Transient stability margin evaluation method and system considering fault current limiting characteristic of converter

Abstract

The invention discloses a transient stability margin evaluation method and system considering the fault current limiting characteristic of a converter, and relates to the technical field of power system optimization control and modeling, and the method comprises the steps: constructing a transient power angle characteristic model of power electronic equipment, and obtaining an active power correction calculation relation generated in a current limiting link in a fault ride-through state of the converter; obtaining a voltage-power angle coupling item based on the active power correction amount in the fault transient state, obtaining a limit clearing angle and limit clearing time according to the voltage-power angle coupling item until a convergence condition is met, and obtaining final limit clearing time; and performing transient stability margin evaluation according to the actual fault clearing time and the final limit clearing time. Influences of converter control characteristics on a system transient process under different control modes such as a network construction mode and a network following mode are fused, a converter fault current limiting strategy is considered on the basis of a traditional equal-area method, and applicability and accuracy of novel power distribution system transient stability margin evaluation are comprehensively improved.

Description

Technical Field

[0001] The present invention relates to the technical field of power system monitoring, and particularly to a transient stability margin evaluation method and system considering the fault current limiting characteristics of converters. Background Technique

[0002] The statements in this part merely provide background technical information related to the present invention and do not necessarily constitute prior art.

[0003] With the low-carbon transformation and development of electric power energy, a large number of distributed power electronic equipment such as photovoltaic, wind power, and energy storage are connected to the new distribution system. These equipment are generally connected to the power grid through converters and generate pulse width modulation signals based on typical active and reactive decoupling control, and then control the switching devices to simulate sinusoidal voltage and current electrical quantities to achieve interaction with the AC distribution system. However, affected by control strategies, control parameters, and physical limitations of switching elements, the dynamic characteristics of converter grid-connected equipment are very different from those of traditional synchronous machines. Under fault transient conditions, system variables are likely to exceed the equipment load limit, triggering relevant limiting links, which has a key impact on the transient stability characteristics of the system. Therefore, it is of great practical significance to consider the fault current limiting characteristics of converters in transient stability assessment.

[0004] Existing transient stability margin evaluation methods include numerical methods, direct methods, and artificial intelligence methods. The numerical method calculates the time-domain motion trajectory based on a specific system and initial state, and then judges the transient stability of the system according to whether the electrical quantities exceed the limits. The direct method is based on Lyapunov stability theory and evaluates the transient stability through the size relationship between the system energy and the critical energy, including the energy function method, the equal area method, etc. The artificial intelligence method establishes a mapping relationship between the characteristic quantities and the transient stability results through offline training of sample data, and then applies it to the online prediction and evaluation of the system stability margin.

[0005] However, among the existing transient stability margin evaluation methods, the numerical method and the artificial intelligence method are only applicable to specific systems, and the calculation results lack generality. The direct method is dominated by the characteristics of traditional synchronous machines and insufficiently considers the transient characteristics of power electronic equipment. Therefore, it is difficult to ensure the accuracy of the transient stability margin evaluation results of the new distribution system. Summary of the Invention

[0006] To solve the above problems, the present invention proposes a transient stability margin evaluation method and system considering the fault current limiting characteristics of converters. Aiming at the transient stability characteristics of the new distribution system dominated by power electronic equipment under fault disturbances, it integrates the influence of the control characteristics of converters under different control modes such as network-forming type and grid-following type on the system transient process, and considers the converter fault current limiting strategy on the basis of the traditional equal area method, comprehensively improving the applicability and accuracy of the transient stability margin evaluation of the new distribution system.

[0007] To achieve the above object, the present invention adopts the following technical solutions:

[0008] In a first aspect, the present invention provides a transient stability margin evaluation method considering the fault current limiting characteristics of a converter, including:

[0009] Construct a transient power angle characteristic model of a power electronic device, and according to the transient power angle characteristic model of the power electronic device, obtain the calculation relationship of the active power correction amount generated by the current limiting link in the converter fault ride-through state;

[0010] In the converter fault ride-through state, according to the impedance data at the current time step of the current fault location and in combination with the calculation relationship of the active power correction amount, obtain the active power correction amount in the fault transient state. Based on the active power correction amount in the fault transient state, obtain the voltage-power angle coupling term, and according to the voltage-power angle coupling term, obtain the critical clearing angle and critical clearing time at the current time step. If the critical clearing angle and critical clearing time at the current time step meet the set convergence conditions, then use the critical clearing time at the current time step as the final critical clearing time;

[0011] Evaluate the transient stability margin according to the relationship between the actual fault clearing time and the final critical clearing time.

[0012] As an alternative implementation, the transient power angle characteristic model of the power electronic device includes a transient power angle characteristic model of a network-forming power electronic device and a transient power angle characteristic model of a grid-following power electronic device;

[0013] The transient power angle characteristic model of the network-forming power electronic device is:

[0014] sδ = Δω

[0015]

[0016] The transient power angle characteristic model of the grid-following power electronic device is:

[0017] sδ′ = Δω′

[0018]

[0019] Among them, s is the first-order differential operator; δ is the power angle between the network-forming power electronic device and the reference power supply; Δω is the rotational speed difference between the network-forming power electronic device and the reference power supply; J is the virtual moment of inertia of the network-forming power electronic device, ω0 is the rated rotational speed, P set is the active power set value, P g is the actual active power value; J′ is the equivalent virtual moment of inertia determined by the proportional and integral coefficients of the phase-locked loop of the grid-following power electronic device, V q ′ is the intermediate variable related to the dynamics of the phase-locked loop, V q$V_{q}$ is the q-axis component of the grid connection point voltage, $\delta'$ is the phase angle between the grid-following power electronic device and the reference power supply; $\Delta\omega'$ is the rotational speed difference between the grid-following power electronic device and the reference power supply.

[0020] The present invention integrates the influence of the control characteristics of converters under different control modes such as grid-forming and grid-following on the system transient process, establishes a mathematical model characterizing the transient power angle characteristics of power electronic devices, improves the expansion ability of the transient stability margin evaluation model for new power electronic equipment, and enhances the applicability of the evaluation model to new distribution systems.

[0021] As an alternative implementation, according to the transient power angle characteristic model of the power electronic device, the calculation relationship of the power output limit is determined, and thus the calculation relationship of the active power correction amount generated by the current limiting link in the converter fault ride-through state is obtained;

[0022] The calculation relationship of the power output limit is:

[0023]

[0024] Where, $I$ d,ref and $I$ q,ref are the d-axis current reference value and the q-axis current reference value respectively; $K$ d and $K$ q are the q-axis voltage response parameter and the d-axis voltage response parameter in the fault state respectively; $V$ LVRT is the low voltage ride-through voltage threshold; $V$ rms is the effective value of the grid connection point voltage; $I$ d,set and $I$ q,set are the d-axis current setting value and the q-axis current setting value; $I$ max is the maximum current, $I$ d,max is the maximum d-axis current, $I$ q is the q-axis current component, $P$ g,max is the maximum active power, $V$ d and $V$ q are the d-axis voltage component and the q-axis voltage component respectively;

[0025] The impedance data includes the system voltage in the fault state the total system impedance $X$ in the fault state (2) , the original power angle value $\delta'$ without considering the current limiting characteristic and the actual active power value $P$ g , then the calculation relationship of the active power correction amount is:

[0026]

[0027] Where, $\Delta P$ fault is the active power correction amount in the fault transient.

[0028] As an alternative embodiment, the voltage-power angle coupling term obtained based on the active power correction amount under the fault transient is:

[0029]

[0030] where A3 is the voltage-power angle coupling term; δ cc is the critical angle for triggering the current limiting state; δ cm is the critical clearing angle, ΔP fault is the active power correction amount under the fault transient, is the system voltage under the fault state, X (2) is the total system impedance under the fault state, δ′ is the original value of the power angle without considering the current limiting characteristic, V rms is the effective value of the grid-connected point voltage, V d and V q are the d-axis voltage component and the q-axis voltage component respectively, I d,max is the maximum value of the d-axis current, I q is the q-axis current component.

[0031] As an alternative embodiment, the calculation formulas for the critical clearing angle and the critical clearing time are respectively:

[0032]

[0033] where δ cm is the critical clearing angle at the current time step, is the critical clearing angle at the previous time step, t cm is the critical clearing time at the current time step, ω is the rotational speed, δ cc is the critical angle for triggering the current limiting state, δ1 is the initial value of the power angle at the start of the fault, δ2 is the critical angle corresponding to the torque balance point after the fault is cleared, V rms is the effective value of the grid-connected point voltage, P g,max is the maximum value of the active power, is the system voltage under the fault state, X (2) is the total system impedance under the fault state, P set is the set value of the active power, X (1) is the total system impedance before the fault, is the system voltage before the fault, X (3) is the total system impedance after the fault is cleared, is the system voltage after the fault is cleared;

[0034] The set convergence condition is: the difference between the critical clearing angle δ cm at the current time step and the critical clearing angle at the previous time step is less than the set first threshold, and the critical clearing time t cmThe difference from the critical clearing time of the previous time step is less than a set second threshold value;

[0035] If the critical clearing angle and the critical clearing time of the current time step do not meet the set convergence conditions, the impedance data is updated at the next time step, and the updated critical clearing angle and the critical clearing time are obtained therefrom until the set convergence conditions are met.

[0036] As an alternative implementation manner, the process of evaluating the transient stability margin according to the relationship between the actual fault clearing time and the final critical clearing time is as follows: if the actual fault clearing time is less than the final critical clearing time, the system is transiently stable; otherwise, it is transiently unstable.

[0037] The present invention provides a transient stability margin evaluation method and system considering the fault current limiting characteristics of a converter. Based on the traditional equal area method, the fault current limiting strategy of the converter is considered. Based on the active and reactive power coupling relationship caused by the current limiting link in the fault ride-through state, the correction amount of the active power in the fault transient is calculated, and then the voltage-power angle coupling term introduced by the fault current limiting characteristics of the converter is increased, which can accurately characterize the fault transient characteristics of the converter and comprehensively improve the accuracy of the transient stability margin evaluation result.

[0038] In a second aspect, the present invention provides a transient stability margin evaluation system considering the fault current limiting characteristics of a converter, including:

[0039] A modeling module configured to construct a transient power angle characteristic model of a power electronic device, and obtain a calculation relationship of the correction amount of the active power generated by the current limiting link in the fault ride-through state of the converter according to the transient power angle characteristic model of the power electronic device;

[0040] A calculation module configured to, in the fault ride-through state of the converter, obtain the correction amount of the active power in the fault transient according to the impedance data at the current time step of the current fault location and in combination with the calculation relationship of the correction amount of the active power, obtain the voltage-power angle coupling term based on the correction amount of the active power in the fault transient, obtain the critical clearing angle and the critical clearing time of the current time step according to the voltage-power angle coupling term, and if the critical clearing angle and the critical clearing time of the current time step meet the set convergence conditions, use the critical clearing time of the current time step as the final critical clearing time;

[0041] An evaluation module configured to evaluate the transient stability margin according to the relationship between the actual fault clearing time and the final critical clearing time.

[0042] As an alternative implementation manner, the transient power angle characteristic model of the power electronic device includes a transient power angle characteristic model of a network-forming power electronic device and a transient power angle characteristic model of a network-following power electronic device;

[0043] The transient power angle characteristic model of the network-forming power electronic device is:

[0044] sδ = Δω

[0045]

[0046] The transient power angle characteristic model of the grid-connected power electronic device is as follows:

[0047] sδ′ = Δω′

[0048]

[0049] Wherein, s is the first-order differential operator; δ is the power angle between the grid-forming power electronic device and the reference power supply; Δω is the rotational speed difference between the grid-forming power electronic device and the reference power supply; J is the virtual moment of inertia of the grid-forming power electronic device, ω0 is the rated rotational speed, P set is the set value of the active power, P g is the actual value of the active power; J′ is the equivalent virtual moment of inertia determined by the proportional and integral coefficients of the phase-locked loop of the grid-following power electronic device, V q ′ is the intermediate variable related to the dynamics of the phase-locked loop, V q is the q-axis component of the grid-connected point voltage, δ′ is the phase angle between the grid-following power electronic device and the reference power supply; Δω′ is the rotational speed difference between the grid-following power electronic device and the reference power supply.

[0050] As an alternative implementation, according to the transient power angle characteristic model of the power electronic device, the calculation relationship of the power output limit is determined, and thus the calculation relationship of the active power correction amount generated by the current-limiting link in the lower limit of the converter fault ride-through state is obtained;

[0051] The calculation relationship of the power output limit is:

[0052]

[0053] Wherein, I d,ref and I q,ref are the d-axis current reference value and the q-axis current reference value respectively; K d and K q are the q-axis voltage response parameter and the d-axis voltage response parameter in the fault state respectively; V LVRT is the low-voltage ride-through voltage threshold; V rms is the effective value of the grid-connected point voltage; I d,set and I q,set are the d-axis current set value and the q-axis current set value; I max is the maximum current, I d,max is the maximum d-axis current, I q is the q-axis current component, P g,max is the maximum active power, V d and V qThey are the d-axis voltage component and the q-axis voltage component respectively;

[0054] The impedance data includes the system voltage under the fault condition The total system impedance X under the fault condition (2) , the original power angle δ′ without considering the current-limiting characteristic and the actual active power value P g , then the calculation relationship of the active power correction amount is:

[0055]

[0056] Where, ΔP fault is the active power correction amount under the fault transient state.

[0057] As an alternative implementation, the voltage-power angle coupling term obtained based on the active power correction amount under the fault transient state is:

[0058]

[0059] Where, A3 is the voltage-power angle coupling term; δ cc is the critical angle for triggering the current-limiting state; δ cm is the critical clearing angle, ΔP fault is the active power correction amount under the fault transient state, is the system voltage under the fault condition, X (2) is the total system impedance under the fault condition, δ′ is the original power angle value without considering the current-limiting characteristic, V rms is the effective value of the grid-connected point voltage, V d and V q are the d-axis voltage component and the q-axis voltage component respectively, I d,max is the maximum value of the d-axis current, I q is the q-axis current component.

[0060] As an alternative implementation, the calculation formulas for the critical clearing angle and the critical clearing time are respectively:

[0061]

[0062] Where, δ cm is the critical clearing angle at the current time step, is the critical clearing angle at the previous time step, t cm is the critical clearing time at the current time step, ω is the rotational speed, δ cc is the critical angle for triggering the current-limiting state, δ1 is the initial power angle value at the start of the fault, δ2 is the critical angle corresponding to the torque balance point after the fault is cleared, V rms is the effective value of the grid-connected point voltage, P g,max is the maximum value of the active power, is the system voltage under the fault condition, X(2) is the total system impedance under fault conditions, P set is the set value of active power, X (1) is the total system impedance before the fault, is the system voltage before the fault, X (3) is the total system impedance after fault clearing, is the system voltage after fault clearing;

[0063] The set convergence condition is: the critical clearing angle δ at the current time step cm and the critical clearing angle at the previous time step have a difference less than the set first threshold, and the critical clearing time t at the current time step cm and the difference between the critical clearing time at the previous time step is less than the set second threshold;

[0064] If the critical clearing angle and critical clearing time at the current time step do not meet the set convergence condition, the impedance data is updated at the next time step, and the updated critical clearing angle and critical clearing time are obtained until the set convergence condition is met.

[0065] As an alternative implementation, the process of evaluating the transient stability margin according to the relationship between the actual fault clearing time and the final critical clearing time is: if the actual fault clearing time is less than the final critical clearing time, the system is transiently stable, otherwise it is transiently unstable.

[0066] In a third aspect, the present invention provides an electronic device, including a memory and a processor, and computer instructions stored on the memory and running on the processor. When the computer instructions are run by the processor, the method described in the first aspect is completed.

[0067] In a fourth aspect, the present invention provides a computer-readable storage medium for storing computer instructions. When the computer instructions are executed by a processor, the method described in the first aspect is completed.

[0068] In a fifth aspect, the present invention provides a computer program product, including a computer program. When the computer program is executed by a processor, the method described in the first aspect is implemented.

[0069] Compared with the prior art, the beneficial effects of the present invention are:

[0070] The present invention proposes a transient stability margin evaluation method and system considering the fault current limiting characteristics of converters, which integrates the influence of converter control characteristics under different control modes such as network-forming type and grid-following type on the system transient process, establishes a mathematical model representing the transient power angle characteristics of power electronic devices based on the power outer loop and current inner loop control links, improves the expansion ability of the transient stability margin evaluation model for new power electronic equipment, and effectively improves the applicability of the evaluation model to new distribution systems.

[0071] The present invention provides a transient stability margin evaluation method and system considering the fault current limiting characteristics of converters. Based on the traditional equal - area method, the fault current limiting strategy of converters is considered. Based on the active - reactive power coupling relationship caused by the current limiting link in the fault - ride - through state, the correction amount of active power under fault transients is calculated. Furthermore, the voltage - power angle coupling term introduced by the fault current limiting characteristics of converters is added. According to the voltage - power angle coupling term, the critical clearing angle and critical clearing time are obtained, and it is judged whether the critical clearing angle and critical clearing time at the current time step meet the set convergence conditions. If they are met, the critical clearing time at the current time step is taken as the final critical clearing time. If not, by updating the impedance data, the updated critical clearing angle and critical clearing time are obtained through iterative calculation until the set convergence conditions are met to obtain the final critical clearing time. The transient stability margin is evaluated according to the relationship between the actual fault clearing time and the final critical clearing time. If the actual fault clearing time is less than the final critical clearing time, the system is transiently stable; otherwise, it is transiently unstable. Thus, the transient characteristics of converter faults can be accurately characterized, and the accuracy of the transient stability margin evaluation results can be comprehensively improved.

[0072] The present invention provides a transient stability margin evaluation method and system considering the fault current limiting characteristics of converters. Aiming at the transient stability characteristics of a new - type distribution system dominated by power electronic devices under fault disturbances, starting from the basic control logic of the power outer - loop and current inner - loop control links, the traditional equal - area method based on synchronous machines is improved to consider the control characteristics of converters, so that the calculation process includes the influence of the dynamics of power electronic equipment on the transient process, and the applicability and accuracy of the transient stability margin evaluation of the new - type distribution system are comprehensively improved.

[0073] Advantages of additional aspects of the present invention will be partly given in the following description, partly will become obvious from the following description, or will be understood through the practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0074] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained according to the provided drawings.

[0075] Figure 1 It is the power curve diagrams before, during, and after the fault provided in Embodiment 1 of the present invention;

[0076] Figure 2 It is the flow chart of the transient stability margin evaluation method considering the fault current limiting characteristics of converters provided in Embodiment 1 of the present invention. Detailed Implementation Manner

[0077] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0078] It should be noted that the following detailed description is exemplary and is intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present invention belongs.

[0079] It should be noted that the terms used herein are only for describing specific implementation manners and are not intended to limit the exemplary embodiments according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular forms are also intended to include the plural forms. In addition, it should be understood that the terms "comprising" and "including" and any variations thereof are intended to cover non-exclusive inclusion. For example, a process, method, system, product or device comprising a series of steps or units is not necessarily limited to those clearly listed steps or units, but may include other steps or units not clearly listed or inherent to these processes, methods, products or devices.

[0080] In the case of no conflict, the embodiments in the present invention and the features in the embodiments can be combined with each other.

[0081] Embodiment 1

[0082] This embodiment provides a transient stability margin evaluation method considering the fault current limiting characteristics of a converter, including:

[0083] Construct a transient power angle characteristic model of a power electronic device, and according to the transient power angle characteristic model of the power electronic device, obtain the calculation relationship of the active power correction amount generated by the current limiting link in the converter fault ride-through state;

[0084] In the converter fault ride-through state, according to the impedance data at the current time step of the current fault location and in combination with the calculation relationship of the active power correction amount, obtain the active power correction amount in the fault transient state. Based on the active power correction amount in the fault transient state, obtain the voltage-power angle coupling term, and according to the voltage-power angle coupling term, obtain the critical clearing angle and critical clearing time at the current time step. If the critical clearing angle and critical clearing time at the current time step meet the set convergence conditions, then use the critical clearing time at the current time step as the final critical clearing time;

[0085] Evaluate the transient stability margin according to the relationship between the actual fault clearing time and the final critical clearing time.

[0086] In this embodiment, as Figure 1The power curves before, during, and after the fault are shown. The power curves before, during, and after the fault respectively refer to the relationship curves between the active power of the power source and the power angle corresponding to the state before the fault (normal operation state), during the fault (fault state), and after the fault removal (fault removal state).

[0087] Based on the mathematical relationship between the power outer loop and current inner loop control links of power electronic devices and the power angle characteristics, this embodiment establishes the voltage-power angle coupling terms under the influence of the fault current limiting control strategies of grid-forming and grid-following power electronic devices, quantifies the influence of the current limiting link on the system transient stability during the converter fault ride-through state, and obtains the expression of the system transient stability margin considering the converter fault current limiting characteristics, that is, the system transient stability margin is evaluated through the actual fault removal time and the critical clearing time. The process is as Figure 2 shown.

[0088] The specific implementation process is as follows:

[0089] Step 1: First, construct the transient power angle characteristic models of power electronic devices, including the transient power angle characteristic model of grid-forming power electronic devices and the transient power angle characteristic model of grid-following power electronic devices; that is, through the basic control strategy of the converter, establish a mathematical model representing the transient power angle characteristics of power electronic devices according to the power outer loop and current inner loop control links.

[0090] Specifically:

[0091] Based on the rotor motion equation, construct the transient power angle characteristic model of grid-forming power electronic devices, specifically:

[0092] sδ=Δω

[0093]

[0094] where s is the first-order differential operator; δ is the power angle between the grid-forming power electronic device and the reference power source; Δω is the speed difference between the grid-forming power electronic device and the reference power source; J is the virtual moment of inertia of the grid-forming power electronic device, ω0 is the rated speed, P set is the active power set value, P g is the actual active power value.

[0095] Based on the Phase Locked Loop (PLL), dynamically establish the transient power angle characteristic model of grid-following power electronic devices, specifically:

[0096] sδ″+=Δω′

[0097]

[0098] Among them, J′ is the equivalent virtual moment of inertia determined by the PLL proportional and integral coefficients of the grid-following power electronic device, and V′ q is an intermediate variable related to the PLL dynamics, and V q is the q-axis component of the grid connection point voltage; δ″ is the phase angle between the grid-following power electronic device and the reference power supply, that is, the PLL output phase; Δω′ is the rotational speed difference between the grid-following power electronic device and the reference power supply.

[0099] This embodiment integrates the influence of the control characteristics of converters under different control modes such as grid-forming and grid-following on the system transient process, establishes a mathematical model characterizing the transient power angle characteristics of power electronic devices based on the power outer loop and current inner loop control links, improves the expansion ability of the transient stability margin evaluation model for new power electronic equipment, and effectively improves the applicability of the evaluation model to new distribution systems.

[0100] Step 2: Obtain the converter fault current limiting control parameters K q and K d , which respectively represent the q-axis voltage response parameter and d-axis voltage response parameter in the fault state. Considering the converter fault current limiting strategy, based on the active and reactive coupling relationship generated by the current limiting link under the fault ride-through state, a calculation relationship for the active power correction amount in the fault transient is constructed.

[0101] Specifically:

[0102] Combined with the transient power angle characteristic model of power electronic devices, aiming at the consistent characteristics of the current limiting link of grid-forming power electronic devices and grid-following power electronic devices under the fault ride-through state, a general calculation relationship for the power output limit is established, specifically:

[0103]

[0104] Among them, I d,ref and I q,ref are the d-axis current reference value and q-axis current reference value respectively; V LVRT is the low voltage ride-through threshold, generally taken as 0.9 p.u.; V rms is the effective value of the grid connection point voltage; I d,set and I q,set are the d-axis current setting value and q-axis current setting value; I max is the maximum current, I d,max is the maximum d-axis current, I q is the q-axis current component, P g,max is the maximum active power, V d and V q are the d-axis voltage component and q-axis voltage component respectively.

[0105] In the converter fault ride-through state, there is a coupling relationship between the active and reactive links, specifically:

[0106] I q <I max

[0107]

[0108] Furthermore, the calculation relationship of the active power correction amount generated by the current limiting link is obtained as follows:

[0109]

[0110] where ΔP fault is the active power correction amount considering the current limiting characteristics of the converter fault, is the system voltage under the fault condition, X (2) is the total system impedance under the fault condition, and δ′ is the original value of the power angle without considering the current limiting characteristics.

[0111] Step 3: In the state of the converter fault ride-through, obtain the impedance data of the current fault location (1, 2,..., N) at the current time step k, and calculate the voltage-power angle coupling term based on the active power correction amount under the fault transient;

[0112] Specifically, the voltage-power angle coupling term characterizing the influence of the fault current limiting characteristics on the transient stability is:

[0113]

[0114] where A3 is the voltage-power angle coupling term considering the current limiting characteristics of the converter fault, which is used to quantify the influence of the current limiting link of the power electronic device on the system transient stability; δ cc is the critical angle for triggering the current limiting state; δ cm is the critical clearing angle.

[0115] Among them, in this embodiment, for each fault location, the corresponding impedance data, voltage data, etc. are respectively substituted into the calculation relationship of the active power correction amount to form an improved index model for each fault location.

[0116] Step 4: On the basis of the equal area method, add the voltage-power angle coupling term introduced by the converter fault current limiting characteristics to obtain the expression of the system transient stability margin considering the converter fault current limiting characteristics, that is, the calculation formula of the critical clearing angle and the critical clearing time, and then evaluate the system transient stability margin through the relationship between the actual fault clearing time and the critical clearing time.

[0117] Specifically, the equal area expression considering the converter fault current limiting characteristics is:

[0118] A1 + A2 + A3 = 0;

[0119] Among them, A1 is the original accelerating area without considering the current limiting link; A3 is the voltage-power angle coupling term considering the current limiting characteristics of the converter fault, representing the correction amount of the accelerating area considering the current limiting link; A2 is the decelerating area after the fault is cleared.

[0120] A1, A2, and A3 are respectively:

[0121]

[0122] Among them, δ1 is the initial value of the power angle at the start of the fault, δ2 is the critical angle corresponding to the torque balance point after the fault is cleared, δ cc is the critical angle for triggering the current limiting state, δ cm is the critical clearing angle, X (1) is the total impedance of the system before the fault, is the system voltage before the fault, X (3) is the total impedance of the system after the fault is cleared, is the system voltage after the fault is cleared.

[0123] The critical angles δ2 and δ cc are respectively:

[0124]

[0125] Furthermore, an iterative calculation method is used to calculate the critical clearing angle and the critical clearing time, which are respectively:

[0126]

[0127] Among them, δ cm is the critical clearing angle at the current time step, is the critical clearing angle at the previous time step, t cm is the critical clearing time at the current time step, ω is the rotational speed.

[0128] If the difference between the critical clearing angle δ cm at the current time step and the critical clearing angle at the previous time step is less than the set first threshold, and the difference between the critical clearing time t cm at the current time step and the critical clearing time at the previous time step is less than the set second threshold, it is determined that the convergence condition is satisfied, and thus the critical clearing time t cm at the current time step is taken as the final critical clearing time;

[0129] If the critical clearing angle and the critical clearing time at the current time step do not satisfy the above convergence condition, the impedance data is updated at the next time step, and the updated critical clearing angle and critical clearing time are obtained until the set convergence condition is satisfied.

[0130] Finally, based on the actual fault clearing time t of the relay protection and circuit breaker c and the final critical clearing time t cm a transient stability margin assessment is carried out; if the actual fault clearing time t c < t cm , the system is transiently stable; otherwise, it is transiently unstable.

[0131] Based on the traditional equal - area method, this embodiment takes into account the converter fault current - limiting strategy. Based on the active - reactive power coupling relationship caused by the current - limiting link in the converter fault - ride - through state, the active - power correction amount in the fault transient is calculated, and then the voltage - power angle coupling term introduced by the converter fault current - limiting characteristic is increased, which can accurately describe the converter fault transient characteristics and comprehensively improve the accuracy of the transient stability margin assessment results.

[0132] Embodiment 2

[0133] This embodiment provides a transient stability margin assessment system considering the converter fault current - limiting characteristic, including:

[0134] A modeling module, configured to construct a transient power - angle characteristic model of power electronic devices, and obtain the calculation relationship of the active - power correction amount generated by the current - limiting link in the converter fault - ride - through state according to the transient power - angle characteristic model of power electronic devices;

[0135] A calculation module, configured to, in the converter fault - ride - through state, obtain the active - power correction amount in the fault transient according to the impedance data at the current time step of the current fault location and in combination with the calculation relationship of the active - power correction amount, obtain the voltage - power angle coupling term based on the active - power correction amount in the fault transient, obtain the critical clearing angle and critical clearing time at the current time step according to the voltage - power angle coupling term, and if the critical clearing angle and critical clearing time at the current time step meet the set convergence conditions, take the critical clearing time at the current time step as the final critical clearing time;

[0136] An assessment module, configured to carry out a transient stability margin assessment according to the relationship between the actual fault clearing time and the final critical clearing time.

[0137] In this embodiment, the transient power - angle characteristic model of power electronic devices includes a transient power - angle characteristic model of network - forming power electronic devices and a transient power - angle characteristic model of grid - following power electronic devices;

[0138] The transient power - angle characteristic model of network - forming power electronic devices is:

[0139] sδ = Δω

[0140]

[0141] The transient power - angle characteristic model of grid - following power electronic devices is:

[0142] sδ′ = Δω′

[0143]

[0144] Wherein, s is the first-order differential operator; δ is the power angle between the network-forming power electronic device and the reference power supply; Δω is the rotational speed difference between the network-forming power electronic device and the reference power supply; J is the virtual moment of inertia of the network-forming power electronic device, ω0 is the rated rotational speed, P set is the set value of active power, P g is the actual value of active power; J′ is the equivalent virtual moment of inertia determined by the phase-locked loop proportional and integral coefficients of the grid-following power electronic device, V q ′ is an intermediate variable related to the dynamics of the phase-locked loop, V q is the q-axis component of the grid-connected point voltage, δ′ is the phase angle between the grid-following power electronic device and the reference power supply; Δω′ is the rotational speed difference between the grid-following power electronic device and the reference power supply.

[0145] In this embodiment, according to the transient power angle characteristic model of the power electronic device, the calculation relationship of the power output limit is determined, and thus the calculation relationship of the active power correction amount generated by the current limiting link in the lower limit of the converter fault ride-through state is obtained;

[0146] The calculation relationship of the power output limit is:

[0147]

[0148] Wherein, I d,ref and I q,ref are the d-axis current reference value and the q-axis current reference value respectively; K d and K q are the q-axis voltage response parameter and the d-axis voltage response parameter in the fault state respectively; V LVRT is the low-ride-through voltage threshold; V rms is the effective value of the grid-connected point voltage; I d,set and I q,set are the d-axis current set value and the q-axis current set value respectively; I max is the maximum current, I d,max is the maximum d-axis current, I q is the q-axis current component, P g,max is the maximum active power, V d and V q are the d-axis voltage component and the q-axis voltage component respectively;

[0149] The impedance data includes the system voltage in the fault state The total system impedance X in the fault state (2) , the original power angle value δ′ and the actual active power value P without considering the current limiting characteristicg , the calculation relationship of the active power correction amount is as follows:

[0150]

[0151] Among them, ΔP fault is the active power correction amount under the fault transient.

[0152] In this embodiment, the voltage-power angle coupling term obtained based on the active power correction amount under the fault transient is:

[0153]

[0154] Among them, A3 is the voltage-power angle coupling term; δ cc is the critical angle for triggering the current limiting state; δ cm is the critical clearing angle, ΔP fault is the active power correction amount under the fault transient, is the system voltage under the fault state, X (2) is the total system impedance under the fault state, δ′ is the original value of the power angle without considering the current limiting characteristic, V rms is the effective value of the grid-connected point voltage, V d and V q are the d-axis voltage component and the q-axis voltage component respectively, I d,max is the maximum value of the d-axis current, I q is the q-axis current component.

[0155] In this embodiment, the critical clearing angle and the critical clearing time are respectively:

[0156]

[0157] Among them, δ cm is the critical clearing angle at the current time step, is the critical clearing angle at the previous time step, t cm is the critical clearing time at the current time step, ω is the rotational speed, δ cc is the critical angle for triggering the current limiting state, δ1 is the initial value of the power angle at the start of the fault, δ2 is the critical angle corresponding to the torque balance point after the fault is cleared, V rms is the effective value of the grid-connected point voltage, P g,max is the maximum value of the active power, is the system voltage under the fault state, X (2) is the total system impedance under the fault state, P set is the set value of the active power, X (1) is the total system impedance before the fault, is the system voltage before the fault, X (3) is the total system impedance after the fault is cleared, is the system voltage after the fault is cleared;

[0158] The set convergence conditions are as follows: the critical clearing angle δ at the current time step cm and the critical clearing angle at the previous time step have a difference less than the set first threshold, and the critical clearing time t at the current time step cm and the difference between the critical clearing time at the current time step and that at the previous time step is less than the set second threshold;

[0159] If the critical clearing angle and critical clearing time at the current time step do not meet the set convergence conditions, the impedance data is updated at the next time step, and thus the updated critical clearing angle and critical clearing time are obtained until the set convergence conditions are met.

[0160] In this embodiment, the process of evaluating the transient stability margin according to the relationship between the actual fault clearing time and the final critical clearing time is as follows: if the actual fault clearing time is less than the final critical clearing time, the system is transiently stable; otherwise, it is transiently unstable.

[0161] It should be noted here that the above modules correspond to the steps described in Embodiment 1. The examples and application scenarios implemented by the above modules and the corresponding steps are the same, but are not limited to the content disclosed in the above Embodiment 1. It should be noted that the above modules, as part of the system, can be executed in a computer system such as a set of computer executable instructions.

[0162] In more embodiments, there is also provided:

[0163] An electronic device, including a memory, a processor, and computer instructions stored on the memory and running on the processor. When the computer instructions are run by the processor, the method described in Embodiment 1 is completed. For the sake of brevity, it will not be elaborated here.

[0164] It should be understood that in this embodiment, the processor may be a central processing unit CPU, and the processor may also be other general-purpose processors, digital signal processors DSP, application-specific integrated circuits ASIC, off-the-shelf programmable gate arrays FPGA, or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. The general-purpose processor may be a microprocessor or the processor may also be any conventional processor, etc.

[0165] The memory may include a read-only memory and a random access memory, and provide instructions and data to the processor. A part of the memory may also include a non-volatile random access memory. For example, the memory may also store information about the device type.

[0166] A computer-readable storage medium for storing computer instructions. When the computer instructions are executed by the processor, the method described in Embodiment 1 is completed.

[0167] The method in Embodiment 1 can be directly implemented by a hardware processor, or by a combination of hardware and software modules in the processor. The software module can be located in a mature storage medium in the art, such as random access memory, flash memory, read-only memory, programmable read-only memory, or electrically erasable programmable memory, registers, etc. This storage medium is located in the memory, and the processor reads the information in the memory and combines its hardware to complete the steps of the above method. To avoid repetition, it will not be described in detail here.

[0168] A computer program product includes a computer program, and when the computer program is executed by a processor, it implements the method described in Embodiment 1.

[0169] The present invention also provides at least one computer program product tangibly stored on a non-transitory computer-readable storage medium. The computer program product includes computer-executable instructions, such as instructions included in program modules, which are executed in a device on a target real or virtual processor to perform the process / method as described above. Generally, program modules include routines, programs, libraries, objects, classes, components, data structures, etc. that perform specific tasks or implement specific abstract data types. In various embodiments, the functions of program modules can be combined or divided as needed. The machine-executable instructions for program modules can be executed within a local or distributed device. In a distributed device, program modules can be located in local and remote storage media.

[0170] The computer program code for implementing the method of the present invention can be written in one or more programming languages. These computer program codes can be provided to the processor of a general-purpose computer, a special-purpose computer, or other programmable data processing devices, so that when the program code is executed by the computer or other programmable data processing devices, the functions / operations specified in the flowchart and / or block diagram are implemented. The program code can be executed entirely on the computer, partially on the computer, as an independent software package, partially on the computer and partially on a remote computer, or entirely on a remote computer or server.

[0171] In the context of the present invention, the computer program code or related data can be carried by any suitable carrier so that the device, apparatus, or processor can perform the various processes and operations described above. Examples of carriers include signals, computer-readable media, etc. Examples of signals can include electrical, optical, radio, sound, or other forms of propagated signals, such as carrier waves, infrared signals, etc.

[0172] Those of ordinary skill in the art can realize that the units and algorithm steps of the examples described in conjunction with this embodiment can be implemented by electronic hardware or a combination of computer software and electronic hardware. Whether these functions are executed in a hardware or software manner depends on the specific application and design constraints of the technical solution. Professional technicians can use different methods to implement the described functions for each specific application, but such implementation should not be considered to exceed the scope of this application.

[0173] Although the specific implementation manners of the present invention have been described above in conjunction with the accompanying drawings, it is not a limitation on the protection scope of the present invention. Those skilled in the art should understand that, based on the technical solution of the present invention, various modifications or deformations that can be made by those skilled in the art without creative efforts are still within the protection scope of the present invention.

Claims

1. A transient stability margin assessment method taking into account the fault current limiting characteristics of a converter, characterized in that: include: Construct a transient power angle characteristic model of power electronic equipment, and obtain the calculation relationship of the active power correction amount generated by the current limiting link under the converter fault ride-through state based on the transient power angle characteristic model of power electronic equipment; In the state of converter fault ride-through, the active power correction amount under fault transient is obtained according to the impedance data of the current fault position under the current time step and the calculation relationship of the active power correction amount. The voltage-power angle coupling term is obtained based on the active power correction amount under fault transient. The limit resection angle and limit resection time of the current time step are obtained according to the voltage-power angle coupling term. If the limit resection angle and limit resection time of the current time step meet the set convergence conditions, the limit resection time of the current time step is taken as the final limit resection time. The transient stability margin is evaluated based on the relationship between the actual fault clearing time and the ultimate limit clearing time.

2. The transient stability margin assessment method taking into account the converter fault current limiting characteristics according to claim 1, characterized in that: The transient power angle characteristic model of power electronic equipment includes the transient power angle characteristic model of grid-building power electronic equipment and the transient power angle characteristic model of grid-following power electronic equipment; The transient power angle characteristic model of grid-connected power electronic equipment is: sδ=Δω The transient power angle characteristic model of grid-following power electronic equipment is: sδ′=Δω′ Where s is the first-order differential operator; δ is the power angle between the grid-type power electronic device and the reference power supply; Δω is the speed difference between the grid-type power electronic device and the reference power supply; J is the virtual moment of inertia of the grid-type power electronic device, ω0 is the rated speed, P set is the active power setting value, P g is the actual value of active power; J′ is the equivalent virtual moment of inertia determined by the proportional and integral coefficient of the phase-locked loop of the grid-following power electronic equipment, V q ′ is an intermediate variable related to the dynamics of the phase-locked loop, V q is the q-axis component of the grid-connected point voltage, δ′ is the phase angle between the grid-following power electronic device and the reference power supply; Δω′ is the speed difference between the grid-following power electronic device and the reference power supply.

3. The transient stability margin assessment method taking into account the converter fault current limiting characteristics according to claim 1, characterized in that: According to the transient power angle characteristic model of power electronic equipment, the power output limit calculation relationship is determined, thereby obtaining the calculation relationship of the active power correction amount generated by the current limiting link under the converter fault ride-through state; The power output limit calculation relationship is: Among them, I d,ref and I q,ref are the d-axis current reference value and the q-axis current reference value respectively; K d and K q are the q-axis voltage response parameters and d-axis voltage response parameters under fault conditions respectively; V LVRT is the low breakdown voltage threshold; V rms is the effective value of the grid connection point voltage; I d,set and I q,set is the d-axis current setting value and the q-axis current setting value; I max is the maximum current, I d,max is the maximum d-axis current, I q is the q-axis current component, P g,max is the maximum active power, V d and V q are the d-axis voltage component and the q-axis voltage component respectively; Impedance data includes system voltage under fault conditions The total system impedance X under fault conditions (2) , the original value of the power angle δ′ and the actual value of active power P without considering the current limiting characteristics g , then the calculation relationship of active power correction is: Among them, ΔP fault It is the active power correction value under fault transient state.

4. The transient stability margin assessment method taking into account the converter fault current limiting characteristics according to claim 1, characterized in that: The voltage-power angle coupling term obtained based on the active power correction under fault transient is: Among them, A3 is the voltage-power angle coupling term; δ cc is the critical angle for triggering the current limiting state; δ cm is the limiting resection angle, ΔP fault is the active power correction value under fault transient state, is the system voltage in the fault state, X (2) is the total system impedance under fault conditions, δ′ is the original value of the power angle without considering the current limiting characteristics, V rms is the effective value of the grid connection point voltage, V d and V q are the d-axis voltage component and the q-axis voltage component, I d,max is the maximum d-axis current, I q is the q-axis current component.

5. The transient stability margin assessment method taking into account the converter fault current limiting characteristics according to claim 1, characterized in that: The calculation formulas for the limit resection angle and limit resection time are: Among them, δ cm is the limit resection angle of the current time step, is the limit resection angle of the previous time step, t cm is the limit removal time of the current time step, ω is the speed, δ cc is the critical angle for triggering the current limiting state, δ1 is the initial value of the power angle at the beginning of the fault, δ2 is the critical angle corresponding to the torque balance point after the fault is removed, V rms is the effective value of the grid connection point voltage, P g,max is the maximum active power, is the system voltage in the fault state, X (2) is the total system impedance under fault conditions, P set is the active power setting value, X (1) is the total system impedance before the fault, is the system voltage before the fault, X (3) is the total system impedance after the fault is cleared, It is the system voltage after the fault is cleared; The convergence condition is set as follows: the limit resection angle δ of the current time step cm The limit resection angle of the previous time step The difference is less than the set first threshold, and the limit cut-off time t of the current time step cm The difference between the limit removal time of the previous time step and the limit removal time of the previous time step is less than the set second threshold value; If the limit resection angle and limit resection time of the current time step do not meet the set convergence conditions, the impedance data is updated in the next time step to obtain updated limit resection angle and limit resection time until the set convergence conditions are met.

6. The transient stability margin assessment method taking into account the converter fault current limiting characteristics according to claim 1, characterized in that: The process of evaluating the transient stability margin based on the relationship between the actual fault removal time and the final limit removal time is as follows: if the actual fault removal time is less than the final limit removal time, the system is transiently stable, otherwise it is transiently unstable.

7. A transient stability margin assessment system taking into account the fault current limiting characteristics of a converter, characterized in that: include: A modeling module is configured to construct a transient power angle characteristic model of a power electronic device, and obtain a calculation relationship of an active power correction amount generated by a current limiting link under a converter fault ride-through state according to the transient power angle characteristic model of the power electronic device; The calculation module is configured to obtain, in a converter fault ride-through state, an active power correction amount under a fault transient state according to impedance data of a current fault position under a current time step and in combination with an active power correction amount calculation relationship, obtain a voltage-power angle coupling term based on the active power correction amount under a fault transient state, obtain a limit resection angle and a limit resection time of a current time step according to the voltage-power angle coupling term, and if the limit resection angle and the limit resection time of the current time step meet a set convergence condition, use the limit resection time of the current time step as the final limit resection time; The evaluation module is configured to evaluate the transient stability margin according to the relationship between the actual fault clearing time and the final limit clearing time.

8. An electronic device, characterized in that: The method comprises a memory and a processor and computer instructions stored in the memory and executed on the processor, wherein when the computer instructions are executed by the processor, the method according to any one of claims 1 to 6 is completed.

9. A computer-readable storage medium, characterized in that: Used to store computer instructions, which, when executed by a processor, complete the method described in any one of claims 1 to 6.

10. A computer program product, characterized in that The invention comprises a computer program, which, when executed by a processor, implements the method according to any one of claims 1 to 6.

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