Short-circuit current calculation method and device taking into account overall control effect under power grid short circuit

Abstract

The present invention discloses a short-circuit current calculation method and device taking into account the overall control effect under the short circuit of the power grid. The method includes obtaining the residual voltage size data of the load point when the power grid is short-circuited; dividing the load into zones according to the residual voltage size data, including near-zone load, middle-zone load and far-zone load; using a conventional load model to calculate the short-circuit current of the middle-zone load and the far-zone load, and using a prefabricated equivalent potential load model to calculate the short-circuit current of the near-zone load. In the case of a short circuit in the power grid, the method described in the present invention divides the load near the short-circuit node into near-zone load, middle-zone load and far-zone load, uses a conventional load model to calculate the short-circuit current for the middle-zone load and the far-zone load, and proposes an equivalent potential load model to calculate the short-circuit current for the near-zone load, thereby solving the problem that the conventional load model has a poor adaptability to the calculation of the short-circuit current of the near-zone load.

Description

Technical Field

[0001] The invention relates to a short-circuit current calculation method and a device taking into account the overall control effect under a power grid short circuit, and belongs to the technical field of power grid short-circuit current calculation. Background Art

[0002] The short-circuit level of the power system (the ratio of the maximum short-circuit current to the rated current) should be maintained at a reasonable value. An excessively large short-circuit level will result in insufficient mechanical strength of electrical equipment and current-breaking capacity of circuit breakers, while an excessively small short-circuit level will result in excessive network losses and reduced synchronization capacity during power system operation.

[0003] The load of the traditional power system is mainly composed of small and medium-sized asynchronous motors and resistors. After a short circuit occurs, the current injected into the short circuit point by the small and medium-sized asynchronous motors and resistors near the short circuit point or the current drawn from the residual voltage bus is much smaller than the current injected into the short circuit point by the large synchronous generator. Therefore, the role of load is often ignored in traditional short-circuit current calculations.

[0004] At present, the influence of various load models on short-circuit current is becoming increasingly greater and difficult to ignore. Small power sources such as distributed generation and variable frequency electrical equipment are increasingly connected to the power system, and these power electronic loads have autonomous control capabilities, so their external or auxiliary current increases. In addition, since the influence of various high-power equipment and medium and large motors on short-circuit current cannot be ignored, it is of great significance to analyze the influence of various power loads on short-circuit current and formulate new load models for calculating short-circuit current.

[0005] Although traditional load models can be used for electromechanical transient analysis, they are mainly aimed at the power response characteristics of loads under high voltage conditions, and are not applicable to the short-circuit current calculation of load nodes in low residual voltage areas after short circuits. Because in the area near the short-circuit point, the voltage drops to a very low level and the current suddenly increases to a large level, the traditional load model can no longer be used to calculate the system faults, and even excessive short-circuit currents can cause some load devices to automatically trip and other actions. Summary of the invention

[0006] The technical problem to be solved by the present invention is to overcome the defects of the prior art, provide a short-circuit current calculation method taking into account the overall control effect under power grid short circuit, and solve the problem of calculating short-circuit current in the prior art in the area near the short-circuit point and the low residual voltage area.

[0007] To achieve the above object, in a first aspect, the present invention provides a short-circuit current calculation method taking into account the overall control effect under a short-circuit of a power grid, comprising the following steps:

[0008] Obtain the residual voltage data of the load point when the power grid is short-circuited;

[0009] The load is divided into zones according to the residual pressure data, including near zone load, middle zone load and far zone load;

[0010] Conventional load models are used to calculate short-circuit currents for central and remote loads, and prefabricated equivalent potential load models are used to calculate short-circuit currents for nearby loads.

[0011] Furthermore, the prefabricated equivalent potential load model includes:

[0012] Construct an equivalent potential load model based on the conventional load mechanism model;

[0013] Obtain simulation curves of detailed models under different short-circuit scenarios as simulation measured models;

[0014] The equivalent potential load model is fitted based on the simulated measured model to obtain the parameter information of the equivalent potential load model.

[0015] Furthermore, the equivalent potential load model includes:

[0016] I=I Z (t)+I i (t)+I p (t)+I G (t);

[0017] Among them, I Z (t) refers to the short-circuit current value of the constant impedance load; I i (t) refers to the short-circuit current value of the constant current load; I P (t) refers to the short-circuit current value of constant power load; I G (t) refers to the short-circuit current value of the motor load equivalent in this chapter.

[0018] Further,

[0019]

[0020] I i (t) = I i

[0021]

[0022]

[0023] Among them, U(t) refers to the system voltage; Z refers to the impedance value of the constant impedance load; P refers to the power value of the constant power load; E(t) refers to the potential inside the induction motor; X G Refers to the internal impedance of an induction motor.

[0024] Furthermore, the equivalent potential load model is fitted based on the simulated measured model, including:

[0025] Obtain the output current of the detailed model and the output current of the equivalent potential load model;

[0026] Compare the output current of the detailed model with the output current of the equivalent potential load model to obtain a difference;

[0027] The difference is corrected to complete the fitting of the equivalent potential load model parameters.

[0028] Furthermore, the method for correcting the difference includes a particle swarm algorithm.

[0029] In a second aspect, the present invention provides a short-circuit current calculation device taking into account the overall control effect under a short circuit of a power grid, characterized in that it includes a processor and a storage medium;

[0030] The storage medium is used to store instructions;

[0031] The processor is used to operate according to the instructions to execute the steps of any one of the methods described in the first aspect.

[0032] The beneficial effects achieved by the present invention are:

[0033] The present invention provides a short-circuit current calculation method and device taking into account the overall control effect under a power grid short circuit. Under the condition of a power grid short circuit, the method described in the present invention divides the load near the short-circuit node into a near-zone load, a middle-zone load and a far-zone load, and adopts a conventional load model to calculate the short-circuit current for the middle-zone load and the far-zone load, and proposes an equivalent potential load model to calculate the short-circuit current for the near-zone load, thereby solving the problem that the conventional load model has a poor adaptability to the calculation of the short-circuit current of the near-zone load.

[0034] The present invention constructs an equivalent potential load model with voltage as input and current as output, superimposes the static load current and the dynamic induction motor load current to complete the construction of the model, and then collects the detailed model under the short-circuit scenario, compares and subtracts the two models, and then performs parameter fitting through the particle swarm algorithm. The equivalent potential load model constructed by the above method can adapt to the problem that the short-circuit current in the low residual voltage area cannot be effectively calculated when the power grid is short-circuited. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 It is a partition modeling strategy diagram based on post-fault residual voltage in a short-circuit current calculation method and device taking into account the overall control effect under power grid short circuit provided by an embodiment of the present invention;

[0036] Figure 2 It is a structural diagram of an equivalent potential load model in a short-circuit current calculation method and a device taking into account the overall control effect under a short-circuit of a power grid provided by an embodiment of the present invention;

[0037] Figure 3 It is a short-circuit current calculation method and a parameter fitting principle diagram of an equivalent potential load mechanism model in a device taking into account the overall control effect under a short circuit of a power grid provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0038] The present invention will be further described below in conjunction with the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present invention, and cannot be used to limit the protection scope of the present invention.

[0039] Embodiment 1:

[0040] The present invention provides a short-circuit current calculation method taking into account the overall control effect under a short-circuit of the power grid, such as Figures 1 to 3 As shown, after a short circuit occurs in the power grid, the residual size data of each load point near the short circuit point are collected, and the load points are divided into near-zone loads, middle-zone loads and far-zone loads according to the residual size values. For the middle-zone loads and far-zone loads, a conventional load model is used to calculate the short-circuit current, and for the near-zone loads, a prefabricated equivalent potential load model is used to calculate the short-circuit current; the method described in the present invention divides the load near the short-circuit node into near-zone loads, middle-zone loads and far-zone loads, and for the middle-zone loads and far-zone loads, a conventional load model is used to calculate the short-circuit current, and for the near-zone loads, an equivalent potential load model is proposed to calculate the short-circuit current, thereby solving the problem that the conventional load model has poor adaptability to the calculation of the short-circuit current of the near-zone load.

[0041] The present invention provides a short-circuit current calculation method taking into account the overall control effect under a power grid short circuit, which specifically comprises the following steps:

[0042] Step 1: Obtain the residual voltage data of the load point when the power grid is short-circuited:

[0043] Step 2: Divide the load into zones according to the residual pressure data. The zones mainly include near zone load, middle zone load and far zone load:

[0044] like Figure 1 As shown, during zoning, the load whose voltage drops to a very low level during short circuit is divided into the near-zone load, the load whose voltage drops to a lower level during short circuit is divided into the middle-zone load, and the load whose voltage is higher during short circuit is divided into the far-zone load.

[0045] Step 3: Use the conventional load model to calculate the short-circuit current of the central area load and the remote area load, and use the prefabricated equivalent potential load model to calculate the short-circuit current of the near area load:

[0046] The reason why the conventional load model is used for the short-circuit current calculation of the central area load and the remote area load, and the prefabricated equivalent potential load model is used for the short-circuit current calculation of the near area load is that the conventional load model is only very suitable for the calculation of the central area load and the remote area load, but is very poorly suitable for the calculation of the near area load. The present invention is based on this reason. First, the equivalent potential load model is prefabricated. The prefabricated equivalent potential load model includes:

[0047] An equivalent potential load model is constructed based on a conventional load mechanism model, but the constructed equivalent potential load model still needs to be fitted;

[0048] To facilitate the fitting operation, the present invention first obtains the simulation curve of the detailed model under different short-circuit scenarios as the simulated measured model, and then fits the equivalent potential load model based on the simulated measured model to solve the parameter information of the equivalent potential load model. The fitting principle of the specific model parameters is as follows: Figure 3 As shown, where I represents the output current of the detailed model SLM under the condition of short-circuit fault in the power system, that is, the simulated waveform data; It represents the output current of the equivalent potential load model VLM constructed by the embodiment of the present invention when the same short circuit fault occurs in the power system.

[0049] from Figure 3 It can be seen that the equivalent potential load model is fitted based on the simulated measured model, including:

[0050] When the same short-circuit fault occurs in the power system, the output current of the detailed model and the output current of the equivalent potential load model provided by the embodiment of the present invention are first obtained, which are I and

[0051] Then the output current of the detailed model is compared with the output current of the equivalent potential load model to obtain the difference after comparison, and then the difference is continuously corrected using methods including particle swarm optimization, thereby completing the fitting of the equivalent potential load model parameters.

[0052] The equivalent potential load model is as follows:

[0053] I=I Z (t)+I i (t)+I p (t)+I G (t);

[0054] Among them, I Z (t) refers to the short-circuit current value of the constant impedance load; I i (t) refers to the short-circuit current value of the constant current load; I P (t) refers to the short-circuit current value of constant power load; I G(t) refers to the short-circuit current value of the motor load equivalent in this chapter.

[0055] At the same time, the specific expressions of each parameter in the formula are as follows:

[0056] I i (t) = I i

[0057]

[0058]

[0059]

[0060] Among them, U(t) refers to the system voltage; Z refers to the impedance value of the constant impedance load; P refers to the power value of the constant power load; E(t) refers to the potential inside the induction motor; X G Refers to the internal impedance of an induction motor.

[0061] From the above, it can be seen that the output current of the equivalent potential load model is the superposition of the static load current and the dynamic induced electromotive force. The static load current includes the short-circuit current value I of the constant impedance load. Z (t), short-circuit current value I of constant current load i (t) and the short-circuit current value I of the constant power load P (t), the dynamic induced electromotive force includes the short-circuit current value I of the equivalent motor load G (t), the structure and principle of the equivalent potential load model are as follows Figure 2 shown.

[0062] The present invention partitions the load points near the short-circuit point, and defines the load whose voltage drops to a very low level during short-circuit as the near-zone load; the load whose voltage drops to a lower level during short-circuit as the middle-zone load; and the load whose voltage is higher during short-circuit as the far-zone load. A new voltage-current mechanism response model, the equipotential load model, is proposed. Through analysis, it is found that the applicability of traditional loads to the calculation of short-circuit current of near-zone loads is very poor, but the calculation applicability of circuit points of middle-zone or far-zone loads is very good. Therefore, the short-circuit current calculation of middle-zone and far-zone loads adopts the conventional load model, and the new equipotential load model is adopted at the load point with lower residual voltage near the short-circuit point, and the strategy and process for the parameter fitting of the equipotential model are formulated. The calculation accuracy of the short-circuit current near the short-circuit point can be improved, and a basis can be provided for the formulation of the operation and control plan of the power grid, which is of great significance to the safe and stable operation of the entire power grid.

[0063] Embodiment 2:

[0064] Based on the first embodiment, the second embodiment of the present invention provides a short-circuit current calculation device taking into account the overall control effect under the short circuit of the power grid, including a processor and a storage medium;

[0065] The storage medium is used to store instructions;

[0066] The processor is used to operate according to the instructions to execute the steps of the method according to any one of the embodiments.

[0067] Those skilled in the art will appreciate that the embodiments of the present application may be provided as methods, systems, or computer program products. Therefore, the present application may adopt the form of a complete hardware embodiment, a complete software embodiment, or an embodiment in combination with software and hardware. Moreover, the present application may adopt the form of a computer program product implemented in one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) that include computer-usable program code.

[0068] The present application is described with reference to the flowcharts and / or block diagrams of the methods, devices (systems), and computer program products according to the embodiments of the present application. It should be understood that each process and / or box in the flowchart and / or block diagram, as well as the combination of the processes and / or boxes in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to generate a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowchart and / or block diagram. Figure 1 A process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0069] These computer program instructions may also be stored in a computer-readable memory capable of directing a computer or other programmable data processing device to operate in a specific manner, so that the instructions stored in the computer-readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 A process or multiple processes and / or boxes Figure 1 A function specified in one or more boxes.

[0070] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operating steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing instructions for implementing the process. Figure 1 A process or multiple processes and / or boxes Figure 1 The steps for the functions specified in one or more boxes.

[0071] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the technical principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A short-circuit current calculation method taking into account the overall control effect under a short-circuit of a power grid, characterized in that: The steps include: Obtain the residual voltage data of the load point when the power grid is short-circuited; The load is divided into zones according to the residual pressure data, including near zone load, middle zone load and far zone load; The conventional load model is used to calculate the short-circuit current of the central area load and the remote area load, and the prefabricated equivalent potential load model is used to calculate the short-circuit current of the near area load; Prefabricated equivalent potential load models include: Construct an equivalent potential load model based on the conventional load mechanism model; Obtain simulation curves of detailed models under different short-circuit scenarios as simulation measured models; Fitting the equivalent potential load model based on the simulated measured model to solve the parameter information of the equivalent potential load model; Fitting the equivalent potential load model based on the simulated measured model includes: Obtain the output current of the detailed model and the output current of the equivalent potential load model; Compare the output current of the detailed model with the output current of the equivalent potential load model to obtain a difference; The difference is corrected to complete the fitting of the equivalent potential load model parameters.

2. The short-circuit current calculation method taking into account the overall control effect under power grid short circuit according to claim 1 is characterized in that: Equivalent potential load models include: ； in, Refers to the short-circuit current value of constant impedance load; Refers to the short-circuit current value of the constant current load; Refers to the short-circuit current value of constant power load; Refers to the short-circuit current value of the equivalent motor load.

3. The short-circuit current calculation method taking into account the overall control effect under power grid short circuit according to claim 2 is characterized in that: ； ； ； ； in, Refers to the system voltage; Refers to the impedance value of the constant impedance load; Refers to the power value of constant power load; Refers to the potential within an induction motor; Refers to the internal impedance of an induction motor.

4. The short-circuit current calculation method taking into account the overall control effect under power grid short circuit according to claim 1 is characterized in that: Methods for correcting the difference include particle swarm optimization.

5. A short-circuit current calculation device taking into account the overall control effect under short-circuit of the power grid, characterized in that: including processors and storage media; The storage medium is used to store instructions; The processor is configured to operate according to the instructions to execute the steps of the method according to any one of claims 1 to 4.

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