A new energy station output current feasible region construction method

Abstract

The application discloses a new energy station output current feasible region construction method, relates to the technical field of new energy stations, and has the following steps: acquiring system parameters and protection parameters of a new energy sending-out line, and defining fault scene variables containing fault types, fault positions, transition resistances and system strengths; in a control space defined by sequence components of new energy station output currents, phase voltages, phase currents and active power oscillation components at a point of common coupling are calculated based on the fault scene variables, an operation safety domain satisfying preset operation safety limits is constructed, a protection correct action domain is constructed based on a power frequency variation distance protection action criterion, an intersection of the operation safety domain and the protection correct action domain is calculated, and a control-protection compatible feasible domain is obtained, so that the operation stability of a new energy grid-connected system during a fault is improved, boundary basis is provided for new energy station fault current control, protection adaptability checking and control-protection cooperation.

Description

Technical Field

[0001] This invention relates to the field of new energy power station technology, and more specifically, to a method for constructing the feasible domain of output current in a new energy power station. Background Technology

[0002] With the large-scale integration of new energy sources such as wind power and photovoltaics into the power system, grid connection of new energy sources via medium- and high-voltage AC transmission lines has become a typical operating mode in new power systems. New energy power plants are typically connected to the grid through power electronic converters. Their fault current output is influenced by strategies such as low-voltage ride-through control and current limiting, exhibiting characteristics such as limited amplitude, controlled phase, and adjustable sequence components. The inverter output current is related to the operational safety of the new energy power plant itself, for example, preventing overvoltage in non-faulty phases, inverter overcurrent, and active power double-frequency oscillation during faults. On the other hand, it directly affects the calculation of the discrimination value for distance protection of line power frequency changes, thus impacting the protection's operational performance.

[0003] To address operational safety issues during renewable energy failures, existing research typically focuses on inverter control, employing methods such as positive-sequence reactive current support, negative-sequence current suppression, and current limiting to ensure renewable energy power plants meet fault ride-through requirements and reduce the risks of overcurrent, overvoltage, and power oscillations. However, these methods primarily focus on the safe operation of renewable energy power plants, neglecting the requirements for correct protection operation. Furthermore, altering the magnitude, phase, and sequence component distribution of the output current during a fault inevitably affects the calculation of protection discrimination parameters, potentially leading to protection failure or maloperation.

[0004] To address the issue of decreased distance protection adaptability after the integration of new energy sources, some studies have explored control-protection synergy methods to improve this adaptability. These methods proactively utilize the controllability of the converter to shape fault characteristics more favorable for protection detection. Additional fault equations are constructed through sequence current redistribution, impedance angle reconstruction, or control state switching to achieve fault identification. While these methods can enhance protection detection capabilities, directly adjusting the amplitude and phase of the positive sequence current or switching the reactive current reference value may conflict with operational safety requirements during low-voltage ride-through.

[0005] The above indicates the necessity of constructing a feasible domain for renewable energy output current that simultaneously satisfies operational safety constraints and correct protection operation constraints within a unified space, and further characterizing its boundary features. In recent years, some studies have begun to focus on the applicability boundaries of traditional protection under large-scale renewable energy integration conditions, but most boundary analyses still revolve around single factors such as renewable energy capacity or penetration rate. Existing research has not yet systematically characterized the control-protection compatibility boundary under the coupled effects of multiple factors such as fault type, fault location, transition resistance, system strength, and converter control strategy.

[0006] Existing research often models based on a single objective: the safe operation of new energy sources or the correct operation of relay protection. The former mainly focuses on operational constraints such as converter phase voltage, phase current, and power oscillations, while the latter mainly focuses on whether protection criteria are met. These two approaches typically employ different variable systems and analytical frameworks, lacking a unified control space for the fault current output of new energy sources, thus making it difficult to simultaneously characterize operational and protection constraints.

[0007] Existing methods can typically only determine whether a control output meets operational safety requirements or protection action requirements separately, making it difficult to further determine whether there is a current output range that can be satisfied by both types of constraints. Therefore, under a given fault scenario, existing technologies cannot directly answer questions such as "whether there is a control-protection compatible feasible solution for the fault current of new energy sources" and "within what current output range does the feasible solution lie?"

[0008] Existing studies on control-protection coordination or protection adaptability often directly propose protection or control improvement measures, but lack a basic assessment of the feasibility of the improvements. In other words, without clarifying whether there is an overlap between the operational safety domain and the correct protection action domain, it is difficult to determine whether the existing control and protection configuration still has feasible output space, and it is also difficult to provide a unified basis for subsequent control strategy selection and protection adaptability verification. Summary of the Invention

[0009] To address the shortcomings of existing technologies, the present invention aims to provide a method for constructing the feasible domain of output current for new energy power plants.

[0010] To achieve the above objectives, the present invention provides the following technical solution:

[0011] A method for constructing the feasible region of output current of a new energy power station includes the following steps:

[0012] Obtain system parameters and protection parameters of new energy transmission lines, and define fault scenario variables including fault type, fault location, transition resistance and system strength;

[0013] In the control space defined by the sequence component of the output current of the new energy power station, an operating safety domain is established based on the fault scenario variables to satisfy the operating safety constraints during the fault period of the new energy power station; wherein, the operating safety domain is used to characterize the output range in which the fault current of the new energy meets the phase voltage limit, phase current limit and active power oscillation limit.

[0014] Based on fault scenario variables in the control space, a correct action domain for protection that satisfies the correct action criterion of distance protection for power frequency variation is established when a fault occurs within the area of ​​the new energy transmission line. The correct action domain is used to characterize the output range in which the distance protection for power frequency variation can correctly identify faults within the area.

[0015] The intersection of the operational safety domain and the protection correct action domain is used to obtain the control-protection compatibility feasible domain; whereby the control-protection compatibility feasible domain is used to characterize the set of new energy fault current outputs that simultaneously meet the requirements of operational safety and protection correct action.

[0016] Preferably, the sequence components of the output current of the new energy power station include positive sequence active current component, positive sequence reactive current component and negative sequence reactive current component.

[0017] Preferably, constructing a runtime security domain includes the following steps:

[0018] Based on the sequence component of the output current of the new energy power station, system parameters and fault scenario variables, the three-phase voltage, three-phase current and active power oscillation component at the point of common coupling are calculated.

[0019] Establish constraints for maximum phase voltage, maximum phase current, and active power oscillation, respectively;

[0020] The operational safety domain is the region in the control space that simultaneously satisfies the maximum phase voltage constraint, the maximum phase current constraint, and the active power oscillation constraint.

[0021] Preferably, the maximum phase voltage constraint is that the maximum value of the three-phase voltage amplitude does not exceed 1.1 times the rated voltage, the maximum phase current constraint is that the maximum value of the three-phase current amplitude does not exceed 1.2 to 1.5 times the rated current, and the active power oscillation constraint is that the amplitude of the active power oscillation component does not exceed a given power oscillation limit.

[0022] Preferably, constructing the protection correct action domain includes the following steps:

[0023] Based on the fault boundary conditions and the composite sequence network, the power frequency change distance protection action criterion is transformed into a quadratic surface equation of the control space with respect to the output current sequence component. The region divided by the quadratic surface equation in the control space is the correct action domain of the protection.

[0024] Preferably, the method further includes the following steps:

[0025] In the three-dimensional control space composed of the sequence components of the output current of the new energy power station, the value of any control variable is fixed, and the other two control variables form a two-dimensional cross-sectional plane; the intersection of the operation safety domain, the protection correct action domain, and the control and protection compatible feasible domain with the two-dimensional cross-sectional plane is obtained respectively, so as to obtain the two-dimensional cross-section of the operation safety domain, the two-dimensional cross-section of the protection correct action domain, and the two-dimensional cross-section of the control and protection compatible feasible domain.

[0026] Preferably, the two-dimensional cross-section includes: a positive sequence active current-positive sequence reactive current cross-section with fixed negative sequence reactive current component, and a positive sequence reactive current-negative sequence reactive current cross-section with fixed positive sequence active current component.

[0027] Preferably, the method further includes the following steps:

[0028] For each set of fault types containing multiple fault types, construct a control and protection compatibility feasible domain corresponding to each fault type;

[0029] Find the intersection of all control and protection compatible feasible regions to obtain the common intersection feasible region for multiple fault types.

[0030] Preferably, the method further includes the following steps:

[0031] Quantization calculations are performed on the control and protection compatible feasible region, the two-dimensional cross section of the control and protection compatible feasible region, or the feasible region of the common intersection of multiple fault types. The quantization calculations include calculating the volume of the feasible region, the area of ​​the two-dimensional cross section, or boundary identification.

[0032] Preferably, boundary identification includes:

[0033] Identify the boundary regions within the operational safety domain dominated by maximum phase voltage constraints, maximum phase current constraints, or active power oscillation constraints, and identify the boundary regions within the control and protection compatibility feasible domain dominated by power frequency variation distance protection action criteria.

[0034] Compared with the prior art, the present invention has the following beneficial effects:

[0035] This invention, based on a control space-based operational safety domain, characterizes the output range of renewable energy fault current while meeting phase voltage, phase current, and active power oscillation limits. This fundamentally ensures the operational safety of renewable energy power plants, effectively avoiding equipment damage risks caused by voltage over-limit, current overload, and excessive power oscillation during faults. It provides a clear safety boundary for fault current control in renewable energy power plants. The constructed correct protection action domain characterizes the current output range of faults within the correct identification zone of the power frequency change distance protection. This solves the problem of protection failure or maloperation caused by changes in renewable energy fault current characteristics, ensuring the reliability and selectivity of line protection actions. It avoids non-faulty line outages due to protection maloperation or fault expansion caused by protection failure, improving the safety and efficiency of power grid fault handling. By finding the intersection of the operational safety domain and the protection correct action domain, the control-protection compatible feasible domain is obtained, achieving the dual goals of equipment operational safety and protection correct action. This provides a clear set of feasible outputs for new energy fault current control, avoiding the problem that the control strategy only considers equipment safety and affects protection action, as well as the problem that only adapts to protection action requirements and exceeds equipment safety limits. This achieves control-protection synergistic optimization, significantly improving the operational stability of the new energy grid-connected system during faults, and providing boundary basis for fault current control, protection adaptability verification, and control-protection synergy in new energy power plants. Attached Figure Description

[0036] Figure 1This is a schematic diagram illustrating a method for constructing the feasible domain of output current in a new energy power station, as provided in an embodiment of the present invention.

[0037] Figure 2 This invention provides a schematic diagram of a 110kV double-ended power supply new energy transmission line in a method for constructing the feasible domain of output current of a new energy power station.

[0038] Figure 3 This is a schematic diagram illustrating the construction of an operational safety domain in a method for constructing the feasible domain of output current at a new energy power station, as provided in an embodiment of the present invention.

[0039] Figure 4 This invention provides a two-dimensional cross-sectional schematic diagram of the operational safety domain under changing operational constraints in a method for constructing the feasible domain of output current of a new energy power station.

[0040] Figure 5 This is a schematic diagram of the feasible region of output current under various fault types in a method for constructing the feasible region of output current of a new energy power station, provided in an embodiment of the present invention.

[0041] Figure 6 This invention provides a schematic diagram of the feasible output current region that satisfies multiple fault types in a method for constructing the feasible output current region of a new energy power station, as provided in an embodiment of the present invention. Detailed Implementation

[0042] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0043] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0044] Secondly, the term "an embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in different places throughout this specification does not necessarily refer to the same embodiment, nor is it a single embodiment or an embodiment selectively excluded from other embodiments.

[0045] Reference Figures 1-6 As shown.

[0046] The embodiments further illustrate the feasible domain construction method for the output current of a new energy power station proposed in this invention.

[0047] A method for constructing the feasible region of output current of a new energy power station includes the following steps:

[0048] Obtain system parameters and protection parameters of new energy transmission lines, and define fault scenario variables including fault type, fault location, transition resistance and system strength;

[0049] This invention is based on Figure 1 The 110 kV double-ended power supply renewable energy transmission line shown is the subject of this study. The M-end is the renewable energy power plant side, and the N-end is the AC system side. Both ends of the line are equipped with power frequency variation distance protection.

[0050] The performance of protection actions is determined by fault characteristics, which are closely related to power supply characteristics, network parameters, and fault conditions. Therefore, this invention defines the scenario variable s as shown in equation (1). Wherein, y, and R g These represent the fault type, fault location, and transition resistance, respectively; the short-circuit ratio (SCR) is used to characterize the system strength; Z L1 Z L0 Z s and Z T These represent the positive sequence impedance of the line, the zero sequence impedance of the line, the power supply impedance on the system side, and the transformer impedance, respectively.

[0051] (1)

[0052] For grid-connected renewable energy power plants, the fault response is mainly manifested as controlled-sequence current output. Considering that actual three-phase three-wire converters usually do not have independent negative-sequence active current control capability, this invention adopts the control variable shown in equation (2). Describe the output current of the renewable energy power station. Among them, , and These represent the positive-sequence active current, positive-sequence reactive current, and negative-sequence reactive current, respectively.

[0053] (2)

[0054] Taking the direction of the current flowing from the new energy power station to the power grid as the positive direction, the sequence current at the point of common coupling is defined as shown in equation (3), and satisfies , , ≥0.

[0055] (3)

[0056] For a given scenario, the operational safety domain H(s) and the protection correct operation domain P(s) are defined within the same control space. H(s) represents the set of output currents that satisfy phase voltage constraints, phase current constraints, and active power oscillation constraints; P(s) represents the set of output currents that ensure correct protection operation during a fault within the line zone. The intersection of these two domains is defined as the feasible domain F(s), as shown in equation (4).

[0057] (4)

[0058] In the control space defined by the sequence component of the output current of the new energy power station, an operating safety domain is established based on the fault scenario variables to satisfy the operating safety constraints during the fault period of the new energy power station; wherein, the operating safety domain is used to characterize the output range in which the fault current of the new energy meets the phase voltage limit, phase current limit and active power oscillation limit.

[0059] Building and running a security domain involves the following steps:

[0060] Based on the sequence component of the output current of the new energy power station, system parameters and fault scenario variables, the three-phase voltage, three-phase current and active power oscillation component at the point of common coupling are calculated.

[0061] Establish constraints for maximum phase voltage, maximum phase current, and active power oscillation, respectively;

[0062] The maximum phase voltage constraint is that the maximum value of the three-phase voltage amplitude does not exceed 1.1 times the rated voltage; the maximum phase current constraint is that the maximum value of the three-phase current amplitude does not exceed 1.2 to 1.5 times the rated current; and the active power oscillation constraint is that the amplitude of the active power oscillation component does not exceed the given power oscillation limit.

[0063] The safe operation of new energy converters requires that phase voltage, phase current, and active power oscillations all not exceed given limits. To establish corresponding constraints, the voltage v at the point of common coupling (PCC) is... αβ and current i αβ Represented in the stationary αβ coordinate system, and decomposed into positive and negative order components, as shown in equations (5) and (6).

[0064] (5)

[0065] (6)

[0066] In the formula, V + and V − They are respectively and amplitude; φ + and φ −These are the phase angles; ω is the angular frequency corresponding to the system frequency f.

[0067] according to Figure 2 The relationship between the sequence voltage at the PCC and the system sequence voltage can be expressed as equation (7).

[0068] (7)

[0069] In the formula, and These represent the positive-sequence voltage and negative-sequence voltage of the system-side bus, respectively; R and L are the positive-sequence impedances of the line, Z, respectively. L1 The corresponding resistance and inductance. These quantities are usually calculated using a line impedance estimator, a mature technology.

[0070] Under asymmetrical faults, the voltage of the non-faulty phases is affected by the fault type and grounding conditions. For phase-to-phase short-circuit faults, the voltage of the non-faulty phases is mainly determined by the superposition of positive and negative sequence voltages; for single-phase ground faults and two-phase ground faults, the zero-sequence path and neutral point offset may further increase the voltage of the non-faulty phases. Therefore, even in an effectively grounded system, the phase voltage may still exceed the allowable operating limit due to the combined influence of zero-sequence impedance and transition resistance.

[0071] By performing the Clarke inverse transform on the voltage expression in equation (5), the three-phase voltage in the ABC coordinate system can be obtained, as shown in equation (8).

[0072] (8)

[0073] The phase voltage limit is typically required to be V. lim Not exceeding the rated voltage U N The maximum phase voltage constraint can be written as equation (9) because the voltage is 1.1 pu.

[0074] (9)

[0075] Substituting equation (7) into equation (9), we can obtain the maximum phase voltage nonlinear boundary in the control space x.

[0076] Due to limitations in the thermal stress and overcurrent capability of semiconductor devices, the output current of new energy converters should be lower than the phase current limit I. lim This limit is typically taken as the rated current I. N 1.2-1.5pu. By performing the Clarke inverse transform on the current expression in equation (6), the three-phase current in the ABC coordinate system can be obtained, as shown in equation (10).

[0077] (10)

[0078] Therefore, the maximum phase current constraint can be expressed as equation (11).

[0079] (11)

[0080] Equation (11) shows that the phase current limit depends not only on the overall amplitude of the output current, but also on the distribution of the positive and negative sequence current components in the three phases. After a fault occurs, the increase in negative sequence current will exacerbate the imbalance of the three-phase current, causing one phase to reach the current limit before the other phases. Therefore, the maximum phase current constraint constitutes one of the important boundaries of the safe operating domain.

[0081] Under asymmetrical fault conditions, the active power output of renewable energy power plants contains a second-harmonic oscillation component, which can cause fluctuations in the DC bus voltage. If the power oscillation amplitude is too large, it may lead to DC-side overvoltage, accelerate the aging of DC bus capacitors, and weaken the stability of the control system. Therefore, it is necessary to set an upper limit on the active power oscillation amplitude.

[0082] According to instantaneous power theory, instantaneous active power p can be decomposed into average components. and oscillating components As shown in equation (12).

[0083] (12)

[0084] To ensure that the DC side operation is within an acceptable range, the oscillation component should be lower than the given limit P. lim Substituting equations (5) and (6) into equation (12), we can obtain the expression for the active power oscillation component, as shown in equation (13).

[0085] (13)

[0086] Therefore, the active power oscillation constraint can be expressed as equation (14).

[0087] (14)

[0088] The operational safety domain is the region in the control space that simultaneously satisfies the maximum phase voltage constraint, the maximum phase current constraint, and the active power oscillation constraint.

[0089] The sequence components of the output current of a new energy power station include positive sequence active current component, positive sequence reactive current component, and negative sequence reactive current component.

[0090] When constructing the operational safety domain, the first step is to transform the three types of operational safety constraints into constraints in the control space. For the maximum phase voltage constraint, the three-phase voltage at the grid connection point of the renewable energy power station is obtained by synthesizing the sequence components. The positive and negative sequence voltage components are directly related to the positive and negative sequence current components output by the renewable energy power station. When the phase voltage amplitude does not exceed the set limit, the corresponding control space region is the region that satisfies the maximum phase voltage constraint.

[0091] For the maximum phase current constraint, the three-phase current output by the new energy power station is also obtained by sequence component synthesis. When the phase current amplitude does not exceed the set limit, the corresponding control space region is the region that satisfies the maximum phase current constraint.

[0092] For active power oscillation constraints, voltage imbalance under fault conditions will cause active power oscillations, which are jointly determined by the cross terms between positive and negative sequence voltages and positive and negative sequence currents. The oscillation amplitude can be derived from the sequence component relationship to obtain an expression related to the three current components. When the active power oscillation amplitude does not exceed the set limit, the corresponding control space region is the region that satisfies the active power oscillation constraint.

[0093] The intersection of the control space regions corresponding to the above three types of constraints yields the operational safety domain. The current output mode corresponding to each point within the operational safety domain must simultaneously meet the limit requirements for phase voltage, phase current, and active power oscillation, ensuring the operational safety of the renewable energy power plant. For example, if the phase voltage corresponding to a certain combination of current components exceeds the limit, that point will be excluded from the operational safety domain. Similarly, if the phase current corresponding to a certain combination of current components exceeds the limit, that point will also be excluded. Furthermore, if the active power oscillation amplitude corresponding to a certain combination of current components exceeds the limit, that point will be excluded from the operational safety domain. Only current component combinations that simultaneously meet all three types of constraints will be retained within the operational safety domain, becoming the safe current output mode that the renewable energy power plant can adopt.

[0094] Maximum phase voltage constraint, maximum phase current constraint, and active power oscillation constraint each form different boundary surfaces in the control space x. The intersection of the regions corresponding to these three types of constraints constitutes the safe operating domain for regulating the output current of the renewable energy source.

[0095] (15)

[0096] In the formula, , , and These represent the voltage and current changes measured at the M and N terminals, respectively, where M and N are the protection installation points; k0 is the zero-sequence compensation coefficient. ; for The zero-order component; Z set To protect the set impedance, it is usually taken as kZ. L1 Where k is typically taken as 0.8 to 0.85. The protection action criterion is shown in equation (16).

[0097] (16)

[0098] In the formula, Let F be the phase voltage amplitude to ground before the fault. When equation (16) is satisfied, the protection determines it to be an internal fault; otherwise, it is determined to be an external fault.

[0099] Based on fault scenario variables in the control space, a correct action domain for protection that satisfies the correct action criterion of distance protection for power frequency variation is established when a fault occurs within the area of ​​the new energy transmission line. The correct action domain is used to characterize the output range in which the distance protection for power frequency variation can correctly identify faults within the area.

[0100] Constructing a protection domain for the correct action involves the following steps:

[0101] Based on the fault boundary conditions and the composite sequence network, the power frequency change distance protection action criterion is transformed into a quadratic surface equation of the control space with respect to the output current sequence component. The region divided by the quadratic surface equation in the control space is the correct action domain of the protection.

[0102] exist Figure 2 The scenario shown illustrates the integration of new energy power stations. and The equivalence relationships in traditional synchronous power systems no longer hold, and distance protection for power frequency variations may operate incorrectly. Therefore, it is necessary to consider the output current characteristics of new energy faults and re-derive the protection action boundaries for different fault types.

[0103] For different fault types, the protection criteria can be uniformly expressed as follows, derived through fault boundary conditions and composite sequence networks:

[0104] (17)

[0105] In the formula, and These represent the positive and negative sequence current changes at the protection installation location, respectively; K1, K2, and K0 are complex coefficients related to the fault type, fault location, transition resistance, and network parameters.

[0106] In practical implementation, protecting the correct action boundary can be represented as a quadratic surface in the control space:

[0107] (18)

[0108] In the formula, Q is a real symmetric matrix, L is a real column vector, and d is a real constant. This quadratic surface is used to describe the boundary of the protected correct action domain.

[0109] The intersection of the operational safety domain and the protection correct action domain is used to obtain the control-protection compatibility feasible domain; whereby the control-protection compatibility feasible domain is used to characterize the set of new energy fault current outputs that simultaneously meet the requirements of operational safety and protection correct action.

[0110] To ensure that the fault current output of new energy sources is applicable not only to a single fault type but also to multiple fault types, this invention further constructs a feasible region of common intersection of multiple fault types.

[0111] Let the set of fault types under consideration be: (19)

[0112] It also includes the following steps:

[0113] In the three-dimensional control space composed of the sequence components of the output current of the new energy power station, the value of any control variable is fixed, and the other two control variables form a two-dimensional cross-sectional plane; the intersection of the operation safety domain, the protection correct action domain, and the control and protection compatible feasible domain with the two-dimensional cross-sectional plane is obtained respectively, so as to obtain the two-dimensional cross-section of the operation safety domain, the two-dimensional cross-section of the protection correct action domain, and the two-dimensional cross-section of the control and protection compatible feasible domain.

[0114] The two-dimensional cross section includes: the positive sequence active current-positive sequence reactive current cross section with fixed negative sequence reactive current component, and the positive sequence reactive current-negative sequence reactive current cross section with fixed positive sequence active current component.

[0115] To facilitate visualization and comparative analysis, this invention further fixes... of - Plane, and fixed of - On the plane, define two-dimensional sections for the operational safety domain, the protection correct action domain, and the feasible domain, denoted as Ω. H Ω P and Ω F .

[0116] It also includes the following steps:

[0117] For each set of fault types containing multiple fault types, construct a control and protection compatibility feasible domain corresponding to each fault type;

[0118] Find the intersection of all control and protection compatible feasible regions to obtain the common intersection feasible region for multiple fault types.

[0119] The feasible region of the common intersection of multiple fault types is represented as: (20)

[0120] In the formula, Indicates fault type y i The corresponding scenario variables. The feasible region of this common intersection represents the set of control outputs that can simultaneously satisfy the requirements of operational safety and correct protection action under all considered fault types.

[0121] It also includes the following steps:

[0122] Quantization calculations are performed on the control and protection compatible feasible region, the two-dimensional cross section of the control and protection compatible feasible region, or the feasible region of the common intersection of multiple fault types. The quantization calculations include calculating the volume of the feasible region, the area of ​​the two-dimensional cross section, or boundary identification.

[0123] Boundary recognition includes:

[0124] Identify the boundary regions within the safe operating domain dominated by maximum phase voltage constraints, maximum phase current constraints, or active power oscillation constraints, and identify the boundary regions within the correct protection operating domain P dominated by the power frequency variation distance protection operating criterion.

[0125] Quantitative calculations are performed on the feasible region of control and protection compatibility, its two-dimensional cross-section, or the feasible region of the common intersection of multiple fault types. These calculations include feasible region volume calculation, two-dimensional cross-sectional area calculation, and boundary identification. Feasible region volume calculation involves numerically solving for the entire spatial range of the feasible region in the three-dimensional control space. Its magnitude directly reflects the richness of current output methods that satisfy operational safety constraints and protection action constraints; a larger volume indicates that the new energy power station has more control and protection compatible current output methods available under fault conditions. Two-dimensional cross-sectional area calculation involves selecting a fixed value on a specific coordinate axis in the three-dimensional control space and solving for the area on the two-dimensional cross-section of the three-dimensional feasible region. This area can intuitively reflect the compatible output range of the other two components under a specific current component constraint. For example, when the positive-sequence active current component is fixed at a certain value, calculating the two-dimensional feasible region cross-sectional area formed by the positive-sequence reactive current component and the negative-sequence reactive current component can intuitively present the current control margin under this operating condition.

[0126] Boundary identification consists of two parts. The first part is identifying the dominant constraint boundaries of the operational safety domain. The operational safety domain is composed of maximum phase voltage constraints, maximum phase current constraints, and active power oscillation constraints. Different boundary regions are dominated by different constraint conditions. When a point on a boundary only satisfies the equality condition of the maximum phase voltage constraint, while the other two types of constraints are in a non-limited state, this boundary region is dominated by the maximum phase voltage constraint. For example, when the amplitude of a phase voltage at the grid connection point of a new energy power plant just reaches the set limit, while the amplitudes of the phase current and active power oscillations do not exceed the limits, the corresponding control space boundary is dominated by the maximum phase voltage constraint. When a point on the boundary only satisfies the equality condition of the maximum phase current constraint, while the other two types of constraints are in a non-limited state, this boundary region is dominated by the maximum phase current constraint. When a point on the boundary only satisfies the equality condition of the active power oscillation constraint, while the other two types of constraints are in a non-limited state, this boundary region is dominated by the active power oscillation constraint.

[0127] The second part involves identifying the dominant constraint boundary of the correct protection action domain. This boundary is dominated by the action criterion of the power frequency change distance protection. When a point on a boundary in the control space exactly satisfies the equation for the action criterion of the power frequency change distance protection, the power frequency change corresponding to the output current of the renewable energy power station just reaches the critical value for protection action. This boundary region is the boundary region dominated by the power frequency change distance protection action criterion. Boundary identification clarifies the source of constraints at different locations within the control-protection compatibility feasible domain, determining which areas are limited by equipment operation safety and which are limited by line protection action requirements. This provides a clear direction for subsequent control strategy optimization. For example, when most boundaries of the feasible domain are dominated by protection criteria, it indicates that the current control of the renewable energy power station needs to prioritize adapting to protection action requirements. When the boundaries of the feasible domain are mostly dominated by equipment safety constraints, it indicates that current control needs to be optimized to meet equipment operation limits.

[0128] Taking a 110 kV double-ended power supply renewable energy transmission line as an example, the two ends of the line are the M end on the renewable energy power station side and the N end on the AC system side, respectively. Both ends of the line are equipped with power frequency variation distance protection. System parameters include the line's positive sequence impedance, zero sequence impedance, line length, system-side power supply impedance, transformer impedance, and distance protection setting coefficient. The operational safety domain is as follows: Figure 3 As shown.

[0129] To further analyze the impact of different operational constraints on the feasible region, Figure 4 The cross-sectional results of the operational safety domain on a typical two-dimensional plane are given.

[0130] Figure 4 Two-dimensional cross section of the operational safety domain under varying operational constraints

[0131] (a) When =0, V lim Changes - The influence of planar cross-sections;

[0132] (b) When I = 0.5, lim Changes - The influence of planar cross-sections;

[0133] (c) When =1, P lim Changes - The influence of planar cross-sections;

[0134] (d) When =1, V lim Changes - The influence of planar cross-sections;

[0135] (e) When I = 0.5, lim Changes - The influence of planar cross-sections;

[0136] (f) When =0, P lim Changes - The influence of planar cross-sections;

[0137] As can be seen from the two-dimensional cross-section, the boundary of the operational safety domain is jointly determined by phase voltage constraints, phase current constraints, and active power oscillation constraints, and different control space locations may be dominated by different constraints. Figure 3 Taking the illustrated operating condition as an example, in some high-current or low-current regions, phase voltage constraints or active power oscillation constraints are more stringent; while in some intermediate regions, phase current constraints become the dominant boundary. When any constraint limit is reduced, the operating safety domain shrinks accordingly; conversely, when the constraint limit is increased, the operating safety domain expands accordingly.

[0138] In practical engineering, the fault current output of new energy power plants needs to adapt to various fault types. Let's assume the fault types include single-phase ground faults, phase-to-phase short-circuit faults, two-phase ground faults, and three-phase short-circuit faults, denoted as AG, BC, BCG, and 3PH, respectively. The three-dimensional intersection feasible region is as follows: Figure 5 As shown;

[0139] Figure 5 In the table, (a)-(d) represent the intersection of the feasible regions of the output current under fault types y1-y4, respectively, satisfying the intersection of the feasible regions under multiple fault types as follows: Figure 6 As shown.

[0140] To quantify the size of the feasible region of the intersection, a sampling range and sampling step size can be set within the control space, and calculations can be performed on all combinations of control variables. For each control variable point x... i The system sequentially checks whether the point meets the constraints of maximum phase voltage, maximum phase current, active power oscillation, and correct protection operation. If all constraints are met, the point is included in the feasible point set.

[0141] In a three-dimensional control space, the volume of the feasible region can be calculated based on the set of feasible points; in a two-dimensional cross-section with a fixed control variable, the area of ​​the feasible cross-section can be calculated based on the set of feasible points. The larger the volume or area of ​​the feasible region, the wider the range of control-protection compatible outputs; the smaller the volume or area of ​​the feasible region, the fewer the selectable control outputs.

[0142] After constructing the feasible region, the feasible region boundary is extracted. Specifically, boundary points are determined based on the adjacency relationship between feasible and infeasible points, or the boundary surface can be directly calculated through constraint equations. For the operational safety region, the boundary includes the maximum phase voltage boundary, the maximum phase current boundary, and the active power oscillation boundary; for the protection correct operation region, the boundary corresponds to the boundary when the power frequency change distance protection criterion is equal.

[0143] By identifying different boundaries, it can be determined what kind of constraints the feasible region is mainly subject to in different areas. For example, when the boundary point satisfies the maximum phase voltage constraint, the boundary is dominated by the phase voltage constraint; when the boundary point satisfies the protection correct operation criterion, the boundary is dominated by the protection correct operation constraint.

[0144] The device embodiments described above are merely illustrative. The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the modules can be selected to achieve the purpose of this embodiment according to actual needs. Those skilled in the art can understand and implement this without any creative effort.

[0145] Through the above description of the embodiments, those skilled in the art can clearly understand that each embodiment can be implemented by means of software plus necessary general-purpose hardware platforms, and of course, it can also be implemented by hardware. Based on this understanding, the above technical solutions, in essence or the part that contributes to the prior art, can be embodied in the form of a software product. This computer software product can be stored in a computer-readable storage medium, such as ROM / RAM, magnetic disk, optical disk, etc., and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute the methods described in the various embodiments or some parts of the embodiments.

[0146] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for constructing the feasible domain of output current of a new energy power station, characterized in that, Includes the following steps: Obtain system parameters and protection parameters of new energy transmission lines, and define fault scenario variables including fault type, fault location, transition resistance and system strength; In the control space defined by the sequence component of the output current of the new energy power station, an operating safety domain is established based on the fault scenario variables to satisfy the operating safety constraints during the fault period of the new energy power station; wherein, the operating safety domain is used to characterize the output range in which the fault current of the new energy meets the phase voltage limit, phase current limit and active power oscillation limit. Based on fault scenario variables in the control space, a correct action domain for protection that satisfies the correct action criterion of distance protection for power frequency variation is established when a fault occurs within the area of ​​the new energy transmission line. The correct action domain is used to characterize the output range in which the distance protection for power frequency variation can correctly identify faults within the area. The intersection of the operational safety domain and the protection correct action domain is used to obtain the control-protection compatibility feasible domain; whereby the control-protection compatibility feasible domain is used to characterize the set of new energy fault current outputs that simultaneously meet the requirements of operational safety and protection correct action.

2. The method for constructing the feasible domain of output current of a new energy power station according to claim 1, characterized in that, The sequence components of the output current of a new energy power station include positive sequence active current component, positive sequence reactive current component, and negative sequence reactive current component.

3. The method for constructing the feasible domain of output current of a new energy power station according to claim 2, characterized in that, Building and running a security domain involves the following steps: Based on the sequence component of the output current of the new energy power station, system parameters and fault scenario variables, the three-phase voltage, three-phase current and active power oscillation component at the point of common coupling are calculated. Establish constraints for maximum phase voltage, maximum phase current, and active power oscillation, respectively; The operational safety domain is the region in the control space that simultaneously satisfies the maximum phase voltage constraint, the maximum phase current constraint, and the active power oscillation constraint.

4. The method for constructing the feasible domain of output current of a new energy power station according to claim 3, characterized in that, The maximum phase voltage constraint is that the maximum value of the three-phase voltage amplitude does not exceed 1.1 times the rated voltage; the maximum phase current constraint is that the maximum value of the three-phase current amplitude does not exceed 1.2 to 1.5 times the rated current; and the active power oscillation constraint is that the amplitude of the active power oscillation component does not exceed the given power oscillation limit.

5. The method for constructing the feasible domain of output current of a new energy power station according to claim 4, characterized in that, Constructing a protection domain for the correct action involves the following steps: Based on the fault boundary conditions and the composite sequence network, the power frequency change distance protection action criterion is transformed into a quadratic surface equation of the control space with respect to the output current sequence component. The region divided by the quadratic surface equation in the control space is the correct action domain of the protection.

6. The method for constructing the feasible domain of output current of a new energy power station according to claim 5, characterized in that, It also includes the following steps: In the three-dimensional control space composed of the sequence components of the output current of the new energy power station, the value of any control variable is fixed, and the other two control variables form a two-dimensional cross-sectional plane. The intersections of the operational safety domain, the protection correct action domain, and the control and protection compatible feasible domain with the two-dimensional cross-sectional plane are obtained respectively to obtain the two-dimensional cross-sections of the operational safety domain, the protection correct action domain, and the control and protection compatible feasible domain.

7. The method for constructing the feasible domain of output current of a new energy power station according to claim 6, characterized in that, The two-dimensional cross-section includes: a positive sequence active current-positive sequence reactive current cross-section with fixed negative sequence reactive current component, and a positive sequence reactive current-negative sequence reactive current cross-section with fixed positive sequence active current component.

8. The method for constructing the feasible domain of output current of a new energy power station according to claim 7, characterized in that, It also includes the following steps: For each set of fault types containing multiple fault types, construct a control and protection compatibility feasible domain corresponding to each fault type; Find the intersection of all control and protection compatible feasible regions to obtain the common intersection feasible region for multiple fault types.

9. The method for constructing the feasible domain of output current of a new energy power station according to claim 8, characterized in that, It also includes the following steps: Quantization calculations are performed on the control and protection compatible feasible region, the two-dimensional cross section of the control and protection compatible feasible region, or the feasible region of the common intersection of multiple fault types. The quantization calculations include calculating the volume of the feasible region, the area of ​​the two-dimensional cross section, or boundary identification.

10. The method for constructing the feasible domain of output current of a new energy power station according to claim 9, characterized in that, Boundary recognition includes: Identify the boundary regions within the operational safety domain dominated by maximum phase voltage constraints, maximum phase current constraints, or active power oscillation constraints, and identify the boundary regions within the control and protection compatibility feasible domain dominated by power frequency variation distance protection action criteria.

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