Inverters, power systems, and islanding detection methods

Abstract

The present application provides an inverter, a power system and an island detection method. The inverter includes an inverter power conversion module and a control module. The input and output ends of the inverter are respectively used to connect to a DC source and a public power grid, and the common coupling point PCC of the inverter and the public power grid is connected to the load; the control module is used to control the inverter power conversion module to output reactive disturbance based on a first disturbance value, and detect the voltage frequency of the PCC, wherein the first disturbance value is the disturbance value corresponding to the first voltage frequency of the PCC in the current sampling period, and is greater than or equal to the second disturbance value corresponding to the second voltage frequency of the PCC in the first sampling period, and the sampling period before the current sampling period is the first sampling period; the control module is also used to detect a power supply island based on the voltage frequency of the PCC, and control the inverter power conversion module to disconnect from the load. The implementation of the present application can realize the rapid detection of power supply islands and improve the efficiency of island detection.

Description

Technical Field

[0001] The present application relates to the field of power electronics technology, and in particular to an inverter, a power system, and an island detection method. Background Art

[0002] Renewable energy generation systems can utilize solar energy, wind energy, energy storage systems, and other technologies to generate direct current (DC). After being converted to AC at the mains frequency by an inverter, the AC power is then output to the public grid for use. Thus, the renewable energy generation system, the grid, and the loads constitute a complex power system. This power system specifically includes a DC source, an inverter, a load, a grid-connected switch, and the public grid. If the power consumed by the loads in this power system matches the power output of the inverter, the inverter can continue to supply power to the loads even if the public grid shuts off. This allows the local grid formed by the inverter and loads to remain energized, creating a power supply island. If a power supply island occurs, the unplanned energization of the outage area and the uncontrolled voltage and frequency can easily pose a safety hazard to power maintenance personnel and electrical equipment. Therefore, timely detection of power supply islands in the power system and the implementation of measures to eliminate them have become urgent technical challenges. Summary of the Invention

[0003] The present application provides an inverter, a power system and an island detection method, which can quickly detect power supply islands and improve the efficiency of island detection.

[0004] In a first aspect, the present application provides an inverter, which includes an inverter power conversion module and a control module. The input end of the inverter power conversion module is used to connect to a DC source, the output end of the inverter power conversion module is coupled to connect to a public power grid, and the common coupling point PCC between the inverter and the public power grid is connected to a load. The control module in the above-mentioned inverter is used to control the inverter power conversion module to output reactive disturbance based on a first disturbance value, and detect the voltage frequency of the PCC, wherein the first disturbance value is a disturbance value corresponding to the first voltage frequency of the PCC in the current sampling period, and is greater than or equal to a second disturbance value corresponding to the second voltage frequency of the PCC in the first sampling period, and the sampling period before the current sampling period is the first sampling period; the control module in the above-mentioned inverter is also used to detect a power supply island based on the voltage frequency of the PCC, and control the inverter power conversion module to disconnect from the load. In other words, the control module in the above-mentioned inverter can control the inverter power conversion module to output reactive disturbance according to the value of reactive disturbance obtained based on the voltage frequency of PCC, so as to detect the power supply island according to the influence of reactive disturbance on the PCC voltage frequency, wherein the value of reactive disturbance calculated by the control module in the inverter changes gradually.

[0005] In this application, the control module in the inverter can control the inverter power conversion module in the inverter to output a reactive disturbance based on a first disturbance value, where the first disturbance value gradually changes over time. In this way, when a power supply island exists, outputting a gradually changing reactive disturbance can accelerate the change in PCC voltage and frequency, enabling rapid detection of power supply islands, ensuring effective island detection, and improving island detection efficiency.

[0006] In a possible embodiment, the control module in the inverter is further used to: obtain the second disturbance value corresponding to the second voltage frequency based on the second voltage frequency, and obtain the first disturbance value based on the disturbance step and the second disturbance value. The disturbance step can be calculated based on a formula. In the present application, by obtaining the first disturbance value based on the disturbance step and the second disturbance value, the obtained reactive disturbance value can be gradually changed according to the disturbance step, thereby causing the reactive disturbance output by the inverter power conversion module of the inverter to gradually change according to equal steps. In this way, the reactive disturbance output by the inverter changes according to equal steps, and in the presence of a power supply island, the change in the voltage frequency of the PCC can be controlled due to the influence of the reactive disturbance, thereby enabling the change in the voltage frequency of the PCC to quickly reach the threshold, meet the detection conditions of the power supply island, and achieve rapid detection of the power supply island.

[0007] In one possible embodiment, the control module in the inverter is further configured to: obtain a first frequency variation based on the first voltage frequency and the average value of the PCC voltage frequency for N consecutive sampling periods prior to the current sampling period; and obtain a first disturbance reference value based on the first frequency variation. N is an integer greater than 1, and the N consecutive sampling periods include the first sampling period. In this application, the value range of N may be 25 to 1000, and a sampling period may refer to a power frequency cycle of the public power grid. Specifically, the first voltage frequency may be understood as the current voltage frequency, and the average value of the PCC voltage frequency for N consecutive sampling periods prior to the current sampling period may be understood as the sliding window average value of the historical voltage frequency. Therefore, the first frequency variation may be obtained by taking the difference between the current voltage frequency and the sliding window average value of the historical voltage frequency. The first disturbance reference value may be obtained by taking the first frequency variation and a certain proportional coefficient. The first disturbance reference value is greater than or equal to the first disturbance value.

[0008] In the present application, the control module in the above-mentioned inverter can obtain an initial disturbance reference value (i.e., a first disturbance reference value) based on the current voltage and frequency changes of the PCC, and can use the disturbance reference value as an upper limit to limit the size of the reactive disturbance output by the inverter power conversion module in the inverter. In this way, when there is no power supply islanding and the voltage and frequency of the public power grid fluctuate normally, the inverter will not directly output reactive disturbance according to the disturbance reference value, but will output a smaller reactive disturbance, thereby reducing the negative impact of the reactive disturbance output by the inverter on the power quality of the public power grid.

[0009] In one possible implementation, the control module in the inverter is configured to: obtain a second disturbance reference value based on the second voltage frequency; and, when the second disturbance reference value is less than the disturbance step size, obtain a preset disturbance value as the second disturbance value. The preset disturbance value may be 0, a smaller value close to 0, or a value close to the second disturbance reference value, and may be set based on the actual scenario, which is not limited by this application. In this way, when the voltage frequency of the PCC changes slightly, a corresponding second disturbance value can be obtained based on the second voltage frequency, and the magnitude of the output reactive disturbance can be controlled according to this value.

[0010] In the present application, when the PCC voltage and frequency change is small, the control module in the inverter can obtain a correspondingly small reactive disturbance value in this way, and output the reactive disturbance based on this value, which can reduce the negative impact of the reactive disturbance output for detecting the islanding effect on the power quality of the power grid, and the implementation process is simple and easy.

[0011] In one possible embodiment, the control module in the inverter is configured to: when the first disturbance reference value is greater than the disturbance step length and the second disturbance reference value is less than the disturbance step length, obtain a preset initial value as the first disturbance value; when the first disturbance reference value is greater than the disturbance step length and the first disturbance reference value is equal to the second disturbance reference value, obtain the first disturbance value based on the disturbance step length and the second disturbance value, wherein the first disturbance value is greater than the second disturbance value. The preset initial value can be set to a fixed value less than the disturbance step length, or to a value equal to the disturbance step length, and can be set specifically according to the actual application scenario, and is not limited in this application.

[0012] In the present application, the control module in the inverter can obtain the first disturbance value in the above-mentioned manner. From the perspective of the longitudinal flow of time, the first disturbance value changes gradually according to the disturbance step, so the reactive disturbance subsequently output by the inverter according to the first disturbance value also changes regularly. In this way, when a power supply island exists, the change in PCC voltage and frequency can be controlled due to the influence of reactive disturbance, thereby accelerating the detection process of the power supply island, reducing the possibility of island detection timeout, and improving the efficiency of island detection.

[0013] In one possible embodiment, the control module in the inverter is further configured to: when a first voltage change corresponding to a first negative-sequence component of the PCC voltage in the current sampling period is greater than a preset threshold, based on a first disturbance value and a short-term disturbance value, control the inverter power conversion module in the inverter to output a reactive disturbance, wherein the short-term disturbance value is derived from the output power of the inverter. In the present application, the preset threshold value can be 1% of the rated voltage of the inverter, and the short-term disturbance value can be equal to 1% to 5% of the instantaneous active power of the inverter, or can be equal to 1% to 5% of the rated active power of the inverter. The specific value can be determined based on the actual application scenario and is not limited by this application. In other words, the control module in the inverter can calculate the reactive disturbance value based on the change in the PCC voltage frequency, or can combine the short-term disturbance value obtained from the change in the PCC voltage negative-sequence component to obtain the reactive disturbance value. The control module can combine the above two methods to obtain a determined reactive disturbance value and control the inverter power conversion module to output the reactive disturbance according to this value.

[0014] In the present application, in addition to calculating the reactive disturbance value based on the PCC voltage-frequency change, the reactive disturbance value can also be calculated in combination with the change in the PCC negative-sequence voltage. In this way, the advantages of both methods can be combined to detect power supply islands, avoiding the phenomenon of island detection timeout that may occur when the PCC voltage-frequency change is small, which is conducive to improving the efficiency of island detection.

[0015] In one possible embodiment, the control module in the inverter is further used to obtain the first voltage variation based on the first voltage negative sequence component and the average value of the voltage negative sequence components of M consecutive sampling periods before the current sampling period. Wherein, M is an integer greater than 1, and in the present application, M can be taken in the range of 25 to 1000. The voltage negative sequence component of the PCC can be obtained specifically through a phase-locked loop, or it can be obtained in other ways. In the present application, the control module in the inverter obtains the first voltage variation based on the sliding window average value of the current PCC voltage negative sequence component and the corresponding historical voltage negative sequence component. It can find the timing when the voltage negative sequence component of the PCC mutates, which is conducive to obtaining the value of the reactive disturbance when the voltage negative sequence component mutates to assist in islanding detection, thereby improving the efficiency of islanding detection.

[0016] In one possible embodiment, the control module in the inverter is used to: when the short-term disturbance value is less than the first disturbance value, control the inverter power conversion module to output reactive disturbance according to the first disturbance value; or, when the short-term disturbance value is greater than the first disturbance value, control the inverter power conversion module to output reactive disturbance according to the short-term disturbance value. In the present application, the control module in the inverter selects the larger value from the short-term disturbance value and the first disturbance value as the value of the reactive disturbance to be output by the inverter power module, and controls the inverter power conversion module to output reactive disturbance according to the value. When a power supply island occurs, a larger reactive disturbance can be output as much as possible, thereby accelerating the island detection speed and avoiding island detection timeout.

[0017] In one possible embodiment, the control module in the inverter is used to: when the short-term disturbance value is greater than the first disturbance value, control the inverter power conversion module to continuously output reactive disturbance within a first preset time period according to the short-term disturbance value, and control the inverter power conversion module to stop outputting reactive disturbance when the end time of the first preset time period arrives. The first preset time period can be set according to the specific scenario, and illustratively, it can be 3 to 5 power frequency cycles. In the present application, the inverter can intermittently output reactive disturbance when there is no islanding and the public power grid produces short-term continuous fluctuations, so as to prevent the output of reactive disturbance from being too frequent, save resources, and reduce the negative impact on the power quality of the power grid.

[0018] In one possible embodiment, the control module in the inverter is used to: when the third voltage frequency of the PCC is continuously greater than the first frequency threshold or continuously less than the second frequency threshold within a first reference time period, or when the frequency change rate corresponding to the third voltage frequency is continuously greater than the first frequency change rate threshold or continuously less than the second frequency change rate threshold within a second reference time period, determine that there is a power supply island in the power system, that is, determine that a power supply island is detected, and control the inverter power conversion module to disconnect from the load, and the third voltage frequency is the voltage frequency of the PCC in the second sampling period after the current sampling period. The above-mentioned first reference time period and second reference time period can be set according to the actual scenario, and this application does not limit this. For example, the above-mentioned two reference time periods can be set to 5 power frequency cycles. In this way, the inverter can detect the island based on whether the voltage frequency of the PCC is affected by reactive disturbances and deviates to exceed the threshold, or can detect the island based on whether the frequency change rate of the PCC exceeds the threshold. In the present application, when the size of the reactive disturbance output by the inverter changes in equal steps, the change in the voltage frequency of the PCC affected by the reactive disturbance is controllable, and the frequency change rate obtained according to the voltage frequency also changes regularly instead of randomly. Therefore, the PCC voltage frequency or frequency change rate can quickly reach the threshold, accelerate the island detection process, and improve the efficiency of island detection.

[0019] In one possible implementation, the control module in the inverter is used to wait for a third reference time period when a power supply island is detected based on the voltage frequency of the PCC, and control the inverter power conversion module to disconnect from the load when the end moment of the third reference time period arrives. The above-mentioned third reference time period can be set according to the actual scenario, such as being set to 2 to 5 power frequency cycles, and this application does not impose any restrictions on this. In this application, in a multi-machine parallel scenario, a single inverter waits for the third reference time period after detecting an island before delaying the shutdown. Compared with the operation of immediately shutting down after detecting an island, this can prevent a negative impact on the island detection effect of other inverters in the scenario.

[0020] In a second aspect, the present application provides a power system comprising at least two inverters as provided in the first aspect and any possible embodiment of the first aspect, wherein the output ends of the at least two inverters are connected in parallel to a public grid and a PCC. The power system may also include a DC source, a public grid, and a load. In the power system, the control module in each inverter is further configured to control the inverter power conversion module to output a reactive disturbance according to the short-term disturbance value when the short-term disturbance value is greater than the first disturbance value. That is, for any one of the at least two inverters, the inverter may obtain a first disturbance value based on a change in the PCC voltage frequency, and a short-term disturbance value based on a change in the negative sequence component of the PCC voltage, and then obtain a reactive disturbance value based on the first disturbance value and the short-term disturbance value, and output a reactive disturbance based on the short-term disturbance value when the short-term disturbance value is greater than the first disturbance value.

[0021] In the present application, in the scenario where multiple inverters are connected in parallel to the PCC, the multiple inverters can synchronously output short-term disturbance values ​​based on the negative sequence component of the PCC voltage. Assuming that the multiple inverters are of the same type, the multiple inverters can synchronously output equal amounts of reactive disturbances in the same direction. In this way, the reactive disturbances output by the multiple inverters at the PCC will not cancel each other out due to sampling or detection differences between the inverters. The reactive disturbances output by the multiple inverters in the same direction are superimposed on the PCC, which can accelerate the deviation of the PCC voltage frequency when the inverter output power is highly matched with the load absorption power, reduce the blind spot of island detection, thereby improving the efficiency of island detection and preventing island detection timeout.

[0022] In a third aspect, the present application provides an island detection method, which is applicable to an inverter, wherein the input end of the inverter is used to connect a DC source, and the output end of the inverter is connected to a load at a common coupling point PCC of a public power grid. The method comprises: based on a first disturbance value, controlling the inverter power conversion module to output reactive disturbance, and detecting the voltage frequency of the PCC, wherein the first disturbance value is a disturbance value corresponding to the first voltage frequency of the PCC in the current sampling period, and the first disturbance value is greater than or equal to the first disturbance value corresponding to the second voltage frequency of the PCC in the first sampling period, and the first sampling period is the sampling period before the current sampling period; based on the voltage frequency of the PCC, a power supply island is detected, and the inverter power conversion module is controlled to disconnect from the load.

[0023] In this application, when power supply islanding occurs, by outputting gradually changing reactive disturbances, the change of PCC voltage frequency can be accelerated, the power supply islanding can be quickly detected, the islanding detection effect can be guaranteed, and the islanding detection efficiency can be improved.

[0024] In one possible implementation, before controlling the inverter power conversion module to output reactive disturbance based on the first disturbance value, the method further includes: obtaining the second disturbance value corresponding to the second voltage frequency based on the second voltage frequency, and obtaining the first disturbance value based on a disturbance step size and the second disturbance value. The disturbance step size can be obtained based on a formula.

[0025] In a possible implementation, before obtaining the first disturbance value based on the disturbance step and the second disturbance value, the method further includes: obtaining a first frequency change based on the first voltage frequency and the average value of the voltage frequency of the PCC in N consecutive sampling periods before the current sampling period, wherein N is an integer greater than 1, and the N consecutive sampling periods include the first sampling period; and obtaining the first disturbance reference value based on the first frequency change.

[0026] In a possible implementation, the obtaining of the second disturbance value corresponding to the second voltage frequency based on the second voltage frequency includes: obtaining a second disturbance reference value based on the second voltage frequency; and obtaining a preset disturbance value as the second disturbance value when the second disturbance reference value is smaller than the disturbance step.

[0027] In a possible embodiment, the obtaining of the first disturbance value based on the disturbance step and the second disturbance value includes: when the first disturbance reference value is greater than the disturbance step and the second disturbance reference value is less than the disturbance step, obtaining a preset initial value as the first disturbance value; when the first disturbance reference value is greater than the disturbance step and the first disturbance reference value is equal to the second disturbance reference value, obtaining the first disturbance value based on the disturbance step and the second disturbance value, wherein the first disturbance value is greater than the second disturbance value.

[0028] In a possible embodiment, the above-mentioned control of the inverter power conversion module to output reactive disturbance based on the first disturbance value includes: when the first voltage change corresponding to the first voltage negative sequence component of the PCC in the above-mentioned current sampling period is greater than a preset threshold, based on the above-mentioned first disturbance value and the short-time disturbance value, controlling the inverter power conversion module to output reactive disturbance, wherein the above-mentioned short-time disturbance value is obtained from the output power of the above-mentioned inverter.

[0029] In a possible embodiment, before controlling the inverter power conversion module to output reactive disturbance based on the first disturbance value, the method further includes: obtaining a first voltage change corresponding to the first voltage negative sequence component based on the first voltage negative sequence component and the average value of the voltage negative sequence components of M consecutive sampling periods before the current sampling period, wherein M is an integer greater than 1.

[0030] In a possible embodiment, the above-mentioned control of the inverter power conversion module to output reactive disturbance based on the above-mentioned first disturbance value and the short-time disturbance value includes: when the above-mentioned short-time disturbance value is less than the above-mentioned first disturbance value, controlling the above-mentioned inverter power conversion module to output reactive disturbance according to the above-mentioned first disturbance value; or, when the above-mentioned short-time disturbance value is greater than the above-mentioned first disturbance value, controlling the above-mentioned inverter power conversion module to continuously output reactive disturbance within a first preset time length according to the above-mentioned short-time disturbance value, and controlling the above-mentioned inverter power conversion module to stop outputting reactive disturbance when the end time of the above-mentioned first preset time length arrives.

[0031] In this application, the inverter output reactive disturbance is controlled according to a first disturbance value obtained based on a disturbance step size and a second disturbance value. When the obtained reactive disturbance value changes gradually according to the disturbance step size, the reactive disturbance output by the inverter also changes gradually according to the same step size. In this way, in the presence of a power supply island, the changes in the PCC voltage and frequency can be controlled due to the influence of the reactive disturbance. This allows the PCC voltage and frequency changes to quickly reach a threshold, meeting the detection conditions for a power supply island, thereby enabling rapid detection of the power supply island. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 This is an application scenario diagram of the power system provided by this application;

[0033] Figure 2 This is another application scenario diagram of the power system provided by this application;

[0034] Figure 3 It is a structural diagram of the power system provided by this application;

[0035] Figure 4 is another structural schematic diagram of the power system provided by this application;

[0036] Figure 5 This is a structural diagram of the inverter provided by this application;

[0037] Figure 6 is another structural schematic diagram of the inverter provided by this application;

[0038] Figure 7 This is a schematic diagram of the process of outputting reactive disturbance based on PCC negative sequence voltage change provided by this application;

[0039] Figure 8 This is a schematic diagram of the change of reactive disturbance and PCC voltage frequency output in equal steps provided by this application;

[0040] Figure 9 This is a schematic diagram of the process of islanding detection performed by the control module in the inverter provided by this application;

[0041] Figure 10 It is a flowchart of the island detection method provided by this application;

[0042] Figure 11 This is a waveform diagram of islanding detection performed on two inverters running in parallel provided by this application. DETAILED DESCRIPTION

[0043] With the continuous increase in energy demand and the proposal of carbon neutrality goals, the proportion of new energy in primary energy consumption continues to increase, and it is accelerating the replacement of fossil energy. As a key industry for energy consumption, the power industry has incorporated new energy power generation into the power system, and used new energy power generation to achieve sustainable utilization of power resources. The small network formed by new energy power generation is incorporated into the public power grid, which can improve the reliability and safety of the public power grid, help expand the coverage of the public power grid, save costs, etc. The power system provided in this application can be a new energy power generation system that uses solar energy, wind energy or energy storage systems to generate electricity. The inverter provided in this application can be applicable to the above-mentioned power system, and can convert the direct current generated by the direct current source in the power system into alternating current of the mains frequency, and then output the alternating current to the public power grid for use by the public power grid and loads. Specifically, it can be used for various large loads (such as industrial electrical equipment such as fans and water pumps) or various small loads (such as household electrical equipment such as refrigerators and televisions), and there is no restriction here. The power system provided in this application can be adapted to different application scenarios, such as photovoltaic power supply scenarios, wind power supply scenarios, photovoltaic hybrid power supply scenarios, etc. Different application scenarios can provide different DC sources for the power system, which can be determined according to the actual application scenarios and are not restricted here.

[0044] See also Figure 1 , Figure 1 This is a schematic diagram of an application scenario of the power system provided by the present application. The power system provided by the present application may specifically include an inverter and may also include a DC source. One end of the inverter is connected to the DC source, the other end of the inverter is coupled to the public power grid, and the common coupling point (PCC) between the inverter and the public power grid is connected to the load. When the public power grid and the inverter are operating normally, the inverter can convert the DC power input from the DC source into AC power and then incorporate it into the public power grid to supply power to various types of loads in the public power grid. Figure 1 In the power system shown, the DC source can be a photovoltaic array, a wind power DC source, or an energy storage power source. Correspondingly, the inverter in the power system can be a photovoltaic inverter, a wind power converter, or an energy storage converter (Power Conversion System, PCS). In other words, in Figure 1 In the power system shown, when the DC source is a photovoltaic array, the inverter is a photovoltaic inverter. The DC input voltage provided by the photovoltaic array is converted into AC voltage by the photovoltaic inverter, which can be used by various types of loads such as motors, water pumps, HVAC or refrigerators in the public power grid. Figure 2 As shown, Figure 2This is another application scenario diagram of the power system provided by this application. In this scenario, the power system may include multiple inverters, and correspondingly multiple DC sources. Multiple inverters are connected in parallel to the PCC, the public grid is coupled to the multiple inverters and connected to the PCC, and the load is connected to the PCC. When the public grid and the multiple inverters are operating normally, the DC power input by the multiple DC sources can be converted by their respective inverters and can be used together to supply power to the loads in the public grid. Figure 2 In the power system shown, the multiple DC sources can be of the same type or different types. The type of each DC source matches the type of the inverter corresponding to the DC source. For example, when a photovoltaic array is used as a DC source, the DC source matches the photovoltaic inverter. Figure 2 The number and type of DC sources and inverters shown are for example purposes only and do not constitute a limitation on the embodiments of the present application. Figure 1 and / or Figure 2 In the power system shown, if the total power output of the inverters matches the power consumed by the loads, the inverters can continue to supply power to the loads even if the public grid is shut down. This keeps the local grid formed by the inverters and loads energized, creating a power supply island. The creation of a power supply island can lead to unplanned energization in the outage area and uncontrolled voltage and frequency, posing a significant safety hazard to power maintenance personnel and electrical equipment.

[0045] The inverter provided by the present application can output reactive disturbance according to the value of reactive disturbance obtained based on the voltage frequency of PCC, and detect power supply island according to the influence of reactive disturbance on PCC voltage frequency, wherein the value of reactive disturbance obtained by the inverter changes gradually. By implementing the present application, when power supply island occurs, the change of PCC voltage frequency can be accelerated by applying reactive disturbance, thereby realizing rapid detection of power supply island, ensuring island detection effect, and improving island detection efficiency. Figure 3-Figure 6 The power system and inverter provided in this application are illustrated by way of example.

[0046] See also Figure 3 , Figure 3 This is a schematic diagram of the structure of the power system provided by this application. Figure 3 The power system shown includes an inverter and may also include a DC source. The input end of the inverter is connected to the DC source, and the output end of the inverter is coupled to the public grid; the common coupling point PCC between the inverter and the public grid is connected to the load. Optionally, the public grid can also be connected to the grid through a grid switch and a transformer ( Figure 3(not shown) is connected to the PCC with an inverter. In the present application, a DC source provides a DC voltage input to the inverter. The inverter is used to convert the DC power generated by the DC source into the AC power required by the public power grid, and output it to the public power grid. The inverter is also used to detect the power supply island in the above-mentioned power system, and control the inverter to disconnect from the load when the power supply island is detected, so as to detect the power supply island in time and take measures to eliminate the power supply island to prevent the harm caused by the island effect. The above-mentioned inverter may be an isolated inverter or a non-isolated inverter, which can be determined according to the actual application scenario requirements and is not limited here. And the above-mentioned inverter may be a three-phase inverter.

[0047] See Figure 4 , Figure 4 This is another schematic diagram of the power system provided by this application. Figure 4 As shown, the power system may include N inverters, and the power system may also include N DC sources. When the power system is in an application scenario where multiple machines (i.e., multiple inverters) are running, N may be an integer greater than 1. Each of the N DC sources is connected to its corresponding inverter, and the N inverters are connected in parallel to the public grid and coupled to the PCC, and the load is connected to the PCC. Each inverter may also be connected to the PCC via its corresponding grid-connected switch, and the public grid may also be connected to the PCC via the grid switch and the N inverters. When the public grid and the N inverters are operating normally, the grid switch and the N grid-connected switches are closed normally, and the DC power input by the N DC sources can be converted by their corresponding inverters to supply power to the load in the public grid. Exemplarily, the power system may be a photovoltaic system, that is, the DC sources included in the power system are all photovoltaic arrays, and the inverters are all photovoltaic inverters.

[0048] See Figure 5 , Figure 5 This is a schematic diagram of the structure of the inverter provided by this application. Figure 5As shown, the inverter includes an inverter power conversion module and a control module. The input end of the inverter power conversion module can be used as the input end of the inverter, and the input end is used to connect a DC source; the output end of the inverter power conversion module can be used as the output end of the inverter, and the output end can be coupled to connect the public power grid to the PCC. In the present application, the inverter power conversion module of the inverter is used to convert the DC power generated by the DC source into the AC power required by the public power grid, and output it to the public power grid. The control module of the inverter is used to detect power supply islands and control the inverter power conversion module of the inverter to disconnect from the load when the power supply island is detected, so as to detect the power supply island in time and take measures to eliminate the power supply island and prevent the harm caused by the island effect. The above-mentioned control module can be a functional unit in the inverter. In other words, the control module can be integrated in the inverter. The above-mentioned inverter power conversion module can include a direct current (DC) / alternating current (AC) conversion circuit, an AC LCL type filter circuit and a grid-connected switch, etc. The inverter can be disconnected from the load by disconnecting the grid-connected switch. As shown Figure 5 The inverter shown can be applied to Figure 3 or Figure 4 In the power system shown, in other words, Figure 3 、 Figure 4 Each inverter in the power system can be Figure 5 The inverter shown. Understandably, Figure 4 Each inverter includes a control module and an inverter power conversion module. The output end of the inverter power conversion module of each inverter in the N inverters is connected in parallel and coupled to the public power grid and connected to the PCC. The control module in each inverter can be used to detect power supply islands and control the inverter power conversion module in the inverter to disconnect from the load when a power supply island is detected.

[0049] See Figure 6 , Figure 6 This is another schematic diagram of the structure of the inverter provided by this application. Figure 5 It can be seen that the inverter provided in this application includes an inverter power conversion module and a control module. Further, as Figure 6As shown, the control module in the inverter can specifically include a signal sampling unit, a signal processing unit and a loop control unit. Among them, the signal sampling unit in the inverter can be used to collect the voltage frequency of the PCC; the signal processing unit in the inverter can be used to obtain a first disturbance value corresponding to the first voltage frequency of the PCC in the current sampling period, and the first disturbance value is greater than or equal to the second disturbance value corresponding to the second voltage frequency of the PCC in the first sampling period (referring to the sampling period before the current sampling period); the loop control unit in the inverter can be used to control the inverter power conversion module to output reactive disturbance based on the first disturbance value; the signal processing unit in the inverter is also used to control the inverter power conversion module of the inverter to disconnect from the load when a power supply island is detected based on the voltage frequency of the PCC in the second sampling period after the current sampling period by the signal sampling unit. It is understood that when a power supply island occurs, the inverter can output a certain reactive disturbance based on the voltage-frequency change of the PCC. The output of this reactive disturbance will cause the voltage-frequency of the PCC to further change. After the inverter continues to output reactive disturbance for a period of time, the change in the voltage-frequency of the PCC may exceed the set threshold, and the inverter can detect the power supply island accordingly. In this application, the inverter in the power system realizes the detection of power supply islands through the mutual cooperation of the signal sampling unit, signal processing unit, and loop control unit included in the control module. Specifically, the signal sampling unit in the inverter can continuously sample and monitor the voltage frequency of the PCC. The signal processing unit in the inverter can calculate the reactive disturbance value that the inverter needs to output based on the voltage frequency obtained by the signal sampling unit, and gradually change the obtained reactive disturbance value in equal steps. The loop control unit in the inverter can control the inverter power conversion module of the inverter to output reactive disturbance based on the calculated reactive disturbance value, affecting the change in the voltage frequency of the PCC. This allows the signal processing unit to promptly detect when the voltage frequency change of the PCC exceeds a threshold through the sampling results of the signal sampling unit, thereby detecting power supply islanding. The signal sampling unit, signal processing unit, and loop control unit can be modular components in the control module of the inverter, or virtual functional modules in the control module. In other words, the control module can be a functional module built into the inverter, and this functional module can perform the functions performed by the signal sampling unit, signal processing unit, and loop control unit. Therefore, the specific functions of the control module in the inverter are described below from the perspective of the signal sampling unit, signal processing unit, and loop control unit, which are the detailed modules included in the control module. The functions performed by these detailed modules can also be executed by the control module in the inverter.

[0050] The control module in the inverter provided by the present application can control the inverter power conversion module in the inverter to output reactive disturbance based on the first disturbance value and detect the voltage frequency of the PCC. If the power supply island is detected based on the voltage frequency of the PCC, the inverter power conversion module is controlled to disconnect from the load. Among them, the first disturbance value is the disturbance value corresponding to the first voltage frequency of the PCC in the current sampling period, and is greater than or equal to the second disturbance value corresponding to the second voltage frequency of the PCC in the first sampling period, and the sampling period before the current sampling period is the first sampling period. That is, from the perspective of the longitudinal flow of time, the first disturbance value changes gradually. That is to say, when the inverter provided by the present application starts to detect the islanding effect, it can output the reactive disturbance according to the value of the reactive disturbance that changes gradually (specifically, it can change gradually according to the disturbance step) obtained based on the voltage frequency of the PCC. In this way, the reactive disturbance output by the inverter changes gradually. In the presence of a power supply island, the change in the voltage and frequency of the PCC can be controlled due to the influence of the reactive disturbance. As a result, the change in the voltage and frequency of the PCC can quickly reach the threshold, meeting the detection conditions for the power supply island, enabling rapid detection of the power supply island and improving the efficiency of island detection.

[0051] In some feasible implementations, in the above power system (the above Figures 1-4 The power system shown, hereinafter referred to as the above-mentioned power system), the reactive disturbance output by the inverter can be reactive power or reactive current as the disturbance quantity, which can be determined according to the actual application scenario and is not limited here. This application uses reactive power as the disturbance quantity as an example to illustrate the reactive disturbance. Furthermore, the disturbance value mentioned in this application refers to the absolute value of the reactive disturbance and does not involve the positive or negative value of the reactive disturbance, that is, the magnitude of the disturbance values ​​such as the first disturbance value, the second disturbance value, the first reference disturbance value, and the second reference disturbance value does not affect whether the reactive disturbance is actually a capacitive disturbance or an inductive disturbance.

[0052] In some feasible implementations, the signal processing unit in the inverter can also be used to obtain a first disturbance reference value based on the first voltage frequency. Specifically, the first voltage frequency in the current sampling period can be understood as the current voltage frequency, and the average value of the voltage frequency of the PCC in N consecutive sampling periods before the current sampling period can be understood as the sliding window average value of the historical voltage frequency. N is an integer greater than 1. In this application, the value range of N can be 25 to 1000, and one sampling period can refer to one power frequency period of the public power grid. Among them, the signal sampling unit in the inverter can obtain the voltage frequency by a zero-crossing detection method or a phase-locked loop, etc., and this application does not impose any restrictions. After obtaining the first voltage frequency and the average value of the voltage frequency of the PCC in the above-mentioned N consecutive sampling periods, the signal processing unit in the inverter can obtain the first frequency change based on the first voltage frequency and the average value of the voltage frequency of the PCC in the above-mentioned N consecutive sampling periods, and then obtain the above-mentioned first disturbance reference value based on the first frequency change. In detail, the first frequency change can be obtained by the difference between the sliding window average value of the current voltage frequency and the historical voltage frequency, and the first disturbance reference value can be obtained by the first frequency change and a certain proportional coefficient. The first disturbance reference value is greater than or equal to the first disturbance value. In this way, the signal processing unit in the inverter can obtain the initial disturbance reference value (i.e., the first disturbance reference value) based on the current voltage and frequency change of the PCC, and can use the disturbance reference value as an upper limit to limit the size of the reactive disturbance output by the inverter power conversion module in the inverter. In this way, when there is no power supply island and the voltage and frequency of the public power grid fluctuate normally, the inverter will not directly output reactive disturbance according to the disturbance reference value, but will output a smaller reactive disturbance, thereby reducing the negative impact of the reactive disturbance output by the inverter on the power quality of the public power grid.

[0053] In some feasible embodiments, the signal processing unit in the inverter can be configured to obtain a second disturbance value corresponding to the second voltage frequency based on the second voltage frequency of the PCC during the first sampling period. Specifically, the signal processing unit in the inverter can first obtain a second disturbance reference value based on the second voltage frequency. The signal processing unit in the inverter can obtain the second disturbance reference value according to the method for obtaining the first frequency change and the first disturbance reference value described above, namely, obtaining the second frequency change based on the difference between the second voltage frequency and a sliding window average of historical voltage frequencies corresponding to the second voltage frequency, and obtaining the second disturbance reference value based on the second frequency change. Then, when the second disturbance reference value obtained by the signal processing unit in the inverter is less than the preset disturbance step size, a preset disturbance value is obtained as the second disturbance value. The preset disturbance value can be 0, a small value close to 0, or a value close to the second disturbance reference value, and can be set based on actual scenarios and is not limited by this application. In this way, the second disturbance value corresponding to the second voltage frequency can be obtained based on the second voltage frequency when the voltage frequency change of the PCC is small. It is understood that in the above-described power system, when both the inverter and the public grid are operating normally, the PCC voltage frequency may fluctuate normally. In this case, the second voltage frequency obtained by the signal sampling unit in the inverter has a smaller change compared to the average value of the historical voltage frequency. The second disturbance value obtained according to the above process is the above-described preset disturbance value and is also smaller. Therefore, the inverter can output a smaller reactive disturbance according to the second disturbance value, and the negative impact of this reactive disturbance on the power quality of the power grid is also smaller. It is understandable that at this time, the inverter can obtain a value equal to the second disturbance value as the first disturbance value, and output the reactive disturbance according to the first disturbance value, which can be regarded as outputting a reactive disturbance according to the second disturbance value. Through the above process, a correspondingly smaller reactive disturbance value can be obtained when the PCC voltage frequency changes slightly. This method is simple and easy to implement, and can reduce the negative impact of the reactive disturbance output for islanding effect detection on the power quality of the power grid.

[0054] In some feasible embodiments, the signal processing unit in the inverter can be configured to obtain a first disturbance value corresponding to the first voltage frequency of the PCC in the current sampling period based on the disturbance step size and the second disturbance value. Specifically, when the first disturbance reference value is greater than the disturbance step size and the second disturbance reference value is less than the disturbance step size, the inverter can detect that the voltage frequency of the PCC obtained in the current sampling period has significantly changed compared to the previous sampling period. This situation may be caused by the generation of a power supply island in the power system. Therefore, the signal processing unit in the inverter can obtain a preset initial value as the first disturbance value, so that the inverter power conversion module in the inverter can be controlled to start outputting reactive power disturbance according to the preset initial value. After the reactive disturbance is output, the power supply island is detected based on whether the voltage frequency of the PCC changes due to the reactive disturbance and the specific change. It is understood that the preset initial value can be set to a fixed value less than the disturbance step size, or set to a value equal to the disturbance step size. The specific setting can be based on the actual application scenario and is not limited by this application. In this application, the above perturbation step size can be calculated according to the following formula (1):

[0055]

[0056] Among them, Gradthres is the perturbation step size, k is the proportional coefficient, which can range from 1.2 to 2.0, Q is the quality factor, R t is the frequency change rate threshold, f res is the load LC resonant frequency, f rate is the rated frequency of the public grid.

[0057] On the other hand, when the above-mentioned first disturbance reference value is greater than the disturbance step size, and the first disturbance reference value is equal to the above-mentioned second disturbance reference value, the signal processing unit in the inverter can obtain the first disturbance value based on the disturbance step size and the second disturbance value. It can be understood that the first disturbance reference value and the second disturbance reference value are obtained based on the corresponding voltage frequency, and the two are equal and greater than the disturbance step size, which means that the change in the voltage frequency of the PCC in the two consecutive sampling periods of the current sampling period and the first sampling period is basically equal. This shows that in this process, due to the influence of the reactive disturbance output by the inverter, the change in the voltage frequency of the PCC is controllable, so the reactive disturbance that needs to be output by the inverter can be calculated according to the method provided in this application. Among them, the above-mentioned obtaining of the first disturbance value based on the disturbance step size and the second disturbance value can refer to obtaining the first disturbance value based on the sum of the second disturbance value and the disturbance step size. It is understood that the first disturbance value may also deviate from the sum value. For example, when the sum value is greater than the first disturbance reference value, the first disturbance value is equal to the first disturbance reference value. This ensures that the first disturbance value never exceeds the first disturbance reference value. Through the above process, the signal processing unit in the inverter can calculate the first disturbance value and use this first disturbance value as the reactive disturbance value to be output by the inverter. When a power supply island exists in the power system, from the perspective of time longitudinal flow, since the first disturbance value gradually changes according to the disturbance step size, the reactive disturbance output according to this first disturbance value also gradually changes. Therefore, the changes in the PCC voltage and frequency affected by the reactive disturbance are controllable and regular. In other words, the inverter obtains a reactive disturbance value that changes in equal steps based on the PCC voltage and frequency changes and outputs the reactive disturbance. This allows the PCC voltage and frequency changes to quickly meet the detection conditions for power supply islands, thereby reducing the possibility of island detection timeouts and improving island detection efficiency.

[0058] Optionally, in some feasible implementations, in addition to calculating the reactive disturbance value based on the voltage-frequency change of the PCC as described above, the inverter can also combine other methods to calculate the reactive disturbance value. For example, the inverter can also obtain the reactive disturbance value based on the three-phase voltage negative sequence component of the PCC (also called negative sequence voltage, hereinafter referred to as voltage negative sequence component). It is understandable that the inverter in the above-mentioned power system is a three-phase inverter, so the DC source outputs three-phase AC power through the three-phase inverter, and the load in the public power grid includes three-phase loads and single-phase loads (which can be regarded as asymmetric three-phase loads). Therefore, the above-mentioned loads can generally be understood as asymmetric three-phase loads. When islanding does not occur, the public power grid operates normally. Since the three-phase voltage imbalance of the public power grid meets the relevant regulations, even if the load is an asymmetric three-phase load, the three-phase voltage of the PCC is basically balanced, so the negative sequence component of the voltage of the PCC is small at this time. When an islanding event occurs, the public grid is disconnected from the inverter and the load. Since the load is an asymmetric three-phase load, the negative-sequence component of the PCC voltage may suddenly increase. Therefore, the inverter can detect the timing of the output reactive disturbance based on the negative-sequence component of the PCC voltage and calculate the value of the reactive disturbance. Specifically, the signal processing unit in the inverter can obtain a first voltage change based on the first negative-sequence component of the current sampling period and the average value of the negative-sequence component of the voltage in M ​​consecutive sampling periods before the current sampling period. The first voltage change can reflect the difference between the current negative-sequence component of the voltage and the sliding window average value of the historical negative-sequence component of the voltage. M is an integer greater than 1. In this application, M can be taken in the range of 25 to 1000. The negative-sequence component of the PCC voltage can be obtained specifically through a phase-locked loop. The phase-locked loop can filter out the DC component and harmonic component of the voltage to obtain a relatively pure fundamental voltage negative-sequence component. Optionally, other methods can be used to obtain the negative sequence component of the PCC voltage, such as obtaining the voltage amplitude and phase and then using a formula to calculate the negative sequence component of the voltage. This application does not limit this. Furthermore, when the first voltage change is greater than a preset threshold, the signal processing unit in the inverter obtains a short-term disturbance value, and obtains a reactive disturbance value based on the short-term disturbance value and the first disturbance value, so that the inverter power conversion module in the inverter can be controlled to output reactive disturbance according to the reactive disturbance value. In this application, the preset threshold can be 1% of the rated voltage of the inverter, and the short-term disturbance value can be obtained from the output power of the inverter. For example, the value of the short-term disturbance value can be equal to 1% to 5% of the instantaneous active power of the inverter, or 1% to 5% of the rated active power of the inverter. The specific value can be determined according to the actual application scenario and is not limited by this application. The instantaneous active power of the inverter can be calculated based on the active current and active voltage collected by the signal sampling unit.Through the above process, the inverter can use the change of the PCC's negative sequence voltage to calculate the value of the reactive disturbance. This can be used to help detect power supply islands in another way, avoiding the phenomenon that may cause island detection timeout when the PCC voltage frequency changes slightly, which is conducive to improving island detection efficiency.

[0059] In some feasible implementations, the signal processing unit in the inverter can calculate the value of the reactive disturbance based on the change in the PCC voltage frequency, or can obtain the value of the reactive disturbance based on the change in the PCC voltage frequency and the change in the negative sequence component of the PCC voltage. If the first disturbance value and the short-term disturbance value obtained in the above manner are both reactive disturbance values ​​to be output at the same moment after the current sampling period, then it is necessary to select one of the first disturbance value and the short-term disturbance value as the reactive disturbance value to be output by the inverter power conversion module of the inverter. Specifically, the larger value can be selected as the reactive disturbance value to be output by the inverter power conversion module of the inverter. That is, when the short-term disturbance value is less than the first disturbance value, the signal processing unit in the inverter selects the first disturbance value as the value of the reactive disturbance to be output by the inverter power conversion module of the inverter, and accordingly, the loop control unit in the inverter controls the inverter power conversion module of the inverter to output reactive disturbance according to the first disturbance value; and when the short-term disturbance value is greater than the first disturbance value, the signal processing unit in the inverter selects the short-term disturbance value as the value of the reactive disturbance to be output by the inverter power conversion module of the inverter, and accordingly, the loop control unit in the inverter controls the inverter power conversion module of the inverter to output reactive disturbance according to the short-term disturbance value. When the short-term reactive disturbance is equal to the first disturbance value, either of the two can be selected as the value of the reactive disturbance to be output by the inverter power conversion module of the inverter, and this application does not limit this. By implementing the above process, the inverter can combine two different ways of obtaining reactive disturbance values ​​to perform islanding detection, which is conducive to improving the efficiency of islanding detection.

[0060] In some feasible implementations, if the loop control unit in the inverter controls the inverter power conversion module in the inverter to output reactive disturbance according to the above-mentioned short-time disturbance value, then further, the loop control unit in the inverter can specifically control the inverter power conversion module to continuously output reactive disturbance within a first preset time period, and when the end time of the first preset time period arrives, control the above-mentioned inverter power conversion module to stop outputting reactive disturbance. The first preset time period can be set according to the specific scenario, and for example, it can be 3 to 5 power frequency cycles. If the inverter stops outputting reactive disturbance for a period of time (for example, 1s), if at a certain moment it meets the two conditions mentioned above: the first voltage change corresponding to the first voltage negative sequence component of the PCC is greater than the preset threshold, and the above-mentioned short-time reactive disturbance value is greater than the first disturbance value, then the inverter can re-perform the above-mentioned process of intermittently outputting reactive disturbance according to the short-time disturbance value. See. Figure 7 , Figure 7 The schematic diagram of the process of outputting reactive disturbance based on PCC negative sequence voltage change provided in this application is as follows: Figure 7 As shown, the inverter follows the short-term disturbance value Q s After the reactive power disturbance is continuously output within the first preset time t0, the reactive power disturbance is locked and stopped within the time t1. After that, if the above two conditions are met again, press Q again. s The inverter continuously outputs reactive power disturbances for a first preset duration t0. This allows the inverter to intermittently output reactive power disturbances when islanding does not occur but the public grid experiences brief, continuous fluctuations. This prevents excessive reactive power disturbance output, conserves resources, and reduces negative impacts on grid power quality.

[0061] In some feasible implementations, the power system provided by this application is as follows: Figure 4 The power system shown in FIG. 1 includes multiple Figure 5 or Figure 6The inverters described above are connected in parallel to the public grid and the PCC at their output terminals. Each of these inverters can obtain reactive disturbance values ​​using the two different methods described above. The signal sampling unit in each inverter can be used to collect the voltage and current of the PCC. For each inverter, when the first voltage variation corresponding to the first voltage negative-sequence component obtained by the signal processing unit in the inverter is greater than a preset threshold, and the short-term disturbance value is greater than the first disturbance value, the loop control unit in the inverter can control the inverter power conversion module of the inverter to output reactive disturbance according to the short-term disturbance value. It can be understood that since the voltage sampled by the signal processing unit in each inverter is the voltage of the PCC, the timing at which each inverter learns that the first voltage variation is greater than the preset threshold is essentially the same. Therefore, the timing at which the inverter power conversion module in the inverter begins outputting reactive disturbances according to the short-term disturbance value is also very close. This can be understood as the aforementioned multiple inverters synchronously outputting reactive disturbances. Furthermore, assuming that the above-mentioned multiple inverters are inverters of the same type, and the short-term disturbance value is obtained according to the rated output power of the inverter, then the short-term disturbance value obtained by each inverter is the same. At this time, the reactive disturbances output by these inverters are equal in magnitude and in the same direction (referring to being both inductive or capacitive). In other words, in a scenario where multiple machines (i.e., multiple inverters) are connected in parallel, the multiple machines can synchronously output equal amounts of reactive disturbances in the same direction. Therefore, compared with other passive island detection methods, the reactive disturbances output by the multiple inverters in the PCC in this application will not offset each other due to sampling or detection differences of the inverters. The reactive disturbances output by multiple inverters in the same direction are superimposed on the PCC, which can speed up the deviation of the PCC voltage frequency when the inverter output power is highly matched with the load absorption power, reduce the island detection blind spot, thereby improving the efficiency of island detection and preventing island detection timeout.

[0062] In some feasible embodiments, after the loop control unit in the inverter controls the inverter power conversion module of the inverter to output reactive power, the signal processing unit in the inverter can detect the power supply island based on the voltage frequency of the PCC in the second sampling period. Specifically, if the signal processing unit in the inverter finds that the third voltage frequency of the PCC in the second sampling period exceeds the frequency threshold, or the frequency change rate corresponding to the third voltage frequency exceeds the frequency change rate threshold, it is determined that the power supply island is detected. It can be understood that the above-mentioned frequency threshold may include a first frequency threshold as an upper limit and a second frequency threshold as a lower limit, which can be specifically determined according to the certification standard that the inverter needs to implement. The above-mentioned frequency change rate threshold may include a first frequency change rate threshold as an upper limit and a second frequency change rate threshold as a lower limit, which can be specifically determined according to the maximum frequency crossing value that the inverter needs to pass. Among them, the frequency change rate (Rate of Change of Frequency, RoCoF) corresponding to the third voltage frequency can be calculated according to the following formula (2):

[0063] RoCoF=(f pcc -f pcclast )×f pcc (2)

[0064] Among them, f pcc is the third voltage frequency mentioned above, f pcclast is the voltage frequency of the sampling period before the second sampling period.

[0065] In some feasible embodiments, the signal processing unit in the inverter can detect power supply islanding based on the following conditions: the third voltage frequency of the PCC is continuously greater than the first frequency threshold or continuously less than the second frequency threshold within a first reference time period, or the frequency change rate corresponding to the third voltage frequency is continuously greater than the first frequency change rate threshold or continuously less than the second frequency change rate threshold within a second reference time period. It is understandable that the third voltage frequency can generally refer to the voltage frequency of any second sampling period after the current sampling period. The third voltage frequency is continuously greater than the first frequency threshold (or less than the second frequency threshold) within the first reference time period, which can refer to the voltage frequencies of several consecutive sampling periods after the current sampling period (the total duration of these sampling periods correspondingly exceeds the first reference time period) that are all greater than the first frequency threshold (or less than the second frequency threshold). Accordingly, the frequency change rate corresponding to the third voltage frequency is continuously greater than the first frequency change rate threshold or continuously less than the second frequency change rate threshold within the second reference time period, which can also be understood with reference to the above description. The above-mentioned first reference time period and second reference time period can be set according to actual scenarios and are not limited in this application. For example, both reference time periods can be set to 5 power frequency cycles. In addition, in some optional embodiments, due to the presence of detection errors, the third voltage frequency collected by the signal sampling unit of the inverter within a single sampling period may fluctuate for a short time. Therefore, before calculating the frequency change rate, the signal processing unit in the inverter can use the sliding average of the voltage frequencies collected in L sampling periods, including the second sampling period, as the above-mentioned third voltage frequency. L can be taken as needed, for example, it can be 5 to 10. That is, in the above-mentioned power system, the signal processing unit in the inverter can perform a sliding average process of 5 to 10 power frequency periods on the voltage frequency collected after the current sampling period to obtain the third voltage frequency. In this way, the inverter can detect islanding based on whether the voltage frequency of the PCC is affected by reactive disturbances and deviates to exceed the threshold, or it can detect islanding based on whether the frequency change rate of the PCC exceeds the threshold. It is understandable that in the present application, the first disturbance value obtained by the signal processing unit in the inverter changes gradually according to the disturbance step size. If the loop control unit in the inverter controls the inverter power conversion module to output reactive disturbance according to the first disturbance value, then the size of the reactive disturbance output by the inverter also changes according to the same step size. The change of the voltage frequency of the PCC affected by the reactive disturbance is controllable, and the frequency change rate obtained according to the voltage frequency also changes regularly instead of randomly. Therefore, the inverter outputs reactive disturbance to make the PCC voltage frequency or frequency change rate quickly reach the threshold, thereby accelerating the island detection process and improving the efficiency of island detection. Figure 8 , Figure 8 This is a schematic diagram of the change of reactive disturbance and PCC voltage frequency output in equal steps provided by this application. Figure 1In the application scenario shown, if the inverter in the power system performs islanding detection in the above manner, then after the power supply islanding occurs, the reactive disturbance output by the inverter changes according to the above disturbance step size (that is, changes in equal steps), as shown in FIG. Figure 8 As shown, the reactive disturbance Q outputted in equal steps is f (like Figure 8 The solid line in the middle right figure shows a linear change, and the corresponding PCC voltage frequency f obtained by the inverter (as shown in Figure 8 The solid line in the middle left figure also changes linearly. Therefore, the voltage-frequency variation of the PCC is regular, which in turn makes the frequency change rate change regularly, ensuring that the inverter can quickly detect islanding. Figure 8 The middle dashed line represents the changing trend of reactive disturbance and PCC voltage frequency in an active islanding detection method using reactive disturbance. The change of frequency change rate in this method may be irregular. Compared with this method, the present application can improve the efficiency of islanding detection.

[0066] In some possible implementations, Figure 4 In the multi-machine parallel scenario shown, for each inverter, after detecting the power supply island, the inverter can wait for the third reference time, and disconnect from the load when the end of the third reference time arrives. Specifically, the inverter can disconnect from the load by taking measures such as blocking the wave and shutting down. The above-mentioned third reference time can be set according to the actual scenario, such as setting it to 2 to 5 power frequency cycles, and this application does not impose any restrictions on this. It is understandable that after the inverter detects the island, it waits for the third reference time before delaying the blocking wave and shutting down. Compared with the operation of blocking the wave and shutting down immediately after the island is detected, it can prevent the negative impact on the island detection effect of other inverters.

[0067] The following combination Figure 9 The process of performing island detection on the control module in the inverter is described below. Figure 9 As shown, the process specifically includes:

[0068] On the one hand, the control module in the inverter can obtain the first voltage frequency of the PCC, and obtain the first frequency change Δf based on the first voltage frequency, and then obtain the first disturbance reference value Q based on the first frequency change Δf. p , and then based on the first disturbance reference value Q p And the disturbance step length Gradthres obtains the first disturbance value Q f On the other hand, the control module in the inverter can also obtain the first voltage negative sequence component of PCC, and obtain the first voltage variation ΔV based on the first voltage negative sequence component. gn , when the first voltage change ΔV gn When the preset threshold is exceeded, the short-term disturbance value Q is obtained s .

[0069] When the first disturbance value Q f and the short-term disturbance value Q s When both can be used as the reactive disturbance value to be output by the inverter at the same moment after the current sampling period, the control module in the inverter can be used to obtain the first disturbance value Q f and the short-term disturbance value Q s The larger one is selected as the value Q to be output by the inverter power conversion module of the inverter for detecting the reactive disturbance of the power supply island airef And by executing the loop control of the power loop, a corresponding pulse width modulation (PWM) drive signal is generated so that the inverter power conversion module of the inverter is calculated according to the reactive disturbance value Q airef The reactive disturbance for detecting power supply islanding is output, and islanding detection is performed based on the impact of the reactive disturbance on the voltage and frequency of the PCC. Figure 9 P in ref and Q ref This value is irrelevant to islanding detection and indicates the active and reactive dispatch values ​​during normal inverter operation.

[0070] In the present application, when the grid-connected inverter supplies power to the load in the public power grid, the control module of the inverter can obtain a first disturbance reference value based on the first voltage frequency of the PCC in the current sampling period, and obtain a corresponding second disturbance value based on the second voltage frequency of the PCC in the sampling period before the current sampling period, and then obtain a first disturbance value based on the second disturbance value, the first disturbance reference value and the disturbance step size, and control the inverter power conversion module of the inverter to output reactive disturbance according to the first disturbance value, so that the voltage frequency or frequency change rate of the PCC is affected by the reactive disturbance to reach a threshold value and the power supply island is detected accordingly, and the inverter is controlled to disconnect from the load after the power supply island is detected. The reactive disturbance in the present application gradually changes according to the disturbance step size, which can make the voltage frequency change of the PCC controllable and regular, which is conducive to accelerating the detection of power islands, avoiding island detection timeouts, and improving the efficiency of island detection. In the present application, the first disturbance value is less than or equal to the first disturbance reference value, which is beneficial to reducing the negative impact of reactive disturbance output on the power quality of the power grid when no power supply island occurs. Furthermore, the present application can also obtain the value of the reactive disturbance to be output based on the change of the negative sequence voltage of the PCC. Combining this method with the above-mentioned method of obtaining the value of the reactive disturbance according to the disturbance step size is beneficial to achieve complementary advantages and improve the efficiency of island detection. In the scenario where multiple inverters are operated in parallel, multiple machines can synchronously output equal amounts of reactive disturbances in the same direction, which is beneficial to reducing the blind spot of island detection and accelerating the deviation of the PCC voltage frequency, thereby accelerating the detection of power supply islands, ensuring the effect of island detection, and improving the efficiency of island detection.

[0071] See also Figure 10 , Figure 10 : is a flow chart of the island detection method provided by the present application. The island detection method provided by the present application is applicable to an inverter, wherein the input end of the inverter can be used to connect a DC source, the output end of the inverter is coupled to the public grid, and the coupling connection point PCC is connected to the load. Exemplarily, the island detection method provided by the present application can be applied to Figure 5 or Figure 6 The inverter shown can be applied to the above Figures 1-4 The power system shown in Figure 1 is as follows. Figure 10 As shown, the method may include the following steps:

[0072] S1001: Obtain a second voltage frequency of a PCC in a first sampling period, and obtain a second disturbance value corresponding to the second voltage frequency based on the second voltage frequency.

[0073] In some feasible embodiments, the inverter can obtain the second voltage frequency of the PCC in the first sampling period (i.e., the sampling period before the current sampling period), and the voltage frequency of the PCC in N consecutive sampling periods before the first sampling period, and then obtain the second frequency change based on the second voltage frequency and the average value of the N voltage frequencies. A second disturbance reference value is obtained based on the second frequency change, and the second disturbance reference value can be used as an upper limit to limit the size of the second disturbance value. When the second disturbance reference value is less than the disturbance step size, a preset disturbance value is obtained as the second disturbance value. Wherein, the disturbance step size is calculated according to the above formula (1).

[0074] S1002: Obtain a first voltage frequency of a PCC in a current sampling period, and obtain a first disturbance reference value based on the first voltage frequency.

[0075] In some feasible implementations, the inverter obtains the first disturbance reference value in the same manner as the second disturbance reference value obtained in step S1001. Specifically, the first voltage frequency of the PCC in the current sampling period and the voltage frequencies of the PCC in N consecutive sampling periods before the current sampling period may be obtained, and then a first frequency variation is obtained based on the first voltage frequency and the average value of the corresponding N voltage frequencies. A first disturbance reference value is obtained based on the first frequency variation, and the first disturbance reference value is used as an upper limit to limit the magnitude of the first disturbance value.

[0076] S1003 : Obtain a first disturbance value corresponding to the first voltage frequency based on the first disturbance reference value, the disturbance step size, and the second disturbance value.

[0077] In some feasible implementations, the inverter may obtain the first disturbance value based on the first disturbance reference value, the disturbance step size, and the second disturbance value. Specifically, when the first disturbance reference value is greater than the disturbance step size and the second disturbance reference value is less than the disturbance step size, a preset initial value is obtained as the first disturbance value; when the first disturbance reference value is greater than the disturbance step size and the first disturbance reference value is equal to the second disturbance reference value, the first disturbance value is obtained based on the disturbance step size and the second disturbance value, wherein the first disturbance value is greater than the second disturbance value. Moreover, the first disturbance value does not exceed the first disturbance reference value.

[0078] By executing steps S1001-S1003, the change in the PCC voltage frequency can be used to obtain a first disturbance value as the value of the reactive disturbance. If the reactive disturbance is subsequently output according to the first disturbance value, the output reactive disturbance changes gradually in equal steps. In other words, outputting the reactive disturbance according to the first disturbance value, on the one hand, can make the change in the PCC voltage frequency controllable when a power supply island exists, thereby accelerating the speed at which the PCC voltage frequency or frequency change rate reaches the island detection condition, ensuring the effectiveness of island detection and avoiding island detection timeouts. On the other hand, when a power supply island does not exist and the public power grid fluctuates normally, the magnitude of the output reactive disturbance can be reduced, thereby reducing the negative impact of the reactive disturbance on the power quality of the power grid.

[0079] S1004: Obtain a first voltage negative sequence component of the PCC in a current sampling period, and obtain a first voltage variation corresponding to the first voltage negative sequence component based on the first voltage negative sequence component.

[0080] In some feasible implementations, the inverter may further obtain a first negative-sequence voltage component of the PCC in a current sampling period and obtain the negative-sequence voltage components of M consecutive sampling periods before the current sampling period to obtain a change in the current negative-sequence voltage component. Specifically, a first voltage change corresponding to the first negative-sequence voltage component may be obtained based on the first negative-sequence voltage component and an average value of the negative-sequence voltage components of the M consecutive sampling periods, where M is an integer greater than 1.

[0081] S1005 , determining whether the first voltage variation is greater than a preset threshold, if so, executing step S1006 .

[0082] S1006, obtaining a short-term disturbance value.

[0083] In some feasible implementations, when the above-mentioned first voltage change is greater than a preset threshold, the control module in the inverter can calculate and obtain a short-term disturbance value. Specifically, the short-term disturbance value can be obtained based on the instantaneous active power or rated active power of the inverter. It can be determined according to the actual application scenario and is not limited here. Execute steps S1004-S1006, and the change of the negative sequence voltage (i.e., the negative sequence component of the voltage) of the PCC can be used to obtain a short-term disturbance value. The short-term disturbance value can be used as one of the sources of the reactive disturbance value to be output by the inverter. In such a case Figure 1 In the scenario shown, if the inverter obtains a short-term disturbance value based on the PCC negative sequence voltage change and controls the inverter to output reactive disturbance according to the short-term disturbance value, then when the PCC voltage frequency change is small (the first disturbance value obtained by steps S1001-S1003 is small at this time), another method is used to supplement the reactive disturbance value, which is beneficial to improving the efficiency of islanding detection. Figure 4 In the scenario shown, if each of the multiple inverters can obtain a short-term disturbance value based on the PCC negative-sequence voltage change and control the inverter to output reactive disturbance according to the short-term disturbance value, then the multiple inverters can synchronously output equal amounts of reactive disturbances in the same direction, which is beneficial for accelerating the PCC voltage-frequency offset when the total power output of the multiple inverters matches the absorbed power of the load, thereby destroying the above-mentioned power matching, accelerating the islanding detection speed, and avoiding islanding detection timeout.

[0084] S1007, determining whether the following conditions are met: the short-term disturbance value has been obtained and the first disturbance value is greater than the short-term disturbance value; if not, executing step S1008; if so, executing step S1009.

[0085] In some feasible implementations, the inverter may only execute steps S1001 to S1003 and not execute steps S1004 to S1006. Then, when executing step S1007, if the result is negative, step S1008 is directly executed.

[0086] Optionally, the inverter may also simultaneously execute step S1004 and step S1005 during the execution of steps S1001 to S1003. If the judgment result of executing step S1005 is negative, the short-term disturbance value cannot be obtained. Then, when executing step S1007, the judgment result is negative, and step S1008 is directly executed. If the judgment result of executing step S1005 is positive, step S1006 may be executed to obtain the short-term disturbance value, and then step S1007 may be executed to determine whether the first disturbance value is greater than the short-term disturbance value. The corresponding subsequent steps are executed according to the judgment result of step S1007.

[0087] In some feasible implementations, if the first disturbance value is obtained by executing step S1003 above and the short-term disturbance value is obtained by executing step S1006, when both disturbance values ​​refer to the magnitude of the reactive disturbance to be output at the same moment after the current sampling period, it is necessary to select one of the first disturbance value and the short-term disturbance value as the reactive disturbance value to be output by the inverter according to certain rules. Specifically, the larger of the first disturbance value and the short-term disturbance value can be selected, and the inverter output reactive disturbance can be controlled according to the selection result. In other words, it is determined whether the first disturbance value is greater than the short-term disturbance value, and step S1008 or step S1009 is selected based on the determination result.

[0088] S1008: Control the inverter to output reactive disturbance according to the first disturbance value.

[0089] S1009: Control the inverter to output reactive disturbance according to the short-term disturbance value.

[0090] In some optional implementations, the inverter can be controlled to continuously output reactive power disturbance for a first reference duration based on the short-term disturbance value, and the inverter can be controlled to stop outputting reactive power disturbance at the end of the first reference duration to avoid excessive reactive power disturbance output and conserve resources. After reactive power is output, step S1010 is then executed.

[0091] S1010: Detect a third voltage frequency, and calculate a frequency change rate corresponding to the third voltage frequency.

[0092] In some feasible implementations, after controlling the inverter to output reactive disturbance, the third voltage frequency is monitored during a second sampling period following the current sampling period. Furthermore, the frequency change rate corresponding to the third voltage frequency can be calculated according to the above formula (2) to detect whether power supply islanding has occurred based on the frequency change rate.

[0093] S1011, determine whether the third voltage frequency exceeds the frequency threshold or the frequency change rate exceeds the frequency change rate threshold. If so, execute step S1012; if not, return to step S1001.

[0094] In some optional embodiments, the inverter continuously monitors the third voltage frequency and the frequency change rate corresponding to the third voltage frequency after outputting the reactive disturbance, and determines whether a power supply island is detected based on whether the following judgment conditions are met: the third voltage frequency exceeds the frequency threshold or the frequency change rate exceeds the frequency change rate threshold. Specifically, the above judgment conditions can also be understood as: the third voltage frequency is continuously greater than the first frequency threshold or less than the second frequency threshold within the first reference time length, or the frequency change rate corresponding to the third voltage frequency is continuously greater than the first frequency change rate threshold or less than the second frequency change rate threshold within the second reference time length. When the above judgment conditions are met, step S1012 is executed. When the above judgment conditions are not met, it is necessary to return to step S1001 and re-obtain the value of the reactive disturbance corresponding to the next sampling period to control the inverter to output the reactive disturbance according to the updated value.

[0095] S1012: Power supply islanding is detected.

[0096] S1013, waiting for a third reference duration.

[0097] In some possible implementations, Figure 4 In the scenario of multiple machines connected in parallel as shown, when any one of the inverters executes the island detection method provided in the present application and detects a power supply island, the inverter can first wait for a third reference time, that is, delay for a period of time, and then execute the subsequent step S1014 to prevent a negative impact on the island detection effect of other inverters.

[0098] S1014: Control the inverter to disconnect from the load.

[0099] In some feasible implementations, the inverter may perform steps such as blocking the wave and disconnecting the grid-connected switch to disconnect the load. The grid-connected switch may be integrated into the inverter.

[0100] In the present application, when the grid-connected inverter supplies power to the load in the public power grid, the control module of the inverter can obtain a first disturbance reference value based on the first voltage frequency of the PCC in the current sampling period, and obtain a corresponding second disturbance value based on the second voltage frequency of the PCC in the sampling period before the current sampling period, and then obtain a first disturbance value based on the second disturbance value, the first disturbance reference value and the disturbance step size, and control the inverter power conversion module of the inverter to output reactive disturbance according to the first disturbance value, so that the voltage frequency or frequency change rate of the PCC is affected by the reactive disturbance to reach a threshold value and the power supply island is detected accordingly, and the inverter is controlled to disconnect from the load after the power supply island is detected. The reactive disturbance in the present application gradually changes according to the disturbance step size, which can make the voltage frequency change of the PCC controllable and regular, which is conducive to accelerating the detection of power islands, avoiding island detection timeouts, and improving the efficiency of island detection. In the present application, the first disturbance value is less than or equal to the first disturbance reference value, which is beneficial to reducing the negative impact of reactive disturbance output on the power quality of the power grid when no power supply island occurs. Furthermore, the present application can also obtain the value of the reactive disturbance to be output based on the change of the negative sequence voltage of the PCC. Combining this method with the above-mentioned method of obtaining the value of the reactive disturbance according to the disturbance step size is beneficial to achieve complementary advantages and improve the efficiency of island detection. In the scenario where multiple inverters are operated in parallel, multiple machines can synchronously output equal amounts of reactive disturbances in the same direction, which is beneficial to reducing the blind spot of island detection and accelerating the deviation of the PCC voltage frequency, thereby accelerating the detection of power supply islands, ensuring the effect of island detection, and improving the efficiency of island detection.

[0101] See also Figure 11 , Figure 11 A waveform diagram of island detection for two inverters running in parallel provided in an embodiment of the present application. Both inverters are three-phase inverters with a rated output power of 20kW, and the above-mentioned island detection process is performed when the output power of the two inverters fully matches the absorbed power of the load. As can be seen from the figure, when inverter 1 and inverter 2 fully match the power of the load, the island protection time can be achieved within 100ms, no island detection timeout occurs, and the wave blocking moments of the two inverters are also relatively consistent. Therefore, by implementing the island detection method provided in the present application, power supply islands can be detected more quickly, ensuring the effectiveness of island detection.

[0102] The above description is merely a specific embodiment of the present application, but the scope of protection of the present application is not limited thereto. Any changes or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in this application should be included in the scope of protection of this application. Therefore, the scope of protection of this application should be based on the scope of protection of the claims.

Claims

1. An inverter, characterized in that: The inverter includes an inverter power conversion module and a control module. The input end of the inverter power conversion module is used to connect to a DC source. The output end of the inverter power conversion module is coupled to a public power grid. The common coupling point PCC between the inverter and the public power grid is connected to a load. The control module is configured to obtain a first disturbance value based on the disturbance step size and the second disturbance value when a first disturbance reference value is greater than a disturbance step size and the first disturbance reference value is equal to a second disturbance reference value, wherein the first disturbance value is a disturbance value corresponding to a first voltage frequency of the PCC in a current sampling period and is greater than the second disturbance value corresponding to a second voltage frequency of the PCC in the first sampling period, the sampling period before the current sampling period is the first sampling period, the first disturbance reference value is obtained by a first frequency change, the first frequency change is obtained according to the first voltage frequency and a sliding window average of historical voltage frequencies corresponding to the first voltage frequency, and the second disturbance reference value is obtained by the second voltage frequency; The control module is configured to control the inverter power conversion module to output reactive disturbance based on the first disturbance value, and detect the voltage frequency of the PCC; The control module is further configured to detect a power supply island based on the voltage frequency of the PCC and control the inverter power conversion module to disconnect from the load.

2. The inverter according to claim 1, characterized in that The control module is further configured to: The second disturbance value corresponding to the second voltage frequency is obtained based on the second voltage frequency.

3. The inverter according to claim 2, characterized in that: The control module is further configured to: Obtaining a first frequency change based on the first voltage frequency and an average value of the voltage frequencies of the PCC in N consecutive sampling periods before the current sampling period, where N is an integer greater than 1, and the N consecutive sampling periods include the first sampling period, and the average value of the voltage frequencies of the PCC in the N consecutive sampling periods before the current sampling period is a sliding window average value of historical voltage frequencies corresponding to the first voltage frequency; A first disturbance reference value is obtained based on the first frequency change.

4. The inverter according to claim 3, characterized in that: The control module is used for: obtaining the second disturbance reference value based on the second voltage frequency; When the second disturbance reference value is smaller than the disturbance step size, a preset disturbance value is obtained as the second disturbance value.

5. The inverter according to claim 4, characterized in that: The control module is further configured to: In a case where the first disturbance reference value is greater than the disturbance step length and the second disturbance reference value is less than the disturbance step length, a preset initial value is obtained as the first disturbance value.

6. The inverter according to any one of claims 1 to 5, characterized in that: The control module is used for: When the first voltage change corresponding to the first voltage negative sequence component of the PCC in the current sampling period is greater than a preset threshold, the inverter power conversion module is controlled to output reactive disturbance based on the first disturbance value and the short-time disturbance value, and the short-time disturbance value is obtained by the output power of the inverter.

7. The inverter according to claim 6, characterized in that: The control module is further configured to: The first voltage variation is obtained based on the first voltage negative sequence component and an average value of the voltage negative sequence components in M ​​consecutive sampling periods before the current sampling period, where M is an integer greater than 1.

8. The inverter according to claim 6, characterized in that: The control module is used for: When the short-term disturbance value is less than the first disturbance value, controlling the inverter power conversion module to output reactive disturbance according to the first disturbance value; Alternatively, when the short-term disturbance value is greater than the first disturbance value, the inverter power conversion module is controlled to output reactive disturbance according to the short-term disturbance value.

9. The inverter according to claim 8, characterized in that: The control module is used for: When the short-term disturbance value is greater than the first disturbance value, the inverter power conversion module is controlled to continuously output reactive disturbance within a first preset time period according to the short-term disturbance value, and when the end time of the first preset time period arrives, the inverter power conversion module is controlled to stop outputting reactive disturbance.

10. The inverter according to any one of claims 1 to 5, characterized in that: The control module is used for: When the third voltage frequency of the PCC is continuously greater than the first frequency threshold or continuously less than the second frequency threshold within the first reference time period, or when the frequency change rate corresponding to the third voltage frequency is continuously greater than the first frequency change rate threshold or continuously less than the second frequency change rate threshold within the second reference time period, the power supply island is detected, and the inverter power conversion module is controlled to disconnect from the load, and the third voltage frequency is the voltage frequency of the PCC in the second sampling period after the current sampling period.

11. The inverter according to any one of claims 1 to 5, characterized in that: The control module is used for: The power supply island is detected based on the voltage frequency of the PCC, a third reference time period is waited, and when the end moment of the third reference time period arrives, the inverter power conversion module is controlled to disconnect from the load.

12. A power system, characterized in that: The power system comprises at least two inverters according to any one of claims 9 to 11, wherein output ends of the at least two inverters are connected in parallel and then connected to the public grid and the PCC; The control module in each inverter is also used to control the inverter power conversion module to output reactive disturbance according to the short-time disturbance value when the short-time disturbance value is greater than the first disturbance value, and the short-time disturbance value is obtained from the output power of the inverter.

13. A method for detecting an island, characterized in that: Applicable to an inverter, wherein the input end of the inverter is used to connect to a DC source, and the output end of the inverter is connected to a load at a point of common coupling (PCC) of a public power grid. The method includes: In a case where a first disturbance reference value is greater than a disturbance step size and the first disturbance reference value is equal to a second disturbance reference value, a first disturbance value is obtained based on the disturbance step size and the second disturbance value, wherein the first disturbance value is a disturbance value corresponding to a first voltage frequency of the PCC in a current sampling period and is greater than the second disturbance value corresponding to a second voltage frequency of the PCC in the first sampling period, a sampling period before the current sampling period is the first sampling period, the first disturbance reference value is obtained by a first frequency change, the first frequency change is obtained according to the first voltage frequency and a sliding window average of historical voltage frequencies corresponding to the first voltage frequency, and the second disturbance reference value is obtained by the second voltage frequency; Based on the first disturbance value, controlling the inverter to output reactive disturbance and detecting the voltage frequency of the PCC; A power supply island is detected based on the voltage and frequency of the PCC, and the inverter is controlled to disconnect from the load.

14. The method according to claim 13, wherein: Before controlling the inverter to output reactive disturbance based on the first disturbance value, the method further includes: The second disturbance value corresponding to the second voltage frequency is obtained based on the second voltage frequency.

15. The method according to claim 14, characterized in that Before obtaining the first disturbance value based on the disturbance step size and the second disturbance value, the method further includes: Obtaining a first frequency change based on the first voltage frequency and an average value of the voltage frequencies of the PCC in N consecutive sampling periods before the current sampling period, where N is an integer greater than 1 and the N consecutive sampling periods include the first sampling period; A first disturbance reference value is obtained based on the first frequency change.

16. The method according to claim 15, characterized in that The obtaining, based on the second voltage frequency, the second disturbance value corresponding to the second voltage frequency includes: obtaining the second disturbance reference value based on the second voltage frequency; When the second disturbance reference value is smaller than the disturbance step size, a preset disturbance value is obtained as the second disturbance value.

17. The method according to claim 16, characterized in that The obtaining of the first disturbance value based on the disturbance step size and the second disturbance value further includes: In a case where the first disturbance reference value is greater than the disturbance step length and the second disturbance reference value is less than the disturbance step length, a preset initial value is obtained as the first disturbance value.

18. The method according to any one of claims 13 to 17, characterized in that: The controlling the inverter to output reactive disturbance based on the first disturbance value further includes: When the first voltage change corresponding to the first voltage negative sequence component of the PCC in the current sampling period is greater than a preset threshold, the inverter is controlled to output reactive disturbance based on the first disturbance value and the short-time disturbance value, and the short-time disturbance value is obtained by the output power of the inverter.

19. The method according to claim 18, characterized in that Before controlling the inverter to output reactive disturbance based on the first disturbance value, the method further includes: A first voltage variation corresponding to the first voltage negative sequence component is obtained based on the first voltage negative sequence component and an average value of the voltage negative sequence components of M consecutive sampling periods before the current sampling period, where M is an integer greater than 1.

20. The method according to claim 18, wherein The controlling the inverter to output reactive disturbance based on the first disturbance value and the short-time disturbance value includes: When the short-term disturbance value is less than the first disturbance value, controlling the inverter to output reactive disturbance according to the first disturbance value; Alternatively, when the short-term disturbance value is greater than the first disturbance value, the inverter is controlled to continuously output reactive disturbance within a first preset time period according to the short-term disturbance value, and the inverter is controlled to stop outputting reactive disturbance when the end time of the first preset time period arrives.

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