy power station in the new power station set S 2 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 S 2 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 power station set S 2 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, obtaining the new energy power stations determined to participate in the emergency control; 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; 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.

[0008] 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: ; 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.

[0009] Furthermore, when the adjustable capacities of two new energy power stations are equal, the ranking is determined according to the adjustment speed; The adjustment speed is calculated according to the following formula: ; 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.

[0010] 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: ; 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, z 0 is the impedance of the branch where the fault point is located.

[0011] Furthermore, the reactive current of the short-circuit branch that the proximal bus can provide is estimated. The specific calculation includes: 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 power sources include synchronous generators and new energy power stations; For multiple proximal buses, the reactive currents of the short-circuit branches that each proximal bus can provide are added together.

[0012] Furthermore, when the power source 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: ; 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, and E G is the internal electromotive force of the synchronous generator under the rated operating condition, and z Gs is the impedance between the internal electromotive force of the synchronous generator and the bus, and z 0 is the impedance of the branch where the short - circuit fault point is located; When the device 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 reactive current of the short - circuit branch 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 the new - energy power station connected to the proximal bus 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.

[0013] Furthermore, the estimation of the reactive current of the short - circuit branch that the distal bus needs to provide specifically includes: ; In the formula, I sf is the reactive current of the short - circuit branch that the distal bus 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 bus can provide.

[0014] Furthermore, the estimation of the reactive current of the short - circuit branch that the new - energy power stations in the new station set S 2 can provide specifically includes: ; In the formula, U tar is the target voltage value of the bus to be supported under the transient voltage condition, I sfm is the reactive current of the short - circuit branch that the m - th new - energy power station in the new station set S 2 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 and the internal resistance of the shortest path from the bus to be supported to the bus where the m - th new - energy power station in the new station set S 2 is located; z fs is the connection impedance from the m - th new - energy power station in the new station set S 2 to the bus it is connected to, and z 0is the branch impedance where the short-circuit fault point is located.

[0015] Further, each of the new energy 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: For any new energy 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 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.

[0016] The second solution is: a voltage emergency control system for coordinated operation of multiple new energy stations, including: A fault point and the bus confirmation module connected to 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; the bus directly connected to the bus to be supported and with a connection impedance less than the set threshold is defined as the proximal bus, and the other buses accessing new energy stations are defined 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 steady-state voltage value of any distal bus as the disturbance degree. When a three-phase short-circuit fault occurs, the new energy stations connected to the distal buses with a disturbance degree exceeding the disturbance degree threshold are used as the preparatory adjustment resources, thereby forming a station set S 1 ; calculate the adjustable capacity of each new energy station in the station set S 1 , and sort the new energy stations in the station set S 1 in descending order according to the adjustable capacity to form a new station set S 2 ; A 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 to estimate the short-circuit branch reactive current that the proximal bus can provide and the short-circuit branch reactive current that the distal bus needs to provide; A new energy power station determination module participating in emergency control is used to estimate a new power station set S 2 The short-circuit branch reactive current that the first new energy power station in can provide; Compare the short-circuit branch reactive current that the first new energy power station in the new power station set S 2 can provide with the short-circuit branch reactive current that the distal bus needs to provide. 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 S 2 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 that the distal bus needs to provide. If the requirement is met, determine that the first new energy power station and the second new energy power station participate in emergency control; If the requirement is not met, continue to calculate the short-circuit branch reactive current that other new energy power stations in the new power station set S 2 can provide in sequence, and accumulate until the requirement of the short-circuit branch reactive current that the distal bus needs to provide is met, to obtain the new energy power stations determined to participate in emergency control; A voltage emergency control command issuing module is used to 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 emergency control; A 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 to the control strategy.

[0017] 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: ; 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.

[0018] Furthermore, 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: ; Wherein, 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, and K avr is the regulation speed of the new energy power station.

[0019] Furthermore, 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, the specific calculation includes: ; Wherein, 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 z 0 is the impedance of the branch where the fault point is located.

[0020] Furthermore, estimating the reactive current of the short-circuit branch that the proximal bus can provide, the specific calculation includes: Estimating 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 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.

[0021] Furthermore, when the power source 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: ; Wherein, 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, and z 0 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, using 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 bus can provide is estimated according to the following formula: ; Wherein, 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, I Cmaxf is the output current limit value of the converter, and N Cfis the number of converters in the new energy power station

[0022] Furthermore, estimating the reactive current of the short - circuit branch that the remote bus needs to provide, the specific calculation includes: ; In the formula, I sf is the reactive current of the short - circuit branch that the remote 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 proximal bus can provide.

[0023] Furthermore, estimating the reactive current of the short - circuit branch that the new energy power stations in the new power station set S 2 can provide, the specific calculation includes: ; 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 power station in the new power station set S 2 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 S 2 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 S 2 to the bus it is connected to, z 0 is the impedance of the branch where the short - circuit fault point is located.

[0024] 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 operation includes: 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 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. This three - phase voltage signal is used as the modulation wave voltage to perform PWM control on the converter.

[0025] Beneficial effects: Compared with the prior art, the present invention has the following advantages: (1) For a severe three - phase short - circuit fault with a long duration, the method of the present invention uses the bus far from the fault point in the bus connected to the fault branch as the bus to be supported, defines the bus connected to this bus with a smaller connection impedance as the proximal bus, and defines the other buses in the power grid connected to new - energy power stations as the distal buses. It screens new - energy power stations that can provide transient voltage support according to the disturbance degree of the distal buses, and sorts the target power stations according to the adjustable capacity and regulation speed indexes; estimates the reactive current required by the distal new - energy power stations based on the reactive current required to improve the transient voltage, and sequentially estimates the support current that each distal power station can provide until the sum of the support currents of each distal power station meets the reactive current demand, and issues an emergency control command to the relevant power stations; selects the converter of the power station to start emergency voltage control, changes from the original double - loop control of power outer loop - current inner loop to current single - loop control, and quickly outputs 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 speed and control quantity accuracy in the current emergency voltage control, can effectively utilize the fast - support characteristics of new - energy converters 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; (2) The method of the present invention improves the transient voltage control of new - energy converters, gives full play to their fast and accurate reactive - power output ability, mobilizes the transient voltage support ability of distal new - energy through emergency control, coordinates the available reactive - power sources of the whole network to provide system support for the power grid, and combines the appropriate transient voltage control strategy of the converter with the emergency control of the power grid, which is an effective way to achieve fast transient voltage support under a high - proportion new - energy power grid, and can ensure the safety and stability of the transient voltage of the new - type power system and improve the safe and stable operation level of the power grid; (3) The method of the present invention gives full play to the fast - regulation 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. Description of the Drawings

[0026] 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; Figure 2 It is a block diagram of an improved transient voltage control strategy for a new - energy power station; Figure 3 It is the target bus voltage waveform under the emergency voltage support of the new energy power station. Specific implementation manners

[0027] The technical solution of the present invention will be further elaborated in combination with the accompanying drawings and embodiments.

[0028] Now in combination with Figure 1 , a voltage emergency control method based on the coordination of multiple new energy power stations proposed in this embodiment will be further described. It mainly includes the following steps: Step 1: Through the wide-area monitoring system, monitor the transient voltage event. 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 busbars connected to its branches, and record this busbar as the busbar to be supported; define the busbars directly connected to this busbar and with a connection impedance less than the set threshold as the proximal busbars, and define the other busbars connected to new energy power stations in the power grid as the distal busbars.

[0029] Step 2: After monitoring the occurrence of a three-phase short-circuit fault, set the absolute value of the difference between the current busbar voltage value and the voltage value under the steady-state condition as the degree of disturbance, and set a threshold for the degree of disturbance. Regard the new energy power stations connected to the distal busbars whose degree of disturbance exceeds the set threshold of the degree of disturbance after the fault occurs as the preparatory adjustment resources for transient voltage support, determine the scope of the transient voltage support power stations, and form a power station set S 1 ={c 1 , c 2 , …, c N}, where N is the number of new energy power stations that meet the conditions, and c N is the new energy power station that meets the conditions.

[0030] Step 3: Characterize the reactive power output capacity of the new energy power stations in the power station set S 1 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 the adjustment speed according to formula (2); finally, form a new power station set S 2 ={C 1 , C 2 , …, C N}; (1) 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, I Cmaxiis the current limit value of the i-th converter.

[0031] (2) Among them, 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 regulation speed of the new energy power station, and s represents the complex variable of the Laplace transform.

[0032] Step 4: According to formula (3), estimate the reactive current I s ; (3) Among them, U tar is the target voltage value of the bus to be supported under transient voltage conditions, and z 0 is the impedance of the branch where the fault point is located.

[0033] 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 this power supply 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.

[0034] When the power supply 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 formula (4): The internal resistance of this synchronous generator includes the impedance of the synchronous motor, transformer, and line impedance.

[0035] (4) 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, and z Gs is the impedance between the internal electromotive force of the synchronous generator and the bus.

[0036] When the power supply connected to the proximal bus is a new energy power station, considering the situation where one side of the bus drops significantly due to the 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 formula (5): (5) 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 uses an LCL filter form, k c is less than 1, ICmaxf is the output current limit value of the converter, N Cf is the number of converters in the new energy power station

[0037] Estimate the reactive current I of the short - circuit branch that the remote bus needs to provide according to Equation (6) sf ; (6) where, I sn is the reactive current provided by the generator or new energy power station connected to the proximal bus

[0038] Step 5: Estimate the reactive current of the short - circuit branch that the new energy power stations in the new station set S can provide according to Equation (7) 2 : (7) where, I sfm is the reactive current of the short - circuit branch provided by the m - th remote new energy power station in the new station set S; I 2 is the reactive current of the short - circuit branch that the proximal bus can provide; z sn is 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 power station in the new station set S is located and the internal resistance; z m0min is the connection impedance from the m - th new energy power station in the new station set S to the bus it is connected to, z 2 is the impedance of the branch where the short - circuit fault point is located fs is the new station set S 2 is the new station set S 0 is the new station set S

[0039] Compare the reactive current of the short - circuit branch that the new energy power station C in the new station set S can provide with the reactive current I of the short - circuit branch that the remote bus needs to provide 2 If the demand can be met, determine that the new energy power station C 1 participates in 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 power station C in the station set S sf can provide, and add it to the reactive current of the short - circuit branch that the new energy power station C 1 can provide, then compare it with the reactive current I of the short - circuit branch that the remote bus needs to provide 2 If the demand is met, determine that the new energy power station C 2 and the new energy power station C 1 participate in emergency control. If the demand cannot be met, continue to calculate the reactive current of the short - circuit branch that other new energy power stations can provide in sequence until the cumulative value meets the reactive current I of the short - circuit branch that the remote bus needs to provide sf 1 2 sf ​​​requirements and determine the remote new energy power stations participating in emergency control.

[0040] Send 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.

[0041] Step 6: 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: 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 inner and 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 and outer 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 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.

[0042] There are various implementation methods for inner and outer loop control. Now, in combination with Figure 2 this, the inner and outer loop control adopted in this embodiment is further described.

[0043] 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.

[0044] In the active power control loop, the difference between the active power given value P ref and the actual active power P is calculated, and 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 a d-axis current given value i gdref ; the d-axis current given value i gdref and the actual d-axis current value i gdThe difference is adjusted by a second proportional-integral controller to output a first intermediate voltage; the first intermediate voltage minus U cd , and the voltage of the inductor L connected to the converter is added to generate the d-axis voltage for controlling the converter U d ; where is the angular velocity.

[0045] In the reactive power control loop, the reactive power reference value Q ref is subtracted from the actual reactive power Q, and the difference between the two is adjusted by a third proportional-integral controller to output the machine-side current of the q-axis converter; under the control signal EN, the machine-side current of the q-axis converter is limited to generate the q-axis current reference value i gqref ; the difference between the q-axis current reference value i gqref and the actual q-axis current i gq is adjusted by a fourth proportional-integral controller to output a second intermediate voltage; the second intermediate voltage minus U cq the voltage of the inductor L connected to the converter is added to generate the q-axis voltage for controlling the converter U q .

[0046] Among them, the actual d-axis current i gd and the actual q-axis current i gq are obtained by inputting the machine-side current of the converter I g and the phase angle obtained by the phase-locked loop θ pll into the abc / dq converter for conversion. There are also different addition or subtraction representation methods according to different dq transformation forms.

[0047] After receiving the emergency voltage control command, the new energy power station switches 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 gmaxis the output current limit value of the converter. The given value of the active current control is compared with the actual value of the active current, which serves as the input for the active current control. The given value of the reactive current control is compared with the actual value of the reactive current, which serves as the input for the reactive current control. The outputs of the active and reactive controls are inversely transformed from dq to 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, with the unit of seconds, and the ordinate is the bus voltage connected to the substation, with the unit of p.u. Curves 1 and 2 are the voltage waveforms of the bus to be supported with only the proximal reactive source and with the reactive power support of the remote new energy substation respectively. The fault occurs at 1 s, and the fault duration is 1 s. It can be seen that the reactive power support of the remote new energy substation 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.

[0048] Step 7: 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.

Claims

1. A voltage emergency control method for multiple renewable energy stations, characterized in that: The following steps are involved: When a three-phase short-circuit fault occurs, the fault point and the bus connected to the branch where the fault point is located are determined, and the bus is recorded as the bus to be supported; the bus directly connected to the bus to be supported and with a connection impedance less than the set threshold is defined as the near-end bus, and other buses connected to the new energy station are defined as the far-end bus; For any remote bus, the absolute value of the difference between its current voltage value and the voltage value in the steady state is defined as the degree of disturbance. When a three-phase short-circuit fault occurs, the new energy station connected to the remote bus whose degree of disturbance exceeds the threshold of the degree of disturbance is used as a reserve adjustment resource, thereby forming a station set S1; the adjustable capacity of each new energy station in the station set S1 is calculated, and the new energy stations in the station set S1 are sorted from large to small according to the adjustable capacity to form a new station set S2; according to the bus connected to the fault point and the branch where the fault point is located, the short-circuit branch reactive current required for transient voltage support is estimated, as well as the short-circuit branch reactive current that can be provided by the proximal bus and the short-circuit branch reactive current that the remote bus needs to provide are estimated; Estimate the short-circuit branch reactive current that can be provided by the first new energy station in the new station set S2; compare the short-circuit branch reactive current that can be provided by the first new energy station in the new station set S2 with the short-circuit branch reactive current that needs to be provided by the remote bus. If the demand is met, the first new energy station is determined to participate in the emergency control; if the demand is not met, estimate the short-circuit branch reactive current that can be provided by the second new energy station in the new station set S2, add it to the short-circuit branch reactive current that can be provided by the first new energy station, and compare the added value with the short-circuit branch reactive current that needs to be provided by the remote bus. If the demand is met, the first new energy station and the second new energy station are determined to participate in the emergency control; if the demand is not met, continue to calculate the short-circuit branch reactive current that can be provided by other new energy stations in the new station set S2 in sequence, accumulate until the demand for the short-circuit branch reactive current required by the remote bus is met, and obtain the new energy station that is determined to participate in the emergency control; Issue voltage emergency control commands to the new energy stations connected to the near-end busbar and the new energy stations determined to participate in emergency control; Each new energy station switches the control strategy to transient voltage emergency control according to the voltage emergency control command to provide reactive power support for the busbar to be supported; After the three-phase short-circuit fault is eliminated, each new energy station will release the transient voltage emergency control and switch to control strategy.

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

3. The voltage emergency control method for multiple renewable energy stations in coordination according to claim 1 is characterized in that: When the adjustable capacities of two new energy stations are equal, the ranking is determined by the speed of adjustment; The speed of adjustment is calculated according to the following formula: ； In the formula, K pi , K ii are the proportional and integral coefficients of the i-th converter in the new energy station, N c is the number of converters in the new energy station, K avr It is the adjustment speed of new energy stations.

4. The voltage emergency control method for multiple renewable energy stations in coordination according to claim 1 is characterized in that: The estimation of the short-circuit branch reactive current required for transient voltage support based on the fault point and the bus connected to the branch where the fault point is located includes: ； In the formula, I s is the short-circuit branch reactive current required for transient voltage support, U tar is the target voltage value of the busbar to be supported under transient voltage conditions, and z0 is the impedance of the branch where the fault point is located.

5. The voltage emergency control method for multiple renewable energy stations in coordination according to claim 1 is characterized by: The estimated short-circuit branch reactive current that the near-end bus can provide includes: According to the type of power source connected to the proximal busbar, estimate the short-circuit branch reactive current that can be provided; the types of power sources include synchronous generators and new energy stations; For multiple proximal busbars, add up the short-circuit branch reactive currents that each proximal busbar can provide.

6. The voltage emergency control method for multiple renewable energy stations in coordination according to claim 5 is characterized by: When the near-end bus is connected to a synchronous generator, the short-circuit branch reactive current that the near-end bus can provide can be estimated using the following formula: ； In the formula, I snG The short-circuit branch reactive current that the synchronous generator connected to the near-end bus can provide, E G is the internal potential of the synchronous generator under rated operating conditions, z Gs is the impedance between the potential inside the synchronous generator and the busbar, z0 is the branch impedance where the short-circuit fault point is located; When the near-end bus 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 short-circuit branch reactive current that the near-end bus can provide is estimated according to the following formula: ； Among them, I snC k is the short-circuit branch reactive current that the new energy station connected to the near-end busbar can provide, 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.

7. The voltage emergency control method for multiple renewable energy stations in coordination according to claim 1 is characterized by: The estimation of the short-circuit branch reactive current required to be provided by the remote busbar specifically includes the following calculations: ； In the formula, I sf The short-circuit branch reactive current required by the remote busbar, I s is the short-circuit branch reactive current required for transient voltage support, I sn It is the short-circuit branch reactive current that can be provided by the near-end busbar.

8. The voltage emergency control method for multiple renewable energy stations in coordination according to claim 1 is characterized by: Estimate the short-circuit branch reactive current that can be provided by the new energy stations in the new station set S2. The specific calculation includes: ； Where U tar is the target voltage value of the busbar to be supported under transient voltage conditions, I sfm I is the short-circuit branch reactive current that can be provided by the mth new energy station in the new station set S2; sn The short-circuit branch reactive current that the near-end busbar can provide; m0min is the sum of the impedance value and internal resistance of the shortest path from the bus to be supported to the mth new energy station in the new station set S2; fs is the connection impedance from the mth new energy station in the new station set S2 to the bus it is connected to, and z0 is the branch impedance where the short-circuit fault point is located.

9. The voltage emergency control method for multiple renewable energy stations in coordination according to claim 1 is characterized by: Each of the above-mentioned new energy stations switches the control strategy to transient voltage emergency control according to the voltage emergency control command to provide reactive power support for the busbar to be supported. The specific operations include: For any new energy 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 station receives a voltage emergency control command, the control signal EN=1, which generates the d-axis voltage for controlling the converter. U d and the q-axis voltage used to control the converter U q The three-phase voltage signal is converted into a three-phase voltage signal, and the three-phase voltage signal is used as a modulated wave voltage to perform PWM control on the converter.

10. A voltage emergency control system for multiple renewable energy stations, characterized by: include: The bus confirmation module of the fault point and the branch where the fault point is located is used to determine the bus connected to the fault point and the branch where the fault point is located when a three-phase short circuit fault occurs, and record the bus as the bus to be supported; define the bus directly connected to the bus to be supported and the connection impedance is less than the set threshold as the near-end bus, and define other buses connected to the new energy station as the far-end bus; The station set forming module is used to define the absolute value of the difference between the current voltage value and the voltage value in the steady state of any remote bus as the disturbance degree. When a three-phase short circuit fault occurs, the new energy station connected to the remote bus whose disturbance degree exceeds the disturbance degree threshold is used as a reserve adjustment resource, thereby forming a station set S1; calculate the adjustable capacity of each new energy station in the station set S1, and sort the new energy stations in the station set S1 according to the adjustable capacity from large to small, so as to form a new station set S2; 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, as well as to estimate the short-circuit branch reactive current that can be provided by the proximal bus and the short-circuit branch reactive current that needs to be provided by the remote bus; The module for determining the new energy station participating in the emergency control is used to estimate the short-circuit branch reactive current that can be provided by the first new energy station in the new station set S2; compare the short-circuit branch reactive current that can be provided by the first new energy station in the new station set S2 with the short-circuit branch reactive current that needs to be provided by the remote bus. If the demand is met, the first new energy station is determined to participate in the emergency control; if the demand is not met, the short-circuit branch reactive current that can be provided by the second new energy station in the new station set S2 is estimated, and the short-circuit branch reactive current that can be provided by the first new energy station is added, and the added value is compared with the short-circuit branch reactive current that needs to be provided by the remote bus. If the demand is met, the first new energy station and the second new energy station are determined to participate in the emergency control; if the demand is not met, the short-circuit branch reactive current that can be provided by other new energy stations in the new station set S2 is calculated in sequence, and the accumulated value is obtained until the demand for the short-circuit branch reactive current required to be provided by the remote bus is met, so as to obtain the new energy station that participates in the emergency control; The voltage emergency control command issuing module is used to issue voltage emergency control commands to the new energy stations connected to the proximal bus and the new energy stations determined to participate in the emergency control; A 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 support for the busbar to be supported; After the three-phase short-circuit fault is eliminated, each new energy station will release the transient voltage emergency control and switch to control strategy.

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

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

13. The voltage emergency control system for coordination of multiple renewable energy stations according to claim 10, characterized in that: The estimation of the short-circuit branch reactive current required for transient voltage support based on the fault point and the bus connected to the branch where the fault point is located includes: ； In the formula, I s is the short-circuit branch reactive current required for transient voltage support, U tar is the target voltage value of the busbar to be supported under transient voltage conditions, and z0 is the impedance of the branch where the fault point is located.

14. The voltage emergency control system for coordination of multiple renewable energy stations according to claim 10, characterized in that: The estimated short-circuit branch reactive current that the near-end bus can provide includes: According to the type of power source connected to the proximal busbar, estimate the short-circuit branch reactive current that can be provided; the types of power sources include synchronous generators and new energy stations; For multiple proximal busbars, add up the short-circuit branch reactive currents that each proximal busbar can provide.

15. A voltage emergency control system for coordination of multiple renewable energy stations according to claim 14, characterized in that: When the near-end bus is connected to a synchronous generator, the short-circuit branch reactive current that the near-end bus can provide can be estimated using the following formula: ； In the formula, I snG The short-circuit branch reactive current that the synchronous generator connected to the near-end bus can provide, E G is the internal potential of the synchronous generator under rated operating conditions, z Gs is the impedance between the potential inside the synchronous generator and the busbar, z0 is the branch impedance where the short-circuit fault point is located; When the near-end bus 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 short-circuit branch reactive current that the near-end bus can provide is estimated according to the following formula: ； Among them, I snC k is the short-circuit branch reactive current that the new energy station connected to the near-end busbar can provide, 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.

16. A voltage emergency control system for coordination of multiple renewable energy stations according to claim 10, characterized in that: The estimation of the short-circuit branch reactive current required to be provided by the remote busbar specifically includes the following calculations: ； In the formula, I sf The short-circuit branch reactive current required by the remote busbar, I s is the short-circuit branch reactive current required for transient voltage support, I sn It is the short-circuit branch reactive current that can be provided by the near-end busbar.

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

18. The voltage emergency control system for coordination of multiple renewable energy stations according to claim 10, characterized in that: Each of the above-mentioned new energy stations switches the control strategy to transient voltage emergency control according to the voltage emergency control command to provide reactive power support for the busbar to be supported. The specific operations include: For any new energy 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 station receives a voltage emergency control command, the control signal EN=1, which generates the d-axis voltage for controlling the converter. U d and the q-axis voltage used to control the converter U q The three-phase voltage signal is converted into a three-phase voltage signal, and the three-phase voltage signal is used as a modulated wave voltage to perform PWM control on the converter.

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