CN109617033B - Current limiting method and device for power distribution system - Google Patents
Current limiting method and device for power distribution system Download PDFInfo
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- CN109617033B CN109617033B CN201910015881.7A CN201910015881A CN109617033B CN 109617033 B CN109617033 B CN 109617033B CN 201910015881 A CN201910015881 A CN 201910015881A CN 109617033 B CN109617033 B CN 109617033B
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Abstract
The application relates to a current limiting method and device for a power distribution system; the current limiting method of the power distribution system comprises the following steps: fault partition processing is carried out on the multi-end flexible direct-current power distribution system to obtain each system partition, and the inter-electrode short-circuit fault in each system partition is analyzed and confirmed; respectively acquiring circuit breakers corresponding to the short-circuit faults between the electrodes, and acquiring peak current flowing through each circuit breaker and peak time of the peak current; sorting the current-limiting difficulty levels of the inter-electrode short-circuit faults according to the peak currents and the peak times to obtain the inter-electrode short-circuit fault with the highest current-limiting difficulty level and the inter-electrode short-circuit fault with the second highest current-limiting difficulty level; and respectively discharging loops under the fault working condition by adopting an electromagnetic transient simulation model of the multi-end flexible direct-current power distribution system to obtain the parameter values of the current limiting device at the outlet of each discharging loop in the multi-end flexible direct-current power distribution system. This application goes to confirm the current limiting device parameter value from whole distribution system angle, has improved fault handling efficiency.
Description
Technical Field
The present application relates to the field of power distribution system fault analysis, and in particular, to a power distribution system current limiting method and apparatus.
Background
With the development of power distribution system technology, a multi-terminal flexible direct-current power distribution system gradually becomes a trend of the development of a future direct-current power grid due to low manufacturing cost and various operation modes. However, with the diversification of the topology and the operation mode, the problem of clearing the fault of the multi-terminal flexible direct current power distribution system becomes more complicated.
At present, the following two common fault clearing measures are adopted: the current-limiting reactor is matched with the direct current breaker, and the superconducting current limiter is matched with the direct current breaker. In the implementation process, the inventor finds that at least the following problems exist in the conventional technology: research aiming at the current limiting parameters mainly focuses on the internal structure of the current limiting module, and the internal parameters are determined aiming at a certain fault, so that the fault processing efficiency is low.
Disclosure of Invention
In view of the above, it is desirable to provide a method and an apparatus for limiting current in a power distribution system, which can improve the efficiency of processing circuit faults.
In order to achieve the above object, an embodiment of the present invention provides a method for limiting a current of a power distribution system, where the method includes:
respectively acquiring short-circuit faults between electrodes in the multi-terminal flexible direct-current power distribution system, and acquiring peak current of each discharge loop and peak time of the peak current; the discharge loop is a loop for discharging a short-circuit point in the interpolar short-circuit fault;
sorting the current-limiting difficulty levels of the inter-electrode short-circuit faults according to the peak currents and the peak times to obtain the inter-electrode short-circuit fault with the highest current-limiting difficulty level and the inter-electrode short-circuit fault with the second highest current-limiting difficulty level;
and simulating the interelectrode short-circuit fault with the highest current-limiting difficulty level and the interelectrode short-circuit fault with the highest current-limiting difficulty level by adopting an electromagnetic transient simulation model to obtain the parameter value of the current-limiting device at the outlet of each discharge loop in the multi-terminal flexible direct-current power distribution system.
In one embodiment, before the step of separately acquiring short-circuit faults between electrodes in the multi-terminal flexible dc power distribution system, the method further includes the steps of:
according to the configuration, the protection strategy and the key position of a direct current breaker of the multi-end flexible direct current power distribution system, fault partitioning is carried out on the multi-end flexible direct current power distribution system to obtain each system partition, and the inter-electrode short circuit fault in each system partition is analyzed and confirmed;
the step of obtaining the peak current of each discharge loop and the peak time of the peak current comprises the following steps:
performing equivalent processing on the discharge loop to obtain an equivalent circuit; and processing the equivalent circuit to obtain the peak current and the peak time.
In one embodiment, the discharge circuit comprises a converter station discharge circuit and a direct current transformer discharge circuit;
processing the equivalent circuit to obtain a peak current and a peak time, wherein the steps comprise:
respectively carrying out equivalent treatment on the converter station discharge loop and the direct-current transformer discharge loop to obtain the converter station equivalent discharge loop and the direct-current transformer equivalent discharge loop;
processing the equivalent discharge loop of the converter station and the equivalent discharge loop of the direct current transformer by adopting a second-order circuit initial condition to respectively obtain the current of the discharge loop of the converter station and the current of the discharge loop of the direct current transformer;
obtaining a current curve graph of the discharging loop of the converter station and a current curve graph of the discharging loop of the direct-current transformer based on the current of the discharging loop of the converter station and the current of the discharging loop of the direct-current transformer;
obtaining the peak current and the peak time of the discharge loop of the converter station according to the current curve graph of the discharge loop of the converter station; and obtaining the peak current and the peak time of the discharge loop of the direct current transformer according to the current curve graph of the discharge loop of the direct current transformer.
In a specific embodiment, in the step of processing the equivalent discharge loop of the converter station and the equivalent discharge loop of the dc transformer by using the second-order circuit initial condition to obtain the current of the discharge loop of the converter station and the current of the discharge loop of the dc transformer, the peak current of the discharge loop of the converter station is obtained based on the following formula:
wherein, I1Current of a discharge loop of the converter station; omega is the oscillation angular frequency of the equivalent discharge loop of the converter station; delta is the time constant of the equivalent discharge loop of the converter station; u shapedcIs the voltage between direct current poles; i is0Is a direct current bus current; l is an equivalent inductance of an equivalent discharge loop of the converter station; omega0The resonant angular frequency of the equivalent discharge loop of the converter station; r is the equivalent resistance of the equivalent discharge loop of the converter station; and C is the equivalent capacitance of the equivalent discharge loop of the converter station.
In a specific embodiment, in the step of processing the equivalent discharge loop of the converter station and the equivalent discharge loop of the dc transformer by using the second-order circuit initial condition to obtain the current of the discharge loop of the converter station and the current of the discharge loop of the dc transformer, the peak current of the discharge loop of the dc transformer is obtained based on the following formula:
wherein, I2The current of a discharge loop of the direct current transformer is obtained; omega1The oscillation angular frequency of the equivalent discharge loop of the direct current transformer is obtained; delta1The time constant of the equivalent discharge loop of the direct current transformer is obtained; u shapedcIs the voltage between direct current poles; i is0Is a direct current bus current; l is1The equivalent inductance is an equivalent discharge loop of the direct current transformer; omega2The resonant angular frequency of the equivalent discharge loop of the direct-current transformer is obtained; r1The equivalent resistance is an equivalent discharge loop of the direct current transformer; c1And the equivalent capacitance of the equivalent discharge loop of the direct current transformer is obtained.
In one embodiment, the step of sorting the current-limiting difficulty levels of the inter-electrode short-circuit faults according to the peak currents and the peak times to obtain the inter-electrode short-circuit fault with the highest current-limiting difficulty level and the inter-electrode short-circuit fault with the highest current-limiting difficulty level includes:
subtracting the on-off current value of the circuit breaker from the maximum current value of the discharge loop within the on-off time of the circuit breaker to obtain a difference value; the breaker is closest to the interelectrode short-circuit fault and isolates the interelectrode short-circuit fault from the multi-terminal flexible direct-current power distribution system; if the peak time is less than or equal to the on-off time, the maximum current value is the value of the peak current; if the peak time is greater than the on-off time, the maximum current value is the current value of the discharge circuit at the end of the on-off time;
and obtaining the current limiting difficulty level sequence of the short-circuit faults between the electrodes according to the magnitude sequence of the difference values.
In one embodiment, the current limiting device parameter value comprises a current limiting reactance value;
the method comprises the following steps of simulating the interelectrode short-circuit fault with the highest current-limiting difficulty level and the interelectrode short-circuit fault with the highest current-limiting difficulty level by adopting an electromagnetic transient simulation model, wherein the steps comprise:
establishing an electromagnetic transient simulation model;
based on an electromagnetic transient simulation model, gradually increasing the current-limiting reactance value at the outlet of the discharge loop corresponding to the interelectrode short-circuit fault with the highest current-limiting difficulty level until the maximum current value of each discharge loop is smaller than a first current-limiting standard current value;
based on an electromagnetic transient simulation model, the current-limiting reactance value at the outlet of the discharge loop corresponding to the interelectrode short-circuit fault with the highest current-limiting difficulty level is gradually increased until the maximum current value of each discharge loop is smaller than a second current-limiting standard current value.
In one embodiment, the first current limiting standard current value is the quotient of the open current value and the number of discharge loops corresponding to the inter-electrode short-circuit fault with the highest current limiting difficulty level;
the second current limiting standard current value is a quotient of the open current value and the number of discharge circuits corresponding to the inter-electrode short-circuit fault with the current limiting difficulty level being the second highest.
In one embodiment, after the step of simulating the inter-electrode short-circuit fault with the highest current-limiting difficulty level and the inter-electrode short-circuit fault with the highest current-limiting difficulty level by using the electromagnetic transient simulation model to obtain the parameter value of the current-limiting device at the outlet of the discharge loop, the method further includes:
checking the interelectrode short-circuit fault of the residual current-limiting difficulty level by adopting the current-limiting device parameter value; the inter-electrode short-circuit faults with the rest current-limiting difficulty level are inter-electrode short-circuit faults except the inter-electrode short-circuit fault with the highest current-limiting difficulty level and the inter-electrode short-circuit fault with the highest current-limiting difficulty level in the multi-terminal flexible direct-current power distribution system;
and when the verification result is failure, simulating the interelectrode short-circuit fault with the residual current-limiting difficulty level by adopting an electromagnetic transient simulation model.
The embodiment of the invention also provides a current limiting device of a power distribution system, which comprises:
the data acquisition module is used for respectively acquiring short-circuit faults between electrodes in the multi-terminal flexible direct-current power distribution system and acquiring peak current of each discharge loop and peak time of the peak current; the discharge loop is a loop for discharging a short-circuit point in the interpolar short-circuit fault;
the sorting module is used for sorting the current-limiting difficulty grades of the inter-electrode short-circuit faults according to the peak currents and the peak times to obtain the inter-electrode short-circuit fault with the highest current-limiting difficulty grade and the inter-electrode short-circuit fault with the second highest current-limiting difficulty grade;
and the simulation module is used for simulating the interelectrode short-circuit fault with the highest current-limiting difficulty level and the interelectrode short-circuit fault with the highest current-limiting difficulty level by adopting an electromagnetic transient simulation model to obtain the parameter value of the current-limiting device at each discharge loop outlet in the multi-terminal flexible direct-current power distribution system.
One of the above technical solutions has the following advantages and beneficial effects:
the current limiting method for the power distribution system divides the power distribution system into regions, and confirms short-circuit points corresponding to the short-circuit faults among the electrodes in each system division region; confirming the current limiting difficulty level of each inter-electrode short-circuit fault according to the peak current and the peak time of a circuit discharging a short-circuit point when the fault occurs; and simulating the interelectrode short-circuit fault with the highest current-limiting difficulty level and the interelectrode short-circuit fault with the highest current-limiting difficulty level by adopting a simulation method to obtain the parameter value of the current-limiting device at the outlet of each discharge loop in the multi-terminal flexible direct-current power distribution system. This application goes to confirm the current limiting device parameter value from whole distribution system angle, has improved fault handling efficiency.
Drawings
Other features, objects and advantages of the present application will become more apparent upon reading of the following detailed description of non-limiting embodiments thereof, made with reference to the accompanying drawings in which:
FIG. 1 is a first schematic flow chart diagram illustrating a method for limiting current in an embodiment of a power distribution system;
FIG. 2 is a second schematic flow chart diagram illustrating a method for limiting current in an embodiment of a power distribution system;
FIG. 3 is a third schematic flow chart diagram illustrating a method for limiting current in an embodiment of a power distribution system;
FIG. 4 is a block diagram illustrating an exemplary configuration of a current limiting device in an embodiment of a power distribution system;
FIG. 5 is a schematic diagram of a power distribution system fault zone in accordance with an exemplary embodiment;
FIG. 6 is a schematic diagram of a fault equivalent circuit in the event of a short circuit fault in the distribution system in an exemplary embodiment;
FIG. 7 is a schematic diagram of an equivalent circuit of a discharge circuit of a power distribution system inverter in accordance with an exemplary embodiment;
FIG. 8 is a schematic diagram of an equivalent circuit of a DC transformer discharge circuit of a power distribution system in accordance with an exemplary embodiment;
FIG. 9 is a diagram illustrating an internal structure of a computer device according to an embodiment.
Detailed Description
In order to make the objects, technical solutions and advantages of the present application more apparent, the present application is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the present application and are not intended to limit the present application.
In one embodiment, as shown in fig. 1, there is provided a method for limiting current in a power distribution system, comprising the steps of:
step S110, short-circuit faults between electrodes in the multi-end flexible direct-current power distribution system are respectively obtained, and peak currents of discharge loops and peak time of the peak currents are obtained; the discharge circuit is a circuit for discharging a short-circuit point in the inter-electrode short-circuit fault.
Specifically, fault analysis is performed on the multi-terminal flexible direct-current power distribution system to obtain an inter-electrode short-circuit fault in the multi-terminal flexible direct-current power distribution system. A short-circuit point corresponding to the inter-electrode short-circuit fault is obtained from the inter-electrode short-circuit fault, and a discharge circuit for discharging to the short-circuit point is confirmed. And processing the discharge loop to obtain the peak current of the discharge loop and the peak time of the peak current.
And step S120, sorting the current-limiting difficulty levels of the inter-electrode short-circuit faults according to the peak currents and the peak times to obtain the inter-electrode short-circuit fault with the highest current-limiting difficulty level and the inter-electrode short-circuit fault with the highest current-limiting difficulty level.
The current limiting difficulty level in step S120 is represented by a difference between a maximum current of the discharging circuit and a current limiting standard value of the circuit breaker during the opening time of the circuit breaker.
Specifically, the current limiting difficulty of the inter-pole short circuit fault can be classified according to the obtained peak currents and peak times. And sequencing the current limiting difficulty grades to obtain the inter-electrode short-circuit fault with the highest current limiting difficulty grade and the inter-electrode short-circuit fault with the highest current limiting difficulty grade.
Step S130, an electromagnetic transient simulation model is adopted to simulate the interelectrode short-circuit fault with the highest current-limiting difficulty level and the interelectrode short-circuit fault with the highest current-limiting difficulty level, so as to obtain the parameter value of the current-limiting device at each discharge loop outlet in the multi-terminal flexible direct-current power distribution system.
The electromagnetic transient simulation model in step S130 may be constructed by simulation software such as PSCAD/EMTDC. The current limiting device parameters are any device parameters capable of limiting current, including a current limiting reactance and a current limiting resistor.
And respectively simulating the interelectrode short-circuit fault with the highest current-limiting difficulty level and the interelectrode short-circuit fault with the highest current-limiting difficulty level by adopting the constructed electromagnetic transient simulation model to obtain the parameter value of the current-limiting device at the outlet of each discharge loop in the multi-terminal flexible direct-current power distribution system.
The current limiting method of the power distribution system is used for partitioning the power distribution system and confirming short-circuit points corresponding to the short-circuit faults among the poles in each system partition; confirming the current limiting difficulty level of each inter-electrode short-circuit fault according to the peak current and the peak time of a circuit discharging a short-circuit point when the fault occurs; and simulating the interelectrode short-circuit fault with the highest current-limiting difficulty level and the interelectrode short-circuit fault with the highest current-limiting difficulty level by adopting a simulation method to obtain the parameter value of the current-limiting device at the outlet of each discharge loop in the multi-terminal flexible direct-current power distribution system. The method confirms the parameter values of the current limiting device from the angle of the whole power distribution system, and improves the fault processing efficiency.
In one embodiment, as shown in fig. 2, there is provided a method for limiting current in a power distribution system, comprising the steps of:
step S210, short-circuit faults between electrodes in the multi-end flexible direct-current power distribution system are respectively obtained, and peak currents of discharge loops and peak time of the peak currents are obtained; the discharge circuit is a circuit for discharging a short-circuit point in the inter-electrode short-circuit fault.
And step S220, sorting the current-limiting difficulty levels of the inter-electrode short-circuit faults according to the peak currents and the peak times respectively to obtain the inter-electrode short-circuit fault with the highest current-limiting difficulty level and the inter-electrode short-circuit fault with the highest current-limiting difficulty level.
And step S230, simulating the interelectrode short-circuit fault with the highest current-limiting difficulty level and the interelectrode short-circuit fault with the highest current-limiting difficulty level by adopting an electromagnetic transient simulation model to obtain the parameter value of the current-limiting device at each discharge loop outlet in the multi-terminal flexible direct-current power distribution system.
Before the step of obtaining short-circuit faults between electrodes in the multi-terminal flexible direct-current power distribution system, the method further comprises the following steps:
step S200, fault partitioning is carried out on the multi-end flexible direct current power distribution system according to the configuration, the protection strategy and the key position of a direct current breaker of the multi-end flexible direct current power distribution system to obtain each system partition, and the inter-electrode short circuit fault in each system partition is analyzed and confirmed;
specifically, the protection strategy mainly refers to the locking of the inverter and the action of the direct current breaker. After the fault occurs, firstly, the converter in the area where the fault is located is locked, and then the action of the direct current breaker is carried out.
The power distribution system is a complex system with multiple voltage levels, multiple equipment types, and multiple load units. The method comprises the steps of carrying out fault partitioning on the multi-terminal flexible direct-current power distribution system based on the configuration, protection strategy and key position of a direct-current breaker of the multi-terminal flexible direct-current power distribution system to obtain each system partition, and analyzing and confirming the inter-electrode short-circuit fault in each system partition.
Further, the step of obtaining the peak current and the peak time of the peak current of each discharge circuit may include:
performing equivalent processing on the discharge loop to obtain an equivalent circuit; and processing the equivalent circuit to obtain the peak current and the peak time.
Specifically, the method for acquiring the peak current of a discharge loop and the peak time of the peak current comprises the following steps: and performing equivalent transformation on the discharge loop to obtain an equivalent circuit, and obtaining the peak current and the peak time from the angle of the equivalent circuit. By adopting the scheme of the application, the peak current of the discharge circuit and the peak time of the peak current can be obtained theoretically, and the operation of computer equipment is facilitated. In one particular example, the discharge circuit includes a converter station discharge circuit and a dc transformer discharge circuit.
Further, the step of processing the equivalent circuit to obtain the peak current and the peak time in the present application may include:
and respectively carrying out equivalent treatment on the converter station discharge loop and the direct-current transformer discharge loop to obtain the converter station equivalent discharge loop and the direct-current transformer equivalent discharge loop.
Specifically, equivalent transformation is respectively carried out on the converter station discharge loop and the direct-current transformer discharge loop, and a simpler circuit is used for replacing an original circuit to obtain the converter station equivalent discharge loop and the direct-current transformer equivalent discharge loop.
And processing the equivalent discharge loop of the converter station and the equivalent discharge loop of the direct current transformer by adopting a second-order circuit initial condition to respectively obtain the current of the discharge loop of the converter station and the current of the discharge loop of the direct current transformer.
Specifically, the equivalent discharge circuit of the converter station and the equivalent discharge circuit of the dc transformer are second-order discharge circuits, and the current of the equivalent discharge circuit of the converter station and the current of the equivalent discharge circuit of the dc transformer can be obtained according to the initial conditions of the second-order circuits.
And obtaining a current curve graph of the discharging loop of the converter station and a current curve graph of the discharging loop of the direct current transformer based on the current of the discharging loop of the converter station and the current of the discharging loop of the direct current transformer.
Specifically, a current curve graph of the converter station discharge loop and a current curve graph of the direct current transformer discharge loop can be obtained according to the current of the converter station discharge loop and the current of the direct current transformer discharge loop.
Obtaining the peak current and the peak time of the discharge loop of the converter station according to the current curve graph of the discharge loop of the converter station; and obtaining the peak current and the peak time of the discharge loop of the direct current transformer according to the current curve graph of the discharge loop of the direct current transformer.
Specifically, the method for obtaining the peak current and the peak time of the discharge circuit may include: the current curve is read and is derived from the formula. In a specific example, the peak current and the peak time of the discharge circuit can be obtained by adopting a current curve diagram mode. In a current curve chart of a discharging loop of the converter station, the peak current and the peak time of the discharging loop of the converter station can be directly read; in the current curve chart of the discharge loop of the direct current transformer, the peak current and the peak time of the discharge loop of the converter station can be directly read.
It should be noted that, in the step of processing the equivalent discharge loop of the converter station and the equivalent discharge loop of the dc transformer by using the second-order circuit initial condition to obtain the current of the discharge loop of the converter station and the current of the discharge loop of the dc transformer, the peak current of the discharge loop of the converter station is obtained based on the following formula:
wherein, I1Current of a discharge loop of the converter station; omega is the oscillation angular frequency of the equivalent discharge loop of the converter station; delta is the time constant of the equivalent discharge loop of the converter station; u shapedcIs the voltage between direct current poles; i is0Is a direct current bus current; l is an equivalent inductance of an equivalent discharge loop of the converter station; omega0The resonant angular frequency of the equivalent discharge loop of the converter station; r is the equivalent resistance of the equivalent discharge loop of the converter station; and C is the equivalent capacitance of the equivalent discharge loop of the converter station.
Obtaining the peak current of the discharge loop of the direct current transformer based on the following formula:
wherein, I2The current of a discharge loop of the direct current transformer is obtained; omega1The oscillation angular frequency of the equivalent discharge loop of the direct current transformer is obtained; delta1The time constant of the equivalent discharge loop of the direct current transformer is obtained; u shapedcIs the voltage between direct current poles; i is0Is a direct current bus current; l is1The equivalent inductance is an equivalent discharge loop of the direct current transformer; omega2The resonant angular frequency of the equivalent discharge loop of the direct-current transformer is obtained; r1The equivalent resistance is an equivalent discharge loop of the direct current transformer; c1And the equivalent capacitance of the equivalent discharge loop of the direct current transformer is obtained.
In a specific embodiment, the step of sorting the current-limiting difficulty levels of the inter-electrode short-circuit faults according to the peak currents and the peak times to obtain the inter-electrode short-circuit fault with the highest current-limiting difficulty level and the inter-electrode short-circuit fault with the highest current-limiting difficulty level may include:
subtracting the on-off current value of the circuit breaker from the maximum current value of the discharge loop within the on-off time of the circuit breaker to obtain a difference value; the breaker is closest to the interelectrode short-circuit fault and isolates the interelectrode short-circuit fault from the multi-terminal flexible direct-current power distribution system; if the peak time is less than or equal to the on-off time, the maximum current value is the value of the peak current; if the peak time is greater than the on-off time, the maximum current value is the current value of the discharge circuit at the end of the on-off time.
Specifically, according to a system protection strategy, a circuit breaker corresponding to an inter-electrode short-circuit fault can be obtained in the multi-terminal flexible direct-current power distribution system. The system protection strategy stipulates that the corresponding breaker is the breaker which is closest to the interelectrode short-circuit fault and can isolate the fault from the multi-terminal flexible direct-current power distribution system.
When the peak time of the discharging loop is less than or equal to the on-off time of the circuit breaker, the maximum current value of the discharging loop in the on-off short time of the circuit breaker is the current peak value of the discharging loop. When the peak time of the discharging circuit is larger than the on-off time of the breaker, the maximum current value of the discharging circuit in the on-off short time of the breaker is the current value at the end of the on-off time. And subtracting the on-off current value of the circuit breaker from the maximum current value of the discharge circuit in the on-off time to obtain a difference value.
And obtaining the current limiting difficulty level sequence of the short-circuit faults between the electrodes according to the magnitude sequence of the difference values.
Specifically, the obtained difference values are sorted. In a specific example, the sorting is performed in a size sequence, the size of the difference corresponds to the level of the current limiting difficulty level of the inter-electrode short-circuit fault, and the larger the difference is, the higher the current limiting difficulty level of the inter-electrode short-circuit fault is.
Further, the step of simulating the interpolar short-circuit fault with the highest current-limiting difficulty level and the interpolar short-circuit fault with the highest current-limiting difficulty level by adopting an electromagnetic transient simulation model comprises the following steps:
and establishing an electromagnetic transient simulation model.
Specifically, the electromagnetic transient simulation model can be constructed by simulation software, including PSCAD and EMTDC. In one particular example, a PSCAD software is used to build an electromagnetic transient simulation model.
Based on an electromagnetic transient simulation model, the current-limiting reactance value at the outlet of the discharge loop corresponding to the interelectrode short-circuit fault with the highest current-limiting difficulty level is gradually increased until the maximum current value of each discharge loop is smaller than a first current-limiting standard current value.
In particular, the current limiting parameter value may comprise a current limiting reactance value. In the simulation model, the interelectrode short-circuit fault with the highest current-limiting difficulty level is simulated, and the current-limiting reactance value at the outlet of the discharge loop corresponding to the interelectrode short-circuit fault is gradually increased until the maximum current value of each discharge loop is smaller than the first current-limiting standard current value.
Based on an electromagnetic transient simulation model, the current-limiting reactance value at the outlet of the discharge loop corresponding to the interelectrode short-circuit fault with the highest current-limiting difficulty level is gradually increased until the maximum current value of each discharge loop is smaller than a second current-limiting standard current value.
Specifically, in the simulation model, the interpolar short-circuit fault with the highest current-limiting difficulty level is simulated, and the current-limiting reactance value at the outlet of the discharge loop corresponding to the interpolar short-circuit fault is gradually increased until the maximum current value of each discharge loop is smaller than the second current-limiting standard current value.
The first current limiting standard current value is a quotient of the number of discharge loops corresponding to the inter-electrode short-circuit fault with the highest current limiting difficulty level and the open current value;
the second current limiting standard current value is a quotient of the open current value and the number of discharge circuits corresponding to the inter-electrode short-circuit fault with the current limiting difficulty level being the second highest.
Specifically, the current limit standard current value is a quotient of the breaker open current value and the number of discharge circuits corresponding to the inter-electrode short-circuit fault. The first current limiting standard current value is the quotient of the number of discharge loops corresponding to the interelectrode short-circuit fault with the highest current limiting difficulty level and the cut-off current value; the second current limiting standard current value is a quotient of the open current value and the number of discharge circuits corresponding to the inter-electrode short-circuit fault with the current limiting difficulty level being the second highest.
In the current limiting method of the power distribution system, the multi-terminal flexible direct-current power distribution system is subjected to fault partitioning according to the configuration, the protection strategy and the key position of the direct-current circuit breaker of the multi-terminal flexible direct-current power distribution system, and the inter-electrode short-circuit fault in each system partition is analyzed and confirmed, so that the inter-electrode short-circuit fault in the system partition can be systematically confirmed. The current of the discharging loop of the converter station and the current of the discharging loop of the direct-current transformer are obtained in an equivalent processing mode, required data can be obtained theoretically, and computer equipment can conveniently calculate. The peak current and the peak time of the discharging loop of the converter station and the peak current and the peak time of the discharging loop of the direct-current transformer are respectively obtained in a current curve diagram mode, and data operation can be simplified.
In one embodiment, as shown in fig. 3, there is provided a method for limiting current in a power distribution system, comprising the steps of:
step S310, short-circuit faults between electrodes in the multi-end flexible direct-current power distribution system are respectively obtained, and peak currents of discharge loops and peak time of the peak currents are obtained; the discharge circuit is a circuit for discharging a short-circuit point in the inter-electrode short-circuit fault.
Step S320, sorting the current-limiting difficulty levels of the inter-electrode short-circuit faults according to the peak currents and the peak times, so as to obtain the inter-electrode short-circuit fault with the highest current-limiting difficulty level and the inter-electrode short-circuit fault with the highest current-limiting difficulty level.
Step S330, an electromagnetic transient simulation model is adopted to simulate the interelectrode short-circuit fault with the highest current-limiting difficulty level and the interelectrode short-circuit fault with the highest current-limiting difficulty level, so as to obtain the parameter value of the current-limiting device at the outlet of each discharge loop in the multi-terminal flexible direct-current power distribution system.
Wherein, adopt the electromagnetism transient state simulation model, to the current-limiting degree of difficulty highest interelectrode short-circuit fault, the current-limiting degree of difficulty level high interelectrode short-circuit fault is simulated, after the step of obtaining the current-limiting device parameter value of the export of discharge circuit, still include:
step S340, checking the interelectrode short-circuit fault with the residual current-limiting difficulty level by adopting the current-limiting device parameter value; the inter-electrode short-circuit faults with the rest current-limiting difficulty level are inter-electrode short-circuit faults except the inter-electrode short-circuit fault with the highest current-limiting difficulty level and the inter-electrode short-circuit fault with the highest current-limiting difficulty level in the multi-terminal flexible direct-current power distribution system.
Specifically, after obtaining the parameter value of the current limiting device at the outlet of the discharge circuit, the parameter value of the current limiting device needs to be verified. In a specific example, the inter-electrode short-circuit fault of the residual current-limiting difficulty level is simulated in the electromagnetic transient simulation model, and the obtained current-limiting device parameters are adopted to verify whether the maximum current value of each discharge circuit in the on-off time is smaller than the current-limiting standard value. The inter-electrode short-circuit faults with the rest current-limiting difficulty level are inter-electrode short-circuit faults except the inter-electrode short-circuit fault with the highest current-limiting difficulty level and the inter-electrode short-circuit fault with the highest current-limiting difficulty level in the multi-terminal flexible direct-current power distribution system.
And when the verification result is failure, simulating the interelectrode short-circuit fault of the residual current-limiting difficulty level by adopting an electromagnetic transient simulation model.
Specifically, under the condition of failed verification, repeating the step S330, simulating the inter-electrode short-circuit fault which fails verification, and increasing the corresponding discharge loop outlet current-limiting parameter value until the maximum current value of each discharge loop is all smaller than the current-limiting standard current value.
According to the current limiting method of the power distribution system, the circuit breakers corresponding to the interelectrode short-circuit faults are obtained according to the system protection strategy, and the current limiting standard current value is provided according to the on-off current of the circuit breakers and the number of the discharging loops corresponding to the faults. The current limiting difficulty grade of the short-circuit fault between the electrodes can be theoretically determined by comparing the current limiting standard value with the maximum current value of each discharge loop in the on-off time of the circuit breaker. After the magnetic transient simulation model is adopted to obtain the parameter value of the current limiting device at the outlet of the discharge loop, the obtained parameter value of the current limiting device is verified at the interelectrode short circuit fault with the residual current limiting difficulty level, and the reliability of the parameter value of the current limiting device is further improved.
In one embodiment, as shown in fig. 4, there is provided a current limiting device for a power distribution system, including:
the data acquisition module 410 is configured to acquire inter-electrode short-circuit faults in the multi-terminal flexible direct-current power distribution system, and acquire peak currents of the discharge loops and peak time of the peak currents; the discharge circuit is a circuit for discharging a short-circuit point in the inter-electrode short-circuit fault.
And the sorting module 420 is configured to sort the current-limiting difficulty levels of the inter-electrode short-circuit faults according to the peak currents and the peak times, so as to obtain the inter-electrode short-circuit fault with the highest current-limiting difficulty level and the inter-electrode short-circuit fault with the highest current-limiting difficulty level.
The simulation module 430 is configured to simulate, by using an electromagnetic transient simulation model, an inter-electrode short-circuit fault with the highest current-limiting difficulty level and an inter-electrode short-circuit fault with the highest current-limiting difficulty level, so as to obtain a current-limiting device parameter value at an outlet of each discharge loop in the multi-terminal flexible dc power distribution system.
In a specific embodiment, the current limiting device of the power distribution system further includes a fault analysis module, configured to perform fault partitioning on the multi-terminal flexible dc power distribution system according to the configuration of the dc circuit breaker, the protection policy, and the key position of the multi-terminal flexible dc power distribution system, to obtain each system partition, and analyze and confirm the inter-electrode short-circuit fault in each system partition.
In a specific example, the data acquisition module is further configured to perform equivalent processing on the discharge circuit to obtain an equivalent circuit; and processing the equivalent circuit to obtain the peak current and the peak time. The discharge loop comprises a converter station discharge loop and a direct current transformer discharge loop.
Specifically, the data acquisition module is further configured to:
respectively carrying out equivalent treatment on the converter station discharge loop and the direct-current transformer discharge loop to obtain the converter station equivalent discharge loop and the direct-current transformer equivalent discharge loop;
processing the equivalent discharge loop of the converter station and the equivalent discharge loop of the direct current transformer by adopting a second-order circuit initial condition to respectively obtain the current of the discharge loop of the converter station and the current of the discharge loop of the direct current transformer;
obtaining a current curve graph of the discharging loop of the converter station and a current curve graph of the discharging loop of the direct-current transformer based on the current of the discharging loop of the converter station and the current of the discharging loop of the direct-current transformer;
obtaining the peak current and the peak time of the discharge loop of the converter station according to the current curve graph of the discharge loop of the converter station; and obtaining the peak current and the peak time of the discharge loop of the direct current transformer according to the current curve graph of the discharge loop of the direct current transformer.
In a specific embodiment, the sorting module is further configured to:
subtracting the on-off current value of the circuit breaker from the maximum current value of the discharge loop within the on-off time of the circuit breaker to obtain a difference value; the breaker is closest to the interelectrode short-circuit fault and isolates the interelectrode short-circuit fault from the multi-terminal flexible direct-current power distribution system; if the peak time is less than or equal to the on-off time, the maximum current value is the value of the peak current; if the peak time is greater than the on-off time, the maximum current value is the current value of the discharge circuit at the end of the on-off time;
and obtaining the current limiting difficulty level sequence of the short-circuit faults between the electrodes according to the magnitude sequence of the difference values.
In a specific embodiment, the simulation module is further configured to:
establishing an electromagnetic transient simulation model;
based on an electromagnetic transient simulation model, gradually increasing the current-limiting reactance value at the outlet of the discharge loop corresponding to the interelectrode short-circuit fault with the highest current-limiting difficulty level until the maximum current value of each discharge loop is smaller than a first current-limiting standard current value;
based on an electromagnetic transient simulation model, the current-limiting reactance value at the outlet of the discharge loop corresponding to the interelectrode short-circuit fault with the highest current-limiting difficulty level is gradually increased until the maximum current value of each discharge loop is smaller than a second current-limiting standard current value.
The simulation module is also used for calculating the current limiting standard current value. The current limit standard current value is a quotient of the open current value and the number of discharge circuits corresponding to the inter-electrode short-circuit fault.
The device also comprises a verification module used for verifying the parameter value of the current limiting device in the inter-electrode short-circuit fault with the residual current limiting difficulty level; the inter-electrode short-circuit faults with the rest current-limiting difficulty level are inter-electrode short-circuit faults except the inter-electrode short-circuit fault with the highest current-limiting difficulty level and the inter-electrode short-circuit fault with the highest current-limiting difficulty level in the multi-terminal flexible direct-current power distribution system;
and when the verification result is failure, simulating the interelectrode short-circuit fault with the residual current-limiting difficulty level by adopting an electromagnetic transient simulation model.
For specific limitations of the current limiting device of the power distribution system, reference may be made to the above limitations of the current limiting method of the power distribution system, and details thereof are not repeated here. The various modules in the current limiting apparatus of the power distribution system described above may be implemented in whole or in part by software, hardware, and combinations thereof. The modules can be embedded in a hardware form or independent from a processor in the computer device, and can also be stored in a memory in the computer device in a software form, so that the processor can call and execute operations corresponding to the modules.
To further illustrate the present solution, the above embodiments are described below with reference to a specific example.
The three-terminal flexible direct current distribution system that this application adopted, specific parameter is as shown in table 1.
Table 1 flexible dc distribution system converter station parameters
According to the configuration, the protection strategy and the key position of the direct current circuit breaker of the multi-end flexible direct current power distribution system, fault partitioning is carried out on the multi-end flexible direct current power distribution system, typical inter-electrode short-circuit faults which may occur in each area are analyzed, and action direct current circuit breakers corresponding to the inter-electrode short-circuit faults are summarized.
Fig. 5 is a schematic diagram of a power distribution system fault zone, as shown in fig. 5, a short-circuit fault between poles in each region is known by a system protection strategy, and in order to isolate the fault, the dc circuit breaker operating under the F1 and F2 faults is DCB 1; the DC circuit breaker which operates under the faults of F3 and F4 is DCB 3; the direct current circuit breakers which act under the faults of F5 and F7 are DCB2, DCB4 and DCB 5; the direct current breaker which acts under the F6 fault is DCB 5; the dc circuit breaker operating in the F8 fault is DCB 4.
A typical inter-electrode short-circuit fault F2 is selected, and an analysis of a fault equivalent circuit is shown in fig. 6, which shows that after the inter-electrode short-circuit fault occurs, the sub-module capacitor of the converter station 2, the sub-module capacitor of the converter station 3, and the voltage stabilizing capacitor on the high-voltage side of the dc transformer all discharge to a short-circuit point.
The short-circuit point discharge circuit of each converter station and the direct current transformer pair is regarded as an independent circuit, and the discharge process can be equivalent to a second-order discharge circuit. The discharging loop of the converter is shown in FIG. 7, and the known bridge arm inductance L0Sub-module capacitance value C0Then the equivalent inductance L of the fault loop is 2/3L0Equivalent inductance L with lineXSum of equivalent capacitance C of
The equivalent resistance R is equivalent resistance R of on-state and switching loss of the power electronic devicefShort circuit contact resistance RsOn-resistance R of direct current breakerdAnd a DC line equivalent resistance RXAnd (4) summing. The discharge circuit of the DC transformer is shown in FIG. 8, the equivalent capacitance C2Is a voltage stabilizing capacitor at the high-voltage side of the DC transformer and has an equivalent resistance L1Is stray inductance, equivalent resistance R1For short-circuiting contact resistance RsEquivalent resistance R of direct current cable lineLOn-resistance R of direct current breakerdAnd (4) summing. The discharge loop current calculation formula can be obtained from the initial conditions of the second-order circuit:
it should be noted that, the current formula of the discharge circuit of the converter station and the current formula of the discharge circuit of the dc transformer in the foregoing are not contradictory to the present formula, and the meaning expressed by the letters in the formula is adaptable to be consistent. In this formula, ωIs the oscillation angular frequency of the discharge circuit; delta is the time constant of the discharge circuit, UdcIs a DC interpolar voltage, I0Is DC bus current, L is equivalent inductance of discharge circuit, omega0For the resonant angular frequency of the discharge loop, β is the initial phase of the trigonometric transformation.
Therefore, the following steps are carried out:
wherein, Udc＝20kV，I0＝1.0kA。
Obtainable from the above formula I2The current peak value is 8.58kA, and the peak time is 3.4 ms; i is3The current peak value is 7.81kA, and the peak time is 3.4 ms; i is4The current peak was 58.76kA and the peak time was 4.7 ms.
According to the breaking capacity of the direct current circuit breaker and the number of discharge currents flowing through the direct current circuit breaker under the fault, current limiting requirements are provided for each discharge loop, and the current limiting difficulty of each discharge loop is analyzed:
the direct current circuit breaker adopted by the system can break short-circuit current within 10kA within 3ms, and under the fault condition, the fault current of the direct current circuit breaker is superposed from discharge currents of three discharge loops, so that the current peak value of each discharge loop is supposed to be less than 3.33kA, and the current limiting difficulty is reflected by the difference value between the current peak value within 3ms and the current limiting standard after the direct current circuit breaker receives a fault signal sent by protection and acts.
In this system, it is known that it takes 2ms for the protection to identify a fault and signal it, and therefore the current limiting scheme should meet the requirement that the current flowing through the dc circuit breaker is less than its maximum cut-off current within 5ms after the fault occurs. I.e. under the F2 fault, the current limiting reactance should ensure that the peak current value of each discharge circuit within 5ms of the fault should be less than 3.33 kA.
The peak current and the peak time of each discharge current of other typical inter-pole short-circuit faults are determined in the same way.
Comparing and analyzing the fault current of the direct current breaker and the current limiting difficulty of each discharging loop under various typical faults, and firstly selecting the F3 fault with the largest current limiting difficulty to simulate and calculate the current limiting reactance parameters of the outlets of the converter station 1 and the converter station 2 and the high-voltage side outlet of the direct current transformer; and simulating and calculating the value of the current-limiting reactor at the outlet of the converter station 3 by using the F2 fault with the current-limiting difficulty, and finally checking whether the parameters of the current-limiting reactor can meet the requirements by using the rest of faults.
And establishing an electromagnetic transient simulation model of the multi-terminal flexible direct-current power distribution system in the PSCAD, and performing simulation calculation and determining parameters of the current limiting devices at all positions of the system according to the calculation sequence of the parameters of the current limiting devices provided by S7.
Firstly, under the F3 fault, the current-limiting reactance parameters of the converter station 1, the converter station 2 and the high-voltage side outlet of the direct-current transformer are determined by simulation, namely, the current-limiting reactor value is gradually increased until the loop fault current can be limited below 3.33 kA. The simulation process takes the converter station 1 as an example, and the simulation calculation process of the outlet current limiting reactor is shown in table 2.
Table 2 converter station 1 outlet current limiting reactance configuration and its discharge current I1
And similarly, obtaining the current limiting parameter values of the outlets of other system partitions. The current limiting scheme determined by the obtained simulation result is as follows: 13mH current-limiting reactance per pole is additionally arranged at an outlet of the converter station 1, 13mH current-limiting reactance per pole is additionally arranged at an outlet of the converter station 2, 9mH reactance per pole is additionally arranged at an outlet of the converter station 3, and 15mH current-limiting reactance per pole is additionally arranged at a high-voltage side outlet of the direct-current transformer.
In addition, the technical scheme of the application can also be used for obtaining the current value flowing through the DCB1 and the current I flowing through the DCB1DCB1Discharging current I for sub-module capacitor of converter station 22And the sub-module capacitor discharge current I of the converter station 33And the discharge current I of the voltage-stabilizing capacitor at the high-voltage side of the DC transformer4The obtained independent loop currents are mutually superposed by neglecting the mutual influence of the capacitors, and the fault current I of the multi-terminal direct current distribution system flowing through the direct current breaker DCB1 under the short-circuit fault is obtainedDCB1The peak was 73.85 and the peak time was 4.4 ms. According to the value of the fault current flowing through the direct current breaker DCB1, the current limiting difficulty of the interelectrode short-circuit fault can be analyzed in an auxiliary mode.
In one embodiment, a computer device is provided, which may be a terminal, and its internal structure diagram may be as shown in fig. 9. The computer device includes a processor, a memory, a network interface, a display screen, and an input device connected by a system bus. Wherein the processor of the computer device is configured to provide computing and control capabilities. The memory of the computer device comprises a nonvolatile storage medium and an internal memory. The non-volatile storage medium stores an operating system and a computer program. The internal memory provides an environment for the operation of an operating system and computer programs in the non-volatile storage medium. The network interface of the computer device is used for communicating with an external terminal through a network connection. The computer program is executed by a processor to implement a method of current limiting a power distribution system. The display screen of the computer equipment can be a liquid crystal display screen or an electronic ink display screen, and the input device of the computer equipment can be a touch layer covered on the display screen, a key, a track ball or a touch pad arranged on the shell of the computer equipment, an external keyboard, a touch pad or a mouse and the like.
Those skilled in the art will appreciate that the architecture shown in fig. 9 is merely a block diagram of some of the structures associated with the disclosed aspects and is not intended to limit the computing devices to which the disclosed aspects apply, as particular computing devices may include more or less components than those shown, or may combine certain components, or have a different arrangement of components.
In one embodiment, there is provided a computer device comprising a memory and a processor, the memory having stored therein a computer program, the processor when executing the computer program implementing the steps of:
respectively acquiring short-circuit faults between electrodes in the multi-terminal flexible direct-current power distribution system, and acquiring peak current of each discharge loop and peak time of the peak current; the discharge loop is a loop for discharging a short-circuit point in the interpolar short-circuit fault;
sorting the current-limiting difficulty levels of the inter-electrode short-circuit faults according to the peak currents and the peak times to obtain the inter-electrode short-circuit fault with the highest current-limiting difficulty level and the inter-electrode short-circuit fault with the second highest current-limiting difficulty level;
and simulating the interelectrode short-circuit fault with the highest current-limiting difficulty level and the interelectrode short-circuit fault with the highest current-limiting difficulty level by adopting an electromagnetic transient simulation model to obtain the parameter value of the current-limiting device at the outlet of each discharge loop in the multi-terminal flexible direct-current power distribution system.
It will be understood by those skilled in the art that all or part of the processes of the methods of the embodiments described above can be implemented by hardware instructions of a computer program, which can be stored in a non-volatile computer-readable storage medium, and when executed, can include the processes of the embodiments of the methods described above. Any reference to memory, storage, database, or other medium used in the embodiments provided herein may include non-volatile and/or volatile memory, among others. Non-volatile memory can include read-only memory (ROM), Programmable ROM (PROM), Electrically Programmable ROM (EPROM), Electrically Erasable Programmable ROM (EEPROM), or flash memory. Volatile memory can include Random Access Memory (RAM) or external cache memory. By way of illustration and not limitation, RAM is available in a variety of forms such as Static RAM (SRAM), Dynamic RAM (DRAM), Synchronous DRAM (SDRAM), Double Data Rate SDRAM (DDRSDRAM), Enhanced SDRAM (ESDRAM), Synchronous Link DRAM (SLDRAM), Rambus Direct RAM (RDRAM), direct bus dynamic RAM (DRDRAM), and memory bus dynamic RAM (RDRAM).
The technical features of the above embodiments can be arbitrarily combined, and for the sake of brevity, all possible combinations of the technical features in the above embodiments are not described, but should be considered as the scope of the present specification as long as there is no contradiction between the combinations of the technical features.
The above examples only express several embodiments of the present application, and the description thereof is more specific and detailed, but not construed as limiting the scope of the invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the concept of the present application, which falls within the scope of protection of the present application. Therefore, the protection scope of the present patent shall be subject to the appended claims.
Claims (10)
1. A method of limiting current in a power distribution system, comprising the steps of:
respectively acquiring short-circuit faults between electrodes in a multi-terminal flexible direct-current power distribution system, and acquiring peak current of each discharge loop and peak time of the peak current; the discharge loop is a loop for discharging a short-circuit point in the interelectrode short-circuit fault;
sorting the current-limiting difficulty levels of the inter-electrode short-circuit faults according to the peak currents and the peak times to obtain the inter-electrode short-circuit fault with the highest current-limiting difficulty level and the inter-electrode short-circuit fault with the second highest current-limiting difficulty level;
and simulating the interelectrode short-circuit fault with the highest current-limiting difficulty level and the interelectrode short-circuit fault with the highest current-limiting difficulty level by adopting an electromagnetic transient simulation model to obtain the parameter value of the current-limiting device at each discharge loop outlet in the multi-terminal flexible direct-current power distribution system.
2. The power distribution system current limiting method according to claim 1, wherein before the step of separately acquiring short-circuit faults between poles in the multi-terminal flexible dc power distribution system, the method further comprises the steps of:
according to the configuration, the protection strategy and the key position of a direct current breaker of the multi-end flexible direct current power distribution system, carrying out fault partition on the multi-end flexible direct current power distribution system to obtain each system partition, and analyzing and confirming the interelectrode short circuit fault in each system partition;
the method comprises the following steps of obtaining peak current of each discharge loop and peak time of the peak current, wherein the steps comprise:
performing equivalent processing on the discharge loop to obtain an equivalent circuit; and processing the equivalent circuit to obtain the peak current and the peak time.
3. The power distribution system current limiting method of claim 2, wherein the discharge circuit comprises a converter station discharge circuit and a dc transformer discharge circuit;
processing the equivalent circuit to obtain the peak current and the peak time, including:
respectively carrying out equivalent treatment on the converter station discharge loop and the direct-current transformer discharge loop to obtain a converter station equivalent discharge loop and a direct-current transformer equivalent discharge loop;
processing the equivalent discharge loop of the converter station and the equivalent discharge loop of the direct current transformer by adopting a second-order circuit initial condition to respectively obtain the current of the discharge loop of the converter station and the current of the discharge loop of the direct current transformer;
obtaining a current curve graph of the converter station discharge loop and a current curve graph of the direct-current transformer discharge loop based on the current of the converter station discharge loop and the current of the direct-current transformer discharge loop;
obtaining the peak current and the peak time of the discharging loop of the converter station according to the current curve graph of the discharging loop of the converter station; and obtaining the peak current and the peak time of the discharge loop of the direct current transformer according to the current curve graph of the discharge loop of the direct current transformer.
4. The power distribution system current limiting method according to claim 3, wherein a second-order circuit initial condition is adopted to process the converter station equivalent discharge loop and the direct current transformer equivalent discharge loop, and in the step of obtaining the current of the converter station discharge loop and the current of the direct current transformer discharge loop respectively, a peak current of the converter station discharge loop is obtained based on the following formula:
wherein, I1Current of a discharge loop of the converter station; omega is the oscillation angular frequency of the equivalent discharge loop of the converter station; delta is the time constant of the equivalent discharge loop of the converter station; u shapedcIs the voltage between direct current poles; i is0Is a direct current bus current; l is the equivalent inductance of the equivalent discharge loop of the converter station; omega0The resonance angular frequency of the equivalent discharge loop of the converter station is obtained; r is the equivalent resistance of the equivalent discharge loop of the converter station; and C is the equivalent capacitance of the equivalent discharge loop of the converter station.
5. The power distribution system current limiting method according to claim 3, wherein a second-order circuit initial condition is adopted to process the converter station equivalent discharge loop and the dc transformer equivalent discharge loop, and in the step of obtaining the current of the converter station discharge loop and the current of the dc transformer discharge loop respectively, a peak current of the dc transformer discharge loop is obtained based on the following formula:
wherein, I2The current of the discharge loop of the direct current transformer is obtained; omega1The oscillation angular frequency of the equivalent discharge loop of the direct current transformer is obtained; delta1The time constant of the equivalent discharge loop of the direct current transformer is taken as the time constant; u shapedcIs the voltage between direct current poles; i.e. i0Is a direct current bus current; l is1The equivalent inductance of the equivalent discharge loop of the direct current transformer is obtained; omega2The resonant angular frequency of the equivalent discharge loop of the direct current transformer is obtained; r1The equivalent resistance is an equivalent discharge loop of the direct current transformer; c1And the equivalent capacitance of the equivalent discharge loop of the direct current transformer is obtained.
6. The method according to claim 1, wherein the step of ranking the current-limiting difficulty levels of the inter-electrode short-circuit faults according to the peak currents and the peak times to obtain the inter-electrode short-circuit fault with the highest current-limiting difficulty level and the inter-electrode short-circuit fault with the highest current-limiting difficulty level comprises:
subtracting the on-off current value of the circuit breaker from the maximum current value of the discharge loop within the on-off time of the circuit breaker to obtain a difference value; the circuit breaker is closest to the interelectrode short-circuit fault and isolates the interelectrode short-circuit fault from the multi-terminal flexible direct-current power distribution system; if the peak time is less than or equal to the on-off time, the maximum current value is the value of the peak current; if the peak time is greater than the on-off time, the maximum current value is the current value of the discharge loop at the end of the on-off time;
and obtaining the current limiting difficulty level sequence of the short-circuit fault between the electrodes according to the magnitude sequence of the difference values.
7. The power distribution system current limiting method of claim 6 wherein the current limiting device parameter values comprise current limiting reactance values;
the method comprises the following steps of simulating the interelectrode short-circuit fault with the highest current-limiting difficulty level and the interelectrode short-circuit fault with the highest current-limiting difficulty level by adopting an electromagnetic transient simulation model, wherein the steps comprise:
establishing the electromagnetic transient simulation model;
based on the electromagnetic transient simulation model, the current-limiting reactance value at the outlet of the discharge loop corresponding to the interelectrode short-circuit fault with the highest current-limiting difficulty level is gradually increased until the maximum current value of each discharge loop is smaller than a first current-limiting standard current value;
and based on the electromagnetic transient simulation model, the current-limiting reactance value at the outlet of the discharge loop corresponding to the interelectrode short-circuit fault with the high current-limiting difficulty level is gradually increased until the maximum current value of each discharge loop is smaller than a second current-limiting standard current value.
8. The method of limiting current in an electrical distribution system according to claim 7,
the first current limiting standard current value is the quotient of the cut-off current value and the number of discharge loops corresponding to the interelectrode short-circuit fault with the highest current limiting difficulty level;
the second current limiting standard current value is the quotient of the cut-off current value and the number of discharge loops corresponding to the interelectrode short-circuit fault with the current limiting difficulty level.
9. The method for limiting current of a power distribution system according to claim 1, wherein after the step of simulating the inter-electrode short-circuit fault with the highest current limiting difficulty level and the inter-electrode short-circuit fault with the highest current limiting difficulty level by using an electromagnetic transient simulation model to obtain the parameter value of the current limiting device at the outlet of the discharge loop, the method further comprises the steps of:
checking the interelectrode short-circuit fault of the residual current-limiting difficulty level by adopting the current-limiting device parameter value; the inter-electrode short-circuit fault with the residual current-limiting difficulty level is an inter-electrode short-circuit fault in the multi-terminal flexible direct-current power distribution system except for the inter-electrode short-circuit fault with the highest current-limiting difficulty level and the inter-electrode short-circuit fault with the next highest current-limiting difficulty level;
and when the verification result is failure, simulating the interelectrode short-circuit fault of the residual current-limiting difficulty level by adopting the electromagnetic transient simulation model.
10. A power distribution system current limiting device, comprising:
the data acquisition module is used for respectively acquiring short-circuit faults between electrodes in the multi-terminal flexible direct-current power distribution system and acquiring peak current of each discharge loop and peak time of the peak current; the discharge loop is a loop for discharging a short-circuit point in the interelectrode short-circuit fault;
the sorting module is used for sorting the current-limiting difficulty level of each inter-pole short-circuit fault according to each peak current and each peak time to obtain the inter-pole short-circuit fault with the highest current-limiting difficulty level and the inter-pole short-circuit fault with the second highest current-limiting difficulty level;
and the simulation module is used for simulating the interelectrode short-circuit fault with the highest current-limiting difficulty level and the interelectrode short-circuit fault with the highest current-limiting difficulty level by adopting an electromagnetic transient simulation model to obtain the parameter value of the current-limiting device at the outlet of each discharge loop in the multi-terminal flexible direct-current power distribution system.
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