New energy grid-connected system harmonic risk evaluation method and device

Abstract

The invention provides a harmonic risk evaluation method for a new energy grid-connected system. The harmonic risk evaluation method comprises the following steps: calculating a grid-connected point harmonic voltage and a key outgoing line harmonic current of the new energy grid-connected system after background harmonic is set through a harmonic node voltage equation; obtaining the harmonic voltage constraint of the grid-connected point and the harmonic current constraint of the key outgoing line; calculating a first deviation factor according to the harmonic voltage of the grid-connected point and the harmonic voltage constraint, calculating a second deviation factor according to the harmonic current of the key outgoing line and the harmonic current constraint, and comparing to obtain the maximum value of the deviation factor; and calculating a harmonic risk comprehensive evaluation index according to the deviation factor maximum value and the harmonic weight factor actual value, and judging the harmonic risk of the new energy grid-connected system under the current operation condition. According to the evaluation method provided by the invention, harmonic risk degrees under different operation conditions can be effectively measured, a safe operation region and a risk operation region are drawn, and safe and stable operation of the new energy grid-connected system is guaranteed.

Description

Technical Field

[0001] The present invention relates to the technical field of power systems, and in particular to a harmonic risk assessment method and device for a new energy grid-connected system. Background Art

[0002] With the rapid development of new power systems, the proportion of renewable energy generation continues to increase, and the extensive application of power electronic equipment has significantly changed the dynamic characteristics of power systems. Due to the widespread use of nonlinear loads and large-scale power electronic equipment, the types and number of harmonic sources continue to increase, resulting in increasingly serious harmonic problems in power systems. Harmonic problems not only cause the deterioration of power quality, but may also lead to equipment overload, accelerated aging, and malfunction of system protection devices, posing a threat to the stable operation of the power system and the safety of equipment.

[0003] In the scenario of renewable energy grid connection, since renewable energy power generation systems generally have the characteristics of low inertia and weak damping, the power system is more susceptible to harmonic interference, and the superposition effect of background harmonics further complicates the problem. Harmonic components of different frequencies in the power grid may couple with certain resonance points of the system, resulting in significant amplification of harmonic amplitudes. This harmonic amplification phenomenon will increase the risk of equipment damage and may cause large-scale renewable energy power generation devices to disconnect from the grid, ultimately threatening the safety and stability of the entire power system.

[0004] Existing harmonic suppression methods mainly target single-frequency harmonics, such as reducing the impact of specific frequency harmonics by installing filters or optimizing equipment control strategies. However, these methods are usually unable to cope with the interaction of multi-frequency harmonics in complex system environments, and cannot effectively solve the comprehensive problem of background harmonics and system resonance. Especially in new power systems, the diversity and complexity of harmonic sources make the comprehensive assessment of harmonic risks particularly important. Therefore, there is an urgent need for a system-level harmonic risk assessment method to provide a theoretical basis and technical support for the prevention and control of harmonic problems. Summary of the invention

[0005] In view of the problems existing in the prior art, the present invention provides a harmonic risk assessment method for a new energy grid-connected system, which can effectively measure the degree of harmonic risk under different operating conditions, accurately characterize the harmonic safety level of the grid-connected system, draw safe operating areas and risky operating areas, and ensure the safe and stable operation of the new energy grid-connected system.

[0006] To achieve the above object, the technical solution adopted by the present invention is as follows: A harmonic risk assessment method for a new energy grid-connected system comprises the following steps:

[0007] Constructing a harmonic frequency domain impedance model based on a new energy grid-connected system; the new energy grid-connected system includes an AC power grid and a new energy station;

[0008] Constructing a harmonic node voltage equation according to the harmonic frequency domain impedance model;

[0009] Based on the new energy grid-connected system, line parameters and measured harmonic data are respectively obtained;

[0010] Setting background harmonics on the new energy grid-connected system based on the measured harmonic data;

[0011] Acquiring current operating condition data based on the new energy grid-connected system that sets the background harmonics;

[0012] Based on the current operating condition data, the harmonic voltage of the grid connection point and the harmonic current of the key transmission line are calculated respectively according to the harmonic node voltage equation; the grid connection point is the common connection point between the AC power grid and the new energy station, and the key transmission line is the transmission line connected to the grid connection point;

[0013] According to the line parameters, respectively obtain the harmonic voltage constraints of the grid connection point and the harmonic current constraints of the key transmission line;

[0014] Calculating a first deviation factor according to a ratio of the grid connection point harmonic voltage to the harmonic voltage constraint, and calculating a second deviation factor according to a ratio of the key transmission line harmonic current to the harmonic current constraint;

[0015] Comparing the first deviation factor and the second deviation factor to obtain a maximum deviation factor;

[0016] Get the initial value of harmonic weight factor;

[0017] Constructing a weight factor calculation formula based on the initial value of the harmonic weight factor;

[0018] Based on the weight factor calculation formula, the actual value of the harmonic weight factor is calculated according to the maximum value of the deviation factor;

[0019] Calculate the comprehensive evaluation index of harmonic risk according to the maximum value of the deviation factor and the actual value of the harmonic weight factor;

[0020] The harmonic risk of the current operating condition of the new energy grid-connected system is judged according to the comprehensive harmonic risk evaluation index.

[0021] Furthermore, the background harmonics include background harmonics based on the AC power grid and background harmonics based on new energy equipment.

[0022] Furthermore, the background harmonics are obtained by using harmonic current source simulation.

[0023] Further, based on the background harmonics of the AC power grid, the background harmonics are set at the grid connection point.

[0024] Furthermore, based on the background harmonics of the new energy equipment, the background harmonics are set on the high-voltage side busbar of the new energy station step-up transformer with the same voltage level as the grid connection point.

[0025] Furthermore, the weight factor calculation formula is:

[0026]

[0027] In the formula, ω h is the actual value of the hth harmonic weight factor, is the initial value of the hth harmonic weight factor, is the maximum value of the deviation factor of the hth harmonic, and h is the frequency of the odd harmonic.

[0028] Furthermore, the comprehensive harmonic risk evaluation index is the difference between the sum of the products of the actual values ​​of the harmonic weight factors of the odd harmonics of each frequency and the maximum value of the deviation factor and 1.

[0029] Furthermore, the step of judging the real-time harmonic risk of the new energy grid-connected system according to the comprehensive harmonic risk evaluation index is as follows:

[0030] When the comprehensive evaluation index of harmonic risk is less than zero, the current operating condition of the new energy grid-connected system has harmonic risk;

[0031] When the comprehensive evaluation index of harmonic risk is greater than zero, there is no harmonic risk in the current operating condition of the new energy grid-connected system;

[0032] When the comprehensive evaluation index of harmonic risk is equal to zero, the current operating condition of the new energy grid-connected system is a critical safety state.

[0033] Further, the new energy grid-connected system is divided into a safe operation area and a risky operation area according to the comprehensive harmonic risk evaluation index;

[0034] The safe operation area is an operation set consisting of all operating conditions where the comprehensive harmonic risk evaluation index is greater than zero;

[0035] The risky operation area is an operation set consisting of all operating conditions where the comprehensive harmonic risk evaluation index is less than zero.

[0036] A device for implementing the harmonic risk assessment method for the renewable energy grid-connected system, comprising a modeling unit, a data acquisition unit, a controller, a harmonic source, a calculation unit and a risk assessment unit;

[0037] The modeling unit:

[0038] Used to construct harmonic frequency domain impedance model based on new energy grid-connected system;

[0039] Used to construct a harmonic node voltage equation according to the harmonic frequency domain impedance model and transmit it to the calculation unit;

[0040] Constructing a weight factor calculation formula based on the initial value of the harmonic weight factor and transmitting it to the calculation unit;

[0041] The data acquisition unit:

[0042] Used to obtain line parameters and measured harmonic data based on the new energy grid-connected system, and transmit the line parameters to the calculation unit and transmit the measured harmonic data to the controller;

[0043] Used to obtain the initial value of the harmonic weight factor and transmit it to the modeling unit;

[0044] Used to obtain current operating condition data of the new energy grid-connected system based on setting the background harmonics and transmit the data to the calculation unit;

[0045] The controller:

[0046] Used to control the harmonic source to set background harmonics on the new energy grid-connected system based on the measured harmonic data;

[0047] The harmonic sources are:

[0048] Used to provide background harmonics to the new energy grid-connected system under the control of the controller;

[0049] The computing unit:

[0050] Used to obtain the harmonic voltage constraints of the grid connection point and the harmonic current constraints of the key transmission line according to the line parameters;

[0051] Used to calculate the grid connection point harmonic voltage and key transmission line harmonic current respectively based on the current operating condition data and the harmonic node voltage equation;

[0052] Used to calculate a first deviation factor according to the ratio of the harmonic voltage at the grid connection point to the harmonic voltage constraint, and calculate a second deviation factor according to the ratio of the harmonic current of the key transmission line to the harmonic current constraint;

[0053] used to compare the first deviation factor and the second deviation factor to obtain a maximum deviation factor;

[0054] Used to calculate the actual value of the harmonic weight factor based on the weight factor calculation formula and according to the maximum value of the deviation factor;

[0055] Used to calculate a comprehensive harmonic risk evaluation index according to the maximum value of the deviation factor and the actual value of the harmonic weight factor, and transmit the comprehensive harmonic risk evaluation index to the risk evaluation unit;

[0056] The risk assessment unit:

[0057] Used to judge the real-time harmonic risk of the new energy grid-connected system according to the comprehensive harmonic risk evaluation index.

[0058] Compared with the prior art, the present invention has the following beneficial effects:

[0059] The present invention provides a harmonic risk assessment method for a new energy grid-connected system, which can effectively measure the degree of harmonic risk under different operating conditions, accurately characterize the harmonic safety level of the grid-connected system, draw safe operating areas and risky operating areas, and ensure the safe and stable operation of the new energy grid-connected system. BRIEF DESCRIPTION OF THE DRAWINGS

[0060] Figure 1 It is a flow chart of the harmonic risk assessment method of the new energy grid-connected system of the present invention;

[0061] Figure 2 A topological diagram of a new energy grid-connected system in an embodiment of the present invention;

[0062] Figure 3 is a frequency domain admittance model of a new energy grid-connected system in an embodiment of the present invention;

[0063] Figure 4 The three-dimensional harmonic safe operation domain and harmonic risk area of ​​the working condition 1 in the embodiment of the present invention;

[0064] Figure 5 The two-dimensional harmonic safe operation domain and harmonic risk area of ​​the working condition 1 in the embodiment of the present invention: (a) is the RES-A / RES-B plane, (b) is the RES-A / RES-C plane, and (c) is the RES-B / RES-C plane;

[0065] Figure 6 The time domain simulation waveform of the working condition 1 in the embodiment of the present invention is: (a) The time domain waveform of The frequency domain FFT analysis diagram of The time domain waveform of Frequency domain FFT analysis diagram;

[0066] Figure 7 The three-dimensional harmonic safe operation domain and harmonic risk area of ​​the working condition 2 in the embodiment of the present invention;

[0067] Figure 8The two-dimensional harmonic safe operation domain and harmonic risk area of ​​the working condition 2 in the embodiment of the present invention: (a) is the RES-A / RES-B plane, (b) is the RES-A / RES-C plane, and (c) is the RES-B / RES-C plane;

[0068] Fig. 9 The time domain simulation waveforms of the second working condition in the embodiment of the present invention are as follows: (a) is the time domain waveform of the harmonic voltage at the grid connection point, (b) is the frequency domain FFT analysis diagram of the harmonic voltage at the grid connection point, and (c) is The time domain waveform of Frequency domain FFT analysis diagram;

[0069] Fig.10 The figure is a schematic diagram of the connection relationship of the devices used to implement the harmonic risk assessment method of the new energy grid-connected system according to the present invention. DETAILED DESCRIPTION

[0070] In order to clearly illustrate the technical features of this solution, this solution is described below through a specific implementation method.

[0071] See also Figure 1 The embodiment of the present invention provides a harmonic risk assessment method for a new energy grid-connected system, comprising the following steps:

[0072] A harmonic frequency domain impedance model is constructed based on a new energy grid-connected system; the new energy grid-connected system includes an AC power grid and a new energy station; the harmonic frequency domain impedance model includes a transmission line harmonic frequency domain impedance model, an AC power grid harmonic frequency domain impedance model, and a harmonic frequency domain impedance model of new energy equipment; among them, the transmission line harmonic frequency domain impedance model adopts an accurate π model, the AC power grid harmonic frequency domain impedance model is obtained by a frequency sweeping method, and the harmonic frequency domain impedance model of new energy equipment ignores the dynamic process of the control outer loop and the phase-locked loop, and only considers the dynamic process of the current inner loop, the main circuit, and the measurement filter link;

[0073] for Figure 2 For the corresponding new energy grid-connected system, firstly, the equivalent frequency domain admittance circuit of the new energy grid-connected system is established, such as Figure 3 As shown; the harmonic node admittance matrix corresponding to the equivalent frequency domain admittance circuit is:

[0074]

[0075] Where Y h is the node admittance matrix of the hth harmonic, h is the harmonic frequency, s is the Laplace operator, when studying harmonics of different frequencies, Y h (s) To regenerate, Y 11 ~Y 66 is the self-admittance of nodes 1 to 6, Y s1 , Y s2, Y sA , Y sB , Y sC Respectively Figure 3 The admittance in corresponds to, where node 1 corresponds to Figure 2 , 3 N1 is the grid connection point, and nodes 2 to 6 correspond to Figure 2 , 3 In N2~N6, the order of node naming in the harmonic node admittance matrix is ​​as follows: grid connection point - connection node directly connected to the grid connection point - high voltage side node of the new energy station step-up transformer;

[0076] The harmonic node admittance matrix is ​​used to calculate the harmonic voltage level at the grid connection point and the harmonic current on the offshore wind power transmission line. Figure 3 , construct the harmonic node admittance matrix as follows:

[0077] The harmonic node voltage equation is constructed based on the harmonic frequency domain impedance model:

[0078] I h =Y h U h ;

[0079] In the formula, I h Inject the harmonic column vector into the node of the hth harmonic, U h is the node harmonic voltage column vector of the hth harmonic;

[0080] Expand the harmonic node voltage equation:

[0081]

[0082] In the formula, I grid is the equivalent background harmonic current of the AC power grid, I windA For new energy station A( Figure 1 The equivalent grid-connected harmonics of RES-A, I windB For new energy station B( Figure 1 Equivalent grid-connected harmonics of RES-B, I windC For new energy station C( Figure 1 Equivalent grid-connected harmonics of RES-C, U pcc is the grid-connected point harmonic voltage, U2~U6 are the harmonic voltages of nodes 2~6 respectively;

[0083] Based on the new energy grid-connected system, line parameters and measured harmonic data are obtained respectively; the measured harmonic data includes the measured harmonic data of the AC power grid and the measured harmonic data of the new energy equipment;

[0084] Setting background harmonics on the renewable energy grid-connected system based on measured harmonic data;

[0085] Background harmonics include background harmonics based on AC power grid and background harmonics based on new energy equipment;

[0086] Based on the background harmonics of the AC power grid, the harmonic current source is used to simulate the background harmonics according to the measured harmonic data of the AC power grid, and the background harmonics are set at the grid connection point, that is, the harmonic current source is placed at the grid connection point;

[0087] Based on the background harmonics of new energy equipment, according to the measured harmonic data of new energy equipment, the background harmonics are simulated by harmonic current source, and the background harmonics are set on the high-voltage side busbar of the new energy station step-up transformer with the same voltage level as the grid connection point, that is, the harmonic current source is placed on the high-voltage side busbar of the new energy station step-up transformer with the same voltage level as the grid connection point;

[0088] Acquire current operating condition data based on the new energy grid-connected system with background harmonics set;

[0089] Based on the current operating condition data, the harmonic voltage at the grid connection point and the harmonic current of the key transmission line are calculated according to the harmonic node voltage equation; the grid connection point is the public connection point between the AC power grid and the new energy station, and the key transmission line is the transmission line connected to the grid connection point; Figure 2 In the corresponding new energy grid-connected system, the grid-connected point is N1, there are two key transmission lines, which are connected to points a and b on N1 respectively. The key transmission line connected to point a is recorded as the first key transmission line, and the key transmission line connected to point b is recorded as the second key transmission line. The harmonic currents of the key transmission lines are recorded as the harmonic currents of the first key transmission line. and the second key transmission line harmonic current Figure 2 , 3 middle, Equivalent to I1, =I2; therefore, according to the number of key transmission lines, the harmonic current of the i-th key transmission line at the hth harmonic is recorded as i is the key sending line number;

[0090] According to the harmonic node voltage equation, the node harmonic voltage is:

[0091]

[0092] In the formula, Y h The inverse matrix of

[0093] The key transmission line harmonic current is:

[0094]

[0095] In the formula, When the harmonic is the hth harmonic, the harmonic current of the first key outgoing line is: When the harmonic is the hth harmonic, the harmonic current of the second key outgoing line is: When the harmonic is the hth harmonic, the grid-connected point harmonic voltage is: The node harmonic voltage of node 2 when is the hth harmonic, The node harmonic voltage of node 3 when the harmonic is h, Y 12 Y h The element Y in row 1 and column 2 s1 , Y 13 Y h The element Y in row 1 and column 3 s2 ;

[0096] The harmonic voltage of the grid connection point and the harmonic current of the key transmission line can be calculated by combining the harmonic voltage of the above nodes and the harmonic current of the key transmission line;

[0097] The harmonic voltage constraints of the grid connection point and the harmonic current constraints of the key transmission lines are obtained according to the line parameters; the calculation methods of the harmonic voltage constraints and the harmonic current constraints refer to the national standard "GB / T 14549-93 Power Quality Public Grid Harmonics";

[0098] On the basis of determining the grid connection point and key transmission lines, the total harmonic current constraint flowing through the grid connection point is calculated according to the short-circuit capacity of the grid connection point. The total harmonic current constraint is:

[0099]

[0100] In the formula, I h is the total harmonic current constraint when the harmonic is the hth order, S k1 is the minimum short-circuit capacity of the grid-connected point, S k2 is the reference short-circuit capacity, I hp is the total harmonic current constraint corresponding to the reference short-circuit capacity at the hth harmonic;

[0101] Minimum short-circuit capacity S of the grid connection point k1 is the minimum short-circuit capacity of the busbar where the grid connection point is located under the minimum operation mode of the external system, which can be calculated by the first formula:

[0102]

[0103] Where U is the rated voltage of the busbar where the grid connection point is located, Z eq is the equivalent impedance of the fundamental frequency node, in ohms;

[0104] Since harmonics are mainly generated by odd harmonics such as the 5th, 7th, 11th, and 13th order, in the calculation of this embodiment, the 5th, 7th, 11th, 13th, 17th, and 19th order harmonics are mainly considered.

[0105] In the national standard "GB / T 14549-93 Power Quality Public Grid Harmonics", the benchmark short-circuit capacity and total harmonic current constraints for different voltage levels are shown in Table 1:

[0106] Table 1 Reference short-circuit capacity of different voltage levels (standard voltage) and total harmonic current constraints corresponding to reference short-circuit capacity

[0107]

[0108] As can be seen from Table 1, for this embodiment, the voltage level corresponding to the rated voltage of the busbar where the grid connection point is located is 220 kV. At this voltage level, the reference short-circuit capacity S k2 The total harmonic current constraint corresponding to the benchmark short-circuit capacity at different harmonic frequencies is:

[0109]

[0110] In the formula, I 5p ,I 7p ,I 11p ,I 13p ,I 17p ,I 19p They are the total harmonic current constraints corresponding to the reference short-circuit capacity at the 5th, 7th, 11th, 13th, 17th and 19th harmonics respectively;

[0111] The above calculation can get the total harmonic current constraint I h The total harmonic current constraint needs to be allocated according to the rated capacity of the connected users. That is, in this embodiment, the number of key transmission lines is 2, and the total harmonic current constraint is allocated according to the rated capacity of the two key transmission lines. The calculation formula of the harmonic current constraint value of the key transmission line is:

[0112]

[0113] In the formula, is the harmonic current constraint value of the i-th key transmission line when the harmonic is h, S i is the power consumption agreement capacity of the i-th key transmission line, S t is the capacity of the power supply equipment at the grid connection point, α is the phase superposition coefficient, and the phase superposition coefficients under different harmonic frequencies in the national standard "GB / T 14549-93 Power Quality Public Grid Harmonics" are shown in Table 2:

[0114] Table 2 Phase superposition coefficients at different harmonic frequencies

[0115]

[0116] According to the calculation formula of the harmonic current constraint value of the key transmission line, the harmonic current constraint value of the key transmission line can be calculated as follows:

[0117] In addition, in the national standard "GB / T 14549-93 Power Quality Public Grid Harmonics", the harmonic voltage constraints for different voltage levels are shown in Table 3:

[0118] Table 3 Harmonic voltage constraints at different voltage levels (standard voltage)

[0119]

[0120] It can be seen from Table 2 that for this embodiment, when the voltage level is 220 kV, the odd harmonic voltage constraint value of the grid connection point is 1.6%;

[0121] Therefore, the harmonic voltage constraints of the grid connection point and the harmonic current constraints of the key transmission lines in this embodiment can be obtained, see Table 4:

[0122] Table 4 Harmonic voltage constraints at the grid connection point and harmonic current constraints at key transmission lines

[0123]

[0124] The first deviation factor is calculated according to the ratio of the harmonic voltage at the grid connection point to the harmonic voltage constraint, and the second deviation factor is calculated according to the ratio of the harmonic current of the key transmission line to the harmonic current constraint. The first deviation factor and the second deviation factor are used to further evaluate the harmonic safety;

[0125] The first deviation factor is used to indicate the degree of excess of the harmonic voltage at the grid connection point relative to the harmonic voltage constraint at the grid connection point. The first deviation factor is:

[0126]

[0127] In the formula, is the first deviation factor, is the hth harmonic voltage constraint;

[0128] The second deviation factor is used to indicate the degree of over-limit of the key transmission line harmonic current relative to the key transmission line harmonic current constraint value. The second deviation factor is:

[0129]

[0130] In the formula, is the second deviation factor of the i-th key delivery line, is the harmonic current constraint value of the i-th key outgoing line of the h-th harmonic, The harmonic current of the i-th key outgoing line when it is the h-th harmonic;

[0131] The same as calculating the harmonic current constraint value of the key transmission line, in this embodiment, h is respectively 5, 7, 11, 13, 17 and 19;

[0132] First Deviation Factor and the second deviation factor are all deviation factors, and the deviation factor is recorded as D. When D>1, it means that the corresponding constraint is exceeded, and when D<1, it means that the corresponding constraint is not exceeded;

[0133] Compare the first deviation factor and the second deviation factor to obtain the maximum deviation factor;

[0134]

[0135] In the formula, is the maximum deviation value when the harmonic is of order h, and max is the maximum value. Similarly, in this implementation, h is 5, 7, 11, 13, 17 and 19, and i is 1 and 2, respectively;

[0136] Obtain the initial value of the harmonic weight factor. For the harmonic calculation in steady state, the initial value of the harmonic weight factor is normalized. The initial value of each harmonic weight factor is weighted as 1, and the initial value of the harmonic weight factor is set to be larger as the harmonic frequency is lower. The initial value of the harmonic weight factor is shown in Table 5.

[0137] Table 5 Initial values ​​of harmonic weight factors

[0138]

[0139] The weight factor calculation formula is constructed based on the initial value of the harmonic weight factor; the weight factor calculation formula is:

[0140]

[0141] In the formula, ω h is the actual value of the hth harmonic weight factor, is the initial value of the hth harmonic weight factor, is the maximum value of the deviation factor of the hth harmonic, where h is the frequency of the odd harmonic;

[0142] when When h =1; when When h =ω h0 ;when When h >ω h0 ;when When h <ω h0 In particular, when studying the harmonic voltage of the grid connection point or the harmonic current of a key transmission line, or even the harmonic current of a line (at this time, is the second deviation factor of the i-th line), the safety situation can be expressed as or

[0143]

[0144] Based on the weight factor calculation formula, the actual value of the harmonic weight factor ω is calculated according to the maximum value of the deviation factor h ;

[0145] The comprehensive harmonic risk evaluation index is calculated based on the maximum value of the deviation factor and the actual value of the harmonic weight factor; the comprehensive harmonic risk evaluation index is the difference between the sum of the actual value of the harmonic weight factor of each frequency odd harmonic and the maximum value of the deviation factor and 1, that is, the comprehensive harmonic risk evaluation index is:

[0146]

[0147] In the formula, H safe is the comprehensive evaluation index of harmonic risk, ω h is the actual value of the hth harmonic weight factor, is the maximum value of the deviation factor of the hth harmonic, h is the frequency of the odd harmonic, and in this embodiment, h is 5, 7, 11, 13, 17 and 19 respectively;

[0148] According to the comprehensive harmonic risk evaluation index, the harmonic risk of the current operating condition of the new energy grid-connected system is judged in the following steps:

[0149] When H safe When <0, there is harmonic risk in the current operating condition of the new energy grid-connected system;

[0150] When H safe > 0, there is no harmonic risk in the current operating condition of the new energy grid-connected system;

[0151] When H safe =0, the current operating condition of the new energy grid-connected system is a critical safety state.

[0152] Furthermore, the new energy grid-connected system is divided into safe operation area and risk operation area according to the comprehensive evaluation index of harmonic risk;

[0153] The safe operating area is H safe The operating set consists of all operating conditions where >0, that is, the safe operating area satisfies the multi-harmonic constraints;

[0154] The risk operation area is H safe The operating set consists of all operating conditions that are less than 0, that is, the risk operating area does not meet the multi-harmonic constraints.

[0155] Working condition 1

[0156] against Figure 2 and Figure 3The China New Energy Grid-connected System sets the AC power grid in normal operation mode, with 3 new energy stations put into operation, 5 AC submarine cables connected to the grid, and a total length of 159.1km of high-voltage AC submarine cables connected to the grid. Figure 1 Conduct harmonic risk assessment in the process.

[0157] Under the conventional operation mode of the AC power grid, after considering the harmonic voltage constraints of the grid connection point and the harmonic current constraints of the key transmission lines, let A, B, and C represent the number of new energy equipment put into operation in the three new energy stations, and take the number of RES-C put into operation as 0, 9, 18, and 27 as an example to show some comprehensive evaluation indicators of harmonic risks H. safe The calculation results are shown in Table 6:

[0158] Table 6 Comprehensive evaluation index of harmonic risk of new energy grid-connected system under conventional operation mode of AC power grid

[0159]

[0160] From Table 1, we can see that the comprehensive evaluation index of harmonic risk H safe It is always a negative value and varies greatly with the number of new energy equipment put into use and retired.

[0161] Figure 4 The middle boundary surface is the polynomial fitting result based on analytical traversal of data points, where the light-colored surface is H safe =0 The boundary of the safety region is the critical safety state. The light-colored dots surrounded by it are the safe operation points obtained by analytical traversal. The dark surface is H safe = -5 fitting boundary, the dark × separated is the traversed H safe <-5, the other unplotted operating points are all -5<H safe <0 point. Figure 4 The two-dimensional safe operating area is as follows Figure 5 As shown, Figure 4 The time domain simulation is carried out at three operating points to verify the Figure 6 shown.

[0162] The working state switching is completed at 1.95s and 2.05s. Figure 6 It can be seen that the 5th harmonic current of the key transmission line corresponding to RES-B and RES-C at operating point 1, that is, the second key transmission line, exceeds the standard, and the 13th harmonic of the key transmission line RES-A at operating point 3, that is, the first key transmission line, exceeds the standard. Only the harmonic currents of the key transmission lines at operating point 2 and the harmonic voltages at the grid connection point meet the constraints, and the time domain simulation verification is consistent with the safety domain characterization.

[0163] Working condition 2: Line disconnection near the grid connection point:

[0164] The multi-harmonic safety domain under the disconnection line near the AC grid connection point is studied. Figure 1 The calculation in step 2 is the same as that in condition 1. At this time, the system operates under full conditions without a safe operation prelude. The calculation results of risk assessment indicators under different operating condition combinations are shown in Table 7.

[0165] Table 7 Comprehensive evaluation index of harmonic risk of new energy grid-connected system under the disconnection line near the AC grid connection point

[0166]

[0167] Comparing Table 1 and Table 2, it can be seen that the comprehensive evaluation index H of harmonic risk under most working conditions safe The calculated result is smaller, and the harmonic risk of line disconnection in the vicinity of the AC grid connection point is higher.

[0168] Figure 7 The light green surface in the middle is the safe operation area that meets the multi-harmonic voltage constraint. The meaning of each symbol is as shown in the legend. Figure 7 Three operating points are used for time domain simulation verification. Fig. 9 shown. Figure 7 The two-dimensional operating domain is Figure 8 shown.

[0169] Fig. 9 9(a) and 9(b) are the time domain waveforms and FFT analysis results of the harmonic voltage at the grid connection point under three working conditions, and 9(c) and 9(d) are the time domain waveforms and FFT analysis results of the harmonic current of the key transmission line corresponding to RES-B and RES-C, that is, the second key transmission line under three working conditions. Fig. 9 (b) It can be seen that only the grid-connected harmonic voltage of operation point 3 meets the constraints, and the time domain simulation results are consistent with the safety domain calculation results. Fig. 9 (d) It can be seen that under the three working conditions of the AC power grid PCC near line break, the fifth harmonic current limit of the key transmission line corresponding to RES-B and RES-C, that is, the second key transmission line, is more serious.

[0170] The simulation and calculation results of the above embodiments prove that the proposed comprehensive harmonic evaluation index can accurately evaluate the system harmonic risk, and the proposed harmonic risk assessment method for the new energy grid-connected system can effectively calculate the harmonic risk conditions and provide guidance for the safe operation of the power system.

[0171] See also Fig.10 , an embodiment of the present invention also provides a device for implementing a harmonic risk assessment method for a new energy grid-connected system, comprising a modeling unit, a data acquisition unit, a controller, a harmonic source, a calculation unit, and a risk assessment unit;

[0172] Modeling unit:

[0173] Used to construct harmonic frequency domain impedance model based on new energy grid-connected system;

[0174] Used to construct harmonic node voltage equations according to the harmonic frequency domain impedance model and transmit them to the calculation unit;

[0175] Constructing a weight factor calculation formula based on the initial value of the harmonic weight factor and transmitting it to the calculation unit;

[0176] Data acquisition unit:

[0177] Used to obtain line parameters and measured harmonic data based on the new energy grid-connected system, and transmit the line parameters to the calculation unit and transmit the measured harmonic data to the controller;

[0178] Used to obtain the initial value of the harmonic weight factor and transmit it to the modeling unit;

[0179] Used to collect the current operating condition data of the new energy grid-connected system based on the set background harmonics and transmit it to the calculation unit;

[0180] Controller:

[0181] Used to control harmonic sources based on measured harmonic data to set background harmonics on renewable energy grid-connected systems;

[0182] Harmonic sources:

[0183] Used to provide background harmonics to the new energy grid-connected system under the control of the controller;

[0184] Computational Unit:

[0185] Used to obtain the harmonic voltage constraints of the grid connection point and the harmonic current constraints of the key transmission lines according to the line parameters;

[0186] Used to calculate the grid connection point harmonic voltage and key transmission line harmonic current based on the current operating condition data according to the harmonic node voltage equation;

[0187] Used to calculate the first deviation factor according to the ratio of the harmonic voltage at the grid connection point to the harmonic voltage constraint, and calculate the second deviation factor according to the ratio of the harmonic current of the key transmission line to the harmonic current constraint;

[0188] Used to compare the first deviation factor and the second deviation factor to obtain the maximum value of the deviation factor;

[0189] Used to calculate the actual value of the harmonic weight factor based on the weight factor calculation formula and the maximum value of the deviation factor;

[0190] Used to calculate the harmonic risk comprehensive evaluation index according to the maximum value of the deviation factor and the actual value of the harmonic weight factor, and transmit the harmonic risk comprehensive evaluation index to the risk evaluation unit;

[0191] Risk Assessment Unit:

[0192] It is used to judge the real-time harmonic risk of the renewable energy grid-connected system based on the comprehensive harmonic risk evaluation index.

[0193] Finally, it should be noted that the above content is only used to illustrate the technical solution of the present invention, rather than to limit the scope of protection of the present invention. Simple modifications or equivalent substitutions of the technical solution of the present invention by ordinary technicians in this field do not deviate from the essence and scope of the technical solution of the present invention.

Claims

1. A harmonic risk assessment method for a new energy grid-connected system, characterized by: The following steps are involved: Constructing a harmonic frequency domain impedance model based on a new energy grid-connected system; the new energy grid-connected system includes an AC power grid and a new energy station; Constructing a harmonic node voltage equation according to the harmonic frequency domain impedance model; Based on the new energy grid-connected system, line parameters and measured harmonic data are respectively obtained; Setting background harmonics on the new energy grid-connected system based on the measured harmonic data; Acquiring current operating condition data based on the new energy grid-connected system that sets the background harmonics; Based on the current operating condition data, the harmonic voltage of the grid connection point and the harmonic current of the key transmission line are calculated respectively according to the harmonic node voltage equation; the grid connection point is the common connection point between the AC power grid and the new energy station, and the key transmission line is the transmission line connected to the grid connection point; According to the line parameters, respectively obtain the harmonic voltage constraints of the grid connection point and the harmonic current constraints of the key transmission line; Calculating a first deviation factor according to a ratio of the grid connection point harmonic voltage to the harmonic voltage constraint, and calculating a second deviation factor according to a ratio of the key transmission line harmonic current to the harmonic current constraint; Comparing the first deviation factor and the second deviation factor to obtain a maximum deviation factor; Get the initial value of harmonic weight factor; Constructing a weight factor calculation formula based on the initial value of the harmonic weight factor; Based on the weight factor calculation formula, the actual value of the harmonic weight factor is calculated according to the maximum value of the deviation factor; Calculate the comprehensive evaluation index of harmonic risk according to the maximum value of the deviation factor and the actual value of the harmonic weight factor; The harmonic risk of the current operating condition of the new energy grid-connected system is judged according to the comprehensive harmonic risk evaluation index.

2. The harmonic risk assessment method for a new energy grid-connected system according to claim 1 is characterized by: The background harmonics include background harmonics based on the AC power grid and background harmonics based on new energy equipment.

3. The harmonic risk assessment method for a new energy grid-connected system according to claim 2 is characterized by: The background harmonics are obtained by using harmonic current source simulation.

4. The harmonic risk assessment method for a new energy grid-connected system according to claim 3 is characterized by: Based on the background harmonics of the AC power grid, the background harmonics are set at the grid connection point.

5. The harmonic risk assessment method for a new energy grid-connected system according to claim 3 is characterized by: Based on the background harmonics of the new energy equipment, the background harmonics are set on the high-voltage side busbar of the new energy station step-up transformer with the same voltage level as the grid connection point.

6. The harmonic risk assessment method for a new energy grid-connected system according to claim 1 is characterized by: The weight factor calculation formula is: In the formula, ω h is the actual value of the hth harmonic weight factor, is the initial value of the hth harmonic weight factor, is the maximum value of the deviation factor of the hth harmonic, and h is the frequency of the odd harmonic.

7. The harmonic risk assessment method for a new energy grid-connected system according to any one of claims 1 to 6, characterized in that: The comprehensive harmonic risk evaluation index is the difference between the sum of the products of the actual values ​​of the harmonic weight factors of the odd harmonics of each frequency and the maximum value of the deviation factor and 1.

8. The harmonic risk assessment method for a new energy grid-connected system according to claim 7 is characterized in that: The steps of judging the real-time harmonic risk of the new energy grid-connected system according to the comprehensive harmonic risk evaluation index are as follows: When the comprehensive evaluation index of harmonic risk is less than zero, the current operating condition of the new energy grid-connected system has harmonic risk; When the comprehensive evaluation index of harmonic risk is greater than zero, there is no harmonic risk in the current operating condition of the new energy grid-connected system; When the comprehensive evaluation index of harmonic risk is equal to zero, the current operating condition of the new energy grid-connected system is a critical safety state.

9. The harmonic risk assessment method for a new energy grid-connected system according to claim 7 is characterized in that: Dividing the new energy grid-connected system into a safe operation area and a risky operation area according to the comprehensive harmonic risk evaluation index; The safe operation area is an operation set consisting of all operating conditions where the comprehensive harmonic risk evaluation index is greater than zero; The risky operation area is an operation set consisting of all operating conditions where the comprehensive harmonic risk evaluation index is less than zero.

10. A device for implementing the harmonic risk assessment method for a new energy grid-connected system according to any one of claims 1 to 9, characterized in that: It includes a modeling unit, a data acquisition unit, a controller, a harmonic source, a calculation unit and a risk assessment unit; The modeling unit: Used to construct harmonic frequency domain impedance model based on new energy grid-connected system; Used to construct a harmonic node voltage equation according to the harmonic frequency domain impedance model and transmit it to the calculation unit; Constructing a weight factor calculation formula based on the initial value of the harmonic weight factor and transmitting it to the calculation unit; The data acquisition unit: Used to obtain line parameters and measured harmonic data based on the new energy grid-connected system, and transmit the line parameters to the calculation unit and transmit the measured harmonic data to the controller; Used to obtain the initial value of the harmonic weight factor and transmit it to the modeling unit; Used to collect the current operating condition data of the new energy grid-connected system based on setting the background harmonics and transmit it to the calculation unit; The controller: Used to control the harmonic source to set background harmonics on the new energy grid-connected system based on the measured harmonic data; The harmonic sources are: Used to provide background harmonics to the new energy grid-connected system under the control of the controller; The computing unit: Used to obtain the harmonic voltage constraints of the grid connection point and the harmonic current constraints of the key transmission line according to the line parameters; Used to calculate the grid connection point harmonic voltage and key transmission line harmonic current respectively based on the current operating condition data and the harmonic node voltage equation; Used to calculate a first deviation factor according to the ratio of the harmonic voltage at the grid connection point to the harmonic voltage constraint, and calculate a second deviation factor according to the ratio of the harmonic current of the key transmission line to the harmonic current constraint; used to compare the first deviation factor and the second deviation factor to obtain a maximum deviation factor; Used to calculate the actual value of the harmonic weight factor based on the weight factor calculation formula and according to the maximum value of the deviation factor; Used to calculate a comprehensive harmonic risk evaluation index according to the maximum value of the deviation factor and the actual value of the harmonic weight factor, and transmit the comprehensive harmonic risk evaluation index to the risk evaluation unit; The risk assessment unit: Used to judge the real-time harmonic risk of the new energy grid-connected system according to the comprehensive harmonic risk evaluation index.

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