An AVC control method and device based on available phase modulation capacity of a constant-speed pumped storage unit

Abstract

This invention pertains to the power industry and discloses an AVC control method and device based on the available phase-shifting capacity of a constant-speed pumped-storage unit. The method includes: acquiring real-time operating status data of the constant-speed pumped-storage unit during phase-shifting operation and calculating the unit's current multi-dimensional safety margin; calculating the phase-shifting capacity boundaries of the unit's lagging and leading phases based on the synchronous machine's steady-state capability, combined with various constraints and the multi-dimensional safety margin, and feeding these boundaries back to the upper-level automatic voltage control system (AVC) as real-time constraints. This allows the AVC to generate a reactive power target value that does not exceed the current safety capacity when distributing reactive power, using these real-time constraints as boundaries; and performing a safety fallback correction locally on the unit when the reactive power target value exceeds the latest available phase-shifting capacity boundary, limiting it within the current safety boundary. This invention can release the phase-shifting capability of the constant-speed pumped-storage unit while ensuring its electrical and thermal stability, thereby improving low-voltage support and overvoltage suppression effects.

Description

Technical Field

[0001] This invention belongs to the field of power, and particularly relates to an AVC control method and device based on the available phase-adjusting capacity of a constant-speed pumped-storage unit. Background Technology

[0002] Pumped storage power stations are an important flexible regulation resource for power systems. Constant-speed pumped storage units can operate as synchronous condensers under phase-changing conditions, regulating reactive power through the excitation system to provide delayed reactive power or absorb advanced reactive power, thereby supporting bus voltage, suppressing overvoltage, and improving voltage stability margin.

[0003] Existing power plant AVC or upstream voltage and reactive power control systems typically allocate reactive power based on rated reactive power capacity, offline PQ capability curves, phase advance test results, or fixed upper and lower reactive power limits. This method is simple to implement and has a large margin, but it is difficult to reflect the impact of real-time changes in generator terminal voltage, stator current, excitation state, power angle, and temperature rise on phase adjustment capability.

[0004] When there are still margins in the terminal voltage, stator current, excitation system, and temperature rise, the unit can provide more delayed reactive power; when the low excitation limit and power angle stability margin are sufficient, the unit can also absorb more advanced reactive power. If the AVC still uses a fixed conservative boundary, it will result in insufficient utilization of the phasing capability. Field tests of existing pumped storage units have shown that the traditional design reactive power range of a 300MW pumped storage unit under pumping conditions is ±6Mvar, and field tests can stably increase reactive power to 70Mvar, while the terminal voltage, excitation current, and temperature do not reach the limit values. This case illustrates that there may be a large difference between the fixed design range and the actual safety capability, and using a fixed conservative boundary may not fully reflect the unit's real-time phasing capability.

[0005] If the AVC directly issues a large reactive power target, and then the generator unit limits it locally, the scheduling target may not be achieved. Therefore, it is necessary for the generator unit to calculate the available phase-shifting capacity boundary in real time and feed it back to the AVC, so that the AVC can use real-time capacity constraints during allocation. Existing technologies mostly rely on offline capacity curves, static phase-shifting tests, or fixed reactive power limits, lacking a real-time available phase-shifting capacity assessment and feedback mechanism for AVC-constrained allocation. Summary of the Invention

[0006] In view of this, the present invention discloses an AVC control method and device based on the available phase-adjusting capacity of a constant-speed pumped-storage unit, which can solve the shortcomings of related technologies.

[0007] To achieve the above objectives, the present invention discloses the following technical solution: According to a first aspect of the present invention, an AVC control method based on the available phase-shifting capacity of a constant-speed pumped-storage unit is proposed, comprising: Real-time operating status data of the constant-speed pumped-storage unit during phase-shifting operation are collected, and the real-time operating status data reflects the electrical and thermal operating status of the unit. Based on the current multi-dimensional safety margin of the real-time operating status quantizer, the multi-dimensional safety margin respectively characterizes the safety distance of the respective safety limits of terminal voltage, stator current, excitation state, low excitation limit, power angle stability and temperature rise distance; Based on the steady-state capability relationship of the synchronous machine, and combined with the stator current limit, overexcitation limit, underexcitation limit, power angle stability limit, and the aforementioned multi-dimensional safety margin, the current available late-phase phase-shifting capacity boundary and the current available early-phase phase-shifting capacity boundary of the constant-speed pumped-storage unit are calculated. The current available late-phase modulation capacity boundary and the current available early-phase modulation capacity boundary are fed back to the upper automatic voltage control system (AVC) as real-time constraints, so that when the AVC performs reactive power distribution, it uses the real-time constraints as the boundary to generate a reactive power target value that does not exceed the current safety capacity. When the reactive power target value exceeds the current latest available phase-shifting capacity boundary, the reactive power target value is corrected locally on the unit to ensure that it is limited to the current safety boundary, and the boundary change and unmet capacity information are fed back to the AVC.

[0008] According to a second aspect of the present invention, an AVC control device based on the available phase-shifting capacity of a constant-speed pumped-storage unit is provided, comprising: Data Acquisition Unit: Collects real-time operating status data of the constant-speed pumped-storage unit during phase-shifting operation. The real-time operating status data reflects the electrical and thermal operating status of the unit. First calculation unit: Based on the real-time operating status quantity, the computer group's current multi-dimensional safety margin, which represents the safety distance of the respective safety limits of terminal voltage, stator current, excitation state, low excitation limit, power angle stability and temperature rise distance; The second calculation unit calculates the current available late-phase phase-shifting capacity boundary and the current available early-phase phase-shifting capacity boundary of the constant-speed pumped-storage unit based on the steady-state capability relationship of the synchronous machine, combined with stator current limit, over-excitation limit, under-excitation limit, power angle stability limit and the multi-dimensional safety margin. Feedback unit: Feeds the current available late-phase modulation capacity boundary and the current available early-phase modulation capacity boundary as real-time constraints to the upper automatic voltage control system (AVC), so that when the AVC performs reactive power distribution, it uses the real-time constraints as the boundary to generate a reactive power target value that does not exceed the current safety capacity. Correction Unit: When the reactive power target value exceeds the current latest available phase-shifting capacity boundary, the unit performs a safety fallback correction on the reactive power target value locally to limit it within the current safety boundary, and feeds back the boundary change and unmet capacity information to the AVC.

[0009] According to a third aspect of the present invention, an electronic device is provided, comprising: processor; Memory used to store processor-executable instructions; The processor implements the steps of the method as described in the first aspect by running the executable instructions.

[0010] According to a fourth aspect of the invention, a computer-readable storage medium is provided having computer instructions stored thereon that, when executed by a processor, implement the steps of the method as described in the first aspect.

[0011] As can be seen from the above technical solutions, the beneficial effects of the AVC control method and device based on the available phase-shifting capacity of a constant-speed pumped-storage unit disclosed in this invention are as follows: First, by collecting the electrical and thermal operating status of the unit in real time, multi-dimensional safety margins are calculated. Based on the steady-state capability relationship of the synchronous machine, combined with stator current limits, overexcitation limits, underexcitation limits, power angle stability limits, and multi-dimensional safety margins, the available late-phase and leading-phase phase-shifting capacity boundaries are calculated online. This enables AVC to obtain the current real available phase-shifting capacity of the constant-speed pumped-storage unit, solving the problem of wasted phase-shifting capacity caused by fixed conservative boundaries.

[0012] Second, the real-time capacity boundary is fed back to the AVC as a constraint, so that when the AVC performs reactive power allocation, it generates a reactive power target value that does not exceed the current safety capacity based on the real-time constraint. This does not replace the original reactive power allocation function of the AVC, but only provides it with a real-time boundary constraint. This avoids the scheduling target from failing due to simple local limiting, and also reduces the capacity waste caused by fixed conservative boundaries.

[0013] Third, when the reactive power target value issued by the AVC exceeds the current latest available phase-shifting capacity boundary, the unit performs a safety fallback correction locally and feeds back the boundary change and unmet capacity information to the AVC, forming a safety closed-loop control. This ensures the electrical and thermal stability and safety of the unit while enabling the AVC to coordinate other reactive power resources within the station for compensation.

[0014] Fourth, the capacity boundary is calculated based on the steady-state capability relationship of the synchronous machine, with clear physical basis and good real-time adaptability. It can fully release the reactive power support capability of the constant-speed pumped-storage unit under phase-shifting conditions and improve the low-voltage support and overvoltage suppression effect. Attached Figure Description

[0015] Figure 1 This is a flowchart of an exemplary embodiment of an AVC control method based on the available phase-shifting capacity of a constant-speed pumped-storage unit; Figure 2This is a flowchart of an exemplary embodiment of a method for online assessment of the available phase-shifting capacity and AVC collaborative control of a constant-speed pumped-storage unit; Figure 3 This is a schematic diagram illustrating a comparison of the phase-shifting capacity boundaries of a constant-speed pumped-storage unit, provided in an exemplary embodiment. Figure 4 This is a schematic diagram illustrating a comparison of bus voltage responses provided in an exemplary embodiment; Figure 5 This is a schematic structural diagram of a device provided in an exemplary embodiment; Figure 6 This is a block diagram of an AVC control device based on the available phase-adjusting capacity of a constant-speed pumped-storage unit, provided as an exemplary embodiment. Detailed Implementation

[0016] Exemplary embodiments will now be described in detail, examples of which are illustrated in the accompanying drawings. When the following description relates to the drawings, unless otherwise indicated, the same numerals in different drawings denote the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with one or more embodiments of the present invention. Rather, they are merely examples of apparatuses and methods consistent with some aspects of one or more embodiments of the present invention as detailed in the appended claims.

[0017] It should be noted that the steps of the corresponding methods in other embodiments are not necessarily performed in the order shown and described in this invention. In some other embodiments, the methods may include more or fewer steps than those described in this invention. Furthermore, a single step described in this invention may be broken down into multiple steps in other embodiments; and multiple steps described in this invention may be combined into a single step in other embodiments.

[0018] To address the shortcomings in related technologies, this invention proposes an AVC control method and device based on the available phase-adjusting capacity of a constant-speed pumped-storage unit.

[0019] Figure 1 This is a flowchart illustrating an exemplary embodiment of an AVC control method based on the available phase-shifting capacity of a constant-speed pumped-storage unit. (See attached diagram.) Figure 1 As shown, the method may include the following steps: Step 101: Collect real-time operating status data of the constant-speed pumped storage unit during phase-shifting operation. The real-time operating status data reflects the electrical and thermal operating status of the unit.

[0020] The unit's local monitoring system, excitation system, and measuring devices periodically collect real-time status data reflecting the unit's electrical and thermal operating conditions.

[0021] Specifically, the real-time operating status quantities include: terminal voltage, grid bus voltage, stator current, excitation current, actual reactive power, equivalent active power loss, rotor power angle, stator winding temperature, rotor winding temperature, core end temperature, under-excitation limit state, and over-excitation limit state.

[0022] The sampling period for electrical status variables is determined based on the real-time performance indicators of the hydropower station's computer monitoring system. The acquisition period for electrical analog quantities and the update period for the real-time database both do not exceed 1 second. Capacity boundaries are recalculated after each batch of electrical status variable updates; therefore, the evaluation period is set to 1 second. Temperature measurements are taken from the latest valid values ​​at the measuring points, typically within 1 second. Collecting real-time operating status variables provides a comprehensive and real-time data foundation for subsequent margin calculations, ensuring that the evaluation results reflect the unit's current true condition.

[0023] Step 102: Based on the current multi-dimensional safety margin of the real-time operating status quantizer, the multi-dimensional safety margin respectively represents the safety distance of the safety limit of the terminal voltage, stator current, excitation state, low excitation limit, power angle stability and temperature rise distance.

[0024] Specifically, the multi-dimensional safety margin includes terminal voltage margin, stator current margin, magnetomotive force margin, under-excitation limitation margin, power angle stability margin, and temperature rise margin. All margins are normalized to the interval [0,1]. When the calculated result is less than zero, the value is zero, and when it is greater than one, the value is one.

[0025] Terminal voltage margin is used to characterize the safe distance between the upper and lower allowable limits of terminal voltage. The terminal voltage margin is the minimum of the following two ratios and the value 1: the first ratio is the difference between the upper allowable limit of terminal voltage and the current terminal voltage, divided by the difference between the upper allowable limit of terminal voltage and the rated terminal voltage; the second ratio is the difference between the current terminal voltage and the lower allowable limit of terminal voltage, divided by the difference between the rated terminal voltage and the lower allowable limit of terminal voltage. The calculation formula is as follows: ; In the formula, This represents the terminal voltage margin within the k-th control cycle, used to characterize the safe distance between the terminal voltage and the upper and lower limits of the allowable range. This represents the terminal voltage collected during the k-th control cycle; Indicates the upper limit of the allowable terminal voltage; Indicates the lower limit of the allowable terminal voltage; This indicates the rated value of the terminal voltage.

[0026] The stator current margin is used to characterize the safe distance between the stator current and its maximum allowable value. The stator current margin is calculated as the difference between the maximum allowable stator current and the current stator current, divided by the difference between the maximum allowable stator current and the rated stator current. The formula is as follows: ; In the formula, This represents the stator current margin during the k-th control cycle; This represents the stator current collected during the k-th control cycle; Indicates the maximum allowable value of stator current; This indicates the rated value of the stator current.

[0027] The excitation potential margin is used to characterize the safe distance between the excitation potential of the synchronous machine and the over-excitation limit. The excitation potential margin is calculated as the difference between the maximum permissible excitation EMF in the current control cycle and the current synchronous machine excitation EMF, divided by the difference between the maximum permissible excitation EMF in the current control cycle and the rated excitation EMF. The calculation formula is as follows: ; In the formula, This represents the excitation potential margin during the k-th control cycle; This represents the synchronous motor excitation electromotive force during the k-th control cycle; This represents the maximum permissible excitation electromotive force during the k-th control cycle; This indicates the rated excitation electromotive force.

[0028] The underexcitation limit margin is used to characterize the safe distance between the synchronous machine's magnetomotive force and the underexcitation limit boundary. The underexcitation limit margin is calculated as the difference between the current synchronous machine magnetomotive force and the minimum permissible magnetomotive force corresponding to the underexcitation limit, divided by the difference between the rated magnetomotive force and the minimum permissible magnetomotive force corresponding to the underexcitation limit. The calculation formula is as follows: ; In the formula, This indicates the low excitation limit margin during the k-th control cycle; This represents the synchronous motor excitation electromotive force during the k-th control cycle; This represents the minimum permissible excitation electromotive force corresponding to the low excitation limit during the k-th control cycle; This indicates the rated excitation electromotive force.

[0029] The power angle stability margin is used to characterize the safe distance between the rotor power angle and the allowable power angle stability limit. The power angle stability margin is calculated as follows: (the difference between the absolute value of the current rotor power angle and the maximum allowable power angle stability limit) divided by the difference between the maximum allowable power angle stability limit and the rated operating power angle. ; In the formula, This represents the power angle stability margin during the k-th control cycle; This represents the rotor power angle during the k-th control cycle; This indicates the maximum permissible power angle stability limit; This indicates the rated operating power angle.

[0030] Temperature rise margin is used to characterize the safe distance between the stator winding, rotor winding, and core end and the upper limit of the allowable temperature. The temperature rise margin is taken as the minimum of the following three ratios: The first ratio is the difference between the maximum allowable temperature of the stator winding and the current stator winding temperature, divided by the difference between the maximum allowable temperature of the stator winding and the rated operating temperature of the stator winding; the second ratio is the difference between the maximum allowable temperature of the rotor winding and the current rotor winding temperature, divided by the difference between the maximum allowable temperature of the rotor winding and the rated operating temperature of the rotor winding; the third ratio is the difference between the maximum allowable temperature of the core end and the current core end temperature, divided by the difference between the maximum allowable temperature of the core end and the rated operating temperature of the core end. The calculation formula is as follows: ; In the formula, This represents the temperature rise margin during the k-th control cycle; These represent the stator winding temperature, rotor winding temperature, and core end temperature during the k-th control cycle, respectively. These represent the maximum allowable temperatures for the stator winding, rotor winding, and core ends, respectively. These represent the rated operating temperatures of the stator winding, rotor winding, and core ends, respectively.

[0031] If any of the above margin calculation results is less than zero, it is set to zero; if it is greater than one, it is set to one.

[0032] Constraints with different dimensions and physical meanings are unified and normalized into safety distance characterization values, providing standardized input for subsequent calculation of comprehensive margin coefficients and capacity boundaries.

[0033] Step 103: Based on the steady-state capability relationship of the synchronous machine, and combined with the stator current limit, overexcitation limit, underexcitation limit, power angle stability limit, and the multi-dimensional safety margin, calculate the current available late-phase phase-shifting capacity boundary and the current available early-phase phase-shifting capacity boundary of the constant-speed pumped-storage unit.

[0034] The steady-state capability of a synchronous machine satisfies the following relationship: the square of the synchronous machine's excitation electromotive force is equal to the square of the sum of the product of the terminal voltage, the direct-axis synchronous reactance, and the reactive power, divided by the terminal voltage, plus the square of the product of the direct-axis synchronous reactance and the equivalent active power loss, divided by the terminal voltage. The calculation formula is as follows: ; in, This represents the synchronous motor excitation electromotive force during the k-th control cycle; This represents the terminal voltage during the k-th control cycle; Indicates direct-axis synchronous reactance; This represents the reactive power of the unit during the k-th control cycle; This represents the active power of the unit in the k-th control cycle. Under phase-shifting conditions, it usually represents the equivalent active power loss calculated from mechanical losses, wind friction losses, and electrical losses. The equivalent active power loss is determined based on the phase-shifting test data of the power plant and the online measured active power of the unit.

[0035] The stator current limit satisfies the condition that the sum of the square of the equivalent active power loss and the square of the reactive power does not exceed the square of the product of the terminal voltage and the maximum allowable stator current. The calculation formula is as follows: ; in, This represents the maximum allowable stator current during the k-th control cycle.

[0036] The power angle stability limit ensures that the rotor power angle does not exceed the maximum permissible power angle stability limit. The power angle stability constraint is expressed by the following formula: ; in, This represents the rotor power angle during the k-th control cycle; This indicates the maximum permissible power angle stability limit.

[0037] Under phase-shifting conditions, the equivalent active power loss represents the equivalent active power loss calculated from mechanical losses, wind friction losses, and electrical losses. It is determined based on the phase-shifting test data of the power plant and the online measured active power of the unit. The typical value range is 1.54% of the rated capacity. For example, for a unit with a rated capacity of 388.9 MVA, the equivalent active power loss is about 6 MW.

[0038] This section provides an accurate mathematical model for capacity boundary calculation. In particular, the non-zero value of the equivalent active power loss reflects the real physical loss under phase modulation conditions, which is different from the assumption of P≈0 in conventional synchronous machines.

[0039] In one embodiment, within each control cycle, based on the multi-dimensional safety margin obtained by the computer within that cycle, the late-phase integrated margin coefficient and the advanced-phase integrated margin coefficient of the current control cycle are respectively formed and used as global safety scaling factors in the corresponding running direction. These factors are used to transfer the minimum margin in the multi-dimensional safety margin to the capacity boundary calculation, so that the final available capacity shrinks proportionally as the tightest constraint tightens.

[0040] The late-phase integrated margin coefficient is taken as the minimum value among the terminal voltage margin, stator current margin, magnetomotive force margin, and temperature rise margin. The expression for the late-phase integrated margin coefficient is as follows: ; In the formula, This represents the late-phase integrated margin coefficient during the k-th control cycle.

[0041] The overall margin factor for the advancing phase is taken as the minimum value among the terminal voltage margin, stator current margin, under-excitation limiting margin, power angle stability margin, and temperature rise margin. The expression for the overall margin factor for the advancing phase is as follows: ; In the formula, This represents the phase advance comprehensive margin coefficient in the k-th control cycle.

[0042] This embodiment clarifies the dynamic formation method and scaling effect of the comprehensive margin coefficient, realizing the weakest link effect—when any constraint is tightened, the comprehensive coefficient automatically decreases, so that the final available capacity is reduced proportionally, ensuring the safety margin under multiple constraints.

[0043] Furthermore, the usable late-phase modulation capacity boundary can be equal to the safety factor multiplied by the late-phase comprehensive margin coefficient, and then multiplied by the smaller of the late-phase reactive power upper limit determined by the stator current limit and the late-phase reactive power upper limit determined by the overexcitation limit; the expression for the usable late-phase modulation capacity boundary is as follows: ; In the formula, This represents the current available late-phase modulation capacity boundary within the k-th control cycle; Indicates the safety factor; Indicates the late-phase aggregation margin coefficient; This indicates the upper limit of delayed reactive power determined by the stator current limit; This represents the upper limit of delayed-phase reactive power determined by the maximum excitation or overexcitation limit; safety factor. Generally, 0.9 is used, which is determined based on the requirement of reserving a 10% reactive power capacity margin in technical guidelines.

[0044] The usable leading-phase adjustment capacity boundary is equal to the safety factor multiplied by the leading-phase comprehensive margin coefficient, and then multiplied by the maximum value among the leading-phase reactive power lower limit determined by stator current limitation, leading-phase reactive power lower limit determined by low excitation limitation, and leading-phase reactive power lower limit determined by power angle stability limitation; the expression for the usable leading-phase adjustment capacity boundary is as follows: ; In the formula, This represents the current available phase advance modulation capacity boundary within the k-th control cycle; Indicates the safety factor; Indicates the overall margin coefficient of the advanced phase; This indicates the lower limit of the advancing reactive power determined by the stator current limit; This represents the lower limit of the advancing reactive power determined by the low excitation limit; The lower limit of reactive power in the leading phase is determined by the power angle stability limit.

[0045] If the lower limit of reactive power for each phase is negative, the maximum value, i.e., the smallest absolute value, is taken, which still corresponds to the strictest restriction.

[0046] This embodiment ensures that the calculated capacity boundary fully releases the phase modulation capability while leaving a safety margin through dual scaling of the safety factor and the comprehensive margin factor, as well as the reasonable logic of taking the minimum for late phase and the maximum for advanced phase.

[0047] Step 104: Feed the current available late-phase modulation capacity boundary and the current available early-phase modulation capacity boundary as real-time constraints to the upper automatic voltage control system (AVC), so that when the AVC performs reactive power distribution, it uses the real-time constraints as the boundary to generate a reactive power target value that does not exceed the current safety capacity.

[0048] This also includes: calculating the current reactive power ramp rate based on the excitation system's response capability, cumulative temperature rise, and voltage over-limit risk. The reactive power ramp rate is taken as the minimum value among the excitation system's permissible reactive power change rate, the voltage constraint's permissible reactive power change rate, and the thermal stability constraint's permissible reactive power change rate.

[0049] The permissible rate of reactive power change in the excitation system is taken as the smaller of the reactive power rate limit calibrated by the excitation system test and the absolute value of the rate of reactive power change caused by the change in excitation current. The formula is as follows: ; In the formula, This represents the unit's current permissible reactive power ramp rate during the k-th control cycle; This indicates the permissible rate of reactive power change determined by the response capability of the excitation system; This indicates the permissible rate of reactive power change determined by voltage constraints; This indicates the permissible rate of reactive power change determined by thermal stability constraints or temperature rise conditions.

[0050] The reactive power change rate allowed by voltage constraints is the minimum value among the quotients obtained by dividing the remaining voltage margin along the adjustment direction at each constrained node by the product of voltage-reactive power sensitivity and voltage prediction time window. The voltage prediction time window is generally set to 5 seconds. The reactive power change rate allowed by thermal stability constraints is equal to the reactive power rate limit calibrated by the temperature rise test multiplied by the current temperature rise margin. The formula is as follows: ; ; ; In the formula, , These are the reactive speed limits calibrated by excitation and temperature rise tests, respectively. For the excitation current speed limit, j is the constrained node. This represents the remaining voltage margin along the adjustment direction. To account for communication and execution delays, a voltage prediction time window is typically set to 5 seconds. This refers to voltage-reactive power sensitivity.

[0051] The information sent to AVC includes the current available late-phase phase modulation capacity boundary, the current available early-phase phase modulation capacity boundary, the late-phase reactive power ramp rate, the early-phase reactive power ramp rate, the late-phase capacity duration, the early-phase capacity duration, and the current main limiting factors, which are combined into a feedback dataset according to formula (18).

[0052] (1) In the formula, This represents the feedback dataset sent from the generator side to the AVC during the k-th control cycle; Indicates the allowable reactive ramp rate for delayed phase; Indicates the permissible reactive ramp rate for the advancing phase; This indicates the duration of the current late-phase modulation capacity; This indicates the duration of the current phase-advancing capacity. This indicates the main limiting factors at present.

[0053] After calculating the reactive power ramp rate and capacity boundary, the reactive power ramp rate and capacity boundary are combined into a feedback dataset and sent to the AVC to provide the AVC with unit regulation speed constraints, so that the reactive power target change rate issued by the AVC does not exceed the actual tracking capacity of the unit, and avoids voltage over-limit or excitation overload due to ramping too fast.

[0054] It also includes: determining the duration of phase modulation capacity and the main limiting factors based on the excitation system response capability, temperature rise accumulation status, and voltage over-limit risk.

[0055] The duration of phase adjustment capacity can be determined under given reactive power target and cooling conditions: the time to reach the temperature limit is determined based on the power plant temperature rise test or a verified thermal model; the remaining allowable time when excitation overload occurs is determined based on the inverse time limit heat accumulation state of the excitation limiter; the target is unavailable when low excitation or power angle stability constraints are not met.

[0056] The main limiting factors are determined according to the actual tightening degree of each individual capacity boundary: the constraint with the smallest upper boundary of reactive power is used in the direction of increasing reactive power, and the constraint with the largest lower boundary of reactive power is used in the direction of decreasing reactive power. When the boundary order changes due to changes in operating conditions, the main limiting factors switch synchronously. Field leading and lagging phase tests show that the dominant constraints change between stator current and voltage-related constraints depending on the operating conditions. Therefore, fixed switching scenarios are not preset, but the limiting factors are determined based on the real-time order of each individual reactive power boundary within each evaluation cycle.

[0057] AVC not only obtains the current boundary value, but also understands how long the boundary can be maintained and the root cause of the current limitation, which facilitates AVC to make more reasonable multi-machine coordination and reactive power scheduling decisions.

[0058] The unit side will use the following to form a feedback dataset: the current available late-phase phasing capacity boundary, the current available leading-phase phasing capacity boundary, the late-phase reactive power ramp rate, the leading-phase reactive power ramp rate, the late-phase capacity duration, the leading-phase capacity sustainability time, and the current main limiting factors. The expression for this dataset is: ; In the formula, This represents the feedback dataset sent from the generator side to the AVC during the k-th control cycle; Indicates the allowable reactive ramp rate for delayed phase; Indicates the permissible reactive ramp rate for the advancing phase; This indicates the duration of the current late-phase modulation capacity; This indicates the duration of the current phase-advancing capacity. This indicates the main limiting factors at present.

[0059] The generating unit periodically sends the feedback dataset through the power plant monitoring communication channel or AVC interface as a real-time capability constraint for AVC to perform reactive power allocation.

[0060] Step 105: When the reactive power target value exceeds the current latest available phase-shifting capacity boundary, the reactive power target value is corrected locally on the unit to ensure it is within the current safety boundary, and the boundary change and unmet capacity information are fed back to the AVC.

[0061] The AVC allocates and executes reactive power target values. Specifically, after receiving real-time constraints, the AVC generates a reactive power target value allocated to the constant-speed pumped-storage unit based on the bus voltage target, bus voltage deviation, the status of other reactive power resources within the station, and the real-time constraints. As an optional reactive power allocation method, the AVC can allocate reactive power regulation according to the proportion of the adjustable margin of each unit. When the sum of the adjustable margins of the participating units is zero, no reactive power regulation is allocated in this cycle. The constant-speed pumped-storage unit receives the reactive power target value, and the excitation system adjusts the excitation current to make the unit's actual reactive power track the target value. The excitation system adjusts the excitation current according to the reactive power deviation, changing the internal electromotive force of the synchronous machine, so that the unit's actual reactive power tracks the reactive power target value.

[0062] Let the total reactive power regulation determined by AVC in the k-th control cycle be . The current reactive power of the i-th unit is Its current available phase-advancing and phase-retarding capacity boundaries are respectively and The adjustable reactive power margin is: ; AVC allocates reactive power regulation according to the proportion of the adjustable margin of each unit: ; In the formula, The set of generating units participating in this reactive power allocation, This represents the adjustable reactive power margin of the i-th generating unit along the current reactive power adjustment direction. This refers to the adjustable reactive power margin of the j-th unit in the set of units participating in the power allocation along the same direction.

[0063] The target reactive power value for the i-th generating unit is: ; When the sum of the adjustable margins of the participating units is zero, no reactive power regulation is allocated in this cycle.

[0064] The AVC allocation and excitation execution features embed real-time boundary constraints into the allocation process without changing the internal allocation algorithm of AVC, ensuring that the allocation result is always within the safe capacity range of the unit.

[0065] Local safety fallback correction and feedback. Specifically, when communication delays, sampling errors, or sudden changes in unit status cause the reactive power target value issued by the AVC to exceed the current latest available phase modulation capacity boundary, the local controller performs a safety fallback correction on the reactive power target value: if the reactive power target value is greater than the current available late-phase phase modulation capacity boundary, it is limited to the current available late-phase phase modulation capacity boundary; if the reactive power target value is less than the current available leading-phase phase modulation capacity boundary, it is limited to the current available leading-phase phase modulation capacity boundary; when the reactive power target value is between the two, it is executed directly.

[0066] Its expression is: ; In the formula, This represents the reactive power setpoint that the local controller ultimately executes within the k-th control cycle; This indicates that the AVC issues a target reactive power value for the given pumped storage unit.

[0067] when When the reactive power setpoint exceeds the current available late-phase modulation capacity boundary, the local controller will limit the reactive power setpoint to the current available late-phase modulation capacity boundary; when When the reactive power setpoint is less than the current available phase-adjusting capacity boundary, the local controller will limit the reactive power setpoint to the current available phase-adjusting capacity boundary; when When the current available phase-advancing capacity boundary and the current available phase-delaying capacity boundary are located between the current available phase-advancing capacity boundary, the reactive power target value is executed directly.

[0068] After the correction is completed, the corrected boundary, the unmet capacity information determined by the difference between the reactive power target value issued by AVC and the reactive power set value actually executed locally, and the new main limiting factors are fed back to AVC so that AVC can coordinate other reactive power resources in the station to make compensation.

[0069] Safety fallback correction and feedback form a two-way information closed loop between the unit side and the AVC side. Even if communication delays or sudden changes in status occur, it can ensure that the unit does not exceed the limits of operation, while allowing the AVC to know the actual execution status and adjust the reactive power output of other units in a timely manner.

[0070] Figure 2 This is a flowchart illustrating an exemplary embodiment of a method for online assessment of the available phase-shifting capacity and AVC coordinated control of a constant-speed pumped-storage unit. (See flowchart for example.) Figure 2 The diagram shows the complete flow of the AVC control method: S1: Collect real-time operating status data of the constant-speed pumped-storage unit during phase-shifting operation. The real-time operating status data include terminal voltage, grid bus voltage, stator current, excitation current, actual reactive power, equivalent active power loss, rotor power angle, stator winding temperature, rotor winding temperature, core end temperature, under-excitation limit state, and over-excitation limit state. S2: Based on the real-time operating status quantities, respectively calculate the computer terminal voltage margin, stator current margin, excitation potential margin, low excitation limit margin, power angle stability margin, and temperature rise margin. S3: Based on the synchronous machine capability relationship, stator current limit, overexcitation limit, underexcitation limit, power angle stability limit and comprehensive margin coefficient, calculate the current available late phase modulation capacity boundary and the current available early phase modulation capacity boundary of the constant speed pumped storage unit online; S4: Based on the excitation system response capability, temperature rise accumulation status, and voltage over-limit risk, calculate the current reactive power ramp rate, phase modulation capacity sustainability time, and main limiting factors. S5: Send the current available late-phase phase modulation capacity boundary, the current available leading-phase phase modulation capacity boundary, the reactive power ramp rate, the phase modulation capacity sustainability time and the main limiting factors to the AVC as real-time constraints for the AVC to perform reactive power distribution. S6: AVC generates the reactive power target value for the constant-speed pumped-storage unit based on the bus voltage target, bus voltage deviation, status of other reactive power resources in the station, and the real-time constraints. S7: The constant-speed pumped storage unit receives the target reactive power value and the excitation system adjusts the excitation current to make the actual reactive power of the unit track the target reactive power value. S8: When communication delay or sudden change in unit status causes the reactive power target value to exceed the current latest available phase-shifting capacity boundary, the local controller will limit the reactive power target value to within the current safety boundary and feed back the boundary change and unmet capacity information to the AVC.

[0071] To verify the effectiveness of this invention, a simulation model based on the capability boundary of a synchronizer can be established. For example... Figure 3 As shown, traditional methods use fixed, conservative phase-adjustment capacity boundaries. The late-phase and leading-phase capacity boundaries obtained through online evaluation in this invention can dynamically change according to the unit's operating status, avoiding the problem of overly conservative traditional fixed boundaries. Figure 4 As shown, during low-voltage and overvoltage disturbances, the bus voltage response is closer to the target voltage and the voltage deviation is reduced after adopting the method of the present invention. This proves that the present invention can fully release the phase adjustment capability of the constant-speed pumped-storage unit and improve the voltage support effect.

[0072] Figure 5 This is a schematic structural diagram of a device provided in an exemplary embodiment. Please refer to... Figure 5 At the hardware level, the device includes a processor 502, an internal bus 504, a network interface 506, memory 508, and non-volatile memory 510, and may also include other hardware required for its functions. One or more embodiments of the present invention can be implemented in software, for example, the processor 502 reads the corresponding computer program from the non-volatile memory 510 into memory 508 and then runs it. Of course, in addition to software implementation, one or more embodiments of the present invention do not exclude other implementation methods, such as logic devices or a combination of hardware and software, etc. That is to say, the execution subject of the following processing flow is not limited to each logic unit, but can also be hardware or logic devices.

[0073] Please refer to Figure 6 An AVC control device based on the available phase-shifting capacity of a constant-speed pumped-storage unit can be applied to, for example... Figure 6 The device shown, in order to implement the technical solution of the present invention, includes: The acquisition unit 601 is used to acquire real-time operating status data of the constant-speed pumped storage unit during phase-changing operation. The real-time operating status data reflects the electrical and thermal operating status of the unit. The first calculation unit 602 is used to calculate the current multi-dimensional safety margin of the computer group based on the real-time operating status. The multi-dimensional safety margin represents the safety distance of the respective safety limits of the terminal voltage, stator current, excitation state, low excitation limit, power angle stability and temperature rise distance. The second calculation unit 603 is used to calculate the current available late-phase phase-shifting capacity boundary and the current available early-phase phase-shifting capacity boundary of the constant-speed pumped-storage unit based on the steady-state capability relationship of the synchronous machine, combined with stator current limit, over-excitation limit, under-excitation limit, power angle stability limit and the multi-dimensional safety margin. Feedback unit 604 is used to feed back the current available late-phase modulation capacity boundary and the current available early-phase modulation capacity boundary as real-time constraints to the upper automatic voltage control system AVC, so that when AVC performs reactive power distribution, it uses the real-time constraints as the boundary to generate a reactive power target value that does not exceed the current safety capacity. The correction unit 605 is used to perform a safety fallback correction on the local unit when the reactive power target value exceeds the current latest available phase modulation capacity boundary, so as to limit it within the current safety boundary, and to feed back the boundary change and unmet capacity information to the AVC.

[0074] Optionally, the real-time operating status quantities include: terminal voltage, grid bus voltage, stator current, excitation current, actual reactive power, equivalent active power loss, rotor power angle, stator winding temperature, rotor winding temperature, core end temperature, under-excitation limit state, and over-excitation limit state.

[0075] Optionally, the multi-dimensional safety margin includes terminal voltage margin, stator current margin, magnetomotive force margin, under-excitation limitation margin, power angle stability margin, and temperature rise margin, which are calculated as follows: The terminal voltage margin is the minimum of the following two ratios and the value 1: the first ratio is the difference between the upper limit of the terminal voltage allowable and the current terminal voltage, divided by the difference between the upper limit of the terminal voltage allowable and the rated value of the terminal voltage; the second ratio is the difference between the current terminal voltage and the lower limit of the terminal voltage allowable, divided by the difference between the rated value of the terminal voltage and the lower limit of the terminal voltage allowable. The stator current margin is the difference between the maximum allowable stator current and the current stator current, divided by the difference between the maximum allowable stator current and the rated stator current. The excitation potential margin is the difference between the maximum permissible excitation EMF in the current control cycle and the current synchronous excitation EMF, divided by the difference between the maximum permissible excitation EMF in the current control cycle and the rated excitation EMF. The underexcitation limit margin is the difference between the current synchronous excitation electromotive force and the minimum permissible excitation electromotive force corresponding to the underexcitation limit, divided by the difference between the rated excitation electromotive force and the minimum permissible excitation electromotive force corresponding to the underexcitation limit. The power angle stability margin is the difference between the maximum allowable power angle stability limit and the absolute value of the current rotor power angle, divided by the difference between the maximum allowable power angle stability limit and the rated operating power angle. The temperature rise margin is taken as the minimum of the following three ratios: the first ratio is the difference between the maximum allowable temperature of the stator winding and the current stator winding temperature, divided by the difference between the maximum allowable temperature of the stator winding and the rated operating temperature of the stator winding; the second ratio is the difference between the maximum allowable temperature of the rotor winding and the current rotor winding temperature, divided by the difference between the maximum allowable temperature of the rotor winding and the rated operating temperature of the rotor winding; the third ratio is the difference between the maximum allowable temperature of the core end and the current core end temperature, divided by the difference between the maximum allowable temperature of the core end and the rated operating temperature of the core end. If any of the above margin calculation results is less than zero, it is set to zero; if it is greater than one, it is set to one.

[0076] Furthermore, the calculation of the currently available late-phase phasing capacity boundary and the currently available leading-phase phasing capacity boundary of the constant-speed pumped-storage unit includes: Within each control cycle, based on the multi-dimensional safety margins obtained by the computer within that cycle, the late-phase integrated margin coefficient and the leading-phase integrated margin coefficient for the current control cycle are formed respectively. These are used as global safety scaling factors in the corresponding operating direction to transfer the minimum margin among the multi-dimensional safety margins to the capacity boundary calculation, so that the final available capacity shrinks proportionally as the tightest constraint tightens. Specifically, the late-phase integrated margin coefficient is the minimum value among the terminal voltage margin, stator current margin, excitation potential margin, and temperature rise margin, while the leading-phase integrated margin coefficient is the minimum value among the terminal voltage margin, stator current margin, under-excitation limit margin, power angle stability margin, and temperature rise margin.

[0077] Furthermore, the available late-phase modulation capacity boundary is equal to the safety factor multiplied by the late-phase comprehensive margin coefficient, and then multiplied by the smaller of the late-phase reactive power upper limit determined by the stator current limit and the late-phase reactive power upper limit determined by the over-excitation limit; the safety factor is generally taken as 0.9; The available phase advance capacity boundary is equal to the safety factor multiplied by the phase advance comprehensive margin coefficient, and then multiplied by the maximum value among the phase advance reactive power lower limit determined by the stator current limit, the phase advance reactive power lower limit determined by the low excitation limit, and the phase advance reactive power lower limit determined by the power angle stability limit; all phase advance reactive power lower limits are negative, and the maximum value is taken, which is the smallest absolute value.

[0078] Optional, The steady-state capability relationship of the synchronous machine satisfies: the square of the excitation electromotive force of the synchronous machine is equal to the square of the sum of the product of the terminal voltage, the direct-axis synchronous reactance and the reactive power divided by the terminal voltage, plus the square of the product of the direct-axis synchronous reactance and the equivalent active power loss divided by the terminal voltage. The stator current limit satisfies the condition that the sum of the square of the equivalent active power loss and the square of the reactive power does not exceed the square of the product of the terminal voltage and the maximum allowable stator current. The power angle stability limit ensures that the rotor power angle does not exceed the maximum allowable power angle stability limit. Under phase-shifting conditions, the equivalent active power loss represents the equivalent active power loss calculated from mechanical losses, wind friction losses, and electrical losses. It is determined based on the phase-shifting test data of the power plant and the online measured active power of the unit, with a typical value range of 1.54% of the rated capacity.

[0079] Optionally, the device further includes: The third calculation unit 606 is used to calculate the current reactive power ramp rate based on the excitation system response capability, temperature rise accumulation status and voltage over-limit risk, and to send the reactive power ramp rate and capacity boundary together to form a feedback dataset to AVC. Wherein, the reactive power ramp rate is the minimum value among the reactive power change rate allowed by the excitation system, the reactive power change rate allowed by voltage constraints, and the reactive power change rate allowed by thermal stability constraints; the reactive power change rate allowed by the excitation system is the smaller value among the reactive power rate limit calibrated by the excitation system test and the absolute value of the reactive power change rate caused by the change in excitation current; the reactive power change rate allowed by voltage constraints is the minimum value among the quotients obtained by dividing the remaining voltage margin along the adjustment direction at each constrained node by the product of voltage-reactive power sensitivity and voltage prediction time window; the reactive power change rate allowed by thermal stability constraints is equal to the reactive power rate limit calibrated by the temperature rise test multiplied by the current temperature rise margin.

[0080] Optionally, the device further includes: The determination unit 607 is used to determine the duration of phase modulation capacity and the main limiting factors based on the excitation system response capability, temperature rise accumulation status and voltage over-limit risk. The duration of the phase adjustment capacity is determined under a given reactive power target and cooling condition: the time to reach the temperature limit is determined based on the power plant temperature rise test or a verified thermal model; the remaining allowable time when excitation overload occurs is determined based on the inverse time limit heat accumulation state of the excitation limiter; the target is unavailable when the low excitation or power angle stability constraint is not met. The main limiting factors are determined according to the actual tightening degree of each individual capacity boundary: the constraint with the smallest upper boundary of reactive power is taken in the direction of increasing reactive power, and the constraint with the largest lower boundary of reactive power is taken in the direction of decreasing reactive power. When the boundary order changes due to changes in operating status, the main limiting factors are switched synchronously.

[0081] Optional, The feedback unit 604 is specifically used for: after receiving the real-time constraint, the AVC generates a reactive power target value allocated to the constant-speed pumped-storage unit based on the bus voltage target, bus voltage deviation, status of other reactive power resources in the station, and the real-time constraint; the constant-speed pumped-storage unit receives the reactive power target value, and the excitation system adjusts the excitation current to make the actual reactive power of the unit track the target value. The correction unit 605 is specifically used to: after the local controller performs a safety fallback correction on the reactive power target value, feed back the corrected boundary, the unmet capacity information determined by the difference between the reactive power target value issued by the AVC and the reactive power setting value actually executed locally, and the new main limiting factors to the AVC, so that the AVC can coordinate other reactive power resources in the station to make compensation.

[0082] The systems, devices, modules, or units described in the above embodiments can be implemented by computer chips or entities, or by products with certain functions. A typical implementation device is a computer, which can take the form of a personal computer, laptop computer, cellular phone, camera phone, smartphone, personal digital assistant, media player, navigation device, email sending and receiving device, game console, tablet computer, wearable device, or any combination of these devices.

[0083] In a typical configuration, a computer includes one or more processors (CPU), input / output interfaces, network interfaces, and memory.

[0084] Memory may include non-persistent storage in computer-readable media, such as random access memory (RAM) and / or non-volatile memory, such as read-only memory (ROM) or flash RAM. Memory is an example of computer-readable media.

[0085] Computer-readable media, including both permanent and non-permanent, removable and non-removable media, can store information using any method or technology. Information can be computer-readable instructions, data structures, modules of programs, or other data. Examples of computer storage media include, but are not limited to, phase-change memory (PRAM), static random access memory (SRAM), dynamic random access memory (DRAM), other types of random access memory (RAM), read-only memory (ROM), electrically erasable programmable read-only memory (EEPROM), flash memory or other memory technologies, CD-ROM, digital versatile optical disc (DVD) or other optical storage, magnetic tape, disk storage, quantum memory, graphene-based storage media or other magnetic storage devices, or any other non-transferable medium that can be used to store information accessible by a computing device. As defined herein, computer-readable media does not include transient computer-readable media, such as modulated data signals and carrier waves.

[0086] For any computer-readable medium (or computer-readable storage medium) as described above or otherwise, computer instructions may be stored thereon, which, when executed by a processor, implement one or more of the embodiments described above, thereby realizing the technical solution of the present invention.

[0087] The present invention also proposes a computer program that, when executed by a processor, implements one or more of the embodiments described above, thereby realizing the technical solution of the present invention. This computer program may be specifically recorded on the above-described or other computer-readable media, and the present invention does not impose any limitations on this.

[0088] It should also be noted that the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0089] The foregoing has described specific embodiments of the invention. Other embodiments are within the scope of the appended claims. In some cases, the actions or steps described in the claims may be performed in a different order than that shown in the embodiments and may still achieve the desired results. Furthermore, the processes depicted in the drawings do not necessarily require the specific or sequential order shown to achieve the desired results. In some embodiments, multitasking and parallel processing are also possible or may be advantageous.

[0090] The terminology used in one or more embodiments of the invention is for the purpose of describing particular embodiments only and is not intended to limit the invention. The singular forms “a,” “the,” and “the” used in one or more embodiments of the invention and in the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise. It should also be understood that the term “and / or” as used herein refers to and includes any or all possible combinations of one or more associated listed items.

[0091] It should be understood that although the terms first, second, third, etc., may be used to describe various information in one or more embodiments of the present invention, such information should not be limited to these terms. These terms are only used to distinguish information of the same type from one another. For example, first information may also be referred to as second information without departing from the scope of one or more embodiments of the present invention, and similarly, second information may also be referred to as first information. Depending on the context, the word "if" as used herein may be interpreted as "when," "when," or "in response to a determination."

[0092] The above description is merely a preferred embodiment of one or more embodiments of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of one or more embodiments of the present invention should be included within the protection scope of one or more embodiments of the present invention.

Claims

1. An AVC control method based on the available phase-shifting capacity of a constant-speed pumped-storage unit, characterized in that, include: Real-time operating status data of the constant-speed pumped-storage unit during phase-shifting operation are collected, and the real-time operating status data reflects the electrical and thermal operating status of the unit. Based on the current multi-dimensional safety margin of the real-time operating status quantizer, the multi-dimensional safety margin respectively characterizes the safety distance of the respective safety limits of terminal voltage, stator current, excitation state, low excitation limit, power angle stability and temperature rise distance; Based on the steady-state capability relationship of the synchronous machine, and combined with the stator current limit, overexcitation limit, underexcitation limit, power angle stability limit, and the aforementioned multi-dimensional safety margin, the current available late-phase phase-shifting capacity boundary and the current available early-phase phase-shifting capacity boundary of the constant-speed pumped-storage unit are calculated. The current available late-phase modulation capacity boundary and the current available early-phase modulation capacity boundary are fed back to the upper automatic voltage control system (AVC) as real-time constraints, so that when the AVC performs reactive power distribution, it uses the real-time constraints as the boundary to generate a reactive power target value that does not exceed the current safety capacity. When the reactive power target value exceeds the current latest available phase-shifting capacity boundary, the reactive power target value is corrected locally on the unit to ensure that it is limited to the current safety boundary, and the boundary change and unmet capacity information are fed back to the AVC.

2. The method according to claim 1, characterized in that, The real-time operating status quantities include: terminal voltage, grid bus voltage, stator current, excitation current, actual reactive power, equivalent active power loss, rotor power angle, stator winding temperature, rotor winding temperature, core end temperature, under-excitation limit state, and over-excitation limit state.

3. The method according to claim 1, characterized in that, The multi-dimensional safety margins include terminal voltage margin, stator current margin, magnetomotive force margin, under-excitation limitation margin, power angle stability margin, and temperature rise margin, which are calculated as follows: The terminal voltage margin is the minimum of the following two ratios and the value 1: the first ratio is the difference between the upper limit of the terminal voltage allowable and the current terminal voltage, divided by the difference between the upper limit of the terminal voltage allowable and the rated value of the terminal voltage; the second ratio is the difference between the current terminal voltage and the lower limit of the terminal voltage allowable, divided by the difference between the rated value of the terminal voltage and the lower limit of the terminal voltage allowable. The stator current margin is the difference between the maximum allowable stator current and the current stator current, divided by the difference between the maximum allowable stator current and the rated stator current. The excitation potential margin is the difference between the maximum permissible excitation EMF in the current control cycle and the current synchronous excitation EMF, divided by the difference between the maximum permissible excitation EMF in the current control cycle and the rated excitation EMF. The underexcitation limit margin is the difference between the current synchronous excitation electromotive force and the minimum permissible excitation electromotive force corresponding to the underexcitation limit, divided by the difference between the rated excitation electromotive force and the minimum permissible excitation electromotive force corresponding to the underexcitation limit. The power angle stability margin is the difference between the maximum allowable power angle stability limit and the absolute value of the current rotor power angle, divided by the difference between the maximum allowable power angle stability limit and the rated operating power angle. The temperature rise margin is taken as the minimum of the following three ratios: the first ratio is the difference between the maximum allowable temperature of the stator winding and the current stator winding temperature, divided by the difference between the maximum allowable temperature of the stator winding and the rated operating temperature of the stator winding; the second ratio is the difference between the maximum allowable temperature of the rotor winding and the current rotor winding temperature, divided by the difference between the maximum allowable temperature of the rotor winding and the rated operating temperature of the rotor winding; the third ratio is the difference between the maximum allowable temperature of the core end and the current core end temperature, divided by the difference between the maximum allowable temperature of the core end and the rated operating temperature of the core end. If any of the above margin calculation results is less than zero, it is set to zero; if it is greater than one, it is set to one.

4. The method according to claim 3, characterized in that, The calculation of the current available late-phase phasing capacity boundary and the current available leading-phase phasing capacity boundary of the constant-speed pumped-storage unit includes: Within each control cycle, based on the multi-dimensional safety margins obtained by the computer within that cycle, the late-phase integrated margin coefficient and the leading-phase integrated margin coefficient for the current control cycle are formed respectively. These are used as global safety scaling factors in the corresponding operating direction to transfer the minimum margin among the multi-dimensional safety margins to the capacity boundary calculation, so that the final available capacity shrinks proportionally as the tightest constraint tightens. Specifically, the late-phase integrated margin coefficient is the minimum value among the terminal voltage margin, stator current margin, excitation potential margin, and temperature rise margin, while the leading-phase integrated margin coefficient is the minimum value among the terminal voltage margin, stator current margin, under-excitation limit margin, power angle stability margin, and temperature rise margin.

5. The method according to claim 4, characterized in that, The available late-phase phasing capacity boundary is equal to the safety factor multiplied by the late-phase comprehensive margin coefficient, and then multiplied by the smaller of the late-phase reactive power upper limit determined by the stator current limit and the late-phase reactive power upper limit determined by the overexcitation limit; the safety factor is generally taken as 0.9; The available phase advance capacity boundary is equal to the safety factor multiplied by the phase advance comprehensive margin coefficient, and then multiplied by the maximum value among the phase advance reactive power lower limit determined by the stator current limit, the phase advance reactive power lower limit determined by the low excitation limit, and the phase advance reactive power lower limit determined by the power angle stability limit; all phase advance reactive power lower limits are negative, and the maximum value is taken, which is the smallest absolute value.

6. The method according to claim 1, characterized in that, The steady-state capability relationship of the synchronous machine satisfies: the square of the excitation electromotive force of the synchronous machine is equal to the square of the sum of the product of the terminal voltage, the direct-axis synchronous reactance and the reactive power divided by the terminal voltage, plus the square of the product of the direct-axis synchronous reactance and the equivalent active power loss divided by the terminal voltage. The stator current limit satisfies the condition that the sum of the square of the equivalent active power loss and the square of the reactive power does not exceed the square of the product of the terminal voltage and the maximum allowable stator current. The power angle stability limit ensures that the rotor power angle does not exceed the maximum allowable power angle stability limit. Under phase-shifting conditions, the equivalent active power loss represents the equivalent active power loss calculated from mechanical losses, wind friction losses, and electrical losses. It is determined based on the phase-shifting test data of the power plant and the online measured active power of the unit, with a typical value range of 1.54% of the rated capacity.

7. The method according to claim 1, characterized in that, The method further includes: Based on the excitation system response capability, temperature rise accumulation status, and voltage over-limit risk, the current reactive power ramp rate is calculated, and the reactive power ramp rate and capacity boundary are combined to form a feedback dataset and sent to AVC. Wherein, the reactive power ramp rate is the minimum value among the reactive power change rate allowed by the excitation system, the reactive power change rate allowed by voltage constraints, and the reactive power change rate allowed by thermal stability constraints; the reactive power change rate allowed by the excitation system is the smaller value among the reactive power rate limit calibrated by the excitation system test and the absolute value of the reactive power change rate caused by the change in excitation current; the reactive power change rate allowed by voltage constraints is the minimum value among the quotients obtained by dividing the remaining voltage margin along the adjustment direction at each constrained node by the product of voltage-reactive power sensitivity and voltage prediction time window; the reactive power change rate allowed by thermal stability constraints is equal to the reactive power rate limit calibrated by the temperature rise test multiplied by the current temperature rise margin.

8. The method according to claim 7, characterized in that, The method further includes: Based on the excitation system response capability, temperature rise accumulation status, and voltage over-limit risk, determine the sustainable time and main limiting factors of phase modulation capacity; The duration of the phase adjustment capacity is determined under a given reactive power target and cooling condition: the time to reach the temperature limit is determined based on the power plant temperature rise test or a verified thermal model; the remaining allowable time when excitation overload occurs is determined based on the inverse time limit heat accumulation state of the excitation limiter; the target is unavailable when the low excitation or power angle stability constraint is not met. The main limiting factors are determined according to the actual tightening degree of each individual capacity boundary: the constraint with the smallest upper boundary of reactive power is taken in the direction of increasing reactive power, and the constraint with the largest lower boundary of reactive power is taken in the direction of decreasing reactive power. When the boundary order changes due to changes in operating status, the main limiting factors are switched synchronously.

9. The method according to claim 1, characterized in that, The step of feeding back the currently available late-phase phase-shifting capacity boundary and the currently available leading-phase phase-shifting capacity boundary as real-time constraints to the upper-level automatic voltage control system (AVC) so that the AVC can generate a reactive power target value that does not exceed the current safety capacity when performing reactive power allocation, using the real-time constraints as the boundary. This includes: after receiving the real-time constraints, the AVC generates a reactive power target value to be allocated to the constant-speed pumped-storage unit based on the bus voltage target, bus voltage deviation, the status of other reactive power resources in the station, and the real-time constraints; the constant-speed pumped-storage unit receives the reactive power target value, and the excitation system adjusts the excitation current to make the actual reactive power of the unit track the target value. The feedback of boundary changes and unmet capacity information to the AVC includes: after the local controller performs a safety fallback correction on the reactive power target value, it feeds back the corrected boundary, the unmet capacity information determined by the difference between the reactive power target value issued by the AVC and the reactive power set value actually executed locally, and the new main limiting factors to the AVC so that the AVC can coordinate other reactive power resources in the station to make compensation.

10. An AVC control device based on the available phase-shifting capacity of a constant-speed pumped-storage unit, characterized in that, include: Data Acquisition Unit: Collects real-time operating status data of the constant-speed pumped-storage unit during phase-shifting operation. The real-time operating status data reflects the electrical and thermal operating status of the unit. First calculation unit: Based on the real-time operating status quantity, the computer group's current multi-dimensional safety margin, which represents the safety distance of the respective safety limits of terminal voltage, stator current, excitation state, low excitation limit, power angle stability and temperature rise distance; The second calculation unit calculates the current available late-phase phase-shifting capacity boundary and the current available early-phase phase-shifting capacity boundary of the constant-speed pumped-storage unit based on the steady-state capability relationship of the synchronous machine, combined with stator current limit, over-excitation limit, under-excitation limit, power angle stability limit and the multi-dimensional safety margin. Feedback unit: Feeds the current available late-phase modulation capacity boundary and the current available early-phase modulation capacity boundary as real-time constraints to the upper automatic voltage control system (AVC), so that when the AVC performs reactive power distribution, it uses the real-time constraints as the boundary to generate a reactive power target value that does not exceed the current safety capacity. Correction Unit: When the reactive power target value exceeds the current latest available phase-shifting capacity boundary, the unit performs a safety fallback correction on the reactive power target value locally to limit it within the current safety boundary, and feeds back the boundary change and unmet capacity information to the AVC.

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