Power control method and system of photovoltaic power station and storage medium

Abstract

The invention discloses a power control method and system of a photovoltaic power station, and belongs to the technical field of photovoltaic power generation. The method comprises the following steps: acquiring an active power set value Pset of a power grid and actual output power Pactual of a power station in real time, and calculating a power deviation delta P and a power margin Pmargin; dynamically selecting a control mode based on the comparison of delta P and Pmargin with a preset threshold: when the power needs to be rapidly and greatly reduced, entering a rapid power reduction mode, and preferentially switching out the inverter with the lowest operation efficiency; when power fine tuning is needed, a power accurate tracking mode is entered, a PI controller is used for generating an adjusting instruction and distributing the adjusting instruction to each inverter, and accurate closed-loop control is realized by adjusting MPPT working points of the inverters. Through cooperation and seamless switching of the two modes, the problem that in the prior art, power control response speed, stability and control precision are difficult to consider at the same time is effectively solved, rapid, stable and high-precision response to a power grid dispatching instruction is achieved, and power generation loss is reduced.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of photovoltaic power generation, in particular to a power control method and system of a photovoltaic power station and a storage medium. BACKGROUND

[0002] With the rapid growth of photovoltaic power generation capacity, its intermittency and volatility have brought challenges to the stable operation of the power grid. The power grid dispatching department often needs to issue power dispatching instructions to the photovoltaic power station according to the real-time load condition of the power grid, and requires it to limit the output power below a certain set value.

[0003] At present, the traditional power control methods mainly include: Light abandonment and power curtailment: directly cut off part of the photovoltaic string or inverter to stop power generation. Although this method is simple, the power reduction is stepwise, which has a great impact on the power grid, and the control precision is low, which easily causes the waste of power generation.

[0004] Constant power factor control: by adjusting the reactive power of the inverter to indirectly affect the active power. This method has limited control ability on active power, and may not meet the requirements of the power grid for reactive power.

[0005] MPPT-based derating operation: by forcibly changing the MPPT operating point of the inverter, the output power is reduced by deviating from the maximum power point. However, the existing method has a contradiction between dynamic response speed and stability in the process of power regulation. Too fast regulation can easily lead to power oscillation and DC side voltage fluctuation; too slow regulation cannot meet the rapid response requirements of the power grid dispatching. In addition, it is difficult to achieve accurate closed-loop control of power when the light and temperature change dramatically.

[0006] Therefore, there is an urgent need in the art for a photovoltaic power station power control method that can achieve fast, smooth and high-precision power control. SUMMARY

[0007] The purpose of the present application is to provide a power control method for a photovoltaic power station to solve the above problems existing in the current photovoltaic power station.

[0008] To achieve the above purpose, the present application adopts the following technical solutions: A power control method for a photovoltaic power station, comprising the following steps: S1, real-time acquisition of an active power set value P_set and an actual output power P_actual of the photovoltaic power station, calculation of a power deviation ΔP and a current power margin P_margin; S2, based on the comparison results of the power deviation ΔP and the power margin P_margin with the preset threshold, selectively entering a fast power reduction mode or a power accurate tracking mode; wherein, In the fast power drop mode, the number of inverters to be cut off is calculated according to the power deviation, and the corresponding number of inverters is cut off to realize the fast drop of power; In the power accurate tracking mode, a closed-loop controller is used to operate the power deviation, to generate a power adjustment instruction, and to distribute the instruction to each operating inverter to adjust its output power, to realize the accurate control of total power.

[0009] 2. The power control method of the photovoltaic power station according to claim 1, wherein the step of selectively entering the control mode comprises: when the power deviation ΔP is less than a negative deviation dead zone threshold and the power margin P_margin is greater than a margin threshold, entering the fast power drop mode; when the power deviation ΔP is greater than a positive deviation dead zone threshold, entering the power accurate tracking mode.

[0010] Further preferably, in the fast power drop mode, when the inverters are cut off, the inverter with the lowest current operating efficiency is preferentially selected to be cut off.

[0011] Further preferably, in the power accurate tracking mode, the closed-loop controller is a proportional-integral (PI) controller, and the power adjustment instruction is distributed in proportion to the rated capacity of each inverter.

[0012] Further preferably, when switching from the fast power drop mode to the power accurate tracking mode, the integral term of the PI controller is initialized, and the initial value is the controller output value corresponding to the power deviation at the switching time.

[0013] Further preferably, in the power accurate tracking mode, it further comprises monitoring the DC side voltage of the inverter, and when the DC side voltage approaches its safe upper limit, the power adjustment instruction distributed to the inverter is limited in amplitude.

[0014] A power control system of a photovoltaic power station for implementing the power control method of the photovoltaic power station, the system comprising: a data acquisition module for acquiring the power station output power, the operating state and parameters of each inverter in real time; an instruction receiving module for receiving the active power set value issued by the power grid dispatching system; a calculation and judgment module for calculating the power deviation and the power margin, and judging the control mode accordingly; a control execution module for generating and executing the inverter cut-off instruction in the fast power drop mode, and generating and distributing the power fine adjustment instruction to each inverter in the power accurate tracking mode; A communication module is configured to connect the control system with the inverter in the station.

[0015] A computer readable storage medium stores a computer program, and the program is executed by a processor to implement a power control method of a photovoltaic power station The present application has the following advantages: The present application introduces a fast power reduction mode, which preferentially cuts out low-efficiency inverters when a large power reduction is needed, thereby achieving fast response of power; the power is finely adjusted and smoothly operated through the power accurate tracking mode and PI control. The two modes work together to overcome the shortcomings of single control. Since a closed-loop control strategy is adopted, the set value and the actual value are compared in real time, and the PI controller eliminates the steady-state error, so that the power output of the power station can accurately track the dispatching instruction. By setting reasonable dead zones and margin judgment thresholds, the mode is prevented from frequently switching at critical points. At the same time, the operating state of the inverter (such as efficiency, voltage) is considered to achieve intelligent resource allocation and equipment protection. In the fast reduction mode, the low-efficiency inverters are preferentially cut out, thereby maximizing the power generation capacity of high-efficiency units and reducing the loss of overall power generation. BRIEF DESCRIPTION OF DRAWINGS

[0016] Figure 1 is the overall flowchart of the power control method of the photovoltaic power station in the embodiment of the present application. DETAILED DESCRIPTION

[0017] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application.

[0018] Figure 1 As shown in the figure, a power control method of a photovoltaic power station includes the following steps: S1: instruction acquisition and power margin calculation: The active power set value P_set issued by the power grid dispatching system in real time is acquired, and the actual output power P_actual of the photovoltaic power station public connection point is collected in real time. The power deviation ΔP = P_set - P_actual is calculated. At the same time, the current maximum power P_max of the power station (which can be obtained by adding the input power of all inverters on the DC side) is calculated, and the power margin P_margin = P_max - P_set is calculated.

[0019] S2: control mode judgment: According to the power deviation ΔP and the power margin P_margin, the control mode to be entered at present is judged: If ΔP < -ΔP_db (ΔP_db is a negative deviation deadband threshold, a small positive number) and P_margin > P_margin_th (P_margin_th is a margin threshold), enter the fast power reduction mode.

[0020] If ΔP > +ΔP_db (ΔP_db is a positive deviation deadband threshold), enter the power accurate tracking mode.

[0021] If the above two conditions are not met, keep the current operating state.

[0022] S3: Multi-mode coordinated control: In the fast power reduction mode: a. According to the size of ΔP, calculate the number of inverters to be cut out N = ceil( |ΔP| / P_inv_rated ), where P_inv_rated is the rated power of a single inverter, and ceil is the ceiling function.

[0023] b. Generate inverter cut-out instructions, and preferentially cut out the N inverters with the lowest current work efficiency to enter standby state.

[0024] c. This mode aims to achieve rapid and large reduction of power by abandoning light.

[0025] In the power accurate tracking mode: a. Use a proportional-integral (PI) controller to operate on the power deviation ΔP to generate a unified power adjustment instruction ΔP_cmd.

[0026] b. Distribute ΔP_cmd to each online inverter in proportion to its rated capacity, as the adjustment amount of its individual power set value P_inv_set(i).

[0027] c. Each inverter receives its individual power set value P_inv_set(i) and adjusts its MPPT operating point (such as raising the DC side voltage) through internal algorithms to make its output power track P_inv_set(i), thereby achieving accurate closed-loop control of the total power of the power station.

[0028] S4: Mode switching and seamless connection: When the system switches from the fast power reduction mode to the power accurate tracking mode, the initial value of the integral term of the PI controller is set to the output value corresponding to the power deviation at the switching time, to avoid the jump of the control instruction and achieve smooth transition between the two modes.

[0029] Preferably, in the power accurate tracking mode of step S3, the monitoring of the DC side voltage of the inverter is also included, when the DC side voltage of any inverter exceeds 95% of its maximum allowed voltage, the upper limit of the power command of the inverter is limited to prevent the DC side overvoltage.

[0030] Preferably, the negative deviation dead zone threshold ΔP_db and the margin threshold P_margin_th can be dynamically adjusted according to the power plant capacity and scheduling requirements.

[0031] The power control method described above will be described in detail below with an example of a 100MW photovoltaic power plant.

[0032] The 100MW photovoltaic power plant contains 200 500kW inverters. The grid dispatches the command to limit the power output of the power plant to 60MW.

[0033] S1: The power plant monitoring system obtains the active power set value P_set = 60MW, and collects the actual output power P_actual = 99MW (current good light). The power deviation ΔP = 60 - 99 = -39 MW is calculated. At the same time, the system calculates the current maximum available power P_max to be about 99MW, and the power margin P_margin = P_max-P_set, that is, 99 - 60 = 39 MW.

[0034] S2: Set the negative deviation dead zone threshold ΔP_db = 1MW, and the margin threshold P_margin_th = 5MW. If ΔP < -ΔP_db (ΔP_db is a small positive number) and P_margin > P_margin_th (P_margin_th is a margin threshold), the system enters the fast power reduction mode, that is, ΔP (-39MW) <- 1MW, and P_margin (39MW) > 5MW, the system determines to enter the fast power reduction mode.

[0035] S3 (fast power reduction): Calculate the number of inverters to be cut out N = ceil( | -39MW | / 0.5MW ) = ceil(78) = 78.

[0036] The system retrieves the real-time efficiency data of each inverter from the monitoring database, selects the 78 inverters with the lowest current efficiency, and sends a shutdown command to them.

[0037] After execution, the power of the power plant is quickly reduced to about 99 - (78 * 0.5) = 60 MW.

[0038] S2 (again judge): After power reduction, the actual output power P_actual becomes about 60.5 MW, and the power deviation ΔP = 60 - 60.5 = -0.5 MW. Since |ΔP| < ΔP_db (1 MW), the system does not meet the fast drop condition, and automatically switches to the power accurate tracking mode.

[0039] S3 (power accurate tracking): The PI controller starts to work. The initial value of the integrator is set to a small value corresponding to the -0.5 MW deviation, to achieve smooth cut-in.

[0040] The PI controller operates on the -0.5 MW deviation, and outputs a small adjustment command ΔP_cmd, for example +0.3 MW (meaning that the power needs to be slightly increased to offset the negative deviation).

[0041] The +0.3 MW command is distributed to the still running 122 inverters. The increased power setting value of each inverter is 0.3 / 122 ≈ 2.46 kW.

[0042] Each inverter fine-tunes its MPPT operating point, slowly increases the output power, and makes the total power of the power plant accurately stable at 60 MW.

[0043] During the entire process, if the maximum available power P_max decreases due to sudden weakening of light, the system will automatically adjust through the power accurate tracking mode, and always maintain the actual output power P_actual ≈ active power set value P_set. If the dispatching command suddenly requires to rise to 80 MW, the power deviation ΔP becomes a positive large value, the system will always be in the power accurate tracking mode, and gradually increase the power through PI control, while the previously cut out inverters can be automatically awakened.

[0044] Another embodiment of the present application also provides a power control system of a photovoltaic power plant, for implementing the power control method of the photovoltaic power plant, the system comprising: a data acquisition module for acquiring the output power of the power plant, the operating state and parameters of each inverter in real time; an instruction receiving module for receiving the active power set value issued by the power grid dispatching system; a calculation and judgment module for calculating the power deviation and the power margin, and judging the control mode accordingly; a control execution module for generating and executing the inverter cut-out instruction in the fast power drop mode, and generating and distributing the power fine-tuning instruction to each inverter in the power accurate tracking mode; a communication module for connecting the control system and the inverter in the power plant.

[0045] The inventive concept and the achievable beneficial effects of the power control method of the photovoltaic power station and the power control system of the photovoltaic power station provided by the embodiments of the present application are the same as those of the foregoing method embodiments, and will not be described herein again.

[0046] The present application further provides a computer readable storage medium storing computer instructions, which cause a computer to execute the power control method of the photovoltaic power station provided by the embodiments of the present application.

[0047] The computer readable medium includes, but is not limited to, any type of disk (including floppy disks, hard disks, optical disks, CD-ROMs, and magneto-optical disks), ROMs, RAMs, EPROMs (Erasable Programmable Read-Only Memory), EEPROMs, flash memories, magnetic cards or optical cards. That is, the readable medium includes any medium that stores or transmits information in a form capable of being read by a device (for example, a computer).

[0048] The inventive concept and the achievable beneficial effects of the power control method of the photovoltaic power station and the computer readable storage medium provided by the embodiments of the present application are the same as those of the foregoing method embodiments, and will not be described herein again.

[0049] Those skilled in the art can understand that the steps, measures and schemes in the various operations, methods and processes discussed in the present application can be alternated, changed, combined or deleted. Further, other steps, measures and schemes in the various operations, methods and processes discussed in the present application can also be alternated, changed, rearranged, decomposed, combined or deleted. Further, the steps, measures and schemes in the various operations, methods and processes in the prior art can also be alternated, changed, rearranged, decomposed, combined or deleted.

[0050] It should be understood that, although each step in the flowchart of the accompanying drawings is shown in sequence according to the indication of the arrow, these steps are not necessarily executed in sequence according to the indication of the arrow. Unless explicitly stated herein, the execution of these steps is not strictly limited in sequence, and they can be executed in other sequences. Moreover, at least part of the steps in the flowchart of the accompanying drawings can include multiple sub-steps or multiple stages, which are not necessarily executed at the same time, but can be executed at different times, and the execution sequence is not necessarily sequential, but can be executed in rotation or alternation with at least part of other steps or sub-steps or stages of other steps.

[0051] Those skilled in the art will appreciate that embodiments of the present application can be readily used as a method, apparatus, device (system) or computer program product. Accordingly, the present application can take the form of an entirely hardware embodiment, an entirely software embodiment or an embodiment combining software and hardware aspects. Furthermore, the present application can take the form of a computer program product on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROMs, optical storage devices, etc.) embodying computer readable program code.

[0052] The present application is described in reference to the flowchart and / or block diagrams of the methods, apparatus (systems) and computer program products according to embodiments of the application. It will be understood that each block of the flowchart and / or block diagrams, and combinations of blocks in the flowchart and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general purpose computer, special purpose computer, embedded processing machine, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions specified in the flowchart and / or block diagram block or blocks. Figure 1 one or more functions specified in the flowchart and / or block diagram block or blocks. Figure 1 one or more functions specified in the flowchart and / or block diagram block or blocks.

[0053] These computer program instructions can also be stored in a computer- readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer-readable memory produce an article of manufacture including instructions which implement the function specified in the flowchart and / or block diagram block or blocks. Figure 1 one or more functions specified in the flowchart and / or block diagram block or blocks. Figure 1 one or more functions specified in the flowchart and / or block diagram block or blocks.

[0054] The computer program instructions can also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart and / or block diagram block or blocks. Figure 1 one or more functions specified in the flowchart and / or block diagram block or blocks. Figure 1 one or more functions specified in the flowchart and / or block diagram block or blocks.

[0055] It is also to be noted that the terms "comprising", "including", and any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but can also include other elements not expressly listed or inherent to such process, method, article, or apparatus. An element proceeded by "comprises a... " does not, without more constraints, exclude the existence of additional identical elements in the process, method, article, or apparatus that comprises the element.

[0056] Obviously, the described embodiments are only a few embodiments of the present application and not all embodiments. All other embodiments obtained by a person of ordinary skill in the art based on the embodiments in the present application are within the scope of protection of the present application.

Claims

1. A power control method for a photovoltaic power station, characterized in that, Includes the following steps: S1. Real-time acquisition of active power setpoint P_set and actual output power P_actual of photovoltaic power station, calculation of power deviation ΔP and current power margin P_margin; S2. Based on the comparison results of the power deviation ΔP and power margin P_margin with the preset threshold, selectively enter the rapid power drop mode or the power precise tracking mode. in, In the rapid power reduction mode, the number of inverters that need to be cut off is calculated based on the power deviation, and the corresponding number of inverters are cut off to achieve rapid power reduction; In the power tracking mode, the closed-loop controller calculates the power deviation, generates a power adjustment command, and distributes the command to each operating inverter to adjust its output power, thereby achieving precise control of the total power.

2. The power control method for a photovoltaic power station according to claim 1, characterized in that, The step of selectively entering the control mode includes: When the power deviation ΔP is less than the negative deviation dead zone threshold and the power margin P_margin is greater than the margin threshold, the system enters the rapid power decrease mode. When the power deviation ΔP is greater than the positive deviation dead zone threshold, the power precise tracking mode is entered.

3. The power control method for a photovoltaic power station according to claim 1, characterized in that, In the rapid power degradation mode, when switching off an inverter, the inverter with the lowest current operating efficiency is selected first.

4. The power control method for a photovoltaic power station according to claim 1, characterized in that, In the power precise tracking mode, the closed-loop controller is a proportional-integral (PI) controller, and the power adjustment commands are distributed according to the rated capacity ratio of each inverter.

5. The power control method for a photovoltaic power station according to claim 1, characterized in that, When switching from the rapid power drop mode to the precise power tracking mode, the integral term of the PI controller is initialized, with its initial value being the controller output value corresponding to the power deviation at the time of switching.

6. The power control method for a photovoltaic power station according to claim 1, characterized in that, The power tracking mode also includes monitoring the inverter's DC-side voltage and limiting the power regulation command allocated to the inverter when the DC-side voltage approaches its safe upper limit.

7. A power control system for a photovoltaic power station, used to implement the method described in any one of claims 1-6, characterized in that, The system includes: The data acquisition module is used to collect the power output of the power station, the operating status and parameters of each inverter in real time; The instruction receiving module is used to receive the active power setpoint issued by the power grid dispatching system; The calculation and judgment module is used to calculate the power deviation and power margin, and determine the control mode accordingly. The control execution module is used to generate and execute inverter cut-out commands in rapid power drop mode, and to generate and distribute power fine-tuning commands to each inverter in power precise tracking mode. A communication module is used to connect the control system with the on-site inverter.

8. A computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the power control method for a photovoltaic power station as described in any one of claims 1-6.

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