Active and reactive power combined control method and system for distributed photovoltaic power station

Abstract

A method for combined active and reactive power control of distributed photovoltaic power stations includes the following steps: S1. Real-time detection of the active power value and reactive power value of each photovoltaic power station in the distributed photovoltaic power grid; the photovoltaic power stations are divided into two categories: the first category of photovoltaic power stations is connected to only one power node, and the second category of photovoltaic power stations can be switched to connect to more than two power nodes; S2. Detecting the active power value of the photovoltaic load for each power node in the distributed photovoltaic power grid; S3. If the photovoltaic power supply active power ratio of any power node deviates from the standard value by more than a set threshold, adjustment is performed. The present invention monitors the operation of the photovoltaic power grid by detecting the photovoltaic power supply active power ratio parameters of each power node, and performs adjustments based on the past stable operating state. In most cases, only the grid-connected state of the photovoltaic generator set is adjusted, and the traditional reactive power adjustment method is used as compensation, thereby simplifying the active and reactive power adjustment methods and extending the service life of the reactive equipment.

Description

Technical Field

[0001] The present invention belongs to the field of electric power technology, relates to photovoltaic power generation technology, and specifically relates to a method and system for joint control of active and reactive power in a distributed photovoltaic power station. Background Art

[0002] A distributed photovoltaic power grid refers to a smaller photovoltaic power generation system configured at the user site or near the power consumption site to meet the needs of specific users, support the economic operation of the existing distribution network, or meet both requirements at the same time. Multiple distributed photovoltaic power stations, users, inverters, etc. form a distributed photovoltaic power grid.

[0003] The basic equipment of a distributed photovoltaic power grid includes photovoltaic cell modules, photovoltaic array brackets, DC combiner boxes, DC distribution cabinets, grid-connected inverters, AC distribution cabinets, and other equipment. In addition, there are power supply system monitoring devices and environmental monitoring devices. Its operating mode is that under solar radiation, the photovoltaic power generation system's solar cell array converts solar energy into output electricity, which is then fed into the DC distribution cabinet through the DC combiner box. The grid-connected inverter then converts the electricity into AC power to supply the building's own loads. Excess or insufficient power is regulated by connecting to the grid.

[0004] Photovoltaic power generation is greatly affected by external factors such as seasons, day and night, and cloudy or sunny weather, which can easily cause frequent voltage fluctuations at the grid connection point of photovoltaic power generation, increasing the difficulty of reactive power regulation. The power generation of the photovoltaic power station itself also changes with factors such as the duration of solar sunshine. Since the predictability of future power generation of photovoltaic power stations is significantly lower than that of hydropower, thermal power, and nuclear power, it is difficult to effectively allocate them. Summary of the Invention

[0005] In order to overcome the defects of the prior art, the present invention discloses a method and system for joint control of active and reactive power of a distributed photovoltaic power station.

[0006] The method for combined active and reactive power control of a distributed photovoltaic power station according to the present invention is characterized in that it comprises the following steps:

[0007] S1. For each photovoltaic power station in the distributed photovoltaic power grid, the active power value FG(i) and the reactive power value WG(i) of the photovoltaic power station are detected in real time, where i represents a different photovoltaic power station;

[0008] The photovoltaic power stations are divided into two categories: the first type of photovoltaic power station is only connected to one power node, and the second type of photovoltaic power station can be switched to connect to more than two power nodes;

[0009] S2. Real-time monitoring of the photovoltaic load active value TG(n) for each power consumption node within the distributed photovoltaic grid. Where n represents a different power consumption node. The statistical photovoltaic load active value is the load active value Tn of the power consumption node minus the load active value provided by the stable power supply.

[0010] S3. Real-time monitoring and comparison of the PV power supply active ratio P2(n) of each power consumption node with the standard value P2S(n). If the PV power supply active ratio P2(n) of any power consumption node deviates from the standard value P2S(n) by more than a set threshold, adjustments are made until the PV power supply active ratio P2(n) of all power consumption nodes deviates from the standard value P2S(n) by no more than the set threshold, where n represents a different power consumption node.

[0011] The adjustment method is to substitute the data obtained in step S1 into the active value FG(i) and the reactive value WG(i) of the photovoltaic power station to adjust the connection relationship between the second type of photovoltaic power station and the power consumption node.

[0012] Preferably, in step S2, the load active power value provided by the stable power supply is calculated in the following manner:

[0013] Based on the total active power value of the power grid over a longer period of time, TA, and the load active power value of each power-consuming node, Tn, the proportion P1 of the active power value of the power-consuming node to the total active power value of the power grid is calculated. P1 = Tn / TA. Then, P1 is multiplied by the total load active power value TW output by the stable power supply to obtain the load active power value provided by the stable power supply.

[0014] Preferably, in step S3, the adjustment method further includes adjusting a reactive compensator connected to the power node.

[0015] Preferably, the adjustment method is any one of the following two methods:

[0016] Method 1: Sort the power consumption nodes by their PV active power ratio P2(n) from the standard value P2S(n) from high to low. First, adjust the power consumption node with the largest deviation to bring it closest to the standard value. Then, adjust the subsequent nodes in sequence until the adjustment is complete.

[0017] Method 2: Sort the power consumption nodes by their PV power supply active ratio P2(n) from the standard value P2S(n) from low to high. First, fix the power consumption nodes whose PV power supply active ratio does not deviate from the standard value to the set threshold. Start with the first power consumption node that exceeds the threshold, and then adjust the subsequent nodes in sequence until the adjustment is complete.

[0018] The present invention also discloses a distributed photovoltaic power station active and reactive joint control system, which includes multiple photovoltaic power stations and multiple power consumption nodes. It is characterized in that it also includes a control system. The photovoltaic power stations are divided into two categories. The first category of photovoltaic power stations is only connected to one power consumption node, and the second category of photovoltaic power stations can be switched to connect to more than two power consumption nodes through the control system; each power consumption node is connected to at least one second category of photovoltaic power station, each photovoltaic power station includes an active value and reactive value detection device, and each power consumption node is connected to a load active value detection device.

[0019] Preferably, each of the power consumption nodes is also connected to a reactive power compensator.

[0020] The distributed photovoltaic power station active and reactive power combined control method and system described in the present invention monitors the operation of the photovoltaic power grid by detecting the photovoltaic power supply active power ratio parameters of each power consumption node, and makes adjustments based on the past stable operating state. Taking into account the active and reactive power of the photovoltaic power station, in most cases only the grid-connected state of the photovoltaic generator set is adjusted, and the traditional reactive power adjustment method is used as compensation, which simplifies the active and reactive power adjustment method and extends the service life of the reactive equipment. The active and reactive power adjustment effect is improved by combining reactive power compensation and photovoltaic unit grid-connected power adjustment. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a schematic diagram of a specific implementation of the distributed photovoltaic power grid of the present invention;

[0022] Figure 2 A schematic diagram of the active power ratio of each power consumption node before adjustment in a specific embodiment of the present invention;

[0023] Figure 3 for Figure 2 A schematic diagram of the active power ratio of each power consumption node after adjustment in the specific implementation manner shown; Figure 2 and Figure 3 The horizontal axis represents different electricity consumption nodes; the vertical axis is the active power ratio of photovoltaic power supply. DETAILED DESCRIPTION

[0024] The specific embodiments of the present invention will be further described in detail below with reference to the accompanying drawings.

[0025] The distributed photovoltaic power station active and reactive power combined control method of the present invention is used for distributed photovoltaic power grid control, comprising the following steps:

[0026] S1. For each photovoltaic power station in the distributed photovoltaic grid, statistics are collected on active and reactive power values in each time period. The statistical time is generally in days.

[0027] FG(i) represents the active value of the photovoltaic power station, WG(i) represents the reactive value of the photovoltaic power station, where i represents a different photovoltaic power station;

[0028] There are two types of photovoltaic power stations: the first type connects to only one power-consuming node, while the second type can switch between connecting to two or more power-consuming nodes. This means that a second type can be connected to different power-consuming nodes at different times, but only to one at any given time, through switching. The connections for second type photovoltaic power stations must ensure that each power-consuming node is connected to at least one second type photovoltaic power station. Spatially colocated photovoltaic power stations can also select only some of their photovoltaic generators as second type photovoltaic power stations.

[0029] Generally speaking, the photovoltaic power station mentioned in the present invention refers to a solar power generation unit. For more accurate regulation, each power consumption node can be connected to multiple second-class photovoltaic power stations, that is, multiple solar power generation units connected to multiple power consumption nodes at the same time. Figure 1 In a specific embodiment shown in the figure, Y1, Y2, Y3, and Y4 represent different photovoltaic power stations, where Y1 and Y4 are first-type photovoltaic power stations, and Y2 and Y3 are second-type photovoltaic power stations. B1, B2, and B3 represent different power consumption nodes, and Y2 and Y3 are connected to two different power consumption nodes, B1 and B2, and B2 and B3, respectively, through switches. Figure 1 WP in Chinese refers to a stable power source such as thermal power, hydropower, nuclear power, etc. that connects to various power consumption nodes.

[0030] S2. For each power consumption node within the distributed photovoltaic power grid, typically an inverter connecting multiple photovoltaic power plants and users, monitor the photovoltaic load active value TG(n) of each power consumption node in real time, where n represents a different power consumption node.

[0031] The statistical photovoltaic load active value is the load active value Tn of the power node minus the load active value provided by the stable power source. The so-called stable power source refers to traditional thermal power, hydropower or nuclear power and other power stations that provide long-term stable power supply relative to photovoltaic power stations.

[0032] The load active power value provided by the stable power supply can be estimated. Based on the total grid active power value TA and the load active power value Tn of each power-consuming node over a longer period of time, such as a month, the proportion P1 of the active power value of the user involved in the inverter to the total grid active power value is calculated. P1 = Tn / TA. Then P1 is multiplied by the total load active power value TW output by the stable power supply. The total load active power value TW output by the stable power supply can usually be detected at the power station end.

[0033] S3. Compare the PV power supply active ratio P2(n) of each power consumption node with the standard value P2S(n). If the PV power supply active ratio P2(n) of any power consumption node deviates from the standard value P2S(n) by more than a set threshold, adjust the PV power supply active ratio until the deviation of the PV power supply active ratio P2(n) of all power consumption nodes from the standard value P2S(n) does not exceed the set threshold.

[0034] The adjustment method is to adjust the connection relationship between the second type of photovoltaic power station and the power consumption node.

[0035] A standard value P2S(n) is set for the photovoltaic power supply active power ratio P2(n) of each power consumption node. P2(n) = Gn / Tn, where Gn is the active power value of all photovoltaic power stations connected to the power consumption node; n represents different power consumption nodes.

[0036] The setting of each standard value P2S(n) can be based on the active power ratio of each power consumption node when the power grid is initially established and operating under optimal conditions. It can be dynamically adjusted at any time as the installed capacity and load change. For example, the active power ratio of stable operation before the last adjustment can be used as the standard value.

[0037] The PV power supply active ratio P2(n) at each consumer node is constantly changing. Assuming the active power input from the stable power source remains stable, these changes can only be caused by two factors: changes in the output power of the PV power station connected to the consumer node and changes in the load at the consumer node. The power supplied to the consumer node by the second-class PV power station can be adjusted to accommodate these changes in the PV power station's output power and the consumer node's load.

[0038] If the photovoltaic power supply active ratio P2(n) of one or more power consumption nodes deviates from the standard value P2S(n) and reaches a set threshold, for example, the set threshold is 5 percentage points, adjustment is performed when the deviation exceeds the standard value by 5 percentage points.

[0039] Distributed photovoltaic power grids are usually equipped with reactive power compensation equipment. However, due to the instability of photovoltaic power generation, it is not advisable to dynamically adjust large reactive power compensation equipment at any time to prevent damage to capacitors caused by excessive operation, and more importantly, to prevent oscillation of the power supply system caused by constant switching of capacitors. Therefore, the present invention preferably adopts the method of adjusting the connection relationship between the second type of photovoltaic power station and each power node. When the adjustment of the connection relationship cannot meet the requirements, the reactive power compensation equipment is adjusted. Adjusting the reactive power compensation equipment of each power node can adjust the power coefficient of the power node.

[0040] , where P represents the active power value of each power source connected to the power node, Q represents the reactive power value, and summation represents the summation of all power sources.

[0041] By adjusting the power coefficient, the active value of the power consumption node is adjusted, and then the active power ratio of photovoltaic power supply is adjusted.

[0042] That is, the adjustment methods described in the present invention generally include two types. The first is to adjust the connection relationship of the second type of photovoltaic power station, and the second is to adjust the reactive compensator connected to the power node, such as increasing or decreasing the capacitance value therein.

[0043] Since various parameters of the power grid have been input into the system, using existing technology, the system can automatically calculate the photovoltaic power supply active ratio of each power consumption node under various circumstances. The typical algorithm is to first sort the power consumption nodes according to the deviation of the photovoltaic power supply active ratio P2(n) from the standard value P2S(n), and sort them from high to low or from low to high. For sorting from high to low, the power consumption node with the largest deviation is first adjusted to make it closest to the standard value, and then the subsequent nodes are adjusted in sequence until the adjustment is completed.

[0044] For sorting from low to high, first fix the power consumption nodes that have not exceeded the standard value to reach the threshold, and start adjusting from the first power consumption node that exceeds the threshold; then adjust the subsequent nodes in turn until the adjustment is completed.

[0045] Regulation can be implemented using iterative programming, which may involve a single or multiple iterations. Both regulation methods are first simulated on the system processor. The current active power value FG(i) and reactive power value WG(i) of the PV power station obtained in step S1 are substituted into the system processor. The PV power supply active power ratio of each power node is calculated and iterated. The iterative processing algorithm is well known in the art and will not be described in detail here. This continues until the deviation values of all power nodes are within the threshold range.

[0046] Distributed photovoltaic power grids are typically used in mountainous rural areas and large industrial parks. These areas are characterized by numerous photovoltaic power stations, widely dispersed users, and numerous inverters. Photovoltaic power stations are typically located in areas with good sunlight, such as southern slopes of mountains or flat land. They are often located in areas with close distances between two or more power-consuming nodes. Photovoltaic power stations built in such areas can be considered Type II photovoltaic power stations.

[0047] Figure 2 and Figure 3 Given a township power grid consisting of fourteen natural villages, the dotted lines represent the upper and lower limits of the set threshold. Each natural village is equipped with an inverter as a power node. In addition to the fixed hydropower station as a stable power source, the township power grid has 12 small photovoltaic power stations to supply power to the grid. Among them, 8 are close to two or more natural villages and are used as second-class photovoltaic power stations. The photovoltaic power station at the same location can also select only some photovoltaic generators as second-class photovoltaic power stations. At a certain moment, the photovoltaic power supply active power of each power node is as follows: Figure 2As shown in the figure, the 5th and 14th power consumption nodes exceeded the standard. After adjustment, each power consumption node is within the allowable deviation range and does not exceed the set threshold. To simplify the description, Figure 2 and Figure 3 In the specific implementation manner shown, the photovoltaic power supply active ratio standard value P2S(n) of each power consumption node is equal, but in actual situations they are usually not equal.

[0048] The distributed photovoltaic power station active and reactive power combined control method and system described in the present invention monitors the operation of the photovoltaic power grid by detecting the photovoltaic power supply active power ratio parameters of each power consumption node, and adjusts it based on the historical best operation data. It comprehensively considers the active power values of the photovoltaic power generation units and traditional power supply units, and combines reactive power compensation with photovoltaic unit grid-connected power adjustment to improve the active and reactive power regulation effect.

[0049] The foregoing are various preferred embodiments of the present invention. Unless the preferred implementation modes in each preferred embodiment are obviously self-contradictory or based on a certain preferred implementation mode, each preferred implementation mode can be arbitrarily superimposed and used in combination. The embodiments and specific parameters in the embodiments are only for the purpose of clearly describing the inventor's invention verification process, and are not intended to limit the patent protection scope of the present invention. The patent protection scope of the present invention shall still be based on its claims. Any equivalent structural changes made using the contents of the description of the present invention should also be included in the protection scope of the present invention.

Claims

1. A method for joint control of active and reactive power in a distributed photovoltaic power station, characterized in that: The process includes the following steps: S1. For each photovoltaic power station in the distributed photovoltaic power grid, the active power value FG(i) and the reactive power value WG(i) of the photovoltaic power station are detected in real time, where i represents a different photovoltaic power station; The photovoltaic power stations are divided into two categories: the first type of photovoltaic power station is only connected to one power node, and the second type of photovoltaic power station can be switched to connect to more than two power nodes; S2. Real-time monitoring of the photovoltaic load active value TG(n) for each power consumption node within the distributed photovoltaic grid. Where n represents a different power consumption node. The statistical photovoltaic load active value is the load active value Tn of the power consumption node minus the load active value provided by the stable power supply. S3. Real-time monitoring and comparison of the PV power supply active ratio P2(n) of each power consumption node with the standard value P2S(n). If the PV power supply active ratio P2(n) of any power consumption node deviates from the standard value P2S(n) by more than a set threshold, adjustments are made until the PV power supply active ratio P2(n) of all power consumption nodes deviates from the standard value P2S(n) by no more than the set threshold, where n represents a different power consumption node. The adjustment method is to substitute the active value FG(i) and the reactive value WG(i) of the photovoltaic power station according to the data obtained in step S1 to adjust the connection relationship between the second type of photovoltaic power station and the power consumption node.

2. The method for controlling active and reactive power of a distributed photovoltaic power station according to claim 1, wherein S2 In the steps, the load active power value provided by the stable power supply is calculated in the following manner: Based on the total active power value of the power grid over a longer period of time, TA, and the load active power value of each power-consuming node, Tn, the proportion P1 of the active power value of the power-consuming node to the total active power value of the power grid is calculated. P1 = Tn / TA. Then, P1 is multiplied by the total load active power value TW output by the stable power supply to obtain the load active power value provided by the stable power supply.

3. The method for joint control of active and reactive power in a distributed photovoltaic power station according to claim 1, wherein: In step S3, the adjustment method further includes adjusting the reactive power compensator connected to the power node.

4. The method for joint control of active and reactive power in a distributed photovoltaic power station according to claim 1, wherein: The adjustment method is any one of the following two methods: Method 1: Sort the power consumption nodes by their PV active power ratio P2(n) from the standard value P2S(n) from high to low. First, adjust the power consumption node with the largest deviation to bring it closest to the standard value. Then, adjust the subsequent nodes in sequence until the adjustment is complete. Method 2: Sort the power consumption nodes by their PV power supply active ratio P2(n) from the standard value P2S(n) from low to high. First, fix the power consumption nodes whose PV power supply active ratio does not deviate from the standard value to the set threshold. Start with the first power consumption node that exceeds the threshold, and then adjust the subsequent nodes in sequence until the adjustment is complete.

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