Maximum power tracking discharge power distribution system and method for photovoltaic group string side energy storage

Abstract

The invention discloses a photovoltaic group string side energy storage maximum power tracking discharge power distribution system and method, the output end of a photovoltaic group string is connected in parallel with an energy storage inverter and then connected to a grid-connected inverter, and the grid-connected inverter realizes normal photovoltaic maximum power tracking and sends electric energy to a power grid. And the energy storage inverter adaptively adjusts an energy storage discharge power value according to photovoltaic output power and a battery discharge stage, so that flexible synchronous access of photovoltaic and energy storage discharge is realized, photovoltaic curve characteristics are kept for a P-V characteristic curve of the grid-connected inverter, and energy storage maximum capacity discharge is realized while photovoltaic maximum power tracking failure is avoided.

Description

Technical Field

[0001] This invention belongs to the field of photovoltaic power generation technology, specifically relating to a maximum power tracking discharge power allocation system and method for photovoltaic string-side energy storage. Background Technology

[0002] Solar photovoltaic (PV) power generation is a clean energy technology that directly converts solar energy into electricity, offering advantages such as renewability, pollution-free operation, and sustainability. In recent years, with increasing global emphasis on environmental protection and sustainable development, solar PV power generation has seen increasingly widespread application and promotion. However, with the implementation of peak-valley pricing for PV power, electricity prices have decreased since the period of strongest sunlight was the lowest. This has led many PV power plants to introduce energy storage devices. Traditional grid-side energy storage methods require large storage capacities, resulting in bulky equipment that cannot be installed in many locations due to safety concerns. Therefore, a PV string-side energy storage method has been proposed to achieve a flexible and compact distributed energy storage solution. While PV strings can output maximum power under strong sunlight or low temperatures, their maximum power output may significantly decrease during cloudy or high-temperature conditions. To prevent grid-connected inverter maximum power tracking failure leading to shutdown, adaptive adjustment of battery discharge power is necessary.

[0003] Therefore, it is necessary to design an adaptive energy coordination and allocation method for photovoltaic string-side battery energy storage and inverter grid connection, so that the output power of the energy storage inverter can be coordinated with the maximum power point tracking (MPPT) requirement of the photovoltaic inverter in both the working and non-working states of the photovoltaic string, while satisfying the maximum energy storage output and avoiding photovoltaic MPPT failure. Summary of the Invention

[0004] To solve the above technical problems, the present invention provides the following technical solution:

[0005] This invention addresses the problems existing in the prior art by providing a maximum power point tracking (MPPT) discharge power distribution system for photovoltaic string-side energy storage, comprising: a photovoltaic string, an energy storage inverter, a grid-connected inverter, and a battery; the output terminal of the photovoltaic string is connected to both the input terminals of the grid-connected inverter and the energy storage inverter, and the energy storage inverter is connected to the battery. The grid-connected inverter achieves maximum power point tracking (MPPT) for photovoltaic (PV) and feeds electricity into the grid. The energy storage inverter executes a discharge method: based on the PV output power and battery charge, it generates a virtual curve simulating the characteristics of PV and adaptively adjusts the output power value. This ensures that the output power of the energy storage inverter is coordinated with the PV inverter's maximum power point tracking requirements in both the PV string operating and non-operating modes, while simultaneously satisfying the maximum PV energy output and normal grid connection of the grid-connected inverter.

[0006] Furthermore, the aforementioned energy storage inverter discharge method is to generate a virtual curve simulating the photovoltaic (PV) characteristics based on the photovoltaic output power and battery charge, and adaptively adjust the output power value so that the output power of the energy storage inverter can be coordinated with the maximum power point tracking requirement of the photovoltaic inverter in both the working and non-working modes of the photovoltaic string, while simultaneously satisfying the maximum photovoltaic energy output and the normal grid connection of the grid-connected inverter.

[0007] Furthermore, the aforementioned maximum power point tracking discharge power distribution system for photovoltaic string-side energy storage has two specific operating modes for the energy storage inverter, based on the energy storage battery capacity and the output of the photovoltaic string.

[0008] Mode 1: When the photovoltaic string is not working (P1=0), the energy storage inverter simulates the output of the photovoltaic string according to the preset inverter power distribution curve, and the energy storage battery alone provides the power required by the grid-connected inverter.

[0009] Mode 2: When the output power of the photovoltaic string P1>0, the energy storage inverter combines the photovoltaic output curve to calculate and update the energy storage discharge power distribution curve in real time. The energy storage battery and the photovoltaic string jointly provide the grid-connected inverter with power, realizing power point tracking.

[0010] The PV characteristic curve is composed as follows:

[0011] The preset PV characteristic curve for mode 1 is as follows:

[0012] ,

[0013] The power distribution curve of the second mode energy storage discharge is as follows

[0014] ,

[0015] Where P m ε is the maximum output power of the grid-connected inverter, ε is the power regulation factor, V0 is the voltage when the photovoltaic string power is 0, and V m The rated maximum power point voltage of the photovoltaic string is determined based on the technical parameters of the photovoltaic string. P1 is the real-time curve of the current photovoltaic output.

[0016] The present invention also provides a discharge power allocation method for a maximum power point tracking discharge power allocation system, the steps of which are as follows:

[0017] Step S1: Determine the photovoltaic output status. When P1=0, the energy storage inverter enters mode one and executes step SA1; when P1>0, the energy storage inverter enters mode two and executes step SB1.

[0018] Step SA1: Collect the current voltage V at the connection point between the photovoltaic string and the energy storage inverter, substitute it into the mode-1 energy storage discharge power calculation formula, and obtain the energy storage discharge power P.模态一 Then proceed to step SA2;

[0019] Step SA2: After a fixed time interval T, return to execute step S1;

[0020] Step SB1: Collect the current voltage V at the connection point between the photovoltaic string and the energy storage inverter, and the current output power P1 of the photovoltaic string. Substitute these values ​​into the mode 2 energy storage discharge power calculation formula to obtain the energy storage discharge power P. 模态二 Then proceed with steps SB2 to SB5;

[0021] Step SB2: At a fixed time interval T, the system enters a short calibration cycle, with the set time interval T... k ;

[0022] Step SB3: Here T k At the beginning, the discharge power of the energy storage inverter is locked at the level of the previous time interval T. At the end, the discharge power of the energy storage inverter is denoted as a fixed value P(k-1). k During the cycle, the energy storage inverter discharges at a constant power of P(k-1);

[0023] Step SB4: Photovoltaic Inverter T k Automatically tracks the new maximum power point within the cycle and records the voltage V at that maximum power point. m (k);

[0024] Step SB5: Receive new regulatory factors (k), If no new regulatory factor is found, the regulatory factor from the previous step will be used. (k-1), In the updated formula for calculating the energy storage discharge power of mode two, V m Regulatory factors Return to step S1.

[0025] Compared with the prior art, the beneficial technical effects of the above technical solution adopted in this invention are as follows: When adopting a direct energy storage structure on the photovoltaic string side, in order not to interfere with the normal operation of the grid-connected inverter's maximum power tracking, especially when the maximum output power of the photovoltaic string is significantly lower than the grid-connected power requirement, the energy storage discharge power is adaptively adjusted so that while the photovoltaic outputs energy, the PV characteristic curve of the energy storage output is similar to the original photovoltaic output curve, preventing the grid-connected inverter's maximum power tracking failure from causing the entire system to shut down. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of a modular energy storage system for photovoltaic string-side batteries provided in an embodiment of the present invention.

[0027] Figure 2The battery discharge PV characteristic curve is provided for an embodiment of the present invention.

[0028] Figure 3 The photovoltaic string output PV characteristic curve and battery discharge PV characteristic curve are provided for embodiments of the present invention.

[0029] Figure 4 The photovoltaic string output PV characteristic curve and the power tracking time battery discharge PV characteristic curve are provided for embodiments of the present invention.

[0030] Figure 5 The time allocation diagram for the intermittent fixed power tracking method provided in the embodiments of the present invention.

[0031] Figure 6 A flowchart illustrating the implementation steps of an embodiment of the present invention. Detailed Implementation

[0032] To better understand the technical content of the present invention, specific embodiments are described below in conjunction with the accompanying drawings.

[0033] In this invention, various aspects of the invention are described with reference to the accompanying drawings, in which numerous illustrative embodiments are shown. Embodiments of the invention are not limited to those depicted in the drawings. It should be understood that the invention is implemented through any of the various concepts and embodiments described above, as well as the concepts and embodiments described in detail below, because the concepts and embodiments disclosed herein are not limited to any particular implementation. Furthermore, some aspects of the invention disclosed may be used alone or in any suitable combination with other aspects of the invention disclosed.

[0034] like Figure 1 As shown, this embodiment provides a maximum power point tracking (MPPT) discharge power distribution system for photovoltaic (PV) string-side energy storage, including: a PV string, an energy storage inverter, a grid-connected inverter, and a battery; the output terminal of the PV string is connected to the input terminals of both the grid-connected inverter and the energy storage inverter, and the energy storage inverter is connected to the battery.

[0035] The grid-connected inverter achieves maximum power point tracking (MPPT) for photovoltaic (PV) and feeds electricity into the grid. The energy storage inverter executes a discharge method: based on the PV output power and battery charge, it generates a virtual curve simulating the characteristics of PV and adaptively adjusts the output power value. This ensures that the output power of the energy storage inverter is coordinated with the PV inverter's maximum power point tracking requirements in both the PV string operating and non-operating modes, while simultaneously satisfying the maximum PV energy output and normal grid connection of the grid-connected inverter.

[0036] The specific parameters set in this embodiment include: the rated output power of the energy storage inverter is 5kWh, the battery connected in the embodiment is a ternary lithium battery, and its discharge power during actual operation is about 0.7 times the rated output power of the inverter. Therefore, 3.5kWh is used as the rated discharge power of the battery in the embodiment; the output voltage of the energy storage inverter, that is, the battery voltage Ue = 80V~100V.

[0037] As a preferred embodiment, the energy storage inverter discharge algorithm includes the following two cases:

[0038] Mode 1: When the photovoltaic string is not working (P1=0), the energy storage inverter simulates the output of the photovoltaic string according to the preset inverter power distribution curve, and the energy storage battery alone provides the power required by the grid-connected inverter.

[0039] Mode 2: When the output power P1 of the photovoltaic string is greater than 0, the energy storage inverter combines the photovoltaic output curve to calculate and update the energy storage discharge power distribution curve in real time. The energy storage battery and the photovoltaic string jointly provide power to the grid-connected inverter to achieve power point tracking.

[0040] As a preferred embodiment, such as Figure 2 and Figure 3 As shown, the energy storage discharge power curves under different photovoltaic output conditions are as follows:

[0041] The formula for calculating the energy storage discharge power in mode 1 is as follows:

[0042] In the formula, P m ε is the maximum output power of the grid-connected inverter, ε is the power regulation factor, v is the current voltage at the connection point between the photovoltaic string and the energy storage inverter, V0 is the open-circuit voltage of the photovoltaic string, and V m1 V is the rated power point voltage of the energy storage inverter. m P1 is the current maximum power point voltage of the photovoltaic string, and P2 is the current output power of the photovoltaic string.

[0043] The formula for calculating the discharge power of the second mode energy storage is:

[0044] In the formula, P m ε is the maximum output power of the grid-connected inverter, ε is the power regulation factor, v is the current voltage at the connection point between the photovoltaic string and the energy storage inverter, V0 is the open-circuit voltage of the photovoltaic string, and V m1 V is the rated power point voltage of the energy storage inverter. m P1 is the current maximum power point voltage of the photovoltaic string, and P2 is the current output power of the photovoltaic string.

[0045] Its synthesis curve has a maximum power point located at P1 + ε.P m At that location, the corresponding voltage is Vm.

[0046] like Figure 4 , Figure 5 , Figure 6 As shown, the present invention also provides a discharge power allocation method applied to the maximum power point tracking discharge power allocation system, the steps of which are as follows:

[0047] Step S1: Determine the photovoltaic output status. When P1=0, the energy storage inverter enters mode one and executes step SA1; when P1>0, the energy storage inverter enters mode two and executes step SB1.

[0048] Step SA1: Collect the current voltage V at the connection point between the photovoltaic string and the energy storage inverter, substitute it into the mode-1 energy storage discharge power calculation formula, and obtain the energy storage discharge power P. 模态一 Then proceed to step SA2;

[0049] In the formula, P m ε is the maximum output power of the grid-connected inverter, ε is the power regulation factor, v is the current voltage at the connection point between the photovoltaic string and the energy storage inverter, V0 is the open-circuit voltage of the photovoltaic string, and V m1 This is the rated power point voltage of the energy storage inverter;

[0050] Step SA2: After a fixed time interval T, return to execute step S1;

[0051] Step SB1: Collect the current voltage V at the connection point between the photovoltaic string and the energy storage inverter, and the current output power P1 of the photovoltaic string. Substitute these values ​​into the mode 2 energy storage discharge power calculation formula to obtain the energy storage discharge power P. 模态二 Then proceed with steps SB2 to SB5; In the formula, P m ε is the maximum output power of the grid-connected inverter, ε is the power regulation factor, v is the current voltage at the connection point between the photovoltaic string and the energy storage inverter, and V0 is the open-circuit voltage of the photovoltaic string. m P1 is the current maximum power point voltage of the photovoltaic string, and P2 is the current output power of the photovoltaic string.

[0052] Step SB2: At a fixed time interval T, the system enters a short calibration cycle, with the set time interval T... k ;

[0053] Step SB3: Here T k At the beginning, the discharge power of the energy storage inverter is locked at the level of the previous time interval T. At the end, the discharge power of the energy storage inverter is denoted as a fixed value P(k-1). k During the cycle, the energy storage inverter discharges at a constant power of P(k-1);

[0054] Step SB4: Photovoltaic Inverter Tk Automatically tracks the new maximum power point within the cycle and records the voltage V at that maximum power point. m (k);

[0055] Step SB5: Receive new regulatory factors (k), If no new regulatory factor is found, the regulatory factor from the previous step will be used. (k-1), In the updated formula for calculating the energy storage discharge power of mode two, V m Regulatory factors Return to step S1.

[0056] This invention employs a simulated energy storage output curve, enabling the energy storage inverter to simulate or coordinate with the characteristics of photovoltaics to output a specific PV characteristic curve. This ensures that the overall curve resulting from the superposition of the energy storage output curve and the photovoltaic curve is still a photovoltaic-like curve with a clearly defined maximum power point. This guarantees that the curve tracked by the photovoltaic inverter is appropriate and that the photovoltaic string always generates electricity at its highest efficiency.

[0057] While the present invention has been described above with reference to preferred embodiments, it is not intended to limit the invention. Those skilled in the art can make various modifications and refinements without departing from the spirit and scope of the invention. Therefore, the scope of protection of the present invention shall be determined by the claims.

Claims

1. A maximum power point tracking discharge power distribution system for photovoltaic string-side energy storage, characterized in that, include: Photovoltaic strings, energy storage inverters, grid-connected inverters, and batteries; The output terminals of the photovoltaic string are connected to the input terminals of both the grid-connected inverter and the energy storage inverter, and the energy storage inverter is connected to the battery. The grid-connected inverter achieves maximum power point tracking (MPPT) for photovoltaic (PV) and feeds electricity into the grid. The energy storage inverter executes a discharge method: based on the PV output power and battery charge, it generates a virtual curve simulating the characteristics of PV and adaptively adjusts the output power value. This ensures that the output power of the energy storage inverter is coordinated with the PV inverter's maximum power point tracking requirements in both the PV string operating and non-operating modes, while simultaneously satisfying the maximum PV energy output and normal grid connection of the grid-connected inverter.

2. The maximum power point tracking discharge power distribution system for photovoltaic string-side energy storage according to claim 1, characterized in that, When the energy storage inverter performs the discharge method, in mode one, when the photovoltaic string is not working and P1=0, the energy storage inverter simulates the output of the photovoltaic string according to the preset energy storage discharge power calculation formula, and the energy storage battery alone provides the power required by the grid-connected inverter.

3. The maximum power point tracking discharge power distribution system for photovoltaic string-side energy storage according to claim 2, characterized in that, When the energy storage inverter performs the discharge method, in mode two, when the output power of the photovoltaic string P1>0, the energy storage inverter combines the photovoltaic output curve and uses periodic photovoltaic string maximum power point tracking to calculate and update the energy storage discharge power allocation formula in real time. The energy storage battery and the photovoltaic string jointly provide the grid-connected inverter with power, realizing the coordinated release of power.

4. The maximum power point tracking discharge power distribution system for photovoltaic string-side energy storage according to claim 2, characterized in that, The formula for calculating the energy storage discharge power in mode 1 is as follows: ， In the formula, P m ε is the maximum output power of the grid-connected inverter, ε is the power regulation factor, v is the current voltage at the connection point between the photovoltaic string and the energy storage inverter, V0 is the open-circuit voltage of the photovoltaic string, and V m1 This is the rated power point voltage of the energy storage inverter.

5. The maximum power point tracking discharge power distribution system for photovoltaic string-side energy storage according to claim 3, characterized in that, The formula for calculating the discharge power of the second mode energy storage is: ， In the formula, P m ε is the maximum output power of the grid-connected inverter, ε is the power regulation factor, v is the current voltage at the connection point between the photovoltaic string and the energy storage inverter, and V0 is the open-circuit voltage of the photovoltaic string. m P1 is the current maximum power point voltage of the photovoltaic string, and P2 is the current output power of the photovoltaic string.

6. A discharge power allocation method applied to the maximum power point tracking discharge power allocation system described in claims 1-5, characterized in that, The steps are as follows: Step S1: Determine the photovoltaic output status. When P1=0, the energy storage inverter enters mode one and executes step SA1; when P1>0, the energy storage inverter enters mode two and executes step SB1. Step SA1: Collect the current voltage V at the connection point between the photovoltaic string and the energy storage inverter, substitute it into the mode-1 energy storage discharge power calculation formula, and obtain the energy storage discharge power P. 模态一 Then proceed to step SA2; Step SA2: After a fixed time interval T, return to execute step S1; Step SB1: Collect the current voltage V at the connection point between the photovoltaic string and the energy storage inverter, and the current output power P1 of the photovoltaic string. Substitute these values ​​into the mode 2 energy storage discharge power calculation formula to obtain the energy storage discharge power P. 模态二 Then proceed with steps SB2 to SB5; Step SB2: At a fixed time interval T, the system enters a short calibration cycle, with the set time interval T... k ; Step SB3: Here T k At the beginning, the discharge power of the energy storage inverter is locked at the level of the previous time interval T. At the end, the discharge power of the energy storage inverter is denoted as a fixed value P(k-1). k During the cycle, the energy storage inverter discharges at a constant power of P(k-1); Step SB4: Photovoltaic Inverter T k Automatically tracks the new maximum power point within the cycle and records the voltage V at that maximum power point. m (k); Step SB5: Receive new regulatory factors (k), If no new regulatory factor is found, the regulatory factor from the previous step will be used. (k-1), In the updated formula for calculating the energy storage discharge power of mode two, V m Regulatory factors Return to step S1.

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