CN111384725A - Short-circuit current calculation method and system for new energy power station - Google Patents
Short-circuit current calculation method and system for new energy power station Download PDFInfo
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- CN111384725A CN111384725A CN201811641065.9A CN201811641065A CN111384725A CN 111384725 A CN111384725 A CN 111384725A CN 201811641065 A CN201811641065 A CN 201811641065A CN 111384725 A CN111384725 A CN 111384725A
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
- H02H7/00—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions
- H02H7/26—Sectionalised protection of cable or line systems, e.g. for disconnecting a section on which a short-circuit, earth fault, or arc discharge has occured
- H02H7/261—Sectionalised protection of cable or line systems, e.g. for disconnecting a section on which a short-circuit, earth fault, or arc discharge has occured involving signal transmission between at least two stations
- H02H7/262—Sectionalised protection of cable or line systems, e.g. for disconnecting a section on which a short-circuit, earth fault, or arc discharge has occured involving signal transmission between at least two stations involving transmissions of switching or blocking orders
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
- H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
- H02J3/46—Controlling of the sharing of output between the generators, converters, or transformers
- H02J3/48—Controlling the sharing of the in-phase component
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
- H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
- H02J3/46—Controlling of the sharing of output between the generators, converters, or transformers
- H02J3/50—Controlling the sharing of the out-of-phase component
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E10/00—Energy generation through renewable energy sources
- Y02E10/70—Wind energy
- Y02E10/76—Power conversion electric or electronic aspects
Abstract
The invention provides a short-circuit current calculation method and a short-circuit current calculation system for a new energy power station, which comprise the following steps: according to a preset short-circuit current fault point, acquiring a short-circuit calculation sequence of each power generation unit in the new energy power station based on the sensitivity under the fault point condition; sequentially carrying out iterative calculation on the short-circuit current of each power generation unit according to the short-circuit calculation sequence; calculating the short-circuit current of the new energy power station according to the short-circuit current of each power generation unit; and when the short-circuit current is subjected to iterative calculation, selecting an equivalent model according to the effective value of the voltage of the new energy power station grid-connected point bus. The method and the system avoid the problem that the traditional short-circuit current calculation method only considers that the new energy is equivalent to a synchronous wind turbine generator with the same capacity, and is not accurate enough when fault analysis is carried out on a power system containing the new energy. Meanwhile, the short-circuit current calculation sequence of each unit is formulated according to the sensitivity, so that the reactive support effect of the sensitive nodes can be preferentially exerted, and the overall convergence speed of the algorithm is improved.
Description
Technical Field
The invention belongs to the technical field of analysis and calculation of short-circuit current of a new energy power system, and particularly relates to a short-circuit current calculation method and system of a new energy power station.
Background
With the increasing proportion of new energy power in the power grid, the influence of the new energy power on the safe operation of the existing power grid is increasingly shown. Especially, after the large-scale new energy is connected into the power grid, the reliability of the existing power grid protection device is challenged. Because the short-circuit current calculation method after the new energy is connected into the power grid is the basis for analyzing the adaptability of the existing relay protection device and providing a new protection principle, the related research of the short-circuit current calculation method after the large-scale new energy is connected into the power grid is receiving more and more attention. However, in the existing related research, when short-circuit current calculation of a large-scale new energy access power grid is performed, the new energy is generally considered to be equivalent to a synchronous wind turbine with the same capacity. Actually, because the new energy has a great difference from the synchronous generator in terms of a power generation mechanism, a grid-connected topology structure, a control mode and the like, the transient characteristic of the new energy during a fault period is greatly changed compared with the generation of the synchronous generator, and the traditional short-circuit current calculation method is not accurate enough when the fault analysis is performed on the power system containing the new energy.
In particular, in recent years, new energy grid-connected specifications are provided by various power companies and power grid operators in the world. In addition to maintaining grid-disconnected operation during a fault, the new energy is required to send reactive power to the system by adjusting a control strategy to support recovery of the grid voltage, that is, the new energy needs to have low-voltage ride-through (LVRT) capability. After the new energy converter has the low voltage ride through capability, the transient characteristic of the new energy is closely related to the low voltage ride through control strategy during the fault, and the short-circuit current characteristic output by the new energy during the fault is more complicated due to the influence of the current limiting and voltage limiting characteristics of the power electronic device of the new energy converter. However, at present, research on the short-circuit current characteristics of new energy, which is related to the influence of a low-voltage ride-through control strategy, is mainly developed based on a simulation method, time domain simulation is performed on the transient process of the new energy by establishing a new energy dynamic model of an electromagnetic/electromechanical transient time scale, and then characteristic extraction and analysis are performed on a short-circuit current waveform. The simulation method is limited by the accuracy of the dynamic model, and when the scale of the new energy power station is large, the calculation time is long, the analysis efficiency is low, and the requirement of relay protection setting engineering cannot be met.
Disclosure of Invention
In order to overcome the defects of the prior art, the invention provides a short-circuit current calculation method and a short-circuit current calculation system for a new energy power station. The method and the system are improved based on the traditional short-circuit current calculation method, the influence of a low-voltage ride-through control strategy on the short-circuit current injected into each power generation unit during the fault period of each power generation unit of the new energy power station is fully considered, the accuracy of the short-circuit current calculation result is effectively improved, the method and the system are suitable for steady-state short-circuit current analysis when the large-scale new energy power station is connected into a power grid, the calculated amount is small, and the analysis speed is high. In addition, the method can be conveniently obtained by improving the existing mainstream commercial program, the implementation steps are relatively simple, and the method has engineering application value.
The adopted solution for realizing the purpose is as follows:
the improvement of a short-circuit current calculation method for a new energy power station is that the method comprises the following steps:
according to a preset short-circuit current fault point, acquiring a short-circuit calculation sequence of each power generation unit in the new energy power station based on the sensitivity under the fault point condition;
sequentially carrying out iterative calculation on the short-circuit current of each power generation unit according to the short-circuit calculation sequence;
calculating the short-circuit current of the new energy power station according to the short-circuit current of each power generation unit;
and when the short-circuit current of each power generation unit is subjected to iterative calculation, selecting an equivalent model according to the effective value of the voltage of the grid-connected point bus of the new energy power station.
The first preferred technical solution provided by the present invention is improved in that the selecting an equivalent model according to the effective value of the voltage of the new energy power station grid-connected point bus comprises:
if the effective value of the grid-connected point bus voltage is in a preset current calculation interval, adopting a current source model as an equivalent model of each power generation unit in the new energy power station;
otherwise, the voltage source model is used as an equivalent model of each power generation unit in the new energy power station, and the control mode of the voltage source model is selected to be an active control priority mode or a failure-free control priority mode according to preset parameters of the power generation units in the new energy power station.
The second preferred technical solution provided by the present invention is improved in that the sequentially performing iterative computation on the short-circuit currents of the power generation units according to the short-circuit computation sequence includes:
step L1: according to the short circuit calculation sequence, calculating the short circuit current of each power generation unit in sequence;
step L2: judging whether the short-circuit currents of all the power generation units are totally converged or not, or whether the iteration number exceeds a preset upper limit of the outer-layer cycle iteration number:
when the two judgment results are negative, the step L1 is carried out;
and when at least one judgment result is yes, ending the iterative computation.
In a third preferred embodiment, the improvement of the present invention is that the calculation of the short-circuit current of the power generation unit includes:
when the equivalent model of the power generation unit is a voltage source model of a reactive control priority mode:
step L11: determining target values of a reactive component and an active component of a short-circuit current of the power generation unit;
step L12: judging whether the difference value between the current short-circuit current reactive component calculation value and the target value is smaller than a preset reactive threshold value:
if yes, go to step L13; otherwise, correcting the value of the series reactance in the voltage source model, updating the calculated value of the reactive component of the short-circuit current and the target value of the active component of the short-circuit current, and turning to the step L13;
step L13: judging whether the current calculation value of the active component of the short-circuit current and the target value are smaller than a preset active threshold value: if yes, go to step L14; otherwise, correcting the value of the series resistor in the voltage source model, updating the calculated value of the active component of the short-circuit current and the target values of the active component and the reactive component of the short-circuit current, and turning to the step L14;
step L14: judging whether the difference value between the calculated value of the active component of the short-circuit current and the target value is smaller than a preset active threshold value and the difference value between the calculated value of the reactive component of the short-circuit current and the target value is smaller than a preset reactive threshold value or not, or whether the cycle number exceeds a preset upper limit of the cycle iteration number of the inner layer or not:
if at least one item is yes, the loop iteration is ended, otherwise, the step L12 is carried out.
In a fourth preferred embodiment of the present invention, the improvement is that the calculation formula of the short-circuit current reactive component target value is as follows:
wherein the subscript q represents reactive, Iq,refIndicating target value of reactive component of short-circuit current, I1Indicating reactive current, I, injected into the grid by the generating unit before the faultNIndicating rated current, U, of the generating unitTBus for indicating power generation unitVoltage per unit value; k is a radical ofqRepresents the proportionality coefficient of reactive component of short-circuit current, and kqSatisfy kq,min≤kq≤kq,max，kq,minRepresenting the lower limit of the proportional coefficient, k, of the reactive component of the preset short-circuit currentq,maxRepresenting the upper limit of the proportion coefficient of the reactive component of the short-circuit current;
the upper limit k of the short-circuit current reactive component proportionality coefficientq,maxThe calculation formula is as follows:
wherein k ismaxRepresenting an inverter power electronics current limit;
the calculation formula of the short-circuit current active component target value is as follows:
wherein the subscript p represents active, Ip,refIndicating the target value, k, of the active component of the short-circuit currentpAnd the scale factor of the active component of the preset short-circuit current is represented.
In a fifth preferred aspect of the present invention, the improvement wherein the calculation of the short-circuit current of the power generation unit includes:
when the equivalent model of the power generation unit is a voltage source model of an active control priority mode:
step L21: determining target values of a reactive component and an active component of a short-circuit current of the power generation unit;
step L22: judging whether the difference value between the current short-circuit current active component calculation value and the target value is smaller than a preset active threshold value:
if yes, go to step L23; otherwise, correcting the value of the series resistor in the voltage source model, updating the calculated value of the active component of the short-circuit current and the target value of the reactive component of the short-circuit current, and turning to the step L23;
step L23: judging whether the difference value between the current short-circuit current reactive component calculation value and the target value is smaller than a preset reactive threshold value:
if yes, go to step L24; otherwise, correcting the value of the series reactance in the voltage source model, updating the calculated value of the reactive component of the short-circuit current and the target values of the active component and the reactive component of the short-circuit current, and turning to the step L24;
step L24: judging whether the difference value between the calculated value of the active component of the short-circuit current and the target value is smaller than a preset active threshold value and the difference value between the calculated value of the reactive component of the short-circuit current and the target value is smaller than a preset reactive threshold value or not, or whether the cycle number exceeds a preset upper limit of the cycle iteration number of the inner layer or not:
if at least one item is yes, the loop iteration is ended, otherwise, the step L22 is carried out.
According to a sixth preferred technical scheme provided by the invention, the improvement is that the target value of the active component of the short-circuit current is set according to actual needs;
the calculation formula of the short-circuit current reactive component target value is as follows:
wherein the subscript q represents reactive, Iq,refIndicating target value of reactive component of short-circuit current, I1Indicating reactive current, I, injected into the grid by the generating unit before the faultNIndicating rated current, U, of the generating unitTRepresenting a per unit value of the bus voltage of the power generation unit; k is a radical ofqRepresents the proportionality coefficient of reactive component of short-circuit current, and kqSatisfy kq,min≤kq≤kq,max，kq,minRepresenting the lower limit of the proportional coefficient, k, of the reactive component of the preset short-circuit currentq,maxRepresenting the upper limit of the proportion coefficient of the reactive component of the short-circuit current;
the upper limit k of the short-circuit current reactive component proportionality coefficientq,maxThe calculation formula is as follows:
wherein k ismaxTo representInverter power electronics current limit;
Iq,refmaximum value of
The constraint is shown as follows:
wherein, Ip,refIndicating the target value of the active component of the short-circuit current and the subscript p indicating the active.
In a seventh preferred aspect of the present invention, the improvement wherein the calculation of the short-circuit current of the power generation unit includes:
when the equivalent model of the power generation unit is a current source model:
step L31: calculating a target value of a short-circuit current phase angle;
step L32: judging whether the difference value between the calculated value of the current short-circuit current phase angle and the target value is smaller than a preset phase angle threshold value or whether the cycle number exceeds a preset inner-layer cycle iteration number upper limit:
if at least one item is yes, ending the loop iteration; otherwise, the calculated value of the phase angle is corrected by changing the ratio of the active component to the reactive component of the current injected by the power generation unit, and the target values of the active component, the reactive component and the phase angle of the short-circuit current are updated, and the step L32 is carried out.
In an eighth preferred aspect of the present invention, the improvement is that the target value calculation formula of the phase angle of the short-circuit current is as follows:
wherein, thetarefTarget value, I, representing the phase angle of the short-circuit currentp,refIndicating the target value of the active component of the short-circuit current, Iq,refThe target value of the reactive component of the short-circuit current is shown, subscript p shows active power, and subscript q shows reactive power; i isq,refThe calculation formula is as follows:
wherein, I1Indicating reactive current, I, injected into the grid by the generating unit before the faultNIndicating rated current, U, of the generating unitTRepresenting a per unit value of the bus voltage of the power generation unit; k is a radical ofqRepresents the proportionality coefficient of reactive component of short-circuit current, and kqSatisfy kq,min≤kq≤kq,max，kq,minRepresenting the lower limit of the proportional coefficient, k, of the reactive component of the preset short-circuit currentq,maxRepresenting the upper limit of the proportion coefficient of the reactive component of the short-circuit current;
the upper limit k of the short-circuit current reactive component proportionality coefficientq,maxThe calculation formula is as follows:
wherein k ismaxRepresenting an inverter power electronics current limit;
Ip,refis calculated as follows:
wherein k ispAnd the scale factor of the active component of the preset short-circuit current is represented.
In a ninth preferred technical solution provided by the present invention, the improvement is that the obtaining of the short circuit calculation order of each power generation unit in the new energy power station based on the sensitivity under the fault point condition includes:
aiming at each power generation unit in the new energy power station, acquiring a value of voltage amplitude change of a new energy power station grid-connected point bus caused by the injection of a reactive current value and the injection of a reactive current of the power generation unit under the fault point condition;
respectively calculating absolute values of the ratio of the amplitude value of the voltage of the bus of the grid-connected point caused by each power generation unit to the value of the injected reactive current;
and sequencing according to the absolute value of the ratio from large to small, and formulating the short circuit calculation sequence of each power generation unit.
In a tenth preferred technical solution provided by the present invention, the improvement is that the short-circuit current of the new energy power station is calculated according to the short-circuit current of each power generation unit as follows:
Ishc＝Ires+Igrid
wherein, IshcRepresents short-circuit current of new energy power station, IgridIndicating short-circuit current, I, supplied from the external grid sideresRepresents the sum of short-circuit currents provided by power generation units in the new energy power station, IresThe calculation formula is as follows:
wherein n represents the number of power generation units in the new energy power station, Ires,iIndicating the short circuit current of the ith power generation cell.
In a new energy power plant short circuit current calculation system, the improvement comprising: the system comprises a calculation sequence module, a unit current module and a power station current module;
the calculation sequence module is used for calculating the short circuit calculation sequence of the electrical unit;
the unit current module is used for sequentially carrying out iterative calculation on the short-circuit current of each power generation unit according to the short-circuit calculation sequence;
the power station current module is used for calculating the short-circuit current of the new energy power station according to the short-circuit current of each power generation unit;
and when the short-circuit current of each power generation unit is subjected to iterative calculation, selecting an equivalent model according to the effective value of the voltage of the grid-connected point bus of the new energy power station.
The eleventh preferred technical solution provided by the present invention is improved by further comprising a model selection module;
the model selection module is used for adopting a current source model as an equivalent model of each power generation unit in the new energy power station if the effective value of the grid-connected point bus voltage is in a preset current calculation interval; otherwise, the voltage source model is used as an equivalent model of each power generation unit in the new energy power station, and the control mode of the voltage source model is selected to be an active control priority mode or a failure-free control priority mode according to preset parameters of the power generation units in the new energy power station.
Compared with the closest prior art, the invention has the following beneficial effects:
the invention provides a short-circuit current calculation method and a short-circuit current calculation system for a new energy power station, wherein according to a preset short-circuit current fault point, a short-circuit calculation sequence of each power generation unit in the new energy power station is obtained based on the sensitivity under the condition of the fault point; sequentially carrying out iterative calculation on the short-circuit current of each power generation unit according to the short-circuit calculation sequence; calculating the short-circuit current of the new energy power station according to the short-circuit current of each power generation unit; and when the short-circuit current of each power generation unit is subjected to iterative calculation, selecting an equivalent model according to the effective value of the voltage of the grid-connected point bus of the new energy power station. The short-circuit current calculation method of the new energy power station selects the equivalent model according to the actual situation, and avoids the problem that the traditional short-circuit current calculation method only considers that the new energy is equivalent to the synchronous wind turbine generator with the same capacity, and is not accurate enough when the fault analysis is carried out on the power system containing the new energy. Meanwhile, the short-circuit current calculation sequence of each unit is formulated according to the sensitivity, so that the reactive support effect of the sensitive nodes can be preferentially exerted, and the overall convergence speed of the algorithm is improved.
During Short-circuit fault, the Short-circuit current contribution amount of each new energy power generation unit is different due to different drop depths of the generator terminal voltage, capacitive or inductive Short-circuit current further changes the generator terminal voltage, and the related international standard 'IEC 60909Short-circuit currents in three-phase-a.c. systems-calculations of currents' or the corresponding national standard 'GB/T15544.1-2013 three-phase alternating current system Short-circuit current Calculation' does not fully consider the interaction process. The method provided by the invention designs a double-layer nested iterative algorithm, effectively takes the dynamic reactive power support capability into consideration, compares the calculation result with a large amount of actual short circuit test data, and verifies the accuracy of the method. The method can provide technical support for the adaptability analysis of the relay protection device after the large-scale new energy is accessed into the power grid and the design of a new protection scheme.
Drawings
Fig. 1 is a schematic flow chart of a short-circuit current calculation method of a new energy power station provided by the invention;
FIG. 2 is a simplified flow chart of an embodiment of a method for calculating a short-circuit current of a new energy power station according to the present invention;
FIG. 3 is a schematic view of a detailed flow chart of iterative calculation of a plurality of power generation units of a new energy power station according to an embodiment of the short-circuit current calculation method for a new energy power station provided by the present invention;
FIG. 4 is a schematic view of a flow chart of iterative calculation of a single power generation unit of a new energy power station according to an embodiment of a method for calculating a short-circuit current of a new energy power station provided by the invention;
FIG. 5 is a schematic diagram of topological connection of each power generation unit of the new energy power station related to the invention;
FIG. 6 is a schematic wiring mode diagram of a double-fed wind power plant Z1 subarea related by the invention;
FIG. 7 is a Thevenin equivalent schematic diagram of the calculation of the short circuit of the new energy power generation unit related to the invention;
FIG. 8 is a Noton equivalent diagram of the new energy power generation unit short circuit calculation according to the present invention;
FIG. 9 is a schematic diagram of low voltage ride through requirements of a GB/T19963-2011 wind power plant related to the invention;
fig. 10 is a schematic diagram of a basic structure of a short-circuit current calculation system of a new energy power station according to the present invention;
fig. 11 is a detailed structural schematic diagram of a short-circuit current calculation system of a new energy power station provided by the invention.
Detailed Description
The following describes embodiments of the present invention in further detail with reference to the accompanying drawings.
Example 1:
the schematic flow chart of the short-circuit current calculation method of the new energy power station provided by the invention is shown in fig. 1, and the method comprises the following steps:
step 1: according to a preset short-circuit current fault point, acquiring a short-circuit calculation sequence of each power generation unit in the new energy power station based on the sensitivity under the fault point condition;
step 2: sequentially carrying out iterative calculation on the short-circuit current of each power generation unit according to the short-circuit calculation sequence;
and step 3: calculating the short-circuit current of the new energy power station according to the short-circuit current of each power generation unit;
and when the short-circuit current of each power generation unit is subjected to iterative calculation, selecting an equivalent model according to the effective value of the voltage of the grid-connected point bus of the new energy power station.
Specifically, a flow of a short-circuit current calculation method of a new energy power station is shown in fig. 2, and includes:
step S1 short-circuit current calculation initialization of new energy power station
The calculation initialization of the short-circuit current of the new energy power station comprises the steps of setting a short-circuit current fault point according to needs, for example: when the type selection and the relay protection setting of each breaker device of the new energy power station are performed, the short-circuit current value at the corresponding position needs to be calculated and the new energy power station grid-connected point P needs to be calculated due to different installation positions of each breaker device1(i.e., high side of booster station) short circuit current, then P is set1Calculating the low-voltage side P of the booster station of the new energy power station as a fault point2Short circuit current value, then set P2Is a failure point, as shown in fig. 5; short type settings, for example: when the relay protection fixed value is determined based on the maximum short-circuit current, the three-phase short-circuit fault type is selected to calculate the maximum short-circuit current, when the relay protection sensitivity is analyzed based on the minimum short-circuit current, the two-phase short-circuit fault type is selected to calculate the minimum short-circuit current, and in addition, if the relay protection sensitivity is the ground fault type, the ground resistance and the ground reactance need to be set.
Step S2: determining short-circuit current calculation sequence of power generation units of new energy power station
The calculation sequence of the short-circuit current of the power generation units of the new energy power station is sorted according to the voltage sensitivity numerical value, the invention defines a voltage sensitivity index with simple and feasible engineering calculation, namely under the initialization condition of the step S1, the new energy power generation unit bus injects reactive current and new energy caused by the reactive currentReciprocal absolute value of ratio of voltage amplitude changes of power station grid-connected point bus
△ I is reactive current injection quantity, △ U is the change value of the new energy power station grid-connected point bus voltage under the corresponding injection quantity, and subscript I represents the ith new energy power generation unit.
The calculation sequence of the short circuit current of the power generation unit of the new energy power station is sorted according to the priority with high sensitivity, so that the convergence rate of the whole algorithm is improved, and the specific analysis is as follows:
new energy power stations such as wind power plants, photovoltaic power stations and the like have the characteristics of small unit capacity, low alternating current side voltage level, large unit types and quantity and the like. For example, the single machine capacity of the current mainstream wind generating set is generally between 1.5 and 3MW, and the typical voltage level of an alternating current side is 690V; the single-machine capacity of the photovoltaic inverter is between several kW and 1MW, and the voltage level of an alternating current side is generally 270-380V. In a wind farm or a photovoltaic power station, tens to hundreds of units (power generation units) are often formed, so that the mode of connecting the units into a power grid is greatly different from that of a conventional power plant. The topological connection of each power generation unit of the new energy power station is shown in fig. 5 and is composed of a plurality of collection lines, each collection line and the power generation unit connected with the collection line are defined as a Zone (Zone), and then a new energy power station consists of a Zone Z1、Z2、Z3…, etc.
Taking a doubly-fed wind farm as an example, as shown in fig. 6, a doubly-fed wind farm Z is provided1Partitioned connection mode, new energy power generation unit G1To GnBus at the generator terminal of new energy power generation unit is respectively connected1To BusnThen each terminal bus passes through the unit transformer T2Access to a collection line (aerial or cable), multiple collection lines connected in parallel to a booster station T1Low voltage side bus bar P2High-voltage side bus P of booster station1And (namely, the Grid of the Grid connection point) is connected with the regional power Grid through a line. The wind turbine generator in the power station firstly passes through the unit transformer T2Boosting the voltage to 10-35 kV, and collecting the voltage to a booster station T through an alternating current collecting line1Boosting the voltage to 110-330 kV, and then further boosting the voltage through an alternating current transmission line and accessing a 500-750 kV transformer substation to be sent into a main network. When new energy power station point of connection P1At or in the collector line P2When short-circuit fault occurs, Bus at the generator end of each generator unit can be caused1、Bus2、……BusnThe voltage drop depths of the current collecting lines are different, and the Bus at the head end of the current collecting line1Is more than the terminal BusnThe voltage drop of (2) is severe. According to the requirements of the existing national/industrial standard on the dynamic reactive support capability during the low voltage ride through period of the new energy, as shown in fig. 9, the dynamic reactive support capability provided by each power generation unit under different falling depths is different, specifically, the voltage per unit value U of the grid-connected point of the new energy power stationTWhen the current drops to the interval of 0.2p.u. -0.9p.u., the dynamic reactive current I injected into the power system by the power generation unit of the new energy power stationq≥1.5×(0.9-UT)INWherein: i isNThe rated current of the power generation unit of the new energy power station is obtained.
FIG. 9 shows the low voltage ride through capability requirement of the wind turbine set specified in the national standard "GB/T19963-2011 wind farm low voltage ride through requirement". During the short-circuit fault period, if the wind power plant grid-connected point voltage per unit value UTIf the voltage drops to 0.2pu, the wind turbine generator is required to be ensured to be disconnected from the grid and continuously run within at least 625ms, and a certain reactive current I is required to be injected during the periodq≥1.05IN(ii) a If the voltage of the grid-connected point UTWhen the voltage drops to 0.2-0 and 9pu, the minimum time of the wind generation set for continuous operation without disconnection is gradually increased from 625ms to 2s, and a certain reactive current I needs to be injected in the periodq≥1.5×(0.9-UT)IN(ii) a If the voltage of the grid-connected point UTWhen the voltage drops below 0.2pu, the fan is allowed to be cut out of the power grid, and no requirement is made on reactive current at the moment; if the voltage of the grid-connected point UTAnd when the voltage drops to 0.9-1pu, the wind turbine generator is required to maintain the reactive current injected into the power grid by the power station before the fault.
The capacitive reactive current that collects current circuit head end Bus1 department and pour into can play the effect of lifting this busbar voltage, and then help the lifting of other busbar voltages in new forms of energy power station, and is same, the terminal Bus of collection current circuitnThe capacitive reactive current injected at the position can be liftedAnd the voltage of other buses of the energy power station. Since Bus1 is greater than BusnThe voltage sensitivity defined by the invention is a sequencing basis, and can preferentially play a reactive support role of a sensitive node and improve the overall convergence speed of the algorithm.
Step S3 iteratively calculates short-circuit current of each power generation unit
After the calculation order of the power generation cells is determined in step S2, the short-circuit current of each power generation cell is iteratively calculated in order. In the prior art, a plurality of power generation units are equivalently simplified into a single synchronous generator for consideration in the new energy, and the influence of a low-voltage ride-through control strategy on the injection of short-circuit current into each power generation unit during a fault period is not taken into consideration. The method fully considers a low voltage ride through control strategy during the fault period of each power generation unit of the new energy power station, and calculates the short-circuit current of each new energy power generation unit by adopting a double-layer nested iterative algorithm. The outer loop of the algorithm is shown in fig. 3, and further, the short-circuit current I of the iOrder new energy power generation unit in fig. 3res,iThe detailed calculation flow of (2) is shown in fig. 4. The method comprises the following specific steps:
firstly, adopting the method introduced by the international standard of IEC 60909Short-circuit currents in three-phase ac system Short-circuit current Calculation or the corresponding national standard of GB/T15544.1-2013 Short-circuit current Calculation, using mainstream commercial software (such as DIgSILENTPOWER Factory in Germany or PSASP in China provides a Calculation function module meeting the above standard) to calculate the Short-circuit current, wherein the Calculation result comprises the bus voltage effective value U of each power generation unit of the new energy power station in the Short-circuit periodcalcEffective value of short-circuit current I injected into each generating unit buscalcAnd phase angle theta thereofcalc. Further, the active component I of the bus injection current of each power generation unit can be obtainedp,calc＝Icalccos(θcalc) And a reactive component Iq,calc＝Icalcsin(θcalc)。
Then, performing equivalent model selection, and calculating the effective value U of the grid-connected point bus voltage according to the bus voltage of each power generation unit of the new energy power station in the short circuit period obtained by the primary short circuit calculationT,calcAnd according to UT,calcDifferent equivalent models are selected. The equivalent models are divided into two types, namely a voltage source model based on Thevenin equivalent and a current source model based on Noton equivalent. The thevenin equivalent of one collection line is shown in fig. 7 and the norton equivalent of one power generation unit is shown in fig. 8. A large number of calculations show that when U isT,calcWhen the current is in a preset current calculation interval, such as 0-0.2p.u or 0.8-1.0p.u, the convergence of the voltage source model is poor, and the current source model is preferably selected, otherwise the voltage source model is preferably selected.
FIG. 7 shows new energy power generation units G on a collection line of a new energy power station1To GnCarrying out Thevenin equivalence (namely, connecting an ideal voltage source and impedance in series) and then respectively connecting the Thevenin equivalence with Bus buses at the generator end of the new energy power generation unit1To Busn. Wherein the series impedance Z of the ith celliRi + jXi. By changing the R value and the X value of the series impedance, the active component and the reactive component of the injection current of the equivalent model can be changed.
FIG. 8 is a diagram illustrating short-circuit calculation norton equivalence of a single new energy power generation unit, i.e. an ideal current source and a parallel admittance YG, and a Bus at a terminal of the new energy power generation unit1Connected with each other, the injected current amount i is the branch current i of the ideal current source1And admittance branch i2And (4) summing. Branch current i of ideal current source1Can be orthogonally decomposed into active components ipAnd a reactive component iqAnd can be controlled individually.
According to the difference between the equivalent model and the control priority, there are three iterative correction paths, as shown in fig. 4, where: loop1 is a voltage source equivalent model and a reactive power control priority mode; loop2 is a voltage source equivalent model and an active control priority mode; loop3 is a current source equivalent model. The active priority and the reactive priority can be selected according to parameters provided by an inverter manufacturer, and most of the inverters are preset to be in a reactive priority mode at present so as to be beneficial to voltage recovery during a fault.
The following description takes Loop1 iterative path (voltage source equivalent model, reactive power control priority mode) as an example:
(1) method for calculating target values of reactive component and active component of short-circuit current in reactive control priority mode
Firstly, calculating a short-circuit current reactive component target value Iq,ref
Wherein: i isNRated current for a new energy power generation unit such as a fan/photovoltaic inverter device; i is1Injecting reactive current into the grid for a pre-fault new energy power generation unit such as a fan/photovoltaic inverter device; u shapeTThe voltage per unit value is a new energy power station grid-connected point bus voltage per unit value; k is a radical ofqIs the proportion coefficient of the reactive component of the short-circuit current.
The above formula short-circuit current reactive component proportionality coefficient kqShould satisfy kq,min≤kq≤kq,max. According to the national standard 'GB/T19963 technical regulation of wind power plant access power system' or 'GB/T19964 technical regulation of photovoltaic power plant access power system', the lower limit k of the short-circuit current reactive component proportionality coefficient q,min1 is ═ 1; determining short-circuit current reactive component proportionality coefficient upper limit k by fan/photovoltaic inverter equipment current limit valueq,max：
Wherein: k is a radical ofq,maxAnd k isq,minThe upper limit value and the lower limit value of the short-circuit current reactive component proportionality coefficient are respectively; k is a radical ofmaxThe value is 1.1 for the current limit of the inverter power electronic device.
Then, according to the obtained short-circuit current reactive component target value Iq,refCalculating the target value of the active component of the short-circuit current
Coefficient k in the formulapK is 0-k p1, since the current national standards do not make uniform requirements on the active component during the short-circuit fault, the value needs to be determined according to the actual low-voltage ride-through control strategy of each fan/photovoltaic inverter manufacturer.
(2) InnerLoop iterative correction process of reactive component and active component of short-circuit current in reactive control priority mode
Comparing the target value I of the reactive component of the short-circuit currentq,refAnd the last short-circuit current calculation result Iq,calcIf Iq,ref-Iq,calc|≥Iq,errmaxChanging the series reactance X, then calculating the short circuit and recalculating a new target value of the active component of the short circuit current; then comparing the active component of the short-circuit current with a new target value Ip,refAnd the latest short circuit calculation result Ip,calcIf Ip,ref-Ip,calc|≥Ip,errmaxThen the series resistance R is changed, then the short circuit calculation is carried out and the new target values of the active component and the reactive component of the short circuit current are recalculated, if Ip,ref-Ip,calc|<Ip,errmaxAnd | Iq,ref-Iq,calc|<Iq,errmaxI.e. the requirement of the error limit is met at the same time, iteration converges and the loop exits. Otherwise, the above process is executed again until the iteration convergence or the iteration number reaches the preset upper limit Max1 of the iteration number of the inner loop, and the loop is exited.
According to ohm's law, when the voltage amplitude of the equivalent voltage source is constant, the larger the value of the series reactance X or the series resistance R is, the more the short-circuit current reactive component I is calculated by the short-circuitq,calcOr a real component Ip,calcThe smaller the value. According to the rule, when the target value is larger than the calculated value, the impedance value should be changed to be smaller, otherwise, the impedance value should be changed to be larger, and each time the step length is modified, 0.1 ohm is recommended.
The iteration path Loop2 (voltage source equivalent model, active control priority mode) is similar to the Loop1 iteration path and is not described in detail.
The iterative path Loop3 (current source equivalent model) is different from Loop1 and Loop 2. Because the current source model can directly control the ratio of the active component and the reactive component of the short-circuit current injected by the current source model, the new energy power generation unitPhase angle target value theta of voltage and injected short-circuit current of unit terminal busrefFor convergence basis, the ratio between the active component and the reactive component is modified by iteration so that the short-circuit current satisfies | thetaref-θcalc|<θerrmaxFurther, the active component of the short circuit current is calculated as Ip,calcAnd a calculated value of reactive component Iq,calcSimultaneously converge to the target value Ip,refAnd Iq,refAnd iteration converges and the loop exits. Wherein, thetaerrmaxRepresenting a predetermined phase angle threshold value, thetacalcRepresenting a calculated value of the phase angle of the short circuit current.
Wherein theta isrefThe calculation formula is as follows:
Ip,refand Iq,refThe calculation method is the same as that in the voltage source model, and is not described in detail.
The convergence/exit criteria for the inner loop and the outer loop are as follows:
the convergence/exit criterion of inner loop InnerLoop is as follows: 1) if the iteration times exceed the upper limit Max1 of the iteration times of the inner loop, the inner loop is directly exited; 2) and if the absolute value of the difference between each target value of the short-circuit current and each calculated value of the short-circuit current is smaller than the preset error limit value, the inner-layer cycle is converged and exited.
The convergence/exit criterion of the outer loop is as follows: 1) if the iteration times exceed the upper limit Max2 of the iteration times of the outer layer loop, directly exiting the outer layer loop; 2) and if all the new energy power generation units meet the convergence/exit criterion, exiting the outer-layer cycle.
Step S4 calculating short-circuit current of new energy power station
When short-circuit fault occurs at a new energy power station grid-connected point P1 or a current collection line P2, P1Or P2Short-circuit current at (c). The short-circuit current comprises two parts, wherein one part is from short-circuit current contribution I of each power generation unit in the new energy power stationres,iThe short-circuit current value is calculated in step S3; part of the external electricity from the new energy power stationShort-circuit current I provided by network sidegridThe short-circuit current value can be obtained by mainstream commercial software (such as DIgSILENTPOWERF, Germany or PSASP, China, both provide a calculation function module meeting the above standard). Total short-circuit current IshcCan be calculated by
Ishc＝Ires+Igrid
Wherein, IshcRepresents short-circuit current of new energy power station, IresRepresents the sum of short-circuit currents provided by power generation units in the new energy power station, IresThe calculation formula is as follows:
wherein n represents the number of power generation units in the new energy power station, Ires,iIndicating the short circuit current of the ith power generation cell.
Example 2:
based on the same invention concept, the invention also provides a short-circuit current calculation system of the new energy power station, and the principle of solving the technical problems of the devices is similar to the short-circuit current calculation method of the new energy power station, so repeated parts are not repeated.
The basic structure of the system is shown in fig. 10, and comprises:
the system comprises a calculation sequence module, a unit current module and a power station current module;
the calculation sequence module is used for calculating the short circuit calculation sequence of the electrical unit;
the unit current module is used for sequentially carrying out iterative calculation on the short-circuit current of each power generation unit according to the short-circuit calculation sequence;
the power station current module is used for calculating the short-circuit current of the new energy power station according to the short-circuit current of each power generation unit;
and when the short-circuit current of each power generation unit is subjected to iterative calculation, selecting an equivalent model according to the effective value of the voltage of the grid-connected point bus of the new energy power station.
A detailed structural schematic diagram of a short-circuit current calculation system of the new energy power station is shown in fig. 11. The system also includes a model selection module;
the model selection module is used for adopting a current source model as an equivalent model of each power generation unit in the new energy power station if the effective value of the voltage of the grid-connected point bus is positioned in a preset current calculation interval; otherwise, the voltage source model is used as an equivalent model of each power generation unit in the new energy power station, and the control mode of the voltage source model is selected to be an active control priority mode or a failure-free control priority mode according to preset parameters of the power generation units in the new energy power station.
Wherein the unit current module includes: a current calculating unit and an outer layer judging unit;
the current calculation unit is used for calculating the short-circuit current of each power generation unit in sequence according to the short-circuit calculation sequence;
the outer layer judging unit is used for judging whether the short-circuit currents of all the power generation units are totally converged or not, or whether the iteration number exceeds a preset outer layer circulation iteration number upper limit or not: when the two judgment results are negative, the current calculation unit continuously calculates the short-circuit current of each power generation unit in sequence; and when at least one judgment result is yes, ending the iterative computation.
Wherein the current calculating unit includes: the active power priority voltage source subunit is connected with the reactive power priority voltage source subunit;
the reactive priority voltage source subunit is used for iteratively calculating the short-circuit current of the power generation unit when the equivalent model of the power generation unit is the voltage source model of the reactive control priority mode;
the active priority voltage source subunit is used for iteratively calculating the short-circuit current of the power generation unit when the equivalent model of the power generation unit is the voltage source model of the active control priority mode;
and the current source subunit is used for iteratively calculating the short-circuit current of the power generation unit when the equivalent model of the power generation unit is a current source model.
The calculation sequence module comprises a current and voltage change unit, a ratio calculation unit and a sequence unit;
the current and voltage change unit is used for acquiring a value of voltage amplitude change of a new energy power station grid-connected point bus caused by the fact that a reactive current value is injected into the power generation unit and a reactive current is injected into the power generation unit under the condition of a fault point for each power generation unit in the new energy power station;
the ratio calculation unit is used for calculating the absolute value of the ratio of the voltage amplitude value change value of the grid-connected point bus caused by each power generation unit to the injected reactive current value;
and the sequence unit is used for sequencing according to the absolute value of the ratio from large to small and formulating the short circuit calculation sequence of each power generation unit.
As will be appreciated by one skilled in the art, embodiments of the present application may be provided as a method, system, or computer program product. Accordingly, the present application may take the form of an entirely hardware embodiment, an entirely software embodiment or an embodiment combining software and hardware aspects. Furthermore, the present application may take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, and the like) having computer-usable program code embodied therein.
The present application is described with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the application. It will be understood that each flow and/or block of the flow diagrams and/or block diagrams, and combinations of flows and/or blocks in the flow diagrams and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer, special purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be stored in a computer-readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer-readable memory produce an article of manufacture including instruction means which implement the function specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
It should be noted that the above-mentioned embodiments are only for illustrating the technical solutions of the present application and not for limiting the scope of protection thereof, and although the present application is described in detail with reference to the above-mentioned embodiments, those skilled in the art should understand that after reading the present application, they can make various changes, modifications or equivalents to the specific embodiments of the application, but these changes, modifications or equivalents are all within the scope of protection of the claims to be filed.
Claims (13)
1. A short-circuit current calculation method of a new energy power station is characterized by comprising the following steps:
according to a preset short-circuit current fault point, acquiring a short-circuit calculation sequence of each power generation unit in the new energy power station based on the sensitivity under the fault point condition;
sequentially carrying out iterative calculation on the short-circuit current of each power generation unit according to the short-circuit calculation sequence;
calculating the short-circuit current of the new energy power station according to the short-circuit current of each power generation unit;
and when the short-circuit current of each power generation unit is subjected to iterative calculation, selecting an equivalent model according to the effective value of the voltage of the grid-connected point bus of the new energy power station.
2. The method of claim 1, wherein selecting the equivalent model according to the effective value of the new energy power station grid-connected point bus voltage comprises:
if the effective value of the grid-connected point bus voltage is in a preset current calculation interval, adopting a current source model as an equivalent model of each power generation unit in the new energy power station;
otherwise, the voltage source model is used as an equivalent model of each power generation unit in the new energy power station, and the control mode of the voltage source model is selected to be an active control priority mode or a failure-free control priority mode according to preset parameters of the power generation units in the new energy power station.
3. The method of claim 1, wherein the iterative calculation of the short circuit current of each power generation unit in sequence according to the short circuit calculation sequence comprises:
step L1: according to the short circuit calculation sequence, calculating the short circuit current of each power generation unit in sequence;
step L2: judging whether the short-circuit currents of all the power generation units are totally converged or not, or whether the iteration number exceeds a preset upper limit of the outer-layer cycle iteration number:
when the two judgment results are negative, the step L1 is carried out;
and when at least one judgment result is yes, ending the iterative computation.
4. A method according to claim 2 or 3, wherein the calculation of the short-circuit current of the power generating unit comprises:
when the equivalent model of the power generation unit is a voltage source model of a reactive control priority mode:
step L11: determining target values of a reactive component and an active component of a short-circuit current of the power generation unit;
step L12: judging whether the difference value between the current short-circuit current reactive component calculation value and the target value is smaller than a preset reactive threshold value:
if yes, go to step L13; otherwise, correcting the value of the series reactance in the voltage source model, updating the calculated value of the reactive component of the short-circuit current and the target value of the active component of the short-circuit current, and turning to the step L13;
step L13: judging whether the current calculation value of the active component of the short-circuit current and the target value are smaller than a preset active threshold value: if yes, go to step L14; otherwise, correcting the value of the series resistor in the voltage source model, updating the calculated value of the active component of the short-circuit current and the target values of the active component and the reactive component of the short-circuit current, and turning to the step L14;
step L14: judging whether the difference value between the calculated value of the active component of the short-circuit current and the target value is smaller than a preset active threshold value and the difference value between the calculated value of the reactive component of the short-circuit current and the target value is smaller than a preset reactive threshold value or not, or whether the cycle number exceeds a preset upper limit of the cycle iteration number of the inner layer or not:
if at least one item is yes, the loop iteration is ended, otherwise, the step L12 is carried out.
5. The method of claim 4, wherein the short circuit current reactive component target value is calculated as follows:
wherein the subscript q represents reactive, Iq,refIndicating target value of reactive component of short-circuit current, I1Indicating reactive current, I, injected into the grid by the generating unit before the faultNIndicating rated current, U, of the generating unitTRepresenting a per unit value of the bus voltage of the power generation unit; k is a radical ofqRepresents the proportionality coefficient of reactive component of short-circuit current, and kqSatisfy kq,min≤kq≤kq,max，kq,minRepresenting the lower limit of the proportional coefficient, k, of the reactive component of the preset short-circuit currentq,maxRepresenting the upper limit of the proportion coefficient of the reactive component of the short-circuit current;
the upper limit k of the short-circuit current reactive component proportionality coefficientq,maxThe calculation formula is as follows:
wherein k ismaxRepresenting an inverter power electronics current limit;
the calculation formula of the short-circuit current active component target value is as follows:
wherein the subscript p represents active, Ip,refIndicating the target value, k, of the active component of the short-circuit currentpAnd the scale factor of the active component of the preset short-circuit current is represented.
6. A method according to claim 2 or 3, wherein the calculation of the short-circuit current of the power generating unit comprises:
when the equivalent model of the power generation unit is a voltage source model of an active control priority mode:
step L21: determining target values of a reactive component and an active component of a short-circuit current of the power generation unit;
step L22: judging whether the difference value between the current short-circuit current active component calculation value and the target value is smaller than a preset active threshold value:
if yes, go to step L23; otherwise, correcting the value of the series resistor in the voltage source model, updating the calculated value of the active component of the short-circuit current and the target value of the reactive component of the short-circuit current, and turning to the step L23;
step L23: judging whether the difference value between the current short-circuit current reactive component calculation value and the target value is smaller than a preset reactive threshold value:
if yes, go to step L24; otherwise, correcting the value of the series reactance in the voltage source model, updating the calculated value of the reactive component of the short-circuit current and the target values of the active component and the reactive component of the short-circuit current, and turning to the step L24;
step L24: judging whether the difference value between the calculated value of the active component of the short-circuit current and the target value is smaller than a preset active threshold value and the difference value between the calculated value of the reactive component of the short-circuit current and the target value is smaller than a preset reactive threshold value or not, or whether the cycle number exceeds a preset upper limit of the cycle iteration number of the inner layer or not:
if at least one item is yes, the loop iteration is ended, otherwise, the step L22 is carried out.
7. The method according to claim 6, characterized in that the target value of the active component of the short-circuit current is set according to actual needs;
the calculation formula of the short-circuit current reactive component target value is as follows:
wherein the subscript q represents reactive, Iq,refIndicating target value of reactive component of short-circuit current, I1Indicating reactive current, I, injected into the grid by the generating unit before the faultNIndicating rated current, U, of the generating unitTRepresenting a per unit value of the bus voltage of the power generation unit; k is a radical ofqRepresents the proportionality coefficient of reactive component of short-circuit current, and kqSatisfy kq,min≤kq≤kq,max，kq,minRepresenting the lower limit of the proportional coefficient, k, of the reactive component of the preset short-circuit currentq,maxRepresenting the upper limit of the proportion coefficient of the reactive component of the short-circuit current;
the upper limit k of the short-circuit current reactive component proportionality coefficientq,maxThe calculation formula is as follows:
wherein k ismaxRepresenting an inverter power electronics current limit;
Iq,refmaximum value of
The constraint is shown as follows:
wherein, Ip,refIndicating the target value of the active component of the short-circuit current and the subscript p indicating the active.
8. A method according to claim 2 or 3, wherein the calculation of the short-circuit current of the power generating unit comprises:
when the equivalent model of the power generation unit is a current source model:
step L31: calculating a target value of a short-circuit current phase angle;
step L32: judging whether the difference value between the calculated value of the current short-circuit current phase angle and the target value is smaller than a preset phase angle threshold value or whether the cycle number exceeds a preset inner-layer cycle iteration number upper limit:
if at least one item is yes, ending the loop iteration; otherwise, the calculated value of the phase angle is corrected by changing the ratio of the active component to the reactive component of the current injected by the power generation unit, and the target values of the active component, the reactive component and the phase angle of the short-circuit current are updated, and the step L32 is carried out.
9. The method of claim 8, wherein the target value of the short circuit current phase angle is calculated as follows:
wherein, thetarefTarget value, I, representing the phase angle of the short-circuit currentp,refIndicating the target value of the active component of the short-circuit current, Iq,refThe target value of the reactive component of the short-circuit current is shown, subscript p shows active power, and subscript q shows reactive power; i isq,refThe calculation formula is as follows:
wherein, I1Indicating reactive current, I, injected into the grid by the generating unit before the faultNIndicating rated current, U, of the generating unitTRepresenting a per unit value of the bus voltage of the power generation unit; k is a radical ofqRepresents the proportionality coefficient of reactive component of short-circuit current, and kqSatisfy kq,min≤kq≤kq,max，kq,minRepresenting the lower limit of the proportional coefficient, k, of the reactive component of the preset short-circuit currentq,maxIndicating short-circuit current idleComponent scaling factor upper limit;
the upper limit k of the short-circuit current reactive component proportionality coefficientq,maxThe calculation formula is as follows:
wherein k ismaxRepresenting an inverter power electronics current limit;
Ip,refis calculated as follows:
wherein k ispAnd the scale factor of the active component of the preset short-circuit current is represented.
10. The method of claim 1, wherein the obtaining a short circuit calculation order for each power generation unit in the new energy power station based on the sensitivity under the fault point condition comprises:
aiming at each power generation unit in the new energy power station, acquiring a value of voltage amplitude change of a new energy power station grid-connected point bus caused by the injection of a reactive current value and the injection of a reactive current of the power generation unit under the fault point condition;
respectively calculating absolute values of the ratio of the amplitude value of the voltage of the bus of the grid-connected point caused by each power generation unit to the value of the injected reactive current;
and sequencing according to the absolute value of the ratio from large to small, and formulating the short circuit calculation sequence of each power generation unit.
11. The method according to claim 1, wherein the calculating of the short-circuit current of the new energy power station from the short-circuit current of each power generation unit is as follows:
Ishc＝Ires+Igrid
wherein, IshcRepresents short-circuit current of new energy power station, IgridIndicating short-circuit current, I, supplied from the external grid sideresTo representShort-circuit current sum I provided by internal power generation unit of new energy power stationresThe calculation formula is as follows:
wherein n represents the number of power generation units in the new energy power station, Ires,iIndicating the short circuit current of the ith power generation cell.
12. A short-circuit current calculation system of a new energy power station is characterized by comprising: the system comprises a calculation sequence module, a unit current module and a power station current module;
the calculation sequence module is used for calculating the short circuit calculation sequence of the electrical unit;
the unit current module is used for sequentially carrying out iterative calculation on the short-circuit current of each power generation unit according to the short-circuit calculation sequence;
the power station current module is used for calculating the short-circuit current of the new energy power station according to the short-circuit current of each power generation unit;
and when the short-circuit current of each power generation unit is subjected to iterative calculation, selecting an equivalent model according to the effective value of the voltage of the grid-connected point bus of the new energy power station.
13. The system of claim 12, further comprising a model selection module;
the model selection module is used for adopting a current source model as an equivalent model of each power generation unit in the new energy power station if the effective value of the grid-connected point bus voltage is in a preset current calculation interval; otherwise, the voltage source model is used as an equivalent model of each power generation unit in the new energy power station, and the control mode of the voltage source model is selected to be an active control priority mode or a failure-free control priority mode according to preset parameters of the power generation units in the new energy power station.
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