Method and device for solving mapping curve of power generation system based on terminal voltage forward

Abstract

The invention relates to a method and a device for solving a mapping curve of a power generation system based on terminal voltage forward. The method comprises the following steps: establishing a generator set model according to a topological structure of the power generation system and a low-voltage penetration control strategy; performing phase reduction on the plurality of power stations to obtain reduced fault current; establishing a mapping curve of the fault current and the line voltage based on the recording data and the generator set model; acquiring a voltage and current phasor relationship of a grid-connected point of the power generation system by adopting a voltage forward calculation mode of a tail-end power generation unit; and obtaining a station equivalence calculation curve according to the voltage and current phasor relationship and the topological structure of the electric power station. According to the method, the mapping relation between a single power generation unit and line voltage is solved, the current and voltage phasors of a grid-connected point are obtained through forward calculation of the voltage of a tail end power generation unit towards the grid-connected point, a fault equivalence curve of a station is obtained, the fault characteristics of a power generation system are correctly described, and multi-machine equivalence parameters are accurately determined.

Description

Technical Field

[0001] The present invention relates to the technical field of short-circuit current equivalent calculation of new energy sources, and in particular to a method and device for obtaining a mapping curve of a power generation system based on terminal voltage forward push. Background Art

[0002] Power system fault analysis is a necessary prerequisite for the design of protection principles and setting configuration of power systems. For areas where large-scale new energy is concentrated and connected to the grid, the fault characteristics of inverter-type new energy power conversion equipment are gradually different from those of traditional power sources, which has a direct impact on the performance of power system protection. However, traditional station equivalent modeling mostly uses single-machine multiplication and clustering algorithms to simplify the station model by selecting characteristic parameter equivalents, or uses iterative algorithms based on unit control strategies to solve them. There are problems such as large errors in equivalent parameters and non-convergence of calculations. At present, there is a lack of effective equivalent analysis and calculation models for power generation system faults, making it difficult to quantitatively analyze the correct action boundaries of protection, and it is impossible to propose targeted improvement methods. Therefore, it is urgent to propose a new equivalent analysis method for power generation system faults to correctly describe the fault characteristics of the power generation system and accurately determine the equivalent parameters of multiple machines. Summary of the invention

[0003] In order to overcome the above-mentioned deficiencies of the prior art, the present invention provides a method and device for obtaining a mapping curve of a power generation system based on terminal voltage forward push, which specifically adopts the following technical solutions:

[0004] A method for obtaining a mapping curve of a power generation system based on terminal voltage forwarding comprises the following steps:

[0005] A generator set model is established according to the topological structure of the power generation system and the low-throughput control strategy; the power generation system includes a plurality of power generation units;

[0006] According to the low-breakdown control strategy of different power generation units in the power generation system, phase reduction is performed on multiple power stations to obtain the calculated fault current;

[0007] Obtain the recorded wave data of the power generation system, and establish a mapping curve between the fault current and line voltage of the corresponding power generation system in combination with the generator set model;

[0008] According to the topological structure and mapping curve of the power generation system, the voltage and current phasor relationship of the power generation system grid connection point is obtained by using the voltage forward calculation method of the terminal power generation unit;

[0009] According to the voltage and current phasor relationship of the power generation system grid connection point and the topological structure of the power station, the station equivalent calculation curve is obtained;

[0010] Based on the generator set model, the single-machine equivalent model of different power generation units in the power generation system is obtained, and the influence of the single-machine equivalent model error on the station equivalent calculation curve is analyzed to evaluate the feasibility and accuracy of the station equivalent calculation curve.

[0011] Optional: The low penetration control strategy includes:

[0012] When a fault occurs, the terminal voltage of the power generation unit drops below 0.9pu, and the control link of the converter will switch from the power outer loop control to the low-through control. By controlling the q-axis current output by the unit, reactive power is firstly increased to support the grid voltage. When the unit output current meets the converter limit, the q-axis current output by the unit is controlled to output active power.

[0013] The current output by the power generation system under different control strategies before and after the fault occurs is:

[0014]

[0015] where i d is the d-axis current output by the unit; i q is the q-axis current output by the unit; α is the unit output coefficient; I N is the rated current of the unit; I m is the converter output current limit value, u d is the d-axis voltage output by the unit; K is the reactive power compensation coefficient; U is the terminal voltage of the generating unit;

[0016] The reactive power and active power output by the power generation system are:

[0017]

[0018] Where P is the active power output by the unit in the power generation system; Q is the reactive power output by the unit in the power generation system.

[0019] Optionally, the step of performing phase reduction calculation on multiple power stations respectively according to the low-through control strategies of different power generation units in the power generation system includes:

[0020] When a fault occurs, the converter in the station uses the phase-locked loop output phase angle as the reference direction to establish a reference coordinate system;

[0021] When calculating the fault current of the station, first convert the fault current of each unit into the same reference coordinate system:

[0022]

[0023] where i di,ref is the d-axis component of the fault current of the i-th unit converted to the reference voltage phase; iqi,ref is the current q-axis component of the fault current of the i-th unit converted to the reference voltage phase; i di are the d-axis components of the current output by the i-th unit according to its own terminal voltage phase; i qi are the q-axis components of the current output by the i-th unit according to its own terminal voltage phase; θ i is the difference between the terminal voltage phase of the ith unit and the reference voltage phase.

[0024] Optionally, the step of establishing a mapping curve of fault current and line voltage of a corresponding power generation system in combination with the generator set model includes:

[0025] A single power generation unit is equivalent to a voltage-controlled voltage source, and the machine-end connection point and the line connection point are respectively regarded as a single node;

[0026] According to the control strategy of a single generating unit after a fault and the transformer parameters, the machine terminal connection point and the line connection point are iteratively calculated respectively:

[0027]

[0028] Among them U w,0 is the voltage phasor at the line connection point; U line is the collector line voltage; U w,k is the voltage phase of the kth unit terminal; I w,k is the output current phasor of the kth unit; Z t is the impedance of the wind and solar power generation unit box transformer; f w () is the current phasor function outputted by the corresponding terminal voltage phasor;

[0029] After each set of voltage and current phasors is obtained, U line The amplitude of the voltage is increased by one step, and the new voltage and current phasors are calculated until U line The amplitude reaches the preset upper limit;

[0030] Based on U line The amplitude change of is obtained to obtain the current phasor of the output current of a single generating unit corresponding to the collector line voltage, and then the single-machine mapping curve of the fault current of a single generating unit and the collector line voltage is obtained.

[0031] Optionally, the step of obtaining the voltage and current phasor relationship of the power generation system grid connection point by using the terminal power generation unit voltage forward calculation method includes:

[0032] Setting the initial voltage and voltage range of the terminal power generation unit in the collector circuit, and obtaining the d-axis current and q-axis current output by the terminal power generation unit based on the voltage of the terminal power generation unit;

[0033] According to the connection topology of the generating units on the collector line, forward calculation is performed from the terminal generating unit to the grid connection point until the voltage phasor and the corresponding current phasor of the grid connection point are obtained:

[0034]

[0035] Among them U line,n is the line voltage of the nth unit; U line,n-1 is the line voltage of the n-1th unit; I line,n-1 is the line output current phasor of the n-1th unit; Z n I is the line impedance between the nth unit and the grid connection point; line,k is the line output current phasor of the kth unit;

[0036] The voltage of the terminal power generation unit is increased by one step, and the d-axis current and q-axis current output by the terminal power generation unit at the corresponding voltage are calculated again, and forward calculation is performed from the terminal power generation unit to the grid connection point until the grid connection point voltage phasor and the corresponding current phasor corresponding to the current voltage of the terminal power generation unit are obtained.

[0037] Optionally, the step of obtaining the station equivalent calculation curve according to the voltage and current phasor relationship of the power generation system grid connection point includes:

[0038] Respectively obtain the corresponding grid connection point voltage phasor and the corresponding current phasor under different voltage conditions of the terminal power generation unit;

[0039] According to the topological structure of the power station, the voltage phasors of the grid connection points corresponding to the units in the station and the corresponding current phasor string numbers are superimposed to obtain the station equivalent calculation curve.

[0040] Optional: When analyzing the influence of the single-machine equivalent model error on the station equivalent calculation curve, when the maximum value of the single-machine equivalent model error of a single unit in the terminal power generation unit is set to δ, the error of the station equivalent calculation curve is less than or equal to δ.

[0041] Optional: The step of evaluating the feasibility and accuracy of the station equivalent calculation curve includes:

[0042] Obtain the single-machine equivalent model error of each unit in the terminal power generation unit and the error of the equivalent calculation curve of the station;

[0043] Determine the maximum value of the station equivalent calculation curve error and the single-machine equivalent model error. If the station equivalent calculation curve error is less than or equal to the maximum value of the single-machine equivalent model error, retain the current station equivalent calculation curve; if the station equivalent calculation curve error is greater than the maximum value of the single-machine equivalent model error, discard the current station equivalent calculation curve and recalculate.

[0044] Furthermore, the present invention also discloses a device for obtaining a mapping curve of a power generation system based on terminal voltage push-forward, the device runs the above-mentioned method for obtaining a mapping curve of a power generation system, and the device comprises:

[0045] A generator set model building module is used to build a generator set model according to the topological structure of the power generation system and the low-throughput control strategy; the power generation system includes a plurality of power generation units;

[0046] The phase reduction module is used to perform phase reduction on multiple power stations according to the low-breakdown control strategies of different power generation units in the power generation system to obtain the calculated fault current;

[0047] A mapping curve establishment module is used to obtain the recorded wave data of the power generation system and establish a mapping curve of the fault current and line voltage of the corresponding power generation system in combination with the generator set model;

[0048] The voltage forward calculation module is used to obtain the voltage and current phasor relationship of the power generation system grid connection point by using the terminal power generation unit voltage forward calculation method according to the topological structure and mapping curve of the power generation system;

[0049] The isovalue curve establishment module obtains the station isovalue calculation curve according to the voltage and current phasor relationship of the power generation system grid connection point and the topological structure of the power station;

[0050] The equivalent curve evaluation module obtains the single-machine equivalent model of different power generation units in the power generation system based on the generator set model, analyzes the impact of the single-machine equivalent model error on the station equivalent calculation curve, and evaluates the feasibility and accuracy of the station equivalent calculation curve.

[0051] Beneficial Effects

[0052] The technical solution of the present invention achieves the following beneficial effects:

[0053] The method of the present invention obtains the mapping relationship between a single power generation unit and the line voltage through two-point iteration, and then calculates the current and voltage phasors of the grid connection point by pushing the voltage of the terminal power generation unit forward to the grid connection point, and then obtains the fault equivalent curve of the station to correctly describe the fault characteristics of the power generation system and accurately determine the equivalent parameters of multiple machines. The feasibility and accuracy of the proposed method are further proved by analyzing the impact of the inherent error of the model. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] Figure 1 The figure is a flow chart of a method for obtaining a mapping curve of a power generation system according to an embodiment of the present invention.

[0055] Figure 2 It is the phasor diagram of the equivalent model of a single machine in an embodiment of the present invention.

[0056] Figure 3Schematic diagram of the structure of the power generation system in an embodiment of the present invention.

[0057] Figure 4 Schematic diagram of a mapping curve between fault current and line voltage of a power generation system in an embodiment of the present invention.

[0058] Figure 5 Schematic diagram of the comparison of the actual recorded data verification stage in the embodiment of the present invention. DETAILED DESCRIPTION

[0059] The present invention will be further described below in conjunction with the accompanying drawings. The following examples are only used to more clearly illustrate the technical solution of the present invention, and cannot be used to limit the scope of protection of the present invention. It should be pointed out that the following detailed descriptions are all exemplary and are intended to provide further explanation of the present application.

[0060] Combination Figure 1 As shown, the present invention specifically discloses a method for obtaining a mapping curve of a power generation system based on terminal voltage forward push, which comprises the following steps:

[0061] Step 1: Establish a generator set model according to the topological structure of the power generation system and the low-throughput control strategy; the power generation system includes multiple power generation units;

[0062] The low penetration control strategy in step 1 includes:

[0063] When a fault occurs, according to the national standard of the inverter power supply low-throughput control strategy, the generator terminal voltage of the power generation unit drops below 0.9pu, and the control link of the converter will switch from the power outer loop control to the low-throughput control. By controlling the q-axis current output by the unit, reactive power is firstly increased to support the grid voltage. When the unit output current meets the converter limit, the q-axis current output by the unit is controlled to output active power.

[0064] The steady-state current calculation for the power generation system can be considered to be the same as the current reference value output by the control link. Therefore, the current output by the power generation system under different control strategies before and after the fault occurs can be obtained as follows:

[0065]

[0066] where i d is the d-axis current output by the unit; i q is the q-axis current output by the unit; α is the unit output coefficient, for example, a wind power generation system is generally the ratio of the actual wind speed to the rated wind speed; I N is the rated current of the unit; I m is the converter output current limit value; u dis the d-axis voltage output by the unit. For example, for a power generation system using fixed d-axis voltage control, the d-axis voltage can be regarded as the terminal voltage. K is the reactive power compensation coefficient, which generally ranges from 1.5 to 3. U is the terminal voltage of the power generation unit.

[0067] The reactive power and active power output by the power generation system are:

[0068]

[0069] Where P is the active power output by the unit in the power generation system; Q is the reactive power output by the unit in the power generation system.

[0070] According to the above, when the units in the power generation system generate reactive power in accordance with the national standard, the actual q-axis current should be a negative number, which is reflected in the dq coordinate system as the q-axis current lagging the d-axis voltage by 90°. Therefore, after the units in the power generation system enter the low-through control, the voltage-current phasor angle shows that the current lags behind the voltage.

[0071] Step 2: According to the low-breakdown control strategies of different power generation units in the power generation system, phase reduction is performed on multiple power stations respectively to obtain the calculated fault current.

[0072] Specifically, in the step 2, after a fault occurs in the power generation system, the converter in the power station uses the phase-locked loop output phase angle, i.e., the machine-end voltage phase, as a reference, and outputs the corresponding dq-axis current according to the established control strategy. However, due to the different geographical locations of the units in the power station, the machine-end voltage phase of each unit is different, which results in a different reference system for each unit. If the reference system 1 is not used, there will be a large error in the calculation result. Therefore, when calculating the fault current of the power station, it is necessary to first calculate the current of each unit to the same coordinate system, and then calculate the fault current of the power station. Specifically, the steps of performing phase calculations on multiple power stations according to the low-through control strategies of different power generation units in the power generation system in the step 2 include:

[0073] When a fault occurs, the converter in the station uses the phase-locked loop output phase angle as the reference direction to establish a reference coordinate system;

[0074] When calculating the fault current of the station, first convert the fault current of each unit into the same reference coordinate system:

[0075]

[0076] where i di,ref is the d-axis component of the fault current of the i-th unit converted to the reference voltage phase; i qi,ref is the current q-axis component of the fault current of the i-th unit converted to the reference voltage phase; i diare the d-axis components of the current output by the i-th unit according to its own terminal voltage phase; i qi are the q-axis components of the current output by the i-th unit according to its own terminal voltage phase; θ i is the difference between the terminal voltage phase of the ith unit and the reference voltage phase.

[0077] From the above analysis, it can be seen that the inverter-type new energy unit exhibits the characteristics of a voltage-controlled current source after a fault, and the main factors affecting the fault steady-state current are the converter control method, the voltage drop degree at the machine end, the voltage phase, and the unit output coefficient. Considering that the parameters of the new energy units and box transformers in the same power station are roughly the same, the main reason for the difference in fault current between the units is the different geographical locations of the units, which in turn makes the output coefficients of each unit and the electrical distance relative to the grid connection point different, resulting in unavoidable errors in the traditional equivalent process. Therefore, the equivalent error caused by the above factors can be avoided by superimposing the calculated fault current to obtain the station-level equivalent curve.

[0078] Step 3: Obtain the recorded wave data of the power generation system, and establish a mapping curve of the fault current and line voltage of the corresponding power generation system in combination with the generator set model.

[0079] Specifically, the step of establishing a mapping curve of fault current and line voltage of the corresponding power generation system in combination with the generator set model in step 3 includes:

[0080] A single power generation unit is equivalent to a voltage-controlled voltage source, and the machine-end connection point and the line connection point are respectively regarded as a single node;

[0081] According to the control strategy of a single generating unit after a fault and the transformer parameters, the machine terminal connection point and the line connection point are iteratively calculated respectively:

[0082]

[0083] Among them U w,0 is the voltage phasor at the line connection point; U line is the collector line voltage; U w,k is the voltage phase of the kth unit terminal; I w,k is the output current phasor of the kth unit; Z t is the impedance of the wind and solar power generation unit box transformer; f w () is the current phasor function outputted by the corresponding terminal voltage phasor;

[0084] After each set of voltage and current phasors is obtained, U line The amplitude of the voltage is increased by one step, and the new voltage and current phasors are calculated until U lineThe amplitude reaches the preset upper limit; the value range of general permanent magnetic field stations is 0.1~1.1pu, and the value range of photovoltaic field stations is 0~1.1pu.

[0085] Based on U line The amplitude change of is obtained to obtain the current phasor of the output current of a single generating unit corresponding to the collector line voltage, and then the single-machine mapping curve of the fault current of a single generating unit and the collector line voltage is obtained.

[0086] Step 4: According to the topological structure and mapping curve of the power generation system, the voltage and current phasor relationship of the power generation system grid connection point is obtained by using the voltage forward calculation method of the terminal power generation unit;

[0087] More specifically, the specific steps of obtaining the voltage and current phasor relationship of the power generation system grid connection point by using the terminal power generation unit voltage forward calculation method in step 4 include:

[0088] First, the initial voltage and voltage range of the terminal power generation unit in the collector circuit are set, and the d-axis current and q-axis current output by the terminal power generation unit are obtained based on the terminal power generation unit voltage. Generally, the initial voltage of the terminal power generation unit in the collector circuit is set to U w,1 , usually set to 0, and set the voltage range of the terminal power generation unit in the collector line to 0~1.1pu. Substituting the voltage Uw,1 into the wind and solar power generation unit output reference value calculation formula can obtain the d-axis and q-axis currents output by the unit, and then substituting the dq-axis currents into the following formula:

[0089] U line,2 =U w,1 -Z 1 (i d,w1 -ji q,w1 );

[0090] Among them U line，2 is the line voltage to which the second unit is connected, I d,w1 ,I q,w1 are the d-axis and q-axis currents output by the terminal power generation unit; j is an imaginary unit; Z 1 is the line impedance between the first unit and the grid connection point.

[0091] Obtain the line voltage U of the second unit line，2 After that, the voltage is brought into the obtained single-machine mapping curve to obtain the corresponding single-machine output current, which is added to the current of the terminal power generation unit to obtain the output current of the two units. Similarly, according to the connection topology of the power generation unit on the collector line, forward calculation is performed from the terminal power generation unit to the grid connection point until the grid connection point voltage phasor and the corresponding current phasor are obtained:

[0092]

[0093] Among them U line,n is the line voltage of the nth unit; U line,n-1 is the line voltage of the n-1th unit; I line,n-1 is the line output current phasor of the n-1th unit; Z n I is the line impedance between the nth unit and the grid connection point; line,k is the line output current phasor of the kth unit;

[0094] Increase the voltage of the terminal power generation unit by one step, and follow the same steps to calculate the d-axis current and q-axis current output by the terminal power generation unit at the corresponding voltage again, and perform forward calculation from the terminal power generation unit to the grid connection point until the voltage range of the terminal power generation unit in the collector line is traversed, and the grid connection point voltage phasor and the corresponding current phasor corresponding to the current voltage of the terminal power generation unit are obtained, that is, the mapping curve of the grid connection point voltage and its corresponding current phasor.

[0095] Then, the station equivalent calculation curve is obtained according to the voltage and current phasor relationship of the power generation system grid connection point and the topological structure of the power station. Specifically, the step of obtaining the station equivalent calculation curve in step 5 includes:

[0096] Firstly, the voltage phasor and the current phasor of the grid connection point corresponding to the different voltage conditions of the terminal power generation unit are obtained respectively;

[0097] According to the topological structure of the power station, the voltage phasors of the grid connection points corresponding to the units in the station and the corresponding current phasor string numbers are superimposed to obtain the station equivalent calculation curve.

[0098] Step 5: Based on the generator set model, obtain the single-machine equivalent model of different power generation units in the power generation system, analyze the impact of the single-machine equivalent model error on the station equivalent calculation curve, and evaluate the feasibility and accuracy of the station equivalent calculation curve.

[0099] Furthermore, to analyze the final error caused by the same error of the whole string of units, we first need to analyze the impact of the fault current error of the terminal unit on the voltage-current relationship at the grid connection point. i The corresponding current error and collector line voltage U line The corresponding current error trends are the same, so the single-machine equivalent model errors analyzed below refer to the current errors before and after the voltage of the same collector line is equivalent. When analyzing the influence of the single-machine equivalent model error on the station equivalent calculation curve in step 6, when the maximum value of the single-machine equivalent model error of a single unit in the terminal power generation unit is set to δ, the error of the station equivalent calculation curve is less than or equal to δ.

[0100] Assuming that the first unit of the terminal power generation unit (referred to as unit 1#) has an error of +δ, the following relationship holds:

[0101] I w1,err =I w1 +ΔI w1,err ;

[0102] Among them I w1,err is the current taking into account the error, I w1 is the real current value, ΔI w1,err is the current error. Considering the extreme case where the current phasor error has the greatest impact on the line voltage drop, the current taking the error into account and the real current have the following relationship:

[0103] I w1,err =(1+δ)I w1 ;

[0104] When only one unit is considered, the voltage and current at the unit overhead line connection point and the grid connection point have the following relationship:

[0105] U pcc =U line +Z 1 I w (U line );

[0106] Then the unit current of the terminal power generation unit taking into account the error has the following relationship:

[0107] U pcc，err =U line +Z 1 I w,err (U line );

[0108] Among them U pcc is the grid connection point voltage without taking into account the error, U pcc,err is the grid connection point voltage taking into account the error, I w (U) and I w,err (U) are the output current of a single unit without and with errors under the corresponding overhead line voltage, Z 1 It is the line impedance between unit 1# and the grid connection point.

[0109] Considering that what needs to be finally determined is the relationship between the voltage and current at the grid connection point, for the convenience of the next step of analysis, it is assumed that the voltage at the grid connection point is U pcc,err Obviously, for the grid connection point voltage at this time, if the equivalent error of the single machine model is considered, the corresponding collector line voltage is U line , the phase relationship is as follows Figure 2 (a) shown.

[0110] Then, for the case where the model equivalent error is not considered, the system satisfies the following relationship:

[0111] U pcc，err =U line，inerr +Z 1 I w (U line,inerr );

[0112] According to the relationship between the current taking into account the error and the real current, we can get Figure 2 (b) shows the phasor diagram. From the above analysis, we can know that for any given grid connection point voltage, U pcc,err For example, the currents without and with errors are I w (U line,inerr ) and I w,err (U line ), where U line,inerr is the collected line voltage without taking into account the error and satisfies:

[0113] U line,inerr ≤U line ;

[0114] At the same time, according to the unit current relationship of the terminal power generation unit taking into account the error, it can be obtained:

[0115] I w,err (U line )=(1+δ)I w (U line,inerr );

[0116] Combined with the corresponding single-machine mapping curve of the unit, it can be seen that the inverter-type new energy unit has the following relationship:

[0117] I w (U line )≤I w (U line,inerr );

[0118] Among them I w (U line ) and I w (U line,inerr ) are all wind-solar power generation unit output current functions corresponding to the collection line voltage without taking into account the error.

[0119] According to the above two formulas, we can get:

[0120] I w,err (U line )≤(1+δ)I w (U line,inerr );

[0121] According to the above, when the equivalent error of a single unit is assumed to be +δ, the error brought to the voltage and current curve of the grid connection point is not greater than +δ. Then, using the above similar proof method, it can be obtained that when the equivalent error of a single unit is -δ, the error brought will not exceed -δ.

[0122] Further consider the case where there are two units in the terminal power generation unit. At this time, the current error caused by the terminal unit 1 does not exceed δ for the voltage of the unit 2 at the collector line access point. Assuming that the equivalent model current error of unit 2 is δ at this time, according to the basic theorem of phasor addition, the current error of the two units will not exceed 1±δ times the true value.

[0123] By referring to the derivation process of the single-machine error, we can also obtain that for the voltage and current curve of the grid connection point, the error caused by the equivalence of the two units will not exceed δ. By analogy, for the entire string of terminal power generation units, the final error of the curve caused by the single-machine equivalent model error will not exceed the maximum value of the single-machine equivalent model error, that is, the error will not be amplified due to the forward process.

[0124] Furthermore, the step of evaluating the feasibility and accuracy of the station equivalent calculation curve in step 5 includes:

[0125] Obtain the single-machine equivalent model error of each unit in the terminal power generation unit and the error of the equivalent calculation curve of the station;

[0126] Determine the maximum value of the station equivalent calculation curve error and the single-machine equivalent model error. If the station equivalent calculation curve error is less than or equal to the maximum value of the single-machine equivalent model error, retain the current station equivalent calculation curve; if the station equivalent calculation curve error is greater than the maximum value of the single-machine equivalent model error, discard the current station equivalent calculation curve and recalculate.

[0127] In order to verify the feasibility of the method proposed in this invention, a typical wind farm topology structure in Inner Mongolia was taken as an example and the following Figure 1 The detailed model of the permanent magnet wind farm shown in the figure includes 3 (number of collector lines) × 11 (number of wind turbines on a single collector line) 5MW permanent magnet wind turbines, with a unit spacing of 1km. Figure 3 This is a detailed model of an inverter-type wind-solar power generation system based on the actual wind farm station topology. The station is mainly composed of permanent magnet wind turbines, overhead collection lines, 35kV and 220kV busbars, box transformers (0.69 / 35kV) and main transformers (35 / 220kV). There are 33 permanent magnet wind turbines, which are distributed according to 11 units per overhead collection line. After being collected to the 35kV busbar, they are connected to the 220kV system outside the station through the main transformer. The main parameters of wind farm components and converters are shown in Table 1:

[0128] Table 1

[0129]

[0130] Figure 4 The wind and solar power generation unit mapping curve is shown in Figure 1. The feasibility and accuracy of the proposed method are verified by using the artificial short-circuit test recording data of Xinjiang Jiangneng Huizhuangzi Wind Farm. The rated power of the permanent magnet synchronous wind turbine in the farm is 1.5MW, and the topology of the wind farm is as follows: Figure 3 The fault points are the 110kV busbar and the 35kV of wind power line 7, and the measuring points are the connection between the collector line and the busbar and the wind turbine unit terminal outlet closest to the 35kV busbar.

[0131] According to the single-machine short-circuit test data and combined with the wind-solar power generation unit control strategy equation, the UI mapping curve of the wind turbine can be obtained through the proposed method, where the reactive compensation coefficient K is 3 and the unit output is 23%. The detailed current expression is as follows:

[0132] The q-axis current is:

[0133]

[0134] The d-axis current is:

[0135]

[0136] where i d is the d-axis current output by the unit; i q is the q-axis current output by the unit; α is the unit output coefficient; I N is the rated current of the unit; I m is the converter output current limit value; u d is the d-axis voltage output by the unit; K is the reactive power compensation coefficient; U is the terminal voltage of the generating unit.

[0137] The UI theoretical curve and measured value curve of a single permanent magnet wind turbine are as follows: Figure 4 As shown in the figure, it can be seen that the mapping curve fits the measured curve well and can be used for further station equivalent calculation.

[0138] Based on the analysis results of the above-mentioned method, the isovalue curves of the fault current and voltage of the collection line can be obtained; Figure 5 The UI curves of 23% and 38% of the unit output are obtained by comparing the short-circuit test data. In view of the method of the present invention, the fault characteristics of the wind and solar power generation system, the difficulty in determining the equivalent parameters of multiple machines, and the difficulty in convergence of iterative calculations can be accurately and concisely described.

[0139] Furthermore, the present invention also discloses a device for obtaining a mapping curve of a power generation system based on terminal voltage push-forward, the device runs the above-mentioned method for obtaining a mapping curve of a power generation system, and the device comprises:

[0140] A generator set model building module is used to build a generator set model according to the topological structure of the power generation system and the low-throughput control strategy; the power generation system includes a plurality of power generation units;

[0141] The phase reduction module is used to perform phase reduction on multiple power stations according to the low-breakdown control strategies of different power generation units in the power generation system to obtain the calculated fault current;

[0142] A mapping curve establishment module is used to obtain the recorded wave data of the power generation system and establish a mapping curve of the fault current and line voltage of the corresponding power generation system in combination with the generator set model;

[0143] The voltage forward calculation module is used to obtain the voltage and current phasor relationship of the power generation system grid connection point by using the terminal power generation unit voltage forward calculation method according to the topological structure and mapping curve of the power generation system;

[0144] The isovalue curve establishment module obtains the station isovalue calculation curve according to the voltage and current phasor relationship of the power generation system grid connection point and the topological structure of the power station;

[0145] The equivalent curve evaluation module obtains the single-machine equivalent model of different power generation units in the power generation system based on the generator set model, analyzes the impact of the single-machine equivalent model error on the station equivalent calculation curve, and evaluates the feasibility and accuracy of the station equivalent calculation curve.

[0146] Furthermore, the present invention also discloses a non-volatile storage medium, which includes a stored program, wherein when the program is run, the device where the non-volatile storage medium is located is controlled to execute the above-mentioned method for obtaining the mapping curve of the power generation system.

[0147] In addition, the present invention also discloses a device including a processor and a memory; the memory stores computer-readable instructions, and the processor is used to run the computer-readable instructions, wherein the computer-readable instructions execute the above-mentioned method for obtaining the mapping curve of the power generation system when running.

[0148] Those skilled in the art will appreciate that embodiments of the present invention may be provided as methods, systems, or computer program products. Therefore, the present invention may take the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware. Moreover, the present invention may take the form of a computer program product implemented on one or more computer-usable non-transient storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0149] The present invention is described with reference to flowcharts and / or block diagrams of methods, devices, and computer program products according to embodiments of the present invention. It should be understood that each process and / or block in the flowchart and / or block diagram, as well as a combination of processes and / or blocks in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowchart and / or block diagram. Figure 1 A process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0150] These computer program instructions may also be stored in a computer-readable memory capable of directing a computer or other programmable data processing device to operate in a specific manner, so that the instructions stored in the computer-readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 A process or multiple processes and / or boxes Figure 1 A function specified in one or more boxes.

[0151] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operating steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing instructions for implementing the process. Figure 1 A process or multiple processes and / or boxes Figure 1 The steps for the functions specified in one or more boxes.

[0152] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the technical principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for obtaining a mapping curve of a power generation system based on terminal voltage forwarding, characterized in that: The following steps are involved: A generator set model is established according to the topological structure of the power generation system and the low-throughput control strategy; the power generation system includes a plurality of power generation units; According to the low-breakdown control strategy of different power generation units in the power generation system, phase reduction is performed on multiple power stations to obtain the calculated fault current; Obtain the recorded wave data of the power generation system, and establish a mapping curve between the fault current and line voltage of the corresponding power generation system in combination with the generator set model; According to the topological structure and mapping curve of the power generation system, the voltage and current phasor relationship of the power generation system grid connection point is obtained by using the voltage forward calculation method of the terminal power generation unit; According to the voltage and current phasor relationship of the power generation system grid connection point and the topological structure of the power station, the station equivalent calculation curve is obtained; Based on the generator set model, the single-machine equivalent model of different power generation units in the power generation system is obtained, and the influence of the single-machine equivalent model error on the station equivalent calculation curve is analyzed to evaluate the feasibility and accuracy of the station equivalent calculation curve.

2. The method for obtaining a mapping curve of a power generation system according to claim 1, characterized in that: The low penetration control strategy includes: When a fault occurs, the terminal voltage of the power generation unit drops below 0.9pu, and the control link of the converter will switch from the power outer loop control to the low-through control. By controlling the q-axis current output by the unit, reactive power is firstly increased to support the grid voltage. When the unit output current meets the converter limit, the q-axis current output by the unit is controlled to output active power. The current output by the power generation system under different control strategies before and after the fault occurs is: where i d is the d-axis current output by the unit; i q is the q-axis current output by the unit; α is the unit output coefficient; I N is the rated current of the unit; I m is the converter output current limit value, u d is the d-axis voltage output by the unit; K is the reactive power compensation coefficient; U is the terminal voltage of the generating unit; The reactive power and active power output by the power generation system are: Where P is the active power output by the unit in the power generation system; Q is the reactive power output by the unit in the power generation system.

3. The method for obtaining a mapping curve of a power generation system according to claim 2, characterized in that: The step of respectively performing phase reduction calculation on multiple power stations according to the low-through control strategies of different power generation units in the power generation system comprises: When a fault occurs, the converter in the station uses the phase-locked loop output phase angle as the reference direction to establish a reference coordinate system; When calculating the fault current of the station, first convert the fault current of each unit into the same reference coordinate system: where i di,ref is the d-axis component of the fault current of the i-th unit converted to the reference voltage phase; i qi,ref is the current q-axis component of the fault current of the i-th unit converted to the reference voltage phase; i di are the d-axis components of the current output by the i-th unit according to its own terminal voltage phase; i qi are the q-axis components of the current output by the i-th unit according to its own terminal voltage phase; θ i is the difference between the terminal voltage phase of the ith unit and the reference voltage phase.

4. The method for obtaining a mapping curve of a power generation system according to claim 3, characterized in that: The step of establishing a mapping curve of fault current and line voltage of a corresponding power generation system in combination with the generator set model comprises: A single power generation unit is equivalent to a voltage-controlled voltage source, and the machine-end connection point and the line connection point are respectively regarded as a single node; According to the control strategy of a single generating unit after a fault and the transformer parameters, the machine terminal connection point and the line connection point are iteratively calculated respectively: Among them U w,0 is the voltage phasor at the line connection point; U line is the collector line voltage; U w,k is the voltage phase of the kth unit terminal; I w,k is the output current phase of the kth unit; Z t is the impedance of the wind and solar power generation unit box transformer; f w () is the current phasor function outputted by the corresponding terminal voltage phasor; After each set of voltage and current phasors is obtained, U line The amplitude of the voltage is increased by one step, and the new voltage and current phasors are calculated until U line The amplitude reaches the preset upper limit; Based on U line The amplitude change of is obtained to obtain the current phasor of the output current of a single generating unit corresponding to the collector line voltage, and then the single-machine mapping curve of the fault current of a single generating unit and the collector line voltage is obtained.

5. The method for obtaining a mapping curve of a power generation system according to claim 4, characterized in that: The step of obtaining the voltage and current phasor relationship of the power generation system grid connection point by using the terminal power generation unit voltage forward calculation method includes: Setting the initial voltage and voltage range of the terminal power generation unit in the collector circuit, and obtaining the d-axis current and q-axis current output by the terminal power generation unit based on the voltage of the terminal power generation unit; According to the connection topology of the generating units on the collector line, forward calculation is performed from the terminal generating unit to the grid connection point until the voltage phasor and the corresponding current phasor of the grid connection point are obtained: Among them U line,n is the line voltage of the nth unit; U line,n-1 is the line voltage of the n-1th unit; I line,n-1 is the line output current phasor of the n-1th unit; Z n I is the line impedance between the nth unit and the grid connection point; line,k is the line output current phasor of the kth unit; The voltage of the terminal power generation unit is increased by one step, and the d-axis current and q-axis current output by the terminal power generation unit at the corresponding voltage are calculated again, and forward calculation is performed from the terminal power generation unit to the grid connection point until the grid connection point voltage phasor and the corresponding current phasor corresponding to the current voltage of the terminal power generation unit are obtained.

6. The method for obtaining a mapping curve of a power generation system according to claim 5, characterized in that: The step of obtaining the station equivalent calculation curve according to the voltage and current phasor relationship of the power generation system grid connection point includes: Respectively obtain the corresponding grid connection point voltage phasor and the corresponding current phasor under different voltage conditions of the terminal power generation unit; According to the topological structure of the power station, the voltage phasors of the grid connection points corresponding to the units in the station and the corresponding current phasor string numbers are superimposed to obtain the station equivalent calculation curve.

7. The method for obtaining a mapping curve of a power generation system according to claim 6, characterized in that: When analyzing the influence of the single-machine equivalent model error on the station equivalent calculation curve, when the maximum value of the single-machine equivalent model error of a single unit in the terminal power generation unit is set to δ, the error of the station equivalent calculation curve is less than or equal to δ.

8. The method for obtaining a mapping curve of a power generation system according to claim 7, characterized in that: The steps of evaluating the feasibility and accuracy of the station equivalent calculation curve include: Obtain the single-machine equivalent model error of each unit in the terminal power generation unit and the error of the equivalent calculation curve of the station; Determine the maximum value of the station equivalent calculation curve error and the single-machine equivalent model error. If the station equivalent calculation curve error is less than or equal to the maximum value of the single-machine equivalent model error, retain the current station equivalent calculation curve; if the station equivalent calculation curve error is greater than the maximum value of the single-machine equivalent model error, discard the current station equivalent calculation curve and recalculate.

9. A device for obtaining a mapping curve of a power generation system based on terminal voltage forwarding, characterized in that: The device runs the method for obtaining a mapping curve of a power generation system according to any one of claims 1 to 8, and the device comprises: A generator set model building module is used to build a generator set model according to the topological structure of the power generation system and the low-throughput control strategy; the power generation system includes a plurality of power generation units; The phase reduction module is used to perform phase reduction on multiple power stations according to the low-breakdown control strategies of different power generation units in the power generation system to obtain the calculated fault current; A mapping curve establishment module is used to obtain the recorded wave data of the power generation system and establish a mapping curve of the fault current and line voltage of the corresponding power generation system in combination with the generator set model; The voltage forward calculation module is used to obtain the voltage and current phasor relationship of the power generation system grid connection point by using the terminal power generation unit voltage forward calculation method according to the topological structure and mapping curve of the power generation system; The isovalue curve establishment module obtains the station isovalue calculation curve according to the voltage and current phasor relationship of the power generation system grid connection point and the topological structure of the power station; The equivalent curve evaluation module obtains the single-machine equivalent model of different power generation units in the power generation system based on the generator set model, analyzes the impact of the single-machine equivalent model error on the station equivalent calculation curve, and evaluates the feasibility and accuracy of the station equivalent calculation curve.

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