A power control method for a photovoltaic hydrogen production system based on a fuzzy logic system

Abstract

This invention discloses a power control method for a photovoltaic hydrogen production system based on a fuzzy logic system, comprising the following steps: S1, acquiring the battery charge state at the previous moment and the photovoltaic output at the current moment, inputting them into the fuzzy logic system, determining the operating mode of the photovoltaic hydrogen production system, and obtaining the power commands of the electrolyzer and battery at the current moment through the operating mode of the photovoltaic hydrogen production system; S2, based on the power commands of the electrolyzer and battery obtained in step S1, using a first-order low-pass filtering algorithm to determine the power values ​​of the electrolyzer, battery, and supercapacitor. This method considers the power control calculation time, and also needs to consider avoiding excessively high start-stop frequencies of the electrolysis unit modules to ensure the safety and service life of the electrolyzer, thereby achieving real-time power control of the photovoltaic hydrogen production system.

Description

Technical Field

[0001] This invention relates to the field of photovoltaic hydrogen production system power technology, specifically to a power control method for photovoltaic hydrogen production systems based on fuzzy logic systems. Background Technology

[0002] Hydrogen energy is an important direction for my country's future energy transformation and industrial development. It is a secondary energy source that is widely available, clean, low-carbon, flexible, efficient, and has a wide range of applications. By using green electricity generated from renewable energy sources to produce hydrogen through water electrolysis in an electrolyzer, true zero carbon emissions can be achieved.

[0003] Considering the risks of low-load operation of the electrolyzer during photovoltaic (PV) hydrogen production, a key challenge for PV hydrogen production systems is how to absorb the PV system's output power when power generation is abundant, and how to utilize the PV output power when power generation is insufficient. Power control of the PV power generation, hydrogen production, and energy storage units can achieve reliable PV power absorption and efficient operation of the hydrogen production unit. Due to the high randomness and volatility of PV power output, the sampling period for PV power in China is typically 1 second. Furthermore, the short-term prediction error of PV power output limits its application in real-time regulation, and the 1-second sampling period also restricts the application of intelligent optimization algorithms. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention proposes a power control method for photovoltaic hydrogen production systems based on fuzzy logic systems. This method considers the power control calculation time while also taking into account avoiding excessively high start-stop frequencies of the electrolysis unit modules, ensuring the safety and lifespan of the electrolyzer, and achieving real-time power control of the photovoltaic hydrogen production system.

[0005] To solve the above-mentioned technical problems, the technical solution of the present invention is as follows:

[0006] The photovoltaic hydrogen production system includes a photovoltaic power generation module, an electrolyzer, a hydrogen storage module, a battery energy storage, a supercapacitor, and an electrical conversion device. The electrolyzer uses electrical energy to electrolyze water to produce hydrogen, which is then stored in the hydrogen storage module. The battery energy storage is used to assist the electrolyzer in absorbing the output of the photovoltaic system. The supercapacitor compensates for power imbalances caused by the slow dynamic response of the electrolyzer and battery energy storage. The electrical conversion device includes several DC / DC converters for electrically connecting various devices to a DC bus.

[0007] This invention relates to a power control method for a photovoltaic hydrogen production system based on a fuzzy logic system, the specific steps of which are as follows:

[0008] Step S100: Preset several operating modes of the photovoltaic hydrogen production system, and combine the battery charge state SOC(t-1) of the previous moment with the photovoltaic output P at the current moment. PV(t) is used as the input to the fuzzy logic system to determine the operating mode of the photovoltaic hydrogen production system, thereby obtaining the current power commands for the electrolyzer and battery. and

[0009] There are five operating modes for the photovoltaic hydrogen production system, including operating mode one, operating mode two, operating mode three, operating mode four and operating mode five.

[0010] In operating mode one, the electrolytic cell is shut down, and the photovoltaic output power is absorbed by the battery, which can be specifically represented as:

[0011]

[0012] In operating mode two, the battery, in conjunction with the photovoltaic output, supplies power to the electrolytic cell, which operates at minimum input power. This can be specifically represented as:

[0013]

[0014] In the above formula, This is the minimum input power of the electrolytic cell;

[0015] In operating mode three, the battery, in conjunction with the photovoltaic output, supplies power to the electrolytic cell, and the input power of the electrolytic cell remains consistent with the previous moment. Specifically, this can be expressed as:

[0016]

[0017] In operating mode four, the battery is not working, and the photovoltaic power output supplies power to the electrolytic cell, which can be specifically represented as:

[0018]

[0019] In operating mode five, the electrolytic cell operates at maximum input power, and the remaining photovoltaic output power is absorbed by the battery. Specifically, this can be represented as:

[0020]

[0021] In the above formula, This is the maximum input power of the electrolytic cell.

[0022] Step S200: Based on the power commands for the electrolyzer and battery obtained in step S100 and A first-order low-pass filtering algorithm is used to determine the power value P of the electrolytic cell, battery, and supercapacitor. EL P BESS and P SC .

[0023] Furthermore, step S200 includes the following steps:

[0024] Step S210: Use a low-pass filtering algorithm to extract the low-frequency power component and high-frequency power component of the power command from the electrolytic cell and the battery;

[0025] Step S211: Extract the electrolytic cell power command obtained in step S100 low-frequency components and high frequency components

[0026]

[0027]

[0028] In the above formula, 'a' is the filter coefficient corresponding to the electrolytic cell;

[0029] Step S212: Extract the battery power command obtained in step S100 low-frequency components and high frequency components

[0030]

[0031]

[0032] In the above formula, b is the filter coefficient corresponding to the battery;

[0033] Step S220: Determine the power values ​​P of the electrolytic cell, battery, and supercapacitor at the current moment. EL (t), P BESS (t) and P SC (t); This step includes:

[0034] Step S221: The low-frequency power component of the power command for the electrolytic cell and battery, i.e., the power value of the electrolytic cell and battery:

[0035]

[0036]

[0037] Step S222: The high-frequency power components of the power commands from the electrolytic cell and battery are compensated and regulated by the supercapacitor.

[0038]

[0039] Furthermore, the power value P of the battery at the current moment obtained in step S221 is used. BESS The battery charge state SOC(t) at the current moment can be calculated from (t) and the battery charge state SOC(t-1), and used as the input of the fuzzy logic system at the next moment. Specifically, it can be expressed as:

[0040]

[0041] In the above formula, Δt is the time interval; η ch and η disc For the charging and discharging power of the battery; C BESS This refers to the capacity of the battery.

[0042] This invention has the following characteristics and beneficial effects:

[0043] This invention relates to five operating modes of a photovoltaic hydrogen production system. Based on the current photovoltaic output and the previous battery charge state, a fuzzy control system is used to determine the operating mode of the photovoltaic hydrogen production system, thereby determining the power command of the electrolyzer and battery at each moment, effectively improving equipment utilization, effectively reducing the start-up and shutdown frequency of the electrolyzer, and extending the service life of the electrolyzer.

[0044] Subsequently, a first-order low-pass filtering algorithm is used to calculate the power values ​​of the electrolyzer, battery, and supercapacitor at the current moment, thereby improving the adaptability of the electrolyzer and battery to power fluctuations in the photovoltaic power generation module.

[0045] The power control method for photovoltaic hydrogen production systems proposed in this invention does not use short-term prediction and intelligent optimization algorithms. The power calculation speed at each moment is in the millisecond range, which enables real-time power control of the photovoltaic hydrogen production system. Attached Figure Description

[0046] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0047] Figure 1 This is a flowchart of the power control method for a photovoltaic hydrogen production system proposed in this invention.

[0048] Figure 2 This is a schematic diagram of a photovoltaic hydrogen production system.

[0049] Figure 3 Let S be the membership function of the battery's state of charge (SOC).

[0050] Figure 4 Powering photovoltaics P PV The membership function.

[0051] Figure 5 This is the membership function for the operation mode of the photovoltaic hydrogen production system.

[0052] Figure 6This represents the real-time power control results for the electrolytic cell and the battery.

[0053] Figure 7 This is the result of real-time power control of the supercapacitor.

[0054] Figure 8 This refers to the operating mode of the photovoltaic hydrogen production system at each moment.

[0055] Figure 9 This is the SOC (State of Charge) curve of the battery. Detailed Implementation

[0056] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other.

[0057] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicating orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention. Furthermore, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined with "first," "second," etc., may explicitly or implicitly include one or more of that feature. In the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0058] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art will understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0059] This embodiment provides a power control method for a photovoltaic hydrogen production system based on a fuzzy logic system, such as... Figure 1 As shown, based on the photovoltaic output and battery charge state at each moment, real-time power control of the electrolyzer, battery, and supercapacitor in the photovoltaic hydrogen production system is achieved. To illustrate the effects of this invention, a specific photovoltaic hydrogen production system is used as the implementation object below. In this embodiment, the photovoltaic power station has a rated power of 20kW, and the minimum input power of the electrolyzer is... The maximum input power of the electrolytic cell is 1kW. It is 10kW. Battery energy storage capacity C BESS The power is 60kW, and the state of charge (SOC) of the battery ranges from 0.2 to 0.8.

[0060] The schematic diagram of the photovoltaic hydrogen production system is shown below. Figure 2 As shown. In this embodiment, the photovoltaic hydrogen production system includes a photovoltaic power generation module, an electrolyzer module, a hydrogen storage module, a battery module, a supercapacitor module, and an electrical conversion module. The electrical conversion module includes several DC / DC converters. The photovoltaic power generation module, electrolyzer, battery, and supercapacitor are each connected to a DC bus via several DC / DC converters; the hydrogen storage module is connected to the hydrogen production module.

[0061] The method of the present invention will be described in detail below:

[0062] Step S100: Preset several operating modes of the photovoltaic hydrogen production system, and combine the battery charge state SOC(t-1) of the previous moment with the photovoltaic output P at the current moment. PV (t) serves as the input to the fuzzy logic system, determining the system's operating mode and thus obtaining the current power commands for the electrolytic cell and battery. and

[0063] The photovoltaic hydrogen production system has five operating modes:

[0064] In operating mode one, the photovoltaic output power is absorbed by the battery, and the electrolytic cell shuts down. This can be specifically represented as follows:

[0065]

[0066] In operating mode two, the battery, in conjunction with the photovoltaic output, supplies power to the electrolytic cell, which operates at minimum input power. This can be specifically represented as:

[0067]

[0068] In the above formula, This is the minimum input power of the electrolytic cell;

[0069] In operating mode three, the battery, in conjunction with the photovoltaic output, supplies power to the electrolytic cell, and the input power of the electrolytic cell remains consistent with the previous moment. Specifically, this can be expressed as:

[0070]

[0071] In operating mode four, the photovoltaic power output supplies power to the electrolytic cell, and the battery does not work. This can be specifically represented as follows:

[0072]

[0073] In operating mode five, the electrolytic cell operates at maximum input power, and the remaining photovoltaic output power is absorbed by the battery. Specifically, this can be represented as:

[0074]

[0075] In the above formula, This is the maximum input power of the electrolytic cell.

[0076] Step S200: Based on the power commands for the electrolyzer and battery obtained in step S100 and A first-order low-pass filtering algorithm is used to determine the power value P of the electrolytic cell, battery, and supercapacitor. EL (t), P BESS (t) and P SC (t).

[0077] Step S210: Use a low-pass filtering algorithm to extract the low-frequency power component and high-frequency power component of the power command from the electrolytic cell and the battery;

[0078] Step S211: Extract the electrolytic cell power command obtained in step S100 low-frequency components and high frequency components

[0079]

[0080]

[0081] In the above formula, 'a' is the filter coefficient corresponding to the electrolytic cell;

[0082] Step S212: Extract the battery power command obtained in step S100 low-frequency components and high frequency components

[0083]

[0084]

[0085] In the above formula, b is the filter coefficient corresponding to the battery;

[0086] Step S220: Determine the power values ​​P of the electrolytic cell, battery, and supercapacitor at the current moment. EL (t), P BESS (t) and P SC (t), this step includes:

[0087] Step S221: The low-frequency power component of the power command for the electrolytic cell and battery, i.e., the power value of the electrolytic cell and battery:

[0088]

[0089]

[0090] Step S222: The high-frequency power components of the power commands from the electrolytic cell and battery are compensated and regulated by the supercapacitor.

[0091]

[0092] The power value P of the battery at the current moment obtained in step S221 BESS The battery charge state SOC(t) at the current moment can be calculated from (t) and the battery charge state SOC(t-1), which is used as the input of the fuzzy logic system at the next moment. Specifically, it can be expressed as:

[0093]

[0094] In the above formula, Δt is the time interval; η ch and η disc For the charging and discharging power of the battery; C BESS This refers to the capacity of the battery.

[0095] In fuzzy logic systems, input and output variables are fuzzified, and membership degrees are assigned to the variables:

[0096] In this embodiment, the fuzzy logic system combines the battery charge state SOC(t-1) of the previous moment with the photovoltaic output P of the current moment. PV (t) is used as input. The continuous universe of discourse for the battery state of charge (SOC) is [0.2, 0.8], and the fuzzy set is {VS, S, M, B, VB} (VS represents very small, S represents small, M represents medium, B represents large, and VB represents very large). The membership function of the battery state of charge (SOC) is as follows: Figure 3 As shown; Photovoltaic output P PV The continuous universe of discourse is [0,20], and the fuzzy set is {VS,S,M,B,VB} (VS represents very small, S represents small, M represents medium, B represents large, and VB represents very large). The photovoltaic output P PV Membership functions such as Figure 4 As shown.

[0097] The output of the fuzzy logic system is the system operating mode. The discrete universe of discourse is [1,2,3,4,5], and the fuzzy set is {MODE1,MODE2,MODE3,MODE4,MODE5} (MODE1 represents operating mode one, MODE2 represents operating mode two, MODE3 represents operating mode three, MODE4 represents operating mode four, and MODE5 represents operating mode five). The membership function of the system operating mode is as follows: Figure 5 As shown.

[0098] In this embodiment, the fuzzy control rules in step S100 are shown in Tables 1 and 2, including fuzzy control rule A and fuzzy control rule B. If the photovoltaic output P at the current moment... PV (t) is greater than the electrolytic cell operating power P at the previous moment. EL At time (t-1), fuzzy control is performed using fuzzy control rule A; if the photovoltaic output P at the current time... PV (t) is less than the electrolytic cell operating power P at the previous moment. EL At time (t-1), fuzzy control is performed using fuzzy control rule B.

[0099] Table 1 Fuzzy Control Rule A

[0100]

[0101] Table 2 Fuzzy Control Rule B

[0102]

[0103] To demonstrate the effectiveness of this method, a specific example is given below. This invention implements a simulation experiment on a typical day, with a sampling time of 1 second. In this embodiment, the power control method for a photovoltaic hydrogen production system based on a fuzzy logic system is simulated on the Matlab platform to obtain operating data. The power calculation time at each moment is 0.0067 seconds. Figure 6 and Figure 7 The power generation curves of the photovoltaic power generation module in the photovoltaic hydrogen production system, as well as the power control results of the electrolyzer, battery, and supercapacitor, are shown. Figure 8 It shows the state of charge of the battery; Figure 9 It demonstrates the operating modes of the photovoltaic hydrogen production system at each moment.

[0104] When the photovoltaic (PV) power generation module first starts working, the power output is low. At this time, the battery's State of Charge (SOC) is low, and the PV power is absorbed by the battery, operating the PV hydrogen production system in mode one. As the PV power generation module's output gradually increases, the electrolyzer starts working, and the PV hydrogen production system transitions from mode one to mode four. When the PV output exceeds the electrolyzer's maximum operating power, the electrolyzer operates at maximum power, and the remaining PV output is absorbed by the battery, operating the PV hydrogen production system in mode five. In the latter half of the day, the PV output gradually decreases to below the electrolyzer's maximum input power. At this point, the battery stores a large amount of electrical power, and its discharge, combined with the PV output, powers the electrolyzer until the PV hydrogen production system transitions from mode three to mode one. During the day's power control process of the PV hydrogen production system, the electrolyzer only starts and stops once. When there are significant power changes in the electrolyzer and battery, the supercapacitor's operating power also increases significantly to balance the power imbalance between the electrolyzer and battery during the PV hydrogen production system's response.

[0105] The embodiments of the present invention have been described in detail above with reference to the accompanying drawings, but the present invention is not limited to the described embodiments. For those skilled in the art, various changes, modifications, substitutions, and variations can be made to these embodiments, including components, without departing from the principles and spirit of the present invention, and these variations still fall within the protection scope of the present invention.

Claims

1. A power control method for a photovoltaic hydrogen production system based on fuzzy logic, characterized in that, Includes the following steps: S1. Preset several operating modes of the photovoltaic hydrogen production system and obtain the battery charge state at the previous moment. And the current photovoltaic output The data is then input into a fuzzy logic system to determine the operating mode of the photovoltaic hydrogen production system, and the current electrolyzer power command is obtained based on the determined operating mode. and battery power command ; In step S1, the photovoltaic hydrogen production system operates in five modes: mode one, mode two, mode three, mode four, and mode five. In the first operating mode, the electrolytic cell is shut down, and the photovoltaic output power is absorbed by the battery, which can be specifically represented as follows: ； In the second operating mode, the battery, in conjunction with the photovoltaic output, supplies power to the electrolytic cell, which operates at minimum input power. Specifically, this can be represented as: ； In the above formula, This is the minimum input power of the electrolytic cell; In the third operating mode, the battery, in conjunction with the photovoltaic output, supplies power to the electrolytic cell, and the input power of the electrolytic cell remains consistent with the previous moment. Specifically, this can be expressed as: ； In the fourth operating mode, the battery is not working, and the photovoltaic power output supplies power to the electrolytic cell. Specifically, this can be represented as follows: ； In the fifth operating mode, the electrolytic cell operates at maximum input power, and the remaining photovoltaic output power is absorbed by the battery, which can be specifically expressed as: ； In the above formula, This is the maximum input power of the electrolytic cell; S2. Electrolyte power command obtained in step S1 and battery power command A first-order low-pass filtering algorithm is used to determine the power value of the electrolyzer. Battery power value and the power value of supercapacitors ; S2 includes the following sub-steps: S2-1. Use a first-order low-pass filtering algorithm to extract the low-frequency power component and high-frequency power component of the power command of the electrolytic cell and the battery. Extract the electrolytic cell power command obtained in step S1 low-frequency components and high frequency components : ； ； In the above formula, These are the filter coefficients corresponding to the electrolytic cell; Extract the battery power command obtained in step S1 low-frequency components and high frequency components : ； ； In the above formula, These are the filter coefficients corresponding to the battery. S2-2. Determine the current electrolytic cell power value. Battery power value and the power value of supercapacitors , The low-frequency power components of the electrolyzer power command and the battery power command are the power values ​​of the electrolyzer and the battery, respectively. ； ； The high-frequency power components of the electrolyzer power command and the battery power command are compensated and regulated by the supercapacitor: 。 2. The power control method for a photovoltaic hydrogen production system based on a fuzzy logic system according to claim 1, characterized in that, The photovoltaic hydrogen production system includes a photovoltaic power generation module, an electrolyzer, a hydrogen storage module, a battery, a supercapacitor, and an electrical conversion module. The electrolyzer uses electrical energy to electrolyze water to produce hydrogen, and stores the hydrogen in the hydrogen storage module; The battery is used in conjunction with the electrolytic cell module to absorb the output of the photovoltaic system; The supercapacitor is used to compensate for the unbalanced power during the response process of the electrolytic cell module and the battery module. The electrical conversion module includes several DC / DC converters, and the photovoltaic power generation module, electrolytic cell, battery, and supercapacitor are respectively connected to the DC bus through the DC / DC converters.

3. The power control method for a photovoltaic hydrogen production system based on a fuzzy logic system according to claim 1, characterized in that, Also includes S3: Battery power value obtained using S2 and battery charge state The current state of charge of the battery can be calculated. The input value for the fuzzy logic system at the next moment, and the current state of charge of the battery. The calculation method is expressed as follows: ； In the above formula, For time intervals; and The charging and discharging power of the battery; This refers to the capacity of the battery.

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