Primary frequency modulation method for distributed photovoltaic power generation system

Abstract

The invention provides a primary frequency modulation method for a distributed photovoltaic power generation system. The method comprises the following steps: firstly, adopting an MPPT (Maximum Power Point Tracking) technology for the distributed photovoltaic power generation system, ensuring that a plurality of paths of access effective inputs in an inverter in the distributed photovoltaic power generation system, further obtaining power parameters of the inverter, and performing power reservation processing according to the power parameters on the basis; then, the current output power of the inverter and the power grid frequency of the grid-connected point are collected in real time, whether the power grid frequency exceeds the primary frequency modulation dead zone or not is judged, and a first judgment result is obtained according to the power grid frequency and the primary frequency modulation dead zone; then, corresponding processing is carried out according to the difference of the first judgment results, if the first judgment results are that the power grid frequency exceeds the primary frequency modulation dead zone, the distributed photovoltaic power generation system carries out primary frequency modulation processing on the inverter, and otherwise, the inverter operates normally.

Description

Technical Field

[0001] The present invention relates to the field of frequency regulation of power generation systems, and in particular to a primary frequency regulation method for a distributed photovoltaic power generation system. Background Art

[0002] At present, in the existing technology, distributed photovoltaic power generation systems are not equipped with energy storage devices. Therefore, the primary frequency regulation function of distributed photovoltaic power generation systems without energy storage devices can only process active power when the grid frequency is higher than 50Hz, but it cannot process active power when the grid frequency is less than 50Hz. Then, distributed photovoltaic power generation systems without energy storage devices are equivalent to only realizing half of the function of "primary frequency regulation", which limits the comprehensiveness and effectiveness of the system in dealing with grid frequency fluctuations. Summary of the invention

[0003] The present invention aims to solve at least one of the technical problems existing in the prior art or related art.

[0004] To this end, a first aspect of the present invention proposes a primary frequency modulation method for a distributed photovoltaic power generation system.

[0005] In view of this, a first aspect of the present invention provides a primary frequency modulation method for a distributed photovoltaic power generation system, comprising: using MPPT technology to connect several inverters to effective inputs to obtain power parameters of the inverter; performing power reservation processing based on the power parameters; real-time collection of the current output power of the inverter and the grid frequency of the grid connection point to determine whether the grid frequency exceeds the primary frequency modulation dead zone, and obtaining a first judgment result; if the first judgment result is that the grid frequency exceeds the primary frequency modulation dead zone, performing primary frequency modulation processing on the inverter, otherwise, the inverter operates normally.

[0006] In addition, the primary frequency modulation method for a distributed photovoltaic power generation system in the above technical solution provided by the present invention may also have the following additional technical features: In some technical solutions of the present invention, optionally, MPPT technology is used to connect several inputs of the inverter to effective inputs to obtain power parameters of the inverter, including: using MPPT technology to ensure that several inputs of the inverter are effective and the difference in maximum input power of any two inputs of the inverter does not exceed 10% of the rated power of the inverter; tracking the maximum power point of any input, and based on the maximum power point, obtaining the real-time maximum power of a single input of the inverter.

[0007] In some technical solutions of the present invention, power reservation processing is optionally performed based on power parameters, including: determining a power reservation value required for performing a frequency modulation processing on the inverter based on the rated power of the inverter; determining a power limit value for the remaining paths of the inverter based on the power reservation value and the real-time maximum power; and performing power reservation processing based on the power limit value.

[0008] In some technical schemes of the present invention, optionally, if the judgment result is that the grid frequency exceeds the frequency modulation dead zone, the inverter is subjected to a frequency modulation process, including: when the grid frequency exceeds the primary frequency modulation dead zone, judging that the grid frequency exceeds the lower limit of the primary frequency modulation dead zone or the grid frequency exceeds the upper limit of the primary frequency modulation dead zone, and obtaining a second judgment result; based on the second judgment result, allowing one of the routes to maintain MPPT mode operation, respectively changing the active power of the remaining routes of the inverter, and resetting the power limit values ​​of the remaining routes of the inverter until the grid frequency returns to the primary frequency modulation dead zone.

[0009] In some technical solutions of the present invention, optionally, based on the second judgment result, one of the paths is maintained in MPPT mode, the active power of the remaining paths of the inverter is changed respectively, and the power limit values ​​of the remaining paths of the inverter are reset until the grid frequency returns to the primary frequency regulation dead zone, including: if the second judgment result is that the grid frequency exceeds the lower limit of the primary frequency regulation dead zone, one of the paths is maintained in MPPT mode, based on the difference between the lower limit of the primary frequency regulation dead zone and the real-time grid frequency, the adjustment target power change is obtained, the active power of a single path of the inverter is increased based on the adjustment target power change, and based on The active power and the current input power are used to reset the power limit values ​​of the remaining paths of the inverter until the grid frequency returns to the primary frequency regulation dead zone; if the second judgment result is that the grid frequency exceeds the upper limit of the primary frequency regulation dead zone, one of the paths is allowed to maintain MPPT mode operation, and the adjustment target power change is obtained based on the difference between the upper limit of the primary frequency regulation dead zone and the real-time grid frequency, and the active power of the single path of the inverter is reduced based on the adjustment target power change, and the power limit values ​​of the remaining paths of the inverter are reset based on the active power and the current input power until the grid frequency returns to the primary frequency regulation dead zone.

[0010] In some technical solutions of the present invention, optionally, based on the broken line function of the grid frequency and the active power, the droop characteristic of the primary frequency modulation processing is realized; wherein the specific formula is as follows: ;in, is the overall active power of the inverter under primary frequency modulation processing, is the current active power of the inverter, is the frequency regulation rate of the new energy source. is the rated power of the inverter, is the current grid frequency, is the rated grid frequency.

[0011] Additional aspects and advantages of the present invention will be given in part in the following description and in part will be obvious from the following description, or will be learned through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] The above and / or additional aspects and advantages of the present invention will become apparent and easily understood from the description of the embodiments in conjunction with the following drawings, in which: Figure 1 The present invention is a flowchart of a primary frequency modulation method for a distributed photovoltaic power generation system according to an embodiment of the present invention. DETAILED DESCRIPTION

[0013] In order to more clearly understand the above-mentioned purpose, features and advantages of the present invention, the present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be noted that the embodiments of the present application and the features in the embodiments can be combined with each other without conflict.

[0014] In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention may also be implemented in other ways different from those described herein. Therefore, the protection scope of the present invention is not limited to the specific embodiments disclosed below.

[0015] Refer to the following Figure 1 A primary frequency modulation method for a distributed photovoltaic power generation system according to some embodiments of the present invention is described.

[0016] like Figure 1 As shown, the first aspect of the present invention provides a primary frequency modulation method for a distributed photovoltaic power generation system, comprising: Step 102, using MPPT technology to connect several paths of the inverter to effective inputs to obtain power parameters of the inverter; Step 104, performing power reservation processing based on the power parameter; Step 106, collecting the current output power of the inverter and the grid frequency of the grid connection point in real time, determining whether the grid frequency exceeds a primary frequency modulation dead zone, and obtaining a first determination result; Step 108: If the first judgment result is that the grid frequency exceeds the primary frequency modulation dead zone, a primary frequency modulation process is performed on the inverter; otherwise, the inverter operates normally.

[0017] The present invention proposes a primary frequency modulation method for a distributed photovoltaic power generation system. First, the MPPT technology is used for the distributed photovoltaic power generation system to ensure that several paths in the inverter in the distributed photovoltaic power generation system are connected to effective inputs, and then the power parameters of the inverter are obtained, and power reservation processing is performed based on the power parameters.

[0018] Then, the current output power of the inverter and the grid frequency of the grid connection point are collected in real time to determine whether the grid frequency exceeds the primary frequency modulation dead zone, and a first determination result is obtained based on the grid frequency and the primary frequency modulation dead zone.

[0019] Then, corresponding processing is performed according to the different first judgment results. If the first judgment result is that the grid frequency exceeds the primary frequency modulation dead zone, the system will perform a frequency modulation process on the inverter in the distributed photovoltaic power generation system. Otherwise, the inverter operates normally.

[0020] By performing frequency modulation using the method proposed in the present invention, when the grid frequency exceeds a primary frequency modulation dead zone, the system can quickly start a primary frequency modulation process, and help the grid restore frequency stability by adjusting the output of the distributed photovoltaic power generation system, thereby ensuring the comprehensiveness and effectiveness of the system in responding to grid frequency fluctuations, thereby ensuring the safe operation of the grid.

[0021] It should be noted that MPPT (Maximum Power Point Tracking) is a power regulation and intelligent electronic control technology used in renewable energy power generation systems such as solar panels and wind turbines, aiming to maximize the output power of power generation equipment.

[0022] Furthermore, in some embodiments of the present invention, MPPT technology is used to connect several inputs of the inverter to effective inputs to obtain power parameters of the inverter, including: using MPPT technology to ensure that several inputs of the inverter are effective and that the difference in maximum input power of any two inputs of the inverter does not exceed 10% of the rated power of the inverter; tracking the maximum power point of any input and obtaining the real-time maximum power of a single input of the inverter based on the maximum power point.

[0023] In this embodiment, first, the MPPT technology is used to make the inputs of several channels in the inverter of the distributed photovoltaic power generation system effective, and according to the technical indicators of the primary frequency modulation of the standard: "the maximum load limit is set to not less than 10% of the rated load", and at the same time, the difference between the maximum input power of any two channels of the inverter does not exceed 10% of the rated power of the inverter. In this way, the MPPT inputs of any two channels of the inverter can be approximately equal.

[0024] On this basis, the maximum power point of any one channel is tracked and the real-time maximum power of the single input of the inverter is obtained according to the tracked maximum power point.

[0025] The above method can be used to obtain the real-time maximum power of a single input of the inverter, thereby facilitating power reservation processing according to the real-time maximum power.

[0026] Specifically, the maximum power point of any one path is tracked after the inverter starts to operate using the MPPT technology. The reference voltage of the single path of the inverter moves from the opening voltage to the maximum power point. The direction of change of the reference voltage should be the same before reaching the maximum power point. The direction of change of each reference voltage is recorded. If the reference voltage decreases, it is recorded as 1, and if it increases, it is recorded as -1. After each calculation of the reference voltage, the current voltage change direction is multiplied by the last change direction. When the value is -1, it means that the reference voltage has reached the vicinity of the maximum power point, and the currently calculated power average is recorded as the real-time maximum power. After that, the reference voltage will always fluctuate near the maximum power point, and the product of the change direction will always be equal to -1, thereby achieving the effect of real-time updating of the real-time maximum power.

[0027] Furthermore, in some embodiments of the present invention, power reservation processing is performed based on power parameters, including: determining the power reservation value required for performing a frequency modulation processing on the inverter based on the rated power of the inverter; determining the power limit value of the remaining paths of the inverter based on the power reservation value and the real-time maximum power; and performing power reservation processing based on the power limit value.

[0028] In this embodiment, the power reserve value required for the inverter to perform a primary frequency modulation process is calculated based on the rated power of the inverter, and then the power limit value of the remaining paths of the inverter is calculated based on the power reserve value and the real-time maximum power. On this basis, the overall power limit of the inverter is realized according to the power limit value, that is, the power reserve process. Through the power reserve process, the active power of the photovoltaic inverter that is not equipped with an energy storage device can be adjusted when the grid frequency is less than 50Hz, thereby realizing a complete primary frequency modulation function.

[0029] Specifically, the power reserve value is 15% of the rated power. Further, in some embodiments of the present invention, if the judgment result is that the grid frequency exceeds the frequency modulation dead zone, the inverter is subjected to a frequency modulation process, including: when the grid frequency exceeds the primary frequency modulation dead zone, it is judged that the grid frequency exceeds the lower limit of the primary frequency modulation dead zone or the grid frequency exceeds the upper limit of the primary frequency modulation dead zone, and a second judgment result is obtained; based on the second judgment result, one of the paths is allowed to maintain the MPPT mode operation, the active power of the remaining paths of the inverter is changed respectively, and the power limit values ​​of the remaining paths of the inverter are reset until the grid frequency returns to the primary frequency modulation dead zone.

[0030] In this embodiment, the situation in which the grid frequency exceeds the primary frequency regulation dead zone is judged, and whether the grid frequency exceeds the lower limit of the primary frequency regulation dead zone or the grid frequency exceeds the upper limit of the primary frequency regulation dead zone is judged, and then a second judgment result is obtained according to the situation.

[0031] According to the second judgment result, one of the paths is kept running in MPPT mode, and the active power of the remaining paths of the inverter is changed respectively, and then the power limit values ​​of the remaining paths of the inverter are reset until the grid frequency returns to the primary frequency modulation dead zone.

[0032] Specifically, the calculation formula for the power limit value of the remaining paths of the inverter is: .in, is the power limit value of the remaining paths of the inverter, is the real-time maximum power, is the rated power of the inverter, The number of specific input paths for the inverter using MPPT technology.

[0033] Specifically, the grid frequency detection resolution should be no greater than 0.003 Hz, the sampling period should be no greater than 100 ms, and the primary frequency regulation dead zone range should be controlled within 50 ± 0.05 Hz.

[0034] Further, in some embodiments of the present invention, based on the second judgment result, one of the paths is maintained in MPPT mode, the active power of the remaining paths of the inverter is changed respectively, and the power limit values ​​of the remaining paths of the inverter are reset until the grid frequency returns to the primary frequency regulation dead zone, including: if the second judgment result is that the grid frequency exceeds the lower limit of the primary frequency regulation dead zone, one of the paths is maintained in MPPT mode, based on the difference between the lower limit of the primary frequency regulation dead zone and the real-time grid frequency, the adjustment target power change is obtained, the active power of the single path of the inverter is increased based on the adjustment target power change, and based on The active power and the current input power are used to reset the power limit values ​​of the remaining paths of the inverter until the grid frequency returns to the primary frequency regulation dead zone; if the second judgment result is that the grid frequency exceeds the upper limit of the primary frequency regulation dead zone, one of the paths is allowed to maintain MPPT mode operation, and the adjustment target power change is obtained based on the difference between the upper limit of the primary frequency regulation dead zone and the real-time grid frequency, and the active power of the single path of the inverter is reduced based on the adjustment target power change, and the power limit values ​​of the remaining paths of the inverter are reset based on the active power and the current input power until the grid frequency returns to the primary frequency regulation dead zone.

[0035] In this embodiment, the system will perform different processing according to the different second judgment results. Among them, if the second judgment result is that the grid frequency exceeds the lower limit of the primary frequency modulation dead zone, firstly, one of the channels is kept in MPPT mode, and then the adjustment target power change is understood and obtained based on the difference between the lower limit of the primary frequency modulation dead zone and the real-time grid frequency. On this basis, the active power of a single channel of the inverter is increased according to the adjustment target power change, and then the power limit value of each remaining channel of the inverter is reset according to the active power and the current input power until the grid frequency returns to the primary frequency modulation dead zone.

[0036] If the second judgment result is that the grid frequency exceeds the upper limit of the primary frequency regulation dead zone, first keep one of the channels in MPPT mode, and then understand and obtain the adjustment target power change based on the difference between the upper limit of the primary frequency regulation dead zone and the real-time grid frequency, reduce the active power of a single channel of the inverter based on the adjustment target power change, and reset the power limit value of each of the remaining channels of the inverter based on the current active power input power until the grid frequency returns to the primary frequency regulation dead zone.

[0037] Through the above method, no matter whether the grid frequency exceeds the lower limit or upper limit of the primary frequency regulation dead zone, the grid frequency can be quickly pulled back to the primary frequency regulation dead zone by accurately calculating and adjusting the target power change and adjusting the active power of the inverter, thereby ensuring the stable operation of the grid.

[0038] Furthermore, in some embodiments of the present invention, the droop characteristic of the primary frequency modulation process is realized based on the broken line function of the grid frequency and the active power; wherein the specific formula is as follows: ;in, is the overall active power of the inverter under primary frequency modulation processing, is the current active power of the inverter, is the frequency regulation rate of the new energy source. is the rated power of the inverter, is the current grid frequency, is the rated grid frequency.

[0039] It needs to be understood that new energy mainly refers to solar energy, wind energy, etc.

[0040] Specifically, if the second judgment result is that the grid frequency exceeds the lower limit of the primary frequency regulation dead zone, the calculation formula for the power limit value of the remaining paths of the inverter is: .in, The value of is the target power change when the grid frequency exceeds the lower limit of the primary frequency regulation dead zone. It means taking the minimum of two values. Indicates the power limit values ​​of the other channels except the one tracking the maximum power point under primary frequency modulation. Specifically, the calculation formula of the overall active power of the inverter when the grid frequency exceeds the lower limit of the primary frequency modulation dead zone is: .in, It is the lower limit of the primary frequency modulation dead zone.

[0041] Specifically, if the second judgment result is that the grid frequency exceeds the upper limit of the primary frequency modulation dead zone, the calculation formula for the power limit value of the remaining paths of the inverter is: .in, The value is the target power change when the grid frequency exceeds the upper limit of the primary frequency regulation dead zone. Specifically, the calculation formula for the overall active power of the inverter when the grid frequency exceeds the upper limit of the primary frequency regulation dead zone is: .in, It is the upper limit of the primary frequency modulation dead zone.

[0042] In one specific embodiment, the technical solution of the present invention is as follows: First, the MPPT technology is used to make the inputs of several channels in the inverter of the distributed photovoltaic power generation system effective, and according to the technical indicators of the primary frequency modulation of the standard: "The maximum load limit is set to not less than 10% of the rated load", and at the same time, the difference between the maximum input power of any two channels of the inverter does not exceed 10% of the rated power of the inverter. In this way, the MPPT inputs of any two channels of the inverter can be approximately equal. On this basis, the maximum power point of any channel is tracked and the real-time maximum power of the single input of the inverter is obtained based on the tracked maximum power point.

[0043] Then, the power reserve value required for the inverter to perform a frequency modulation process is calculated based on the rated power of the inverter, and then the power limit value of the remaining paths of the inverter is calculated based on the power reserve value and the real-time maximum power. On this basis, the overall power limit of the inverter is realized according to the power limit value, that is, power reserve processing.

[0044] The situation where the grid frequency exceeds the primary frequency regulation dead zone is judged. If the second judgment result is that the grid frequency exceeds the lower limit of the primary frequency regulation dead zone, firstly, one of the channels is kept in MPPT mode, and then the adjustment target power change is understood and obtained based on the difference between the lower limit of the primary frequency regulation dead zone and the real-time grid frequency. On this basis, the active power of a single channel of the inverter is increased according to the adjustment target power change, and then the power limit value of each remaining channel of the inverter is reset according to the active power and the current input power until the grid frequency returns to the primary frequency regulation dead zone.

[0045] If the second judgment result is that the grid frequency exceeds the upper limit of the primary frequency regulation dead zone, first keep one of the channels in MPPT mode, and then understand and obtain the adjustment target power change based on the difference between the upper limit of the primary frequency regulation dead zone and the real-time grid frequency, reduce the active power of a single channel of the inverter based on the adjustment target power change, and reset the power limit value of each of the remaining channels of the inverter based on the current active power input power until the grid frequency returns to the primary frequency regulation dead zone. In the claims, specification and drawings of the present invention, the term "multiple" refers to two or more than two. Unless otherwise clearly defined, the orientation or positional relationship indicated by the terms "upper" and "lower" is based on the orientation or positional relationship shown in the drawings, which is only for the purpose of more conveniently describing the present invention and making the description process simpler, rather than indicating or implying that the device or element referred to must have the specific orientation described, be constructed and operated in a specific orientation, so these descriptions cannot be understood as limiting the present invention; the terms "connect", "install", "fix" and the like should be understood in a broad sense. For example, "connection" can be a fixed connection between multiple objects, or a detachable connection between multiple objects, or an integral connection; it can be a direct connection between multiple objects, or an indirect connection between multiple objects through an intermediate medium. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood based on the specific circumstances of the above data.

[0046] In the claims, specification and drawings of the present invention, the description of the terms "one embodiment", "some embodiments", "specific embodiments" and the like means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In the claims, specification and drawings of the present invention, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner.

[0047] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A primary frequency modulation method for a distributed photovoltaic power generation system, characterized in that: include: Using MPPT technology, several paths of the inverter are connected to effective input to obtain power parameters of the inverter; Based on the power parameter, performing power reservation processing; Collecting the current output power of the inverter and the grid frequency of the grid connection point in real time, determining whether the grid frequency exceeds a primary frequency modulation dead zone, and obtaining a first determination result; If the first judgment result is that the grid frequency exceeds the primary frequency modulation dead zone, a primary frequency modulation process is performed on the inverter, Otherwise, the inverter operates normally.

2. The primary frequency modulation method based on system power reservation according to claim 1, characterized in that: The MPPT technology is used to connect several inverters to effective inputs to obtain the power parameters of the inverter, including: MPPT technology is used to ensure that the inputs of several channels of the inverter are valid and the difference between the maximum input powers of any two channels of the inverter does not exceed 10% of the rated power of the inverter; The maximum power point of any one input is tracked, and based on the maximum power point, the real-time maximum power of the single input of the inverter is obtained.

3. The primary frequency modulation method based on system power reservation according to claim 2, characterized in that: The performing power reservation processing based on the power parameter includes: Based on the rated power of the inverter, determining a power reserve value required for performing a frequency modulation process on the inverter; Determining power limit values ​​of remaining paths of the inverter based on the power reserve value and the real-time maximum power; Power reservation processing is performed based on the power limit value.

4. The primary frequency modulation method based on system power reservation according to claim 1, characterized in that: If the judgment result is that the grid frequency exceeds the frequency modulation dead zone, performing a frequency modulation process on the inverter, including: When the grid frequency exceeds the primary frequency modulation dead zone, it is determined that the grid frequency exceeds a lower limit of the primary frequency modulation dead zone or the grid frequency exceeds an upper limit of the primary frequency modulation dead zone, and a second determination result is obtained; Based on the second judgment result, one of the paths is kept running in MPPT mode, the active power of the remaining paths of the inverter is changed respectively, and the power limit values ​​of the remaining paths of the inverter are reset until the grid frequency returns to the primary frequency modulation dead zone.

5. The primary frequency modulation method based on system power reservation according to claim 4, characterized in that: Based on the second judgment result, one of the paths is allowed to maintain the MPPT mode operation, the active power of the remaining paths of the inverter is changed respectively, and the power limit values ​​of the remaining paths of the inverter are reset until the grid frequency returns to the primary frequency modulation dead zone, including: If the second judgment result is that the grid frequency exceeds the lower limit of the primary frequency modulation dead zone, one of the channels is allowed to maintain the MPPT mode operation, and based on the difference between the lower limit of the primary frequency modulation dead zone and the real-time grid frequency, the adjustment target power change is obtained, and the active power of the single channel of the inverter is increased based on the adjustment target power change, and based on the active power and the current input power, the power limit values ​​of the remaining channels of the inverter are reset respectively until the grid frequency returns to the primary frequency modulation dead zone; If the second judgment result is that the grid frequency exceeds the upper limit of the primary frequency modulation dead zone, one of the channels is allowed to maintain MPPT mode operation, and the adjustment target power change is obtained based on the difference between the upper limit of the primary frequency modulation dead zone and the real-time grid frequency. The active power of a single channel of the inverter is reduced based on the adjustment target power change, and the power limit values ​​of the remaining channels of the inverter are reset based on the active power and the current input power until the grid frequency returns to the primary frequency modulation dead zone.

6. The primary frequency modulation method based on system power reservation according to claim 1, characterized in that: Based on the broken line function of the grid frequency and active power, a droop characteristic of the primary frequency modulation process is realized; The specific formula is as follows: ； in, is the overall active power of the inverter under primary frequency modulation processing, is the current active power of the inverter, is the frequency regulation rate of the new energy source. is the rated power of the inverter, is the current grid frequency, is the rated grid frequency.

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