A method and system for testing frequency adaptability of reactive power compensation device in photovoltaic power station

Abstract

A method and system for testing frequency adaptability of reactive compensation devices in photovoltaic power stations, characterized in that the method comprises the following steps: Step 1, replacing the secondary voltage signal of the reactive compensation device connected to the photovoltaic power station with the input signal of the frequency disturbance generating device; Step 2, generating frequency signals of different frequencies based on the frequency disturbance generating device at the nominal voltage, and using the frequency signal to continuously disturb the reactive compensation device to obtain the output current of the reactive compensation device; Step 3, judging whether the frequency adaptability function of the reactive compensation device meets the requirements based on the output current of the reactive compensation device. The method of the present invention is simple in concept, convenient in implementation, time-saving, low in cost, and has accurate test results.

Description

Technical Field

[0001] The present invention relates to the technical field of renewable energy power generation, and more specifically, to a method and system for testing frequency adaptability of a reactive power compensation device in a photovoltaic power station. Background Art

[0002] With the continuous development of the economy and society, the continuous growth of energy production and consumption, the large-scale development and use of fossil energy has caused prominent problems such as resource shortage, environmental pollution, climate warming, glacier melting, and sea level rise, which seriously threaten human survival and sustainable development. According to statistics, my country's coal, oil, and natural gas reserve-production ratios are 31 years, 11.9 years, and 28 years, respectively, far below the world average. The high total energy consumption and high external dependence on oil and natural gas have led to a particularly severe energy situation. New energy sources such as photovoltaics and wind power are not only clean, efficient, and renewable, but also have abundant reserves. Therefore, the efficient use of clean energy, the transformation of energy structure, and clean energy substitution are strongly advocated. By the end of 2019, my country's cumulative installed capacity of new energy exceeded 400 million kilowatts, and the annual power generation of new energy was 510.2 billion kilowatt-hours. Among them, the installed capacity of wind power and solar power generation was 169 million and 177 million kilowatts, respectively, and the level of new energy utilization continued to improve.

[0003] However, there are still various problems in renewable energy power generation technology. For example, there is a lack of coordinated planning between renewable energy power generation and traditional power generation, and a lack of solutions for renewable energy power transmission and power consumption. Renewable energy power generation has the characteristics of randomness, intermittency, and distribution, which makes it difficult to adjust the frequency of generator sets and connect to the grid, and it is easy to cause shocks and dangers to the power grid. In addition, since renewable energy power generation is prone to frequency fluctuations, voltage fluctuations, voltage flickers, voltage drops, and harmonics, it will also lead to poor power quality, making it impossible to accurately formulate and implement power generation plans, which puts pressure on power grid dispatching.

[0004] In order to solve the above series of problems, the grid-connected operation technology and grid-connected operation strategy of new energy are constantly developing and improving. In the existing technology, reactive power compensation devices such as reactive power compensation devices are often used to measure and compensate for the voltage drop and voltage fluctuation of the power grid caused by the grid-connected process of new energy, so as to ensure the stability of the grid voltage, improve the performance of the grid, improve the transmission capacity, improve the power factor of the power supply and use system, and reduce power loss.

[0005] Taking SVG (Static VAR Generator) as an example, reactive power compensation devices, as one of the important links in the stable operation of the entire power system, have been widely used in photovoltaic power stations. Generally speaking, SVG consists of a converter and a DC side capacitor, so it can achieve the purpose of reactive power compensation by generating the reverse reactive current of the same magnitude required in the power grid. Due to the continuous regulation of reactive power, voltage imbalance, current harmonics and other problems in the power system where the photovoltaic power station is located can be suppressed.

[0006] However, there are various types of reactive power compensation devices with different performances. There is no equipment specifically used for photovoltaic power stations. Selecting a suitable reactive power compensation device is crucial to the performance of the power grid. In addition, with the access of large-scale photovoltaic power stations, the voltage and frequency fluctuations of the power grid have further intensified. When the frequency of the grid connection point fluctuates, the photovoltaic power station should keep running at the prescribed time. Its most important voltage regulation reactive power compensation device should have the same frequency adaptability as the photovoltaic power station. However, there is currently no reliable and convenient method to conduct capacity testing for this. Therefore, it is crucial to understand whether the reactive power compensation device and the photovoltaic power station have the same frequency adaptability.

[0007] The prior art CN112269087A discloses a high and low voltage ride-through capability detection system for a reactive compensation device. In this system, a method for detecting the performance of a reactive compensation device can only be performed through voltage changes, and protection of the safety of the power grid is achieved based on qualified equipment. However, only detecting the performance of a reactive compensation device based on voltage changes cannot fully guarantee the reliability of reactive compensation. For example, the major power outage in the UK on August 9, 2019 was caused by the simultaneous tripping of two power stations, resulting in a sharp drop in system frequency. If there is a reactive compensation device in this power grid system that provides reasonable compensation based on power disturbances and repeatedly meets the compensation requirements, the fault range will be further controlled and the power outage fault loss will be reduced. However, in the prior art, there is no method and system for determining the performance of a reactive compensation device based on power disturbances.

[0008] Therefore, in order to ensure that the reactive power compensation device and the power system in which the photovoltaic power station is located have the same or similar frequency adaptability, a method and system for testing the frequency adaptability of the reactive power compensation device of a photovoltaic power station is urgently needed. Summary of the invention

[0009] In order to solve the deficiencies in the prior art, the purpose of the present invention is to provide a method and system for testing the frequency adaptability of a reactive compensation device in a photovoltaic power station, by performing simulated frequency disturbances on the reactive compensation device to test the response of the reactive compensation device to different frequency disturbances, and obtain the frequency adaptability capability of the reactive compensation device.

[0010] The present invention adopts the following technical solution.

[0011] The first aspect of the present invention relates to a method for testing the frequency adaptability of a reactive compensation device in a photovoltaic power station, wherein the method comprises the following steps: step 1, replacing the secondary voltage signal of the reactive compensation device connected to the photovoltaic power station with the input signal of a frequency disturbance generating device; step 2, generating frequency signals of different frequencies based on the frequency disturbance generating device at the nominal voltage, and using the frequency signal to continuously disturb the reactive compensation device to obtain the output current of the reactive compensation device; step 3, determining whether the frequency adaptability function of the reactive compensation device meets the requirements based on the output current of the reactive compensation device.

[0012] Preferably, the nominal voltage of the frequency disturbance generating device is 100V.

[0013] Preferably, the frequency range of frequency signals of different frequencies is determined based on the allowable operating frequency of the photovoltaic power station inverter and the allowable grid-connected frequency of the photovoltaic power station specified in GB / T 34931-2017 Technical Specification for Detection of Reactive Compensation Devices in Photovoltaic Power Stations; the frequency range is between 48 Hz and 50.55 Hz.

[0014] Preferably, the frequencies of the frequency signal are set to 48.05 Hz and 49.45 Hz respectively, and the frequency signal is used to continuously disturb the reactive power compensation device for 600 seconds; if the reactive power compensation device cannot maintain continuous operation during the continuous disturbance, it is determined that the frequency adaptability function of the reactive power compensation device does not meet the requirements.

[0015] Preferably, the frequencies of the frequency signal are set to 49.55 Hz and 50.15 Hz respectively, and the frequency signal is used to continuously disturb the reactive power compensation device for 1800 s; if the reactive power compensation device cannot maintain continuous operation during the continuous disturbance, it is determined that the frequency adaptability function of the reactive power compensation device does not meet the requirements.

[0016] Preferably, the frequencies of the frequency signal are set to 50.25 Hz and 50.45 Hz respectively, and the frequency signal is used to continuously disturb the reactive power compensation device for 120 seconds; if the reactive power compensation device cannot maintain continuous operation during the continuous disturbance, it is determined that the frequency adaptability function of the reactive power compensation device does not meet the requirements.

[0017] Preferably, the frequency of the frequency signal is set to 50.55 Hz, and the frequency signal is used to continuously disturb the reactive power compensation device for 5 seconds; if the reactive power compensation device cannot stop running immediately, it is determined that the frequency adaptability function of the reactive power compensation device does not meet the requirements.

[0018] Preferably, if the reactive compensation device meets all of the following conditions, it is determined that the frequency adaptability function of the reactive compensation device meets the requirements: when the frequency of the frequency signal is 48.05 Hz or 49.45 Hz, the reactive compensation device continuously operates for more than 600 s; when the frequency of the frequency signal is 49.55 Hz or 50.15 Hz, the reactive compensation device continuously operates for more than 1800 s; when the frequency of the frequency signal is 50.25 Hz or 50.45 Hz, the reactive compensation device continuously operates for more than 120 s.

[0019] The second aspect of the present invention relates to a frequency adaptability testing system for a reactive compensation device in a photovoltaic power station as described in the frequency adaptability testing method for a reactive compensation device in a photovoltaic power station in the first aspect of the present invention, wherein the system comprises a photovoltaic distribution network, a reactive compensation device, a frequency disturbance generating device and a data recording and analyzing instrument; the photovoltaic distribution network is formed by photovoltaic power stations connected to both ends of a main substation and a power grid respectively; the reactive compensation device is connected to the photovoltaic distribution network, and its secondary side voltage signal input end is connected to the frequency disturbance generating device, for obtaining an output current based on a frequency signal generated by the frequency disturbance generating device; the data recording and analyzing instrument is respectively connected to the secondary side current loops of the frequency disturbance generating device and the reactive compensation device, for detecting and comparing the frequency signal and the output current.

[0020] Preferably, the reactive power compensation device collects the secondary voltage signal and the secondary current signal in the photovoltaic power distribution network respectively, and simultaneously accesses the frequency signal of the frequency disturbance generating device for frequency signal simulation based on the frequency disturbance generating device.

[0021] Preferably, one input port of the data recorder and analyzer is connected to the input signal of the frequency disturbance generating device, and the other input port is connected to the acquisition port of the secondary current signal in the reactive power compensation device.

[0022] Preferably, the frequency disturbance generating device is of three-phase four-wire type, the output frequency range is wider than 1-100 Hz, the output frequency error is lower than 0.002 Hz, and the signal generation period is less than or equal to 100 ms.

[0023] Preferably, the photovoltaic power distribution network has a voltage transformer and a current transformer for collecting secondary voltage signals and secondary current signals with a collection accuracy greater than or equal to level 0.2.

[0024] Preferably, the sampling frequency of the data recorder analyzer is greater than or equal to 20 kHz, and the bandwidth is greater than or equal to 2.5 kHz.

[0025] The beneficial effect of the present invention is that, compared with the prior art, the method and system for testing the frequency adaptability of a reactive power compensation device in a photovoltaic power station can test the reaction of the reactive power compensation device to different frequency disturbances by performing simulated frequency disturbances on the reactive power compensation device, and obtain the frequency adaptability of the reactive power compensation device. The method of the present invention is simple in concept, convenient in implementation, time-saving, low in cost, and has accurate test results.

[0026] The beneficial effects of the present invention also include:

[0027] 1. The method of the present invention does not measure based on voltage value, but selects the frequency disturbance value under the nominal voltage as the measurement parameter, so as to be more capable of calculating the active power component that mainly causes the frequency disturbance in the power grid. Usually, the deviation of active power occurs when the converter valve is locked due to continuous commutation failure, partial compliance or the power supply is suddenly disconnected from the grid due to a fault. Therefore, in the present invention, the frequency disturbance is measured, which can more accurately and effectively identify the problems of fault disconnection, converter valve locking, etc. in the power grid under the condition of fully eliminating interference, and provide effective compensation for the abnormal power grid output caused by the above problems.

[0028] 2. In the present invention, the reactive power compensation device used in the power system where the photovoltaic power station is located can realize performance testing through frequency disturbance, so that when frequency disturbance-related faults occur in the power grid, the device can be effectively ensured to operate stably, and reactive power support can be provided for the power system, thereby preventing huge risks and accidents related to frequency disturbances.

[0029] 3. The method of the present invention is based on the requirements of GB / T19964-2012 "Technical Regulations for Photovoltaic Power Station Access to Power System", and fully considers the allowable frequency of photovoltaic power station inverters, different operating modes of photovoltaic power stations, machine cutting strategies, grid connection strategies, power transmission strategies, etc., so as to set different test frequencies to accurately simulate the frequency disturbances that occur in the reactive compensation device during the actual operation of the photovoltaic power station, thereby ensuring the effectiveness and accuracy of the test.

[0030] 4. With the gradual advancement of the dual carbon goals and the gradual development of photovoltaic projects, the penetration rate of photovoltaic power generation in the future power grid will be further expanded, and the frequency fluctuations caused by photovoltaic power generation and other new energy power generation technologies will also become more frequent. The method in the present invention can make the power system where photovoltaic power stations and other new energy power stations are located have better frequency adaptability, so it is more in line with the needs of future development.

[0031] 5. Since the power grid simulation device is large in size and difficult to transport, the detection test needs to be carried out on the 35KV or 10KV high-voltage side, which has problems such as wiring difficulties, high safety risks, and long detection time. Therefore, the method of the present invention can avoid the occurrence of the above problems, provide a simple and convenient testing method, reduce wiring difficulties, risk factors, reduce detection time, and improve detection efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 It is a wiring diagram of a reactive power compensation device connected to a new energy plant in the prior art of the present invention;

[0033] Figure 2 A wiring diagram of a method and system for testing frequency adaptability of a reactive power compensation device in a photovoltaic power station according to the present invention;

[0034] Figure 3 It is a schematic diagram of an output current curve of a reactive power compensation device when the frequency signal is 48 Hz in a frequency adaptability test method of a reactive power compensation device in a photovoltaic power station of the present invention;

[0035] Figure 4 It is a schematic diagram of an output current curve of a reactive power compensation device when the frequency signal is 48.05 Hz in a frequency adaptability test method of a reactive power compensation device in a photovoltaic power station according to the present invention;

[0036] Figure 5 It is a schematic diagram of an output current curve of a reactive power compensation device when the frequency signal is 49.45 Hz in a frequency adaptability test method of a reactive power compensation device in a photovoltaic power station according to the present invention;

[0037] Figure 6 It is a schematic diagram of an output current curve of a reactive power compensation device when the frequency signal is 49.55 Hz in a frequency adaptability test method of a reactive power compensation device in a photovoltaic power station according to the present invention;

[0038] Figure 7 It is a schematic diagram of an output current curve of a reactive power compensation device when the frequency signal is 50.15 Hz in a frequency adaptability test method of a reactive power compensation device in a photovoltaic power station of the present invention;

[0039] Figure 8 It is a schematic diagram of an output current curve of a reactive power compensation device when the frequency signal is 50.25 Hz in a frequency adaptability test method of a reactive power compensation device in a photovoltaic power station according to the present invention;

[0040] Fig. 9 It is a schematic diagram of an output current curve of a reactive power compensation device when the frequency signal is 50.45 Hz in a frequency adaptability test method of a reactive power compensation device in a photovoltaic power station according to the present invention;

[0041] Fig.10It is a schematic diagram of an output current curve of a reactive power compensation device when the frequency signal is 50.55 Hz in a frequency adaptability testing method of a reactive power compensation device in a photovoltaic power station according to the present invention. DETAILED DESCRIPTION

[0042] The present application is further described below in conjunction with the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present invention, and cannot be used to limit the protection scope of the present application.

[0043] Figure 1 The figure is a wiring diagram of a reactive power compensation device connected to a new energy plant in the prior art of the present invention. Figure 1 As shown in Figure 1, reactive power compensation devices are widely used in power systems as one of the important links in the stability of power systems. For example, reactive power compensation devices are widely used in photovoltaic power stations to maintain voltage stability and achieve power wavelength.

[0044] exist Figure 1 In the process, the primary current signal and primary voltage signal of the reactive power compensation device are respectively connected to the primary end of the distribution network, that is, the current transformer and voltage transformer at the end where the photovoltaic power station is connected to the substation, to record the primary current and voltage in the power grid. The secondary current signal and secondary voltage signal are respectively connected to the secondary end of the distribution network, that is, the current transformer and voltage transformer set at the access point of the power grid that will affect the distribution network during the access process. In this way, the reactive power compensation device can measure the secondary current and secondary voltage in the power grid.

[0045] Specifically, the reactive power compensation device usually includes a converter and a DC side capacitor, wherein the converter can achieve reactive power compensation by generating the reactive current of the same magnitude in the opposite direction required by the power grid. Implementing the reactive power compensation device in this way can overcome the problems of high maintenance cost and slow response speed of the early reactive power compensation devices, and can achieve continuous regulation of reactive power while suppressing voltage imbalance and current harmonics.

[0046] However, when the reactive power compensation device is applied to a photovoltaic power station, it should be ensured that the reactive power compensation device has the same frequency adaptability as the photovoltaic power station. Otherwise, the reactive power compensation device will not only fail to achieve the same frequency adaptability as the photovoltaic power station, and thus fail to provide reasonable compensation to the distribution network when the photovoltaic power station is in different working states, but also fail to ensure the safe and stable operation of the distribution network to which the photovoltaic power station is connected.

[0047] In order to ensure that the reactive power compensation device has the same frequency adaptability as the photovoltaic power station, the present invention provides a method for testing the performance of the reactive power compensation device.

[0048] Figure 2 The figure is a wiring diagram of a method and system for testing frequency adaptability of a reactive power compensation device in a photovoltaic power station according to the present invention. Figure 2 As shown, the first aspect of the present invention relates to a method for testing the frequency adaptability of a reactive compensation device in a photovoltaic power station, wherein the method comprises the following steps: Step 1, replacing the secondary voltage signal of the reactive compensation device connected to the photovoltaic power station with the input signal of the frequency disturbance generating device; Step 2, generating frequency signals of different frequencies based on the frequency disturbance generating device at the nominal voltage, and using the frequency signal to continuously disturb the reactive compensation device to obtain the output current of the reactive compensation device; Step 3, judging whether the frequency adaptability function of the reactive compensation device meets the requirements based on the output current of the reactive compensation device.

[0049] It is understandable that in the present invention, the reactive power compensation device of the photovoltaic power station is connected differently from the usual connection method in the prior art. In order to implement the test, the input end of the actually connected secondary voltage signal can be disconnected and connected to the frequency disturbance generating device. In this way, the interference of the frequency disturbance generating device on the reactive power compensation device can be achieved. In one embodiment of the present invention, the reactive power compensation device can be a reactive power compensation device SVG.

[0050] During the detection process, the state of the reactive power compensation device can be determined based on the frequency signals of different frequencies generated by the frequency disturbance generating device. Generally speaking, when the frequency signal generated by the frequency disturbance generating device is too large or too small, the reactive power compensation device should be shut down immediately or after a delay. When the frequency signal is within the normal range, the reactive power compensation device should be able to maintain a normal working state.

[0051] It is understandable that the frequency being too large or too small mentioned here is compared with the normal working frequency of the photovoltaic power station. When the working frequency of the reactive power compensation device matches the normal working frequency of the photovoltaic power station, it can be determined that the reactive power compensation device is working normally, otherwise, the reactive power compensation device should be quickly shut down.

[0052] The expected working state of the reactive power compensation device described above is compared with the actual working state of the reactive power compensation device to determine whether the frequency adaptability function of the device meets the requirements.

[0053] Preferably, the nominal voltage of the frequency disturbance generating device is 100V.

[0054] It is understandable that in the present invention, in order to determine the function of the device only for the influencing factor of frequency, other related parameters can be set to nominal values ​​during the test, and only the frequency parameter item can be changed. For example, although in the actual operation of the power grid, the SVG device can change its state not only according to the change of frequency, but also according to the change of voltage, the method in the present invention only tests the performance of SVG for frequency disturbance. Similar to the method in the prior art, the frequency can also be set to the nominal value and the voltage disturbance can be tested.

[0055] Preferably, the frequency range of frequency signals of different frequencies is determined based on the allowable operating frequency of the photovoltaic power station inverter and the allowable grid-connected frequency of the photovoltaic power station specified in GB / T 34931-2017 Technical Specification for Detection of Reactive Compensation Devices in Photovoltaic Power Stations; the frequency range is between 48 Hz and 50.55 Hz.

[0056] In the present invention, the frequency disturbance range is not selected randomly, but after consulting a large amount of relevant information, the frequency disturbance range is calculated based on the standard GB / T34931-2017 "Technical Code for Detection of Reactive Compensation Devices in Photovoltaic Power Stations".

[0057] In this standard, the requirements for the frequency adaptability of photovoltaic power stations are shown in Table 1.

[0058]

[0059] Table 1 Photovoltaic power station frequency adaptability table

[0060] According to the above table, when the frequency range in the photovoltaic power station is reduced to below 48Hz, it will be lower than the minimum frequency allowed for the photovoltaic power station inverter to operate. At this time, the inverter will not work, which will affect the power supply or transmission of the grid. If the SVG equipment is still in normal working condition at this time, it will cause damage to the inverter and other equipment.

[0061] In addition, when the frequency range in the photovoltaic power station exceeds 50.5Hz, the power supply to the grid line should be stopped. If the power supply continues, the grid line may be overloaded and cause failure. Therefore, the present invention also stipulates the operating range of the SVG device based on the above data, and sets its frequency disturbance range between 48Hz and 50.55Hz.

[0062] With this setup, if the SVG device meets the requirements during the test, it means that the SVG device can remain connected to the grid together with the PV power plant during a grid failure or frequency fluctuation, and can even provide a certain amount of reactive power to the grid through the compensation function, thereby supporting the grid to recover to normal.

[0063] In the present invention, various test methods can be implemented based on a data recorder analyzer. The data recorder analyzer can record the frequency disturbance signal with a nominal voltage of 100V and different frequencies generated by the frequency disturbance generating device, and can also restore the primary current signal through the transformation ratio. By comparing the two, the actual operating state of the SVG can be analyzed, such as whether the SVG is in an operating state or in a shutdown state.

[0064] Preferably, the frequency of the frequency signal is set to 48 Hz, and the frequency signal is used to continuously disturb the reactive power compensation device for 10 seconds; if the reactive power compensation device cannot stop running immediately, it is determined that the frequency adaptability function of the reactive power compensation device does not meet the requirements.

[0065] Figure 3 This is a schematic diagram of the output current curve of the reactive power compensation device when the frequency signal is 48 Hz in a method for testing the frequency adaptability of the reactive power compensation device in a photovoltaic power station according to the present invention. Figure 3 As shown, during the actual operation of the photovoltaic power station, the frequency fluctuations caused by power shortage or failure that the SVG device may usually receive should be within the range of 48Hz to 50.55Hz. Therefore, in the present invention, a minimum frequency of 48Hz is set, and the disturbance is carried out for 10 seconds under this frequency state. If it is found that the reactive power compensation device stops running immediately at this time, it means that the frequency adaptability performance of the reactive power compensation device meets the requirements. Otherwise, it does not meet the requirements.

[0066] It is understandable that this setting ensures that when the operating frequency of the photovoltaic power station inverter is too low to operate normally, the reactive power compensation device will not continue to compensate the primary current end of the photovoltaic power station. In this way, problems can be identified and discovered early, and power generation failures can be confirmed.

[0067] Preferably, the frequencies of the frequency signal are set to 48.05 Hz and 49.45 Hz respectively, and the frequency signal is used to continuously disturb the reactive power compensation device for 600 seconds; if the reactive power compensation device cannot maintain continuous operation during the continuous disturbance, it is determined that the frequency adaptability function of the reactive power compensation device does not meet the requirements.

[0068] Figure 4 It is a schematic diagram of an output current curve of a reactive power compensation device when the frequency signal is 48.05 Hz in a frequency adaptability testing method of a reactive power compensation device in a photovoltaic power station according to the present invention. Figure 5 This is a schematic diagram of the output current curve of the reactive power compensation device when the frequency signal is 49.45 Hz in a frequency adaptability test method of a reactive power compensation device in a photovoltaic power station of the present invention. Figure 3 and Figure 4As shown, it can be understood that when the photovoltaic power station operates between 48Hz and 49.5Hz, although the photovoltaic power station can operate normally, its frequency is still lower than the normal frequency. In this state, the reactive power compensation device can provide compensation for the power grid for a period of time, but in order to complete the commissioning of the power system as soon as possible and restore the normal state, the compensation time should be within the specified 10 minutes. Therefore, the duration of the two disturbances of 48.05 and 49.45Hz is set to 600s in the present invention. If the SVG device cannot maintain a continuous working state within 600s, it means that the compensation capacity of the SVG device cannot meet the requirements of the power system.

[0069] Preferably, the frequencies of the frequency signal are set to 49.55 Hz and 50.15 Hz respectively, and the frequency signal is used to continuously disturb the reactive power compensation device for 1800 s; if the reactive power compensation device cannot maintain continuous operation during the continuous disturbance, it is determined that the frequency adaptability function of the reactive power compensation device does not meet the requirements.

[0070] Figure 6 It is a schematic diagram of an output current curve of a reactive power compensation device when the frequency signal is 49.55 Hz in a frequency adaptability testing method of a reactive power compensation device in a photovoltaic power station of the present invention. Figure 7 This is a schematic diagram of the output current curve of the reactive power compensation device when the frequency signal is 50.15 Hz in a method for testing the frequency adaptability of the reactive power compensation device in a photovoltaic power station according to the present invention. Figure 6 and Figure 7 As shown, based on the provisions of the existing technical standards, when the frequency is between 49.5Hz and 50.2Hz, the power grid should be able to operate continuously, and the SVG device should also be able to operate continuously with weak compensation or no compensation at all. Therefore, the disturbance time can be set to 1800s, and the state of the SVG device under the disturbance state during this period is detected. If the SVG device cannot maintain normal operation for half an hour at this time, it means that the SVG device does not meet the system requirements.

[0071] Preferably, the frequencies of the frequency signal are set to 50.25 Hz and 50.45 Hz respectively, and the frequency signal is used to continuously disturb the reactive power compensation device for 120 seconds; if the reactive power compensation device cannot maintain continuous operation during the continuous disturbance, it is determined that the frequency adaptability function of the reactive power compensation device does not meet the requirements.

[0072] Figure 8 It is a schematic diagram of an output current curve of a reactive power compensation device when the frequency signal is 50.25 Hz in a frequency adaptability testing method of a reactive power compensation device in a photovoltaic power station of the present invention. Fig. 9This is a schematic diagram of the output current curve of the reactive power compensation device when the frequency signal is 50.45 Hz in a method for testing the frequency adaptability of the reactive power compensation device in a photovoltaic power station according to the present invention. Figure 8 and Fig. 9 As shown, it can be understood that, generally speaking, for photovoltaic power stations with a frequency exceeding 50.2 Hz but less than 50.5 Hz, a reduction process or high-frequency shedding strategy under the grid dispatching agency should be implemented. At the same time, in order to prevent excessive load, the grid connection of photovoltaic power stations should also be avoided.

[0073] In this case, although the SVG device can provide reverse compensation, the time should not be too long, otherwise even if the SVG device exists, it will cause a fault. In this article, according to the standard setting, 2 minutes is selected as the time limit. For disturbance signals within this frequency range, the SVG device should perform a shutdown operation after a time limit of 120 seconds. Therefore, the same parameters are set for the test indicators, and it is determined whether the frequency adaptability function of the reactive power compensation device meets the requirements.

[0074] Preferably, the frequency of the frequency signal is set to 50.55 Hz, and the frequency signal is used to continuously disturb the reactive power compensation device for 5 seconds; if the reactive power compensation device cannot stop running immediately, it is determined that the frequency adaptability function of the reactive power compensation device does not meet the requirements.

[0075] Fig.10 This is a schematic diagram of the output current curve of the reactive power compensation device when the frequency signal is 50.55 Hz in a frequency adaptability test method of a reactive power compensation device in a photovoltaic power station of the present invention. Fig.10 As shown, it can be understood that if the frequency of the frequency signal in the present invention exceeds the maximum load frequency of the photovoltaic power station, it should stop running immediately, which is conducive to power outage of the photovoltaic power station and reduces the output of active power, thereby facilitating the frequency to return to a normal lower level.

[0076] Preferably, if the reactive compensation device meets all of the following conditions, it is determined that the frequency adaptability function of the reactive compensation device meets the requirements: when the frequency of the frequency signal is 48 Hz or 50.55 Hz, the reactive compensation device stops running immediately; when the frequency of the frequency signal is 48.05 Hz or 49.45 Hz, the reactive compensation device continues to operate for more than 600 s; when the frequency of the frequency signal is 49.55 Hz or 50.15 Hz, the reactive compensation device continues to operate for more than 1800 s; when the frequency of the frequency signal is 50.25 Hz or 50.45 Hz, the reactive compensation device continues to operate for more than 120 s.

[0077] It is understandable that, in the above process of testing frequency signals at different frequencies, if each test can obtain that the working state of the reactive compensation device meets the expected requirements, it can be determined that the reactive compensation device as a whole meets the frequency adaptability requirements.

[0078] The second aspect of the present invention relates to a frequency adaptability testing system for a reactive compensation device in a photovoltaic power station as described in the frequency adaptability testing method for a reactive compensation device in a photovoltaic power station in the first aspect of the present invention, wherein the system comprises a photovoltaic distribution network, a reactive compensation device, a frequency disturbance generating device and a data recording and analyzing instrument; the photovoltaic distribution network is formed by photovoltaic power stations connected to both ends of a main substation and a power grid respectively; the reactive compensation device is connected to the photovoltaic distribution network, and its secondary side voltage signal input end is connected to the frequency disturbance generating device, for obtaining an output current based on a frequency signal generated by the frequency disturbance generating device; the data recording and analyzing instrument is respectively connected to the secondary side current loops of the frequency disturbance generating device and the reactive compensation device, for detecting and comparing the frequency signal and the output current.

[0079] like Figure 2 As shown, the reactive power compensation device in the present invention is different from the normal connection mode. After the secondary voltage signal terminal is disconnected, the analog disturbance signal input by the frequency disturbance generating device is connected. In order to test the working state of the reactive power compensation device under disturbance, the present invention also introduces a data recording and analysis instrument to test the disturbance signal and the current output by the reactive power compensation device respectively.

[0080] Preferably, the reactive power compensation device collects the secondary voltage signal and the secondary current signal in the photovoltaic power distribution network respectively, and simultaneously accesses the frequency signal of the frequency disturbance generating device for frequency signal simulation based on the frequency disturbance generating device.

[0081] like Figure 2 As shown, three of the four ports of the reactive power compensation device are still connected to the original signal to provide feedback compensation based on the corresponding data in the distribution network. In order to realize the test, one of the ports is connected to the frequency disturbance generator. One input port of the data recorder analyzer is connected to the input signal of the frequency disturbance generator, and the other input port is connected to the acquisition port of the secondary current signal in the reactive power compensation device.

[0082] Preferably, the frequency disturbance generating device is of three-phase four-wire type, the output frequency range is wider than 1-100 Hz, the output frequency error is lower than 0.002 Hz, and the signal generation period is less than or equal to 100 ms.

[0083] It is understandable that in the present invention, in order to adapt to the three-phase current of the distribution network, the frequency disturbance generating device also adopts a three-phase four-wire system. In addition, not only the range and error of the output frequency are specified, but also the voltage output range and error are specified. Among them, the voltage output range can be set wider than 0-135V, and the output voltage error is less than or equal to ±0.1%. In order to prevent phase error, it is determined that the phase output error should also be less than or equal to ±0.1%. At the same time, in order to ensure that the frequency disturbance generating device can generate disturbances of various frequencies, it should also be ensured that the period of signal generation is less than or equal to 100ms. In order to facilitate the understanding and intuitive display of the signal output by the frequency disturbance generating device, the device can have the basic function of voltage curve editing.

[0084] Preferably, the photovoltaic power distribution network has a voltage transformer and a current transformer for collecting secondary voltage signals and secondary current signals with a collection accuracy greater than or equal to level 0.2.

[0085] It is understandable that in order to ensure that the relevant data of the primary and secondary signals received by the SVG device are sufficiently accurate, thereby improving the test accuracy, the acquisition accuracy of the voltage and current sensors may also be specified.

[0086] Preferably, the sampling frequency of the data recorder analyzer is greater than or equal to 20kHz, and the bandwidth is greater than or equal to 2.5kHz. Since the sampling frequency of the data recorder analyzer is much greater than the disturbance frequency of the frequency signal in the present invention, the input and output voltage and current of the SVG device can be accurately sampled and obtained.

[0087] In one embodiment of the present invention, the test results of the SVG device are as follows: Figures 3 to 10 As shown in Figure 3 When the frequency of the frequency signal is 48Hz, the primary current signal end of the SVG device is immediately cut off and reduced to 0A, indicating that the SVG device immediately enters the state of stopping operation. Figure 4 , 5 ,At these two frequencies, SVG has been running for more than 600s, and Figure 6 , 7 In the SVG device, the running state is maintained for more than 1800 seconds. Figure 8 , 9 In the example, the continuous operation time of the SVG device is also greater than 120 seconds. Finally, when the frequency changes to 50.55 Hz, the SVG device is quickly shut down within 1 second. According to the results in the embodiment, it can be seen that the tested SVG device meets the requirements of the frequency adaptability test and can be used in an actual power grid.

[0088] The beneficial effect of the present invention is that, compared with the prior art, the method and system for testing the frequency adaptability of a reactive power compensation device in a photovoltaic power station can test the reaction of the reactive power compensation device to different frequency disturbances by performing simulated frequency disturbances on the reactive power compensation device, and obtain the frequency adaptability of the reactive power compensation device. The method of the present invention is simple in concept, convenient in implementation, time-saving, low in cost, and has accurate test results.

[0089] The applicant of the present invention has made a detailed explanation and description of the implementation examples of the present invention in conjunction with the drawings in the specification. However, those skilled in the art should understand that the above implementation examples are only preferred implementation schemes of the present invention, and the detailed description is only to help readers better understand the spirit of the present invention, but not to limit the scope of protection of the present invention. On the contrary, any improvements or modifications based on the inventive spirit of the present invention should fall within the scope of protection of the present invention.

Claims

1. A method for testing frequency adaptability of a reactive power compensation device in a photovoltaic power station, characterized in that: The method comprises the following steps: Step 1, replacing the secondary side voltage of the reactive power compensation device connected to the photovoltaic power station with the input signal of the frequency disturbance generating device; Disconnecting the input terminal connected to the secondary side voltage of the reactive power compensation device, and connecting the input terminal to the input signal of the frequency disturbance generating device, so as to achieve interference of the frequency disturbance generating device to the reactive power compensation device; Step 2, generating frequency signals of different frequencies at a nominal voltage based on the frequency disturbance generating device, and using the frequency signals to continuously disturb the reactive power compensation device to obtain an output current of the reactive power compensation device; Step 3, determining whether the frequency adaptability function of the reactive power compensation device meets the requirements based on the output current of the reactive power compensation device; The output current determination at least includes: If the frequency range of the frequency signal is outside the range of 48 Hz to 50.55 Hz, the output current should immediately return to zero in the continuous disturbance; When the frequency of the frequency signal is 48.05 Hz or 49.45 Hz, the reactive power compensation device operates continuously for more than 600 seconds; When the frequency of the frequency signal is 49.55 Hz or 50.15 Hz, the reactive power compensation device operates continuously for more than 1800 seconds; When the frequency of the frequency signal is 50.25 Hz or 50.45 Hz, the reactive power compensation device continues to operate for more than 120 seconds.

2. A method for testing frequency adaptability of a reactive power compensation device in a photovoltaic power station according to claim 1, characterized in that: The nominal voltage of the frequency disturbance generating device is 100V.

3. A method for testing frequency adaptability of a reactive power compensation device in a photovoltaic power station according to claim 2, characterized in that: The frequency range of the frequency signals of different frequencies is determined based on the permitted operating frequency of the photovoltaic power station inverter and the permitted grid-connected frequency of the photovoltaic power station specified in GB / T 34931-2017 Technical Specification for Detection of Reactive Compensation Devices in Photovoltaic Power Stations; The frequency range is between 48 Hz and 50.55 Hz.

4. A method for testing frequency adaptability of a reactive power compensation device in a photovoltaic power station according to claim 3, characterized in that: The frequency of the frequency signal is set to 50.55 Hz, and the reactive power compensation device is disturbed continuously for 5 seconds using the frequency signal; If the reactive power compensation device cannot stop running immediately, it is determined that the frequency adaptability function of the reactive power compensation device does not meet the requirements.

5. A frequency adaptability test system for reactive power compensation device of photovoltaic power station, characterized by: The system is implemented by a frequency adaptability testing method for a reactive power compensation device of a photovoltaic power station as described in any one of claims 1 to 4; The system includes a photovoltaic power distribution network, a reactive power compensation device, a frequency disturbance generating device and a data recording and analyzing instrument; wherein, The photovoltaic power distribution network is formed by photovoltaic power stations connected to both ends of the main substation and connected to the power grid; The reactive power compensation device is connected to the photovoltaic power distribution network, and its secondary side voltage signal input terminal is connected to the frequency disturbance generating device, and is used to obtain an output current based on the frequency signal generated by the frequency disturbance generating device; The data recorder and analyzer are respectively connected to the secondary side current loops of the frequency disturbance generating device and the reactive power compensation device, and are used to detect and compare the frequency signal and the output current.

6. A frequency adaptability test system for reactive power compensation device of photovoltaic power station according to claim 5, characterized in that: The reactive power compensation device collects the secondary voltage signal and the secondary current signal in the photovoltaic power distribution network respectively, and simultaneously accesses the frequency signal of the frequency disturbance generating device for frequency signal simulation based on the frequency disturbance generating device.

7. A frequency adaptability test system for reactive power compensation device of photovoltaic power station according to claim 5, characterized in that: One input port of the data recorder and analyzer is connected to the input signal of the frequency disturbance generating device, and the other input port is connected to the acquisition port of the secondary current signal in the reactive power compensation device.

8. A frequency adaptability test system for reactive power compensation device of photovoltaic power station according to claim 5, characterized in that: The frequency disturbance generating device is of three-phase four-wire type, the output frequency range is wider than 1-100 Hz, the output frequency error is lower than 0.002 Hz, and the signal generation period is less than or equal to 100 ms.

9. A frequency adaptability test system for reactive power compensation device of photovoltaic power station according to claim 5, characterized in that: The photovoltaic power distribution network has a voltage transformer and a current transformer for collecting secondary voltage signals and secondary current signals, and the collection accuracy is greater than or equal to level 0.

2.

10. A frequency adaptability test system for reactive power compensation device of photovoltaic power station according to claim 5, characterized in that: The data recorder and analyzer has a sampling frequency greater than or equal to 20 kHz and a bandwidth greater than or equal to 2.5 kHz.

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