Hybrid energy direct-current micro-grid for traffic tunnel

Abstract

The invention provides a traffic tunnel hybrid energy direct-current micro-grid, which comprises a plurality of sections of direct-current buses, an energy storage battery, a distributed power supply, an emergency mobile power supply and a local direct-current load, the multiple sections of direct-current buses are connected with the energy storage battery, and the multiple sections of direct-current buses comprise a direct-current bus I arranged in the center of the tunnel, a direct-current bus II arranged at the entrance of the tunnel and a direct-current bus III arranged at the exit of the tunnel; the direct current bus I is connected to a mains supply through a one-way AC / DC converter, the direct current bus II and the direct current bus III are connected to a distributed power supply and an emergency mobile power supply, and the direct current bus I is networked with the direct current bus II and the direct current bus III through a two-way DC / DC converter. Third harmonics existing in the system can be greatly reduced, the electric energy quality of the system is improved, the use amount of copper consumables is obviously reduced, and the equipment composition of the system is simplified; the open type system is plug-and-play, provides convenience for access of power generation of various new energy sources, utilizes renewable energy sources as much as possible to generate power sources, and achieves energy conservation and emission reduction.

Description

Technical Field

[0001] The present invention relates to the technical field of microgrids, and in particular to a hybrid energy direct current microgrid in a traffic tunnel. Background Art

[0002] The low-voltage power load of a traffic tunnel includes fire-fighting loads and non-fire-fighting loads, of which the average annual total power consumption of non-fire-fighting loads accounts for more than 80% of the tunnel's total annual power consumption, including lighting, monitoring, traffic signals, and electro-optical signs. The low-voltage power distribution of tunnel non-fire-fighting DC loads is usually distributed by the tunnel non-fire-fighting dual power supply switching cabinet to the distribution cabinets of tunnel lighting, traffic signals, electro-optical signs, and monitoring equipment, and then the distribution cabinet distributes AC220V distribution circuits to the loads. Since tunnel lighting, traffic signals, electro-optical signs, and monitoring equipment are all DC loads, each device needs to be equipped with a single-phase rectifier (AC / DC) device at the end.

[0003] However, due to the use of the above-mentioned low-voltage AC power supply, DC loads must be equipped with AC / DC single-phase rectifier circuits, resulting in prominent third harmonic problems, three-phase imbalance, and prominent power quality problems; in addition, affected by the third harmonic, the distribution line loss is large (including reactive power loss and active power loss); the DC equipment terminal drive power supply includes single-phase rectifier filtering, and there is a power loss of about 15%; at the same time, the distribution line loss is large, the copper core cable used has a large cross-section, and the copper consumables are high; and there are abundant renewable energy sources outside the traffic tunnel, including wind energy, photovoltaics, mechanical energy, etc., and the existing low-voltage AC system cannot meet the convenient access of various new energy power generation. Important loads in non-fire loads (backup lighting, electro-optical signs, monitoring) need to be equipped with EPS or UPS as emergency power supplies according to different load types, and there are many energy storage devices.

[0004] In view of this, the present invention proposes a hybrid energy DC microgrid in a traffic tunnel. Summary of the invention

[0005] The purpose of the present invention is to propose a hybrid energy DC microgrid for a traffic tunnel, which adopts low-voltage DC power distribution and centrally sets three-phase full-wave rectification. The non-fire DC load in the tunnel no longer contains a single-phase rectification circuit, which greatly reduces the third harmonic in the system, eliminates the three-phase imbalance, and improves the power quality of the system; and completely eliminates the reactive power loss of the line and equipment, and greatly reduces the influence of the third harmonic, the loss of the distribution line is greatly reduced, and the power loss of a single device is also significantly reduced; due to the outstanding power transmission capacity of the DC system, the cross-section of the copper core cable for DC load distribution can be reduced by about 50% compared with the prior art, and the use of copper consumables is significantly reduced; energy storage batteries are centrally set as emergency power sources for important loads, which simplifies the equipment composition of the system; the DC microgrid is an open system, which meets the plug-and-play function and provides convenience for the access of various new energy power generation.

[0006] To achieve the above purpose, the technical solution of the present invention is: a hybrid energy DC microgrid in a traffic tunnel, including multiple sections of DC bus, energy storage battery, distributed power supply, emergency mobile power supply, and local DC load; the multiple sections of DC bus are connected to the energy storage battery, and the multiple sections of DC bus include DC bus I arranged in the center of the tunnel, DC bus II arranged at the entrance of the tunnel, and DC bus III arranged at the exit of the tunnel; the DC bus I is connected to the mains power supply through a unidirectional AC / DC converter, the DC bus II and DC bus III are connected to the distributed power supply and the emergency mobile power supply, the DC bus I is respectively connected to the DC bus II and the DC bus III through a bidirectional DC / DC converter to realize the power transmission between different DC buses; wherein the bidirectional DC / DC converter adopts a high-frequency isolated bidirectional DC / DC converter. The local DC load includes the basic tunnel lighting, facility electro-optical signs, traffic lights, monitoring equipment electricity powered by the DC bus I, and the tunnel enhanced lighting powered by the DC bus II and DC bus III.

[0007] Preferably, the number of the DC busbars I is set according to the power supply radius of the DC busbar I and the tunnel length to achieve power supply for evenly distributed DC loads in the tunnel.

[0008] Preferably, the distributed power source includes photovoltaic power generation and wind power generation, and the emergency mobile power source includes mobile diesel power generation.

[0009] Preferably, the operation control of the DC microgrid adopts a three-layer hierarchical mode: the first layer of control adopts droop control, and a plurality of control units participating in the DC bus voltage control jointly maintain the DC bus voltage stability; the second layer of control is implemented by an industrial computer to realize secondary regulation of the DC bus voltage, power distribution of each control unit, and switching of the DC bus operation mode; the third layer of control is implemented by a computer in the tunnel control center to realize energy scheduling between different DC buses, and by formulating a DC microgrid operation scheduling strategy, flexible scheduling of the mains power supply, distributed power supply, energy storage battery, and DC load is achieved to ensure safe and economical operation of the system.

[0010] Preferably, in the first layer of control, the control unit involved in the DC bus voltage control includes a unidirectional AC / DC converter, a bidirectional DC / DC converter, a distributed power supply controller, and an energy storage unit controller; the droop control is to control the voltage and current of the converter or controller to run on a droop curve, and the droop curve expression is as follows:

[0011] U d =U0-k×I

[0012] Where U dis the output voltage of the converter or controller; U0 is the set value of the DC bus voltage; k is the droop curve coefficient; I is the output current of the converter or controller.

[0013] Preferably, in the second layer of control,

[0014] The DC bus voltage secondary regulation and the power distribution of each control unit are specifically as follows: a hybrid compensation method is adopted to simultaneously compensate the DC bus voltage setting value U0 and the coefficient k of the droop curve, and the information of each control unit, including voltage, current and droop curve coefficient, is obtained by means of industrial computer bus communication, and the droop curve coefficient compensation amount Δk and the vertical intercept compensation amount ΔU are obtained by using the average voltage compensator, the average current compensator and the curve coefficient compensator, and then the droop curve is translated and the coefficient is adjusted respectively; wherein, the average voltage compensator eliminates the output DC voltage deviation of each unit by translating the curve, and the average current compensator and the curve coefficient compensator achieve rapid load distribution by adjusting the coefficient of the droop curve;

[0015] The switching of the DC bus operation mode is specifically as follows: three operation modes are set for DC bus I, II, and III respectively, and the DC bus operation mode is switched according to the difference between the input power supply of the DC bus and the DC load; wherein the input power of the DC bus is controlled by setting the voltage control point U H \U M \U L And the DC bus voltage setting value U0, and the input power supply priority is distributed power supply > energy storage battery > mains power.

[0016] Preferably, the DC busbars I, II and III are respectively configured with three operation modes:

[0017] DC bus I operation mode:

[0018] Operation mode 1: DC bus II and III have surplus power, and the DC bus I input power includes AC power, energy storage batteries and distributed power supply; the DC bus I load is the basic lighting of the tunnel, facility electro-optical signs, traffic lights, and monitoring equipment; U DCI Indicates the DC bus I voltage value;

[0019] U DCI >U H :The DC bus voltage is too high, the energy storage battery reaches the upper limit and cannot continue to charge. The power generation system as a distributed power source abandons energy and operates in constant voltage mode to maintain voltage stability;

[0020] U H >U DCI >U M:The power generated by the power generation system is greater than the power consumed by the DC load and there is a surplus, and the energy storage battery works in constant current charging mode; the power generation system is in droop control to maintain the stability of the DC bus voltage;

[0021] U M >U DCI >U L :The power generated by the power generation system is not enough to provide the power consumed by the DC load. In order to maximize the use of renewable energy, the power generation system always works in the maximum power tracking mode. In order to maintain the stability of the bus voltage, the energy storage battery is discharged and works in the droop control state;

[0022] U L >U DCI >U O :The sum of the power generated by the power generation system and the power provided by the energy storage battery is less than the power consumed by the AC and DC loads. The power generation system works in MPPT mode, the energy storage battery is discharged, and the mains power supply is in a droop control state to maintain the stability of the DC bus voltage;

[0023] Operation mode 2: DC bus II and III are short of power, and the DC bus I input power includes AC power and energy storage batteries; the DC bus I loads include basic tunnel lighting, facility electro-optical signs, traffic lights, monitoring equipment power, and DC bus II and III loads;

[0024] Operation mode 3: When the mains fails, the DC bus I input power source includes energy storage batteries, distributed power sources and emergency mobile power sources; the DC bus I load is the emergency lighting and facility electro-optical signs in the basic tunnel lighting;

[0025] U DCI >U H :The DC bus voltage is too high, the energy storage battery reaches the upper limit and cannot continue to charge, the power generation system abandons energy and operates in constant voltage mode to maintain voltage stability;

[0026] U H >U DCI >U M :The power generated by the power generation system is greater than the power consumed by the DC load and there is a surplus. The energy storage battery works in constant current charging mode, and the power generation system is in droop control to maintain the stability of the DC bus voltage;

[0027] U M >U DCI >U L :The power generated by the power generation system is not enough to provide the power consumed by the DC load. In order to maximize the use of renewable energy, the power generation system always works in the maximum power tracking mode. In order to maintain the stability of the bus voltage, the energy storage battery is discharged and works in the droop control state;

[0028] U L >U DCI >U O : The sum of the power generated by the power generation system and the power provided by the energy storage battery is less than the power consumed by the DC load. The power generation system works in MPPT mode, the energy storage battery is discharged, and the DC bus II and III are connected to the emergency mobile power supply to supplement the power;

[0029] DC bus II / III operation mode:

[0030] Operation mode 1: During the day, the DC bus II / DC bus III input power source includes distributed power supply, energy storage battery and AC power supply; the DC bus II / DC bus III load is tunnel enhanced lighting, U DC Indicates the DC bus II voltage value or the DC bus III voltage value;

[0031] U DC >U H :The DC bus voltage is too high, the energy storage battery reaches the upper limit and cannot continue to charge, the power generation system abandons energy and operates in constant voltage mode to maintain voltage stability;

[0032] U H >U DC >U M :The power generated by the power generation system is greater than the power consumed by the DC load and there is a surplus. The energy storage battery works in constant current charging mode, and the power generation system is in droop control to maintain the stability of the DC bus voltage;

[0033] U M >U DC >U L :The power generated by the power generation system is not enough to provide the power consumed by the DC load. In order to maximize the use of renewable energy, the power generation system always works in the maximum power tracking mode. At this time, in order to maintain the stability of the bus voltage, the energy storage battery is discharged and works in the droop control state;

[0034] U L >U DC >U O :The sum of the power generated by the power generation system and the power provided by the energy storage battery is less than the power consumed by the AC and DC loads. The power generation system works in MPPT mode, the energy storage battery is discharged, and the mains power supply is in a droop control state to maintain the stability of the DC bus voltage;

[0035] Operation mode 2: During daytime, the DC bus II / DC bus III input power source includes distributed power supply and energy storage battery; the DC bus II / DC bus III load is tunnel enhanced lighting and DC bus I load;

[0036] UDC >U H :The DC bus voltage is too high, the energy storage battery reaches the upper limit and cannot continue to charge, the power generation system abandons energy and operates in constant voltage mode to maintain voltage stability;

[0037] U H >U DC >U M :The power generated by the power generation system is greater than the power consumed by the DC load and there is a surplus. The energy storage battery works in constant current charging mode, and the power generation system is in droop control to maintain the stability of the DC bus voltage;

[0038] U M >U DC >U L :The power generated by the power generation system is not enough to provide the power consumed by the DC load. In order to maximize the use of renewable energy, the power generation system always works in the maximum power tracking mode. In order to maintain the stability of the bus voltage, the energy storage battery is discharged and works in the droop control state;

[0039] Operation mode 3: At night, the DC bus II / DC bus III input power includes distributed power supply and energy storage battery; the DC bus II / DC bus III load is the DC bus I load;

[0040] U DC >U H :The DC bus voltage is too high, the energy storage battery reaches the upper limit and cannot continue to charge, the power generation system needs to abandon energy and operate. To maintain voltage stability, the power generation system operates in constant voltage mode;

[0041] U H >U DC >U M :The power generated by the power generation system is greater than the power consumed by the DC load and there is a surplus. The energy storage battery works in constant current charging mode, and the power generation system is in droop control to maintain the stability of the DC bus voltage;

[0042] U M >U DC >U L :The power generated by the power generation system is not enough to provide the power consumed by the DC load. In order to maximize the use of renewable energy, the power generation system always operates in the maximum power tracking mode. In order to maintain the stability of the bus voltage, the energy storage battery is discharged and operates in the droop control state.

[0043] Preferably, the DC microgrid operation dispatching strategy in the third layer control includes two dispatching schemes, specifically:

[0044] Scheduling plan 1:

[0045] In non-emergency situations, the output power of the basic lighting in the tunnel is adjusted within the range of 50% to 100%, and the output power of the enhanced lighting in the tunnel is adjusted within the range of 15% to 100%. Traffic lights, electro-optical signs, and monitoring equipment operate at full power around the clock. The time T1 when night turns to daytime and the time T2 when day turns to nighttime are set according to the longitude and latitude, and the current time is judged according to the preset time intervals of T1 and T2 to determine whether it is daytime or nighttime.

[0046] If it is daytime, the power consumption Q1 of DC bus II / DC bus III and the power generation Q2 of distributed generation are predicted according to the statistical hourly traffic volume and the weather forecast results. If Q1 is less than Q2 and the energy storage of DC bus II / DC bus III is sufficient, DC bus II / DC bus III supplies power to DC bus I, and DC bus I operates in mode 1, and DC bus II / DC bus III operates in mode 2. If the energy storage of DC bus II / DC bus III is insufficient or Q1 is greater than or equal to Q2, DC bus I supplies power to DC bus II / DC bus III, and DC bus I operates in mode 2, and DC bus II / DC bus III operates in mode 1.

[0047] If it is night time, DC bus II / DC bus III supplies power to DC bus I, DC bus I operates in mode 1, and DC bus II / DC bus III operates in mode 3;

[0048] Scheduling plan 2:

[0049] In an emergency, if the city power fails or the AC system fails, the distributed power supply and emergency mobile power supply will be used to supply power, and some DC loads will be cut off, leaving only the emergency lighting and facility electro-optical signs in the basic lighting; the power consumption Q'1 of the DC bus I and the power generation Q'2 of the distributed power supply will be predicted; the time T1 when night turns to daytime and the time T2 when day turns to nighttime will be set according to the longitude and latitude, and it will be determined whether it is daytime or nighttime according to the preset time interval based on T1 and T2;

[0050] If it is daytime, DC bus II / DC bus III supplies power to DC bus I, DC bus I operates in mode 3, and DC bus II / DC bus III operates in mode 2. On this basis, it is determined whether the following conditions are met: Q'1 is greater than Q'2 and the DC bus I voltage U DCI Less than U L , if the conditions are met, connect to the emergency mobile power supply, otherwise return;

[0051] If it is night time, DC bus II / DC bus III supplies power to DC bus I, DC bus I operates in mode 3, and DC bus II / DC bus III operates in mode 3. On this basis, it is determined whether the following conditions are met: Q'1 is greater than Q'2 and U DCILess than U L If the conditions are met, connect to the emergency mobile power supply, otherwise return.

[0052] Preferably, the electric shock protection design of the DC microgrid includes: setting 400mA as the upper limit of the human contact current that may be expected in the low-voltage DC system; the low-voltage DC adopts the IT power grounding system to achieve 30mA leakage protection and insulation monitoring dual protection; the DC bus voltage is selected by adopting an enumeration comparison method, combining the actual length of the tunnel and the load power, respectively calculating the line cable cross-sectional area at different DC voltages, and selecting the DC voltage corresponding to the minimum cross-sectional area as the selected DC bus voltage. The different DC voltages include DC375V, DC220V, and DC110V. The calculation of the line cable cross-sectional area of ​​each DC voltage is specifically as follows:

[0053] Calculate the DC load line current:

[0054]

[0055] Among them, I js Calculate the current for the DC load line, P e1 , P e2 , P e3 is the power of a single DC device within the set length range, and U is a DC voltage tentatively determined by the enumeration method;

[0056] According to I js ≥1.1×I N Determine the rated current I of the miniature circuit breaker N value, and according to I L ≥1.1×I N Determine the cable current carrying capacity I L value;

[0057] Calculate the cross-sectional area:

[0058] S”≥(P×l)÷(5×γ×U 2 ×0.001×5%)

[0059] Where P is the total power of the line, l is the equivalent power supply distance of the line, S' is the calculated value of the cable cross-sectional area, γ is the conductivity of the cable conductor at 50 °C, and U' is the nominal voltage;

[0060] According to the cable current carrying capacity I L The corresponding cable cross-sectional area is determined by the value, recorded as the cable cross-sectional area query value S', and the cable cross-sectional area query value S' is compared with the cable cross-sectional area calculation value S", and the larger value is taken as the cable cross-sectional area S to be checked for sensitivity verification:

[0061]

[0062] k T =1+a×(θ-20)

[0063] Sensitivity

[0064] Where ρ is the cable conductor resistivity at 20°C, L is the line cable length, k T is the resistance temperature conversion coefficient, a is the resistance temperature coefficient, θ is the actual working temperature of the conductor, I d It is the single-phase short-circuit current at the farthest end of the line;

[0065] Judgment sensitivity L m Is it greater than or equal to 1? If so, the cross-sectional area S of the cable to be checked is used as the cross-sectional area of ​​the line cable of the DC voltage. Otherwise, a larger nominal cross-sectional area of ​​the cable core is selected and the sensitivity check is performed again.

[0066] Preferably, the power and capacity of the wind-solar-storage system equipment are designed as follows:

[0067] Obtain the annual average wind speed, effective wind speed annual statistical duration, solar radiation, peak sunshine annual statistical duration, and DC load annual power consumption Q at the location of the traffic tunnel. n , DC load power consumption daily peak value Q rF , DC load power consumption daily valley value Q rG ; Determine whether the annual average wind speed is greater than 3m / s to determine whether wind energy is available, and determine whether the daily average radiation is greater than 3.3kWh / m 2 To determine whether solar energy is available, set the available distributed energy generation ratio k, the initial value of k is 30%, and calculate the ratio of the annual statistical duration of effective wind speed to the annual statistical duration of peak sunshine, A:B.

[0068] Calculate the wind power generation allocation value Q a =Q n ×k×A / (A+B), according to the formula Q for the average annual power generation of wind turbines 1n =P1×T 1n ×m calculate the output power P1 of the wind turbine at rated wind speed, where Q 1n is the annual power generation of the wind turbine, T 1n is the effective wind speed annual statistical duration, m is the coefficient considering losses; then the equipment power P of the wind turbine is calculated according to the following formula e

[0069] P1=P e ×(average wind speed in the highly calibrated wind speed segment / rated wind speed) 3 ;

[0070] Calculate the photovoltaic power generation allocation value Q b =Q n×k×B / (A+B), according to the annual average power generation of photovoltaic generators, the formula Q 2n =P2×T 2n ×m calculate the rated power P2 of the solar cell array, where Q 2n Annual power generation of solar cell array, T 2n is the annual statistical duration of peak sunshine, and m is the coefficient considering loss;

[0071] Calculate the difference between the maximum daily power generation and the minimum daily power consumption as well as the 2h daily peak value of the DC load, and take the larger value as the required energy storage battery capacity Q js , substitute into the formula energy storage battery capacity calculation formula Q C =Q js / (m c ×n c ) Calculate the energy storage battery capacity Q C , where m c is the efficiency of the energy storage battery, n c is the discharge depth of the energy storage battery;

[0072] Calculate the total investment in wind, solar, and energy storage, as well as the annual energy savings, and combine the service life of the power generation equipment and energy storage batteries to determine whether the cost can be recovered within the half-life cycle. If so, the equipment power P of the wind turbine calculated under the previous coefficient is e , the rated power of the solar cell array P2 and the energy storage battery capacity Q C As the designed wind-solar-storage system equipment power and capacity, otherwise the coefficient k is increased by 10% and the equipment power P of the wind turbine generator is recalculated. e , the rated power of the solar cell array P2 and the energy storage battery capacity Q C .

[0073] Compared with the prior art, the present invention has the following beneficial effects:

[0074] ① The DC microgrid of this application adopts low-voltage DC power distribution and centrally sets up three-phase full-wave rectification. The non-fire DC load in the tunnel no longer contains a single-phase rectification circuit, which greatly reduces the third harmonic in the system, eliminates three-phase imbalance, and improves the power quality of the system.

[0075] ② The DC microgrid of this application adopts low-voltage DC power distribution, which completely eliminates the reactive power loss of lines and equipment, and greatly reduces the impact of third harmonics. The loss of distribution lines is greatly reduced; the power loss of a single device is also significantly reduced.

[0076] ③ The DC microgrid of this application adopts a low-voltage DC distribution system. Due to the outstanding power transmission capacity of the DC system, the cross-section of the copper core cable for DC load distribution can be reduced by about 50% compared with the existing technology, the use of copper consumables is significantly reduced, and the low-carbon effect is obvious.

[0077] ④ The DC microgrid proposed in this application centrally sets up energy storage batteries in the DC integrated cabinet AM1 as emergency power supply for important loads (backup lighting, electro-optical signs, monitoring), which simplifies the equipment composition of the system.

[0078] ⑤The DC microgrid proposed in this application is an open system that meets the plug-and-play function and facilitates the access of various renewable energy power generation.

[0079] ⑥ The DC microgrid proposed in this application adopts a special "entry-center...center-exit" hand-in-hand distributed topology. The DC integrated cabinet of this structure is deep in the load center, which is convenient for the access of renewable energy generation outside the tunnel and the access of emergency power supply (mobile diesel generator set). And through high-frequency isolation bidirectional DC / DC equipment, the bidirectional transmission of system power is realized, providing a hardware channel for making full use of renewable energy generation.

[0080] ⑦ The DC microgrid proposed in this application adopts a hierarchical control structure and control method to achieve the plug-and-play control requirements of the system. The first layer (device level) control adopts a droop control mode, and there are multiple units involved in the DC bus voltage control in the system; the second layer (industrial control level) control is used to achieve secondary regulation of the DC bus voltage, power distribution of each control unit, and switching of the system operation mode; the third layer (center level) control is used to achieve energy scheduling between different DC buses. While ensuring the normal operation of the load, this application can utilize as much renewable energy power generation as possible to achieve energy conservation and emission reduction, and save at least 40% of energy.

[0081] ⑧ In order to realize the above hierarchical control functions and strengthen the monitoring and management of field equipment, the DC microgrid proposed in this application sets up a distributed automatic control network architecture with centralized management and decentralized control consisting of a three-layer architecture (central monitoring level, field control level, and detection execution level). BRIEF DESCRIPTION OF THE DRAWINGS

[0082] Figure 1 This is a topological diagram of the DC microgrid of the present invention;

[0083] Figure 2 This is a hierarchical control structure diagram of a DC microgrid according to the present invention;

[0084] Figure 3 This is a flow chart of the third layer control scheduling scheme of the present invention;

[0085] Figure 4 This is a flow chart of the second layer control scheduling scheme of the present invention;

[0086] Figure 5 This is a flow chart for selecting the DC bus voltage of the present invention;

[0087] Figure 6This is a diagram of the tunnel power supply and distribution system of the present invention;

[0088] Figure 7 This is a system diagram of the non-fire-fighting dual-power switch cabinet AT of the present invention;

[0089] Figure 8 This is the system diagram of the DC integrated cabinet AM1 of the present invention;

[0090] Fig. 9 This is the system diagram of the DC integrated cabinet AM2 of the present invention;

[0091] Fig.10 This is a schematic diagram of hourly traffic volume statistics for many years in one embodiment of the present invention:

[0092] Fig.11 This is a flow chart of the engineering design of the wind, solar and storage system of the present invention. DETAILED DESCRIPTION

[0093] The technical solution of the present invention is described in detail below in conjunction with the accompanying drawings.

[0094] like Figure 1 The present invention proposes a hybrid energy DC microgrid for a traffic tunnel, comprising a multi-section DC bus, an energy storage battery, a distributed power supply, an emergency mobile power supply, and a DC local load; the multi-section DC bus is connected to the energy storage battery, and the multi-section DC bus includes a DC bus I arranged in the center of the tunnel, a DC bus II arranged at the entrance of the tunnel, and a DC bus III arranged at the exit of the tunnel; the DC bus I is connected to the mains power supply through a unidirectional AC / DC converter, the DC bus II and the DC bus III are both connected to the distributed power supply and the emergency mobile power supply through different converters, the DC bus I is respectively connected to the DC bus II and the DC bus III through a bidirectional DC / DC converter to realize the power transmission between different DC buses; wherein the bidirectional DC / DC converter adopts a high-frequency isolated bidirectional DC / DC converter. The DC local load includes the basic tunnel lighting, facility electro-optical signs, traffic lights, monitoring equipment electricity powered by the DC bus I, and the tunnel enhanced lighting powered by the DC bus II and the DC bus III.

[0095] The number of the DC busbars I is set according to the power supply radius of the DC busbar and the tunnel length to realize the power supply of uniformly distributed DC loads in the tunnel. For example, for a traffic tunnel with a power supply radius of each central DC busbar of less than 1 km and greater than 2 km, at least two central DC busbars need to be set.

[0096] The distributed power source includes photovoltaic power generation and wind power generation; using photovoltaic power generation as one of the system energy sources can effectively improve the economy of system operation, and the input voltage of the DC-DC converter is adjusted by controlling the on and off of the power switch tube in the DC-DC converter; a permanent magnet direct-drive wind turbine system is used as a wind energy utilization device, which has a simple structure and high power generation efficiency. Since the output power of the wind turbine is affected by the wind speed and wind direction, it is necessary to stabilize the output first when connecting to the DC bus, and convert the low-voltage AC power into the required DC voltage through the AC-DC converter.

[0097] In the DC microgrid, the output power of the connected distributed power source is unstable; in order to maintain the normal power supply of the important loads in the tunnel, the DC microgrid is connected to the AC large grid: AC380V AC is converted into stable DC power through the AC-DC unidirectional rectifier module and connected to the DC bus; in addition, the energy storage battery (lithium battery) can absorb excess energy when the photovoltaic and wind energy is sufficient, and supplement the insufficient energy when the photovoltaic and wind energy is insufficient, thereby balancing the system energy and stabilizing the bus voltage. The emergency mobile power supply includes a mobile diesel generator.

[0098] Basic calculation formula:

[0099] ① Calculation formula for wind turbine power generation

[0100] Q 1n =P1×T 1n ×m (annual power generation); where Q 1n Indicates the annual power generation of the wind turbine, kWh; T 1n It represents the annual statistical wind duration of the average wind speed calculated based on the wind frequency, in h; P1 represents the output power of the wind turbine generator converted to the rated wind speed by the average wind speed of each wind speed segment according to the power characteristic curve, in kW; when the average wind speed of each wind speed segment is less than the rated wind speed, P1 = P e ×(average wind speed in the highly calibrated wind speed segment / rated wind speed) 3 ; When the average wind speed in each wind speed segment is ≥ rated wind speed, P1=P e ; m represents the coefficient of loss consideration, which is 0.85;

[0101] Wind speed height correction formula: V i =V x ×(h i / h x ) a ; Where V i Indicates the height to be corrected h i Wind speed at V, m / s; x Indicates height h x= Wind speed at a point 10 m away, m / s; a represents an index determined by atmospheric stability and surface roughness; for islands, coasts, lakeshores, deserts, etc., the value is 0.12; for open fields, rural areas, urban suburbs, etc., the value is 0.16; for densely populated urban areas, the value is 0.2.

[0102] ② Calculation formula for power generation of solar cell array

[0103] Q 2n =P m ×T 2n ×m (annual power generation); where Q 2n Indicates the annual power generation of the solar cell array, kWh; T 2n Indicates the annual statistical value of solar peak sunshine hours, h; P m represents the rated (peak) power of the solar cell array, kW; m represents the coefficient considering losses, which is 0.9.

[0104] ③Energy storage battery capacity calculation formula

[0105] Q C =Q js / (m×n); where Q C Indicates the capacity of the energy storage battery, kWh; Q js represents the energy storage battery capacity required for calculation, kWh; m represents the efficiency of the energy storage battery, which is 0.95; n represents the discharge depth of the energy storage battery, which is 1.0.

[0106] like Figure 2 The operation control of the DC microgrid adopts a three-layer hierarchical mode: the first layer of control adopts droop control, and a plurality of control units participating in the DC bus voltage control jointly maintain the DC bus voltage stability; the second layer of control is implemented by the industrial computer to realize the secondary regulation of the DC bus voltage, the power distribution of each control unit, and the switching of the DC bus operation mode; the third layer of control is implemented by the computer in the tunnel control center to realize the energy scheduling between different DC buses, and by formulating the operation scheduling strategy of the DC microgrid, the flexible scheduling of the mains power supply, distributed power supply, energy storage battery, and DC load is realized, and the renewable energy is used as much as possible to generate electricity and ensure the safe and economical operation of the system.

[0107] In the first layer of control, the control unit involved in the DC bus voltage control includes a unidirectional AC / DC converter, a bidirectional DC / DC converter, a distributed power supply controller, and an energy storage unit controller; the droop control is to control the voltage and current of the converter or controller to run on a droop curve, and the droop curve expression is as follows:

[0108] U d =U0-k×I

[0109] Where Ud is the output voltage of the converter or controller; U0 is the set value of the DC bus voltage; k is the droop curve coefficient; I is the output current of the converter or controller.

[0110] The DC microgrid system proposed in this application is a multi-source, multi-load system. The single use of droop control has limitations, so it is necessary to set up secondary regulation of the DC bus voltage.

[0111] In the second-level control, the DC bus voltage secondary regulation and the power distribution of each control unit are specifically as follows: a hybrid compensation method is adopted to simultaneously compensate the DC bus voltage setting value U0 (vertical intercept) and coefficient k of the droop curve, and the voltage and current (U0) of each unit are obtained through the industrial computer bus communication method. 1～n ,I 1～n ) and droop curve coefficient (k 1～n ), and then use the average voltage compensator, average current compensator and curve coefficient compensator to obtain the droop curve coefficient compensation Δk and the vertical intercept compensation ΔU, and then translate and adjust the coefficient of the droop curve respectively; wherein the average voltage compensator eliminates the output DC voltage deviation of each unit by translating the curve, and the average current compensator and curve coefficient compensator achieve rapid load distribution by adjusting the coefficient of the droop curve;

[0112] The DC busbars I, II and III are respectively set to three operating modes:

[0113] 1. DC bus I operation mode

[0114] ① Operation mode 1 (DC bus II, III have surplus power) The DC bus I power input unit includes the AC power AC / DC unit, the energy storage battery unit and the bus-link bidirectional DC / DC unit (flow direction: DC bus II, III to DC bus I); the DC bus load is basic lighting, traffic signals, monitoring equipment, and electro-optical signs.

[0115] U DCI >U H :The DC bus voltage is too high, the energy storage battery reaches the upper limit and cannot continue to charge, and the renewable energy (photovoltaic, wind) power generation system needs to abandon energy and operate. In order to maintain voltage stability, the power generation system operates in constant voltage mode.

[0116] U H >U DCI >U M :The power generated by the renewable energy power generation system is greater than the power consumed by the DC load and there is a surplus. The energy storage battery works in constant current charging mode, and the renewable energy power generation system is in droop control to maintain the stability of the DC bus voltage.

[0117] U M>U DCI >U L :The power generated by the renewable energy power generation system is not enough to provide the power consumed by the DC load. In order to maximize the use of renewable energy, the power generation system always operates in the maximum power tracking mode. At this time, in order to maintain the stability of the bus voltage, the energy storage battery is discharged and operates in the droop control state.

[0118] U L >U DCI >U O :The sum of the power generated by renewable energy photovoltaics and the power provided by the energy storage battery is less than the power consumed by the AC and DC loads. The renewable energy power generation system operates in MPPT mode, the energy storage battery is discharged, and the AC / DC module of the mains operates in a droop control state to maintain the stability of the DC bus voltage.

[0119] U0 is the DC bus voltage setting value; U H \U M \U L To set the voltage control point, reference value: U DCI is the DC bus I voltage value;

[0120] U L =(1+1%)×U0; U M =(1+1%)×U L ; U H =(1+1%)×U M .

[0121] ② Operation mode 2 (DC bus II, III lacks power): The power input unit of DC bus I includes AC / DC unit and energy storage battery; the DC bus load includes basic lighting, traffic signals, monitoring equipment, electro-optical signs and the DC bus load of AW2(3) (flow direction: DC bus I to DC bus II, III).

[0122] ③ Operation mode three (emergency: AC power failure): DC bus I power input unit energy storage battery unit and bus-link bidirectional DC / DC unit (flow direction: DC bus II, III to DC bus I); DC bus load is basic lighting (emergency lighting) and electro-optical signs.

[0123] U DCI >U H :The DC bus voltage is too high, the energy storage battery reaches the upper limit and cannot continue to charge, and the renewable energy (photovoltaic, wind) power generation system needs to abandon energy and operate. In order to maintain voltage stability, the power generation system operates in constant voltage mode.

[0124] U H >U DCI >U M:The power generated by the renewable energy power generation system is greater than the power consumed by the DC load and there is a surplus. The energy storage battery works in constant current charging mode, and the renewable energy power generation system is in droop control to maintain the stability of the DC bus voltage.

[0125] U M >U DCI >U L :The power generated by the renewable energy power generation system is not enough to provide the power consumed by the DC load. In order to maximize the use of renewable energy, the power generation system always operates in the maximum power tracking mode. At this time, in order to maintain the stability of the bus voltage, the energy storage battery is discharged and operates in the droop control state.

[0126] U L >U DCI >U O :The sum of the power generated by renewable energy photovoltaics and the power provided by the energy storage battery is less than the power consumed by the AC and DC loads. The renewable energy power generation system works in MPPT mode, the energy storage battery is discharged, and the DC bus II and III consider connecting to a mobile diesel generator to supplement power.

[0127] 2. DC bus II (III) operation mode (U DC is the DC bus II voltage value or DC bus III voltage value)

[0128] Ensure the stability of the power supply system, use renewable energy to generate electricity as much as possible, and achieve safe and economical operation of the system. Set different power supply priorities for renewable energy generation, energy storage and mains power to implement different power flow control strategies. Power supply priority: renewable energy generation > energy storage > mains power.

[0129] ① Operation mode 1 (daytime): The DC bus power input unit includes a wind power generation unit, a photovoltaic power generation unit, an energy storage battery unit, and a bidirectional DC / DC unit (derived from the DC bus I); the DC bus load is an enhanced lighting load.

[0130] According to the DC bus voltage, it is divided into 4 working modes: U0, U L , U M , U H They are the bus voltage values ​​corresponding to each working mode.

[0131] U DC >U H :The DC bus voltage is too high, the energy storage battery reaches the upper limit and cannot continue to charge, and the renewable energy (photovoltaic, wind) power generation system needs to abandon energy and operate. In order to maintain voltage stability, the power generation system operates in constant voltage mode.

[0132] U H >U DC >UM :The power generated by the renewable energy power generation system is greater than the power consumed by the DC load and there is a surplus. The energy storage battery works in constant current charging mode, and the renewable energy power generation system is in droop control to maintain the stability of the DC bus voltage.

[0133] U M >U DC >U L :The power generated by the renewable energy power generation system is not enough to provide the power consumed by the DC load. In order to maximize the use of renewable energy, the power generation system always operates in the maximum power tracking mode. At this time, in order to maintain the stability of the bus voltage, the energy storage battery is discharged and operates in the droop control state.

[0134] U L >U DC >U O :The sum of the power generated by renewable energy photovoltaics and the power provided by the energy storage battery is less than the power consumed by the AC and DC loads. The renewable energy power generation system operates in MPPT mode, the energy storage battery is discharged, and the AC power bidirectional DC / DC module operates in a droop control state to maintain the stability of the DC bus voltage.

[0135] ② Operation mode 2 (daytime): the DC bus power input unit includes a wind power generation unit, a photovoltaic power generation unit, and an energy storage battery unit; the DC bus load is an enhanced lighting load and DC bus I.

[0136] U DC >U H :The DC bus voltage is too high, the energy storage battery reaches the upper limit and cannot continue to charge, and the renewable energy (photovoltaic, wind) power generation system needs to abandon energy and operate. In order to maintain voltage stability, the power generation system operates in constant voltage mode.

[0137] U H >U DC >U M :The power generated by the renewable energy power generation system is greater than the power consumed by the DC load and there is a surplus. The energy storage battery works in constant current charging mode, and the renewable energy power generation system is in droop control to maintain the stability of the DC bus voltage.

[0138] U M >U DC >U L :The power generated by the renewable energy power generation system is not enough to provide the power consumed by the DC load. In order to maximize the use of renewable energy, the power generation system always operates in the maximum power tracking mode. At this time, in order to maintain the stability of the bus voltage, the energy storage battery is discharged and operates in the droop control state.

[0139] ③ Operation mode three (night): the DC bus power input unit includes a wind power generation unit and an energy storage battery unit; the DC bus load is DC bus I.

[0140] U DC >U H :The DC bus voltage is too high, the energy storage battery reaches the upper limit and cannot continue to charge, and the renewable energy (photovoltaic, wind) power generation system needs to abandon energy and operate. In order to maintain voltage stability, the power generation system operates in constant voltage mode.

[0141] U H >U DC >U M :The power generated by the renewable energy power generation system is greater than the power consumed by the DC load and there is a surplus. The energy storage battery works in constant current charging mode, and the renewable energy power generation system is in droop control to maintain the stability of the DC bus voltage.

[0142] U M >U DC >U L :The power generated by the renewable energy power generation system is not enough to provide the power consumed by the DC load. In order to maximize the use of renewable energy, the power generation system always operates in the maximum power tracking mode. At this time, in order to maintain the stability of the bus voltage, the energy storage battery is discharged and operates in the droop control state.

[0143] The DC microgrid operation dispatching strategy in the third layer of control includes two dispatching schemes, specifically:

[0144] Scheduling plan 1:

[0145] The output power adjustment range of basic tunnel lighting is 50% to 100%, and the output power adjustment range of enhanced tunnel lighting is 15% to 100%. Traffic lights, electro-optical signs, and monitoring equipment operate at full power around the clock. The dispatching plan process is as follows: Figure 3 .

[0146] The time T1 when night turns into daytime and the time T2 when day turns into nighttime are set according to the longitude and latitude, and the time T1 and T2 are used to determine whether the current time is daytime or nighttime according to the preset time interval;

[0147] If it is daytime, the power consumption Q1 of DC bus II / DC bus III and the power generation Q2 of distributed generation are predicted according to the statistical hourly traffic volume and the weather forecast results. If Q1 is less than Q2 and the energy storage of DC bus II / DC bus III is sufficient, DC bus II / DC bus III supplies power to DC bus I, and DC bus I operates in mode 1, and DC bus II / DC bus III operates in mode 2. If the energy storage of DC bus II / DC bus III is insufficient or Q1 is greater than or equal to Q2, DC bus I supplies power to DC bus II / DC bus III, and DC bus I operates in mode 2, and DC bus II / DC bus III operates in mode 1.

[0148] If it is night time, DC bus II / DC bus III supplies power to DC bus I, DC bus I operates in mode 1, and DC bus II / DC bus III operates in mode 3;

[0149] Dispatch Plan 2 (Emergency):

[0150] When two 10KV mains fail at the same time or the AC system fails, the system power supply completely relies on renewable energy generation and mobile diesel generator sets. In an emergency, some DC loads are cut off, and only important loads are retained: emergency lighting and electro-optical signs in basic lighting; the process of dispatch plan 2 is as follows Figure 4 .

[0151] Predict the power consumption Q'1 of the DC bus I and the power generation Q'2 of the distributed power source; set the time T1 when night turns into daytime and the time T2 when day turns into nighttime according to the longitude and latitude, and judge whether it is daytime or nighttime according to T1 and T2 according to the preset time interval;

[0152] If it is daytime, DC bus II / DC bus III supplies power to DC bus I, DC bus I operates in mode 3, and DC bus II / DC bus III operates in mode 2. On this basis, it is determined whether the following conditions are met: Q'1 is greater than Q'2 and the DC bus I voltage U DCI Less than U L , if the conditions are met, connect to the emergency mobile power supply, otherwise return;

[0153] If it is night time, DC bus II / DC bus III supplies power to DC bus I, DC bus I operates in mode 3, and DC bus II / DC bus III operates in mode 3. On this basis, it is determined whether the following conditions are met: Q'1 is greater than Q'2 and U DCI Less than U L If the conditions are met, connect to the emergency mobile power supply, otherwise return.

[0154] The electric shock protection design of the DC microgrid includes: setting 400mA as the upper limit of the human contact current that may be expected in the low-voltage DC system; the low-voltage DC adopts single-pole wiring, specifically adopting the IT power grounding system to achieve 30mA leakage protection and insulation monitoring dual protection. The electric shock protection performance of the low-voltage DC IT system (DC375V and below) is higher than that of the low-voltage AC TN-S system in the prior art.

[0155] The DC bus voltage can be selected as DC375V, DC220V, and D110V. The enumeration comparison method is adopted to calculate the line cable cross-sectional area at different DC voltages in combination with the actual tunnel length and load power. The DC voltage corresponding to the minimum cross-sectional area is selected as the selected DC bus voltage. The design process is as follows: Figure 5 , the calculation of the line cable cross-sectional area for each DC voltage is as follows:

[0156] Calculate the DC load line current:

[0157]

[0158] Among them, I js Calculate the current for the DC load line, P e1 , P e2 , P e3 is the power of a single DC device within the set length range, and U is a DC voltage tentatively determined by the enumeration method;

[0159] According to I js ≥1.1×I N Determine the rated current I of the miniature circuit breaker N value, and according to I L ≥1.1×I N Determine the cable current carrying capacity I L value;

[0160] Calculate the cross-sectional area:

[0161] S”≥(P×l)÷(5×γ×U 2 ×0.001×5%)

[0162] Where P is the total power of the line, l is the equivalent power supply distance of the line, S' is the calculated value of the cable cross-sectional area, γ is the conductivity of the cable conductor at 50 °C, and U' is the nominal voltage;

[0163] According to the cable current carrying capacity I L The corresponding cable cross-sectional area is determined by the value, which is recorded as the cable cross-sectional area query value S'; L The rated current carrying capacity of a cable with a certain number of cores and a certain cross-sectional area specified in the cable manual; LThe corresponding cable cross-sectional area can be obtained by checking the manual; compare the cable cross-sectional area query value S' with the cable cross-sectional area calculation value S", and take the larger value as the cable cross-sectional area S to be checked for sensitivity verification:

[0164]

[0165] k T =1+a×(θ-20)

[0166] Sensitivity

[0167] Where ρ is the cable conductor resistivity at 20°C, L is the line cable length, k T is the resistance temperature conversion coefficient, a is the resistance temperature coefficient, θ is the actual working temperature of the conductor, I d It is the single-phase short-circuit current at the farthest end of the line;

[0168] Judgment sensitivity L m Is it greater than or equal to 1? If so, the cross-sectional area S of the cable to be checked is used as the cross-sectional area of ​​the line cable of the DC voltage. Otherwise, a larger nominal cross-sectional area of ​​the cable core is selected and the sensitivity check is performed again.

[0169] Compare the cross-sectional areas of the cables under the three voltage conditions, and select the DC transmission voltage corresponding to the minimum cross-sectional area as the selected DC bus voltage.

[0170] DC arc fault protection and insulation monitoring and positioning; the present application adopts a discrete detection and disconnecting device, and AFD and AFI are respectively set in the DC outgoing line circuit of the DC distribution cabinet; a DC arc fault detection and disconnecting controller is set in the monitoring cabinet; the controller communicates with the industrial computer via RS232, and the fault arc current information, occurrence time, fault circuit number, AFI disconnecting signal and other information are uploaded to the central storage via the industrial Ethernet ring network; in addition, insulation detection terminals are respectively set in the DC outgoing line circuit of the DC distribution cabinet; an insulation detection controller is set in the monitoring cabinet; the controller communicates with the industrial computer via RS232, and the fault insulation information, location and other information are uploaded to the central storage via the industrial Ethernet ring network.

[0171] The following provides the engineering design of the main equipment of a DC microgrid.

[0172] 1. Equipment overall layout

[0173] This application proposes to disperse multiple DC integrated cabinets AM1~AM3 (DC busbars I~III): AM1 is set in the center of the tunnel, and supplies power to the loads (basic lighting, electro-optical signs, traffic signals, monitoring equipment) on both sides. The incoming power is drawn from the three-phase AC system; AM2 is set at the entrance of the tunnel, and supplies power to the loads (enhanced lighting) on ​​one side. The power supply includes DC busbar I, renewable energy generation, and mobile diesel generator sets. It is set at the entrance to facilitate the access of renewable energy generation units and mobile diesel generator sets and to go deep into the load center (enhanced lighting is located at the entrance and exit of the tunnel); AM3 is set at the exit of the tunnel, and the power supply is the same as AM2. By setting up a DC / DC high-frequency isolation bidirectional converter (set in AM2, AM3), the bidirectional transmission of electric energy between DC buses of different voltage levels is realized. A non-fire-fighting dual-power switching cabinet AT is set on the AM1 side of the central tunnel. Dual power switching and intelligent high-frequency DC modules are set in AT, and DC power is distributed from AT to AM1. AT, AM1~AM3 are set in the power distribution room in the tunnel. Wind power generation, photovoltaic power generation and energy storage equipment are set outside the tunnel.

[0174] Industrial computers are installed in DC integrated cabinets AM1~3 to realize secondary control of DC system, power distribution and monitoring of related equipment. The control center computer communicates with the partitioned industrial computers in the tunnel through industrial Ethernet switches and optical fibers to form a Gigabit Ethernet.

[0175] 2. Voltage DC power distribution system

[0176] 1. Power distribution system diagram

[0177] like Figure 6-9 The low-voltage DC power distribution system shown in the figure, wherein the DC integrated cabinet AM3 power distribution system diagram is the same as the DC integrated cabinet AM2, in which:

[0178] ①AC380V dual power automatic switching device: used for automatic switching of two AC380V mains power supplies.

[0179] ②AC three-pole molded case circuit breaker: used to provide overload, short circuit, overvoltage and undervoltage protection for three-phase AC distribution circuits.

[0180] ③ DC two-pole micro leakage (30mA) circuit breaker: used for overload, short circuit, overvoltage and undervoltage protection of DC power distribution circuit. 30mA leakage is used for additional protection of direct contact.

[0181] ④ DC two-pole contactor: used to switch the load DC distribution circuit on and off.

[0182] ⑤Insulation monitoring terminal: used for insulation monitoring of DC bus and DC distribution circuit.

[0183] ⑥ DC arc fault detection and disconnection terminal: Arc detector (AFD) is a device used to detect arc on the DC side and send out fault alarm signals. Arc interrupter (AFI) is a device that receives arc detection signals and implements arc extinguishing function by means of isolation, short circuit or switch.

[0184] ⑦AC busbar: copper busbar. ⑧Ground busbar: copper busbar. ⑨DC busbar: copper busbar.

[0185] 2. Main complete equipment

[0186] 2.1. Intelligent high-frequency DC module

[0187] This application proposal uses multiple intelligent high-frequency DC modules in parallel as the power supply for the low-voltage DC bus I. The DC module used is an intelligent high-frequency complete set of equipment, which occupies a small space, supports hot plugging, has a high protection level, and is suitable for tunnel working scenarios. Main technical requirements:

[0188] 2.2. High-frequency isolated bidirectional DC / DC module

[0189] This application proposal uses a high-frequency isolated bidirectional DC / DC module as a networking device between the low-voltage DC bus I and the DC bus II and III to achieve bidirectional transmission of electric energy. The isolated bidirectional DCDC converter uses a transformer to achieve electrical isolation between input and output, which has high safety. Considering the low energy consumption of high-voltage transmission lines, the module is installed in DC cabinets AW2 and AW3 where the DC buses II and III with lower voltage levels are located, and the line transmission voltage is the DC bus I voltage. The bidirectional DC / DC module is also used for charging and discharging energy storage batteries. The bidirectional DC / DC module used is an intelligent high-frequency complete set of equipment, which occupies a small space, supports hot plugging, has a high protection level, and is suitable for tunnel working scenarios.

[0190] 2.3. DC bus

[0191] This application proposes that the DC busbar adopts flame-retardant insulated copper busbar, and the distance between the positive and negative busbars of the copper busbar should be no less than 60mm. The maximum busbar current is calculated based on the maximum power value that can be connected to the DC busbar and the busbar voltage. The rated current of the DC busbar should be greater than the calculated maximum busbar current and take into account an appropriate margin (about 10%). Select a DC busbar of corresponding specifications according to the rated current of the DC busbar, such as TM-40x4, 50x5, 80x8, etc. The DC busbar adopts heat shrink tubing or other electric shock protection measures, and a warning sign should be set in a conspicuous location.

[0192] The maximum DC bus current calculation formula is: I js is the maximum DC bus current, A; P e1 , P e2 , P e3: For DC bus I, it is the maximum output power of the DC module when the AC power is connected; for DC bus II and III, it is the maximum output power of the bidirectional DC / DC module when the AC power is connected; U is the designed DC bus voltage, V.

[0193] 2.4. Energy storage battery

[0194] This application proposes to install energy storage batteries in DC cabinet AW1 as emergency backup power supply for tunnels (emergency lighting, electro-optical signs and monitoring equipment). The battery can provide continuous power for 30 minutes.

[0195] 2.5. Cross-section design of low voltage DC distribution cables

[0196] ①AM1 cabinet incoming cables 1 to 4

[0197] The cable is led from the AT cabinet to the AM1 cabinet. The cable length is less than 3 meters. The ZB1YJV cable is used. The cable is laid openly along the wall in the power distribution room. The distance between cables in different circuits is greater than 1 times the outer diameter. The ambient temperature value needs to be based on the actual temperature of the project location. Cable cross-sectional area (current carrying capacity): Select the long-term allowable current carrying capacity of the cable according to the laying method and environmental conditions, and verify the thermal stability according to the short-circuit current.

[0198] Calculation formula: I C ≤I N ≤I Z , I C is the maximum operating current, A; I N is the long-delay setting current of the DC leakage circuit breaker, A; I Z The allowable continuous current carrying capacity of the conductor, A.

[0199] Calculation formula: S is the cable cross-sectional area, mm2; I is the maximum short-circuit current, A; k is the coefficient; t is the action time of the protective device (DC leakage circuit breaker) to automatically cut off the current, s

[0200] ②AM1 cabinet incoming cable 5~6 (or AM2~3 cabinet incoming cable 1)

[0201] The cable is led from the AM2-3 cabinet to the AM1 cabinet. The cable length is about half of the total length of the tunnel. It is relatively long. ZB1YJV cable is used and laid along the cable trench brackets on both sides of the tunnel. The spacing between cables in different loops is greater than 1 times the outer diameter. The ambient temperature value needs to be based on the actual temperature of the project location. Cable cross-sectional area (current carrying capacity): select the long-term allowable current carrying capacity of the cable according to the laying method and environmental conditions, and verify the thermal stability according to the short-circuit current; in addition, the line is long, and the cable cross-section needs to be verified according to the line voltage drop requirements (<5%), and the sensitivity of the short-circuit protection at the end of the line needs to be verified.

[0202] The calculation method for selecting the long-term allowable current carrying capacity of the cable and the short-circuit thermal stability verification is the same as ① according to the laying method and environmental conditions.

[0203] ③Outgoing cables 1 to 10 from AM1 cabinet (or outgoing cables 1 to 2 from AM2 to 3 cabinets)

[0204] The cable is led out from the AM1~3 cabinet to the LED tunnel light. The cable is long and uses ZB1YJV cable. It is laid along the cable trays on both sides of the tunnel ceiling. The distance between cables in different loops is greater than 1 times the outer diameter. The ambient temperature value needs to be based on the actual temperature of the project location. Cable cross-sectional area (current carrying capacity): Select the long-term allowable current carrying capacity of the cable according to the laying method and environmental conditions; in addition, the line is long, and the cable cross-section needs to be verified according to the line voltage drop requirements (<5%), and the sensitivity of the short-circuit protection at the end of the line needs to be verified.

[0205] The calculation method for selecting the long-term allowable current carrying capacity of the cable based on the laying method and environmental conditions is the same as ①.

[0206] In addition, the outgoing cables 1 to 4 of the AM1 cabinet (or the outgoing cables 1 to 2 of the AM2 to 3 cabinets) all use 5-core cables with equal cross-section (two DC circuits, L+, L-, L+, L-, and a common PE). Under the same power supply distance, the cross-section of the copper core cable used is much lower than that of the existing technology (AC380V); the line loss is greatly reduced, and the energy saving effect is obvious; the use of copper materials is greatly reduced, and the effect of reducing carbon emissions is obvious. The remaining output circuits all use 3-core cables with equal cross-section.

[0207] ④AM2~3 cabinet incoming cable 2~5

[0208] The cable is led from the equipment outside the tunnel to the AM2~3 cabinet. The cable is long and uses ZB1YJV cable. It is laid along the cable trench bracket outside the tunnel. The distance between cables in different loops is greater than 1 times the outer diameter. The ambient temperature value needs to be based on the actual temperature of the project location. Cable cross-sectional area (current carrying capacity): Select the long-term allowable current carrying capacity of the cable according to the laying method and environmental conditions, and verify the thermal stability according to the short-circuit current; in addition, if the line is long, the cable cross-section needs to be verified according to the line voltage drop requirements (<5%), and the sensitivity of the short-circuit protection at the end of the line needs to be verified.

[0209] The calculation method for selecting the long-term allowable current carrying capacity of the cable and the short-circuit thermal stability verification is the same as ① according to the laying method and environmental conditions.

[0210] 3. Voltage DC power distribution system

[0211] This application proposes to set up a centralized management and decentralized control distributed automatic control network architecture consisting of a three-layer architecture of central monitoring level, on-site control level and detection execution level.

[0212] ①Central monitoring level

[0213] Located in the control center (supporting building outside the tunnel). Set up 3 sets of central monitoring computers as central monitoring SCADA clients (2 of which are operator stations; 1 set is an engineer station and also serves as a backup operator station) to monitor the operation process of the DC microgrid. Set up a historical data server to compress, store and manage historical data. The central monitoring-level upper configuration software also has a WEB publishing component, which can realize remote management and information publishing of the SCADA system.

[0214] ② Field control level

[0215] It consists of industrial control computers, touch screens and industrial Ethernet switches in the DC integrated cabinets AM1~3 in the tunnel, and is mainly responsible for the automatic control of various equipment and data collection.

[0216] ③Detection execution level

[0217] It consists of various complete control systems, including DC arc fault protection controller, insulation monitoring controller, intelligent instrument, high-frequency isolated bidirectional DC / DC, energy storage battery controller, photovoltaic power generation controller, and wind power generation controller. Each complete control system is connected to the monitoring system through the MODBUS bus.

[0218] ④Communication network

[0219] 1000M optical fiber fast industrial Ethernet is used to form a ring redundant structure. At the field control level, MODBUS bus communication is used between the field control station and the complete equipment control system.

[0220] A monitoring computer and communication cabinet (including Gigabit industrial Ethernet switch, network integrated communicator, UPS, surge protection and other equipment) are set up in the control center outside the tunnel; a communication cabinet (including Gigabit industrial Ethernet switch, industrial computer, surge protection and other equipment) is set up in the tunnel power distribution room. The control center computer communicates with the partitioned industrial computer in the tunnel through the industrial Ethernet switch and optical fiber to form a Gigabit Ethernet. The optical fiber ring network topology based on switch technology is adopted to replace the traditional point-to-point distributed structure. The ring network has unidirectional transmission, which is suitable for optical fiber applications, with high transmission rate and high real-time performance; there is a bypass, and a node failure can be automatically bypassed without causing downtime, and the reliability is high.

[0221] 4. Wind, solar and storage system engineering design

[0222] The wind turbine generator adopts a full permanent magnetic suspension horizontal axis wind turbine generator, which requires the starting wind speed of the generator to be less than 1.5m / s and the cut-in wind speed to be no more than 2.5m / s. The solar cell module adopts high-transmittance low-iron tempered glass with a transmittance greater than 91.3%, and adopts high-quality monocrystalline silicon cells. High-efficiency lithium iron phosphate batteries are used as energy storage batteries.

[0223] The following is a case study to illustrate the engineering design method for wind and solar equipment power and energy storage battery capacity:

[0224] Meteorological data of the case location: the average wind speed for many years is 4.9m / s (10m height), the annual wind speed is greater than 3m / s (that is, the wind speed that can be used for wind turbines to generate electricity) for 5783h, and the daily average is 15.84h, which belongs to the area where wind resources can be used. The average daily radiation is 3.33kWh / m2, the average peak sunshine is 4.5h, and the annual statistical duration is 1642h. The solar energy resources are average, and the wind resources are more abundant.

[0225] Basic lighting day dimming coefficient: LED light output is adjusted (power is adjusted) according to changes in tunnel traffic volume. Usually, several dimming levels are set based on the statistical average of hourly traffic volume in the tunnel over many years. Different tunnels determine the average daily dimming coefficient based on the statistical hourly traffic volume values ​​of their location. Enhanced lighting day dimming coefficient: Dimming based on traffic volume is the same as basic lighting; in addition, LED light output (power is adjusted) needs to be adjusted according to changes in tunnel opening brightness (mainly determined by weather conditions). High opening brightness corresponds to high LED luminous flux output, and low opening brightness corresponds to low LED luminous flux output. Several dimming levels are set. Different tunnels determine the average daily dimming coefficient based on the statistical hourly traffic volume and opening brightness values ​​of their location over many years.

[0226] The national standard GB / T 33589-2017 "Technical Regulations for Microgrid Access to Power System" stipulates that the annual power generation of distributed generation should not be less than 30% of the total power consumption of the microgrid. The total power of wind turbines and solar panels should be considered in combination with the meteorological data of the project location (wind speed and annual statistical duration of available wind speed (>3m / s), light intensity and available light duration), and the annual average power consumption of the tunnel DC microgrid to ensure that the annual power generation of distributed generation is greater than 30% of the annual power consumption of the DC microgrid. Areas with rich wind resources should mainly use wind power generation, supplemented by photovoltaic power generation; areas with rich solar energy resources should mainly use photovoltaic power generation, supplemented by wind power generation. Photovoltaic power generation only operates during the day, while wind power generation can operate during the day and at night.

[0227] In the above case, the annual power consumption of a single tunnel is 186703kWh. Wind and solar energy resources are abundant, and the power generation of the photovoltaic and wind power generation equipment should be greater than 30% of the annual power consumption of the two tunnels: 2x186703x30%=112022kWh. The annual wind duration at the location of the case project is 5783h (wind speed>3m / s), and the annual peak sunshine duration is 1642h. The ratio of wind power and photovoltaic power generation is estimated based on the duration: 5783:1642≈7:2.

[0228] According to the above formula ①, the average annual power generation of wind turbines is:

[0229] Q1n =P1×T 1n ×m=P1×5783×0.9=112022×7 / 9=87128kWh;

[0230] Total installed power of wind turbines:

[0231] P1=87128 / (5783×0.9)=16.7kW, the annual average wind speed is 4.9m / s (10m height), the rated wind speed of the wind turbine is <10m / s, the installation height is 20m, and the height and wind speed conversion of formula ① is used to calculate the equipment power P of the selected wind turbine. e =30kW, which is the sum of the equipment powers of the wind turbines outside the tunnel in both directions. A single high-power device or a combination of multiple low-power devices can be used in engineering applications.

[0232] Average annual photovoltaic power generation:

[0233] Q 2n =P2×T 2n ×m=P2×1642×0.9=112002×2 / 9=24889kWh;

[0234] Total installed power of photovoltaic solar panels:

[0235] P2=24889 / (1642×0.9)=16.8kW, take the nominal value P2=18kW.

[0236] 3. Capacity of energy storage battery

[0237] All tunnels are equipped with stable and reliable mains power supply. Wind power generation and photovoltaic power generation are energy-saving and consumption-reducing equipment, which supplement the mains power supply. The battery capacity configuration does not take into account the independent operation of the system after the renewable energy stops generating electricity and the mains power supply is lost.

[0238] The capacity configuration of energy storage batteries takes into account the following two boundary conditions:

[0239] ① The national standard GB / T 33589-2017 "Technical Regulations for Microgrid Access to Power System" stipulates that in the independent operation mode of the microgrid, the continuous specified time for the load should not be less than 2 hours.

[0240] like Fig.10According to the hourly traffic statistics for many years, since the enhanced lighting in the tunnel DC load is turned off at night, the maximum DC load is considered to occur during the day when the traffic volume is heavy and the brightness outside the tunnel is the highest. Reason: When the traffic volume is heavy, the dimming coefficient of the LED is high, and the output power of the LED is high; when the brightness outside the tunnel is high, the dimming coefficient of the enhanced lighting LED is high, and the output power of the ED is high. According to the above traffic volume data, the period of heavy daytime traffic volume is: 7 to 12 o'clock; the case is located in the area north of the Tropic of Cancer in the Northern Hemisphere, and the strongest sunshine of the year occurs at noon on the summer solstice of that year.

[0241] The largest continuous 2-hour high load of the whole year occurs from 10:00 to 12:00 on the summer solstice of that year. The daily peak power consumption is shown in Table 1:

[0242] Table 1.

[0243]

[0244] According to formula ③, the energy storage battery capacity configuration is:

[0245] 101.2kWh / (0.95x1)≈106.5kWh, the value is 110kWh.

[0246] ② The capacity of the energy storage battery should take into account the principle of no waste of new energy power generation, that is, it should meet the storage of excess new energy power generation (without considering the surplus power to the grid). The battery capacity should be greater than the difference between the maximum daily power generation and the minimum daily power consumption. This case is mainly based on wind power generation. The difference between the maximum daily power generation and the minimum daily power consumption occurs during continuous rainy periods, and the average wind speed during this period is significantly higher than the average wind speed throughout the year. Photovoltaic power generation is basically zero; the brightness at the cave entrance is the lowest, and the enhanced lighting dimming coefficient is as low as 0.1. The minimum daily power consumption is shown in Table 2:

[0247] Table 2

[0248]

[0249] If the wind power and photovoltaic power generation are taken as 90% of the annual power consumption of Shuangdong, according to the above formula ①, the equipment power of the wind turbine is P e =90kW, daily power generation of wind turbines during continuous rainy periods:

[0250] Q 1r =P1×T 1r ×m = 90 × (6.6 / 10) × 20 × 0.9 = 1069 kWh; (6.6 is the wind speed during rainy days converted according to height)

[0251] According to formula ③, the energy storage battery capacity configuration is: (1069-421x2)kWh / 0.95≈240kWh.

[0252] Taking the above two boundary conditions into consideration, the energy storage battery capacity is configured according to condition ②, and the value is 240kWh (this value is the sum of the equipment outside the two tunnels, and 120kWh is allocated to each tunnel).

[0253] If the proportion of wind and solar power generation is low (such as 30% in the previous article), the difference between the maximum daily power generation and the minimum daily power consumption may be less than the 2h daily peak value of the DC load. At this time, the energy storage battery capacity should be configured according to condition ①.

[0254] 4. Economic benefit estimation

[0255] The power configuration of photovoltaic and wind power generation equipment needs to consider economic indicators. According to the current statistical data of the photovoltaic and wind power generation industries, the investment in photovoltaic and wind power generation is approximately RMB 8,000 / kW; the investment in lithium batteries is approximately RMB 1,000 / kWh; the effective service life of photovoltaic and wind power generation is approximately 25 years; the effective service life of lithium batteries is approximately 5 years; the configuration of wind, light and storage equipment should consider recovering costs by saving electricity within half of the service life, and the remaining half of the equipment life is the energy-saving benefit period.

[0256] ① When wind and solar power generation accounts for 30% of the total electricity consumption, the wind turbine power P e =30kW, the peak power of the photovoltaic equipment used P2 = 18kW, the lithium battery capacity C = 110kWh. Total investment: (30+18)×0.8+110×0.1×(25 / 5)=934,000 yuan. Annual energy saving is about 120,000kWh, equivalent to about 60,000 yuan. It takes about 16 years to recover the cost.

[0257] ② When wind and solar power generation accounts for 40% of the total electricity consumption, the power of the wind turbine equipment used is P e =40kW, the peak power of the photovoltaic equipment used P2 = 24kW, the lithium battery capacity C = 110kWh. Total investment: (40+24)×0.8+110×0.1×(25 / 5)=1.062 million yuan. Annual energy saving is about 160,000 kWh, equivalent to about 80,000 yuan. It takes about 14 years to recover the cost.

[0258] ③ When wind and solar power generation accounts for 50% of the total electricity consumption, the power of the wind turbine equipment used is P e =50kW, the peak power of the photovoltaic equipment used P2 = 30kW, the lithium battery capacity C = 110kWh. Total investment: (50+30)×0.8+110×0.1×(25 / 5)=1.19 million yuan. Annual energy saving is about 200,000kWh, equivalent to about 100,000 yuan. It takes about 12 years to recover the cost.

[0259] In summary, for this case, when wind and solar power generation accounts for 50% of the total electricity consumption, the cost can be recovered by saving electricity within half of the service life of the wind, solar and storage equipment, which has good economic benefits.

[0260] Wind, solar and storage system engineering design process Fig.10 .

[0261] The above are preferred embodiments of the present invention. Any changes made according to the technical solution of the present invention, as long as the resulting functions do not exceed the scope of the technical solution of the present invention, belong to the protection scope of the present invention.

Claims

1. Traffic tunnel hybrid energy DC microgrid, characterized by: It includes multiple sections of DC bus, energy storage battery, distributed power supply, emergency mobile power supply and local DC load; the multiple sections of DC bus are connected to the energy storage battery, and the multiple sections of DC bus include DC bus I arranged in the center of the tunnel, DC bus II arranged at the entrance of the tunnel, and DC bus III arranged at the exit of the tunnel; the DC bus I is connected to the mains power supply through a unidirectional AC / DC converter, the DC bus II and DC bus III are connected to the distributed power supply and the emergency mobile power supply, the DC bus I is respectively connected to the DC bus II and the DC bus III through a bidirectional DC / DC converter to realize the power transmission between different DC buses; the local DC load includes the basic tunnel lighting, facility electro-optical signs, traffic lights, monitoring equipment power supplied by the DC bus I and the tunnel enhanced lighting supplied by the DC bus II and the DC bus III.

2. The hybrid energy DC microgrid for a traffic tunnel according to claim 1 is characterized in that: The number of the DC busbars I is set according to the power supply radius of the DC busbar I and the length of the tunnel to achieve power supply of evenly distributed DC loads in the tunnel.

3. The hybrid energy DC microgrid for a traffic tunnel according to claim 1 is characterized in that: The distributed power source includes photovoltaic power generation and wind power generation, and the emergency mobile power source includes mobile diesel power generation.

4. The hybrid energy DC microgrid for a traffic tunnel according to claim 1 is characterized in that: The operation control of the DC microgrid adopts a three-layer hierarchical mode: the first layer of control adopts droop control, and a plurality of control units participating in the DC bus voltage control jointly maintain the DC bus voltage stability; the second layer of control is implemented by an industrial computer to realize the secondary regulation of the DC bus voltage, the power distribution of each control unit, and the switching of the DC bus operation mode; the third layer of control is implemented by a computer in a tunnel control center to realize the energy scheduling between different DC buses, and by formulating a DC microgrid operation scheduling strategy, the flexible scheduling of the mains power supply, distributed power supply, energy storage battery, and DC load is realized to ensure the safe and economical operation of the system.

5. The hybrid energy DC microgrid for a traffic tunnel according to claim 4 is characterized in that: In the first layer of control, the control unit involved in the DC bus voltage control includes a unidirectional AC / DC converter, a bidirectional DC / DC converter, a distributed power supply controller, and an energy storage unit controller; the droop control is to control the voltage and current of the converter or controller to run on a droop curve, and the droop curve expression is as follows: U d =U0-k×I Where U d is the output voltage of the converter or controller; U0 is the set value of the DC bus voltage; k is the droop curve coefficient; I is the output current of the converter or controller.

6. The hybrid energy DC microgrid for a traffic tunnel according to claim 5 is characterized in that: In the second-level control, the DC bus voltage secondary regulation and the power distribution of each control unit are specifically as follows: a hybrid compensation method is adopted to simultaneously compensate the DC bus voltage setting value U0 and the coefficient k of the droop curve, and the information of each control unit, including voltage, current and droop curve coefficient, is obtained by means of industrial computer bus communication, and the droop curve coefficient compensation amount Δk and the longitudinal intercept compensation amount ΔU are obtained by using the average voltage compensator, the average current compensator and the curve coefficient compensator, and then the droop curve is translated and the coefficient is adjusted respectively; wherein, the average voltage compensator eliminates the output DC voltage deviation of each unit by translating the curve, and the average current compensator and the curve coefficient compensator achieve rapid load distribution by adjusting the coefficient of the droop curve; The switching of the DC bus operation mode is specifically as follows: three operation modes are set for DC bus I, II, and III respectively, and the DC bus operation mode is switched according to the difference between the input power supply of the DC bus and the DC load; wherein the input power of the DC bus is controlled by setting the voltage control point U H \U M \U L And the DC bus voltage setting value U0, and the input power supply priority is distributed power supply > energy storage battery > mains power.

7. The hybrid energy DC microgrid in a traffic tunnel according to claim 6 is characterized in that: The DC buses I, II and III are respectively configured with three operation modes: DC bus I operation mode: Operation mode 1: DC bus II and III have surplus power, and the DC bus I input power includes AC power, energy storage batteries and distributed power supply; the DC bus I load is the basic lighting of the tunnel, facility electro-optical signs, traffic lights, and monitoring equipment; U DCI Indicates the DC bus I voltage value; U DCI >U H :The DC bus voltage is too high, the energy storage battery reaches the upper limit and cannot continue to charge. The power generation system as a distributed power source abandons energy and operates in constant voltage mode to maintain voltage stability; U H >U DCI >U M :The power generated by the power generation system is greater than the power consumed by the DC load and there is a surplus, and the energy storage battery works in constant current charging mode; the power generation system is in droop control to maintain the stability of the DC bus voltage; U M >U DCI >U L :The power generated by the power generation system is not enough to provide the power consumed by the DC load. In order to maximize the use of renewable energy, the power generation system always works in the maximum power tracking mode. In order to maintain the stability of the bus voltage, the energy storage battery is discharged and works in the droop control state; U L >U DCI >U O :The sum of the power generated by the power generation system and the power provided by the energy storage battery is less than the power consumed by the AC and DC loads. The power generation system works in MPPT mode, the energy storage battery is discharged, and the mains power supply is in a droop control state to maintain the stability of the DC bus voltage; Operation mode 2: DC bus II and III are short of power, and the DC bus I input power includes AC power and energy storage batteries; the DC bus I loads include basic tunnel lighting, facility electro-optical signs, traffic lights, monitoring equipment power, and DC bus II and III loads; Operation mode 3: When the mains fails, the DC bus I input power source includes energy storage batteries, distributed power sources and emergency mobile power sources; the DC bus I load is the emergency lighting and facility electro-optical signs in the basic tunnel lighting; U DCI >U H :The DC bus voltage is too high, the energy storage battery reaches the upper limit and cannot continue to charge, the power generation system abandons energy and operates in constant voltage mode to maintain voltage stability; U H >U DCI >U M :The power generated by the power generation system is greater than the power consumed by the DC load and there is a surplus. The energy storage battery works in constant current charging mode, and the power generation system is in droop control to maintain the stability of the DC bus voltage; U M >U DCI >U L :The power generated by the power generation system is not enough to provide the power consumed by the DC load. In order to maximize the use of renewable energy, the power generation system always works in the maximum power tracking mode. In order to maintain the stability of the bus voltage, the energy storage battery is discharged and works in the droop control state; U L >U DCI >U O : The sum of the power generated by the power generation system and the power provided by the energy storage battery is less than the power consumed by the DC load. The power generation system works in MPPT mode, the energy storage battery is discharged, and the DC bus II and III are connected to the emergency mobile power supply to supplement the power; DC bus II / III operation mode: Operation mode 1: During the day, the DC bus II / DC bus III input power source includes distributed power supply, energy storage battery and AC power supply; the DC bus II / DC bus III load is tunnel enhanced lighting; U DC Indicates the DC bus II voltage value or DC bus III voltage value; U DC >U H :The DC bus voltage is too high, the energy storage battery reaches the upper limit and cannot continue to charge, the power generation system abandons energy and operates in constant voltage mode to maintain voltage stability; U H >U DC >U M :The power generated by the power generation system is greater than the power consumed by the DC load and there is a surplus. The energy storage battery works in constant current charging mode, and the power generation system is in droop control to maintain the stability of the DC bus voltage; U M >U DC >U L :The power generated by the power generation system is not enough to provide the power consumed by the DC load. In order to maximize the use of renewable energy, the power generation system always works in the maximum power tracking mode. At this time, in order to maintain the stability of the bus voltage, the energy storage battery is discharged and works in the droop control state; U L >U DC >U O :The sum of the power generated by the power generation system and the power provided by the energy storage battery is less than the power consumed by the AC and DC loads. The power generation system works in MPPT mode, the energy storage battery is discharged, and the mains power supply is in a droop control state to maintain the stability of the DC bus voltage; Operation mode 2: During daytime, the DC bus II / DC bus III input power source includes distributed power supply and energy storage battery; the DC bus II / DC bus III load is tunnel enhanced lighting and DC bus I load; U DC >U H :The DC bus voltage is too high, the energy storage battery reaches the upper limit and cannot continue to charge, the power generation system abandons energy and operates in constant voltage mode to maintain voltage stability; U H >U DC >U M :The power generated by the power generation system is greater than the power consumed by the DC load and there is a surplus. The energy storage battery works in constant current charging mode, and the power generation system is in droop control to maintain the stability of the DC bus voltage; U M >U DC >U L :The power generated by the power generation system is not enough to provide the power consumed by the DC load. In order to maximize the use of renewable energy, the power generation system always works in the maximum power tracking mode. In order to maintain the stability of the bus voltage, the energy storage battery is discharged and works in the droop control state; Operation mode 3: At night, the DC bus II / DC bus III input power includes distributed power supply and energy storage battery; the DC bus II / DC bus III load is the DC bus I load; U DC >U H :The DC bus voltage is too high, the energy storage battery reaches the upper limit and cannot continue to charge, the power generation system needs to abandon energy and operate. To maintain voltage stability, the power generation system operates in constant voltage mode; U H >U DC >U M :The power generated by the power generation system is greater than the power consumed by the DC load and there is a surplus. The energy storage battery works in constant current charging mode, and the power generation system is in droop control to maintain the stability of the DC bus voltage; U M >U DC >U L :The power generated by the power generation system is not enough to provide the power consumed by the DC load. In order to maximize the use of renewable energy, the power generation system always operates in the maximum power tracking mode. In order to maintain the stability of the bus voltage, the energy storage battery is discharged and operates in the droop control state.

8. The hybrid energy DC microgrid for a traffic tunnel according to claim 7 is characterized in that: The DC microgrid operation dispatching strategy in the third layer of control includes two dispatching schemes, specifically: Scheduling plan 1: In non-emergency situations, the output power of the basic lighting in the tunnel is adjusted within the range of 50% to 100%, and the output power of the enhanced lighting in the tunnel is adjusted within the range of 15% to 100%. Traffic lights, electro-optical signs, and monitoring equipment operate at full power around the clock. The time T1 when night turns to daytime and the time T2 when day turns to nighttime are set according to the longitude and latitude, and the current time is judged according to the preset time intervals of T1 and T2 to determine whether it is daytime or nighttime. If it is daytime, the power consumption Q1 of DC bus II / DC bus III and the power generation Q2 of distributed generation are predicted according to the statistical hourly traffic volume and the weather forecast results. If Q1 is less than Q2 and the energy storage of DC bus II / DC bus III is sufficient, DC bus II / DC bus III supplies power to DC bus I, and DC bus I operates in mode 1, and DC bus II / DC bus III operates in mode 2. If the energy storage of DC bus II / DC bus III is insufficient or Q1 is greater than or equal to Q2, DC bus I supplies power to DC bus II / DC bus III, and DC bus I operates in mode 2, and DC bus II / DC bus III operates in mode 1. If it is night time, DC bus II / DC bus III supplies power to DC bus I, DC bus I operates in mode 1, and DC bus II / DC bus III operates in mode 3; Scheduling plan 2: In an emergency, if the city power fails or the AC system fails, the distributed power supply and emergency mobile power supply will be used to supply power, and some DC loads will be cut off, leaving only the emergency lighting and facility electro-optical signs in the basic lighting; the power consumption Q'1 of the DC bus I and the power generation Q'2 of the distributed power supply will be predicted; the time T1 when night turns to daytime and the time T2 when day turns to nighttime will be set according to the longitude and latitude, and it will be determined whether it is daytime or nighttime according to the preset time interval based on T1 and T2; If it is daytime, DC bus II / DC bus III supplies power to DC bus I, DC bus I operates in mode 3, and DC bus II / DC bus III operates in mode 2. On this basis, it is determined whether the following conditions are met: Q'1 is greater than Q'2 and the DC bus I voltage U DCI Less than U L , if the conditions are met, connect to the emergency mobile power supply, otherwise return; If it is night time, DC bus II / DC bus III supplies power to DC bus I, DC bus I operates in mode 3, and DC bus II / DC bus III operates in mode 3. On this basis, it is determined whether the following conditions are met: Q'1 is greater than Q'2 and U DCI Less than U L If the conditions are met, connect to the emergency mobile power supply, otherwise return.

9. The hybrid energy DC microgrid for a traffic tunnel according to claim 1, characterized in that: The electric shock protection design of the DC microgrid includes: setting 400mA as the upper limit of the human contact current that may be expected in the low-voltage DC system; the low-voltage DC adopts the IT power grounding system to achieve 30mA leakage protection and insulation monitoring dual protection; the DC bus voltage is selected by using the enumeration comparison method, combined with the actual length of the tunnel and the load power, and the line cable cross-sectional area at different DC voltages is calculated respectively, and the DC voltage corresponding to the minimum cross-sectional area is selected as the selected DC bus voltage. The different DC voltages include DC375V, DC220V, and DC110V. The calculation of the line cable cross-sectional area of ​​each DC voltage is specifically as follows: Calculate the DC load line current: Among them, I js Calculate the current for the DC load line, P e1 , P e2 , P e3 is the power of a single DC device within the set length range, and U is a DC voltage tentatively determined by the enumeration method; According to I js ≥1.1×I N Determine the rated current I of the miniature circuit breaker N value, and according to I L ≥1.1×I N Determine the cable current carrying capacity I L value; Calculate the cross-sectional area: S”≥(P×l)÷(5×γ×U 2 ×0.001×5%) Where P is the total power of the line, l is the equivalent power supply distance of the line; S” is the calculated value of the cable cross-sectional area, and γ is the conductivity of the cable conductor at 50°C; According to the cable current carrying capacity I L The corresponding cable cross-sectional area is determined by the value, recorded as the cable cross-sectional area query value S', and the cable cross-sectional area query value S' is compared with the cable cross-sectional area calculation value S", and the larger value is taken as the cable cross-sectional area S to be checked for sensitivity verification: k T =1+a×(θ-20) Sensitivity Where ρ is the cable conductor resistivity at 20°C, L is the line cable length, k T is the resistance temperature conversion coefficient, a is the resistance temperature coefficient, θ is the actual working temperature of the conductor, I d It is the single-phase short-circuit current at the farthest end of the line; Judgment sensitivity L m Is it greater than or equal to 1? If so, the cable cross-sectional area S to be checked is used as the line cable cross-sectional area of ​​the DC voltage. Otherwise, a larger cable core nominal cross-sectional area is selected and the sensitivity check is performed again.

10. The hybrid energy DC microgrid in a traffic tunnel according to claim 3, characterized in that: The design of wind, solar and storage system equipment power and capacity is as follows: Obtain the annual average wind speed, annual statistical duration of effective wind speed, solar radiation, annual statistical duration of peak sunshine, and annual power consumption Q of DC load at the location of the traffic tunnel n , DC load power consumption daily peak value Q rF , DC load power consumption daily valley value Q rG ; Determine whether the annual average wind speed is greater than 3m / s to determine whether wind energy is available, and determine whether the daily average radiation is greater than 3.3kWh / m 2 To determine whether solar energy is available, set the available distributed energy generation ratio k, the initial value of k is 30%, and calculate the ratio of the annual statistical duration of effective wind speed to the annual statistical duration of peak sunshine, A:B. Calculate the wind power generation allocation value Q a =Q n ×k×A / (A+B), according to the formula Q for calculating the average annual power generation of wind turbines 1n =P1×T 1n ×m calculate the output power P1 of the wind turbine at rated wind speed, where Q 1n is the annual power generation of the wind turbine, T 1n is the effective wind speed annual statistical duration, m is the coefficient considering losses; then the equipment power P of the wind turbine is calculated according to the following formula e P1=P e ×(average wind speed in the highly calibrated wind speed segment / rated wind speed) 3 ; Calculate the photovoltaic power generation allocation value Q b =Q n ×k×B / (A+B), according to the annual average power generation of photovoltaic generators, the formula Q 2n =P2×T 2n ×m calculate the rated power P2 of the solar cell array, where Q 2n is the annual power generation of the solar cell array, T 2n is the annual statistical duration of peak sunshine, and m is the coefficient considering loss; Calculate the difference between the maximum daily power generation and the minimum daily power consumption as well as the 2h daily peak value of the DC load, and take the larger value as the required energy storage battery capacity Q js , substitute into the formula energy storage battery capacity calculation formula Q C =Q js / (m c ×n c ) Calculate the energy storage battery capacity Q C , where m c is the efficiency of the energy storage battery, n c is the discharge depth of the energy storage battery; Calculate the total investment in wind, solar, and energy storage, as well as the annual energy savings, and combine the service life of the power generation equipment and energy storage batteries to determine whether the cost can be recovered within the half-life cycle. If so, the equipment power P of the wind turbine calculated under the previous coefficient is e , the rated power of the solar cell array P2 and the energy storage battery capacity Q C As the designed wind-solar-storage system equipment power and capacity, otherwise the coefficient k is increased by 10% and the equipment power P of the wind turbine generator is recalculated. e , the rated power of the solar cell array P2 and the energy storage battery capacity Q C .

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