CN119093308A

CN119093308A - Hybrid Energy DC Microgrid in Traffic Tunnel

Info

Publication number: CN119093308A
Application number: CN202411155241.3A
Authority: CN
Inventors: 王晓喜
Original assignee: Fuzhou Planning And Design Institute Group Co ltd
Current assignee: Fuzhou Planning And Design Institute Group Co ltd
Priority date: 2024-08-22
Filing date: 2024-08-22
Publication date: 2024-12-06

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, wherein the plurality of sections of direct-current buses are connected with the energy storage battery and comprise a direct-current bus I arranged in the center of a tunnel, a direct-current bus II arranged at an inlet of the tunnel and a direct-current bus III arranged at an outlet of the tunnel, the direct-current bus I is connected with a mains supply through a unidirectional AC/DC converter, the direct-current buses II and III are connected with the distributed power supply and the emergency mobile power supply, and the direct-current buses I are respectively connected with the direct-current buses II and III through a bidirectional DC/DC converter. The invention can greatly reduce the third harmonic existing in the system, improve the electric energy quality of the system, obviously reduce the use amount of copper consumption materials, simplify the equipment composition of the system, and realize the energy conservation and emission reduction by the open system plug and play, thereby providing convenience for the access of various new energy power generation and utilizing renewable energy power generation sources as much as possible.

Description

Traffic tunnel hybrid energy direct-current micro-grid

Technical Field

The invention relates to the technical field of micro-grids, in particular to a traffic tunnel hybrid energy direct-current micro-grid.

Background

The low-voltage electricity loads of the traffic tunnel comprise fire-fighting loads and non-fire-fighting loads, wherein the average annual total electricity consumption of the non-fire-fighting loads accounts for more than 80% of the annual total electricity consumption of the tunnel, and the low-voltage electricity loads comprise illumination, monitoring, traffic signals and electro-optical marks. The low-voltage power distribution of the tunnel non-fire-fighting direct-current load is generally that a plurality of AC380V power distribution loops are distributed to distribution power cabinets of tunnel lighting, traffic signals, electro-optical identifiers and monitoring equipment by a tunnel non-fire-fighting dual-power supply switching cabinet, and then the AC220V power distribution loops are distributed to the load by the distribution power cabinets. Because the tunnel illumination, traffic signals, electro-optical identification and monitoring equipment are all direct current loads, each equipment needs to be provided with single-phase rectification (AC/DC) equipment at the tail end.

However, due to the adoption of the low-voltage alternating current power supply, an AC/DC single-phase rectifying circuit is required to be configured for direct current loads, so that the third harmonic problem is outstanding, three-phase imbalance exists, the electric energy quality problem is outstanding, in addition, the loss of a distribution line is large (including reactive loss and active loss) due to the influence of the third harmonic, the loss of power of about 15% is generated due to the fact that a driving power supply at the tail end of the direct current equipment comprises single-phase rectifying filtering, meanwhile, the loss of the distribution line is large, the section of a copper core cable is large, the copper consumption material is high, abundant renewable energy sources including wind energy, photovoltaic and mechanical energy exist outside a traffic tunnel hole, and the conventional low-voltage alternating current system cannot meet the convenient access of various new energy power generation. Important loads (standby lighting, electro-optical identification and monitoring) in non-fire loads are respectively provided with EPS or UPS as emergency power sources according to different load types, and more energy storage devices are provided.

In view of the above, the invention provides a traffic tunnel hybrid energy direct current micro-grid.

Disclosure of Invention

The invention aims to provide a traffic tunnel hybrid energy direct current micro-grid, which adopts low-voltage direct current distribution, intensively sets three-phase full-wave rectification, a tunnel non-fire-protection direct current load no longer comprises a single-phase rectifying circuit, greatly reduces third harmonic existing in a system, eliminates three-phase unbalance, improves the power quality of the system, thoroughly eliminates reactive power loss of lines and equipment, greatly reduces the influence of the third harmonic, greatly reduces the loss of a distribution line, obviously reduces the power loss of single equipment, reduces the cross section of a copper core cable for direct current load distribution by about 50 percent compared with the prior art due to the outstanding power transmission capacity of the direct current system, obviously reduces the using amount of copper consumption, and simplifies the equipment composition of the system by intensively setting an energy storage battery as an emergency power source of an important load.

The technical scheme includes that the traffic tunnel hybrid energy direct-current micro-grid 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, wherein the sections of direct-current buses are connected with the energy storage battery and comprise a direct-current bus I arranged in the center of a tunnel, a direct-current bus II arranged at an entrance of the tunnel and a direct-current bus III arranged at an exit of the tunnel, the direct-current bus I is connected with a mains supply through a unidirectional AC/DC converter, the direct-current buses II and the direct-current bus III are connected with the distributed power supply and the emergency mobile power supply, the direct-current buses I are respectively connected with the direct-current buses II and the direct-current bus III through bidirectional DC/DC converters so as to realize electric energy transmission among different direct-current buses, and the bidirectional DC/DC converters adopt high-frequency isolation bidirectional DC/DC converters. The local direct current load comprises tunnel basic lighting powered by a direct current bus I, facility electro-optical identification, traffic signal lamps, monitoring equipment electricity consumption and tunnel enhanced lighting powered by a current bus II and a direct current bus III.

Preferably, the number of the direct current buses I is set according to the power supply radius of the direct current buses I and the tunnel length so as to realize power supply of uniformly distributed direct current loads in the tunnel.

Preferably, the distributed power source comprises photovoltaic power generation and wind power generation, and the emergency mobile power source comprises mobile diesel power generation.

The operation control of the direct current micro-grid adopts a three-layer grading mode, wherein the first-layer control adopts droop control, the voltage stability of the direct current bus is commonly maintained through a plurality of control units participating in the voltage control of the direct current bus, the second-layer control realizes secondary adjustment of the voltage of the direct current bus, power distribution of each control unit and switching of the operation mode of the direct current bus by an industrial personal computer, the third-layer control realizes energy scheduling among different direct current buses by a computer in a tunnel control center, and flexible scheduling of a mains supply, a distributed power supply, an energy storage battery and a direct current load is realized by formulating a direct current micro-grid operation scheduling strategy so as to ensure safe and economic operation of the system.

Preferably, in the first-layer control, the control unit participating in the voltage control of the direct current bus includes a unidirectional AC/DC converter, a bidirectional DC/DC converter, a distributed power controller, and an energy storage unit controller, where droop control is to control the voltage and current of the converter or the controller to run on a lower whip line, and the droop curve expression is as follows:

U_d＝U₀-k×I

Wherein U _d is the output voltage of the converter or the controller, U ₀ is the set value of the DC bus voltage, k is the coefficient of the sagging curve, and I is the output current of the converter or the controller.

Preferably, in the second layer control,

The method comprises the steps of adopting a hybrid compensation mode, compensating a direct current bus voltage set value U ₀ and a coefficient k of a sagging curve, obtaining information of each control unit through an industrial personal computer bus communication mode, comprising voltage, current and sagging curve coefficients, and obtaining sagging curve coefficient compensation quantity delta k and longitudinal intercept compensation quantity delta U through an average voltage compensator, an average current compensator and a curve coefficient compensator, and respectively carrying out translation and coefficient adjustment on the sagging curve, wherein the average voltage compensator eliminates output direct current voltage deviation of each unit through a translation curve, and the average current compensator and the curve coefficient compensator realize rapid load distribution through adjusting the coefficient of the sagging curve;

The switching of the DC bus operation modes comprises setting three operation modes respectively for a DC bus I, a DC bus II and a DC bus III, and switching the DC bus operation modes according to the difference between the input power source and the DC load of the DC bus, wherein the input power source of the DC bus is determined by setting a voltage control point U _H\U_M\U_L and a DC bus voltage set value U ₀, and the power supply priority of the input power source is distributed power source > energy storage battery > mains supply.

Preferably, the three operation modes of the direct current buses I, II and III are respectively set as follows,

DC bus I operation mode:

The system comprises a first operation mode, a second operation mode and a third operation mode, wherein the electric energy of a direct current bus II and a direct current bus III is surplus, and an input power supply of the direct current bus I comprises a mains supply, an energy storage battery and a distributed power supply;

U _DCI＞U_H, wherein the voltage of a direct current bus is higher, an energy storage battery reaches the upper limit and cannot be charged continuously, the power generation system serving as a distributed power supply can not operate, and the power generation system works in a constant voltage mode for maintaining stable voltage;

u _H＞U_DCI＞U_M, wherein the power generated by the power generation system is larger than the power consumed by the direct current load and has surplus energy, and the energy storage battery works in a constant current charging mode;

U _M＞U_DCI＞U_L, the power generated by the power generation system is insufficient to provide power consumed by the direct current load, in order to utilize renewable energy sources to the maximum extent, the power generation system always works in a maximum power tracking mode, and in order to maintain the stability of bus voltage, the energy storage battery discharges and works in a sagging control state;

U _L＞U_DCI＞U_O, wherein the sum of the power generated by the power generation system and the power provided by the energy storage battery is smaller than the power consumed by the AC/DC load, the power generation system works in an MPPT mode, the energy storage battery discharges, the mains supply is in a sagging control state, and the voltage stability of a DC bus is maintained;

the DC bus I is used for tunnel basic lighting, facility electro-optical identification, traffic signal lamps, monitoring equipment power consumption and DC bus II and III loads;

the system comprises a third operation mode, a third operation mode and a fourth operation mode, wherein the mains supply fault, the input power of a direct current bus I comprises an energy storage battery, a distributed power supply and an emergency mobile power supply, and the load of the direct current bus I is an emergency lighting and facility electro-optic mark in tunnel basic lighting;

U _DCI＞U_H, the direct current bus voltage is higher, the energy storage battery reaches the upper limit and can not be charged continuously, the power generation system can not run, and in order to maintain the voltage stable, the power generation system works in a constant voltage mode;

U _H＞U_DCI＞U_M, wherein the power generated by the power generation system is larger than the power consumed by the direct current load and has surplus energy, the energy storage battery works in a constant current charging mode, the power generation system is under droop control, and the voltage stability of the direct current bus is maintained;

U _L＞U_DCI＞U_O, wherein the sum of the power generated by the power generation system and the power provided by the energy storage battery is smaller than the power consumed by the direct current load, the power generation system works in an MPPT mode, the energy storage battery discharges, and the direct current buses II and III are connected into an emergency mobile power supply to supplement electric energy;

DC bus II/III mode of operation:

under the daytime condition, the direct current bus II/direct current bus III input power supply comprises a distributed power supply, an energy storage battery and a mains supply, wherein a direct current bus II/direct current bus III load is tunnel enhanced illumination, and U _DC represents a direct current bus II voltage value or a direct current bus III voltage value;

u _DC＞U_H, the direct current bus voltage is higher, the energy storage battery reaches the upper limit and can not be charged continuously, the power generation system can not run, and in order to maintain the voltage stable, the power generation system works in a constant voltage mode;

u _H＞U_DC＞U_M, wherein the power generated by the power generation system is larger than the power consumed by the direct current load and has surplus energy, the energy storage battery works in a constant current charging mode, the power generation system is under droop control, and the voltage stability of the direct current bus is maintained;

U _M＞U_DC＞U_L, wherein the power generated by the power generation system is insufficient to provide power consumed by the direct current load, so that the power generation system always works in a maximum power tracking mode to furthest utilize renewable energy, and at the moment, in order to maintain the stability of bus voltage, the energy storage battery discharges and works in a sagging control state;

U _L＞U_DC＞U_O, wherein the sum of the power generated by the power generation system and the power provided by the energy storage battery is smaller than the power consumed by the AC/DC load, the power generation system works in an MPPT mode, the energy storage battery discharges, the mains supply is in a sagging control state, and the voltage stability of a DC bus is maintained;

In the second operation mode, under the daytime condition, the direct current bus II/direct current bus III input power supply comprises a distributed power supply and an energy storage battery, wherein the direct current bus II/direct current bus III load is a tunnel enhanced illumination and direct current bus I load;

U _M＞U_DC＞U_L, the power generated by the power generation system is insufficient to provide power consumed by the direct current load, in order to utilize renewable energy sources to the maximum extent, the power generation system always works in a maximum power tracking mode, and in order to maintain the stability of bus voltage, the energy storage battery discharges and works in a sagging control state;

the third operation mode is that under the condition of night, the input power supply of the direct current bus II/the direct current bus III comprises a distributed power supply and an energy storage battery, and the load of the direct current bus II/the direct current bus III is the load of the direct current bus I;

u _DC＞U_H, wherein the voltage of the direct current bus is higher, the energy storage battery reaches the upper limit and cannot be charged continuously, the power generation system needs to be abandoned and operated, and the power generation system works in a constant voltage mode in order to maintain the voltage stable;

And U _M＞U_DC＞U_L, wherein the power generated by the power generation system is insufficient to provide power consumed by the direct current load, the power generation system always works in a maximum power tracking mode to furthest utilize renewable energy, and the energy storage battery discharges to maintain the stability of bus voltage and works in a sagging control state.

Preferably, the dc micro-grid operation scheduling policy in the third layer control includes two scheduling schemes, specifically:

scheduling scheme one:

Under the non-emergency condition, the basic illumination output power adjustment range of the tunnel is 50% -100%, the enhanced illumination output power adjustment range of the tunnel is 15% -100%, and the traffic signal lamp, the electro-optical sign and the monitoring equipment run at all weather full power;

If the current day time is the day time, the electricity consumption Q1 of the direct current bus II/the direct current bus III and the electricity generation Q2 of the distributed power supply are predicted according to the time period where the traffic volume of the statistical hour and the weather prediction result are located, if the Q1 is smaller than the Q2 and the energy storage of the direct current bus II/the direct current bus III is sufficient, the direct current bus II/the direct current bus III supplies power to the direct current bus I, and the direct current bus I operates in a first mode and the direct current bus II/the direct current bus III operates in a second mode;

If the current night time is the current night time, the direct current bus II/the direct current bus III supplies power to the direct current bus I, the direct current bus I operates in a first mode, and the direct current bus II/the direct current bus III operates in a third mode;

Scheduling scheme II:

Under emergency, the utility power is lost or an alternating current system fails, the distributed power supply and the emergency mobile power supply are used for supplying power, partial direct current load is cut off, only the emergency lighting in basic lighting and the facility electro-optical identification are reserved, the power consumption Q '1 of the direct current bus I and the power generation Q'2 of the distributed power supply are predicted, the night entering daytime time T ₁ and the night entering nighttime time T ₂ are set according to longitude and latitude, and the current daytime time or the night time is judged according to the preset time interval according to T ₁ and T ₂;

If the current time is daytime, the direct current bus II/the direct current bus III supplies power to the direct current bus I, the direct current bus I operates in a mode III, and the direct current bus II/the direct current bus III operates in a mode II;

If the night time is currently, the direct current bus II/the direct current bus III supplies power to the direct current bus I, the direct current bus I operates in a mode III, the direct current bus II/the direct current bus III operates in a mode III, whether the condition is met or not is judged on the basis that Q '1 is larger than Q'2 and U _DCI is smaller than U _L, if the condition is met, an emergency mobile power supply is connected, and otherwise, the emergency mobile power supply returns.

The electric shock protection design of the direct current micro-grid comprises the steps of setting 400mA as the upper limit of human body contact current which possibly occurs in a low-voltage direct current system, adopting an IT power supply grounding system for low-voltage direct current to realize double protection of 30mA leakage protection and insulation monitoring, adopting an enumeration comparison method for selecting direct current bus voltage, combining the actual length of a tunnel and load power, respectively calculating the sectional areas of line cables when different direct current voltages are adopted, selecting the direct current voltage corresponding to the minimum sectional area as the selected direct current bus voltage, wherein the different direct current voltages comprise DC375V, DC220,220, 220V, DC110V, and the calculation of the sectional area of the line cable of each direct current voltage is specifically as follows:

Calculating direct current load line current:

Wherein, I _js is the current calculated by the DC load circuit, P _e1、P_e2、P_e3 is the power of a single DC device within a set length range, U is a certain temporary DC voltage by an enumeration method;

Determining a rated current I _N value of the miniature circuit breaker according to I _js≥1.1×I_N, and determining a cable current-carrying capacity I _L value according to I _L≥1.1×I_N;

Calculating the sectional area:

S”≥(P×l)÷(5×γ×U²×0.001×5%)

Wherein 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 sectional area of the cable, the conductivity of the cable conductor when gamma is 50 ℃, and U' is the nominal voltage;

The corresponding cable sectional area is determined according to the current-carrying capacity I _L value of the cable and is recorded as a cable sectional area inquiry value S ', the cable sectional area inquiry value S ' is compared with a cable sectional area calculation value S ', and a large value is taken as the cable sectional area S to be checked to carry out sensitivity check:

k_T=1+a×(θ-20)

Sensitivity of

Wherein, rho is the resistivity of the cable conductor at 20 ℃, L is the length of the line cable, k _T is the temperature conversion coefficient of resistance, a is the temperature coefficient of resistance, θ is the actual working temperature of the lead, and I _d is the most-far-end single-phase short-circuit current of the line;

Judging whether the sensitivity L _m is greater than or equal to 1, if so, taking the cross section S of the cable to be checked as the cross section of the line cable of the direct-current voltage, otherwise, selecting a larger-level cable core nominal cross section, and then performing sensitivity check again.

Preferably, the design of the power and the capacity of the wind-solar energy storage system equipment is as follows:

Obtaining the annual average wind speed, the effective wind speed annual statistical time length, the solar energy radiation quantity and the peak sunshine annual statistical time length of a traffic tunnel, obtaining the annual power consumption Q _n of a direct current load, the daily peak power consumption Q _rF of the direct current load and the daily valley value Q _rG of the direct current load, judging whether the annual average wind speed is greater than 3m/s to determine whether wind energy is available, judging whether the daily average radiation quantity is greater than 3.3kWh/m ² to determine whether solar energy is available, setting the available distributed energy power generation proportion k, setting the initial value of k to be 30 percent, calculating the ratio A to B of the effective wind speed annual statistical time length and the peak sunshine annual statistical time length,

Calculating a wind power generation amount distribution value Q _a＝Q_n x k x A/(A+B), and calculating the output power P ₁ of the rated wind speed of the wind power generator according to an annual average power generation amount calculation formula Q _1n＝P₁×T_1n x m of the wind power generator, wherein Q _1n is the annual power generation amount of the wind power generator, T _1n is the annual statistical time length of the effective wind speed, and m is the coefficient considering loss, and calculating the equipment power P of the wind power generator according to the following formula _e

P ₁＝P_e × (highly verified wind speed segment average wind speed/rated wind speed) ³;

Calculating a photovoltaic power generation amount distribution value Q _b＝Q_n xk x B/(A+B), and calculating a solar cell matrix rated power P ₂ according to a photovoltaic power generator annual average power generation amount calculation formula Q _2n＝P₂×T_2n xm, wherein the annual power generation amount of the solar cell matrix Q _2n, T _2n is peak sunshine annual statistical duration, and m is a coefficient considering loss;

Calculating a difference value between the maximum daily power generation amount and the minimum daily power consumption amount and a 2-hour daily peak value of the direct current load, taking a larger value of the difference value and the maximum daily power generation amount as a required energy storage battery capacity Q _js, substituting the larger value into a formula energy storage battery capacity calculation formula Q _C＝Q_js/(m_c×n_c) to calculate the energy storage battery capacity Q _C, wherein m _c is the efficiency of the energy storage battery, and n _c is the depth of discharge of the energy storage battery;

And (3) calculating wind, light, total investment and annual energy conservation, judging whether the cost is recovered in a service life half period by combining the service lives of the power generation equipment and the energy storage battery, if so, using the equipment power P _e of the wind power generator, the rated power P ₂ of the solar battery square matrix and the capacity Q _C of the energy storage battery calculated under the previous coefficient as the designed equipment power and capacity of the wind power storage system, otherwise, lifting the coefficient k by 10%, and then recalculating the equipment power P _e of the wind power generator, the rated power P ₂ of the solar battery square matrix and the capacity Q _C of the energy storage battery.

Compared with the prior art, the invention has the following beneficial effects:

① The DC micro-grid adopts low-voltage DC power distribution, three-phase full-wave rectification is arranged in a concentrated manner, a tunnel non-firefighting DC load does not contain a single-phase rectification circuit, third harmonic existing in the system is greatly reduced, three-phase unbalance is eliminated, and the power quality of the system is improved.

② The direct-current micro-grid adopts low-voltage direct-current power distribution, thoroughly eliminates reactive power loss of lines and equipment, greatly reduces the influence of third harmonic, greatly reduces the loss of a power distribution line, and obviously reduces the power loss of single equipment.

③ The direct-current micro-grid adopts the low-voltage direct-current power distribution system, the cross section of the copper core cable for direct-current load power distribution can be reduced by about 50% compared with the prior art due to the outstanding power transmission capability of the direct-current system, the consumption of copper consumables is obviously reduced, and the low-carbon effect is obvious.

④ The direct-current micro-grid provided by the application has the advantages that the energy storage batteries are intensively arranged in the direct-current integrated cabinet AM1 to serve as emergency power supplies of important loads (standby illumination, electro-optical identification and monitoring), so that the equipment composition of the system is simplified.

⑤ The direct-current micro-grid provided by the application is an open system, and can meet the plug-and-play function, thereby providing convenience for the access of various new energy power generation.

⑥ The proposed direct current microgrid adopts a special "inlet-central..central-outlet" hand-held distributed topology. The direct current integrated cabinet with the structure goes deep into a load center, is convenient for the access of renewable energy power generation outside a tunnel, and is convenient for the access of an emergency power supply (mobile diesel generator set). And the bidirectional transmission of system electric energy is realized through high-frequency isolation bidirectional DC/DC equipment, and a hardware channel is provided for fully utilizing renewable energy sources to generate power.

⑦ The direct-current micro-grid provided by the application adopts a layered control structure and a control method to realize the control requirement of plug and play of the system. The first layer (equipment level) control adopts a droop control mode, a plurality of units participating in direct current bus voltage control exist in the system, the second layer (industrial control level) control is used for realizing secondary adjustment of the direct current bus voltage, power distribution of each control unit and switching of the system operation mode, and the third layer (central level) control is used for realizing energy scheduling among different direct current buses. Under the condition of ensuring normal operation of the load, the application can utilize renewable energy sources as much as possible to generate power, realize energy conservation and emission reduction, and save at least 40% of energy sources.

⑧ The application provides a centralized management and decentralized control distributed automatic control network framework which consists of three layers of frameworks (a central monitoring stage, a field control stage and a detection execution stage) for realizing the layered control function and enhancing the monitoring management of field devices.

Drawings

FIG. 1 is a topology of a DC micro-grid of the present invention;

FIG. 2 is a hierarchical control structure diagram of the DC micro-grid of the invention;

FIG. 3 is a flow chart of a third layer control scheduling scheme according to the present invention;

FIG. 4 is a second flowchart of a third layer control scheduling scheme according to the present invention;

FIG. 5 is a flow chart of the DC bus voltage selection according to the present invention;

FIG. 6 is a diagram of a tunnel power supply and distribution system of the present invention;

FIG. 7 is a diagram of a non-fire-fighting dual power switching cabinet AT system according to the present invention;

FIG. 8 is a system diagram of a direct current integrated cabinet AM1 of the invention;

FIG. 9 is a system diagram of a DC integrated cabinet AM2 according to the invention;

FIG. 10 is a diagram of a multi-year statistics hour traffic volume according to an embodiment of the present invention:

FIG. 11 is a flow chart of the wind, light and storage system engineering design of the present invention.

Detailed Description

The technical scheme of the invention is specifically described below with reference to the accompanying drawings.

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 direct-current local load, wherein the plurality of sections of direct-current buses are connected with the energy storage battery, each section of direct-current bus comprises a direct-current bus I arranged in the center of a tunnel, a direct-current bus II arranged at an entrance of the tunnel and a direct-current bus III arranged at an exit of the tunnel, the direct-current buses I are connected with a mains supply through a unidirectional AC/DC converter, the direct-current buses II and III are connected with the distributed power supply and the emergency mobile power supply through different converters, the direct-current buses I are respectively connected with the direct-current buses II and III through bidirectional DC/DC converters so as to realize electric energy transmission among the different direct-current buses, and the bidirectional DC/DC converters adopt high-frequency isolation bidirectional DC/DC converters. The direct current local load comprises tunnel basic lighting powered by a direct current bus I, facility electro-optical identification, traffic signal lamps, monitoring equipment power consumption and tunnel enhanced lighting powered by a direct current bus II and a direct current bus III.

The number of the direct current buses I is set according to the power supply radius of the direct current buses and the tunnel length so as to realize power supply of uniformly distributed direct current loads in the tunnel. For example, each central dc bus has a power supply radius of less than 1 km and greater than 2 km for a traffic tunnel, and the central dc bus needs to be disposed at least 2 places.

The distributed power supply comprises photovoltaic power generation and wind power generation, wherein the photovoltaic power generation is used as one of system energy sources, the economical efficiency of system operation can be effectively improved, the input voltage of the DC-DC converter is regulated by controlling the on-off of a power switch tube in the DC-DC converter, the permanent magnet direct-driven wind power generator system is used as wind energy utilization equipment, the structure is simple, the power generation efficiency is high, and the output power of the wind power generator is influenced by the wind speed and the wind direction, and the power is firstly stably output when being connected to a DC bus, so that low-voltage alternating current is converted into required direct current voltage through the AC-DC converter.

In the direct-current micro-grid, the output power of the accessed distributed power supply has instability; in order to maintain normal power supply of important loads of tunnels, the direct-current micro-grid is connected with an alternating-current large grid, wherein alternating current (AC 380V) is changed into stable direct current through an AC-DC unidirectional rectifying module to be connected with a direct-current bus, and in addition, an energy storage battery (lithium battery) can absorb excessive energy when photovoltaic and wind energy are abundant, and supplement insufficient energy when the photovoltaic and wind energy are insufficient, so that system energy is balanced, and bus voltage is stabilized. The emergency mobile power supply comprises mobile diesel power generation.

The basic calculation formula:

① Calculation formula of generating capacity of wind driven generator

Q _1n＝P₁×T_1n ×m (annual power generation), wherein Q _1n represents annual energy production of the wind driven generator, kWh, T _1n represents annual statistical wind time length of average wind speed calculated according to wind frequency, h, P ₁ represents output power of the average value of wind speeds of all wind speed sections converted to rated wind speed of the wind driven generator according to a power characteristic curve, kW, P ₁＝P_e × (highly verified average wind speed/rated wind speed) ³ when the average wind speed of each wind speed section is less than the rated wind speed, P ₁＝P_e when the average wind speed of each wind speed section is more than or equal to the rated wind speed, and m represents a coefficient considering loss, and 0.85 is taken;

The wind speed height correction formula is V _i＝V_x×(h_i/h_x)^a, wherein V _i represents the wind speed at the height h _i to be corrected, m/s, V _x represents the wind speed at the height h _x =10m, m/s, a represents an index determined by the atmospheric stability and the surface roughness, 0.12 is taken under the conditions of islands, coasts, lakesides, deserts and the like, 0.16 is taken under the conditions of open field rural areas, urban suburban areas and the like, and 0.2 is taken under the conditions of urban areas with dense houses and the like.

② Solar cell matrix power generation capacity calculation formula

Q _2n＝P_m×T_2n Xm (annual power generation), wherein Q _2n represents annual energy production of a solar cell matrix, kWh, T _2n represents a solar peak solar time annual statistic value, h, P _m represents rated (peak) power of the solar cell matrix, kW, and m represents a coefficient considering loss, and 0.9 is taken.

③ Energy storage battery capacity calculation formula

Q _C＝Q_js/(m x n), wherein Q _C represents the capacity of the energy storage battery, kWh, Q _js represents the capacity of the energy storage battery required for calculation, kWh, m represents the efficiency of the energy storage battery, 0.95 is taken, and n represents the depth of discharge of the energy storage battery, 1.0 is taken.

In FIG. 2, the operation control of the DC micro-grid adopts a three-layer hierarchical mode, wherein the first-layer control adopts droop control, the voltage stability of the DC buses is commonly maintained through a plurality of control units participating in the voltage control of the DC buses, the second-layer control realizes secondary adjustment of the voltage of the DC buses, power distribution of each control unit and switching of the operation mode of the DC buses by an industrial personal computer, the third-layer control realizes energy scheduling among different DC buses by a computer in a tunnel control center, and flexible scheduling of a mains supply, a distributed power supply, an energy storage battery and a DC load is realized by formulating an operation scheduling strategy of the DC micro-grid, and renewable energy sources are utilized as much as possible to generate power and ensure safe and economic operation of the system.

In the first-layer control, the control unit participating in the voltage control of the direct current bus comprises a unidirectional AC/DC converter, a bidirectional DC/DC converter, a distributed power supply controller and an energy storage unit controller, wherein the droop control is to control the voltage and current of the converter or the controller to run on a lower whip line, and the droop curve expression is as follows:

U_d＝U₀-k×I

The direct current micro-grid system provided by the application is a multi-source and multi-load system, and single droop control is adopted, so that secondary regulation of direct current bus voltage is required to be arranged.

In the second-layer control, the secondary adjustment of the DC bus voltage and the power distribution of each control unit are carried out by adopting a hybrid compensation mode, compensating the DC bus voltage set value U ₀ (longitudinal intercept) and the coefficient k of a sagging curve, acquiring the voltage, the current (U _1～n、I_1～n), the sagging curve coefficient (k _1～n) and other information of each unit through an industrial personal computer bus communication mode, and obtaining the sagging curve coefficient compensation quantity delta k and the longitudinal intercept compensation quantity delta U by utilizing an average voltage compensator, an average current compensator and a curve coefficient compensator, and respectively carrying out translation and coefficient adjustment on the sagging curve, wherein the average voltage compensator eliminates the output DC voltage deviation of each unit through a translation curve, and the average current compensator and the curve coefficient compensator realize rapid load distribution through adjusting the coefficient of the sagging curve;

three operation modes are respectively set for the direct current buses I, II and III:

1. DC bus I operation mode

① The power input unit of the DC bus I in the first operation mode (the surplus electric energy of the DC buses II and III) comprises a commercial power AC/DC unit, an energy storage battery unit and a bus connection bidirectional DC/DC unit (the power flow direction is from the DC buses II and III to the DC bus I), wherein the DC bus load is basic illumination, traffic signals, monitoring equipment and an electro-optical identifier.

And U _DCI＞U_H, wherein the voltage of the direct current bus is higher, the energy storage battery reaches the upper limit and can not be charged continuously, the renewable energy (photovoltaic and wind power) power generation system needs to be abandoned for energy operation, and the power generation system works in a constant voltage mode for maintaining the voltage stability.

And U _H＞U_DCI＞U_M, wherein the power generated by the renewable energy power generation system is larger than the power consumed by the direct current load and has surplus energy, the energy storage battery works in a constant current charging mode, and the renewable energy power generation system is under droop control to maintain the stability of the voltage of the direct current bus.

And U _M＞U_DCI＞U_L, the power generated by the renewable energy power generation system is insufficient to provide power consumed by the direct current load, and the power generation system always works in a maximum power tracking mode to furthest utilize renewable energy, and at the moment, in order to maintain the stability of bus voltage, the energy storage battery discharges and works in a sagging control state.

And U _L＞U_DCI＞U_O, wherein the sum of the power generated by the renewable energy photovoltaic and the power provided by the energy storage battery is smaller than the power consumed by the AC/DC load, the renewable energy power generation system works in an MPPT mode, the energy storage battery discharges, and the commercial power AC/DC module works in a sagging control state to maintain the stability of the voltage of the DC bus.

U ₀ is a direct current bus voltage set value, U _H\U_M\U_L is a set voltage control point, and U _DCI is a direct current bus I voltage value;

U_L＝(1+1％)×U₀;U_M＝(1+1％)×U_L;U_H＝(1+1％)×U_M。

② The power input unit of the DC bus I in the second operation mode (the DC buses II and III are insufficient in electric energy) comprises a commercial power AC/DC unit and an energy storage battery, wherein the DC bus load is a basic lighting, traffic signals, monitoring equipment, an electro-optical sign and a DC bus load (a power flow direction: the DC buses I to II and III) of the AW2 (3).

③ And in the third operation mode (emergency: mains failure), the power input unit of the DC bus I stores energy in a battery unit and the bus-connected bidirectional DC/DC unit (the power flow direction: the DC buses II and III to the DC bus I) is used for basic illumination (emergency illumination) and electro-optical identification.

And U _L＞U_DCI＞U_O, wherein the sum of the power generated by the renewable energy photovoltaic and the power provided by the energy storage battery is smaller than the power consumed by the AC/DC load, the renewable energy power generation system works in an MPPT mode, the energy storage battery discharges, and the DC buses II and III consider that the mobile diesel generator is accessed to supplement electric energy.

2. DC bus II (III) operation mode (U _DC is DC bus II voltage or DC bus III voltage)

The stability of the power supply system is ensured, renewable energy sources are utilized as much as possible to generate power, and the safe and economical operation of the system is realized. Renewable energy power generation, energy storage and commercial power set different power supply priorities, so that different tide control strategies are realized. And the power supply priority is that renewable energy power generation > energy storage > mains supply.

① The first operation mode (daytime) is that the direct current bus power input unit comprises a wind power generation unit, a photovoltaic power generation unit, an energy storage battery unit and a bidirectional DC/DC unit (from a direct current bus I), and the direct current bus load is an enhanced lighting load. .

According to the voltage of the direct current bus, the bus is divided into 4 working modes, and U ₀、U_L、U_M、U_H is the bus voltage value corresponding to each working mode.

And U _DC＞U_H, wherein the voltage of the direct current bus is higher, the energy storage battery reaches the upper limit and can not be charged continuously, the renewable energy (photovoltaic and wind power) power generation system needs to be abandoned for energy operation, and the power generation system works in a constant voltage mode for maintaining the voltage stability.

And U _H＞U_DC＞U_M, wherein the power generated by the renewable energy power generation system is larger than the power consumed by the direct current load and has surplus energy, the energy storage battery works in a constant current charging mode, and the renewable energy power generation system is under droop control to maintain the stability of the voltage of the direct current bus.

And U _M＞U_DC＞U_L, the power generated by the renewable energy power generation system is insufficient to provide power consumed by the direct current load, and the power generation system always works in a maximum power tracking mode to furthest utilize renewable energy, and at the moment, in order to maintain the stability of bus voltage, the energy storage battery discharges and works in a sagging control state.

And U _L＞U_DC＞U_O, wherein the sum of the power generated by the renewable energy photovoltaic and the power provided by the energy storage battery is smaller than the power consumed by the AC/DC load, the renewable energy power generation system works in an MPPT mode, the energy storage battery discharges, and the commercial power bidirectional DC/DC module works in a sagging control state to maintain the stability of the voltage of a DC bus.

② The second operation mode (daytime) is that the direct current bus power input unit comprises a wind power generation unit, a photovoltaic power generation unit and an energy storage battery unit, and the direct current bus load is an enhanced illumination load and a direct current bus I.

③ The operation mode III (night) is that the direct current bus power input unit comprises a wind power generation unit and an energy storage battery unit, and the direct current bus load is a direct current bus I.

The direct current micro-grid operation scheduling strategy in the third layer control comprises two scheduling schemes, specifically:

scheduling scheme one:

the adjustment range of the basic illumination output power of the tunnel is 50% -100%, the adjustment range of the enhanced illumination output power of the tunnel is 15% -100%, the traffic signal lamp, the electro-optical sign and the monitoring equipment are all-weather full-power running, and a first flow of a scheduling scheme is shown in figure 3.

Setting a daytime entering moment T ₁ and a nighttime entering moment T ₂ at night according to longitude and latitude, and judging whether the current daytime time or nighttime time exists according to a preset time interval according to T ₁ and T ₂;

scheduling scheme two (emergency):

The two paths of 10KV commercial power are simultaneously powered off or an alternating current system fails, the system power supply completely depends on renewable energy sources to generate power and a mobile diesel generator set, partial direct current load is cut off in emergency, only important loads, namely emergency lighting and electro-optical identification in basic lighting are reserved, and a second scheduling scheme is shown in a figure 4.

Setting a night entering daytime time T ₁ and a daytime entering nighttime time T ₂ according to longitude and latitude, and judging whether the current daytime time or nighttime time is in a preset time interval according to T ₁ and T ₂;

The electric shock protection design of the direct current micro-grid comprises the steps of setting 400mA as the upper limit of human body contact current which possibly occurs in a low-voltage direct current system, adopting a monopole wiring for low-voltage direct current, specifically adopting an IT power supply grounding system, realizing double protection of 30mA electric leakage protection and insulation monitoring, and ensuring that the electric shock protection performance of the low-voltage direct current IT system (DC 375V and below) is higher than that of a low-voltage alternating current TN-S system in the prior art.

The DC bus voltage may be selected as DC375V, DC220, 220V, D110,110v, and by adopting an enumeration comparison method, and combining the actual length of the tunnel and the load power, the sectional areas of the line cables when different DC voltages are respectively calculated, and selecting the DC voltage corresponding to the minimum sectional area as the selected DC bus voltage, the design flow is as shown in fig. 5, and the calculation of the sectional area of the line cable of each DC voltage is specifically as follows:

Calculating direct current load line current:

Calculating the sectional area:

S”≥(P×l)÷(5×γ×U²×0.001×5%)

The corresponding cable sectional area is determined according to the current-carrying capacity I _L value of the cable and is recorded as a cable sectional area inquiry value S ', wherein I _L is a certain core number specified in a cable manual and a rated current-carrying capacity corresponding to a cable with a certain sectional area, the corresponding cable sectional area can be obtained by looking up the manual according to I _L, the cable sectional area inquiry value S ' is compared with a cable sectional area calculation value S ' and a large value is taken as the cable sectional area S to be checked to carry out sensitivity check:

k_T=1+a×(θ-20)

Sensitivity of

And comparing the sectional areas of the cables under the three voltage conditions, and selecting the direct current transmission voltage corresponding to the minimum sectional area value as the selected direct current bus voltage.

The application adopts a discrete detection breaking device, wherein an AFD and an AFI are respectively arranged in a direct current outgoing line loop of a direct current power distribution cabinet, a direct current arc fault detection breaking controller is arranged in the monitoring cabinet, the controller is communicated with an industrial personal computer through an RS232, fault arc current information, occurrence time, fault loop number, AFI breaking signals and other information are uploaded to a central storage through an industrial Ethernet ring, in addition, an insulation detection terminal is respectively arranged in the direct current outgoing line loop of the direct current power distribution cabinet, an insulation detection controller is arranged in the monitoring cabinet, the controller is communicated with the industrial personal computer through the RS232, and fault insulation information, position and other information are uploaded to the central storage through the industrial Ethernet ring.

The following provides a main equipment engineering design of the dc micro-grid.

1. Overall layout of equipment

The application proposes to dispersedly arrange a plurality of direct current integrated cabinets AM 1-AM 3 (direct current buses I-III), wherein AM1 is arranged in the center of a tunnel, power is supplied to loads (basic lighting, electro-optical identification, traffic signals and monitoring equipment) from two sides, an incoming line power supply is led from a three-phase alternating current system, AM2 is arranged at an entrance of the tunnel, power is supplied to the loads (enhanced lighting) from one side, the power supply comprises a direct current bus I, renewable energy power generation and a mobile diesel generator set, the power supply is arranged at the entrance and is convenient for the renewable energy power generation unit and the mobile diesel generator set to access and go deep into the center of the load (enhanced lighting is positioned at an entrance of the tunnel), and AM3 is arranged at an exit of the tunnel, and the power supply condition is the same as AM2. The DC/DC high-frequency isolation bidirectional converter (arranged in AM2 and AM 3) is arranged to realize bidirectional electric energy transmission between direct current buses with different voltage levels. A non-fire-fighting dual-power switch cabinet AT is arranged on the side of a tunnel center AM1, a dual-power switch and intelligent high-frequency direct-current module is arranged in the AT, and the AT distributes direct-current power to the AM1.AT, AM1~ AM3 set up in the tunnel distribution room. Wind power generation, photovoltaic power generation and energy storage equipment are arranged outside the tunnel.

And the direct current comprehensive cabinets AM 1-3 are respectively provided with an industrial control computer for realizing secondary control, power distribution and monitoring of related equipment of the direct current system. The control center computer communicates with the regional industrial control computer in the tunnel through the industrial Ethernet switch and the optical fiber to form the gigabit Ethernet.

2. DC-DC power distribution system

1. Distribution system diagram

The low-voltage direct current power distribution system as shown in fig. 6-9, wherein the direct current integrated cabinet AM3 power distribution system is shown in the same graph as the direct current integrated cabinet AM2, and the graph is as follows:

① An AC380V dual-power automatic switching device is used for automatically switching two-way AC380V mains supply.

② The three-pole AC plastic-case circuit breaker is used for providing overload, short circuit, overvoltage and undervoltage protection for a three-phase AC distribution circuit.

③ The miniature DC leakage (30 mA) breaker is used for overload, short circuit, overvoltage and undervoltage protection of DC distribution circuit. The 30mA leakage was used for additional protection of direct contact.

④ The direct-current two-pole contactor is used for switching in and out of a load direct-current distribution circuit.

⑤ And the insulation monitoring terminal is used for insulation monitoring of the direct current bus and the direct current distribution loop.

⑥ And the direct current arc fault detection breaking terminal is a device for detecting the direct current side arc and sending out a fault alarm signal by an arc detector (AFD). An arc breaker (AFI) receives the arc detection signal and adopts the modes of isolation, short circuit or switch to realize the arc extinguishing function.

⑦ Alternating current busbar, copper busbar. ⑧ And the grounding busbar is a copper busbar. ⑨ Direct current busbar, copper busbar.

2. Main complete equipment

2.1. Intelligent high-frequency direct current module

The application proposes that a plurality of intelligent high-frequency direct current modules are connected in parallel and used as a power supply of a low-voltage direct current bus I. The adopted direct current module is intelligent high-frequency complete equipment, occupies small space, supports hot plug and high protection level, and is suitable for tunnel working scenes. The main technical requirements are as follows:

2.2. High-frequency isolation bidirectional DC/DC module

The application proposes to adopt a high-frequency isolation bidirectional DC/DC module as networking equipment between a low-voltage direct current bus I and direct current buses II and III, so as to realize bidirectional transmission of electric energy. The isolated bidirectional DCDC converter realizes electrical isolation between input and output through the transformer, and has high safety. Considering that the energy consumption of the high-voltage transmission line is low, the module is arranged in the direct current cabinets AW2 and AW3 where the direct current buses II and III with low voltage levels are located, and the line transmission voltage is the voltage of the direct current bus I. The bidirectional DC/DC module is used for charging and discharging the energy storage battery at the same time. The adopted bidirectional DC/DC module is intelligent high-frequency complete equipment, occupies small space, supports hot plug and high protection level, and is suitable for tunnel working scenes.

2.3. DC bus

The direct current bus adopts a flame-retardant insulating copper bus, and the distance between the positive electrode bus and the negative electrode bus of the copper bus is not less than 60mm. The maximum bus current is calculated according to the maximum power value which can be connected with the direct current bus and the bus voltage, and the rated current of the direct current bus is larger than the calculated maximum bus current and the proper allowance (about 10%) is considered. The DC bus of corresponding specification is selected according to the rated current of the DC bus, such as TM-40x4, 50x5, 80x8, etc. The direct current bus adopts heat shrink tube or other electric shock protective measures, and a warning sign is set at a striking position.

The maximum direct current bus current calculation formula: I _js is the maximum DC bus current, A, P _e1、P_e2、P_e3 is the maximum output power of the direct current module connected with the commercial power for the DC bus I, and the maximum output power of the bidirectional DC/DC direct current module connected with the commercial power for the DC buses II and III, and U is the designed DC bus voltage and V.

2.4. Energy storage battery

The application proposes that the direct current cabinet AW1 is provided with an energy storage battery as a tunnel emergency standby power supply (emergency lighting, an electric sign and monitoring equipment power supply). The battery was powered for 30 minutes.

2.5. Low-voltage direct-current distribution cable section design

① AM1 cabinet incoming cable 1-4

The cable is led to the AM1 cabinet by the AT cabinet, the cable length is less than 3 meters, the ZB1YJV cable is adopted, the cable is adopted to be laid along the wall in the distribution room, the cable spacing of different loops is greater than 1 time of the outer diameter, and the environmental temperature value needs to be according to the actual condition of the ground air temperature of the project. The cable cross section area (current-carrying capacity) is selected according to the laying mode and environmental condition, the cable long-term allowable current-carrying capacity is selected, and the thermal stability is checked according to the short-circuit current.

The calculation formula is that I _C≤I_N≤I_Z,I_C is the maximum working current, A, I _N is the long-delay setting current of the direct current leakage circuit breaker, A, I _Z is the allowable continuous current-carrying capacity of the conductor, A.

The calculation formula is as follows: s is the cable sectional area, mm2, I is the maximum short-circuit current, A, k is the coefficient, t is the action time of automatically cutting off the current of the protection electric appliance (direct current leakage breaker), S

② AM1 cabinet incoming cable 5-6 (or AM 2-3 cabinet incoming cable 1)

The cable is led to the AM1 cabinet from the AM2 cabinet to the AM 3 cabinet, the cable length is about half of the total length of the tunnel, the ZB1YJV cable is adopted, the cable is laid along cable channel brackets on two sides of the tunnel, the cable spacing of different loops is larger than 1 time of the outer diameter, and the environmental temperature value needs to be according to the actual condition of the ground air temperature of the project. The cable section area (current-carrying capacity) is selected according to the laying mode and environmental condition, the cable is allowed to carry out long-term current-carrying capacity, and thermal stability is checked according to short-circuit current, in addition, the cable section is required to be checked according to the requirement of circuit voltage drop (< 5%), and the sensitivity of short-circuit protection at the tail end of the circuit is required to be checked.

And selecting a cable long-term allowable current-carrying capacity and a short-circuit thermal stability verification calculation method according to the laying mode and the environmental conditions, wherein the calculation method is same as ①.

③ AM1 cabinet outgoing cable 1-10 (or AM 2-3 cabinet outgoing cable 1-2)

The cable is LED out to the LED tunnel lamp from the AM 1-3 cabinet, the cable length is long, ZB1YJV cables are adopted, the cables are laid along cable bridges on two sides of a tunnel ceiling, the distance between the cables of different loops is larger than 1 time of the outer diameter, and the value of the environmental temperature is required to be according to the actual condition of the ground air temperature of the project. The cable section area (current-carrying capacity) is selected according to the laying mode and environmental condition, and the cable is allowed to carry out long-term current-carrying capacity, in addition, the line is longer, the cable section is required to be checked according to the voltage drop requirement (< 5%), and the sensitivity of the short-circuit protection at the tail end of the line is required to be checked.

And a calculation method for the long-term allowable current-carrying capacity of the cable is same as ① according to the laying mode and the environmental condition.

In addition, 5-core constant-section cables (two direct current loops, L+, L-, co-PE) are adopted for the outgoing cables 1-4 of the AM1 cabinet (or the outgoing cables 1-2 of the AM 2-3 cabinet), the section of the adopted copper core cable is far lower than that of the copper core cable in the prior art (AC 380V) under the condition of the same power supply distance, the line loss is greatly reduced, the energy-saving effect is obvious, the use of copper materials is greatly reduced, and the carbon emission effect is obvious. The other output loops all adopt 3-core constant-section cables.

④ AM 2-3 cabinet incoming cable 2-5

The cable is led to an AM 2-3 cabinet from outside the tunnel, the cable length is long, ZB1YJV cables are adopted, the cable is laid along the cable channel support outside the tunnel, the distance between different loops of cables is larger than 1 time of the outer diameter, and the environmental temperature value needs to be according to the actual condition of the ground air temperature where the project is located. The cable section area (current-carrying capacity) is selected according to the laying mode and environmental condition, the cable is allowed to carry out long-term current-carrying capacity, and thermal stability is checked according to short-circuit current, in addition, the cable section is required to be checked according to the requirement of circuit voltage drop (< 5%), and the sensitivity of short-circuit protection at the tail end of the circuit is required to be checked.

3. DC-DC power distribution system

The application proposes a set of centralized management and distributed automatic control network framework which consists of a central monitoring stage, a field control stage and a detection execution stage and is formed by three layers of frameworks.

① Central monitoring stage

Is positioned in a control center (a matched building outside a tunnel). And setting 3 sets of central monitoring computers as central monitoring SCADA clients (2 sets of central monitoring SCADA clients are used as operator stations, and 1 set of central monitoring computers are used as engineer stations and also are used as standby operator stations) and performing monitoring operation on the operation flow of the direct current micro-grid. And setting 1 set of history data server to compress, store and manage history data. The central monitoring level uploading pattern software is also provided with a WEB release component, so that remote management and informationized release of the SCADA system can be realized.

② On-site control stage

The system consists of industrial control computers, touch screens and industrial Ethernet switches in the direct current integrated cabinets AM 1-3 in tunnels, and is mainly responsible for the automatic control and data acquisition of each device.

③ Detection execution stage

The system consists of a set of control systems, including a direct current arc fault protection controller, an insulation monitoring controller, an intelligent instrument, a high-frequency isolation bidirectional DC/DC, an energy storage battery controller, a photovoltaic power generation controller and a wind power generation controller. And each set of control system is connected with the monitoring system through the MODBUS bus.

④ Communication network

And a 1000M optical fiber rapid industrial Ethernet is adopted to form an annular redundant structure. In the field control stage, a MODBUS bus communication mode is adopted between the field control station and the complete equipment control system.

A monitoring computer and a communication cabinet (including a gigabit industrial Ethernet switch, a network comprehensive communicator, a UPS, anti-surge equipment and the like) are arranged in the tunnel external control center, and a communication sub-cabinet (including a gigabit industrial Ethernet switch, an industrial control computer, anti-surge equipment and the like) is arranged in the tunnel distribution room. The control center computer communicates with the regional industrial personal computers in the tunnels through the industrial Ethernet switch and the optical fiber to form the gigabit Ethernet. And the optical fiber ring network topology structure based on the switch technology is adopted to replace the traditional point-to-point distributed structure. The ring network unidirectional transmission is suitable for optical fiber application, has high transmission rate and high real-time performance, and has a bypass, and a certain node can be automatically bypassed when faults occur, so that shutdown is not caused, and the reliability is high.

4. Engineering design of wind, light and storage system

The wind driven generator adopts a full permanent magnetic suspension horizontal axis wind driven generator, the starting wind speed of the generator is required to be less than 1.5m/s, and the cut-in wind speed is not more than 2.5m/s. The solar cell module adopts high-light-transmittance low-iron toughened glass, the light transmittance is more than 91.3%, and high-quality monocrystalline silicon cell pieces are adopted. And a high-efficiency lithium iron phosphate battery is adopted as an energy storage battery.

The following provides a case for describing wind, optical equipment power and energy storage battery capacity engineering design method:

The meteorological data of the place where the case is, the average wind speed of years is 4.9m/s (10 m height), the statistical wind time length of the wind speed of the whole year is more than 3m/s (namely the wind speed for generating electricity by the wind driven generator) is 5783h, the daily average is 15.84h, and the wind power generation device belongs to a wind power resource available area. The daily average radiation quantity is 3.33kWh/m < 2 >, the average peak sunlight is 4.5 hours, the annual statistical time length is 1642 hours, the solar energy resources are general, and the wind power resources are more abundant.

The basic lighting day dimming coefficient is that the light output (power adjustment) of the LED is adjusted according to the change of the traffic volume of the tunnel, and a plurality of dimming grades are usually set according to the years of statistical average value of the traffic volume of the tunnel hour. The average daily dimming coefficient is determined by different tunnels according to the statistical hour traffic value of the place. The dimming coefficient of the illumination day is enhanced by dimming according to traffic volume and basic illumination, in addition, the light output (power adjustment) of the LEDs is required to be adjusted according to the change of the brightness (mainly determined by weather conditions) of tunnel openings, the brightness of a high opening corresponds to the high light flux output of the LEDs, the brightness of a low opening corresponds to the low light flux output of the LEDs, and a plurality of dimming grades are set. And determining average daily dimming coefficients by different tunnels according to the annual statistical hour traffic volume and the annual statistical entrance brightness value of the place.

The national standard GB/T33589-2017 'technical regulation for accessing micro-grid into power system' specifies that the annual energy production of distributed generation is not lower than 30% of the total power consumption of the micro-grid. The total power of the wind driven generator and the solar cell panel is combined with weather data (wind speed and available wind speed (> 3 m/s) annual statistical time, illumination intensity and available illumination time) of the place where the project is located and the overall consideration of the statistical annual average power consumption of the tunnel direct-current micro-grid, so that the annual energy production of distributed power generation is ensured to be more than 30% of the statistical annual power consumption of the direct-current micro-grid. The region with abundant wind power resources is mainly subjected to wind power generation and is assisted by photovoltaic power generation, and the region with abundant solar energy resources is mainly subjected to photovoltaic power generation and is assisted by wind power generation. Photovoltaic power generation only runs in daytime, and wind power generation can run in daytime and at night.

In the above cases, the annual energy consumption of a tunnel in a single hole is 186703kWh, the wind energy and solar energy resources are rich, and the generated energy of the configured photovoltaic and wind power generation equipment is more than 30% of the annual energy consumption of a double hole, namely 2x186703x30% = 112022kWh. The wind time length is 5783h (wind speed >3 m/s) in the place of the case project, and the peak sunshine time length 1642h in the year is counted. The ratio of wind power to photovoltaic power generation is 5783:1642 approximately equal to 7:2 according to the duration interim estimate.

Annual average power production of a wind turbine according to the foregoing equation ①:

Q_1n＝P₁×T_1n×m＝P₁×5783×0.9=112022×7/9=87128kWh;

Total installed power of wind driven generator:

P ₁ = 87128/(5783 x 0.9) = 16.7kW, the annual average wind speed is 4.9m/s (10 m height), the rated wind speed of the wind driven generator is less than 10m/s, the installation height is 20m, the equipment power P _e = 30kW of the selected wind driven generator is converted by the height and the wind speed of a formula ①, the power is the equipment power sum of the wind driven generator outside the tunnel in two directions, and a single high-power equipment or a combination of a plurality of low-power equipment can be adopted in engineering application.

Annual average power generation of photovoltaic power generation:

Q_2n＝P₂×T_2n×m＝P₂×1642×0.9=112002×2/9=24889kWh;

total power of photovoltaic solar panel installation:

P ₂ = 24889/(1642×0.9) =16.8 kW, taking the nominal value P ₂ =18 kW.

3. Capacity of energy storage battery

The tunnel is provided with a stable and reliable commercial power supply, wind power generation and photovoltaic power generation are used as energy-saving and consumption-reducing equipment, the energy-saving and consumption-reducing equipment is complementary to the commercial power supply, and the storage battery capacity is configured without considering that a system after renewable energy sources stop generating and the commercial power supply is in a missing state operates independently.

The capacity configuration of the energy storage battery considers the boundary conditions of the following two aspects:

① The independent running mode of the micro power grid is regulated in the national standard GB/T33589-2017 'technical regulation of micro power grid access power system', and the duration of the independent running mode to the load is not suitable to be lower than 2 hours.

As shown in fig. 10, since the boost lighting in the night tunnel dc load is in an off state, the maximum dc load is considered to occur in a period where daytime traffic is large and the outside brightness is highest, according to the number of years of statistics of hour traffic. The LED dimming control system has the advantages of high traffic, high LED dimming coefficient, high LED output power, high outdoor brightness, high LED dimming coefficient, and high ED output power. According to the traffic data, the occurrence period of daytime large traffic is 7-12 hours, the case is located in the north region of the northern hemisphere where the northern hemisphere returns to the line, and the highest sunlight in the whole year occurs in the midday between summer and the day of the current year.

The maximum continuous 2h high load of the whole year occurs in the summer to the day of the year 10:00-12:00, and the peak value of the electricity consumption day is shown in table 1:

Table 1.

The energy storage battery capacity is configured according to formula ③:

101.2 kWh/(0.95x1) ≡106.5kWh, which is a value of 110kWh.

② The capacity of the energy storage battery should consider the principle that new energy generation is not wasted, namely, the energy storage battery should meet the requirement of storing the surplus new energy generation electric energy (without considering the surplus electricity to be on the internet). The battery capacity should be greater than the difference between the maximum daily power generation and the minimum daily power. The case mainly uses wind power generation, the difference value between the maximum daily power generation amount and the minimum daily power generation amount occurs in a continuous overcast and rainy period, the average wind speed in the period is obviously higher than the annual average wind speed, the photovoltaic power generation is basically zero, the brightness of a tunnel portal is the lowest, and the illumination dimming coefficient is enhanced to be as low as 0.1. The minimum daily electricity consumption is shown in table 2:

TABLE 2

If the wind power and photovoltaic power generation take value of 90% of the annual energy consumption of the double-hole, according to the formula ①, the equipment power of the wind power generator is P _e =90 kW, and the daily power generation of the wind power generator in the continuous overcast and rainy period is as follows:

Q _1r＝P₁×T_1r ×m=90× (6.6/10) ×20×0.9=1069kWh; (6.6 is wind speed during overcast and rainy days after conversion according to altitude)

The energy storage cell capacity is configured to (1069-421 x 2) kWh/0.95≡240kWh according to formula ③.

Considering the two boundary conditions comprehensively, the capacity configuration of the energy storage battery is considered according to the condition ②, and the value is 240kWh (the value is the sum of two devices outside the tunnel, and each tunnel opening is allocated with 120 kWh).

If the wind-solar power generation configuration proportion is low (such as 30% of the foregoing), the difference between the maximum daily power generation amount and the minimum daily power generation amount may be smaller than the 2-hour peak value of the direct current load, and the energy storage battery capacity should be configured according to the condition ①.

4. Economic benefit estimation

The power allocation of the photovoltaic and wind power generation equipment needs to consider economic indexes, the investment of photovoltaic and wind power generation is about 0.8 ten thousand yuan/kW of RMB, the investment of lithium battery is about 0.1 ten thousand yuan/kWh of RMB, the effective service life of the photovoltaic and wind power generation is about 25 years, the effective service life of the lithium battery is about 5 years, and the equipment allocation of wind, light and storage is suitable for considering the recovery cost of electric energy in the half period of the service life, and the rest half period equipment is energy-saving and profitable period.

① When the wind-solar generating capacity accounts for 30% of the total power consumption, the adopted wind-driven generator equipment power P _e =30 kW, the adopted peak power P ₂ =18 kW of the photovoltaic equipment, and the lithium battery capacity C=110 kWh. Total investment (30+18) ×0.8+110×0.1× (25/5) =93.4 ten thousand yuan. The electric energy is saved by about 120000kWh per year, which is equivalent to about 6 ten thousand yuan for RMB. About 16 years of recovery costs.

② When the wind-solar generating capacity is 40% of the total power consumption, the adopted wind-driven generator equipment power P _e =40 kW, the adopted peak power P ₂ =24 kW of the photovoltaic equipment, and the lithium battery capacity C=110 kWh. Total investment (40+24) ×0.8+110×0.1× (25/5) =106.2 ten thousand yuan. The electric energy is saved by about 160000kWh each year, which is equivalent to about 8 ten thousand yuan for RMB. About 14 years of reclaiming costs.

③ When the wind-solar generating capacity is 50% of the total power consumption, the adopted wind-driven generator equipment power P _e =50 kW, the adopted peak power P ₂ =30 kW of the photovoltaic equipment, and the lithium battery capacity C=110 kWh. Total investment (50+30) ×0.8+110×0.1× (25/5) =119 ten thousand yuan. The electric energy is saved by 200000kWh each year, which is equivalent to about 10 ten thousand yuan for RMB. About 12 years of reclaiming costs.

In summary, for the case, when the wind-solar energy generating capacity accounts for 50% of the total electricity consumption, the recovery cost of the electric energy can be saved in the service life half period of wind, light and storage equipment, and the method has good economic benefit.

The engineering design flow of the wind, light and storage system is shown in figure 10.

The above is a preferred embodiment of the present invention, and all changes made according to the technical solution of the present invention belong to the protection scope of the present invention when the generated functional effects do not exceed the scope of the technical solution of the present invention.

Claims

1. The traffic tunnel hybrid energy direct current micro-grid is characterized by comprising 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, wherein the plurality of sections of direct current buses are connected with the energy storage battery, the plurality of sections of direct current buses comprise a direct current bus I arranged in the center of a tunnel, a direct current bus II arranged at an entrance of the tunnel and a direct current bus III arranged at an exit of the tunnel, the direct current buses I are connected with a mains supply through a unidirectional AC/DC converter, the direct current buses II and the direct current buses III are connected with the distributed power supply and the emergency mobile power supply, the direct current buses I are respectively connected with the direct current buses II and the direct current buses III through a bidirectional DC/DC converter so as to realize electric energy transmission among different direct current buses, and the local direct current load comprises tunnel basic lighting powered by the direct current buses I, facility identification, traffic signal lamps, monitoring equipment standby power and tunnel enhanced lighting powered by the direct current buses II and the direct current buses III.

2. The traffic tunnel hybrid energy direct current micro-grid according to claim 1, wherein the number of the direct current buses I is set according to the power supply radius of the direct current buses I and the tunnel length so as to realize power supply of uniformly distributed direct current loads in the tunnel.

3. The traffic tunnel hybrid energy direct current micro grid according to claim 1, wherein the distributed power source comprises photovoltaic power generation and wind power generation, and the emergency mobile power source comprises mobile diesel power generation.

4. The traffic tunnel hybrid energy direct current micro-grid according to claim 1 is characterized in that the operation control of the direct current micro-grid adopts a three-layer hierarchical mode, wherein the first-layer control adopts droop control, the voltage stability of a direct current bus is commonly maintained through a plurality of control units participating in the voltage control of the direct current bus, the second-layer control realizes secondary adjustment of the voltage of the direct current bus, power distribution of each control unit and switching of the operation mode of the direct current bus by an industrial personal computer, the third-layer control realizes energy scheduling among different direct current buses by a computer in a tunnel control center, and flexible scheduling of a mains supply, a distributed power supply, an energy storage battery and a direct current load is realized by formulating an operation scheduling strategy of the direct current micro-grid so as to ensure safe and economic operation of the system.

5. The traffic tunnel hybrid energy direct current micro grid according to claim 4, wherein in the first layer control, the control unit participating in direct current bus voltage control comprises a unidirectional AC/DC converter, a bidirectional DC/DC converter, a distributed power controller and an energy storage unit controller, wherein the droop control is to control the voltage and current of the converter or the controller to run on a lower whip line, and the droop curve expression is as follows:

U_d＝U₀-k×I

6. The traffic tunnel hybrid energy direct current micro-grid according to claim 5, wherein in the second layer of control, the direct current bus voltage secondary regulation and the power distribution of each control unit are specifically implemented by adopting a hybrid compensation mode, compensating a direct current bus voltage set value U ₀ and a coefficient k of a sagging curve, acquiring information of each control unit by an industrial personal computer bus communication mode, including voltage, current and sagging curve coefficients, and obtaining a sagging curve coefficient compensation quantity delta k and a longitudinal intercept compensation quantity delta U by utilizing an average voltage compensator, an average current compensator and a curve coefficient compensator, and respectively carrying out translation and coefficient adjustment on the sagging curve, wherein the average voltage compensator eliminates the output direct current voltage deviation of each unit by translating the curve, and the average current compensator and the curve coefficient compensator realize rapid load distribution by adjusting the coefficient of the sagging curve;

7. The traffic tunnel hybrid energy direct current micro grid according to claim 6, wherein the three operation modes are respectively set by the direct current buses I, II and III,

DC bus I operation mode:

DC bus II/III mode of operation:

The operation mode I is that under the daytime condition, the input power supply of the direct current bus II/direct current bus III comprises a distributed power supply, an energy storage battery and a mains supply, wherein a load of the direct current bus II/direct current bus III is tunnel enhanced illumination, and U _DC represents a voltage value of the direct current bus II or a voltage value of the direct current bus III;

8. The traffic tunnel hybrid energy dc micro-grid according to claim 7, wherein the dc micro-grid operation scheduling strategy in the third layer control comprises two scheduling schemes, specifically:

scheduling scheme one:

Scheduling scheme II:

9. The traffic tunnel hybrid energy direct current micro-grid according to claim 1, wherein the electric shock protection design of the direct current micro-grid comprises the steps of setting 400mA as an upper limit of human body contact current which possibly occurs in a low-voltage direct current system, adopting an IT power grounding system for low-voltage direct current to realize double protection of 30mA leakage protection and insulation monitoring, adopting an enumeration comparison method for selecting direct current bus voltage, respectively calculating the sectional area of a line cable when different direct current voltages are combined with the actual length of a tunnel and load power, selecting the direct current voltage corresponding to the minimum sectional area as the selected direct current bus voltage, wherein the different direct current voltages comprise DC375V, DC220,220, 220V, DC110,02v, and the calculation of the sectional area of the line cable of each direct current voltage is specifically as follows:

Calculating direct current load line current:

Calculating the sectional area:

S”≥(P×l)÷(5×γ×U²×0.001×5%)

Wherein 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 sectional area of the cable, and gamma is the conductivity of the cable conductor at 50 ℃;

k_T=1+a×(θ-20)

Sensitivity of

10. The traffic tunnel hybrid energy direct current micro-grid according to claim 3, wherein the design of the power and the capacity of the wind-solar energy storage system equipment is specifically as follows:

Calculating a photovoltaic power generation amount distribution value Q _b＝Q_n multiplied by k multiplied by B/(A+B), and calculating a solar cell matrix rated power P ₂ according to a photovoltaic power generator annual average power generation amount calculation formula Q _2n＝P₂×T_2n multiplied by m, wherein Q _2n is solar cell matrix annual power generation amount, T _2n is peak sunlight annual statistical time length, and m is a coefficient considering loss;