Micro-grid refinement model and source-load-storage coordination control method

Abstract

The invention discloses a micro-grid refined model and a source-load-storage coordinated control method, and the method comprises the steps: constructing a micro-grid dynamic mathematical model which comprises a photovoltaic unit, a fan, an electrolytic cell, a hydrogen fuel cell, a storage battery and a supercapacitor according to an operation mechanism, and achieving the precise system simulation; the source-load-storage coordination control method is provided according to the new energy power generation and load state, the stability and reliability of the system are improved, and effective technical support is provided for economic operation and environmental protection of the micro-grid.

Description

Technical Field

[0001] The present invention relates to the field of microgrid control technology, and in particular to a microgrid refined model and a source-load-storage coordinated control method. Background Art

[0002] Microgrids, as carriers for absorbing and managing renewable energy such as wind and solar energy, can integrate renewable energy generation systems and user load demands in the region, and can be separated from the main grid to achieve self-management and control of source-load supply and demand in the region. However, wind power and photovoltaic power generation are intermittent and volatile. These unfavorable factors have gradually become prominent with the substantial growth of installed capacity and the continuous increase in grid penetration, causing a significant negative impact on the stable operation of the grid and the quality of electric energy, and are increasingly being paid attention to. Among them, the absorption problem of wind and solar power generation is particularly prominent, and a single energy storage technology cannot simultaneously meet the stability and flexibility of microgrids.

[0003] Compared with a single energy storage system, a multi-hybrid energy storage system couples different types of energy storage technologies, which can give full play to the characteristics of each energy storage technology and improve the stability and flexibility of the microgrid. However, due to the differences in the development of different energy systems, energy supply is often planned, designed, and operated independently, lacking coordination between each other, resulting in low energy utilization, overall safety of the energy supply system, and weak self-healing ability. Summary of the invention

[0004] In view of the above problems, the present invention proposes a microgrid refined model and a source-load-storage coordinated control method, aiming to improve the operating efficiency and stability of the microgrid.

[0005] In order to solve the above technical problems, the first aspect of the present invention proposes a microgrid refinement model, and the construction process of the model includes the following steps:

[0006] The wind turbine power generation system, photovoltaic power generation system, electrolyzer, hydrogen fuel cell, battery energy storage system and supercapacitor are connected to the DC bus through a DC / DC converter, wherein the hydrogen produced by the electrolyzer is stored in a hydrogen storage tank;

[0007] Calculate the volt-ampere characteristics of the photovoltaic power generation system under standard conditions, and the parameter changes of the photovoltaic power generation system when the lighting conditions and the ambient temperature change;

[0008] Calculating wind energy capture power, wind turbine mechanical input torque, output voltage, rotor motion inertia, and electromagnetic torque of the wind turbine power generation system;

[0009] Calculating the volt-ampere characteristic of the electrolytic cell and the hydrogen production flow rate;

[0010] The state of charge of the battery energy storage system, the characteristics of the hydrogen fuel cell, and the pressure of the hydrogen storage tank are calculated.

[0011] The second aspect of the present invention proposes a microgrid source-load-storage coordinated control method, which is used for the above-mentioned microgrid refined model, and includes the following steps:

[0012] Calculating redundant power according to the source load power situation in the target area, and decomposing the redundant power into high-frequency redundant power and low-frequency redundant power by using variational mode decomposition;

[0013] Setting a number of consumption conditions according to the low-frequency redundant power and the maximum power of the electrolyzer;

[0014] The wind turbine power generation system adopts maximum power point tracking, keeps the pitch angle at 0, and operates in variable speed-variable frequency mode, allowing the rotor speed to change synchronously with the wind speed, so that the tip speed ratio is maintained at an optimal value;

[0015] The voltage at the maximum power point of the photovoltaic power generation system is calculated by the MPPT algorithm as an outer loop voltage reference value, and then passed through a proportional integral controller as an inner loop current reference value, and after passing through the proportional controller, it becomes a switch tube drive signal;

[0016] The electrolyzer is controlled by a double closed loop using an inner current loop and an outer power loop;

[0017] The power outer loop of the hydrogen fuel cell adopts proportional integral control, and the current inner loop adopts proportional control. And the hysteresis control switch is used;

[0018] The battery energy storage system is connected to the DC bus through a current-type two-quadrant bidirectional DC-DC conversion circuit. According to the charge and discharge power reference value, the difference between the power of the battery energy storage system and the reference value is obtained through a proportional integral link to obtain a control signal, and a switching signal of the bidirectional DC-DC conversion circuit is generated through a PWM modulator.

[0019] In some implementations, the redundant power is calculated as follows:

[0020] ΔP=P pv +P wd -P load

[0021] Among them, P pv is the photovoltaic power generation power, P wd is the wind turbine power, P load For electrical load demand.

[0022] In some embodiments, the consumption conditions include:

[0023] The first working condition: when 0≤ΔP L ≤Pel-max , the electrolyzer absorbs all the low-frequency redundant power, when P el =ΔP L , the supercapacitor absorbs the high-frequency redundant power according to the state of charge;

[0024] Second working condition: When ΔP L ≥P el-max , the electrolyzer operates at maximum power, P el =P el-max , battery energy storage system charging, P bat =ΔP L -P el-max , the supercapacitor absorbs the high frequency redundant power according to the state of charge;

[0025] The third working condition: When ΔP L ≤0, the electrolyzer is not running, or, when P el = 0, hydrogen in the hydrogen storage tank is injected into the hydrogen fuel cell to work, P FC =ΔP L , the supercapacitor absorbs the high-frequency redundant power according to the state of charge, or when SOC sc-min ≤SOC sc ≤SOC sc-max , all high-frequency power is absorbed by the supercapacitor;

[0026] Where ΔP H is the high frequency redundant power, ΔP L is the low frequency redundant power, P el is the electrolytic cell power, P el-max is the maximum power of the electrolytic cell, P FC is the power of the battery energy storage system, P SC is the supercapacitor power, P bat is the power of the state of charge, SOC bat SOC is the state of charge of the battery energy storage system. sc SOC is the state of charge of the supercapacitor sc-max , SOC sc-min They are the highest state of charge and the lowest state of charge of the supercapacitor, respectively.

[0027] In some embodiments, in the third operating condition, when the supercapacitor cannot meet the high-frequency power absorption, the battery energy storage system is used to compensate.

[0028] The beneficial effects of the present invention are as follows: a dynamic mathematical model of a microgrid including photovoltaics, wind turbines, electrolyzers, hydrogen fuel cells, batteries, and supercapacitors is constructed according to the operating mechanism, so that accurate system simulation can be achieved; a source-load-storage coordinated control method is proposed according to the renewable energy power generation and load status, which improves the system stability and reliability, and provides effective technical support for the economic operation and environmental protection of the microgrid. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is a schematic diagram of the architecture of the microgrid refinement model disclosed in the first embodiment of the present invention. DETAILED DESCRIPTION

[0030] In order to make the purpose, technical solution and advantages of the present invention clearer and more specific, the content of the present invention is further described in detail below in conjunction with the accompanying drawings and specific implementation methods. It is understood that the specific embodiments described herein are only used to explain the present invention, rather than to limit the present invention. It should also be noted that, for the convenience of description, only the parts related to the present invention are shown in the accompanying drawings, rather than all the contents.

[0031] Embodiment 1

[0032] This embodiment proposes a microgrid refinement model, and the model construction process includes the following steps:

[0033] S1, such as Figure 1 As shown, the wind turbine power generation system, photovoltaic power generation system, electrolyzer, hydrogen fuel cell, battery energy storage system and supercapacitor are connected to the DC bus through a DC / DC converter, wherein the hydrogen produced by the electrolyzer is stored in a hydrogen storage tank.

[0034] S2, calculates the volt-ampere characteristics of the photovoltaic power generation system under standard conditions, as well as the parameter changes of the photovoltaic power generation system when the lighting conditions and ambient temperature change.

[0035] Under standard conditions, the ambient temperature is 25°C and the light intensity is 1000W / m 2 When , the UI characteristic equation of the photovoltaic power generation system is:

[0036]

[0037] Among them, I SC is the short-circuit current, U OC is the open circuit voltage, U m and I m are the voltage and current when the maximum power is obtained.

[0038] When the lighting conditions and ambient temperature change, the parameters of the photovoltaic cells change as follows:

[0039]

[0040] Among them, α, β, and γ are correction coefficients, which are 0.0025, 0.5, and 0.00288 respectively.

[0041] S3, calculates the wind energy capture power, wind turbine mechanical input torque, output voltage, rotor motion inertia, and electromagnetic torque of the wind turbine power generation system.

[0042] The wind energy capture formula is: Where: ρ is air density; R is blade radius; v is wind speed; C p is the wind energy utilization coefficient.

[0043] C p The calculation method is as follows:

[0044]

[0045] Where: θ is the pitch angle; λ is the tip speed ratio; ω is the mechanical speed of the fan.

[0046] The mechanical input torque of the fan is expressed as:

[0047] In the dq reference system, the voltage equation of the wind turbine power generation system is expressed as

[0048]

[0049] Among them, i ds and i qs are the d-axis and q-axis components of the stator current respectively; L d and L q are the stator d-axis and q-axis inductances respectively; R a is the stator resistance; ω e is the electrical angular velocity, ω e =n p ω, where n p Indicates the number of pole pairs of the generator rotor; λ m is the permanent magnet flux; u ds and u qs They are the d-axis and q-axis components of the motor voltage respectively.

[0050] The equation of motion of the rotor is Among them, J is the moment of inertia of the rotor; ω is the rotor speed; B is the viscosity coefficient.

[0051] The electromagnetic torque expression is: T e =1.5n p i qs λ m .

[0052] S4, calculate the volt-ampere characteristics of the electrolyzer and the hydrogen production flow rate.

[0053] At any temperature, the UI characteristic equation of the electrolytic cell is:

[0054]

[0055] Where: r 1 , r 2 is the ohmic parameter of the electrolyte; A cell is the electrolysis module area; I el is the electrolytic cell current; s 1 ,s 2 ,s 3 , t 1 , t 2 , t 3 All are overvoltage coefficients; V rev is the reversible voltage of the electrolytic cell.

[0056] The hydrogen production rate of the electrolyzer is Where η is the hydrogen production efficiency of the electrolyzer; N el is the number of cells; F is the Faraday constant.

[0057] The electrolytic cell efficiency η is expressed as

[0058]

[0059] In the formula, a 1 , a 2 , a 3 , a 4 , a 5 are the Faraday efficiency coefficients.

[0060] S5, calculating the state of charge of the battery energy storage system, the characteristics of the hydrogen fuel cell, and the pressure of the hydrogen storage tank.

[0061] According to the ampere-hour integration method, the charge and discharge current at each moment is obtained, and the charge and discharge amount is obtained by integration. After comparing it with the capacity of the energy storage battery, it is added or subtracted from the initial state of charge to obtain the state of charge at this moment. The expression is as follows:

[0062]

[0063] Where: SOC(t) is the SOC value at time t; SOC(t 0 ) is the SOC value at the initial moment; C N is the rated capacity of the battery; I bat It is the instantaneous current when the battery is charging or discharging.

[0064] Further transformation, the SOC value at the next moment is obtained directly through the SOC value at this moment and the charge and discharge power instruction, taking into account the expression between the state of charge and the charge and discharge power under the charge and discharge efficiency of the energy storage battery:

[0065]

[0066] Among them, SOC(t+1) is the SOC value of the energy storage battery at the next moment; P in , P out are the charging and discharging power of the energy storage battery respectively; η in , η out are the charging and discharging efficiencies of the energy storage battery respectively.

[0067] Fuel cells convert chemical energy directly into electrical energy. The energy released by the reaction can be calculated by the difference between the energy of the reactants and the energy of the products. The Gibbs free energy of the reaction is:

[0068]

[0069] in, is the standard Gibbs free energy; R is the gas constant; T st is the reaction temperature in the fuel cell; is water activity, the value is 1; is the cathode hydrogen partial pressure; is the anode oxygen partial pressure.

[0070] If losses are not considered, all Gibbs free energy will be converted into electrical energy:

[0071]

[0072] And satisfy

[0073]

[0074] Combined with the above analysis, the Nernst voltage of the fuel cell is:

[0075]

[0076] In the actual process, the chemical energy of the fuel cannot be completely converted into electrical energy. There are losses caused by heat dissipation and material transfer, which makes the actual output voltage lower than the derived internal theoretical electromotive force. Therefore, the actual output voltage of the fuel cell is less than the Nentes voltage. The output voltage of the fuel cell is expressed as

[0077] V cell =EV act -V ohm -V con

[0078] Among them, Vact is the activation overvoltage, which is caused by overcoming the activation energy of the chemical reaction on the electrode surface; V ohm is the ohmic polarization overvoltage, caused by the equivalent impedance during the reaction; V con is the concentration polarization overvoltage, which is caused by the resistance encountered during the diffusion of reactants. Its mathematical expressions are:

[0079]

[0080] V ohm =iR ohm

[0081]

[0082] Where α is the transmission coefficient; n is the number of electrons transmitted by the reaction; i 0 is the exchange current density between the two electrodes; R ohm is the unit equivalent resistance; is the maximum current density of the fuel cell.

[0083] The pressure of the hydrogen storage tank is expressed by the ideal state equation:

[0084]

[0085] Where, P(t+1) is the pressure of the hydrogen storage tank at the next moment; P(t) is the initial pressure of the hydrogen storage tank; V is the volume of the hydrogen storage tank; n in is the amount of hydrogen entering the hydrogen storage tank; n out is the amount of hydrogen leaving the hydrogen storage tank; T is the temperature inside the tank; R is the ideal gas constant.

[0086] Embodiment 2

[0087] This embodiment proposes a microgrid source-load-storage coordinated control method, which is used for the microgrid refined model described in Embodiment 1, and includes the following steps:

[0088] S1, calculate the redundant power according to the source load power situation in the target area, and use variational mode decomposition to decompose the redundant power into high-frequency redundant power and low-frequency redundant power.

[0089] The calculation method of redundant power is:

[0090] ΔP=P pv +P wd -P load

[0091] Among them, P pv is the photovoltaic power generation power, P wd is the wind turbine power, P load For electrical load demand.

[0092] S2, set several consumption conditions according to the low-frequency redundant power and the maximum power of the electrolyzer.

[0093] Consumption conditions include:

[0094] The first working condition: when 0≤ΔP L ≤P el-max , the electrolyzer consumes all the low-frequency redundant power, when P el =ΔP L , the supercapacitor absorbs high-frequency redundant power according to the state of charge;

[0095] Second working condition: When ΔP L ≥P el-max , the electrolyzer operates at maximum power, P el =P el-max , battery energy storage system charging, P bat =ΔP L -P el-max ,Supercapacitors absorb high-frequency redundant power according to the state of charge;

[0096] The third working condition: When ΔP L ≤0, the electrolyzer is not running, or, when P el = 0, hydrogen in the hydrogen storage tank is injected into the hydrogen fuel cell to work, P FC =ΔP L ,Supercapacitors absorb high-frequency redundant power according to the state of charge, or when SOC sc-min ≤SOC sc ≤SOC sc-max , all high-frequency power is absorbed by the supercapacitor;

[0097] Where ΔP H is the high frequency redundant power, ΔP L is the low frequency redundant power, P el is the electrolytic cell power, P el-max is the maximum power of the electrolytic cell, P FC is the power of the battery energy storage system, P SC is the supercapacitor power, P bat is the power of the state of charge, SOC bat SOC is the state of charge of the battery energy storage system. sc SOC is the state of charge of the supercapacitor sc-max , SOC sc-min They are the highest state of charge and the lowest state of charge of the supercapacitor, respectively.

[0098] In the third operating condition, when the supercapacitor cannot meet the high-frequency power absorption, the battery energy storage system is compensated.

[0099] S3, the wind turbine power generation system adopts maximum power point tracking, keeps the pitch angle at 0, and operates in variable speed-variable frequency mode, allowing the rotor speed to change synchronously with the wind speed, so that the tip speed ratio is maintained at the optimal value.

[0100] Specifically, the wind turbine power generation system adopts maximum power point tracking, keeps the pitch angle at 0, and the PMSG operates in variable speed-variable frequency mode, allowing the rotor speed to change synchronously with the wind speed, so that the tip speed ratio is maintained at the optimal value. ref The corresponding angular velocity reference value ω can be obtained ref , the minimum value of the maximum power speed angle and the speed reference value is used as the reference value for speed control. d-ref =0, that is, the reactive power is 0.

[0101] S4, calculates the voltage at the maximum power point of the photovoltaic power generation system through the MPPT algorithm as the outer loop voltage reference value, and then passes through the proportional integral controller as the inner loop current reference value, and after passing through the proportional controller, it becomes the switch tube drive signal.

[0102] The photovoltaic power generation system is connected to the bus through a Boost converter to ensure a wide operating range, and adopts maximum power point tracking control (MPPT) based on an improved disturbance observation method. The voltage at the maximum power point is calculated through the MPPT algorithm as the outer loop voltage reference value, and then passed through a proportional-integral controller as the inner loop current reference value. After passing through the proportional controller, it becomes the switch tube drive signal.

[0103] S5, uses the current inner loop and power outer loop to perform double closed-loop control on the electrolytic cell.

[0104] EL uses the difference between the electrolysis power reference value and the product of the actual current and the actual voltage of the alkaline electrolyzer to obtain the reference current through the proportional integral link, and the reference current is then passed through the proportional integral link to obtain the control signal. That is, the double closed-loop control of the current inner loop and the power outer loop is adopted, and the obtained control signal is passed through the PWM modulator to generate the switching signal of the Buck circuit.

[0105] S6, the power outer loop of the hydrogen fuel cell adopts proportional integral control, the current inner loop adopts proportional control, and the hysteresis loop is used to control the switch on and off.

[0106] FC is used as a backup power source. By collecting the working voltage and current of the hydrogen fuel cell, the real-time power can be calculated. The outer loop of power adopts proportional integral control, and the inner loop of current adopts proportional control. At the same time, in order to avoid bus voltage oscillation, hysteresis control is adopted.

[0107] S7, the battery energy storage system is connected to the DC bus through a current-type two-quadrant bidirectional DC-DC conversion circuit. According to the charge and discharge power reference value, the difference between the power of the battery energy storage system and the reference value is obtained through a proportional integral link to obtain a control signal, and a switching signal of the bidirectional DC-DC conversion circuit is generated through a PWM modulator.

[0108] The above embodiments are only for illustrating the technical concept and features of the present invention, and their purpose is to enable ordinary technicians in the field to understand the content of the present invention and implement it accordingly, and they cannot be used to limit the protection scope of the present invention. Any equivalent changes or modifications made based on the essence of the content of the present invention should be included in the protection scope of the present invention.

Claims

1. A microgrid refinement model, characterized in that: The model construction process includes the following steps: The wind turbine power generation system, photovoltaic power generation system, electrolyzer, hydrogen fuel cell, battery energy storage system and supercapacitor are connected to the DC bus through a DC / DC converter, wherein the hydrogen produced by the electrolyzer is stored in a hydrogen storage tank; Calculate the volt-ampere characteristics of the photovoltaic power generation system under standard conditions, and the parameter changes of the photovoltaic power generation system when the lighting conditions and the ambient temperature change; Calculating wind energy capture power, wind turbine mechanical input torque, output voltage, rotor motion inertia, and electromagnetic torque of the wind turbine power generation system; Calculating the volt-ampere characteristic of the electrolytic cell and the hydrogen production flow rate; The state of charge of the battery energy storage system, the characteristics of the hydrogen fuel cell, and the pressure of the hydrogen storage tank are calculated.

2. A microgrid source-load-storage coordinated control method, used for the microgrid refined model according to claim 1, characterized in that: The following steps are involved: Calculating redundant power according to the source load power situation in the target area, and decomposing the redundant power into high-frequency redundant power and low-frequency redundant power by using variational mode decomposition; Setting a number of consumption conditions according to the low-frequency redundant power and the maximum power of the electrolyzer; The wind turbine power generation system adopts maximum power point tracking, keeps the pitch angle at 0, and operates in variable speed-variable frequency mode, allowing the rotor speed to change synchronously with the wind speed, so that the tip speed ratio is maintained at an optimal value; The voltage at the maximum power point of the photovoltaic power generation system is calculated by the MPPT algorithm as an outer loop voltage reference value, and then passed through a proportional integral controller as an inner loop current reference value, and after passing through the proportional controller, it becomes a switch tube drive signal; The electrolyzer is controlled by a double closed loop using an inner current loop and an outer power loop; The power outer loop of the hydrogen fuel cell adopts proportional integral control, and the current inner loop adopts proportional control. And the hysteresis control switch is used; The battery energy storage system is connected to the DC bus through a current-type two-quadrant bidirectional DC-DC conversion circuit. According to the charge and discharge power reference value, the difference between the power of the battery energy storage system and the reference value is obtained through a proportional integral link to obtain a control signal, and a switching signal of the bidirectional DC-DC conversion circuit is generated through a PWM modulator.

3. The microgrid source-load-storage coordinated control method according to claim 2, characterized in that: The calculation method of the redundant power is: ΔP=P pv +P wd -P load , Among them, P pv is the photovoltaic power generation power, P wd is the wind turbine power, P load For electrical load demand.

4. The microgrid source-load-storage coordinated control method according to claim 3, characterized in that: The consumption conditions include: The first working condition: when 0≤ΔP L ≤P el-max , the electrolyzer absorbs all the low-frequency redundant power, when P el =ΔP L , the supercapacitor absorbs the high-frequency redundant power according to the state of charge; Second working condition: When ΔP L ≥P el-max , the electrolyzer operates at maximum power, P el =P el-max , battery energy storage system charging, P bat =ΔP L -P el-max , the supercapacitor absorbs the high frequency redundant power according to the state of charge; The third working condition: When ΔP L ≤0, the electrolyzer is not running, or, when P el = 0, hydrogen in the hydrogen storage tank is injected into the hydrogen fuel cell to work, P FC =ΔP L , the supercapacitor absorbs the high frequency redundant power according to the state of charge, or when SOC sc-min ≤SOC sc ≤SOC sc-max , all high-frequency power is absorbed by the supercapacitor; Among them, ΔP H is the high frequency redundant power, ΔP L is the low frequency redundant power, P el is the electrolytic cell power, P el-max is the maximum power of the electrolytic cell, P FC is the power of the battery energy storage system, P SC is the supercapacitor power, P bat is the power of the state of charge, SOC bat SOC is the state of charge of the battery energy storage system. sc SOC is the state of charge of the supercapacitor sc-max , SOC sc-min They are the highest state of charge and the lowest state of charge of the supercapacitor, respectively.

5. The microgrid source-load-storage coordinated control method according to claim 4, characterized in that: In the third working condition, when the supercapacitor cannot meet the high-frequency power absorption, the battery energy storage system is used to compensate.

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