CN107745644A - City rail traffic battery energy storage system discharge threshold dynamic adjustment control method based on energy transfer - Google Patents
City rail traffic battery energy storage system discharge threshold dynamic adjustment control method based on energy transfer Download PDFInfo
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B60—VEHICLES IN GENERAL
- B60L—PROPULSION OF ELECTRICALLY-PROPELLED VEHICLES; SUPPLYING ELECTRIC POWER FOR AUXILIARY EQUIPMENT OF ELECTRICALLY-PROPELLED VEHICLES; ELECTRODYNAMIC BRAKE SYSTEMS FOR VEHICLES IN GENERAL; MAGNETIC SUSPENSION OR LEVITATION FOR VEHICLES; MONITORING OPERATING VARIABLES OF ELECTRICALLY-PROPELLED VEHICLES; ELECTRIC SAFETY DEVICES FOR ELECTRICALLY-PROPELLED VEHICLES
- B60L58/00—Methods or circuit arrangements for monitoring or controlling batteries or fuel cells, specially adapted for electric vehicles
- B60L58/10—Methods or circuit arrangements for monitoring or controlling batteries or fuel cells, specially adapted for electric vehicles for monitoring or controlling batteries
- B60L58/12—Methods or circuit arrangements for monitoring or controlling batteries or fuel cells, specially adapted for electric vehicles for monitoring or controlling batteries responding to state of charge [SoC]
- B60L58/13—Maintaining the SoC within a determined range
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B60—VEHICLES IN GENERAL
- B60L—PROPULSION OF ELECTRICALLY-PROPELLED VEHICLES; SUPPLYING ELECTRIC POWER FOR AUXILIARY EQUIPMENT OF ELECTRICALLY-PROPELLED VEHICLES; ELECTRODYNAMIC BRAKE SYSTEMS FOR VEHICLES IN GENERAL; MAGNETIC SUSPENSION OR LEVITATION FOR VEHICLES; MONITORING OPERATING VARIABLES OF ELECTRICALLY-PROPELLED VEHICLES; ELECTRIC SAFETY DEVICES FOR ELECTRICALLY-PROPELLED VEHICLES
- B60L58/00—Methods or circuit arrangements for monitoring or controlling batteries or fuel cells, specially adapted for electric vehicles
- B60L58/10—Methods or circuit arrangements for monitoring or controlling batteries or fuel cells, specially adapted for electric vehicles for monitoring or controlling batteries
- B60L58/12—Methods or circuit arrangements for monitoring or controlling batteries or fuel cells, specially adapted for electric vehicles for monitoring or controlling batteries responding to state of charge [SoC]
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
- H02J3/28—Arrangements for balancing of the load in a network by storage of energy
- H02J3/32—Arrangements for balancing of the load in a network by storage of energy using batteries with converting means
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B60—VEHICLES IN GENERAL
- B60L—PROPULSION OF ELECTRICALLY-PROPELLED VEHICLES; SUPPLYING ELECTRIC POWER FOR AUXILIARY EQUIPMENT OF ELECTRICALLY-PROPELLED VEHICLES; ELECTRODYNAMIC BRAKE SYSTEMS FOR VEHICLES IN GENERAL; MAGNETIC SUSPENSION OR LEVITATION FOR VEHICLES; MONITORING OPERATING VARIABLES OF ELECTRICALLY-PROPELLED VEHICLES; ELECTRIC SAFETY DEVICES FOR ELECTRICALLY-PROPELLED VEHICLES
- B60L2200/00—Type of vehicles
- B60L2200/26—Rail vehicles
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B60—VEHICLES IN GENERAL
- B60L—PROPULSION OF ELECTRICALLY-PROPELLED VEHICLES; SUPPLYING ELECTRIC POWER FOR AUXILIARY EQUIPMENT OF ELECTRICALLY-PROPELLED VEHICLES; ELECTRODYNAMIC BRAKE SYSTEMS FOR VEHICLES IN GENERAL; MAGNETIC SUSPENSION OR LEVITATION FOR VEHICLES; MONITORING OPERATING VARIABLES OF ELECTRICALLY-PROPELLED VEHICLES; ELECTRIC SAFETY DEVICES FOR ELECTRICALLY-PROPELLED VEHICLES
- B60L2240/00—Control parameters of input or output; Target parameters
- B60L2240/40—Drive Train control parameters
- B60L2240/54—Drive Train control parameters related to batteries
- B60L2240/547—Voltage
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B60—VEHICLES IN GENERAL
- B60L—PROPULSION OF ELECTRICALLY-PROPELLED VEHICLES; SUPPLYING ELECTRIC POWER FOR AUXILIARY EQUIPMENT OF ELECTRICALLY-PROPELLED VEHICLES; ELECTRODYNAMIC BRAKE SYSTEMS FOR VEHICLES IN GENERAL; MAGNETIC SUSPENSION OR LEVITATION FOR VEHICLES; MONITORING OPERATING VARIABLES OF ELECTRICALLY-PROPELLED VEHICLES; ELECTRIC SAFETY DEVICES FOR ELECTRICALLY-PROPELLED VEHICLES
- B60L2240/00—Control parameters of input or output; Target parameters
- B60L2240/40—Drive Train control parameters
- B60L2240/54—Drive Train control parameters related to batteries
- B60L2240/549—Current
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E40/00—Technologies for an efficient electrical power generation, transmission or distribution
- Y02E40/10—Flexible AC transmission systems [FACTS]
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
- Y02T10/00—Road transport of goods or passengers
- Y02T10/60—Other road transportation technologies with climate change mitigation effect
- Y02T10/70—Energy storage systems for electromobility, e.g. batteries
Abstract
The present invention relates to urban track traffic energy storage technology, specifically a kind of city rail traffic battery energy storage system discharge threshold dynamic adjustment control method based on energy transfer.The present invention method be：The control system of battery energy storage system is communicated with battery management system, obtains the voltage of battery, electric current, SOC parameter in real time；Busbar voltage can be obtained by voltage sensorU dc；The SOC of setting reference value SOCref, by energy-storage system actual soc-value and SOCrefCompare, obtain both difference △ SOC, the correction △ U of discharge threshold are obtained by segmentation scales adjuster, according to initial discharge threshold valueU dis0And discharge threshold correction △ U obtain actual discharge threshold Udis.The present invention makes energy-storage system SOC fluctuate within a certain range, prevents that energy-storage system SOC is too high or too low；Discharge capacity of the energy-storage system in peak period is increased, reduces electric substation's power output peak value.
Description
Technical Field
The invention relates to an urban rail transit energy storage technology, in particular to a dynamic discharge threshold value adjustment control method of an urban rail transit battery energy storage system based on energy transfer.
Background
Urban rail transit is an important component in a public transport system and an important means for solving urban traffic congestion, and has the operation characteristics of short station spacing and frequent starting and braking in the operation process. When the train is braked, the motor works in a power generation state, and the generated electric energy returns to a power grid, which is called regenerative braking; if the regenerative braking energy cannot be effectively absorbed by the adjacent traction train, the energy of the traction network is accumulated and the network pressure is lifted, so that the regeneration failure is caused. Meanwhile, with the increase of population, the departure time interval in the peak period of urban rail transit is correspondingly reduced, and if more traction vehicles are in the same section, the voltage drop of a traction network is caused, and the traction performance of the vehicles is influenced.
The utilization of an energy storage system to recover the residual regenerative braking energy and stabilize the network pressure become the current research focus. In recent years, the lithium ion battery technology is rapidly developed, the capacity grade and the power grade of the lithium ion battery can meet the requirements of absorption and release of regenerative braking energy of rail transit, and the lithium ion battery is gradually popularized and applied internationally.
FIG. 1 shows the energy flow of a DC network when a train is in a traction and braking condition, when the train brakes, a part of the regenerated energy of the train is supplied to the traction of an adjacent train for use, and the rest regenerated energy is absorbed by a battery; when the train is in traction, the battery releases energy to supply the train for traction and utilization, and the rest energy is provided by the adjacent train and traction power transformation.
The battery energy storage system is composed of a bidirectional DC/DC converter (Buck/Boost converter) and a battery pack, as shown in fig. 2. The bidirectional DC/DC converter performs the functions of system voltage level conversion and energy management. FIG. 3 is a closed-loop control link of the energy storage system, which usually adopts a voltage-current double closed loop, and a DC bus voltageThe battery current is an inner ring, and the inner ring and the outer ring are both controlled by PI regulators. Wherein U is char To charge threshold, U dis To discharge threshold, U dc Is the bus voltage, P char Charging power requirement for the battery, P dis For battery discharge power requirements, P ref For battery charging and discharging power requirements, P battmax For the limit value of the charge-discharge power of the battery, P battref Is a battery charge-discharge power command value, U batt Is the battery voltage, I battref Is a battery current command value, I batt Is the battery current and d is the control output. The relationship between the charge-discharge state of the battery energy storage system and the bus voltage is shown in the figure when U is used dc ≥U char When the system is in a Buck mode, the DC/DC converter works, the system enters a charging state, and the residual regenerative braking energy is recovered; when U is turned dc ≤U dis When the system is in a charging state, the DC/DC converter works in a Boost mode, and the system enters a charging state to provide energy for a train and inhibit the network voltage from dropping; when U is turned dis ≤U dc ≤U char At the time, the system is in a standby state and neither charges nor discharges. For coordinating charging and discharging of substation and energy storage system, U dis <U d0 ,U char >U d0 。
FIG. 4 illustrates the SOC limiting module operating principle, wherein SOC is min 、SOC max Is a boundary constraint condition for normal operation of the battery energy storage system. When the SOC is min ≤SOC≤SOC max In the meantime, the battery can be charged and discharged normally; when SOC is reached<SOC min When the battery is charged, the battery energy storage system can be charged normally, and discharge is forbidden, so that over-discharge is prevented; when SOC is reached>SOC max And in time, the battery energy storage system can normally discharge and forbid charging, so that overcharging is prevented.
The passenger flow of urban rail transit belongs to dynamic flow, and the train departure interval T d The minimum departure interval can reach 2min, the longest departure interval can reach 10min, and the urban rail transit operation has obvious early-late peak characteristics. At different departure intervals T d The number of trains running simultaneously on the line is different, and the number of trains running simultaneously on the line is as shown in formula (1)Wherein T is the train running time from the starting station to the terminal station, floor means rounding down, ceil means rounding up, the distance between train stations and the train power demand are related to the line data. For a particular line, at different departure intervals, when the line is full of trains, the traction energy and the braking energy of the trains are the same in the running time of a single departure interval, regardless of the departure interval. But as the departure interval changes, the load is dynamically changing: in a low peak period (a departure interval is small), the number of trains which run simultaneously on a line is small, the power requirement is low, the output power of a substation is low, the interaction of braking energy among the trains is small, and the residual regenerative braking energy is large; during the peak period (the departure interval is larger), the number of trains which run simultaneously on the line is larger, the power demand is larger, the power output by the substation is larger, the interaction of the braking energy among the trains is more, and the residual regenerative braking energy is less.
n＝floor(T/T d )～ceil(T/T d ) (1)
Aiming at the load characteristics of urban rail traffic under different departure intervals, it can be known that if a fixed charge-discharge threshold value is adopted, the SOC of the energy storage system is too high or too low due to charge-discharge imbalance, and the energy storage system can quit operation in order to prevent overcharge and overdischarge.
Aiming at the fact that the SOC of the energy storage system is too high or too low due to charging and discharging imbalance under the fixed threshold strategy, an SOC adjusting strategy is proposed, and is shown in figure 6.
The SOC adjustment strategy is to comprehensively consider a fixed threshold strategy and SOC adjustment, wherein I max Is the maximum value of the charge and discharge current of the battery, I t To regulate the current. When U is turned dc ≥U char Or U dc ≤U dis When the battery energy storage system is charged and discharged normally; when U is turned dis ≤U dc ≤U char Then, the actual detected SOC and the set SOC are compared a ,SOC b Comparing when the SOC is a <SOC<SOC b When the energy storage system is in standby; when SOC is reached<SOC a When the battery is charged, the energy storage system carries out low-current charging, and the SOC of the battery is increased; when SOC is reached>SOC b While, the energy storage system is inDischarging with small current to reduce the SOC of the battery; in short, the SOC of the battery is adjusted by charging and discharging with a small current so as to maintain the SOC within a certain range.
Through the analysis, the control strategy adjusts the SOC of the battery through unnecessary charging and discharging during the standby period, so that the service life attenuation of the energy storage system is accelerated, the replacement cost of the energy storage system is increased, and the economical efficiency is poor. In addition, the SOC adjustment function is limited by the adjustment current I t The adjustment current is too small, and the SOC adjustment speed is slow; the adjustment current is too large, and the load (charging) of the substation is increased.
In view of the battery life decay, a dynamic threshold strategy is proposed, as shown in fig. 7.
The strategy dynamically adjusts the charge-discharge threshold value of the battery according to the real-time detected battery SOC value, when the battery SOC value is detected>SOC b When the charging and discharging threshold value is increased, the discharging energy of the energy storage system is increased, and the charging energy of the energy storage system is reduced, so that the SOC is reduced; when the battery SOC<SOC a When the charging and discharging threshold is reduced, the discharging energy of the energy storage system is reduced, and the charging energy of the energy storage system is increased, so that the SOC is increased; when the SOC is a <SOC<SOC b The charge and discharge threshold is constant.
The strategy does not affect the service life of the energy storage system, but the charging threshold is increased or decreased according to the SOC, and when the charging threshold is smaller, the energy storage system can rob train interaction energy or when the charging threshold is higher, the energy-saving effect of the energy storage system can be reduced. In addition, the power requirements of the urban rail transit at different departure intervals are different from the residual regenerative braking energy, the strategy fixes the working interval of the SOC, and the high energy density characteristic of the energy storage system and the load characteristic of the urban rail transit are not comprehensively considered.
Disclosure of Invention
The invention aims to solve the technical problem that the dynamic discharge threshold value adjustment control method of the urban rail transit battery energy storage system based on energy transfer can realize the following steps: 1. the problem of unbalanced charging and discharging of the battery energy storage system is solved, and the energy storage system is realized on the premise of not influencing the energy-saving effectControlling the SOC to enable the SOC of the energy storage system to fluctuate within a certain range, and preventing the SOC of the energy storage system from being too high or too low; 2. providing an SOC dynamic adjustment strategy based on energy transfer, and adjusting the SOC according to departure intervals ref On the premise of not influencing the recovery of the regenerative braking energy, the energy storage system is utilized to transfer the part of the regenerative braking energy recovered in the low peak period/flat peak period to the high peak period, so that the discharge capacity of the energy storage system in the high peak period is increased, and the peak value of the output power of the substation is reduced.
The patent provides a dynamic adjustment method of a discharge threshold value of a battery energy storage system based on SOC tracking, and a charging threshold value U char Regenerative braking energy E that affects energy storage system recovery c Discharge threshold U dis Will influence the discharge capacity E of the energy storage system d In order to ensure the effective absorption of the residual regenerative braking energy, the charging threshold value is determined according to the traditional method, is fixed and unchanged, and the discharging amount E of the energy storage system is controlled by dynamically adjusting the discharging threshold value d And dynamic balance of charging and discharging energy of the energy storage system is realized.
The specific method of the invention is as follows: the control system of the battery energy storage system is communicated with a Battery Management System (BMS) to obtain the voltage, the current and the SOC parameters of the battery in real time; bus voltage U can be obtained through a voltage sensor dc (ii) a Reference value SOC of set SOC ref The actual SOC value and SOC of the energy storage system ref Comparing to obtain difference value delta SOC, and obtaining correction quantity delta U of discharge threshold value by using segmented proportional regulator (the proportion P is different under different difference values), wherein U is dis0 To initial discharge threshold, Δ U dis For discharge threshold control parameters, related to train departure intervals, U dis0 Following the no-load voltage U d0 Fluctuation of and departure interval changes; according to an initial discharge threshold U dis0 And obtaining actual discharge threshold U by discharge threshold correction amount DeltaU dis (ii) a Specifically, the formula is (2):
current delta SOC>a 1 When the discharge amount is increased, the correction value is increased along with the increase of the delta SOC, so that the discharge threshold value is increased, and the discharge amount is increased; when a is 1 <△SOC<a 2 Then, the discharge threshold is not corrected, and the initial discharge threshold U is maintained dis0 Normal discharge; when 0 is present<△SOC<a 1 The correction value is decreased with the decrease of delta SOC, and the discharge threshold U is set dis Reducing, namely gradually reducing the output of the energy storage system; current delta SOC&When the voltage is 0, the discharge threshold value is smaller than the output voltage of the substation, and the energy storage system is forbidden to discharge; a is 1 ,a 2 For discharge threshold adjustment criterion, k 1 ,k 2 A is a discharge threshold change slope, and a is a safety margin; thus, the discharge capacity of the energy storage system is adjusted according to the delta SOC, the dynamic balance of the charge and discharge energy of the energy storage system is realized, and the SOC of the battery dynamically tracks the SOC ref Fluctuating within a certain range.
Further, the method of the invention also comprises the following steps: adjusting SOC reference value SOC of battery according to departure interval ref At low peak/flat peak, make SOC ref Gradually increasing to enable the energy released by the energy storage system to be smaller than the recovered regenerative braking energy, and gradually storing the energy by the energy storage system; during peak period, make SOC ref And the energy is gradually reduced, and the energy stored in the energy storage system is gradually released, so that the discharge capacity of the energy storage system is larger than the recovered regenerative braking energy.
Further, the SOC reference value SOC at the current moment ref (k) According to the SOC reference value SOC of the last moment ref (k-1), current departure interval T d And the remaining sustained actual T of the current departure interval h Determining, as shown in formula (3):
k 1 is SOC ref Change slope, Δ t is SOC ref The time of the update is the time of the update,for the expected SOC at the current departure interval ref The final value of (c).
Furthermore, in order to prevent the over-charge and over-discharge of the battery, the working interval of the SOC of the battery is limited, and the SOC is min ≤SOC≤SOC max Wherein SOC is min Is the battery SOC lower limit, SOC max At the upper limit of the SOC of the battery, when the SOC is>SOC max When the energy storage system is charged, the energy storage system is forbidden to charge; when SOC is reached<SOC max When the energy storage system is not discharged, the energy storage system is not discharged; when SOC is reached min ≤SOC≤SOC max When the energy storage system is charged and discharged normally; to prevent SOC ref Excessive impact on recovery of residual regenerative braking energy, and SOC ref The variation range is limited to SOC min ～SOC max -b, smaller than the actual SOC operating interval.
The advantages of the invention are embodied in that:
1. based on the load characteristics of the urban rail transit at different departure intervals, a discharge threshold dynamic adjustment strategy of the battery energy storage system based on SOC tracking is designed, on the premise that the regenerative braking energy recovery is not influenced, the charge and discharge of the energy storage system are dynamically balanced, and the SOC of the battery is prevented from being too high or too low;
2. based on the high energy density characteristic of the battery energy storage system, an SOC dynamic adjustment strategy based on energy transfer is designed, the battery energy storage system is utilized to transfer part of regenerative braking energy recovered in a low peak period/flat peak period to a high peak period, and the peak power and output energy of a power substation in the high peak period are reduced.
Drawings
FIG. 1 is a flow chart of DC net energy during train traction braking in a prior art method;
FIG. 2 is a battery energy storage system in a prior art approach;
FIG. 3 is a prior art method for controlling the voltage and current of an energy storage system in a double closed loop;
FIG. 4 is a schematic diagram of energy storage system mode switching in a prior art approach;
FIG. 5 is a schematic diagram of train distribution in a prior art method;
FIG. 6 is a diagram of SOC adjustment strategies in a prior art method;
FIG. 7 is a graph of a discharge threshold dynamic adjustment strategy in a prior art approach;
FIG. 8 shows the SOC of the battery under the energy transfer control method according to the embodiment of the present invention ref And an SOC map;
FIG. 9 is a block diagram of a control system of an embodiment of the present invention;
fig. 10 is a schematic diagram of a method for dynamically adjusting the battery energy storage discharge threshold based on energy transfer according to the present invention.
Detailed Description
The patent provides a method for dynamically adjusting a discharge threshold value of a battery energy storage system based on SOC tracking, namely a charging threshold value U char Regenerative braking energy E that affects energy storage system recovery c Discharge threshold U dis Will influence the discharge capacity E of the energy storage system d In order to ensure the effective absorption of the residual regenerative braking energy, the charging threshold value is determined according to the traditional method, is fixed and unchanged, and the discharging amount E of the energy storage system is controlled by dynamically adjusting the discharging threshold value d And dynamic balance of charging and discharging energy of the energy storage system is realized.
The specific method of the invention is as follows: the control system of the battery energy storage system is communicated with a Battery Management System (BMS) to obtain the voltage, the current and the SOC parameters of the battery in real time; bus voltage U can be obtained through a voltage sensor dc (ii) a Reference value SOC of set SOC ref Comparing the actual SOC value and SOC of the energy storage system ref Comparing to obtain difference value delta SOC, and obtaining correction quantity delta U of discharge threshold value by using segmented proportional regulator (the proportion P is different under different difference values), wherein U is dis0 To initial discharge threshold, Δ U dis For discharge threshold control parameters, related to train departure intervals, U dis0 Following the no-load voltage U d0 Fluctuation of and departure interval changes; according to the initial discharge threshold U dis0 And obtaining actual discharge threshold U by discharge threshold correction amount DeltaU dis (ii) a Specifically, the formula is (2):
current delta SOC>a 1 Then, the correction value is increased along with the increase of the delta SOC, so that the discharge threshold value is increased, and the discharge amount is increased; when a is 1 <△SOC<a 2 While maintaining the initial discharge threshold U without correcting the discharge threshold dis0 Normal discharge; when 0 is present<△SOC<a 1 The correction value is decreased with the decrease of delta SOC, and the discharge threshold U is set dis Reducing, namely gradually reducing the output of the energy storage system; current delta SOC&When the voltage is 0, the discharge threshold value is smaller than the output voltage of the substation, and the energy storage system is forbidden to discharge; a is 1 ,a 2 For discharge threshold adjustment criterion, k 1 ,k 2 The slope of the change of the discharge threshold value and a are safety margins which are all parameters to be determined and can be input by a human-computer interaction module; thus, the discharge capacity of the energy storage system is adjusted according to the delta SOC, the dynamic balance of the charge and discharge energy of the energy storage system is realized, and the SOC of the battery dynamically tracks the SOC ref Fluctuating within a certain range.
In addition, the load characteristic of urban rail transit and the high energy density characteristic of the battery energy storage system are comprehensively considered, and the invention further comprises a battery energy storage system control method based on energy transfer. The urban rail transit has obvious morning and evening peak characteristics during operation, the total traction energy and the total braking energy of the trains are the same (irrelevant to the size of the departure interval) in a single departure interval, but in a low peak period or a flat peak period, the number of the trains which are operated simultaneously on a line is small, the interaction of the braking energy among the trains is small, and the residual regenerative braking energy is large, so that the recoverable energy of an energy storage system is large; during the peak period, the number of trains running on the line simultaneously is large, the total power demand of the trains is large, the output power of the substation is large, the interaction of braking energy among the trains is large, and the residual regenerative braking energy is small. Therefore, if the high energy density characteristic of the battery energy storage system is utilized, the regenerative braking energy recovered in the low peak period/flat peak period is partially stored in the battery and is gradually released in the high peak period, the energy storage system can be enlargedDischarge quantity E of system in peak period d The method increases the discharge power and the discharge time of the energy storage system, reduces the peak power and the output energy of the substation in the peak period, and has important significance for reducing the urban construction cost of the substation or increasing the distance between the substations.
Therefore, the SOC reference value SOC of the battery is adjusted according to the departure interval ref At low peak/flat peak, make SOC ref Gradually increasing to enable the energy released by the energy storage system to be smaller than the recovered regenerative braking energy, and gradually storing the energy by the energy storage system; during peak period, make SOC ref And gradually reducing, and gradually releasing the energy stored in the energy storage system to ensure that the discharge capacity of the energy storage system is greater than the recovered regenerative braking energy. The energy transferred from the low/flat period to the high period is via SOC ref And (6) determining.
For actual urban rail line, train parameter and line data and departure interval T of train d The method is known, energy flow, residual regenerative braking energy and peak power of a substation at different departure intervals can be obtained according to an urban rail traction power supply simulation platform, and a peak period, a low peak period and a peak leveling period can be divided according to the data. The compilation of the Train operation diagram and the adjustment of the departure interval are realized by an Automatic Train monitoring system (ATS), and the communication between the ATS and the energy storage system control system can obtain the departure interval of the Train at different moments and the residual continuous actual T of the current departure interval h Can determine the SOC reference value SOC at the current moment ref (k) According to the SOC reference value SOC of the last moment ref (k-1), current departure interval T d And the remaining sustained actual T of the current departure interval h Determining, as shown in formula (3):
k 1 is SOC ref Change slope, Δ t is SOC ref The time of the update is the time of the update,for the expected SOC at the current departure interval ref The final value of (c).
To prevent the battery from being overcharged and overdischarged, the working interval of the SOC of the battery is limited, and the SOC is min ≤SOC≤SOC max Wherein SOC is min Is the battery SOC lower limit, SOC max At the upper limit of the SOC of the battery, when the SOC is>SOC max When the energy storage system is charged, the energy storage system is forbidden to charge; when the SOC is<SOC max When the energy storage system is not discharged, the energy storage system is not discharged; when SOC is reached min ≤SOC≤SOC max When the energy storage system is charged and discharged normally; to prevent SOC ref Excessive impact on recovery of residual regenerative braking energy, and SOC ref The variation range is limited to SOC min ～SOC max -b, smaller than the actual SOC operating interval. Slope k of change 1 According to SOC ref (k-1) andand the remaining duration T of the current departure interval h Real-time update is carried out, thereby avoiding SOC in one day ref The difference in initial values or the influence of the adjustment of departure intervals on the energy transfer. During the low peak period and the moderate peak periodEnsuring that the battery stores as much energy as possible at the end of the low peak period/flat peak period; during peak periodsSo that the SOC is at the end of the peak period ref ＝SOC min The stored energy of the battery is effectively released. It can be seen that at different departure intervals, k 1 Different, peak, k 1 <0，SOC ref Decrease; in the low peak period/flat peak period, k 1 >0，SOC ref Increasing as shown in fig. 8.
Under the control strategy, in the low peak period/flat peak period, the energy flow relation of the energy storage system is shown as the formula (4), and the energy E recovered by the energy storage system c A part of the energy is stored in an energy storage system (E) s ) Impedance and converter (E) with a part of the losses in the energy storage system loss ) The remainder being used for train traction (E) d ) (ii) a During peak hours, the energy flow relationship of the energy storage system is as shown in equation (5), energy E for train traction d Equal to the energy recovered by the energy storage system (E) c ) And the energy stored by the energy storage system itself (E) s ) Minus losses (E) of the energy storage system itself loss ). In the existing control strategy E s And =0. The energy transferred from the low/flat period to the high period depends on the capacity configuration of the energy storage system and the set SOC operating interval.
E d ＝E c -E s -E loss (4)
E d ＝E c +E s -E loss (5)
The structural block diagram of the control system provided by the patent is shown in fig. 9, and the strategy for dynamically adjusting the discharge threshold of the battery energy storage system based on energy transfer is shown in fig. 10.
The principle explanation and the control strategy design are carried out on the battery energy storage and discharge threshold dynamic adjustment strategy based on energy transfer, the strategy thought can be used for urban rail transit such as subways and trams, the utilization rate of an energy storage system is increased, the peak power requirement of a substation can be effectively reduced on the premise of not influencing regenerative braking energy recovery, the important significance is achieved on reducing the installation cost of the substation or prolonging the distance between the substations, the peak power reduction rate is related to the capacity allocation of the energy storage system, and the set SOC working interval and specific lines are related.
Claims (5)
1. A method for dynamically adjusting and controlling a discharge threshold of an energy storage system of an urban rail transit battery based on energy transfer is characterized by comprising the following steps: the control system of the battery energy storage system is communicated with the battery management system to obtain the voltage, the current and the SOC parameters of the battery in real time; bus voltage U can be obtained through a voltage sensor dc (ii) a Reference value SOC of set SOC ref The actual SOC value and SOC of the energy storage system ref Comparing to obtain difference value delta SOC, and obtaining correction quantity delta U of discharge threshold value by using segmented proportional regulator, wherein U is dis0 To initial discharge threshold, Δ U dis For discharge threshold control parameters, associated with train departure intervals, U dis0 Following the no-load voltage U d0 Fluctuation of and departure interval changes; according to the initial discharge threshold U dis0 And obtaining actual discharge threshold U by discharge threshold correction amount DeltaU dis (ii) a Specifically, the formula is (2):
current delta SOC>a 1 Then, the correction value is increased along with the increase of the delta SOC, so that the discharge threshold value is increased, and the discharge amount is increased; when a is 1 <△SOC<a 2 While maintaining the initial discharge threshold U without correcting the discharge threshold dis0 Normal discharge; when 0 is present<△SOC<a 1 The correction value is decreased with the decrease of delta SOC, and the discharge threshold U is set dis Reducing, namely gradually reducing the output of the energy storage system; when Δ SOC&When 0, making the discharge threshold value less than the output voltage of the transformer substation, forbidding the energy storage system to discharge; a is 1 ,a 2 For discharge threshold adjustment criterion, k 1 ,k 2 A is a discharge threshold change slope, and a is a safety margin; thus, the discharge capacity of the energy storage system is adjusted according to the delta SOC, the dynamic balance of the charge and discharge energy of the energy storage system is realized, and the SOC of the battery dynamically tracks the SOC ref Fluctuating within a certain range.
2. The method for dynamically adjusting and controlling the discharge threshold of the energy storage system of the urban rail transit battery based on energy transfer as claimed in claim 1, wherein the method comprises the following steps: adjusting SOC reference value SOC of battery according to departure interval ref At low peak/flat peak, make SOC ref Gradually increasing to enable the energy released by the energy storage system to be smaller than the recovered regenerative braking energy, and gradually storing the energy by the energy storage system; during peak period, make SOC ref And gradually reducing, and gradually releasing the energy stored in the energy storage system to ensure that the discharge capacity of the energy storage system is greater than the recovered regenerative braking energy.
3. The method for dynamically adjusting and controlling the discharge threshold of the energy storage system of the urban rail transit battery based on energy transfer as claimed in claim 2, wherein the method comprises the following steps: SOC reference value SOC at the current moment ref (k) According to the SOC reference value SOC of the last moment ref (k-1), current departure interval T d And the remaining sustained actual T of the current departure interval h Determining, as shown in formula (3):
k 1 is SOC ref Change slope, Δ t is SOC ref The time of the update is the time of the update,for the expected SOC at the current departure interval ref The final value of (c).
4. The method for dynamically adjusting and controlling the discharge threshold of the energy storage system of the urban rail transit battery based on energy transfer as claimed in claim 3, wherein the method comprises the following steps: to prevent the battery from being overcharged and overdischarged, the working interval of the SOC of the battery is limited, and the SOC is min ≤SOC≤SOC max Wherein SOC is min Is the battery SOC lower limit, SOC max At the upper limit of the SOC of the battery, when the SOC is>SOC max When the energy storage system is charged, the energy storage system is forbidden to charge; when SOC is reached<SOC max When the energy storage system is not discharged, the energy storage system is not discharged; when SOC is reached min ≤SOC≤SOC max And when the energy storage system is charged and discharged normally.
5. The method for dynamically adjusting and controlling the discharge threshold of the energy storage system of the urban rail transit battery based on energy transfer as claimed in claim 3, wherein the method comprises the following steps: to prevent SOC ref Excessive impact on recovery of residual regenerative braking energy, and SOC ref The variation range is limited to SOC min ～SOC max -b, smaller than the actual SOC operating interval.
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