CN115825539B - Method and system for determining voltage and current of wind power grid-connected two-phase ground fault - Google Patents
Method and system for determining voltage and current of wind power grid-connected two-phase ground fault Download PDFInfo
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Abstract
The application provides a method and a system for determining voltage and current of a wind power grid-connected two-phase ground fault, wherein the method comprises the following steps: obtaining corresponding fault current and non-fault phase voltage when the wind power is sent out of the system through flexible direct transmission and two phases of ground faults occur; determining negative sequence overcurrent of the wind power soft direct-sending-out system in the case of two-phase grounding faults according to the fault current; and determining the overvoltage of the wind power after the wind power is sent out from the system through the flexible direct transmission when the two phases are grounded according to the voltage of the non-fault phase. According to the technical scheme provided by the application, the accuracy of the maximum value of the overvoltage and the maximum value of the negative sequence overcurrent of the wind power through the flexible direct-sending system is improved, and the accuracy of a control strategy for passing through the two-phase ground faults is further improved.
Description
Technical Field
The application relates to the field of overcurrent and overvoltage, in particular to a method and a system for determining voltage and current of a wind power grid-connected two-phase ground fault.
Background
At present, a grid-connected technology of wind power through a flexible direct current output system becomes one of the important focusing directions. While a two-phase ground fault is one of the most common faults in power systems. When an alternating current system between a wind farm network side converter (grid side converters, GSC) and a transmitting end multi-level converter (modular multilevel converter, MMC) has a two-phase ground fault, the system can generate larger transient over-current and over-voltage under the influence of negative sequence current. Due to the low overcurrent and low overvoltage characteristics of the power electronic devices, the system is difficult to realize fault ride-through, so that the safe and reliable operation of the system is affected. Therefore, the negative sequence current control strategy under the two-phase ground fault has great significance.
In the prior art, a control strategy for realizing the penetration of the two-phase ground faults of the offshore wind power system through flexible direct delivery already exists, in the control strategy, the MMC is equivalent to a voltage source, the fan GSC inhibits the negative sequence current of the MMC to be zero, and at the moment, the negative sequence current in the system completely flows into the MMC. Meanwhile, in order to prevent the MMC from over-current, the MMC adjusts the amplitude of the negative sequence modulation voltage to enable the sum of positive sequence current and negative sequence current flowing into the MMC to be smaller than a set safety value, so that fault ride-through is realized. The control method effectively solves the problems of overvoltage and overcurrent when the MMC presents the voltage source characteristic, thereby realizing fault ride-through. However, the calculation of the overvoltage and the overcurrent is inaccurate, which results in inaccurate control strategy for the two-phase ground fault ride-through, so a scheme for quantifying the overvoltage and the overcurrent under the two-phase ground fault according to the fault position is needed.
Disclosure of Invention
The application provides a method and a system for determining voltage and current of a wind power grid-connected two-phase ground fault, which are used for at least solving the technical problem of inaccurate calculation of overvoltage and overcurrent in the prior art.
An embodiment of a first aspect of the present application provides a method for determining voltage and current of a wind power grid-connected two-phase ground fault, the method comprising:
obtaining corresponding fault current and non-fault phase voltage when the wind power is sent out of the system through flexible direct transmission and two phases of ground faults occur;
determining negative sequence overcurrent of the wind power soft direct-sending-out system in the case of two-phase grounding faults according to the fault current;
And determining the overvoltage of the wind power after the wind power is sent out from the system through the flexible direct transmission when the two phases are grounded according to the voltage of the non-fault phase.
Preferably, the obtained fault current is a negative sequence fault current.
Further, the determining, according to the fault current, a negative sequence overcurrent of the wind power soft direct sending-out system in a two-phase ground fault includes:
Obtaining the distance from a fault point when the wind power goes through a soft straight sending system to generate a two-phase ground fault to a multi-level converter at a sending end in the soft straight sending system;
And determining the maximum value of the fault current according to the distance, and taking the maximum value of the fault current as the negative sequence overcurrent.
Further, the maximum value of the fault current is calculated as follows:
Wherein I fanmax is the maximum value of negative sequence fault current, U mp is positive sequence voltage output by a power supply end multi-level converter in a wind power soft and straight output system, X all is the total reactance value corresponding to the wind power soft and straight output system, alpha is the distance from a fault point to the power supply end multi-level converter in the wind power soft and straight output system, and I wp is alternating current positive sequence current output by a fan.
Preferably, the determining the overvoltage of the wind power through the soft direct sending-out system when two phases of ground faults according to the voltage of the non-fault phase comprises:
Obtaining the distance from a fault point when the wind power goes through a soft straight sending system to generate a two-phase ground fault to a multi-level converter at a sending end in the soft straight sending system;
and determining a voltage maximum value of the non-fault phase according to the distance, and taking the voltage maximum value as the overvoltage.
Further, the calculation formula of the voltage maximum value of the non-fault phase is as follows:
Wherein U famax is the voltage maximum value of a non-fault phase, U mp is the positive sequence voltage output by the wind power through the multi-level converter at the transmitting end in the soft and straight transmitting system, X all is the total reactance value corresponding to the wind power through the soft and straight transmitting system, alpha is the distance from a fault point to the multi-level converter at the transmitting end in the soft and straight transmitting system, and I wp is the alternating current positive sequence current output by the fan.
Preferably, the method further comprises:
determining overvoltage corresponding to a common connection point of a wind turbine in the wind power soft direct sending system when two-phase ground faults occur according to the distance from the fault point to a multi-level converter at a sending end in the wind power soft direct sending system;
The overvoltage corresponding to the common connection point of the fan comprises the following steps: positive sequence overvoltage and negative sequence overvoltage corresponding to the common connection point of the fans.
Further, positive sequence overvoltage U wpmax corresponding to the common connection point of the fan when the two-phase ground fault occurs is determined according to the following formula:
And determining a negative sequence overvoltage U wnmax corresponding to the common connection point of the fans when two-phase ground faults occur according to the following steps:
Wherein U mp is positive sequence voltage output by a transmitting-end multi-level converter in a wind power soft and straight transmitting system, I wp is alternating current positive sequence current output by a fan, X all is total reactance value corresponding to the wind power soft and straight transmitting system, alpha is distance from a fault point to the transmitting-end multi-level converter in the wind power soft and straight transmitting system, X weq is reactance value corresponding to a fan converter reactor, and alpha is distance from the fault point to the transmitting-end multi-level converter in the wind power soft and straight transmitting system.
An embodiment of a second aspect of the present application provides a voltage and current determining system for a wind power grid-connected two-phase ground fault, including:
the acquisition module is used for acquiring fault current and voltage of a non-fault phase corresponding to the wind power when the two phases of the wind power are subjected to the ground fault through the flexible direct sending system;
The first determining module is used for determining negative sequence overcurrent of the wind power soft direct sending-out system in the case of two-phase grounding faults according to the fault current;
and the second determining module is used for determining the overvoltage of the wind power through the soft direct delivery system when the two phases of the ground faults occur according to the voltage of the non-fault phase.
Preferably, the obtained fault current is a negative sequence fault current.
The technical scheme provided by the embodiment of the application at least has the following beneficial effects:
The application provides a method and a system for determining voltage and current of a wind power grid-connected two-phase ground fault, wherein the method comprises the following steps: obtaining corresponding fault current and non-fault phase voltage when the wind power is sent out of the system through flexible direct transmission and two phases of ground faults occur; determining negative sequence overcurrent of the wind power soft direct-sending-out system in the case of two-phase grounding faults according to the fault current; and determining the overvoltage of the wind power after the wind power is sent out from the system through the flexible direct transmission when the two phases are grounded according to the voltage of the non-fault phase. According to the technical scheme provided by the application, the negative sequence overcurrent and overvoltage during the two-phase ground fault are determined according to the corresponding fault current and the voltage of the non-fault phase during the two-phase ground fault, so that the precision of the negative sequence overcurrent and overvoltage during the two-phase ground fault is improved, and the precision of a control strategy for passing through the two-phase ground fault is further improved.
Additional aspects and advantages of the application will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the application.
Drawings
The foregoing and/or additional aspects and advantages of the application will become apparent and may be better understood from the following description of embodiments taken in conjunction with the accompanying drawings in which:
FIG. 1 is a flow chart of a method for determining voltage and current of a wind power grid-connected two-phase ground fault according to one embodiment of the application;
FIG. 2 is a schematic diagram of a MMC control process according to one embodiment of the present application;
FIG. 3 is a schematic diagram of a control process of a GSC according to an embodiment of the application;
FIG. 4 is a diagram of an equivalent circuit of a system in a full-scale mode according to an embodiment of the present application;
FIG. 5 is a diagram of an equivalent circuit of the system in the current limit mode according to one embodiment of the present application;
FIG. 6 is a diagram of an equivalent circuit of the system at the time of a b and c phase-to-earth fault provided in accordance with one embodiment of the present application;
FIG. 7 is a schematic diagram of a two-phase ground fault at α provided in accordance with one embodiment of the present application;
FIG. 8 is a graph of the relationship between the ground coefficient and the fault point provided in accordance with one embodiment of the present application;
FIG. 9 is a graph of negative sequence current coefficient versus fault point provided in accordance with one embodiment of the present application;
FIG. 10 is a graph of PCC point positive sequence voltage versus fault point for a GSC provided according to an embodiment of the application;
FIG. 11 is a schematic diagram of a two-phase ground fault equivalent circuit in a current limited mode according to one embodiment of the present application;
FIG. 12 is a first block diagram of a voltage and current determination system for a wind grid-connected two-phase ground fault according to one embodiment of the present application;
FIG. 13 is a second block diagram of a voltage and current determination system for a wind grid-connected two-phase ground fault according to one embodiment of the present application.
Detailed Description
Embodiments of the present application are described in detail below, examples of which are illustrated in the accompanying drawings, wherein like or similar reference numerals refer to like or similar elements or elements having like or similar functions throughout. The embodiments described below by referring to the drawings are illustrative and intended to explain the present application and should not be construed as limiting the application.
The application provides a method and a system for determining voltage and current of a wind power grid-connected two-phase ground fault, wherein the method comprises the following steps: obtaining corresponding fault current and non-fault phase voltage when the wind power is sent out of the system through flexible direct transmission and two phases of ground faults occur; determining negative sequence overcurrent of the wind power soft direct-sending-out system in the case of two-phase grounding faults according to the fault current; and determining the overvoltage of the wind power after the wind power is sent out from the system through the flexible direct transmission when the two phases are grounded according to the voltage of the non-fault phase. According to the technical scheme provided by the application, the negative sequence overcurrent and overvoltage during the two-phase ground fault are determined according to the corresponding fault current and the voltage of the non-fault phase during the two-phase ground fault, so that the precision of the negative sequence overcurrent and overvoltage during the two-phase ground fault is improved, and the precision of a control strategy for passing through the two-phase ground fault is further improved.
The voltage and current determining method and system for wind power grid-connected two-phase ground faults are described below with reference to the accompanying drawings.
Example 1
Fig. 1 is a flowchart of a voltage and current determining method for a wind power grid-connected two-phase ground fault according to an embodiment of the present application, as shown in fig. 1, where the method includes:
step 1: obtaining corresponding fault current and non-fault phase voltage when the wind power is sent out of the system through flexible direct transmission and two phases of ground faults occur;
It should be noted that the obtained fault current is a negative sequence fault current.
Step 2: determining negative sequence overcurrent of the wind power soft direct-sending-out system in the case of two-phase grounding faults according to the fault current;
In an embodiment of the present disclosure, the step 2 specifically includes:
step 2-1: obtaining the distance from a fault point when the wind power goes through a soft straight sending system to generate a two-phase ground fault to a multi-level converter at a sending end in the soft straight sending system;
Step 2-2: and determining the maximum value of the fault current according to the distance, and taking the maximum value of the fault current as the negative sequence overcurrent.
Wherein, the maximum value of the fault current is calculated as follows:
Wherein I fan max is the maximum value of negative sequence fault current, U mp is positive sequence voltage output by a power supply end multi-level converter in a wind power soft and straight output system, X all is the total reactance value corresponding to the wind power soft and straight output system, alpha is the distance from a fault point to the power supply end multi-level converter in the wind power soft and straight output system, and I wp is alternating current positive sequence current output by a fan.
Step 3: and determining the overvoltage of the wind power after the wind power is sent out from the system through the flexible direct transmission when the two phases are grounded according to the voltage of the non-fault phase.
In an embodiment of the present disclosure, the step3 specifically includes:
step 3-1: obtaining the distance from a fault point when the wind power goes through a soft straight sending system to generate a two-phase ground fault to a multi-level converter at a sending end in the soft straight sending system;
Step 3-2: and determining a voltage maximum value of the non-fault phase according to the distance, and taking the voltage maximum value as the overvoltage.
Wherein, the calculation formula of the voltage maximum value of the non-fault phase is as follows:
Wherein U famax is the voltage maximum value of a non-fault phase, U mp is the positive sequence voltage output by the wind power through the multi-level converter at the transmitting end in the soft and straight transmitting system, X all is the total reactance value corresponding to the wind power through the soft and straight transmitting system, alpha is the distance from a fault point to the multi-level converter at the transmitting end in the soft and straight transmitting system, and I wp is the alternating current positive sequence current output by the fan.
In an embodiment of the present disclosure, the method provided by the present invention further includes:
Step 4: determining overvoltage corresponding to a common connection point of a wind turbine in the wind power soft direct sending system when two-phase ground faults occur according to the distance from the fault point to a multi-level converter at a sending end in the wind power soft direct sending system;
The overvoltage corresponding to the common connection point of the fan comprises the following steps: positive sequence overvoltage and negative sequence overvoltage corresponding to the common connection point of the fans.
The positive sequence overvoltage U wpmax corresponding to the common connection point of the fan when the two-phase ground fault occurs is determined according to the following formula:
And determining a negative sequence overvoltage U wnmax corresponding to the common connection point of the fans when two-phase ground faults occur according to the following steps:
Wherein U mp is positive sequence voltage output by a transmitting-end multi-level converter in a wind power soft and straight transmitting system, I wp is alternating current positive sequence current output by a fan, X all is total reactance value corresponding to the wind power soft and straight transmitting system, alpha is distance from a fault point to the transmitting-end multi-level converter in the wind power soft and straight transmitting system, X weq is reactance value corresponding to a fan converter reactor, and alpha is distance from the fault point to the transmitting-end multi-level converter in the wind power soft and straight transmitting system.
It should be noted that, when the ac positive sequence current I wp output by the fan lags behind the positive sequence voltage U mp ° output by the wind power through the multi-level converter at the transmitting end in the flexible and direct transmitting system, that is, when the fan only transmits reactive power, the fault point non-fault phase overvoltage level reaches its maximum value U famax, the system negative sequence current level reaches the maximum value I fanmax, and the positive and negative sequence voltages at the PCC point of the fan also reach the maximum values U wpmax and U wnmax, respectively.
In the embodiments of the present disclosure, to simplify the analysis, a wind farm may be equivalently one GSC; the MMC and the GSC adopt a double closed-loop control strategy, comprising a voltage outer loop and a current inner loop, and meanwhile, in order to control the negative sequence current, the negative sequence control is respectively added into the MMC and the GSC.
The control process of the MMC is as shown in fig. 2:
The MMC adopts the traditional VF control strategy, firstly, the controller directly integrates the time with the frequency of 50Hz to generate the phase angle theta MMC of the MMC modulation voltage, the phase angle is respectively sent to a Park conversion (T abc/dq) module and an inverse Park conversion (T dq/abc) module, Collecting current I m of MMC and PCC point voltage U ms, separating positive and negative sequence components and d and q axis components respectively as I mdqp、Imdqn、Umsdqp、Umsdqn, comparing the PCC point voltage positive sequence component U msdqp with reference values thereof, The error amount is input into the PI controller to obtain a command value of the positive sequence current, then the positive sequence current I mdqp is compared with the command value thereof, the error amount is input into the PI controller, the generated modulation voltage is added/subtracted with a cross-coupling term (omega L eqImdqp) and a voltage feedforward term (U msdqp), Thereby generating a positive sequence modulation voltage, and then generating an actual positive sequence modulation voltage U mcdqp by a positive sequence modulation voltage limiter. Similarly, the negative sequence control only retains the inner loop control strategy, compares the negative sequence current I mdqn with its command value, inputs the error amount to the PI controller, adds/subtracts the cross-coupling term (ωL eqImdqn) and the voltage feedforward term (U msdqn) to the generated modulation voltage, Thereby generating a negative sequence modulated voltage U mcdqn. After passing the positive and negative sequence modulation voltages through inverse Park conversion (T dq/abc), a three-phase modulation voltage is generated. In the figure, U mc is the voltage at the MMC AC outlet, U ms is the voltage at the PCC point, I m is the MMC AC voltage, U wc is the voltage at the GSC AC outlet, U ws is the PCC point voltage, I w is GSC alternating voltage, I dc、umdc is GSC direct current side current and MMC direct current side voltage respectively, theta MMC、θVSC is the phase angle of the MMC and GSC side PCC points respectively, X line is the impedance of the alternating current transmission line, X w and X m are the impedance from the fault point to the GSC outlet and the fault point to the MMC outlet respectively, and X weq and X meq are the converter reactors of GSC and MMC respectively. f (1) denotes a single-phase earth fault.
The control process of the GSC is shown in fig. 3, the GSC adopts a grid-following control strategy, firstly, a phase-locked loop (PLL) is used to collect positive sequence voltage phase θ VSC of a fan PCC point, the phase angle is transmitted to a Park conversion (T abc/dq) module and a reverse Park conversion (T dq/abc) module, the current and the PCC point voltage of the GSC are collected, positive sequence components, negative sequence components, d axis components and q axis components are separated, I wdqp、Iwdqn、Uwsdqp、Uwsdqn are separated, the direct current U wdc of the GSC is compared with a reference value of the direct current U wdc, the error amount is input into a PI controller, so as to obtain a command value of the positive sequence current, then the positive sequence current I wdqp is compared with the command value of the positive sequence current I wdqp, the error amount is input into the PI controller, and the generated modulation voltage is added/subtracted by a cross coupling term (ωli wdqp) and a voltage feedforward term (U wsdqp), so as to generate the positive sequence modulation voltage. Similarly, the negative sequence control retains only the inner loop control strategy, compares the negative sequence current I wdqn with its command value, inputs the error amount to the PI controller, and adds/subtracts the cross-coupling term (ωli wdqn) and the voltage feedforward term (U wsdqn) to the generated modulation voltage, thereby generating the negative sequence modulation voltage. After passing the positive and negative sequence modulation voltages through inverse Park transformation (T dq/abc), three-phase modulation voltages U wcp and U wcn are generated.
When shallow faults occur, the MMC outputs positive sequence current which is smaller than the current limiting value, and the MMC is in a full modulation mode and can be equivalently used as a voltage source; when a deep fault occurs, the MMC outputs positive sequence current to be limited in limiting value, the MMC is in a current limiting mode and can be equivalent to a current source, and the GSC can be equivalent to the current source. Wherein, the system equivalent circuit is shown in fig. 4 when the full-tuning mode is not considered, the system equivalent circuit is shown in fig. 5 when the full-tuning mode is not considered, the negative-tuning mode is not considered, in the drawings, U mcplim and I mlim are respectively the MMC positive-sequence voltage limiting value and the MMC total current limiting value, U wc is the MMC ac outlet voltage, X w is the impedance from the fault point to the GSC outlet, I w is the GSC ac current, I m is the MMC ac current, X m is the impedance from the fault point to the MMC outlet, and f (n) is the fault point.
The following description is made regarding the full modulation mode:
The key to realize two-phase ground fault ride through is to acquire key influencing factors of system overvoltage and overcurrent. Therefore, the invention adopts an analysis method of decoupling circuit characteristics and control characteristics, ignores the negative sequence control of MMC and GSC to obtain the expressions of the overcurrent and overvoltage of the system, and extracts key influencing factors therein.
When the system has two-phase ground fault, taking the b-phase and c-phase faults as examples, and neglecting the system resistance, the equivalent circuit of the system is shown in FIG. 6, wherein the calculation formula of the fault current can be as follows Wherein I fap is the positive sequence current of the system in the case of b-phase and c-phase earth faults, I fan is the negative sequence current of the system in the case of b-phase and c-phase earth faults, I fa0 is the zero sequence current of the system in the case of b-phase and c-phase earth faults, U mp is the positive sequence voltage output by a transmitting-end multi-level converter in the system, X n0＝Xn'+X0',X mn is the negative sequence component of the impedance from the fault point to the MMC outlet, X wn is the negative sequence component of the impedance from the fault point to the GSC outlet, X m0 is the zero sequence component of the impedance from the fault point to the MMC outlet, X w0 is the zero sequence component of the impedance from the fault point to the GSC outlet, X mp is the positive sequence component of the impedance from the fault point to the MMC outlet, X n0 is the sum of the negative sequence and the zero sequence impedance, and in a system, a transformer is usually directly grounded, so that the positive, negative and zero sequence impedances in the system are the same. When a two-phase ground fault occurs at α as shown in FIG. 7, X mp、Xn 'and X 0' can be represented asWherein X all represents all the reactance from the GSC AC outlet to the MMC AC outlet, including MMC converter reactors, line reactance, GSC filters and converter reactors thereof. The formula is given bySubstitution intoIn the middle, it can be found that when GSC output current lags MMC output voltage by 90 DEG, that is, the fan only emits reactive power, the negative sequence current in the system reaches the maximum, which isThe formula X n0＝Xn'+X0' is then applied, Substitution intoIn (3) finishing to obtainWherein ki is a negative sequence current coefficient, and the expression isAnd then obtain
Meanwhile, according to the operation characteristics of the power grid, transient overvoltage can occur to a non-fault phase, the overvoltage level of a fault point is highest, and the problem that a fan is disconnected due to overvoltage is also considered by PCC points of GSC.
The sound phase voltage (a phase) of the fault point isThe sound phase amplitude of the fault point is U famax＝ku(Ump+αIwpXall), wherein ku is the two-phase short circuit grounding coefficient,The positive sequence voltage and the negative sequence voltage of PCC points of the GSC are the following when the output current of the GSC lags behind the MMC voltage by 90 DEG, namely the GSC only gives out reactive power, and the sound phase voltage of the fault point is the maximumU wn＝αjIfanXweq shows that when the output current of the GSC lags behind the MMC voltage by 90 DEG, that is, the GSC only gives out reactive power, the amplitude of the positive and negative sequence voltages is at most
Further, based on the relationship between the ground coefficient and the fault point α as shown in fig. 8, the relationship between the negative sequence current coefficient and the fault point α as shown in fig. 9, and the relationship between the positive sequence voltage of the PCC point of the GSC and the fault point α as shown in fig. 10, it is possible to obtain: when GSC positive sequence current lags MMC positive sequence voltage by 90 degrees, the overvoltage and overcurrent level of the system are highest; the closer the fault point is to the MMC, the higher the system overvoltage and overcurrent levels are; the system negative sequence current level and the overvoltage level are related to the GSC positive sequence current I wp.
The following description is made regarding the current limit mode:
When the alternating current system has a deep fault, the fault current reaches the MMC current limiting value, and at the moment, the MMC presents the current source characteristic and is in the current limiting mode. The system overvoltage is significantly lower in the current limit mode than in the full modulation mode, so that the system overvoltage level is not analyzed in the current limit mode. However, in the current limiting mode, the MMC output current is equal to the current limiter limiting value, reaches the upper limit of system protection, is larger than the current in the full modulation mode, the negative sequence current is further increased, and the problem of over-current of an MMC bridge arm is further aggravated.
In the current limiting mode, as shown in fig. 11, the two-phase ground fault equivalent circuit has a negative sequence current of I fan＝-(Iwp+Imp, and it can be found that the magnitude of the system negative sequence current is independent of the fault location, and is only related to the magnitude and phase of the MMC and GSC output currents. When the GSC output current is in phase with the MMC output current, namely the GSC only sends out reactive power, the negative sequence current of the system is maximum. In the current limit mode, the negative sequence current at the time of the two-phase ground short circuit fault can be reduced to some extent by reducing the positive sequence current in the system, as in the full modulation mode.
In summary, according to the method for determining the voltage and the current of the wind power grid-connected two-phase ground fault, which is provided by the application, the negative sequence overcurrent and the overvoltage of the two-phase ground fault are determined according to the corresponding fault current and the voltage of the non-fault phase when the two-phase ground fault occurs, so that the precision of the negative sequence overcurrent and the overvoltage of the two-phase ground fault is improved, and the precision of a control strategy for passing the two-phase ground fault is further improved.
Example two
Fig. 12 is a voltage and current determining system for a wind power grid-connected two-phase ground fault according to an embodiment of the present application, as shown in fig. 12, including:
The acquisition module 100 is used for acquiring fault current and voltage of a non-fault phase corresponding to the occurrence of two-phase ground faults of the wind power through the flexible direct-sending system;
The first determining module 200 is configured to determine a negative sequence overcurrent of the wind power through the soft direct delivery system when two phases of ground faults occur according to the fault current;
and the second determining module 300 is used for determining the overvoltage of the wind power through the soft direct delivery system when the two phases are grounded according to the voltage of the non-fault phase.
In an embodiment of the present disclosure, the obtained fault current is a negative sequence fault current.
Further, the first determining module 200 includes:
a first obtaining unit 201, configured to obtain a distance from a fault point when the wind power generates a two-phase ground fault through the soft direct sending system to a multi-level converter at a sending end in the wind power soft direct sending system;
A first determining unit 202, configured to determine a maximum value of the fault current according to the distance, and take the maximum value of the fault current as the negative sequence overcurrent.
Wherein, the maximum value of the fault current is calculated as follows:
Wherein I fanmax is the maximum value of negative sequence fault current, U mp is positive sequence voltage output by a power supply end multi-level converter in a wind power soft and straight output system, X all is the total reactance value corresponding to the wind power soft and straight output system, alpha is the distance from a fault point to the power supply end multi-level converter in the wind power soft and straight output system, and I wp is alternating current positive sequence current output by a fan.
In the disclosed embodiment, the root second determining module 300 includes:
The second obtaining unit 301 is configured to obtain a distance from a fault point when the wind power generates a two-phase ground fault through the soft direct sending system to a multi-level converter at a sending end in the wind power soft direct sending system;
A second determining unit 302, configured to determine a voltage maximum value of the non-fault phase according to the distance, and take the voltage maximum value as the overvoltage.
Wherein, the calculation formula of the voltage maximum value of the non-fault phase is as follows:
Wherein U famax is the voltage maximum value of a non-fault phase, U mp is the positive sequence voltage output by the wind power through the multi-level converter at the transmitting end in the soft and straight transmitting system, X all is the total reactance value corresponding to the wind power through the soft and straight transmitting system, alpha is the distance from a fault point to the multi-level converter at the transmitting end in the soft and straight transmitting system, and I wp is the alternating current positive sequence current output by the fan.
In an embodiment of the present disclosure, as shown in fig. 13, the system further includes:
The third determining module 300 is configured to determine, according to a distance from the fault point to a multi-level converter at a transmitting end in a wind power soft and straight transmitting system, an overvoltage corresponding to a common connection point of a wind motor in the wind power soft and straight transmitting system when a two-phase ground fault occurs;
The overvoltage corresponding to the common connection point of the fan comprises the following steps: positive sequence overvoltage and negative sequence overvoltage corresponding to the common connection point of the fans.
The positive sequence overvoltage U wpmax corresponding to the common connection point of the fan when the two-phase ground fault occurs is determined according to the following formula:
And determining a negative sequence overvoltage U wnmax corresponding to the common connection point of the fans when two-phase ground faults occur according to the following steps:
Wherein U mp is positive sequence voltage output by a transmitting-end multi-level converter in a wind power soft and straight transmitting system, I wp is alternating current positive sequence current output by a fan, X all is total reactance value corresponding to the wind power soft and straight transmitting system, alpha is distance from a fault point to the transmitting-end multi-level converter in the wind power soft and straight transmitting system, X weq is reactance value corresponding to a fan converter reactor, and alpha is distance from the fault point to the transmitting-end multi-level converter in the wind power soft and straight transmitting system.
In summary, the voltage and current determining system for the wind power grid-connected two-phase ground fault improves the accuracy of the negative sequence overcurrent and overvoltage during the two-phase ground fault, and further improves the accuracy of the control strategy for the two-phase ground fault crossing.
In the description of the present specification, a description referring to terms "one embodiment," "some embodiments," "examples," "specific examples," or "some examples," etc., means that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the present application. In this specification, schematic representations of the above terms are not necessarily directed to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples. Furthermore, the different embodiments or examples described in this specification and the features of the different embodiments or examples may be combined and combined by those skilled in the art without contradiction.
Any process or method descriptions in flow charts or otherwise described herein may be understood as representing modules, segments, or portions of code which include one or more executable instructions for implementing specific logical functions or steps of the process, and additional implementations are included within the scope of the preferred embodiment of the present application in which functions may be executed out of order from that shown or discussed, including substantially concurrently or in reverse order from that shown or discussed, depending on the functionality involved, as would be understood by those reasonably skilled in the art of the embodiments of the present application.
While embodiments of the present application have been shown and described above, it will be understood that the above embodiments are illustrative and not to be construed as limiting the application, and that variations, modifications, alternatives and variations may be made to the above embodiments by one of ordinary skill in the art within the scope of the application.
Claims (6)
1. The method for determining the voltage and the current of the wind power grid-connected two-phase ground fault is characterized by comprising the following steps:
obtaining corresponding fault current and non-fault phase voltage when the wind power is sent out of the system through flexible direct transmission and two phases of ground faults occur;
determining negative sequence overcurrent of the wind power soft direct-sending-out system in the case of two-phase grounding faults according to the fault current;
Determining the overvoltage of the wind power after the wind power is sent out from the system through the flexible direct transmission when two phases of ground faults occur according to the voltage of the non-fault phase;
The determining the negative sequence overcurrent of the wind power through the soft direct sending-out system when the two phases of ground faults occur according to the fault current comprises the following steps:
Obtaining the distance from a fault point when the wind power goes through a soft straight sending system to generate a two-phase ground fault to a multi-level converter at a sending end in the soft straight sending system;
Determining the maximum value of the fault current according to the distance, and taking the maximum value of the fault current as the negative sequence overcurrent;
The maximum value of the fault current is calculated as follows:
Wherein I fanmax is the maximum value of negative sequence fault current, U mp is positive sequence voltage output by a power supply end multi-level converter in a wind power soft and straight output system, X all is the total reactance value corresponding to the wind power soft and straight output system, alpha is the distance from a fault point to the power supply end multi-level converter in the wind power soft and straight output system, and I wp is alternating current positive sequence current output by a fan;
the step of determining the overvoltage of the wind power through the soft direct delivery system when two phases of ground faults occur according to the voltage of the non-fault phase comprises the following steps:
Obtaining the distance from a fault point when the wind power goes through a soft straight sending system to generate a two-phase ground fault to a multi-level converter at a sending end in the soft straight sending system;
determining a voltage maximum value of the non-fault phase according to the distance, and taking the voltage maximum value as the overvoltage;
the voltage maximum of the non-faulty phase is calculated as follows:
Wherein U famax is the voltage maximum value of a non-fault phase, U mp is the positive sequence voltage output by the wind power through the multi-level converter at the transmitting end in the soft and straight transmitting system, X all is the total reactance value corresponding to the wind power through the soft and straight transmitting system, alpha is the distance from a fault point to the multi-level converter at the transmitting end in the soft and straight transmitting system, and I wp is the alternating current positive sequence current output by the fan.
2. The method of claim 1, wherein the fault current obtained is a negative sequence fault current.
3. The method of claim 1, wherein the method further comprises:
Determining overvoltage corresponding to a common connection point of a wind turbine in the wind power soft direct sending system when two-phase ground faults occur according to the distance from a fault point to a multi-level converter at a sending end in the wind power soft direct sending system;
The overvoltage corresponding to the common connection point of the fan comprises the following steps: positive sequence overvoltage and negative sequence overvoltage corresponding to the common connection point of the fans.
4. The method of claim 3, wherein a positive sequence overvoltage U wpmax corresponding to the fan common connection point when a two-phase ground fault occurs is determined as follows:
And determining a negative sequence overvoltage U wnmax corresponding to the common connection point of the fans when two-phase ground faults occur according to the following steps:
Wherein U mp is positive sequence voltage output by a multi-level converter at a transmitting end in a soft and straight transmitting system of wind power, I wp is alternating current positive sequence current output by a fan, X all is total reactance value corresponding to the soft and straight transmitting system of wind power, alpha is distance from a fault point to the multi-level converter at the transmitting end in the soft and straight transmitting system of wind power, and X weq is reactance value corresponding to a fan converter reactor.
5. The utility model provides a voltage and electric current determining system of wind-powered electricity generation grid-connected two looks earth fault which characterized in that includes:
the acquisition module is used for acquiring fault current and voltage of a non-fault phase corresponding to the wind power when the two phases of the wind power are subjected to the ground fault through the flexible direct sending system;
The first determining module is used for determining negative sequence overcurrent of the wind power soft direct sending-out system in the case of two-phase grounding faults according to the fault current;
The second determining module is used for determining the overvoltage of the wind power when the two phases of the wind power are grounded through the flexible direct-current sending-out system according to the voltage of the non-fault phase;
The determining the negative sequence overcurrent of the wind power through the soft direct sending-out system when the two phases of ground faults occur according to the fault current comprises the following steps:
Obtaining the distance from a fault point when the wind power goes through a soft straight sending system to generate a two-phase ground fault to a multi-level converter at a sending end in the soft straight sending system;
Determining the maximum value of the fault current according to the distance, and taking the maximum value of the fault current as the negative sequence overcurrent;
The maximum value of the fault current is calculated as follows:
Wherein I fanmax is the maximum value of negative sequence fault current, U mp is positive sequence voltage output by a power supply end multi-level converter in a wind power soft and straight output system, X all is the total reactance value corresponding to the wind power soft and straight output system, alpha is the distance from a fault point to the power supply end multi-level converter in the wind power soft and straight output system, and I wp is alternating current positive sequence current output by a fan;
the step of determining the overvoltage of the wind power through the soft direct delivery system when two phases of ground faults occur according to the voltage of the non-fault phase comprises the following steps:
Obtaining the distance from a fault point when the wind power goes through a soft straight sending system to generate a two-phase ground fault to a multi-level converter at a sending end in the soft straight sending system;
determining a voltage maximum value of the non-fault phase according to the distance, and taking the voltage maximum value as the overvoltage;
the voltage maximum of the non-faulty phase is calculated as follows:
Wherein U famax is the voltage maximum value of a non-fault phase, U mp is the positive sequence voltage output by the wind power through the multi-level converter at the transmitting end in the soft and straight transmitting system, X all is the total reactance value corresponding to the wind power through the soft and straight transmitting system, alpha is the distance from a fault point to the multi-level converter at the transmitting end in the soft and straight transmitting system, and I wp is the alternating current positive sequence current output by the fan.
6. The system of claim 5, wherein the fault current obtained is a negative sequence fault current.
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| RU2457593C1 (en) * | 2011-05-27 | 2012-07-27 | Государственное образовательное учреждение высшего профессионального образования "Национальный исследовательский Томский политехнический университет" | Method for building remote protection of double-end line and detection of short-circuit fault therein |
| CN109038658B (en) * | 2018-07-24 | 2021-04-20 | 全球能源互联网研究院有限公司 | Open sea wind power flexible direct current sending-out system and onshore alternating current single-phase earth fault ride-through method |
| CN111413643A (en) * | 2020-04-16 | 2020-07-14 | 贵州电网有限责任公司 | Power distribution network single-phase earth fault identification method |
| CN113203950B (en) * | 2021-04-30 | 2022-02-15 | 华中科技大学 | Method and system for diagnosing ground fault degree of generator stator of marine nuclear power platform |
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| CN106921157A (en) * | 2015-12-28 | 2017-07-04 | 国网智能电网研究院 | A kind of AC singlephase earth fault control method of flexible ring net controller |
| CN107069679A (en) * | 2017-03-30 | 2017-08-18 | 华中科技大学 | A kind of symmetrical bipolar MMC DC sides monopolar grounding fault is passed through and restoration methods |
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