A new energy grid-connected system harmonic risk evaluation method and device

Abstract

The application provides a new energy grid-connected system harmonic risk evaluation method, comprising the following steps: calculating the grid-connected point harmonic voltage of the new energy grid-connected system and the key outgoing line harmonic current after setting the background harmonic through the 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 the first deviation factor according to the grid-connected point harmonic voltage and the harmonic voltage constraint, calculating the second deviation factor according to the key outgoing line harmonic current and the harmonic current constraint, and comparing to obtain the maximum value of the deviation factor; calculating the harmonic risk comprehensive evaluation index according to the maximum value of the deviation factor and the harmonic weight factor actual value and judging the harmonic risk of the current operation condition of the new energy grid-connected system. The evaluation method provided by the application can effectively measure the harmonic risk degree under different operation conditions, draw the safe operation area and the risk operation area, and guarantee the safe and stable operation of the new energy grid-connected system.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of power systems, in particular to a new energy grid-connected system harmonic risk evaluation method and device. BACKGROUND

[0002] With the rapid development of new power systems, the proportion of new energy power generation continues to increase, and the large-scale 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 quantities of harmonic sources are increasing, leading to more serious harmonic problems in power systems. Harmonic problems not only cause deterioration of power quality, but also may cause equipment overload, accelerated aging, and misoperation of system protection devices, etc., which threaten the stable operation of power systems and the safety of equipment.

[0003] In the new energy grid-connected scenario, due to the characteristics of low inertia and weak damping of new energy power generation systems, power systems are more susceptible to harmonic interference, and the superposition effect of background harmonics further complicates the problem. Different frequency harmonic components in the power grid may be coupled with certain resonant points of the system, leading to significant amplification of harmonic amplitude. This harmonic amplification phenomenon can exacerbate the risk of equipment damage and may cause large-scale new energy power generation devices to be disconnected 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 installing filters or optimizing device control strategies to reduce the impact of specific frequency harmonics. However, these methods are often difficult to deal with the interaction of multi-frequency harmonics in complex system environments, and cannot effectively solve the comprehensive problem of background harmonics and system resonance. In particular, in new power systems, the diversity and complexity of harmonic sources make comprehensive assessment of harmonic risk particularly important, so there is an urgent need for a system-level harmonic risk evaluation method to provide theoretical basis and technical support for the prevention and control of harmonic problems. SUMMARY

[0005] The present application provides a new energy grid-connected system harmonic risk evaluation method that can effectively measure the degree of harmonic risk under different operating conditions, accurately depict the harmonic safety level of the grid-connected system, draw safe and risky operating regions, and ensure the safe and stable operation of the new energy grid-connected system.

[0006] To achieve the above purpose, the technical scheme adopted by the present application is as follows: a new energy grid-connected system harmonic risk evaluation method, comprising the following steps:

[0007] A harmonic frequency domain impedance model is constructed based on a new energy grid-connected system; the new energy grid-connected system includes an alternating current 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 obtained respectively;

[0010] Based on the measured harmonic data, a background harmonic is set on the new energy grid-connected system;

[0011] Based on the new energy grid-connected system with the background harmonic set, current operating condition data are obtained;

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

[0013] According to the line parameters, harmonic voltage constraints of the grid-connected point and harmonic current constraints of the key outgoing line are obtained respectively;

[0014] A first deviation factor is calculated according to the ratio of the grid-connected point harmonic voltage to the harmonic voltage constraint, and a second deviation factor is calculated according to the ratio of the key outgoing line harmonic current to the harmonic current constraint;

[0015] The maximum value of the deviation factor is obtained by comparing the first deviation factor and the second deviation factor;

[0016] An initial value of a harmonic weight factor is obtained;

[0017] A weight factor calculation formula is constructed based on the initial value of the harmonic weight factor;

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

[0019] A harmonic risk comprehensive evaluation index is calculated 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 harmonic risk comprehensive evaluation index.

[0021] Further, the background harmonic includes an AC power grid-based background harmonic and a new energy equipment-based background harmonic.

[0022] Further, the background harmonic is obtained by simulating a harmonic current source.

[0023] Further, based on the AC power grid-based background harmonic, the background harmonic is set at the grid-connected point.

[0024] Further, based on the background harmonic of the new energy equipment, the background harmonic is arranged on a high-voltage side bus of a new energy station step-up transformer in the same voltage level as the grid connection point.

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

[0026]

[0027] ω h = ω h 0 + ω h 1 * (ω h 0 - ω h 1 ) / ω h 0 h ω h 0 is an actual value of an hth harmonic weight factor, ω h 1 is an initial value of the hth harmonic weight factor, ω h 1 is an initial value of the hth harmonic weight factor,

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

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

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

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

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

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

[0034] The safe operation region is an operation set composed of all operating conditions with the harmonic risk comprehensive evaluation index greater than zero.

[0035] The risk operation region is an operation set composed of all operating conditions with the harmonic risk comprehensive evaluation index less than zero.

[0036] An apparatus for implementing the harmonic risk evaluation method of the new energy grid-connected system includes a modeling unit, a data acquisition unit, a controller, a harmonic source, a calculation unit, and a risk evaluation unit.

[0037] The modeling unit:

[0038] is configured to construct a harmonic frequency domain impedance model based on the new energy grid-connected system.

[0039] constructing a harmonic node voltage equation according to the harmonic frequency domain impedance model and transmitting to the calculation unit;

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

[0041] The data acquisition unit:

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

[0043] For obtaining harmonic weight factor initial value and transmitting to the modeling unit;

[0044] For based on the new energy grid-connected system set the background harmonic to obtain the current operating condition data and transmit to the calculation unit;

[0045] The controller:

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

[0047] The harmonic source:

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

[0049] The calculation unit:

[0050] For according to the line parameters respectively get harmonic voltage constraints of grid-connected point and harmonic current constraints of key outgoing line;

[0051] For based on the current operating condition data, according to the harmonic node voltage equation respectively calculate the harmonic voltage of grid-connected point and the harmonic current of key outgoing line;

[0052] For according to the ratio of the harmonic voltage of grid-connected point and the harmonic voltage constraint to calculate the first deviation factor, according to the ratio of the harmonic current of key outgoing line and the harmonic current constraint to calculate the second deviation factor;

[0053] For comparing the first deviation factor and the second deviation factor to obtain the maximum deviation factor;

[0054] For based on the weight factor calculation formula, according to the maximum deviation factor to calculate the harmonic weight factor actual value;

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

[0056] The risk evaluation unit:

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

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

[0059] The present application provides a new energy grid-connected system harmonic risk evaluation method, which can effectively measure the harmonic risk degree under different operating conditions, accurately depict the harmonic safety level of the grid-connected system, draw a safe operation region and a risk operation region, and guarantee the safe and stable operation of the new energy grid-connected system. BRIEF DESCRIPTION OF DRAWINGS

[0060] Figure 1 The flowchart of the new energy grid-connected system harmonic risk evaluation method of the present application;

[0061] Figure 2 The topology diagram of the new energy grid-connected system in the embodiment of the present application;

[0062] Figure 3 The frequency domain admittance model of the new energy grid-connected system in the embodiment of the present application;

[0063] Figure 4 The three-dimensional harmonic safe operation domain and harmonic risk region of operating condition one in the embodiment of the present application;

[0064] Figure 5 The two-dimensional harmonic safe operation domain and harmonic risk region of operating condition one in the embodiment of the present application: (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 operating condition one in the embodiment of the present application: (a) is the time domain waveform diagram of , (b) is the frequency domain FFT analysis diagram of , (c) is the time domain waveform diagram of , and (d) is the frequency domain FFT analysis diagram of ;

[0066] Figure 7 The three-dimensional harmonic safe operation domain and harmonic risk region of operating condition two in the embodiment of the present application;

[0067] Figure 8For the two-dimensional harmonic safe operation domain and harmonic risk area of the working condition two in the embodiment of the application: (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] Figure 9 For the time-domain simulation waveform of the working condition two in the embodiment of the application: (a) is a time-domain waveform diagram of the harmonic voltage at the grid-connected point, (b) is a frequency-domain FFT analysis diagram of the harmonic voltage at the grid-connected point, (c) is a time-domain waveform diagram of , and (d) is a frequency-domain FFT analysis diagram of ;

[0069] Figure 10 The device connection relationship schematic diagram for realizing the harmonic risk evaluation method of the new energy grid-connected system according to the application is shown in Fig. 1. DETAILED DESCRIPTION

[0070] In order to clearly illustrate the technical features of the present application, the present application will be described below through specific embodiments.

[0071] Referring to Fig. 1, Figure 1 the embodiment of the application provides a harmonic risk evaluation method of a new energy grid-connected system, including the following steps:

[0072] A harmonic frequency-domain impedance model is constructed based on the new energy grid-connected system; the new energy grid-connected system includes an alternating current grid and a new energy station; the harmonic frequency-domain impedance model includes a transmission line harmonic frequency-domain impedance model, an alternating current grid harmonic frequency-domain impedance model and a harmonic frequency-domain impedance model of a new energy device; wherein the transmission line harmonic frequency-domain impedance model adopts an accurate pi model, the alternating current grid harmonic frequency-domain impedance model is obtained by using a sweep method, and the harmonic frequency-domain impedance model of the new energy device ignores the dynamic process of a control outer ring and a phase-locked loop, and only considers the dynamic process of a current inner ring, a main circuit and a measurement filter link;

[0073] For the corresponding new energy grid-connected system, an equivalent frequency-domain admittance circuit of the new energy grid-connected system is first established, as shown in Fig. 2; Figure 2 The harmonic node admittance matrix corresponding to the equivalent frequency-domain admittance circuit is: Figure 3

[0074]

[0075] In the formula, Y h is the node admittance matrix of the hth harmonic, h is the harmonic frequency, s is the Laplace operator, and Y h (s) is regenerated when different frequency harmonics are studied, Y 11 ~ Y 66 are the self-admittances of node 1~node 6, Y s1 and Y s2 ​, Y sA , Y sB , Y sC are respectively corresponding to the admittance in Figure 3 , where node 1 corresponds to Figure 2 , 3 N1 in Figure 2 , 3 N2-N6, the order of node naming in the harmonic node admittance matrix from small to large is in turn the grid-connected point-the connection node directly connected with the grid-connected point-the high-voltage side node of the booster transformer in the new energy power station;

[0076] The harmonic voltage level of the grid-connected point and the harmonic current on the offshore wind power transmission line are calculated by using the harmonic node admittance matrix. Figure 3 According to , the harmonic node admittance matrix is constructed as follows:

[0077] According to the harmonic frequency domain impedance model, the harmonic node voltage equation is constructed as follows:

[0078] I h =Y h U h ;

[0079] In the formula, I h is the node injection harmonic column vector of h-th harmonic, and U h is the node harmonic voltage column vector of h-th harmonic;

[0080] The harmonic node voltage equation is expanded as follows:

[0081]

[0082] In the formula, I grid is the equivalent background harmonic current of the alternating current grid, I windA is the equivalent grid-connected harmonic of the new energy power station A (RES-A in Figure 1 ), I windB is the equivalent grid-connected harmonic of the new energy power station B (RES-B in Figure 1 ), I windC is the equivalent grid-connected harmonic of the new energy power station C (RES-C in Figure 1 ), and U pcc is the grid-connected point harmonic voltage, and U2-U6 are respectively the harmonic voltages of node 2-node 6;

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

[0084] Based on the measured harmonic data, the background harmonic is set on the new energy grid-connected system;

[0085] The background harmonics include AC power grid-based background harmonics and new energy equipment-based background harmonics;

[0086] The AC power grid-based background harmonics are obtained by using a harmonic current source simulation according to measured harmonic data of the AC power grid, and the background harmonics are set at the grid-connected point, that is, the harmonic current source is placed at the grid-connected point.

[0087] The new energy equipment-based background harmonics are obtained by using a harmonic current source simulation according to measured harmonic data of the new energy equipment, and the background harmonics are set at a high-voltage side bus of a step-up transformer of a new energy station in the same voltage level as the grid-connected point, that is, the harmonic current source is placed at the high-voltage side bus of the step-up transformer of the new energy station in the same voltage level as the grid-connected point.

[0088] Current operating condition data are obtained based on the new energy grid-connected system with the set background harmonics.

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

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

[0091]

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

[0093] The key outgoing line harmonic current is:

[0094]

[0095] In the formula, is the first key outgoing line harmonic current at the h-th harmonic,​ the node harmonic voltage of node 2 at hth harmonic, the harmonic voltage of the grid-connected point at hth harmonic, the node harmonic voltage of node 2 at hth harmonic, the node harmonic voltage of node 3 at hth harmonic, Y 12 Y h the element Y in the first row and the second column in the matrix s1 Y 13 Y h the element Y in the first row and the third column in the matrix s2 ;

[0096] The harmonic voltage of the grid-connected point and the harmonic current of the key outgoing line can be calculated by simultaneously solving the above node harmonic voltage and the key outgoing line harmonic current;

[0097] The harmonic voltage constraint of the grid-connected point and the harmonic current constraint of the key outgoing line are obtained according to the line parameters; the calculation method of the harmonic voltage constraint and the harmonic current constraint respectively refers to the national standard "GB / T 14549-93 Power Quality Public Grid Harmonics";

[0098] On the basis of determining the grid-connected point and the key outgoing line, the total harmonic current flowing through the grid-connected point is calculated according to the short-circuit capacity of the grid-connected point, and the total harmonic current constraint is:

[0099]

[0100] In the formula, I h is the total harmonic current constraint at hth harmonic, 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 hth harmonic;

[0101] The minimum short-circuit capacity S k1 of the grid-connected point is the minimum short-circuit capacity of the bus where the grid-connected point is located under the minimum operating mode of the external system, which can be calculated by the first formula, and the first formula is:

[0102]

[0103] In the formula, U is the rated voltage of the bus where the grid-connected point is located, and Z eq is the equivalent impedance of the bus at fundamental frequency, with the unit of ohm;

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

[0105] In the national standard "GB / T 14549-93 Power Quality Public Power Grid Harmonic", the reference short-circuit capacity and the total harmonic current constraint corresponding to the reference short-circuit capacity of different voltage levels are shown in Table 1:

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

[0107]

[0108] As can be seen from Table 1, for the present embodiment, the voltage level corresponding to the rated voltage of the bus at the grid-connected point is 220 kV, and under this voltage level, the reference short-circuit capacity S k2 is 2000 MVA, and the total harmonic current constraint corresponding to the reference short-circuit capacity under different harmonic frequencies is:

[0109]

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

[0111] The above can be calculated to obtain the total harmonic current constraint I h ; the total harmonic current constraint needs to be distributed according to the rated capacity of the connected users, that is, in the present embodiment, the number of key outgoing lines is 2, and the total harmonic current constraint is distributed according to the rated capacity of the two key outgoing lines, and the calculation formula of the harmonic current constraint value of the key outgoing line is:

[0112]

[0113] In the formula, I is the harmonic current constraint value of the i-th key outgoing line under hth harmonic frequency, S i is the power agreement capacity of the i-th key outgoing line, S t is the power supply equipment capacity of the grid-connected point, and α is the phase superposition coefficient. In the national standard "GB / T 14549-93 Power Quality Public Power Grid Harmonic", the phase superposition coefficients under different harmonic frequencies are shown in Table 2:

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

[0115]

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

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

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

[0119]

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

[0121] Thus, the harmonic voltage constraints of the grid connection point and the harmonic current constraints of the key outgoing line in the embodiment can be obtained, as shown in Table 4:

[0122] Table 4 Harmonic voltage constraints of the grid connection point and harmonic current constraints of the key outgoing line

[0123]

[0124] The first deviation factor is calculated according to the ratio of the harmonic voltage of 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 outgoing line to the harmonic current constraint, and 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 represent the over-limit degree of the harmonic voltage of the grid connection point relative to the harmonic voltage constraint of the grid connection point, and 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 represent the over-limit degree of the harmonic current of the key outgoing line relative to the harmonic current constraint value of the key outgoing line, and the second deviation factor is:

[0129]

[0130] In the formula, is the second deviation factor of the ith key outgoing line, is the hth harmonic current constraint value of the ith key outgoing line, is the hth harmonic current of the ith key outgoing line;

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

[0132] First deviation factor Second deviation factor All are deviation factors, denoted as D. When D > 1, it means that the corresponding constraint has been exceeded; when D < 1, it means that the corresponding constraint has not been exceeded.

[0133] The maximum value of the deviation factor is obtained by comparing the first deviation factor and the second deviation factor.

[0134]

[0135] In the formula, The maximum deviation is the hth harmonic, and max is the maximum value. Similarly, in this implementation, h takes the values ​​5, 7, 11, 13, 17 and 19 respectively, and i takes the values ​​1 and 2 respectively.

[0136] To obtain the initial value of the harmonic weighting factor, for harmonic calculation under steady state, the initial value of the harmonic weighting factor is normalized. The initial values ​​of each harmonic weighting factor are weighted by 1, and the initial value of the harmonic weighting factor is set to be larger as the harmonic frequency is lower. The initial values ​​of the harmonic weighting factor are shown in Table 5.

[0137] Table 5 Initial values ​​of weighting factors for each harmonic order

[0138]

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

[0140]

[0141] In the formula, ω h The actual value of the h-th harmonic weighting factor. The initial value of the h-th harmonic weighting factor is... The maximum value of the deviation factor for the h-th harmonic is given, where h is the frequency of the odd harmonic.

[0142] when When, ω h =1; when When, ω h =ω h0 ;when When, ω h >ω h0 ;when When, ω h <ω h0 Specifically, when studying harmonic voltage at the grid connection point, harmonic current of a key transmitting line, or even harmonic current of a single line (in this case, For the safety of the second deviation factor of the i-th line, let the formula be... or

[0143]

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

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

[0146]

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

[0148] The harmonic risk of the current operating condition of the new energy grid-connected system is determined according to the harmonic risk comprehensive evaluation index, and the steps are as follows.

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

[0150] When H safe > 0, the current operating condition of the new energy grid-connected system does not have a harmonic risk;

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

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

[0153] The safe operation region is an operation set composed of all operating conditions with H safe > 0, that is, the safe operation region satisfies the multi-harmonic constraint;

[0154] The risk operation region is an operation set composed of all operating conditions with H safe < 0, that is, the risk operation region does not satisfy the multi-harmonic constraint.

[0155] Case one

[0156] For Figure 2 and Figure 3The China New Energy Grid Connection System is set to operate in conventional AC grid mode, with three new energy power plants in operation and five AC submarine cables connected to the grid, totaling 159.1 km in length. According to... Figure 1 Harmonic risk assessment is conducted during the process.

[0157] Under the conventional operation mode of the AC power grid, considering the harmonic voltage constraints at the grid connection point and the harmonic current constraints of key transmission lines, let A, B, and C represent the number of new energy equipment in operation at the three new energy power stations. Taking RES-C with 0, 9, 18, and 27 units in operation as examples, some comprehensive harmonic risk evaluation indicators H are shown. safe The calculation results are shown in Table 6:

[0158] Table 6 Comprehensive Evaluation Indicators of Harmonic Risk for New Energy Grid-Connected Systems under Conventional AC Grid Operation Mode

[0159]

[0160] Table 1 shows that the comprehensive evaluation index of harmonic risk H safe It is always a negative value, and varies considerably with the number of new energy equipment put into operation or decommissioned.

[0161] Figure 4 The middle boundary surface is the result of a polynomial fitting based on analytical traversal of data points, where the light-colored surface is H. safe =0 represents the critical safety state. The light-colored dots enclosed by this boundary are the safe operating points determined by analytical traversal, and the dark-colored surface is H. safe = -5 is the fitting boundary, and the dark × signs separating them represent the traversed H. safe Points less than -5, and all other unplotted running points are -5 < H. safe <0 point. Figure 4 Two-dimensional safe operating area such as Figure 5 As shown, for Figure 4 Time-domain simulation verification was carried out at three operating points, such as Figure 6 As shown.

[0162] The operating condition switch is completed at times of 1.95s and 2.05s, by... Figure 6 It can be seen that the 5th harmonic current of the critical output line corresponding to RES-B and RES-C at operating point 1, namely the 2nd critical output line, exceeds the standard, and the 13th harmonic current of the critical output line RES-A at operating point 3, namely the 1st critical output line, exceeds the standard. Only the harmonic current of each critical output line and the harmonic voltage at the grid connection point at operating point 2 meet the constraints. The time-domain simulation verification is consistent with the safety domain characterization.

[0163] Operating Condition 2: Network Disconnection Near the Grid Connection Point

[0164] The study investigates the multi-harmonic safety domain of the near-field fault line at the grid connection point of an AC power grid, based on...Figure 1 In step 2, the same as condition 1, there is no safety operation sequence for the whole operation condition of the system, and the calculation results of the risk evaluation indexes under different condition combinations are shown in Table 7.

[0165] Table 7 Harmonic risk comprehensive evaluation index of new energy grid-connected system under the condition of power grid near the grid-connected point being disconnected

[0166]

[0167] Comparing Table 1 and Table 2, it can be seen that the harmonic risk comprehensive evaluation index H safe is smaller, and the harmonic risk of the power grid near the grid-connected point being disconnected is higher.

[0168] Figure 7 The light green surface is the operation safety domain meeting the multi-harmonic voltage constraint, and the symbols have the meanings shown in the legend. Figure 7 The time-domain simulation verification of the three operation points is shown in Figure 9 . Figure 7 The two-dimensional operation domain is shown in Figure 8 .

[0169] Figure 9 (a) and 9(b) are respectively the time-domain waveforms and FFT analysis results of the grid-connected point harmonic voltage under three conditions, and 9(c) and 9(d) are respectively the time-domain waveforms and FFT analysis results of the harmonic current of the second key sending-out line corresponding to RES-B and RES-C under three conditions. Figure 9 (b) can be seen that only the grid-connected point harmonic voltage of operation point 3 meets the constraint, and the time-domain simulation result is consistent with the safety domain calculation result. In addition, from Figure 9 (d), it can be seen that under the three conditions of the power grid PCC near the disconnection, the 5th harmonic current of the key sending-out line corresponding to RES-B and RES-C, that is, the second key sending-out line, is seriously out of limit.

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

[0171] Referring to Figure 10 , the embodiment of the present application also provides a device for implementing the new energy grid-connected system harmonic risk evaluation method, which comprises a modeling unit, a data acquisition unit, a controller, a harmonic source, a calculation unit and a risk evaluation unit.

[0172] The modeling unit comprises:

[0173] a harmonic frequency domain impedance model is constructed based on the new energy grid-connected system.

[0174] constructing a harmonic node voltage equation according to a harmonic frequency domain impedance model and transmitting to a calculation unit;

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

[0176] a data acquisition unit:

[0177] for acquiring line parameters and measured harmonic data based on a new energy grid-connected system, and transmitting the line parameters to the calculation unit and the measured harmonic data to the controller;

[0178] for acquiring the initial value of the harmonic weight factor and transmitting to the modeling unit;

[0179] for acquiring the current operating condition data of the new energy grid-connected system based on the set background harmonic and transmitting to the calculation unit;

[0180] a controller:

[0181] for controlling the harmonic source to set the background harmonic on the new energy grid-connected system based on the measured harmonic data;

[0182] a harmonic source:

[0183] for providing the background harmonic to the new energy grid-connected system under the control of the controller;

[0184] a calculation unit:

[0185] for acquiring the harmonic voltage constraint of the grid-connected point and the harmonic current constraint of the key outgoing line based on the line parameters respectively;

[0186] for calculating the harmonic voltage of the grid-connected point and the harmonic current of the key outgoing line based on the current operating condition data according to the harmonic node voltage equation respectively;

[0187] for calculating a first deviation factor according to the ratio of the harmonic voltage of the grid-connected point to the harmonic voltage constraint, and a second deviation factor according to the ratio of the harmonic current of the key outgoing line to the harmonic current constraint;

[0188] for obtaining a maximum deviation factor by comparing the first deviation factor and the second deviation factor;

[0189] for calculating the actual value of the harmonic weight factor according to the maximum deviation factor based on the weight factor calculation formula;

[0190] for calculating a harmonic risk comprehensive evaluation index according to the maximum deviation factor and the actual value of the harmonic weight factor, and transmitting the harmonic risk comprehensive evaluation index to a risk evaluation unit;

[0191] a risk evaluation unit:

[0192] The application discloses a real-time harmonic risk judging method for a new energy grid-connected system according to a harmonic risk comprehensive evaluation index.

[0193] Finally, it should be noted that the above content is only used to illustrate the technical solutions of the present application, and is not a limitation on the scope of protection of the present application. Simple modifications or equivalent replacements of the technical solutions of the present application made by those skilled in the art do not deviate from the essence and scope of the technical solutions of the present application.

Claims

1. A method for evaluating harmonic risk of a new energy grid-connected system, characterized in that: The method comprises the following steps: constructing a harmonic frequency domain impedance model based on a new energy grid-connected system; the new energy grid-connected system comprises an alternating current power grid and a new energy station; constructing a harmonic node voltage equation according to the harmonic frequency domain impedance model; acquiring line parameters and measured harmonic data respectively based on the new energy grid-connected system; setting a background harmonic 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 with the background harmonic set; calculating grid-connected point harmonic voltage and key outgoing line harmonic current respectively according to the harmonic node voltage equation based on the current operating condition data; the grid-connected point is a common connection point of the alternating current power grid and the new energy station, and the key outgoing line is an outgoing line connected to the grid-connected point; acquiring harmonic voltage constraints of the grid-connected point and harmonic current constraints of the key outgoing line respectively according to the line parameters; calculating a first deviation factor according to a ratio of the grid-connected point harmonic voltage to the harmonic voltage constraints, and calculating a second deviation factor according to a ratio of the key outgoing line harmonic current to the harmonic current constraints; obtaining a maximum deviation factor by comparing the first deviation factor and the second deviation factor; acquiring a harmonic weight factor initial value; constructing a weight factor calculation formula based on the harmonic weight factor initial value; calculating a harmonic weight factor actual value according to the maximum deviation factor based on the weight factor calculation formula; calculating a harmonic risk comprehensive evaluation index according to the maximum deviation factor and the harmonic weight factor actual value; judging a harmonic risk of a current operating condition of the new energy grid-connected system according to the harmonic risk comprehensive evaluation index.

2. The method of claim 1, wherein the method further comprises: determining a harmonic risk of the new energy grid-connected system based on the harmonic risk index. The background harmonic comprises an alternating current power grid-based background harmonic and a new energy equipment-based background harmonic.

3. The method of claim 2, wherein the method further comprises: determining a harmonic risk of the new energy grid-connected system based on the harmonic risk index. The background harmonic is obtained by simulating a harmonic current source.

4. The method of claim 3, wherein the method further comprises: determining a harmonic risk of the new energy grid-connected system based on the harmonic risk index. The alternating current power grid-based background harmonic is set at the grid-connected point.

5. The method of claim 3, wherein the method further comprises: determining a harmonic risk of the new energy grid-connected system based on the harmonic risk index. The new energy equipment-based background harmonic is set on a high-voltage side bus of a new energy station step-up transformer at a voltage level same as that of the grid-connected point.

6. The method of claim 1, wherein the method further comprises: determining a harmonic risk of the new energy grid-connected system based on the harmonic risk index. The weight factor calculation formula is: ωh= ωh0+ Δωh h ωh= ωh0+ Δωh ωh= ωh0+ Δωh ωh= ωh0+ Δωh 7. The method of claim 1-6, wherein the method further comprises: determining the harmonic risk of the new energy grid-connected system based on the harmonic risk of the new energy grid-connected system. The harmonic risk comprehensive evaluation index is a difference between a sum of products of harmonic weight factor actual values of each frequency odd harmonic and the maximum deviation factor and 1. 8.The method of claim 7, wherein the method further comprises: determining a harmonic risk of the new energy grid-connected system based on the harmonic risk index. The step of judging a real-time harmonic risk of the new energy grid-connected system according to the harmonic risk comprehensive evaluation index is: when the harmonic risk comprehensive evaluation index is less than zero, the current operating condition of the new energy grid-connected system has a harmonic risk; when the harmonic risk comprehensive evaluation index is greater than zero, the current operating condition of the new energy grid-connected system has no harmonic risk; when the harmonic risk comprehensive evaluation index is equal to zero, the current operating condition of the new energy grid-connected system is in a critical safe state. 9.The method of claim 7, wherein: The new energy grid-connected system is divided into a safe operation region and a risk operation region according to the harmonic risk comprehensive evaluation index; the safe operation region is an operation set composed of all operating conditions with the harmonic risk comprehensive evaluation index greater than zero; the risk operation region is an operation set composed of all operating conditions with the harmonic risk comprehensive evaluation index less than zero.

10. An apparatus for implementing the method for evaluating harmonic risk of a new energy grid-connected system according to any one of claims 1-9, characterized in that: The modeling unit, the data acquisition unit, the controller, the harmonic source, the calculation unit and the risk evaluation unit are included. The modeling unit is configured to: construct a harmonic frequency domain impedance model based on a new energy grid-connected system; construct a harmonic node voltage equation based on the harmonic frequency domain impedance model and transmit the harmonic node voltage equation to the calculation unit; construct a weight factor calculation formula based on the harmonic weight factor initial value and transmit the weight factor calculation formula to the calculation unit; The data acquisition unit is configured to: acquire line parameters and measured harmonic data based on the new energy grid-connected system, respectively, and transmit the line parameters to the calculation unit and the measured harmonic data to the controller; acquire a harmonic weight factor initial value and transmit the harmonic weight factor initial value to the modeling unit; acquire current operating condition data of the new energy grid-connected system based on the set background harmonic and transmit the current operating condition data to the calculation unit; The controller is configured to: control the harmonic source to set a background harmonic on the new energy grid-connected system based on the measured harmonic data; The harmonic source is configured to: provide a background harmonic to the new energy grid-connected system under the control of the controller; The calculation unit is configured to: acquire harmonic voltage constraints of grid-connected points and harmonic current constraints of key outgoing lines based on the line parameters, respectively; calculate grid-connected point harmonic voltages and key outgoing line harmonic currents based on the harmonic node voltage equation and the current operating condition data, respectively; calculate a first deviation factor based on a ratio of the grid-connected point harmonic voltages to the harmonic voltage constraints and a second deviation factor based on a ratio of the key outgoing line harmonic currents to the harmonic current constraints; obtain a maximum deviation factor by comparing the first deviation factor and the second deviation factor; calculate a harmonic weight factor actual value based on the maximum deviation factor and the weight factor calculation formula; calculate a harmonic risk comprehensive evaluation index based on the maximum deviation factor and the harmonic weight factor actual value, and transmit the harmonic risk comprehensive evaluation index to the risk evaluation unit; The risk evaluation unit is configured to: determine a real-time harmonic risk of the new energy grid-connected system based on the harmonic risk comprehensive evaluation index.

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