A method and system for testing power quality of offshore wind farms

Abstract

The present invention relates to the technical field of power quality evaluation, and discloses a method and system for testing power quality of an offshore wind farm. The method performs a power quality test according to the operating status of the offshore wind farm to be tested, obtains a power quality test index value corresponding to the operating status, and if it is determined that other offshore wind farms are connected to the offshore wind farm to be tested, performs power quality tests on the grid connection point of the offshore wind farm to be tested and the grid connection points of other offshore wind farms to which it is connected, compares the power quality test index value with its corresponding power quality index limit value, and evaluates the power quality of the offshore wind farm to be tested according to the power quality index comparison result based on preset evaluation rules to determine whether the power quality of the offshore wind farm to be tested is qualified. The method takes into account offshore wind farms with different topological structures and operating statuses, adds two indicators, voltage deviation and three-phase voltage imbalance, and improves the accuracy of offshore wind farm power quality testing.

Description

Technical Field

[0001] The present invention relates to the technical field of power quality evaluation, and in particular to a method and system for testing power quality of an offshore wind farm. Background Art

[0002] Offshore wind energy resources are abundant, generate large amounts of power, and require no onshore land. Offshore wind power generation has become a key development direction in the wind power sector. Direct-drive and doubly-fed wind turbines, commonly found in offshore wind turbines, are widely used variable-speed constant-frequency (VSCF) wind turbines. The power electronic components in the wind turbine converters and frequency converters generate harmonics, which can even cause harmonic resonance amplification issues with inductors, capacitors, and other components in the system. Offshore wind power transmission systems utilize a large number of long, highly capacitive submarine cables. When these cables connect to inductive components such as transformers, parallel resonance is highly likely to occur. Large harmonic components in wind farms can cause overvoltage and overcurrent, leading to component overheating and loss, and in severe cases, insulation failure, even causing serious power outages. With the rapid development of offshore wind power, the harmonics generated by offshore wind farms connected to the grid pose a threat to the safety and stability of the power grid system. Conducting power quality testing at offshore wind farms to assess whether the power quality at the wind farm connection point meets relevant standards provides valuable practical data support for necessary wind farm power quality management.

[0003] Chinese invention patent publication number CN 104793067 B discloses a wind farm power regulation and power quality assessment system and method. The system uses power quality data measured at power close to 0% as background power quality data, and assesses wind farm power quality by dividing the wind farm output power from 0% to 100% of rated power into 10 power intervals, with each 10% of rated power being used.

[0004] At the same time, the Chinese invention patent application with publication number CN 110865259 A discloses a method and device for evaluating the power quality of a wind farm, which regards the maximum value Pmax and the minimum value Pmin of the measured power within a certain test time as the upper and lower limits of the power range. The data within the power interval is approximately the wind farm outage data, which is used as the background power quality data; the data is equally spaced according to the power interval. The measured data is divided into 10 power intervals during normal operation of the wind farm to evaluate the power quality of the wind farm.

[0005] According to the national standard "Technical Regulations for Wind Farm Access to Power System" (GB / T 19963-2011), it is clearly stated that the power quality of wind farms includes voltage deviation, flicker, and harmonic current. The revised "Technical Regulations for Wind Farm Access to Power System Part 1: Onshore Wind Power" (GB / T 19963.1-2021) updates the power quality of wind farms to include voltage deviation, flicker, harmonic current, interharmonics, and three-phase voltage imbalance. Based on this, the power quality test items for offshore wind farms should include voltage deviation, flicker, harmonic current, interharmonics, and three-phase voltage imbalance. However, the above two invention patents only consider flicker, harmonics, and interharmonics, and do not take into account the two indicators of voltage deviation and three-phase voltage imbalance, which leads to low accuracy of the power quality test results of offshore wind farms.

[0006] There are various forms of offshore wind farms connected to the grid. There are independent offshore wind farms, that is, offshore wind farms that are directly connected to the grid without going through other offshore wind farms, and there are also offshore wind farms that transmit electricity through other offshore wind farms; there are also cases where electricity from other offshore wind farms is transmitted through this offshore wind farm. For offshore wind farms with the first two topologies, the voltage at the wind farm grid connection point and the current of the transmission line are generated by the wind farm itself. The power quality monitoring system or portable power quality test device configured at the wind farm station can be used to test and evaluate the power quality of the grid connection point. For offshore wind farms with the third topology, only the power quality test and evaluation of the grid connection point is performed, which makes it difficult to truly reflect the power quality of the offshore wind farm itself. This leads to lower accuracy of the power quality test results for offshore wind farms with different topologies.

[0007] At the same time, for grid-connected wind farms, since the wind farm's own power consumption is often around (3-4)% of the rated power, whether the power quality data measured at a power close to 0% is used as background power quality data, or the data within the power interval is approximated as wind farm shutdown data, as background power quality data, the harmonic current generated by the wind turbines corresponding to the test phase has an impact on the harmonic voltage at the test point. Therefore, it is obviously not accurate enough as a background power quality test when the wind farm is shut down. Summary of the Invention

[0008] The present invention provides a method and system for testing power quality of an offshore wind farm, which solves the technical problem of low accuracy of power quality test results of an offshore wind farm.

[0009] In view of this, a first aspect of the present invention provides a method for testing power quality of an offshore wind farm, comprising the following steps:

[0010] S1. Obtaining the operating status of the offshore wind farm to be tested, where the operating status includes an outage state and a normal operating state;

[0011] S2. Performing a power quality test on a preset test point based on the operating status of the offshore wind farm to be tested. If the operating status of the offshore wind farm to be tested is an outage state, performing a power quality test on the grid connection point of the offshore wind farm to be tested to obtain background power quality test index values, which include voltage deviation, long-term flicker value, harmonic voltage, interharmonic voltage, three-phase voltage total harmonic distortion rate, and three-phase voltage imbalance, and executing step S4. If the operating status of the offshore wind farm to be tested is a normal operating state, executing the next step.

[0012] S3. Determine whether there are other offshore wind farms connected to the offshore wind farm to be tested based on the topological structure of the offshore wind farm to be tested; if it is determined that there are other offshore wind farms connected to the offshore wind farm to be tested, perform power quality tests on the grid connection point of the offshore wind farm to be tested and the grid connection points of other offshore wind farms to which it is connected, respectively, to obtain normal operating power quality test index values ​​corresponding to the grid connection point of the offshore wind farm to be tested and the grid connection points of other offshore wind farms; if it is determined that there are no other offshore wind farms connected to the offshore wind farm to be tested, perform power quality tests on the grid connection point of the offshore wind farm to be tested, and obtain normal operating power quality test index values ​​corresponding to the grid connection point of the offshore wind farm to be tested, wherein the normal operating power quality test index values ​​include voltage deviation, long-term flicker value, harmonic current, interharmonic voltage, and three-phase voltage imbalance;

[0013] S4. According to the operating status of the offshore wind farm to be tested, a corresponding power quality index limit is obtained by matching in a local database, and the power quality test index value is compared with the corresponding power quality index limit to obtain a power quality index comparison result;

[0014] S5. Based on a preset evaluation rule, the power quality of the offshore wind farm to be measured is evaluated according to the power quality index comparison result to obtain a power quality evaluation result of the offshore wind farm to be measured.

[0015] Preferably, the method further comprises:

[0016] The output power of the offshore wind farm to be tested is increased from 0 to 100% of the rated power, with 10% of the rated power as the power interval. In each phase of each power interval, the instantaneous voltage measurement values ​​and the instantaneous current measurement values ​​of multiple preset time series of preset test points in a preset effective test period are collected. The maximum values ​​corresponding to the voltage deviation, long-term flicker value, harmonic current, interharmonic voltage and three-phase voltage imbalance of each preset test point are also collected. Among them, the preset effective test period is the period when more than 95% of the wind turbines in the wind farm are put into normal operation.

[0017] Preferably, before step S4, the following steps are included:

[0018] S41. Setting power quality index limits according to the operating status of the offshore wind farm to be tested. If the operating status of the offshore wind farm to be tested is an outage state, setting background power quality test index limits; if the operating status of the offshore wind farm to be tested is normal operation, setting normal operation power quality test index limits;

[0019] S42. Construct a mapping relationship between the operating status of the offshore wind farm to be tested and its corresponding power quality test index limit, and store the mapping relationship in a local database.

[0020] Preferably, step S4 specifically includes:

[0021] S401. According to the operating state of the offshore wind farm to be tested, a corresponding power quality index limit is obtained by matching in a local database. If the operating state of the offshore wind farm to be tested is an outage state, a background power quality test index limit is obtained by matching in the local database, and step S402 is executed; if the operating state of the offshore wind farm to be tested is a normal operating state, a normal operating power quality test index limit is obtained by matching in the local database, and step S403 is executed.

[0022] S402: Compare the background power quality test index value with the background power quality test index limit; if the background power quality test index value exceeds the background power quality test index limit, determine that the corresponding background power quality test index value is unqualified; if the background power quality test index value does not exceed the background power quality test index limit, determine that the corresponding background power quality test index value is qualified;

[0023] S403. Compare the normal operating power quality test index value with the normal operating power quality test index limit; if the normal operating power quality test index value exceeds the normal operating power quality test index limit, determine that the corresponding normal operating power quality test index value is unqualified; if the normal operating power quality test index value does not exceed the normal operating power quality test index limit, determine that the corresponding normal operating power quality test index value is qualified.

[0024] Preferably, the method further comprises:

[0025] According to the operating status of the offshore wind farm to be tested, the corresponding evaluation rules are matched in the local database. The evaluation rules include:

[0026] If the operating state of the offshore wind farm to be tested is an outage state, then determining the power quality evaluation result of the offshore wind farm to be tested according to the comparison result of the power quality indicators corresponding to the grid connection point of the offshore wind farm to be tested;

[0027] If the operating state of the offshore wind farm to be tested is a normal operating state and no other offshore wind farm is connected to the offshore wind farm to be tested, then determining the power quality evaluation result of the offshore wind farm to be tested according to the comparison result of the power quality indicators corresponding to the grid connection point of the offshore wind farm to be tested;

[0028] If the operating status of the offshore wind farm to be tested is a normal operating status and other offshore wind farms are connected to the offshore wind farm to be tested, the power quality evaluation result of the offshore wind farm to be tested is determined by jointly coordinating the comparison results of the power quality indicators corresponding to the grid connection point of the offshore wind farm to be tested and the grid connection points of other offshore wind farms to which it is connected.

[0029] In a second aspect, the present invention further provides an offshore wind farm power quality testing system for executing the above-mentioned offshore wind farm power quality testing method, comprising: a data acquisition terminal, a local data processing terminal, a communication module, and a remote control terminal, wherein the data acquisition terminal is connected to the local data processing terminal via a wired communication interface, and both the data acquisition terminal and the local data processing terminal are communicatively connected to the remote control terminal via the communication module;

[0030] The data acquisition terminal is used to obtain the operating status of the offshore wind farm to be tested, and the operating status includes the shutdown state and the normal operating state; it is also used to perform power quality tests on preset test points according to the operating status of the offshore wind farm to be tested, collect voltage data and current data of the preset test points, and is also used to perform power quality tests on the grid connection points of the offshore wind farm to be tested if the operating status of the offshore wind farm to be tested is the shutdown state, and obtain background power quality test index values, and the background power quality test index values ​​include voltage deviation, long-term flicker value, harmonic voltage, interharmonic voltage, three-phase voltage total harmonic distortion rate and three-phase voltage imbalance; it is also used to judge the topology of the offshore wind farm to be tested if the operating status of the offshore wind farm to be tested is the normal operating state. Determine whether there are other offshore wind farms connected to the offshore wind farm to be tested; if it is determined that there are other offshore wind farms connected to the offshore wind farm to be tested, perform power quality tests on the grid connection point of the offshore wind farm to be tested and the grid connection points of other offshore wind farms to which it is connected, respectively, to obtain normal operating power quality test index values ​​corresponding to the grid connection point of the offshore wind farm to be tested and the grid connection points of other offshore wind farms; if it is determined that there are no other offshore wind farms connected to the offshore wind farm to be tested, perform power quality tests on the grid connection point of the offshore wind farm to be tested, and obtain normal operating power quality test index values ​​corresponding to the grid connection point of the offshore wind farm to be tested, wherein the normal operating power quality test index values ​​include voltage deviation, long-term flicker value, harmonic current, interharmonic voltage and three-phase voltage imbalance;

[0031] The data local processing terminal is used to receive the voltage data, current data, the background power quality test index value and the normal operating power quality test index value corresponding to the preset test point, and is also used to match the corresponding power quality index limit value in the local database according to the operating status of the offshore wind farm to be tested, compare the power quality test index value with its corresponding power quality index limit value, and obtain a power quality index comparison result; it is also used to evaluate the power quality of the offshore wind farm to be tested based on the power quality index comparison result based on preset evaluation rules, and obtain a power quality evaluation result of the offshore wind farm to be tested; it is also used to send the voltage data, current data, the background power quality test index value, the normal operating power quality test index value, the power quality index comparison result and the power quality evaluation result corresponding to the preset test point to the remote control terminal for remote viewing by the user.

[0032] Preferably, the data acquisition terminal includes a power quality data acquisition device and a wind farm energy management module;

[0033] The power quality data acquisition device is used to collect voltage data and current data of preset test points of the wind farm to be tested, and is also used to calculate background power quality test index values ​​and normal operation power quality test index values;

[0034] The wind farm energy management module is used to collect the active power and wind turbine operating status data of the wind farm to be tested.

[0035] Preferably, the data local processing terminal is connected to the power quality data acquisition device via a wired communication interface; the data local processing terminal is used to receive the voltage and current data and the background power quality test index value and the normal operation power quality test index value collected by the power quality data acquisition device;

[0036] It is also used to configure parameters of the power quality data acquisition device, the parameter configuration includes the transformation ratio of voltage data and the transformation ratio of current data, and is also used to locally store the voltage data, current data, background power quality test index values, and normal operating power quality test index values ​​collected by the power quality data acquisition device, and is also used to determine whether the number of samples of voltage data and current data collected by the power quality data acquisition device meets the preset number of samples.

[0037] Preferably, the remote control terminal is connected to the energy management module through the communication module, and is used to obtain the active power and wind turbine operating status data of the wind farm to be tested collected by the energy management module; it is also used to determine whether the power quality test is a valid test period, wherein the valid test period is a period when more than 95% of the wind turbines in the wind farm are put into normal operation; it is also used to monitor the operating status of the power quality data acquisition equipment and the data local processing terminal.

[0038] It can be seen from the above technical solutions that the present invention has the following advantages:

[0039] The present invention performs a power quality test according to the operating status of the offshore wind farm to be tested, and different operating statuses correspond to different test points. The power quality test is performed on the preset test points to obtain the power quality test index value corresponding to the operating status. It also determines whether other offshore wind farms are connected to the offshore wind farm to be tested based on the topological structure of the offshore wind farm to be tested. If it is determined that other offshore wind farms are connected to the offshore wind farm to be tested, power quality tests are performed on the grid connection point of the offshore wind farm to be tested and the grid connection points of other offshore wind farms connected to it, and power quality test index values ​​corresponding to the two grid connection points are obtained. The power quality test index value is compared with the corresponding power quality index limit value. Based on the preset evaluation rules, the power quality of the offshore wind farm to be tested is evaluated according to the power quality index comparison result to determine whether the power quality of the offshore wind farm to be tested is qualified. The present invention takes into account offshore wind farms with different topological structures and operating statuses, adds two indicators, voltage deviation and three-phase voltage imbalance, and improves the accuracy of offshore wind farm power quality testing. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 A flow chart of a method for testing power quality of an offshore wind farm provided by an embodiment of the present invention;

[0041] Figure 2 A schematic diagram of a topological structure in which other offshore wind farms are connected to the offshore wind farm to be tested, provided in an embodiment of the present invention;

[0042] Figure 3 A schematic diagram of a topological structure of an offshore wind farm to be tested connected to other offshore wind farms provided in an embodiment of the present invention;

[0043] Figure 4 A schematic diagram of a topological structure of an offshore wind farm to be tested provided by an embodiment of the present invention without any other offshore wind farms connected thereto;

[0044] Figure 5 A schematic structural diagram of a power quality testing system for an offshore wind farm provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0045] In order to enable those skilled in the art to better understand the solutions of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts shall fall within the scope of protection of the present invention.

[0046] For easier understanding, see Figure 1 The present invention provides a method for testing the power quality of an offshore wind farm, comprising the following steps:

[0047] S1. Obtain the operating status of the offshore wind farm to be tested, where the operating status includes a shutdown state and a normal operating state.

[0048] S2. Perform power quality tests on preset test points based on the operating status of the offshore wind farm to be tested. If the operating status of the offshore wind farm to be tested is an outage state, perform power quality tests on the grid connection point of the offshore wind farm to be tested to obtain background power quality test index values, which include voltage deviation, long-term flicker value, harmonic voltage, interharmonic voltage, three-phase voltage total harmonic distortion rate, and three-phase voltage imbalance. Then execute step S4. If the operating status of the offshore wind farm to be tested is a normal operating state, execute the next step.

[0049] Among them, the test cycle of the test point of the background power quality test index value is 24 hours. When conducting power quality testing, the voltage signal test point is the voltage of the wind farm grid connection point, and the current signal test point is the wind farm transmission line current.

[0050] S3. Determine whether there are other offshore wind farms connected to the offshore wind farm to be tested based on the topological structure of the offshore wind farm to be tested. If it is determined that there are other offshore wind farms connected to the offshore wind farm to be tested, Figure 2 and 3 As shown, Figure 2 The topological structure diagram of the offshore wind farm to be tested with other offshore wind farms connected to it is shown. Figure 3 The topological structure diagram of the offshore wind farm to be tested connected to other offshore wind farms is shown. The grid connection points of the offshore wind farm to be tested and the grid connection points of other offshore wind farms to which it is connected are respectively subjected to power quality tests to obtain the normal operation power quality test index values ​​corresponding to the grid connection points of the offshore wind farm to be tested and the grid connection points of other offshore wind farms. If it is determined that no other offshore wind farms are connected to the offshore wind farm to be tested, such as Figure 4 As shown, Figure 4A schematic diagram of the topological structure of the offshore wind farm to be tested (independent offshore wind farm) is shown. The grid connection point of the offshore wind farm to be tested is subjected to a power quality test to obtain the normal operating power quality test index values ​​corresponding to the grid connection point of the offshore wind farm to be tested. The normal operating power quality test index values ​​include voltage deviation, long-term flicker value, harmonic current, interharmonic voltage and three-phase voltage imbalance.

[0051] The voltage signal test points are the grid connection point voltage of this wind farm and the grid connection point voltage of other wind farms connected to this wind farm, and the current signal test points are the outgoing line current of this wind farm and the incoming line current of other wind farms.

[0052] In one example, if there are few submarine cables outgoing from the wind farm booster station under test and the actual distance between the measurement terminals corresponding to each test signal is short, and if other offshore wind farms transmit power through this offshore wind farm, the onshore currents of all outgoing submarine cables from the wind farm booster station under test and the high-voltage side currents of the SVG step-down transformer can be used as current signal test points during normal operation power quality testing. During power quality testing, the current signals from all test points can be synchronously added together via a synchronization line, and the summed result can be used to evaluate the power quality of the current generated by the wind farm under test.

[0053] Long-term flicker value P caused by wind farm alone lt2 According to the formula Calculated, where P lt2 is the long-term flicker value at time t2, P lt0 is the long-term flicker value at time t0, P lt1 is the long-term flicker value at time t1.

[0054] In one example, the output power of the offshore wind farm to be tested needs to be increased from 0 to 100% of the rated power, with 10% of the rated power as the power interval. The instantaneous voltage measurement values ​​and instantaneous current measurement values ​​of multiple preset time series of preset test points in each phase of each power interval are collected. The maximum values ​​corresponding to the voltage deviation, long-term flicker value, harmonic current, interharmonic voltage and three-phase voltage imbalance of each preset test point are also collected. Among them, the preset effective test period is the period when more than 95% of the wind turbines in the wind farm are put into normal operation.

[0055] S4. According to the operating status of the offshore wind farm to be tested, the corresponding power quality index limit is matched in the local database, and the power quality test index value is compared with the corresponding power quality index limit to obtain a power quality index comparison result.

[0056] Among them, the power quality test index value includes the background power quality index value and the normal operation power quality test index value.

[0057] S5. Based on a preset evaluation rule, the power quality of the offshore wind farm to be measured is evaluated according to the comparison result of the power quality indicators to obtain a power quality evaluation result of the offshore wind farm to be measured.

[0058] It should be noted that the present invention provides a method for testing the power quality of an offshore wind farm. The power quality test is performed according to the operating state of the offshore wind farm to be tested. Different operating states correspond to different test points. The power quality test is performed on the preset test points to obtain the power quality test index value corresponding to the operating state. It is also determined based on the topological structure of the offshore wind farm to be tested whether there are other offshore wind farms connected to the offshore wind farm to be tested. If it is determined that there are other offshore wind farms connected to the offshore wind farm to be tested, the grid connection point of the offshore wind farm to be tested and the other offshore wind farms connected to it are connected. The grid connection points of the wind farm are respectively subjected to power quality tests, and the power quality test index values ​​corresponding to the two grid connection points are obtained. The power quality test index values ​​are compared with their corresponding power quality index limits. Based on the preset evaluation rules, the power quality of the offshore wind farm to be tested is evaluated according to the power quality index comparison results to determine whether the power quality of the offshore wind farm to be tested is qualified. It takes into account offshore wind farms with different topological structures and operating conditions, adds two indicators, voltage deviation and three-phase voltage imbalance, and improves the accuracy of offshore wind farm power quality testing.

[0059] In a specific embodiment, step S4 includes:

[0060] S41. Set power quality index limits according to the operating status of the offshore wind farm to be tested. If the operating status of the offshore wind farm to be tested is an outage state, set background power quality test index limits; if the operating status of the offshore wind farm to be tested is normal operation, set normal operation power quality test index limits.

[0061] S42. Construct a mapping relationship between the operating status of the offshore wind farm to be tested and its corresponding power quality test index limit, and store the mapping relationship in a local database.

[0062] In one example, setting a background power quality indicator limit includes:

[0063] Voltage deviation: According to GB / T 12325-2008, the sum of the absolute values ​​of positive and negative deviations of the supply voltage of 35kV and above should not exceed 10% of the nominal grid voltage, where the nominal grid voltage is 220kV. If the upper and lower voltage deviations have the same sign (both positive or negative), the larger absolute value of the deviation shall be used as the measurement basis.

[0064] Harmonic voltage and total harmonic distortion rate of three-phase voltage: According to GB / T 14549-93, the harmonic voltage (phase voltage) limits of 220kV public power grid are shown in Table 1.

[0065] Table 1 Harmonic voltage limits of public power grid

[0066]

[0067] Interharmonic voltage: According to the national standard GB / T 24337-2009, the interharmonic voltage content rate at the common connection point (PCC) of the 220kV power system should not exceed the limit values ​​in Table 2.

[0068] Table 2 Interharmonic voltage content rate limit (%)

[0069]

[0070] Three-phase voltage imbalance: According to the national standard GB / T 15543-2008, when the power grid is operating normally, the negative sequence voltage imbalance at the common connection point of the power system shall not exceed 2%, and shall not exceed 4% for a short time.

[0071] Setting normal power quality indicator limits includes:

[0072] Voltage deviation: According to GB / T 19963.1-2021, for wind farms connected to the public power grid with a voltage level of 220kV and below, the voltage deviation should be within the range of -3% to +7% of the nominal voltage; for wind farms in a wind farm group that are boosted to a voltage level of 500kV through a 220kV wind power collection system and connected to the public power grid, the voltage deviation should be within the range of 0% to +10% of the nominal voltage.

[0073] Flicker: According to GB / T 12326-2008, the long-term flicker value Plt2 should meet the flicker limit requirements in Table 3.

[0074] Table 3 Flicker Limits

[0075]

[0076] For a single high-voltage interference source, that is, a wind farm alone, the long-term flicker caused by the source must be less than the assigned flicker limit. The flicker limit for each source is determined based on the ratio of its grid-connected capacity Si to its total power supply capacity St, taking into account factors such as the impact of flicker transmission from the previous level to the next (transmission from the next level to the previous level is generally ignored). The flicker limit for a wind farm is calculated as follows.

[0077] First, find the total limit value G of flicker generated by all loads connected to the PCC point:

[0078]

[0079] Where: L P is the long-term flicker value P corresponding to the voltage level of the PCC point lt Limit value; L H is the long-term flicker value P of the previous voltage level lt Limit value; T is the flicker transfer coefficient from the previous voltage level to the next voltage level, recommended to be 0.8. Flicker transfer from the extra-high voltage (EHV) system to the next voltage level system is not considered.

[0080] Wind farm flicker limit E i for:

[0081]

[0082] Where: F is the simultaneous coefficient of fluctuating load, which is 0.3 (but must meet S i / F≤S t )

[0083] Harmonic current: According to GB / T 14549-93, the harmonic current components injected into the 220kV common connection point by all users should not exceed the allowable values ​​shown in Table 4.

[0084] Table 4 Permissible values ​​of harmonic current injected into the common connection point

[0085] The allowable value of harmonic current injected into the power grid by a single user must also be converted according to the following method.

[0086] (1) Allowable value of harmonic current injected into the common connection point

[0087]

[0088] When the minimum short-circuit capacity at the common connection point is different from the reference short-circuit capacity in Table 4, the allowable value of the total harmonic current injected into the common connection point shall be corrected as follows:

[0089]

[0090] Where: S k1 - minimum short-circuit capacity of the common connection point, MVA;

[0091] S k2 ——Benchmark short-circuit capacity, MVA;

[0092] I hp ——the hth harmonic current allowable value specified in the regulations, A;

[0093] I h ——Permissible value of the hth harmonic current when the short-circuit capacity is Sk1, A.

[0094] (2) Allowable value of harmonic current injected into the common connection point by a single interference source

[0095] The allowable value of the hth harmonic current of the i-th user at the common connection point is calculated as follows:

[0096] I hi =I h ·(S i / S t ) 1 / α

[0097] Where: I h ——the allowable value of the hth harmonic current of the node, A;

[0098] S i ——The power consumption capacity of the interference source, MVA;

[0099] S t - capacity of the power supply equipment at the point of common connection, MVA;

[0100] α——Phase superposition coefficient, take the value according to Table 5.

[0101] Table 5 Phase superposition coefficient of harmonics

[0102] h 3 5 7 11 13 9|>13|even times α 1.1 1.2 1.4 1.8 1.9 2

[0103] Interharmonic voltage: According to the national standard GB / T 24337-2009, the interharmonic voltage content rate at the common connection point (PCC) of the 220kV power system should not exceed the limit values ​​in Table 2.

[0104] Three-phase voltage imbalance: According to the national standard GB / T 15543-2008, when the power grid is operating normally, the negative sequence voltage imbalance at the common connection point of the power system shall not exceed 2%, and shall not exceed 4% for a short time.

[0105] Wherein, for a topological structure in which the offshore wind farm to be tested has other connected offshore wind farms, the wind farm capacity used for the power quality limit of the offshore wind farm to be tested is the total capacity of the wind farm itself and the connected wind farms.

[0106] In a specific embodiment, step S4 specifically includes:

[0107] S401. According to the operating state of the offshore wind farm to be tested, the corresponding power quality index limit is matched in the local database. If the operating state of the offshore wind farm to be tested is an outage state, the background power quality test index limit is matched in the local database, and step S402 is executed; if the operating state of the offshore wind farm to be tested is a normal operating state, the normal operating power quality test index limit is matched in the local database, and step S403 is executed.

[0108] S402. Compare the background power quality test index value with the background power quality test index limit value. If the background power quality test index value exceeds the background power quality test index limit value, determine that the corresponding background power quality test index value is unqualified. If the background power quality test index value does not exceed the background power quality test index limit value, determine that the corresponding background power quality test index value is qualified.

[0109] S403. Compare the normal operating power quality test index value with the normal operating power quality test index limit. If the normal operating power quality test index value exceeds the normal operating power quality test index limit, determine that the corresponding normal operating power quality test index value is unqualified. If the normal operating power quality test index value does not exceed the normal operating power quality test index limit, determine that the corresponding normal operating power quality test index value is qualified.

[0110] In a specific embodiment, the method further comprises:

[0111] The corresponding evaluation rules are matched in the local database according to the operating status of the offshore wind farm to be tested. The evaluation rules include:

[0112] If the operating state of the offshore wind farm to be tested is an outage state, then determining the power quality evaluation result of the offshore wind farm to be tested according to the comparison result of the power quality indicators corresponding to the grid connection point of the offshore wind farm to be tested;

[0113] If the operating state of the offshore wind farm to be tested is a normal operating state and no other offshore wind farm is connected to the offshore wind farm to be tested, then the power quality evaluation result of the offshore wind farm to be tested is determined according to the comparison result of the power quality indicators corresponding to the grid connection point of the offshore wind farm to be tested;

[0114] If the operating status of the offshore wind farm to be tested is normal operation and other offshore wind farms are connected to the offshore wind farm to be tested, the power quality evaluation result of the offshore wind farm to be tested is determined by coordinating the comparison results of the power quality indicators corresponding to the grid connection point of the offshore wind farm to be tested and the grid connection points of other offshore wind farms to which it is connected.

[0115] Among them, the power quality evaluation principles of offshore wind farms are shown in Table 6.

[0116] Table 6 Principles for evaluating power quality of offshore wind farms

[0117]

[0118] It should be noted that determination is an objective evaluation and recognition is a subjective judgment of the applicability of the project.

[0119] The above is a detailed description of an embodiment of an offshore wind farm power quality testing method provided by the present invention. The following is a detailed description of an embodiment of an offshore wind farm power quality testing system provided by the present invention.

[0120] like Figure 5 As shown, the present invention provides an offshore wind farm power quality test system for executing the above-mentioned offshore wind farm power quality test method, comprising: a data acquisition terminal 1, a local data processing terminal 2, a communication module 3, and a remote control terminal 4. The data acquisition terminal 1 is connected to the local data processing terminal 2 via a wired communication interface, and both the data acquisition terminal 1 and the local data processing terminal 2 are communicatively connected to the remote control terminal 4 via the communication module 3.

[0121] The data acquisition terminal 1 is used to obtain the operating status of the offshore wind farm to be tested, and the operating status includes the shutdown state and the normal operating state; it is also used to perform power quality tests on preset test points according to the operating status of the offshore wind farm to be tested, collect voltage data and current data of the preset test points, and is also used to perform power quality tests on the grid connection points of the offshore wind farm to be tested if the operating status of the offshore wind farm to be tested is the shutdown state, and obtain background power quality test index values, which include voltage deviation, long-term flicker value, harmonic voltage, interharmonic voltage, three-phase voltage total harmonic distortion rate and three-phase voltage imbalance; it is also used to judge the topology of the offshore wind farm to be tested if the operating status of the offshore wind farm to be tested is the normal operating state. Determine whether there are other offshore wind farms connected to the offshore wind farm to be tested. If it is determined that there are other offshore wind farms connected to the offshore wind farm to be tested, perform power quality tests on the grid connection point of the offshore wind farm to be tested and the grid connection points of other offshore wind farms to which it is connected, and obtain normal operating power quality test index values ​​corresponding to the grid connection point of the offshore wind farm to be tested and the grid connection points of other offshore wind farms. If it is determined that there are no other offshore wind farms connected to the offshore wind farm to be tested, perform power quality tests on the grid connection point of the offshore wind farm to be tested, and obtain normal operating power quality test index values ​​corresponding to the grid connection point of the offshore wind farm to be tested. The normal operating power quality test index values ​​include voltage deviation, long-term flicker value, harmonic current, interharmonic voltage and three-phase voltage imbalance;

[0122] The data local processing terminal 2 is used to receive voltage data, current data, background power quality test index values ​​and normal operating power quality test index values ​​corresponding to preset test points, and is also used to match the corresponding power quality index limit values ​​in the local database according to the operating status of the offshore wind farm to be tested, compare the power quality test index values ​​with their corresponding power quality index limit values, and obtain power quality index comparison results; it is also used to evaluate the power quality of the offshore wind farm to be tested based on the power quality index comparison results based on preset evaluation rules, and obtain the power quality evaluation results of the offshore wind farm to be tested; it is also used to send the voltage data, current data, background power quality test index values, normal operating power quality test index values, power quality index comparison results and power quality evaluation results corresponding to the preset test points to the remote control terminal 4 for remote viewing by the user.

[0123] In a specific embodiment, the data acquisition terminal 1 includes a power quality data acquisition device and a wind farm energy management module;

[0124] The power quality data acquisition equipment is used to collect voltage data and current data of preset test points of the wind farm to be tested, and is also used to calculate background power quality test index values ​​and normal operation power quality test index values.

[0125] The power quality data acquisition device may be a portable power quality data acquisition device.

[0126] The wind farm energy management module is used to collect the active power and wind turbine operating status data of the wind farm to be tested.

[0127] Among them, the wind farm energy management module mainly collects the wind farm active power and wind turbine operating status data, and sends it to the remote control terminal 4 through the communication module 3 to count whether more than 95% of the wind turbines in the wind farm are in normal operation during the power quality test.

[0128] In a specific embodiment, the data local processing terminal 2 is connected to the power quality data acquisition device via a wired communication interface; the data local processing terminal 2 is used to receive the voltage and current data and the background power quality test index value and the normal operation power quality test index value collected by the power quality data acquisition device;

[0129] It is also used to configure parameters of the power quality data acquisition device, including the transformation ratio of voltage data and the transformation ratio of current data. It is also used to locally store the voltage data, current data, background power quality test index values ​​and normal operating power quality test index values ​​collected by the power quality data acquisition device. It is also used to determine whether the number of samples of voltage data and current data collected by the power quality data acquisition device meets the preset number of samples.

[0130] The local data processing terminal 2 may be a portable local power quality data processing computer, which mainly has the following features and functions:

[0131] (1) It is connected to the portable power quality data acquisition device through a wired communication interface to achieve two-way high-speed and reliable data transmission; it can receive the voltage, current data and other required physical quantity data uploaded by the power quality data acquisition device in real time.

[0132] Before data collection, the parameters of the power quality data acquisition equipment can be configured, including but not limited to setting the transformation ratio of voltage and current data, selecting other required physical quantity data, etc., setting the storage time of each data packet, for example, according to standard requirements, setting the storage time of each data packet to 10 minutes, storage path, file name format of storage file, etc.; on the other hand, during the data collection process, the data is stored in real time in the portable power quality data local processing computer itself (such as a local hard disk) or an external storage medium (such as a mobile hard disk).

[0133] By analyzing and statistically processing each data packet, the effectiveness and quantity of the collected data can be judged based on the statistical results. For example, the output power of the wind farm ranges from 0 to 100% of the rated power, with 10% of the rated power as the interval. The 10-minute time series instantaneous current and voltage measurement values ​​collected at the wind farm grid connection point in each power interval and each phase must reach 5 or more.

[0134] At the same time, using the communication module 3, the energy management module sends the wind farm active power and wind turbine operating status data to the remote control terminal 4. The local power quality data processing computer can receive remote monitoring instructions from the remote control computer, allowing test personnel to remotely view the operating status of the data acquisition terminal and the local data processing terminal, and remotely control them and analyze test data.

[0135] Remote control terminal 4 and local data processing terminal 2 are connected via communication module 3, enabling two-way communication. Communication module 3 is equipped with a wired / wireless network card and has a fixed IP address, allowing for wired / wireless access to the Internet. Remote control terminal 4 accesses local data processing terminal 2 via TCP / IP protocol, enabling two-way data transmission.

[0136] In a specific embodiment, the remote control terminal 4 is connected to the energy management module through the communication module 3, and is used to obtain the active power and wind turbine operating status data of the wind farm to be tested collected by the energy management module; it is also used to determine whether the power quality test is a valid test period, wherein the valid test period is a period when more than 95% of the wind turbines in the wind farm are put into normal operation; it is also used to monitor the operating status of the power quality data acquisition equipment and the data local processing terminal 2.

[0137] The remote control terminal 4 may be a remote control computer, which can remotely monitor the data local processing terminal 2 via a wired / wireless network and the communication module 3 .

[0138] In this embodiment, the remote control terminal 4 is installed with remote control software, connected to the energy management module through the communication module 3, and receives the active power of the wind farm and the operating status data of the wind turbines. It can regularly count the time period during the test when more than 95% of the wind turbines in the wind farm are put into normal operation, that is, the effective test period; and count the power range of the active power in the corresponding effective test period, and preliminarily evaluate whether the test data can cover all power ranges of 0%-100% of the wind farm, and whether there are more than 5 consecutive 10-minute sequences in each 10% power range.

[0139] In addition, the remote control terminal 4 can be used to check the equipment status of the power quality data acquisition equipment and the local data processing terminal 2 online at any time, such as whether there is a power outage, freeze, or abnormality. Once an abnormality occurs, the wind farm on-site operation and maintenance personnel will be notified in time for processing; the results of the power quality data analysis and statistical software can also be checked at any time.

[0140] Combined with the preliminary assessment of the energy management platform, further determine whether the on-site test data is sufficient. When the amount of valid data collected is sufficient, go to the wind farm site to dismantle the portable power quality data collection equipment, portable power quality data local processing computer, etc., restore the test site to the state before the test, and complete the normal operation power quality test. If the amount of valid data collected is insufficient, continue the test.

[0141] When the wind farm is out of power and the conditions for background power quality testing are met, local 24h continuous power quality testing can be carried out using only portable power quality data acquisition equipment and portable power quality data local processing computers.

[0142] Those skilled in the art will clearly understand that, for the convenience and brevity of description, the specific working process of the system described above can refer to the corresponding process in the aforementioned method embodiment, and will not be repeated here.

[0143] In the several embodiments provided by the present invention, it should be understood that the disclosed devices and methods can be implemented in other ways. For example, the device embodiments described above are merely illustrative. For example, the division of units is merely a logical function division. In actual implementation, there may be other division methods, such as multiple units or components can be combined or integrated into another system, or some features can be ignored or not executed. In addition, the mutual coupling or direct coupling or communication connection shown or discussed can be through some interface, indirect coupling or communication connection of devices or units, which can be electrical, mechanical or other forms.

[0144] Units described as separate components may or may not be physically separate, and components shown as units may or may not be physical units, that is, they may be located in one place or distributed across multiple network units. Some or all of these units may be selected to achieve the purpose of this embodiment according to actual needs.

[0145] In addition, the functional units in the various embodiments of the present invention may be integrated into a single processing unit, each unit may exist physically separately, or two or more units may be integrated into a single unit. The aforementioned integrated units may be implemented in the form of hardware or software functional units.

[0146] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A method for testing power quality of an offshore wind farm, characterized in that: The following steps are involved: S1. Obtaining the operating status of the offshore wind farm to be tested, where the operating status includes an outage state and a normal operating state; S2. Performing a power quality test on a preset test point based on the operating status of the offshore wind farm to be tested. If the operating status of the offshore wind farm to be tested is an outage state, performing a power quality test on the grid connection point of the offshore wind farm to be tested to obtain background power quality test index values, which include voltage deviation, long-term flicker value, harmonic voltage, interharmonic voltage, three-phase voltage total harmonic distortion rate, and three-phase voltage imbalance, and executing step S4. If the operating status of the offshore wind farm to be tested is a normal operating state, executing the next step. S3. Determine whether there are other offshore wind farms connected to the offshore wind farm to be tested based on the topological structure of the offshore wind farm to be tested; if it is determined that there are other offshore wind farms connected to the offshore wind farm to be tested, perform power quality tests on the grid connection point of the offshore wind farm to be tested and the grid connection points of other offshore wind farms to which it is connected, respectively, to obtain normal operating power quality test index values ​​corresponding to the grid connection point of the offshore wind farm to be tested and the grid connection points of other offshore wind farms; if it is determined that there are no other offshore wind farms connected to the offshore wind farm to be tested, perform power quality tests on the grid connection point of the offshore wind farm to be tested, and obtain normal operating power quality test index values ​​corresponding to the grid connection point of the offshore wind farm to be tested, wherein the normal operating power quality test index values ​​include voltage deviation, long-term flicker value, harmonic current, interharmonic voltage, and three-phase voltage imbalance; S4. According to the operating status of the offshore wind farm to be tested, a corresponding power quality index limit is obtained by matching in a local database, and the power quality test index value is compared with the corresponding power quality index limit to obtain a power quality index comparison result; S5. Based on a preset evaluation rule, the power quality of the offshore wind farm to be measured is evaluated according to the power quality index comparison result to obtain a power quality evaluation result of the offshore wind farm to be measured.

2. The offshore wind farm power quality testing method according to claim 1, characterized in that: Also includes: The output power of the offshore wind farm to be tested is increased from 0 to 100% of the rated power, with 10% of the rated power as the power interval. In each phase of each power interval, the instantaneous voltage measurement values ​​and the instantaneous current measurement values ​​of multiple preset time series of preset test points in a preset effective test period are collected. The maximum values ​​corresponding to the voltage deviation, long-term flicker value, harmonic current, interharmonic voltage and three-phase voltage imbalance of each preset test point are also collected. Among them, the preset effective test period is the period when more than 95% of the wind turbines in the wind farm are put into normal operation.

3. The offshore wind farm power quality testing method according to claim 1, characterized in that: The steps before step S4 include: S41. Setting power quality index limits according to the operating status of the offshore wind farm to be tested. If the operating status of the offshore wind farm to be tested is an outage state, setting background power quality test index limits; if the operating status of the offshore wind farm to be tested is normal operation, setting normal operation power quality test index limits; S42. Construct a mapping relationship between the operating status of the offshore wind farm to be tested and its corresponding power quality test index limit, and store the mapping relationship in a local database.

4. The offshore wind farm power quality testing method according to claim 3, characterized in that: Step S4 specifically includes: S401. According to the operating state of the offshore wind farm to be tested, a corresponding power quality index limit is obtained by matching in a local database. If the operating state of the offshore wind farm to be tested is an outage state, a background power quality test index limit is obtained by matching in the local database, and step S402 is executed; if the operating state of the offshore wind farm to be tested is a normal operating state, a normal operating power quality test index limit is obtained by matching in the local database, and step S403 is executed. S402: Compare the background power quality test index value with the background power quality test index limit; if the background power quality test index value exceeds the background power quality test index limit, determine that the corresponding background power quality test index value is unqualified; if the background power quality test index value does not exceed the background power quality test index limit, determine that the corresponding background power quality test index value is qualified; S403. Compare the normal operating power quality test index value with the normal operating power quality test index limit; if the normal operating power quality test index value exceeds the normal operating power quality test index limit, determine that the corresponding normal operating power quality test index value is unqualified; if the normal operating power quality test index value does not exceed the normal operating power quality test index limit, determine that the corresponding normal operating power quality test index value is qualified.

5. The offshore wind farm power quality testing method according to claim 4, characterized in that: Also includes: According to the operating status of the offshore wind farm to be tested, the corresponding evaluation rules are matched in the local database. The evaluation rules include: If the operating state of the offshore wind farm to be tested is an outage state, then determining the power quality evaluation result of the offshore wind farm to be tested according to the comparison result of the power quality indicators corresponding to the grid connection point of the offshore wind farm to be tested; If the operating state of the offshore wind farm to be tested is a normal operating state and no other offshore wind farm is connected to the offshore wind farm to be tested, then determining the power quality evaluation result of the offshore wind farm to be tested according to the comparison result of the power quality indicators corresponding to the grid connection point of the offshore wind farm to be tested; If the operating status of the offshore wind farm to be tested is a normal operating status and other offshore wind farms are connected to the offshore wind farm to be tested, the power quality evaluation result of the offshore wind farm to be tested is determined by jointly coordinating the comparison results of the power quality indicators corresponding to the grid connection point of the offshore wind farm to be tested and the grid connection points of other offshore wind farms to which it is connected.

6. An offshore wind farm power quality testing system, used to execute the offshore wind farm power quality testing method according to any one of claims 1 to 5, characterized in that: include: A data acquisition terminal, a local data processing terminal, a communication module, and a remote control terminal, wherein the data acquisition terminal is connected to the local data processing terminal via a wired communication interface, and both the data acquisition terminal and the local data processing terminal are communicatively connected to the remote control terminal via the communication module; The data acquisition terminal is used to obtain the operating status of the offshore wind farm to be tested, and the operating status includes the shutdown state and the normal operating state; it is also used to perform power quality tests on preset test points according to the operating status of the offshore wind farm to be tested, collect voltage data and current data of the preset test points, and is also used to perform power quality tests on the grid connection points of the offshore wind farm to be tested if the operating status of the offshore wind farm to be tested is the shutdown state, and obtain background power quality test index values, and the background power quality test index values ​​include voltage deviation, long-term flicker value, harmonic voltage, interharmonic voltage, three-phase voltage total harmonic distortion rate and three-phase voltage imbalance; it is also used to judge the topology of the offshore wind farm to be tested if the operating status of the offshore wind farm to be tested is the normal operating state. Determine whether there are other offshore wind farms connected to the offshore wind farm to be tested; if it is determined that there are other offshore wind farms connected to the offshore wind farm to be tested, perform power quality tests on the grid connection point of the offshore wind farm to be tested and the grid connection points of other offshore wind farms to which it is connected, respectively, to obtain normal operating power quality test index values ​​corresponding to the grid connection point of the offshore wind farm to be tested and the grid connection points of other offshore wind farms; if it is determined that there are no other offshore wind farms connected to the offshore wind farm to be tested, perform power quality tests on the grid connection point of the offshore wind farm to be tested, and obtain normal operating power quality test index values ​​corresponding to the grid connection point of the offshore wind farm to be tested, wherein the normal operating power quality test index values ​​include voltage deviation, long-term flicker value, harmonic current, interharmonic voltage and three-phase voltage imbalance; The local data processing terminal is used to receive the voltage data, current data, the background power quality test index value, and the normal operation power quality test index value corresponding to the preset test point, and is further used to match the corresponding power quality index limit value in the local database according to the operating status of the offshore wind farm to be tested, and compare the power quality test index value with the corresponding power quality index limit value to obtain a power quality index comparison result; It is also used to evaluate the power quality of the offshore wind farm to be measured based on the power quality index comparison result based on a preset evaluation rule, and obtain a power quality evaluation result of the offshore wind farm to be measured; It is also used to send the voltage data, current data, background power quality test index value, normal operation power quality test index value, power quality index comparison result and power quality evaluation result corresponding to the preset test point to the remote control terminal for remote viewing by the user.

7. The offshore wind farm power quality testing system according to claim 6, characterized in that: The data acquisition terminal includes a power quality data acquisition device and a wind farm energy management module; The power quality data acquisition device is used to collect voltage data and current data of preset test points of the wind farm to be tested, and is also used to calculate background power quality test index values ​​and normal operation power quality test index values; The wind farm energy management module is used to collect the active power and wind turbine operating status data of the wind farm to be tested.

8. The offshore wind farm power quality testing system according to claim 7, characterized in that: The local data processing terminal is connected to the power quality data acquisition device via a wired communication interface; the local data processing terminal is used to receive the voltage and current data as well as the background power quality test index value and the normal operation power quality test index value collected by the power quality data acquisition device; It is also used to configure parameters of the power quality data acquisition device, the parameter configuration includes the transformation ratio of voltage data and the transformation ratio of current data, and is also used to locally store the voltage data, current data, background power quality test index values, and normal operating power quality test index values ​​collected by the power quality data acquisition device, and is also used to determine whether the number of samples of voltage data and current data collected by the power quality data acquisition device meets the preset number of samples.

9. The offshore wind farm power quality testing system according to claim 8, characterized in that: The remote control terminal is connected to the energy management module via the communication module, and is used to obtain the active power and wind turbine operating status data of the wind farm to be tested collected by the energy management module; It is also used to determine whether the power quality test is in a valid test period, wherein the valid test period is a period when more than 95% of the wind turbines in the wind farm are in normal operation; It is also used to monitor the operating status of the power quality data acquisition equipment and the data local processing terminal.

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