CN109698495B - A DC Microgrid System Based on Supercapacitor - Google Patents

Abstract

The invention provides a super-capacitor-based direct-current micro-grid system, which comprises a direct-current bus, a super capacitor, an energy storage battery pack, an auxiliary power generation unit, a distributed new energy power generation unit, a local load and a micro-grid control center, wherein the super capacitor is connected with the direct-current bus; the super capacitor, the energy storage battery pack, the auxiliary power generation unit, the distributed new energy power generation unit, the local load and the microgrid control center are respectively connected with the direct current bus, and the direct current bus is connected with the power distribution network; the micro-grid control center respectively controls the power flow among the super capacitor, the energy storage battery pack, the auxiliary power generation unit and the direct current bus and the power flow among the direct current bus and the power distribution network. According to the invention, the super capacitor is used as a unique and continuous voltage source to absorb high-frequency power fluctuation in the direct-current micro-grid, so that voltage fluctuation and surge current at the moment of switching between a grid-connected mode and an off-grid mode can be effectively inhibited.

Description

A DC Microgrid System Based on Supercapacitor

technical field

Embodiments of the present invention relate to the technical field of microgrids, and more particularly, to a supercapacitor-based DC microgrid system.

Background technique

The massive utilization of renewable energy can not only solve the current energy crisis, but also greatly reduce the emission of pollutants and achieve better energy-saving and emission-reduction benefits. Renewable energy power generation units have shortcomings such as unstable power generation. Therefore, the energy storage system has become an important part of the distributed power generation system that uses solar energy and wind energy as the main energy source, that is, the microgrid system, which has important research significance.

At present, my country has clearly proposed to vigorously build new energy microgrid demonstration projects, and the microgrid system has entered a stage of rapid development in my country. At present, there are two main operating modes in my country's microgrid system: grid-connected mode and off-grid mode. Among them, the off-grid mode is also called the island mode.

In the traditional control strategy, in the grid-connected mode, the bus voltage of the microgrid is always directly dominated by the grid voltage or indirectly dominated by the power converter; there is an uncertain power exchange between the microgrid and the distribution grid, which makes the power The power dispatching of the system is complex, which brings risks to the stability of the power system of the entire distribution network. Especially with the increasing trend of the proportion of new energy in the microgrid at this stage, the distribution network will have to limit the number of microgrids and the proportion of new energy in it to prevent grid instability. The bus voltage of the microgrid is controlled by the grid voltage in grid-connected mode.

When switching to the off-grid mode, the control source will be switched to the energy storage system, and the insufficient response of the energy storage system will cause fluctuations in the microgrid and affect the stability of the microgrid. At this time, the determining source of the bus voltage of the microgrid will be transformed into the energy storage system inside the microgrid. Before reconnecting to the grid in the off-grid mode, there are two voltage sources, the microgrid and the distribution grid. The grid connection needs to achieve seamless switching, and the surge current caused by the voltage difference must be suppressed by advanced technology.

At the same time, the energy management methods of the grid-connected mode and the off-grid mode are very different, and the fast switching between off-grid and grid-connected moments is also very important. Therefore, the current DC microgrid is prone to power fluctuations in grid-connected mode or off-grid mode, or when switching between grid-connected mode and off-grid mode, which affects the stability of the microgrid.

SUMMARY OF THE INVENTION

In order to solve the above problems, an embodiment of the present invention provides a super capacitor-based DC microgrid system, which includes: a DC bus, a super capacitor, an energy storage battery pack, an auxiliary power generation unit, a distributed new energy power generation unit, and a local load and microgrid control center; super capacitor, energy storage battery pack, auxiliary power generation unit, distributed new energy generation unit, local load and microgrid control center are respectively connected to the DC bus, and the DC bus is connected to the distribution network; the microgrid control center Control the power flow between the supercapacitor, energy storage battery pack and auxiliary power generation unit and the DC bus, and between the DC bus and the distribution network, respectively.

Preferably, the distributed new energy power generation unit includes a photovoltaic array and a wind turbine sub-unit, and the photovoltaic array and the wind turbine sub-unit are respectively connected to the DC bus.

Preferably, the system further includes a first bidirectional dc/dc converter, a second bidirectional dc/dc converter, a third bidirectional dc/dc converter, a dc/ac inverter, a unidirectional dc/dc converter, and a rectifier , bidirectional dc/ac bus power converter and common coupling point; the super capacitor is connected to the DC bus through the first bidirectional dc/dc converter, and the energy storage battery pack is connected to the DC bus through the second bidirectional dc/dc converter to assist power generation The unit is connected to the DC bus through a third bidirectional dc/dc converter, the local load is connected to the DC bus through a dc/ac inverter, the photovoltaic array is connected to the DC bus through a unidirectional dc/dc converter, and the fan is connected to the DC bus through a rectifier The DC bus is in turn connected to the distribution network through a bidirectional dc/ac bus power converter and a point of common coupling.

Preferably, the fluctuating power of the DC microgrid includes high-frequency power and low-frequency power; if the high-frequency power is in the output state, the supercapacitor turns on the generating state; if the high-frequency power is in the input state, the supercapacitor turns on the absorbing state; if the low-frequency power is in the absorbing state If the low-frequency power is in the output state and the low-frequency power is greater than the maximum output power of the energy storage battery pack, the auxiliary power generation unit is turned on; if the low-frequency power is in the output state and the low-frequency power is less than the maximum output power of the energy storage battery pack, the energy storage battery pack is turned on. Power generation state; if the low-frequency power is in the input state and the low-frequency power is greater than the maximum input power of the energy storage battery pack, the auxiliary power generation unit turns on the absorption state; if the low-frequency power is in the input state and the low-frequency power is less than the maximum input power of the energy storage battery pack, then The energy storage battery pack is turned on and the absorption state is turned on.

Preferably, the fluctuating power of the DC microgrid is the sum of the interactive powers of the distributed new energy power generation unit, the local load, the energy storage battery pack, and the auxiliary power generation unit, respectively, and the DC bus, and the difference between the preset average power of the DC microgrid; The preset average power is an average value of the fluctuating power within one year.

Preferably, the capacitance value of the super capacitor is:

Among them, C is the capacitance value of the supercapacitor, _Vnom is the rated voltage of the DC microgrid, _Vmin is the cut-off working voltage of the DC microgrid, _Vnom-c is the rated voltage of the supercapacitor, and Vmin _-c is the first bidirectional voltage The minimum allowable working voltage of the dc/dc converter, t is the continuous working time of the DC microgrid, and I is the load current of the DC bus.

Preferably, the auxiliary power generation unit includes a water storage subunit, a hydrogen production subunit and a fuel cell subunit.

Preferably, the local loads include resistive loads and power loads.

The embodiment of the present invention provides a DC microgrid system based on a super capacitor. The super capacitor is the only and continuous voltage source in the system, which can effectively suppress the voltage fluctuation at the moment of switching between the grid-connected mode and the off-grid mode, and absorb the DC microgrid at the same time. High-frequency power fluctuations in the power grid; energy storage battery packs and auxiliary power generation units absorb low-frequency power fluctuations due to their slow response, complementing supercapacitors to achieve the coexistence of high power density and high energy density in the energy storage system; Both use supercapacitors as voltage sources, thus effectively suppressing voltage fluctuations and inrush currents when switching between grid-connected or off-grid modes. At the same time, the system adopts the inflow and outflow method of preset value power, which eliminates the uncertainty of the energy interaction between the distribution network and the microgrid, which can effectively increase the proportion of new energy and increase the number of microgrid access.

Description of drawings

In order to illustrate the embodiments of the present invention or the technical solutions in the prior art more clearly, the following briefly introduces the accompanying drawings that are required in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present invention, and for those of ordinary skill in the art, other drawings can also be obtained from these drawings without creative effort.

1 is a schematic structural diagram of a supercapacitor-based DC microgrid system according to an embodiment of the present invention;

2 is a control block diagram of a supercapacitor-based DC microgrid system according to an embodiment of the present invention;

in:

1. DC bus 2. Super capacitor

3. Energy storage battery pack 4. Auxiliary power generation unit

5. Distributed new energy power generation unit 6. Bidirectional dc/ac bus power converter

7. Local load 8. Microgrid control center

9. Point of common coupling 10. First bidirectional dc/dc converter

11. Second bidirectional dc/dc converter 12. Third bidirectional dc/dc converter

13. Unidirectional dc/dc converter 14. Rectifier

15. dc/ac inverter 16. Photovoltaic array

17. Fan 18 Distribution network.

Detailed ways

In order to make the purposes, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly described below with reference to the drawings in the embodiments of the present invention. Obviously, the described embodiments are the Some, but not all, embodiments are disclosed. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

In the traditional control strategy, in the grid-connected mode, the bus voltage of the microgrid is always directly dominated by the grid voltage or indirectly dominated by the power converter; there is an uncertain power exchange between the microgrid and the distribution grid, which makes the power The power dispatching of the system is complex, which brings risks to the stability of the power system of the entire distribution network. Especially with the increasing trend of the proportion of new energy in the microgrid at this stage, the distribution network will have to limit the number of microgrids and the proportion of new energy in it to prevent grid instability. The bus voltage of the microgrid is controlled by the grid voltage in grid-connected mode.

When switching to the off-grid mode, the control source will be switched to the energy storage system, and the insufficient response of the energy storage system will cause fluctuations in the microgrid and affect the stability of the microgrid. At this time, the determining source of the bus voltage of the microgrid will be transformed into the energy storage system inside the microgrid. Before reconnecting to the grid in the off-grid mode, there are two voltage sources, the microgrid and the distribution grid. The grid connection needs to achieve seamless switching, and the surge current caused by the voltage difference must be suppressed by advanced technology.

At the same time, the energy management methods of the grid-connected mode and the off-grid mode are very different, and the fast switching between off-grid and grid-connected moments is also very important. Therefore, the current DC microgrid is prone to power fluctuations in grid-connected mode or off-grid mode, or when switching between grid-connected mode and off-grid mode, which affects the stability of the microgrid.

FIG. 1 is a schematic structural diagram of a supercapacitor-based DC microgrid system according to an embodiment of the present invention. As shown in FIG. 1 , an embodiment of the present invention provides a supercapacitor-based DC microgrid system, which includes: DC bus 1, super capacitor 2, energy storage battery pack 3, auxiliary power generation unit 4, distributed new energy generation unit 5, local load 7 and microgrid control center 8; super capacitor 2, energy storage battery pack 3, auxiliary power generation unit 4. The distributed new energy generation unit 5, the local load 7 and the microgrid control center 8 are respectively connected to the DC bus 1, and the DC bus 1 is connected to the distribution network 18; the microgrid control center 8 respectively controls the super capacitor 2 and the energy storage battery Power flow between group 3 and auxiliary generating unit 4 and DC bus 1 , and power flow between DC bus 1 and distribution grid 18 .

Specifically, the super capacitor 2, the energy storage battery pack 3, the auxiliary power generation unit 4, and the distributed new energy power generation unit 5 are respectively connected to the DC bus 1 as the energy input or output device of the DC microgrid system, and the local load 7 is used as the DC microgrid. The energy output device of the system, the DC bus 1 is connected to the distribution network 18 to exchange electrical energy with the distribution network 18, and the micro-grid control center 8 respectively controls the super capacitor 2, the energy storage battery pack 3, the auxiliary power generation unit 4, the distributed The power flow between the new energy power generation unit 5 and the DC bus 1, and the power flow between the DC bus 1 and the distribution network 18, so as to control the power flow of the entire DC microgrid system.

Among them, the energy storage battery pack 3 and the auxiliary power generation unit 4 meet the requirements of the microgrid system for energy density due to their high energy density. However, due to the limitation of the electrochemical reaction rate, the power density of the energy storage battery pack 3 and the auxiliary power generation unit 4 is relatively small. When the load power suddenly changes, the target power cannot be absorbed or released quickly, and it is difficult to meet the dynamic requirements of the system. When the supercapacitor 2 is charged and discharged, it is a physical change, which has the characteristics of high power density. It can provide large power in a short time and provide buffers for other equipment, but the energy density is low. Therefore, the energy storage battery pack 3 and auxiliary The power generation unit 4 and the super capacitor 2 have strong complementarity in performance.

The embodiment of the present invention provides a DC microgrid system based on a super capacitor 2. As a unique and continuous voltage source, the super capacitor 2 can effectively suppress the voltage fluctuation and Inrush current can absorb high-frequency power fluctuations in the microgrid at the same time; the energy storage battery pack 3 and the auxiliary power generation unit 4 are used to absorb low-frequency power fluctuations in the microgrid due to their slow response. The unit 4 is complementary to the supercapacitor 2, so that the microgrid can achieve the coexistence of high power density and high energy density in terms of energy storage.

It should be noted that, at present, distributed energy mainly includes internal combustion engines, micro gas turbines, solar power, wind power or biomass power that use liquid or gas as fuel. The distributed new energy power generation unit 5 in the embodiment of the present invention includes photovoltaics. The sub-units of the array 16 and the fan 17, and the sub-units of the photovoltaic array 16 and the fan 17 are respectively connected to the DC bus 1 for inputting distributed energy to the microgrid.

Further, the type of distributed energy included in the distributed new energy power generation unit 5 can also be selected according to needs.

Based on the above embodiment, the system further includes a first bidirectional dc/dc converter 10, a second bidirectional dc/dc converter 11, a third bidirectional dc/dc converter 12, a dc/ac inverter 15, and a unidirectional dc /dc converter 13, rectifier 14, bidirectional dc/ac bus power converter 6 and point of common coupling 9; the super capacitor 2 is connected to the DC bus 1 through the first bidirectional dc/dc converter 10, and the energy storage battery pack 3 is connected to the DC bus 1 through the first bidirectional dc/dc converter 10. Two bidirectional dc/dc converters 11 are connected to the DC bus 1 , the auxiliary generating unit 4 is connected to the DC bus 1 through the third bidirectional dc/dc converter 12 , and the local load 7 is connected to the DC bus 1 through a dc/ac inverter 15 , the photovoltaic array 16 is connected to the DC bus 1 through the unidirectional dc/dc converter 13, the fan 17 is connected to the DC bus 1 through the rectifier 14, and the DC bus 1 is sequentially connected to the DC bus 1 through the bidirectional dc/ac bus power converter 6 and the common coupling point 9 The distribution network 18 is connected.

Specifically, since the supercapacitor 2, the energy storage battery pack 3 and the auxiliary power generation unit 4 are the energy input or output devices of the microgrid system, the supercapacitor 2, the energy storage battery pack 3 and the auxiliary power generation unit 4 pass through a bidirectional dc/ The dc converter is connected to the DC bus 1, and inputs or absorbs electrical energy to the DC bus 1. The distributed new energy generation unit 5 is the energy input device of the microgrid system, so the unidirectional DC bus 1 inputs energy, wherein the photovoltaic array 16 is connected to the DC bus 1 through the unidirectional dc/dc converter 13, and the fan 17 passes through The rectifier 14 is connected to the DC bus 1 , and the photovoltaic array 16 and the fan 17 respectively input electrical energy to the DC bus 1 . Since the electrical appliances are generally AC electrical appliances, the local load 7 is connected to the DC bus 1 through the dc/ac inverter 15 , and the dc/ac inverter 15 converts the DC power output from the DC bus 1 into AC power for the local load 7 powered by. The distribution network 18 is alternating current, and the DC bus 1 is connected to the distribution network 18 through the bidirectional dc/ac bus power converter 6 and the common coupling point 9 in turn.

Based on the above embodiment, FIG. 2 is a control block diagram of a supercapacitor-based DC microgrid system according to an embodiment of the present invention. As shown in FIG. 2 , the fluctuating power of the DC microgrid is the distributed new energy generation unit 5, the local The sum of the interactive powers of the load 7, the energy storage battery pack 3, and the auxiliary power generation unit 4 and the DC bus 1, respectively, and the difference between the preset average power of the DC microgrid; the preset average power is the average value of the fluctuating power within one year.

Specifically, the power meter of the distributed new energy power generation unit 5 is P _gen , and the sum of the interactive power of the local load 7 , the energy storage battery pack 3 , the auxiliary power generation unit 4 and the DC bus 1 is calculated as P _load , when the super power is not calculated When the capacitor 2 interacts with the energy of the DC microgrid, the DC microgrid has excess or missing energy P _x , so P _x =P _gen -P _load .

It should be noted that since the energy interaction direction between the energy storage battery pack 3 and the auxiliary power generation unit 4 and the DC bus 1 is uncertain, the interaction power between the local load 7, the energy storage battery pack 3, and the auxiliary power generation unit 4 and the DC bus 1 respectively The sum P _load is an algebraic sum.

Further, the excess or lack of energy _Px in the DC microgrid will fluctuate in a short time due to the volatility of distributed energy, so the average value of the excess or lack of energy _Px in the DC microgrid is taken as The preset average power P _avg of the DC micro-grid, the difference between the excess or lacking energy P _x of the DC micro-grid and the preset average power P _avg is taken as the fluctuating power P _w of the DC micro-grid, so P _w =P _x − _Pavg . Among them, since the preset average power P _avg of the DC microgrid is the average value of the excess or lacking energy _Px possessed by the DC microgrid, the preset average power P _avg of the DC microgrid is not a fixed value, but a Slowly fluctuate in years, and by tracking the power change curve of the DC microgrid in previous years, the bidirectional dc/ac bus power converter 6 is used to enable the DC microgrid to achieve power interaction with the distribution network 18 .

Based on the above embodiment, the fluctuating power P _w of the DC microgrid includes high frequency power P _wh and low frequency power P _wl ; if the high frequency power P _wh is in the output state, the super capacitor 2 turns on the power generation state; if the high frequency power P _wh is In the input state, the super capacitor 2 opens the absorption state; if the low frequency power P _wl is the output state and the low frequency power is greater than the maximum output power of the energy storage battery pack 3, then the auxiliary power generation unit 4 opens the power generation state; if the low frequency power P _wl is the output state And the low frequency power is less than the maximum output power of the energy storage battery pack 3, then the energy storage battery pack 3 is turned on to turn on the power generation state; if the low frequency power _Pwl is the input state and the low frequency power _Pwl is greater than the maximum input power of the energy storage battery pack 3, then The auxiliary power generation unit 4 turns on the absorption state; if the low frequency power _Pwl is the input state and the low frequency power _Pwl is less than the maximum input power of the energy storage battery 3, the energy storage battery 3 turns on the absorption state.

Based on the above embodiment, the capacitance value of the super capacitor 2 is determined according to the energy required for the DC microgrid to maintain stability under high frequency power fluctuations and the energy output by the super capacitor 2 is equal.

Specifically, the energy P _keep required by the DC microgrid to maintain voltage stability under high-frequency power fluctuations is:

Among them, P _keep is the energy required by the DC microgrid to maintain voltage stability under high-frequency power fluctuations, _Vnom is the rated voltage of the DC microgrid, _Vmin is the cut-off operating voltage of the DC microgrid, and t is the DC microgrid continuous Working time, I is the load current of DC bus 1.

The energy P _loss output by the supercapacitor 2 is:

Among them, P _loss is the energy output by the super capacitor 2 , V _nom-c is the rated voltage of the super capacitor 2 , V _min-c is the minimum allowable operating voltage of the first bidirectional dc/dc converter 10 , and C is the voltage of the super capacitor 2 capacitance value.

According to the energy P keep required by the DC microgrid to maintain voltage stability under high frequency power fluctuations, the energy P _keep is equal to the energy P _loss output by the supercapacitor 2, that is, P _keep = P _loss , the capacitance value C of the supercapacitor 2 can be obtained as:

Among them, C is the capacitance value of the supercapacitor 2, _Vnom is the rated voltage of the DC microgrid, _Vmin is the cut-off working voltage of the DC microgrid, _Vnom-c is the rated voltage of the supercapacitor 2, and Vmin _-c is the first The minimum allowable working voltage of a bidirectional dc/dc converter 10 , t is the continuous working time of the DC microgrid, and I is the load current of the DC bus 1 .

Further, the auxiliary power generation unit 4 includes a water storage subunit, a hydrogen production subunit and a fuel cell subunit, and the corresponding auxiliary power generation unit can be selected according to the actual situation.

Further, the local load 7 includes a resistive load and a power load.

The embodiment of the present invention provides a DC micro-grid system based on a super capacitor. The super capacitor is the only and continuous voltage source in the system, which can effectively suppress the voltage fluctuation at the moment of switching and absorb high-frequency power fluctuation at the same time; the energy storage battery pack Due to its slow response and the auxiliary power generation unit, it absorbs low-frequency power fluctuations and forms a complement to the super capacitor. The super capacitor provides or absorbs large power in a short period of time to provide buffers for other equipment, while the energy storage battery pack and auxiliary power generation unit can be used. Absorbs or releases more power for a long time, thus realizing the advantages of high power density and high energy density of the energy storage system; since the super capacitor is used as the voltage source before and after switching between the grid-connected mode or the off-grid mode, it effectively inhibits the Voltage fluctuation and inrush current when switching between grid-connected or off-grid mode. At the same time, the system adopts the inflow and outflow method of preset value power, which eliminates the uncertainty of the energy interaction between the distribution network and the microgrid, which can effectively increase the proportion of new energy and increase the number of microgrid access.

Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, but not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that it can still be Modifications are made to the technical solutions described in the foregoing embodiments, or some technical features thereof are equivalently replaced; and these modifications or replacements do not make the essence of the corresponding technical solutions depart from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims (7)

1. A supercapacitor-based DC microgrid system is characterized in that, comprising: DC bus, supercapacitor, energy storage battery pack, auxiliary power generation unit, distributed new energy generation unit, local load and microgrid control center; The super capacitor, energy storage battery pack, auxiliary power generation unit, distributed new energy power generation unit, local load and micro-grid control center are respectively connected to the DC bus, and the DC bus is connected to the distribution network; the micro-grid controls The center controls the power flow between the super capacitor, the energy storage battery pack and the auxiliary power generation unit and the DC bus, and the power flow between the DC bus and the power distribution network, respectively; The fluctuating power of the DC microgrid includes high frequency power and low frequency power; If the high-frequency power is in an output state, the supercapacitor is in a power generation state; if the high-frequency power is in an input state, the supercapacitor is in an absorption state; If the low-frequency power is in the output state and the low-frequency power is greater than the maximum output power of the energy storage battery pack, the auxiliary power generating unit turns on the power-generating state; if the low-frequency power is in the output state and the low-frequency power is less than the maximum output power of the energy storage battery pack the maximum output power of the energy storage battery pack, the energy storage battery pack is turned on to generate electricity; If the low-frequency power is in the input state and the low-frequency power is greater than the maximum input power of the energy storage battery pack, the auxiliary power generating unit turns on the absorption state; if the low-frequency power is in the input state and the low-frequency power is less than the maximum input power of the energy storage battery If the maximum input power of the energy storage battery pack is reached, the energy storage battery pack is turned on to the absorption state. 2. A supercapacitor-based DC microgrid system according to claim 1, wherein the distributed new energy power generation unit comprises a photovoltaic array and a wind turbine sub-unit, the photovoltaic array and the wind turbine sub-unit are respectively connected with the DC bus bars. 3. A supercapacitor-based DC microgrid system according to claim 2, further comprising a first bidirectional dc/dc converter, a second bidirectional dc/dc converter, and a third bidirectional dc/dc converter converters, dc/ac inverters, unidirectional dc/dc converters, rectifiers, bidirectional dc/ac bus power converters and points of common coupling; The super capacitor is connected to the DC bus through the first bidirectional dc/dc converter, the energy storage battery pack is connected to the DC bus through the second bidirectional dc/dc converter, and the auxiliary power generation The unit is connected to the DC bus through the third bidirectional dc/dc converter, the local load is connected to the DC bus through the dc/ac inverter, and the photovoltaic array is connected to the unidirectional dc/dc The dc converter is connected to the DC bus, the fan is connected to the DC bus through the rectifier, and the DC bus is sequentially connected to the power distribution network through a bidirectional dc/ac bus power converter and a common coupling point. 4. A supercapacitor-based DC microgrid system according to claim 1, wherein the fluctuating power of the DC microgrid is the distributed new energy generation unit, the local load, the storage The sum of the interactive power between the battery pack, the auxiliary power generation unit and the DC bus, and the difference between the preset average power of the DC microgrid; the preset average power is the average value of the fluctuating power within one year . 5. a kind of supercapacitor-based DC microgrid system according to claim 3, is characterized in that, the capacitance value of described supercapacitor is:

Among them, C is the capacitance value of the supercapacitor, _Vnom is the rated voltage of the DC microgrid, _Vmin is the cut-off working voltage of the DC microgrid, _Vnom-c is the rated voltage of the supercapacitor, and Vmin _-c is the first bidirectional voltage The minimum allowable working voltage of the dc/dc converter, t is the continuous working time of the DC microgrid, and I is the load current of the DC bus. 6 . The supercapacitor-based DC microgrid system according to claim 1 , wherein the auxiliary power generation unit includes a water storage subunit, a hydrogen production subunit, and a fuel cell subunit. 7 . 7 . The supercapacitor-based DC microgrid system according to claim 1 , wherein the local loads include resistive loads and power loads. 8 .

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