CN108512239B - Hybrid energy source system for electric vehicle and control strategy thereof - Google Patents
Hybrid energy source system for electric vehicle and control strategy thereof Download PDFInfo
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- CN108512239B CN108512239B CN201810442005.8A CN201810442005A CN108512239B CN 108512239 B CN108512239 B CN 108512239B CN 201810442005 A CN201810442005 A CN 201810442005A CN 108512239 B CN108512239 B CN 108512239B
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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
- B60L55/00—Arrangements for supplying energy stored within a vehicle to a power network, i.e. vehicle-to-grid [V2G] arrangements
-
- 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
- B60L58/18—Methods or circuit arrangements for monitoring or controlling batteries or fuel cells, specially adapted for electric vehicles for monitoring or controlling batteries of two or more battery modules
- B60L58/20—Methods or circuit arrangements for monitoring or controlling batteries or fuel cells, specially adapted for electric vehicles for monitoring or controlling batteries of two or more battery modules having different nominal voltages
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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
- H02J3/24—Arrangements for preventing or reducing oscillations of power in networks
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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
- H02J7/00—Circuit arrangements for charging or depolarising batteries or for supplying loads from batteries
- H02J7/0013—Circuit arrangements for charging or depolarising batteries or for supplying loads from batteries acting upon several batteries simultaneously or sequentially
- H02J7/0014—Circuits for equalisation of charge between batteries
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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
- H02J7/00—Circuit arrangements for charging or depolarising batteries or for supplying loads from batteries
- H02J7/34—Parallel operation in networks using both storage and other dc sources, e.g. providing buffering
- H02J7/345—Parallel operation in networks using both storage and other dc sources, e.g. providing buffering using capacitors as storage or buffering devices
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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 invention discloses a hybrid energy source system for an electric automobile and a control strategy thereof, wherein the hybrid energy source system comprises a hardware circuit and a controller; the hardware circuit includes: the system comprises a battery pack, a super capacitor pack, a first bidirectional DC/DC interface circuit and a second bidirectional DC/DC interface circuit, wherein the battery pack and the super capacitor pack are respectively connected with a direct current bus; the controller includes an interface circuit controller and an energy management controller. The interface circuit controller can maintain the dynamic balance of the voltage of each battery monomer in the charging and discharging process according to the charging and discharging voltage-sharing control program of the battery pack; and a control signal can be generated to realize the direct energy exchange of the two types of energy storage sources, so that the super capacitor operates in a better charge state and the power regulation capability of the super capacitor is fully exerted. The energy management controller achieves a reasonable distribution of power between the battery and the super capacitor.
Description
Technical Field
The invention relates to the field of energy storage technology and power supply, in particular to a hybrid energy source system for an electric automobile and a control strategy thereof, which are suitable for hybrid energy source systems of electric automobiles, urban rail transit and the like.
Background
Under the circumstances that the environmental awareness of the public is obviously enhanced due to the shortage of petroleum, the government promotes, laws and regulations are increasingly perfected, and the acceptance of the public on electric automobiles is improved, the electric automobiles are leading the development trend of the automobile industry in the world. The super capacitor is used as a novel energy storage element, has excellent performance, especially has high power density, so the super capacitor can be used as an auxiliary energy source and forms a mixed energy source of the electric automobile with a power battery, the defects of the traditional electric automobile are overcome, high power for short time during automobile starting, accelerating and climbing is provided, especially when the electric automobile runs down a slope or decelerates, the super capacitor absorbs energy, the braking energy recovery is realized, the battery is protected from the impact of large current, the health of the battery is maintained, and the energy recovery efficiency is improved.
Because the voltage level of the power battery monomer is low, a power battery pack with high voltage level needs to be obtained by connecting a plurality of power battery monomers in series, and research and practice show that the service life of the series battery pack is far shorter than that of a single power battery due to the characteristic difference between the battery monomers.
The electric automobile can fully exert the excellent performances of acceleration, deceleration, starting and braking, which are inseparable from the reliable work of the super capacitor, and when the electric automobile is started or accelerated, more energy needs to be stored in the super capacitor to ensure the acceleration performance of the electric automobile; when the automobile is braked or decelerated, relatively less energy should be stored so as to accept more energy in the braking process, and therefore, the charge state of the super capacitor is extremely important for the reliable operation of the electric automobile and the improvement of the running performance of the automobile.
The hybrid energy storage system plays an important role in stabilizing the fluctuation of load power, keeping the power balance of the system and stabilizing the voltage of a direct current bus. Considering the characteristics of large energy density of a power battery, high power density of a super capacitor and high response speed, reasonable power distribution between the power battery and the super capacitor is crucial in a hybrid energy storage system, and the method plays an important role in reducing the impact of sudden change of system power on the battery and prolonging the service life of the battery.
In view of this, it is necessary to invent a new hybrid energy source system, which uses an effective control strategy and has a low cost, not only to solve the problem of dynamic voltage equalization during charging and discharging of the battery pack, but also to operate the super capacitor in a better state of charge so as to reliably operate, and finally, to implement an efficient and reliable hybrid energy source system in consideration of two important control targets of system power distribution and dc bus voltage stabilization.
Disclosure of Invention
The invention aims to provide a hybrid energy source system for an electric vehicle and a control strategy thereof aiming at the technical problems in the hybrid energy source electric vehicle.
The technical scheme adopted by the invention is as follows: a hybrid energy source system for an electric vehicle comprises a hardware circuit and a controller;
the hardware circuit includes:
a battery pack including a plurality of battery cells,
the super capacitor group is provided with a plurality of super capacitors,
the battery pack and the super capacitor pack are respectively connected with a bidirectional DC/DC interface circuit I and a bidirectional DC/DC interface circuit II which are connected with a direct current bus,
an interface circuit between the battery pack and the supercapacitor pack;
the controller includes an interface circuit controller and an energy management controller.
The control strategy of the hybrid energy source system for the electric vehicle comprises the following steps:
the interface circuit controller can acquire voltage signals of each battery monomer in the battery pack in real time, generate control signals to drive a switch network in the interface circuit and the super capacitor to be switched properly to form a voltage-sharing circuit of the battery pack, and maintain dynamic balance of the voltage of each battery monomer in the charging and discharging processes according to a charging and discharging voltage-sharing control program of the battery pack; the system can also acquire the SOC signal of the super capacitor in real time and combine the SOC signal with the vehicle condition prediction control to generate a control signal to realize the direct energy exchange of the two types of energy storage sources, so that the super capacitor operates in a better charge state and fully exerts the power regulation capacity of the super capacitor, thereby effectively improving the power performance of the whole vehicle and the recovery efficiency of regenerative braking energy;
the energy management controller enables two energy sources, namely a battery and a super capacitor, to respond to the change of load power in time by controlling the first bidirectional DC/DC interface circuit and the second bidirectional DC/DC interface circuit, and according to a power coordination control strategy of a voltage-current double closed loop, when frequent and violent load power fluctuation is responded, the storage battery provides a medium-low frequency component of the load power fluctuation to bear the main force of an energy storage system, and the super capacitor provides a high-frequency component in the load power fluctuation, so that reasonable distribution of power between the storage battery and the super capacitor is realized, the direct-current bus voltage can be stabilized, and the reliability and the economy of the system are improved.
Preferably, the interface circuit controller firstly charges the super capacitor by the battery with high terminal voltage through the action of the switch, then discharges the battery monomer with low terminal voltage by the super capacitor, and achieves the purpose of voltage balance by changing the average value of charging current of the two battery monomers;
the voltage-sharing control flow during charging is as follows: detecting the voltage values of n battery monomers, comparing the voltage values, and finding out the maximum value U of the voltagemaxAnd minimum value Umin，Recording the number of the battery monomer with the highest current voltage by max, and recording the maximum value U of the current voltagemaxAnd the set maximum allowable charging voltage value UaMaking a comparison if UmaxGreater than or equal to a set value UaIf not, charging is continued, and U is addedmaxAnd UminIs different from the allowable minimum pressure difference UgMaking a comparison if UmaxAnd UminIs less than the minimum allowable differential pressure UgAnd the voltage equalizing process is finished. If max is 1, starting the voltage equalizing module 1, and if max is n, starting the voltage equalizing module n-1; otherwise, judging Vmax+1And Vmax-1If V ismax+1>Vmax-1Then starting the battery cell Bmax-1And BmaxThe voltage equalizing module max-1 is not required, otherwiseThen starting the battery cell BmaxAnd Bmax+1The voltage equalizing module max. The process slows down the voltage rising speed of the battery monomer with the maximum voltage, so that the voltage of other battery monomers with smaller voltage rises relatively fast, the voltage of the battery monomer with the maximum voltage rises relatively slow, the voltage-sharing process is continuously and circularly carried out, the dynamic voltage-sharing of the series battery pack in the charging process can be well completed, and finally the voltages of all the battery monomers tend to be consistent;
the voltage-sharing control flow during discharging is as follows: detecting the voltage values of n battery monomers, comparing the voltage values, and finding out the maximum value U of the voltagemaxAnd minimum value UminRecording the number of the battery monomer with the lowest current voltage by using min, and recording the minimum value U of the current voltageminAnd the set minimum allowable discharge voltage value UbMaking a comparison if UminLess than or equal to a set value UbIf not, discharging is continued, and U is addedmaxAnd UminIs different from the allowable minimum pressure difference UgMaking a comparison if UmaxAnd UminIs less than the minimum allowable differential pressure UgAnd the voltage equalizing process is finished. If min is equal to 1, starting the voltage equalizing module 1, and if min is equal to n, starting the voltage equalizing module n-1; otherwise, judging Vmin+1And Vmin-1If V ismin+1>Vmin-1Then starting the battery cell BminAnd Bmin+1The voltage equalizing module min is started, otherwise, the battery monomer B is startedmin-1And BminThe voltage-sharing module min-1 slows down the voltage drop speed of the battery monomer with small voltage in the process, so that the voltage drop of other battery monomers with larger voltage is relatively fast, the voltage drop of the battery monomer with the minimum voltage is relatively slow, the voltage-sharing process is continuously and circularly carried out, the dynamic voltage sharing of the series battery pack in the discharging process can be well completed, and finally the voltage of each battery monomer tends to be consistent.
Preferably, the super capacitor SOC control strategy is: state of charge (SOC) of supercapacitorsc(t)) Representing the amount of the stored electricity, and can be divided into a discharge warning area (0) according to the value<SOCsc(t)<SOCscmin) Object, objectRegion (SOC)scmin<SOCsc(t)<SOCscmax) And a charging alert zone (SOC)scmax<SOCsc(t)<1) Three regions, and the control target is the SOC of the super capacitorsc(t) the vehicle is kept in a target area as much as possible during the running of the vehicle, the dynamic performance of the vehicle is effectively exerted, and the recovery efficiency of the regenerative braking energy is improved. The road condition state information on a future road section is obtained by advanced technologies such as a vehicle-mounted GPS and intelligent traffic, and the change of the automobile running state on a future section of road is predicted. When the automobile is pre-accelerated, if the SOC of the super capacitor is at the momentsc(t) lower than lower limit value SOCscminIf the power battery is required to be controlled to charge the super capacitor through the interface circuit, the super capacitor absorbs energy until the SOC of the super capacitorsc(t) increase to SOCscmaxReleasing energy for accelerating the automobile; when the automobile is about to brake or decelerate, if the SOC of the super capacitor is at the momentsc(t) higher than the upper limit value SOCscmaxControlling the super capacitor to charge the power battery through the interface circuit, and releasing energy by the super capacitor until the SOC of the super capacitorsc(t) decrease to SOCscminAnd recovering the energy of the automobile brake.
Preferably, the power coordination control strategy adopting the voltage-current double closed loop comprises the following parts:
(6) a DC bus voltage control loop; the method comprises the steps that the stability of bus voltage is achieved through the adjustment of the DC bus voltage, and a reference value of load power is obtained;
PL_ref＝VDC*(IC+IO)
wherein ICFor current through the bus capacitance, VDCAnd VDC_refActual and reference values, K, respectively, of the DC bus voltagePvAnd KIvProportional and integral constants, P, of PI regulators for the voltage control loop, respectivelyL_refIs a reference value of the load power, IOTo load electricityA stream;
(7) load power distribution; respectively obtaining reference power of a battery and reference power of a super capacitor by the obtained load power through a first-order low-pass filter;
in the formula: s is Laplace operator, T is filter time constant, PB_ref、PUC_refA reference value for battery and super capacitor power;
(8) calculating a reference current; dividing the reference power of the battery and the reference power of the super capacitor by the terminal voltage of the battery and the super capacitor respectively to obtain the reference current of the super capacitor as follows:
in the formula: i isB_ref、IUC_refReference value, V, of the respective battery and supercapacitor currentsBAnd VUCVoltages of the battery and the supercapacitor, IL1_ref、IL2_refAre respectively a through inductor L1、L2A reference value of the current;
(9) a current control loop; the current through the inductor may generate a transient voltage, i.e. the voltage of the inductor, taking into account the V-I characteristic of the inductive elementL1、IL2Designing PI regulator as control variable to obtain inductance L1、L2The instantaneous voltages on are:
in the formula: i isL1、IL2Are respectively a through inductor L1、L2Current, VL1、VL2Are respectively an inductance L1、L2Voltage across, KP1、KI1Proportional constants and integral constants of a PI regulator in a battery current control loop are respectively; kP2、KI2Proportional constants and integral constants of a PI regulator in the super-capacitor current control loop are respectively provided;
(10) duty ratio calculation; obtaining the IGBT of the switching tube according to kirchhoff's voltage law1And IGBT3Respectively is
In the formula: dBAnd DUCAre respectively a switch tube IGBT1And IGBT3Duty cycle of (d);
(11) generating a PWM signal; and comparing the obtained duty ratio signal with the triangular carrier signal to obtain control signals of the two interface circuits.
Has the advantages that:
1) the hybrid energy source system adopts a simple voltage balance control method, improves the voltage-sharing speed and precision of each battery monomer in the charging and discharging processes, and is very suitable for the energy storage system of the electric automobile.
2) The interface circuit of two kinds of energy sources of direct connection in the hybrid energy source system for the state of charge of super capacitor can be adjusted in the car developments dynamically, can effectively improve the power performance of whole car and the recovery efficiency of regenerative braking energy.
3) The power coordination control strategy of the voltage and current double closed loop used by the hybrid energy source system can reliably ensure the reasonable distribution of the load power between the storage battery and the super capacitor, stabilize the direct current bus voltage and improve the reliability and the economy of the energy storage system.
Drawings
Fig. 1 is a diagram of a hybrid energy source system for an electric vehicle and a control circuit thereof.
Fig. 2(a) and 2(b) are schematic voltage-sharing diagrams of a single voltage-sharing module in the interface circuit (2) during charging and discharging.
Fig. 3(a) and 3(b) are flow charts of voltage-sharing control procedures during charging and discharging of the battery pack.
Fig. 4(a) and 4(b) are schematic diagrams illustrating energy exchange between two energy sources through an interface circuit.
FIG. 5 is a schematic diagram of the control of the super capacitor SOC.
FIG. 6 is an energy management control schematic.
Fig. 7(a) and 7(b) are waveform diagrams of battery pack voltage equalization during charging and discharging processes.
Fig. 8(a) and 8(b) are SOC waveform diagrams of a battery and a super capacitor during starting (or accelerating) and braking (or decelerating) of an automobile.
Fig. 9 is a waveform of load power, battery power, super capacitor power, and dc bus voltage for a hybrid energy source system.
Detailed Description
The invention is further described with reference to the following drawings and detailed description.
As shown in fig. 1, a hybrid energy source system for an electric vehicle includes a hardware circuit and a controller; the hardware circuit includes: the system comprises a battery pack and a super capacitor pack, wherein the battery pack and the super capacitor pack are respectively connected with a first bidirectional DC/DC interface circuit 1 and a second bidirectional DC/DC interface circuit 3 of a direct current bus, and an interface circuit 2 is arranged between the battery pack and the super capacitor pack; the controller includes an interface circuit controller and an energy management controller.
The control strategy of the hybrid energy source system for the electric vehicle comprises the following steps:
the interface circuit controller can acquire voltage signals of each battery monomer in the battery pack in real time, generate control signals to drive a switch network in the interface circuit and the super capacitor to be switched properly to form a voltage-sharing circuit of the battery pack, and maintain dynamic balance of the voltage of each battery monomer in the charging and discharging processes according to a charging and discharging voltage-sharing control program of the battery pack; the system can also acquire the SOC signal of the super capacitor in real time and combine the SOC signal with the vehicle condition prediction control to generate a control signal to realize the direct energy exchange of the two types of energy storage sources, so that the super capacitor operates in a better charge state and fully exerts the power regulation capacity of the super capacitor, thereby effectively improving the power performance of the whole vehicle and the recovery efficiency of regenerative braking energy;
the energy management controller enables two energy sources, namely a battery and a super capacitor, to respond to the change of load power in time by controlling the first bidirectional DC/DC interface circuit and the second bidirectional DC/DC interface circuit, and according to a power coordination control strategy of a voltage-current double closed loop, when frequent and violent load power fluctuation is responded, the storage battery provides a medium-low frequency component of the load power fluctuation to bear the main force of an energy storage system, and the super capacitor provides a high-frequency component in the load power fluctuation, so that reasonable distribution of power between the storage battery and the super capacitor is realized, the direct-current bus voltage can be stabilized, and the reliability and the economy of the system are improved.
The interface circuit controller firstly charges the super capacitor by the battery with high terminal voltage through the action of the switch (state 1), then the super capacitor discharges the battery monomer with low terminal voltage (state 2), and the purpose of voltage balance is achieved by changing the average value of the charging current of the two battery monomers. The charge-discharge voltage-sharing diagrams are shown in fig. 2(a) and (b), respectively.
FIG. 3(a) is a flowchart of the voltage-equalizing process during charging, in which the voltage values of n cells are detected, compared, and the maximum value U of the voltage is foundmaxAnd minimum value UminRecording the number of the battery cell with the highest current voltage by max, and recording the maximum value U of the current voltagemaxAnd the set maximum allowable charging voltage value UaMaking a comparison if UmaxGreater than or equal to a set value UaIf not, charging is continued, and U is addedmaxAnd UminDifference of (2) to the minimum allowedDifferential pressure UgMaking a comparison if UmaxAnd UminIs less than the minimum allowable differential pressure UgAnd the voltage equalizing process is finished. If max is 1, starting the voltage equalizing module 1, and if max is n, starting the voltage equalizing module n-1; otherwise, judging Vmax+1And Vmax-1If V ismax+1>Vmax-1Then starting the battery cell Bmax-1And BmaxThe voltage equalizing module max-1 is adopted, otherwise, the battery monomer B is startedmaxAnd Bmax+1The voltage equalizing module max. The process slows down the voltage rising speed of the battery monomer with the maximum voltage, so that the voltage of other battery monomers with smaller voltage rises relatively fast, the voltage of the battery monomer with the maximum voltage rises relatively slow, the voltage-sharing process is continuously and circularly carried out, the dynamic voltage-sharing of the series battery pack in the charging process can be well completed, and finally the voltages of the battery monomers tend to be consistent.
FIG. 3(b) is a flowchart of the voltage-equalizing process during discharging, which detects the voltage values of n cells, compares them, and finds out the maximum value U of the voltagemaxAnd minimum value UminRecording the number of the battery monomer with the lowest current voltage by using min, and recording the minimum value U of the current voltageminAnd the set minimum allowable discharge voltage value UbMaking a comparison if UminLess than or equal to a set value UbIf not, discharging is continued, and U is addedmaxAnd UminIs different from the allowable minimum pressure difference UgMaking a comparison if UmaxAnd UminIs less than the minimum allowable differential pressure UgAnd the voltage equalizing process is finished. If min is equal to 1, starting the voltage equalizing module 1, and if min is equal to n, starting the voltage equalizing module n-1; otherwise, judging Vmin+1And Vmin-1If V ismin+1>Vmin-1Then starting the battery cell BminAnd Bmin+1The voltage equalizing module min is started, otherwise, the battery monomer B is startedmin-1And BminPressure equalizing module min-1. The process slows down the voltage drop speed of the battery cell with small voltage, so that the voltage drops of other battery cells with larger voltage relatively fast, and the voltage drop of the battery cell with minimum voltage is slowerThe voltage-sharing process is continuously and circularly carried out, so that the dynamic voltage sharing of the series battery pack in the discharging process can be well completed, and finally the voltage of each battery monomer tends to be consistent.
Fig. 4 is a schematic diagram of energy exchange between two energy sources through an interface circuit. Wherein, fig. 4(a) is a charging process of the super capacitor, and energy is transferred to the super capacitor by the power battery. Fig. 4(b) shows the discharging process of the super capacitor, and energy is transferred from the super capacitor to the power battery.
FIG. 5 is a schematic diagram of the control of the super capacitor SOC. State of charge (SOC) of supercapacitorsc(t)) Representing the amount of the stored electricity, and can be divided into a discharge warning area (0) according to the value<SOCsc(t)<SOCscmin) Target region (SOC)scmin<SOCsc(t)<SOCscmax) And a charging alert zone (SOC)scmax<SOCsc(t)<1) Three regions, and the control target is the SOC of the super capacitorsc(t) the vehicle is kept in a target area as much as possible during the running of the vehicle, the dynamic performance of the vehicle is effectively exerted, and the recovery efficiency of the regenerative braking energy is improved. The road condition state information on a future road section is obtained by advanced technologies such as a vehicle-mounted GPS and intelligent traffic, and the change of the automobile running state on a future section of road is predicted. When the automobile is pre-accelerated, if the SOC of the super capacitor is at the momentsc(t) lower than lower limit value SOCscminIf the power battery is required to be controlled to charge the super capacitor through the interface circuit, the super capacitor absorbs energy until the SOC of the super capacitorsc(t) increase to SOCscmaxReleasing energy for accelerating the automobile; when the automobile is about to brake or decelerate, if the SOC of the super capacitor is at the momentsc(t) higher than the upper limit value SOCscmaxControlling the super capacitor to charge the power battery through the interface circuit, and releasing energy by the super capacitor until the SOC of the super capacitorsc(t) decrease to SOCscminAnd recovering the energy of the automobile brake.
FIG. 6 is an energy management control diagram of the entire hybrid energy source system. And a voltage-current double closed loop power coordination control strategy is adopted. The device mainly comprises the following parts:
(1) and a direct current bus voltage control loop. The bus voltage is stabilized by adjusting the dc bus voltage,
and obtains a reference value of the load power.
PL_ref＝VDC*(IC+IO)
Wherein ICFor current through the bus capacitance, VDCAnd VDC_refActual and reference values, K, respectively, of the DC bus voltagePvAnd KIvProportional and integral constants, P, of PI regulators for the voltage control loop, respectivelyL_refIs a reference value of the load power, IOIs the load current.
(2) And (4) load power distribution. And respectively obtaining the reference power of the battery and the reference power of the super capacitor by the obtained load power through a first-order low-pass filter.
In the formula: s is Laplace operator, T is filter time constant, PB_ref、PUC_refIs a reference value for battery and super capacitor power.
(3) And calculating a reference current. Dividing the reference power of the battery and the reference power of the super capacitor by the terminal voltage of the battery and the super capacitor respectively to obtain the reference current of the super capacitor as follows:
in the formula: i isB_ref、IUC_refReference value, V, of the respective battery and supercapacitor currentsBAnd VUCVoltages of the battery and the supercapacitor, IL1_ref、IL2_refAre respectively a through inductor L1、L2A reference value of the current.
(4) A current control loop. The current through the inductor may generate a transient voltage, i.e. the voltage of the inductor, taking into account the V-I characteristic of the inductive elementL1、IL2Designing PI regulator as control variable to obtain inductance L1、L2The instantaneous voltages on are:
in the formula: i isL1、IL2Are respectively a through inductor L1、L2Current, VL1、VL2Are respectively an inductance L1、L2Voltage across, KP1、KI1Proportional and integral constants of the PI regulator in the battery current control loop, respectively. KP2、KI2Respectively are proportional and integral constants of a PI regulator in the super capacitor current control loop.
(5) And (4) duty ratio calculation. Obtaining the IGBT of the switching tube according to kirchhoff's voltage law1And IGBT3Respectively is
In the formula: dBAnd DUCAre respectively a switch tube IGBT1And IGBT3The duty cycle of (c).
(6) A PWM signal is generated. And comparing the obtained duty ratio signal with the triangular carrier signal to obtain control signals of the two interface circuits.
Fig. 7 is a simulation waveform of terminal voltage of a battery cell (the number of battery cells is 3) during charging and discharging. Fig. 7(a) is a waveform of the terminal voltage of the battery cell during the charging process, the rated voltages of the selected three battery cells are 1.8V, 2V, and 2.2V, respectively, and the terminal voltages of the three battery cells finally rise to 2V after stabilization, without occurrence of an overcharge phenomenon; fig. 7(b) is a waveform of the battery terminal voltage during the discharging process, the rated voltages of the selected three battery cells are respectively 3.5V, 3.3V, and 3.1V, and the terminal voltages of the three battery cells finally drop to 0 after stabilization, and no over-discharge occurs. Therefore, the effect of dynamic voltage equalization is very obvious in the charging and discharging processes.
Fig. 8 is a waveform diagram showing SOC variation of two energy sources, namely a power battery and a super capacitor, during starting or accelerating and braking or decelerating of the automobile. The parameter table of the components used is shown in the following table, and the current generated during acceleration (positive value) and deceleration (negative value) of the automobile is simulated by using the current source during simulation.
Fig. 8(a) is a waveform diagram of SOC variation of two energy sources, namely, a power battery and a super capacitor, during starting or accelerating of an automobile, where an initial SOC value of the super capacitor is set to 10%, which obviously cannot meet the requirement of starting or accelerating of the automobile, but through stage 1 (charging the super capacitor by the battery), the super capacitor has the capability of accelerating the automobile, as shown in stage 2; fig. 8(b) is a waveform diagram of SOC variation of two energy sources, i.e. a power battery and a super capacitor, during braking or deceleration of an automobile, where the initial SOC value of the super capacitor is set to 90%, which is not favorable for absorption of regenerative braking energy of the automobile, but through stage 1 (charging the battery capacitor with the super capacitor), the super capacitor has a strong ability to absorb regenerative braking energy, as shown in stage 2; two energy storage sources are subjected to bidirectional energy exchange, so that the SOC of the super capacitor is maintained in a target area (50% -80%) during the running of the automobile, the good acceleration performance of the automobile is ensured, and the recovery efficiency of regenerative braking energy is improved.
FIG. 9 is a graph of load power, battery power, super capacitor power, and DC bus voltage waveforms. The parameters of the components used are shown in the table below, with a cut-off frequency of 1.5Hz and a switching frequency of 10kHz for the low-pass filter. Therefore, for given load power fluctuation, the storage battery and the super capacitor are matched, and the reasonable distribution of the load power between the battery and the super capacitor is realized; the storage battery provides medium and low frequency components of power fluctuation, bears the main force of the energy storage system, the super capacitor has high power response speed, provides high frequency fluctuation, and reduces the pressure of the storage battery. When the load power changes suddenly, the bus voltage fluctuates, and is rapidly stabilized at 500V under the action of the hybrid energy storage. Thus, the dc bus voltage may reflect whether the system power is in equilibrium.
It should be noted that, for those skilled in the art, without departing from the principle of the present invention, several improvements and modifications can be made, and these improvements and modifications should also be construed as the protection scope of the present invention. All the components not specified in the present embodiment can be realized by the prior art.
Claims (4)
1. A control method of a hybrid energy source system for an electric vehicle is characterized by comprising the following steps: the hybrid energy source system for the electric automobile comprises a hardware circuit and a controller;
the hardware circuit includes:
a battery pack including a plurality of battery cells,
the super capacitor group is provided with a plurality of super capacitors,
the battery pack and the super capacitor pack are respectively connected with a bidirectional DC/DC interface circuit I and a bidirectional DC/DC interface circuit II which are connected with a direct current bus,
an interface circuit between the battery pack and the supercapacitor pack;
the controller comprises an interface circuit controller and an energy management controller;
the control strategy of the hybrid energy source system for the electric automobile is as follows: the interface circuit controller firstly charges the super capacitor by the battery with high terminal voltage through the action of the switch, then discharges the battery monomer with low terminal voltage by the super capacitor, and achieves the purpose of voltage balance by changing the average value of charging current of the two battery monomers;
the voltage-sharing control flow during charging is as follows: detecting the voltage values of n battery monomers, comparing the voltage values, and finding out the maximum value U of the voltagemaxAnd minimum value UminRecording the number of the battery cell with the highest current voltage by max, and recording the maximum value U of the current voltagemaxAnd the set maximum allowable charging voltage value UaMaking a comparison if UmaxGreater than or equal to a set value UaIf not, charging is continued, and U is addedmaxAnd UminIs different from the allowable minimum pressure difference UgMaking a comparison if UmaxAnd UminIs less than the minimum allowable differential pressure UgIf yes, ending the pressure equalizing process; if max is 1, starting the voltage equalizing module 1, and if max is n, starting the voltage equalizing module n-1; otherwise, judging Vmax+1And Vmax-1If V ismax+1>Vmax-1Then starting the battery cell Bmax-1And BmaxThe voltage equalizing module max-1 is adopted, otherwise, the battery monomer B is startedmaxAnd Bmax+1The voltage equalizing module max; the process slows down the voltage rising speed of the battery monomer with the maximum voltage, so that the voltage of other battery monomers with smaller voltage rises relatively fast, the voltage of the battery monomer with the maximum voltage rises relatively slow, the voltage-sharing process is continuously and circularly carried out, the dynamic voltage-sharing of the series battery pack in the charging process can be well completed, and finally the voltages of all the battery monomers tend to be consistent;
the voltage-sharing control flow during discharging is as follows: detecting the voltage values of n battery monomers, comparing the voltage values, and finding out the maximum value U of the voltagemaxAnd minimum value UminThe number of the battery monomer with the lowest current voltage is recorded by min,the minimum value U of the current voltageminAnd the set minimum allowable discharge voltage value UbMaking a comparison if UminLess than or equal to a set value UbIf not, discharging is continued, and U is addedmaxAnd UminIs different from the allowable minimum pressure difference UgMaking a comparison if UmaxAnd UminIs less than the minimum allowable differential pressure UgIf yes, ending the pressure equalizing process; if min is equal to 1, starting the voltage equalizing module 1, and if min is equal to n, starting the voltage equalizing module n-1; otherwise, judging Vmin+1And Vmin-1If V ismin+1>Vmin-1Then starting the battery cell BminAnd Bmin+1The voltage equalizing module min is started, otherwise, the battery monomer B is startedmin-1And BminThe voltage-sharing module min-1 slows down the voltage drop speed of the battery monomer with small voltage in the process, so that the voltage drop of other battery monomers with larger voltage is relatively fast, the voltage drop of the battery monomer with the minimum voltage is relatively slow, the voltage-sharing process is continuously and circularly carried out, the dynamic voltage sharing of the series battery pack in the discharging process can be well completed, and finally the voltage of each battery monomer tends to be consistent.
2. The control method of the hybrid energy source system for an electric vehicle according to claim 1, characterized in that: the method comprises the following steps:
the interface circuit controller can acquire voltage signals of each battery monomer in the battery pack in real time, generate control signals to drive a switch network in the interface circuit and the super capacitor to be switched properly to form a voltage-sharing circuit of the battery pack, and maintain dynamic balance of the voltage of each battery monomer in the charging and discharging processes according to a charging and discharging voltage-sharing control program of the battery pack; the system can also acquire the SOC signal of the super capacitor in real time and combine the SOC signal with the vehicle condition prediction control to generate a control signal to realize the direct energy exchange of the two types of energy storage sources, so that the super capacitor operates in a better charge state and fully exerts the power regulation capacity of the super capacitor, thereby effectively improving the power performance of the whole vehicle and the recovery efficiency of regenerative braking energy;
the energy management controller enables two energy sources, namely a battery and a super capacitor, to respond to the change of load power in time by controlling the first bidirectional DC/DC interface circuit and the second bidirectional DC/DC interface circuit, and according to a power coordination control strategy of a voltage-current double closed loop, when frequent and violent load power fluctuation is responded, the storage battery provides a medium-low frequency component of the load power fluctuation to bear the main force of an energy storage system, and the super capacitor provides a high-frequency component in the load power fluctuation, so that reasonable distribution of power between the storage battery and the super capacitor is realized, the direct-current bus voltage can be stabilized, and the reliability and the economy of the system are improved.
3. The control method of the hybrid energy source system for an electric vehicle according to claim 2, characterized in that: the super capacitor SOC control strategy is as follows: SOC of super capacitorsc(t)Representing the amount of the stored electric quantity, and can be divided into a discharge warning area 0 according to the value of the stored electric quantity<SOCsc(t)<SOCscminTarget region SOCscmin<SOCsc(t)<SOCscmaxAnd charging alert zone SOCscmax<SOCsc(t)<1 three regions, and the control target is to make the SOC of the super capacitorsc(t) the vehicle is kept in a target area as much as possible during the running of the vehicle, the power performance of the vehicle is effectively exerted, and the recovery efficiency of regenerative braking energy is improved; acquiring road condition state information on a future road section by utilizing a vehicle-mounted GPS and an intelligent traffic advanced technology, and predicting the change of the running condition of an automobile on a future section of road; when the automobile is pre-accelerated, if the SOC of the super capacitor is at the momentsc(t) lower than lower limit value SOCscminIf the power battery is required to be controlled to charge the super capacitor through the interface circuit, the super capacitor absorbs energy until the SOC of the super capacitorsc(t) increase to SOCscmaxReleasing energy for accelerating the automobile; when the automobile is about to brake or decelerate, if the SOC of the super capacitor is at the momentsc(t) higher than the upper limit value SOCscmaxControlling the super capacitor to charge the power battery through the interface circuit, and releasing energy by the super capacitor until the SOC of the super capacitorsc(t) decrease to SOCscminAnd recovering the energy of the automobile brake.
4. The control method of the hybrid energy source system for an electric vehicle according to claim 2, characterized in that: the power coordination control strategy according to the voltage and current double closed loop comprises the following parts:
4.1 DC bus voltage control loop; the method comprises the steps that the stability of bus voltage is achieved through the adjustment of the DC bus voltage, and a reference value of load power is obtained;
PL_ref＝VDC*(IC+IO)
wherein ICFor current through the bus capacitance, VDCAnd VDC_refActual and reference values, K, respectively, of the DC bus voltagePvAnd KIvProportional and integral constants, P, of PI regulators for the voltage control loop, respectivelyL_refIs a reference value of the load power, IOIs the load current;
4.2 load power distribution; respectively obtaining reference power of a battery and reference power of a super capacitor by the obtained load power through a first-order low-pass filter;
in the formula: s is Laplace operator, T is filter time constant, PB_ref、PUC_refA reference value for battery and super capacitor power;
4.3 calculating a reference current; dividing the reference power of the battery and the reference power of the super capacitor by the terminal voltage of the battery and the super capacitor respectively to obtain the reference current of the super capacitor as follows:
in the formula: i isB_ref、IUC_refReference value, V, of the respective battery and supercapacitor currentsBAnd VUCVoltages of the battery and the supercapacitor, IL1_ref、IL2_refAre respectively a through inductor L1、L2A reference value of the current;
4.4 current control loop; the current through the inductor may generate a transient voltage, i.e. the voltage of the inductor, taking into account the V-I characteristic of the inductive elementL1、IL2Designing PI regulator as control variable to obtain inductance L1、L2The instantaneous voltages on are:
in the formula: i isL1、IL2Are respectively a through inductor L1、L2Current, VL1、VL2Are respectively an inductance L1、L2Voltage across, KP1、KI1Proportional constants and integral constants of a PI regulator in a battery current control loop are respectively; kP2、KI2Proportional constants and integral constants of a PI regulator in the super-capacitor current control loop are respectively provided;
4.5 duty cycle calculation; obtaining the IGBT of the switching tube according to kirchhoff's voltage law1And IGBT3Respectively is
In the formula: dBAnd DUCAre respectively a switch tube IGBT1And IGBT3Duty cycle of (d);
generating a PWM signal; and comparing the obtained duty ratio signal with the triangular carrier signal to obtain control signals of the two interface circuits.
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