Load distribution method of photo-hydrogen storage direct current micro-grid

Abstract

The invention belongs to the technical field of electric power, and discloses a real-time load distribution method for a photo-hydrogen storage direct current microgrid, and the photo-hydrogen storage direct current microgrid comprises a photovoltaic power generation unit, a storage battery unit and a fuel cell unit. The photovoltaic power generation unit comprises a photovoltaic array and a BOOST type current converter; the storage battery unit comprises a storage battery and a bidirectional buck-boost converter; the fuel cell unit comprises a hydrogen storage tank, a fuel cell and a BOOST type converter; the high-voltage sides of the converters of the three units are connected to a direct-current bus; the five loads are all of a constant resistance type and are connected to the direct current bus in a parallel connection mode, under the condition that the output power of a photovoltaic unit in the photo-hydrogen storage direct current micro-grid is not enough to meet the load requirement, real-time power balance of the micro-grid is maintained by coordinating the discharge power of the fuel cell unit and the discharge power of the storage cell unit, and the voltage of the direct current bus is maintained in a stable domain. Load distribution is realized, and microgrid power supply quality is improved.

Description

Technical Field

[0001] The present invention belongs to the field of electric power technology, and in particular relates to a load distribution method for a photovoltaic hydrogen storage DC microgrid. Background Art

[0002] Since traditional thermal power generation consumes a large amount of fossil energy and causes environmental pollution, renewable energy generation has developed rapidly. In particular, photovoltaic power generation systems have been widely used due to their flexibility and scalability, and photovoltaic power generation technology has attracted widespread attention in academia and industry. However, the output of photovoltaic power generation systems has characteristics such as volatility and intermittency, which affects the reliability of complex power flows on relay protection, which leads to limited connection with the main power grid, and to a certain extent restricts the application of photovoltaic power generation technology.

[0003] Energy storage technology can effectively solve the negative impact of the volatility and intermittency of photovoltaic power generation. Various storage methods, such as mechanical energy storage, electrical energy storage, thermal energy storage, and electrochemical energy storage, have different advantages and disadvantages. Lead-acid batteries are currently the most widely used electrochemical storage method, with advantages such as high efficiency and convenience, but their service life and available capacity decrease with the increase of usage time. Electrolysis hydrogen production technology is an emerging renewable energy utilization technology that can be used to store light energy. Electrolysis hydrogen production technology mainly includes high-temperature solid oxide hydrogen production technology, proton exchange membrane hydrogen production technology, and alkaline electrolysis hydrogen production technology. The advantage of solid oxide hydrogen production is high conversion efficiency, but it has strict technical requirements for the hydrogen production process and has not yet been industrialized; proton exchange membrane technology is pollution-free, high cost, and low degree of industrialization; alkaline electrolysis hydrogen production technology is the most mature, low cost, and the highest degree of commercialization.

[0004] Therefore, combining battery energy storage, electrolytic hydrogen energy storage and photovoltaic power generation systems to form a photovoltaic hydrogen storage microgrid is an effective renewable energy utilization model. Among them, photovoltaic hydrogen storage DC microgrids for end users have a wider application space in low-voltage networks. Although photovoltaic hydrogen storage DC microgrids have the advantages of both electricity storage technology and hydrogen storage technology, their internal real-time power balance control is highly complex. In particular, the DC microgrid is small in scale and the local load randomness is more obvious. Meeting the load demand by controlling the charging and discharging power of the energy storage unit has become the primary task of microgrid operation.

[0005] At present, solar hydrogen storage DC microgrids have feasible solutions for energy storage unit power control, such as: droop control methods based on energy storage unit efficiency characteristics or short-term operating costs, and methods for alternating charging and discharging based on the actual value of the energy state of the energy storage unit. Both methods can achieve real-time power balance and load distribution of DC microgrids. However, the former cannot guarantee the stability of the DC bus voltage, and the latter will increase the start-stop frequency of individual energy storage units, affecting their service life. Summary of the invention

[0006] The purpose of the present invention is to provide a load distribution method for a solar hydrogen storage DC microgrid to solve the above-mentioned technical problems.

[0007] In order to solve the above technical problems, the specific technical solution of a load distribution method of a photovoltaic hydrogen storage DC microgrid of the present invention is as follows:

[0008] A load distribution method for a photovoltaic hydrogen storage DC microgrid, the photovoltaic hydrogen storage DC microgrid comprising a photovoltaic power generation unit, a battery unit, and a fuel cell unit; the photovoltaic power generation unit comprises a photovoltaic array and a BOOST converter; the battery unit comprises a battery and a bidirectional buck-boost converter; the fuel cell unit comprises a hydrogen storage tank, a fuel cell, and a BOOST converter;

[0009] The high-voltage side of the converters of the three units is connected to the DC bus; the five loads are all constant resistance type and connected to the DC bus in parallel. When the output power of the photovoltaic unit in the photovoltaic hydrogen storage DC microgrid is insufficient to meet the load demand, the real-time power balance of the microgrid is maintained by coordinating the discharge power of the fuel cell unit and the battery unit, and the DC bus voltage is maintained in a stable domain. The specific steps are as follows:

[0010] Step 1: Measure the maximum output power of the photovoltaic unit, the amount of hydrogen in the hydrogen storage tank, and the charge of the battery;

[0011] Step 2: Establish a set of dispatchable energy storage units;

[0012] Step 3: Determine the real-time power shortage of the microgrid;

[0013] Step 4: When the maximum power of the dispatchable energy storage unit set is greater than or equal to the microgrid shortfall power, all units in the dispatchable energy storage unit set jointly bear the microgrid shortfall power;

[0014] Step 5: When the maximum power in the dispatchable energy storage unit set is less than the microgrid's insufficient power, the load reduction operation is performed, and all units in the dispatchable energy storage unit set share the reduced load. Furthermore, in step 1, the photovoltaic unit adopts a maximum power control strategy, and the actual output power of the photovoltaic unit is obtained through real-time measurement; the actual amount of hydrogen in the hydrogen storage tank and the actual charge of the battery are obtained through real-time measurement; the sampling interval of each real-time data is set by the microgrid energy manager, and the sampled data is sent to the microgrid energy manager via the communication network.

[0015] Furthermore, in step 2, the dispatchable energy storage unit set is composed of a battery unit whose real-time charge is less than the upper limit of the charge and a fuel cell unit whose real-time hydrogen volume is less than the upper limit of the hydrogen volume. The dispatchable energy storage unit set is a time domain update variable set. The maximum power of the dispatchable energy storage unit set is the sum of the maximum output powers of all units in the dispatchable energy storage unit set, that is:

[0016] P Θ =ΣP i max ,i∈Θ (1)

[0017] In formula (1), Θ is the set of dispatchable energy storage units, P Θ is the maximum power of the dispatchable energy storage unit set, P i max is the maximum output power of unit i in the dispatchable energy storage unit set.

[0018] Furthermore, in step 3, the microgrid shortfall power is equal to the difference between the microgrid planned load power and the maximum output power of the photovoltaic unit. The maximum output power of the photovoltaic unit is obtained by real-time measurement, and the microgrid planned load power is calculated according to formula (2):

[0019]

[0020] in, is the equivalent resistance of all loads connected to the DC bus, is the DC bus voltage reference value, P l dis Plan the load power for the microgrid.

[0021] Furthermore, in step 4, each unit determines its own load current according to the droop control strategy, and the equation of the droop controller is:

[0022]

[0023] In formula (3), U i is the actual value of the high-voltage bus voltage of unit i in the dispatchable energy storage unit set; is the voltage reference value of the droop controller of unit i; i,a , i,b are the proportional coefficient and integral coefficient of the droop controller voltage compensation module of unit i; U bus is the actual value of DC bus voltage; k i is the gain coefficient of the droop controller of unit i, and the gain coefficient is adjusted according to formula (4):

[0024]

[0025] In formula (4), ζ iis the actual energy value of unit i in the set of dispatchable energy storage units, specifically the charge of the battery or the amount of hydrogen in the hydrogen storage tank; and are the upper and lower limits of the energy of unit i, specifically the upper and lower limits of the battery charge or the upper and lower limits of the hydrogen volume in the hydrogen storage tank; ζ j , are the actual energy value, energy upper limit and energy lower limit of unit j in the dispatchable energy storage unit set; α is the allocation factor; k0 is the adjustment factor; the allocation factor and adjustment factor of each unit take the same value. Further, in step 5, when the maximum power of the dispatchable energy storage unit set is less than the microgrid shortfall power, the load reduction calculation is first performed, and the actual load resistance reduction should meet the following requirements:

[0026]

[0027] In formula (5), is the actual load resistance reduction, is the critical load equivalent resistance, which is determined according to formula (6):

[0028]

[0029] In formula (6), is the maximum output power of the photovoltaic unit;

[0030] Secondly, after the load reduction calculation, the photovoltaic unit and all the energy storage units in the dispatchable energy storage unit set are made to share the reduced load power. The photovoltaic unit adopts the maximum power control strategy, and each energy storage unit determines its own load current according to the droop control strategy. The droop controller is designed according to formula (3), and the gain coefficient is adjusted according to formula (4).

[0031] The load distribution method of a photovoltaic hydrogen storage DC microgrid of the present invention has the following advantages:

[0032] The load distribution method of the photovoltaic hydrogen storage DC microgrid provided by the present invention can adjust the output power of the energy storage unit by controlling the droop of each energy storage unit, thereby achieving three effects: (1) when there is a power shortage in the DC microgrid, the power balance of the microgrid is maintained and load distribution is realized; (2) different types of energy storage units are discharged synchronously under different initial energy states, and the situation of discharging in different time periods due to different initial energies will not occur, which is beneficial to the long-term economic operation of the microgrid. (3) The steady-state value of the DC bus voltage is maintained within a stable domain, thereby improving the power supply quality of the microgrid. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 This is a schematic diagram of the structure of a photovoltaic hydrogen storage DC microgrid;

[0034] Figure 2 A flow chart for implementing the load distribution method of the photovoltaic hydrogen storage DC microgrid;

[0035] Figure 3 It is a schematic diagram of the droop control strategy of the energy storage unit;

[0036] Figure 4 It is the output power curve of the photovoltaic power generation unit when the microgrid deficit power is constant;

[0037] Figure 5 It is a curve diagram of battery charge and hydrogen volume in hydrogen storage tank when the microgrid power shortage is constant;

[0038] Figure 6 It is the droop coefficient curve of each energy storage unit when the microgrid deficit power is constant;

[0039] Figure 7 It is the high-voltage side current curve of the converter of each energy storage unit when the shortfall power of the microgrid is constant;

[0040] Figure 8 It is a curve diagram of DC bus voltage when the shortfall power of microgrid is constant;

[0041] Fig. 9 It is the output power curve of the photovoltaic power generation unit when the power shortage of the microgrid changes continuously;

[0042] Fig.10 It is a curve diagram of the battery charge and hydrogen volume in the hydrogen storage tank when the microgrid power shortage changes continuously;

[0043] Fig.11 It is the droop coefficient curve diagram of each energy storage unit when the microgrid deficit power changes continuously;

[0044] Fig.12 It is the current curve diagram of the high-voltage side of the converter of each energy storage unit when the power shortage of the microgrid changes continuously;

[0045] Fig.13 This is a curve diagram of the DC bus voltage when the microgrid power shortage changes continuously. DETAILED DESCRIPTION

[0046] In order to better understand the purpose, structure and function of the present invention, the load distribution method of the photovoltaic hydrogen storage DC microgrid of the present invention is further described in detail below with reference to the accompanying drawings.

[0047] like Figure 1As shown, a solar hydrogen storage DC microgrid of the present invention includes 1 photovoltaic power generation unit, 1 battery unit, and 1 fuel cell unit; the photovoltaic power generation unit includes a photovoltaic array and a BOOST converter; the battery unit includes a battery and a bidirectional buck-boost converter; the fuel cell unit includes a hydrogen storage tank, a fuel cell, and a BOOST converter; the high-voltage sides of the converters of the three units are connected to the DC bus; the five loads are all constant resistance type and are connected to the DC bus in parallel.

[0048] The specific parameters of each unit in the photovoltaic hydrogen storage DC microgrid are as follows: the number of photovoltaic unit series modules and photovoltaic unit parallel modules are 20 and 9 respectively, the number of series batteries and parallel batteries in each module are 6 and 6; the volume of the hydrogen storage tank is 10L, and the upper and lower limits of the hydrogen storage capacity are 80% and 25%; the maximum discharge power of the storage is 5kW, and the upper and lower limits of the charge are 80% and 20% respectively; the maximum discharge power of the fuel cell is 4kW; the resistance values ​​of the five constant resistance loads are R1=3.08Ω, R2=40.1Ω, R3=40.1Ω, R4=26.6Ω, and R5=124.2Ω respectively, and the switches G1~G5 respectively control the input and removal of the corresponding loads.

[0049] The load distribution method of the photovoltaic hydrogen storage DC microgrid of the present invention can maintain the real-time power balance of the microgrid by coordinating the discharge power of the fuel cell unit and the battery unit when the output power of the photovoltaic unit in the photovoltaic hydrogen storage DC microgrid does not fully meet the load demand, and maintain the DC bus voltage in a stable domain. Figure 2 As shown, the specific steps are as follows:

[0050] Step 1: Measure the maximum output power of the photovoltaic unit, the amount of hydrogen in the hydrogen storage tank, and the charge of the battery.

[0051] The photovoltaic unit adopts a maximum power control strategy, and the actual output power of the photovoltaic unit is obtained through real-time measurement; the actual amount of hydrogen in the hydrogen storage tank and the actual charge of the battery are obtained through real-time measurement; the sampling interval of each real-time data is set by the microgrid energy manager, and the sampled data is sent to the microgrid energy manager via the communication network.

[0052] Step 2: Establish a set of dispatchable energy storage units.

[0053] The dispatchable energy storage unit set consists of battery units whose real-time charge is less than the upper limit of charge and fuel cell units whose real-time hydrogen volume is less than the upper limit of hydrogen volume. The dispatchable energy storage unit set is a time domain update variable set. The maximum power of the dispatchable energy storage unit set is the sum of the maximum output powers of all units in the dispatchable energy storage unit set, that is:

[0054] P Θ =ΣP i max ,i∈Θ (1)

[0055] In formula (1), Θ is the set of dispatchable energy storage units, P Θ is the maximum power of the dispatchable energy storage unit set, P i max is the maximum output power of unit i in the dispatchable energy storage unit set.

[0056] Step 3: Determine the real-time power shortage of the microgrid.

[0057] The power deficit of the microgrid is equal to the difference between the planned load power of the microgrid and the maximum output power of the photovoltaic unit. The maximum output power of the photovoltaic unit is obtained through real-time measurement, and the planned load power of the microgrid is calculated according to formula (2):

[0058]

[0059] in, is the equivalent resistance of all loads connected to the DC bus, is the DC bus voltage reference value, P l dis Plan the load power for the microgrid.

[0060] Step 4: When the maximum power of the dispatchable energy storage unit set is greater than or equal to the microgrid shortfall power, all units in the dispatchable energy storage unit set jointly bear the microgrid shortfall power, and each unit determines its own load current according to the droop control strategy. The principle of the droop controller is as follows: Figure 3 As shown, the equation for the droop controller is:

[0061]

[0062] In formula (3), U i is the actual value of the high-voltage bus voltage of unit i in the dispatchable energy storage unit set; is the voltage reference value of the droop controller of unit i; i,a , i,b are the proportional coefficient and integral coefficient of the droop controller voltage compensation module of unit i; U bus is the actual value of DC bus voltage; k i is the gain coefficient of the droop controller of unit i, and the gain coefficient is adjusted according to formula (4):

[0063]

[0064] In formula (4), ζ i is the actual energy value of unit i in the set of dispatchable energy storage units, specifically the charge of the battery or the amount of hydrogen in the hydrogen storage tank; and are the upper and lower limits of the energy of unit i, specifically the upper and lower limits of the battery charge or the upper and lower limits of the hydrogen volume in the hydrogen storage tank; ζ j , are the actual energy value, energy upper limit and energy lower limit of unit j in the dispatchable energy storage unit set; α is the allocation factor; k0 is the adjustment factor; the allocation factor and adjustment factor of each unit take the same value.

[0065] Step 5: When the maximum power of the dispatchable energy storage unit set is less than the microgrid shortfall power, the load reduction calculation is first performed, and the actual load resistance reduction should meet the following requirements:

[0066]

[0067] In formula (5), is the actual load resistance reduction, is the critical load equivalent resistance, which is determined according to formula (6):

[0068]

[0069] In formula (6), is the maximum output power of the photovoltaic unit.

[0070] Secondly, after the load reduction calculation, the photovoltaic unit and all the energy storage units in the dispatchable energy storage unit set are made to share the reduced load power. The photovoltaic unit adopts the maximum power control strategy, and each energy storage unit determines its own load current according to the droop control strategy. The droop controller is designed according to formula (3), and the gain coefficient is adjusted according to formula (4).

[0071] Example:

[0072] Combination Figure 1 to Figure 3 The solar hydrogen storage DC microgrid system and load distribution method are described, and the effectiveness of the method is verified when the microgrid power shortage remains unchanged and the microgrid power shortage changes frequently.

[0073] Figure 1 Middle: L p and C p They are the filter inductor and voltage stabilizing capacitor of the photovoltaic unit Boost converter, U p,l ,I p,l are the voltage and output current of the photovoltaic array, S is the light intensity, T is the atmospheric temperature; L b and C b They are the filter inductor and voltage stabilizing capacitor of the battery converter, U b,l ,I b,l are the battery voltage and output current, k b is the gain coefficient of the battery unit droop controller; L fand C f are the filter inductor and voltage stabilizing capacitor of the fuel cell converter, U f,l ,I f,l are the voltage and output current of the fuel cell, k f is the gain coefficient of the fuel cell unit droop controller.

[0074] Figure 3 Medium: I i,h with I i,l are the high-voltage side current and low-voltage side current of the converter of energy storage unit i respectively; i,a , i,b are the proportional coefficient and integral coefficient of the voltage compensation module of the droop controller of the energy storage unit i; β i,a , β i,b are the proportional coefficient and integral coefficient of the outer loop of the droop controller of energy storage unit i; δ i,a ,δ i,b are the proportional coefficient and integral coefficient of the inner loop of the droop controller of energy storage unit i; P q is the power shortage of the microgrid; ζ1~ζ N is the actual energy value of unit 1 to unit N in the dispatchable energy storage unit set, and N is the number of energy storage units in the dispatchable energy storage unit set.

[0075] Working condition (1): Implementation results of the method when the microgrid power shortage remains unchanged

[0076] In the initial operation state of this working condition, switches G1~G3 are closed, loads 1, 2, and 3 are running; the light intensity is 1000W / m 2 , the air temperature is 25℃; the initial charge of the battery is 60%, and the initial hydrogen content of the hydrogen storage tank is 25%.

[0077] According to formulas (1) to (2), the power shortage of the microgrid is 4.2kW. The battery and fuel cell discharge synchronously according to the droop control strategy to supplement the power shortage of the microgrid; the photovoltaic unit always maintains the maximum power output, such as Figure 4 As shown; the battery charge and hydrogen volume of the hydrogen storage tank, the droop coefficient of the battery and fuel cell, the high-voltage side bus output current of the battery and fuel cell, and the DC bus voltage of the microgrid are shown as follows: Figures 5 to 8 shown. Figure 5 In, h is the real-time hydrogen volume in the hydrogen storage tank, ζ c It is the real-time charge of the battery; Figure 6 In, k f is the gain coefficient of the fuel cell droop controller, k b is the gain coefficient of the battery droop controller; Figure 7 middle, I f ,Ib They are the high-voltage side current of the fuel cell inverter and the high-voltage side current of the battery inverter respectively.

[0078] Figure 5 It shows that under the load distribution method, the battery with a larger charge will discharge at a larger discharge rate, and the fuel cell unit with a smaller amount of hydrogen will discharge at a smaller discharge rate. The two energy storage units reach their respective energy lower limits at the same time and end the discharge synchronously.

[0079] Figure 6 It is shown that the method described can adaptively adjust the droop coefficient in real-time operation, and the droop coefficient of each energy storage unit is related to its own energy state and the energy state of other energy storage units.

[0080] Figure 7 It shows that the load current allocated by the energy storage unit is negatively correlated with the droop coefficient, and the droop coefficient can well adjust the output current of the energy storage unit, thereby realizing dynamic load distribution.

[0081] Figure 8 It shows that the steady-state value of the DC bus voltage can be controlled at the target value more accurately during the discharge process of the energy storage unit.

[0082] Summarizing the operating results of this condition, it can be seen that when the microgrid power deficit is constant, the method can effectively control the discharge power of the battery unit and the fuel cell unit, achieve synchronous discharge, accurately share the microgrid load and maintain a constant DC bus voltage.

[0083] Condition (2): Results of the implementation of the method when the microgrid power shortage changes frequently

[0084] Under this condition, the light intensity is always maintained at 1000W / m 2 , atmospheric temperature 25℃; the initial hydrogen content of the hydrogen storage tank is 54%, and the initial charge of the battery is 60%; the switch state and load operating conditions are shown in Table 1.

[0085] Table 1 Switch status and load operation status

[0086] Time Switch Status Operation load 0-20s G1, G2, G3 are closed, G4, G5 are open R1, R2, R3 20-30s G1, G2 are closed, G3, G4, G5 are open R1, R2 30-40s G1 is closed, G2, G3, G4, G5 are open R1 40-50s G1, G4 are closed, G2, G3, G5 are open R1, R4 50-60s G1, G4, G5 are closed, G2, G3 are open R1, R4, R5

[0087] Due to the change of load, the power shortage of the microgrid changes. Under the continuously changing power shortage, the battery and fuel cell discharge synchronously according to the droop control strategy to supplement the power shortage of the microgrid, and the photovoltaic unit always maintains the maximum power output. Fig. 9 The battery charge and hydrogen volume in the hydrogen storage tank, the droop coefficient of the battery and fuel cell, the high-voltage bus output current of the battery and fuel cell, and the DC bus voltage of the microgrid are shown as follows. Figure 10 to Figure 13 shown. Fig.13 In the figure, dU1~dU5 are the maximum steady-state voltage deviations in each time period.

[0088] Fig.10 It shows that under the load distribution method, the fuel cell and the battery continue to discharge, and the hydrogen amount in the hydrogen storage tank and the battery charge do not change suddenly.

[0089] Fig.11 It is shown that the method described can adaptively adjust the droop coefficient in real-time operation, a fuel cell with a smaller amount of hydrogen maintains a larger droop coefficient in operation, and a battery with a larger charge maintains a smaller droop coefficient in operation.

[0090] Fig.12 It shows that the load current allocated to the energy storage unit is negatively correlated with the respective droop coefficient. In each time period, the energy storage unit with a larger droop coefficient has a smaller output current, and the energy storage unit with a smaller droop coefficient has a larger output current.

[0091] Fig.13 It shows that, except for transient voltage fluctuations, the deviation of the steady-state value of the DC bus voltage in each time period is within a small margin.

[0092] Summarizing the operating results of this working condition, it can be seen that when the continuous change of load causes the change of the microgrid power shortage, the method can effectively control the output power of the battery unit and the fuel cell unit, quickly and accurately supplement the real-time power shortage of the microgrid, realize load distribution, and control the steady-state value of the DC bus voltage near the target value.

[0093] It is to be understood that the present invention is described by some embodiments, and it is known to those skilled in the art that various changes or equivalent substitutions may be made to these features and embodiments without departing from the spirit and scope of the present invention. In addition, under the teachings of the present invention, these features and embodiments may be modified to adapt to specific circumstances and materials without departing from the spirit and scope of the present invention. Therefore, the present invention is not limited by the specific embodiments disclosed herein, and all embodiments falling within the scope of the claims of this application are within the scope of protection of the present invention.

Claims

1. A load distribution method for a photovoltaic hydrogen storage DC microgrid, wherein the photovoltaic hydrogen storage DC microgrid comprises a photovoltaic power generation unit, a battery unit, and a fuel cell unit; the photovoltaic power generation unit comprises a photovoltaic array and a BOOST type converter; the battery unit comprises a battery and a bidirectional buck-boost converter; the fuel cell unit comprises a hydrogen storage tank, a fuel cell, and a BOOST type converter; The high voltage side of the converters of the three units is connected to the DC bus; the five loads are all constant resistance type and connected to the DC bus in parallel, characterized in that: When the output power of the photovoltaic unit in the solar hydrogen storage DC microgrid is insufficient to meet the load demand, the real-time power balance of the microgrid is maintained by coordinating the discharge power of the fuel cell unit and the battery unit, and the DC bus voltage is maintained in a stable domain. The specific steps are as follows: Step 1: Measure the maximum output power of the photovoltaic unit, the amount of hydrogen in the hydrogen storage tank, and the charge of the battery; Step 2: Establish a set of dispatchable energy storage units; Step 3: Determine the real-time power shortage of the microgrid; Step 4: When the maximum power of the dispatchable energy storage unit set is greater than or equal to the microgrid shortfall power, all units in the dispatchable energy storage unit set jointly bear the microgrid shortfall power; Step 5: When the maximum power in the dispatchable energy storage unit set is less than the microgrid's deficit power, load reduction is performed, and all units in the dispatchable energy storage unit set share the reduced load.

2. The load distribution method of the solar hydrogen storage DC microgrid according to claim 1 is characterized in that: In step 1, the photovoltaic unit adopts a maximum power control strategy, and the actual output power of the photovoltaic unit is obtained through real-time measurement; the actual amount of hydrogen in the hydrogen storage tank and the actual charge of the battery are obtained through real-time measurement; the sampling interval of each real-time data is set by the microgrid energy manager, and the sampled data is sent to the microgrid energy manager via the communication network.

3. The load distribution method of the solar hydrogen storage DC microgrid according to claim 1 is characterized in that: In step 2, the dispatchable energy storage unit set is composed of battery units whose real-time charge is less than the upper limit of the charge and fuel cell units whose real-time hydrogen volume is less than the upper limit of the hydrogen volume. The dispatchable energy storage unit set is a time domain update variable set. The maximum power of the dispatchable energy storage unit set is the sum of the maximum output powers of all units in the dispatchable energy storage unit set, that is: P Θ =ΣP i max ,i∈Θ (1) In formula (1), Θ is the set of dispatchable energy storage units, P Θ is the maximum power of the dispatchable energy storage unit set, P i max is the maximum output power of unit i in the dispatchable energy storage unit set.

4. The load distribution method of the solar hydrogen storage DC microgrid according to claim 1 is characterized in that: In step 3, the microgrid shortfall power is equal to the difference between the microgrid planned load power and the maximum output power of the photovoltaic unit. The maximum output power of the photovoltaic unit is obtained through real-time measurement. The microgrid planned load power is calculated according to formula (2): in, is the equivalent resistance of all loads connected to the DC bus, is the DC bus voltage reference value, P l dis Plan the load power for the microgrid.

5. The load distribution method of the solar hydrogen storage DC microgrid according to claim 1 is characterized in that: In step 4, each unit determines its own load current according to the droop control strategy, and the equation of the droop controller is: In formula (3), U i is the actual value of the high-voltage bus voltage of unit i in the dispatchable energy storage unit set; is the voltage reference value of the droop controller of unit i; i,a , i,b are the proportional coefficient and integral coefficient of the droop controller voltage compensation module of unit i; U bus is the actual value of DC bus voltage; k i is the gain coefficient of the droop controller of unit i, and the gain coefficient is adjusted according to formula (4): In formula (4), ζ i is the actual energy value of unit i in the set of dispatchable energy storage units, specifically the charge of the battery or the amount of hydrogen in the hydrogen storage tank; and are the upper and lower limits of the energy of unit i, specifically the upper and lower limits of the battery charge or the upper and lower limits of the hydrogen volume in the hydrogen storage tank; ζ j , are the actual energy value, upper energy limit and lower energy limit of unit j in the dispatchable energy storage unit set respectively; α is the allocation factor; k0 is the adjustment factor; the allocation factor and adjustment factor of each unit take the same value.

6. The load distribution method of the solar hydrogen storage DC microgrid according to claim 5 is characterized in that: In step 5, when the maximum power of the dispatchable energy storage unit set is less than the insufficient power of the microgrid, the load reduction calculation is first performed, and the actual load resistance reduction should meet the following requirements: In formula (5), is the actual load resistance reduction, is the critical load equivalent resistance, which is determined according to formula (6): In formula (6), is the maximum output power of the photovoltaic unit; Secondly, after the load reduction calculation, the photovoltaic unit and all the energy storage units in the dispatchable energy storage unit set are made to share the reduced load power. The photovoltaic unit adopts the maximum power control strategy, and each energy storage unit determines its own load current according to the droop control strategy. The droop controller is designed according to formula (3), and the gain coefficient is adjusted according to formula (4).

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