JP2008260346A - Power source system for hybrid electric vehicle, and its control device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a power source system for a hybrid electric vehicle having a characteristic as a high energy density type battery and capable of easily performing detection of a transfer timing from an EV traveling mode to an HEV traveling mode. <P>SOLUTION: The power source system for the hybrid electric vehicle has a composite battery 5 in which parallel-connected batteries 20 having two kinds of secondary batteries having different charging state vs voltage characteristic connected in parallel are further connected in series; a voltage detector 7 or 8 for detecting the battery voltage of the composite battery 5. In the parallel-connected batteries 20, a first secondary battery 30 having almost non- or small reduction tendency of an open circuit voltage relative to reduction of the charging state (SOC) and a second secondary battery 40 having large reduction tendency of the open circuit voltage relative to reduction of the charging state are connected in parallel. Thereby, the in-parallel connection batteries 20 are constituted as a battery having the charging state vs voltage characteristic in which the reduction tendency of the open circuit voltage relative to reduction of the charging state is almost no or small and it becomes large near the last stage of discharge. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a hybrid electric vehicle power supply system using a composite battery in which two types of secondary batteries are combined with a hybrid electric vehicle power supply, and a control device therefor.

  Conventionally, as a power source for driving a motor of an electric vehicle (EV) or a hybrid electric vehicle (HEV), a composite battery combining two types of secondary batteries as described in Patent Document 1 has been proposed. The composite battery of Patent Document 1 includes a high output battery (high output density battery) in which a plurality of cells are connected in series, and a high capacity battery (high energy density battery) in which a plurality of cells are connected in series. Are connected in parallel to meet the requirement to obtain a high energy density while maintaining a high output density above a certain level, and the requirement to obtain a high output density while maintaining a high energy density above a certain level. Is.

On the other hand, in a plug-in hybrid electric vehicle that can charge an in-vehicle secondary battery with a household power source, the secondary battery is charged by external charging and then an electric vehicle driving mode (EV driving) using an electric motor as a drive source. When the vehicle is running as long as possible and the battery is near the end of discharge, the engine is started and the hybrid running mode (HEV running) in which the engine and the electric motor are used together is entered. The timing of transition from EV traveling to HEV traveling can be known from the terminal voltage of the battery corresponding to the time when the state of charge (SOC) of the secondary battery reaches the end of discharge.
Japanese Patent Laid-Open No. 2004-111242

  However, in the composite battery in which the high-power battery and the high-capacity battery of Patent Document 1 are connected in parallel, the terminal voltage is almost reduced in the interval from the SOC 100% to the remaining SOC 20%, for example, from the SOC 100%. In addition, the terminal voltage sharply decreases in the interval from the remaining SOC 20% to SOC 0%. For this reason, it is difficult to accurately detect the transition timing from the change in the battery voltage to the HEV traveling mode, and as a result, there is a problem that the transition to the HEV traveling mode cannot be performed at an appropriate timing.

  Of course, if the characteristics of secondary batteries connected in parallel are similar to those of a high power battery (high power density type battery) in which the battery voltage changes greatly due to a decrease in the state of charge of the battery, the voltage drop of the battery voltage It is easy to detect the state of charge of the secondary battery using as a parameter. However, in the secondary battery having such characteristics, there is a problem that the energy density of the secondary battery decreases as the battery voltage decreases. In particular, in the case of a plug-in hybrid electric vehicle, since there is a demand for traveling in the electric vehicle traveling mode (EV traveling mode) for a while after charging, the energy density of the battery is a characteristic that decreases early, This directly leads to the problem that the EV travel section distance is shortened.

  The present invention has been made in order to solve the above-described problems, and has a characteristic as a high energy density battery, and is a hybrid electric vehicle that can easily detect the transition timing from the EV traveling mode to the HEV traveling mode. Provided is a power supply system for a vehicle and a control device for a power supply system for a hybrid electric vehicle capable of making a transition to the HEV travel mode at an appropriate time in view of a tendency of the open circuit voltage to decrease with respect to a decrease in the state of charge of the battery. There is.

  The above object of the present invention is achieved by the following means.

  (1) As a power source for a hybrid electric vehicle, a parallel connection battery in which two types of secondary batteries having different charge state versus voltage characteristics are connected in parallel or a series / parallel connection battery in which this parallel connection battery is further connected in series is used. The parallel connection battery which has a composite battery and the voltage detector which detects the battery voltage of the composite battery, and the parallel battery which comprises the composite battery has the tendency of the open circuit voltage to fall with respect to the reduction | decrease of a state of charge (SOC). A first secondary battery having a first charge state vs. voltage characteristic with little or less, and (b) a decreasing tendency of the open circuit voltage (OCV) with respect to a decrease in the charge state (SOC). A second secondary battery having a second charge state-to-voltage characteristic larger than the voltage characteristic is connected in parallel, and (c) a tendency of the open circuit voltage to decrease with respect to a decrease in the state of charge (SOC) is at least 3rd charge which is little or small in the 1st charge state area until it exceeds the state of charge (SOC) of the minute, and becomes large in the 2nd charge state area after the 1st charge state period to the end of the discharge A power system for a hybrid electric vehicle, characterized in that it is configured as a battery having state-to-voltage characteristics.

  (2) A control device for the above hybrid electric vehicle power supply system, wherein the voltage detector detects a battery voltage of the composite battery during an electric vehicle running mode, and the voltage detector Transition control means for starting the engine and transitioning to the hybrid travel mode when the detected battery voltage drops to a predetermined travel mode transition voltage value, and the transition control means includes the parallel-connected battery. The travel mode transition voltage value is set at a portion where the open circuit voltage tends to decrease with respect to the decrease in the state of charge (SOC) in the third state of charge versus voltage characteristic, and is detected by the voltage detecting means. When the cell voltage determined from the battery voltage reaches the set mode transition voltage value, the hybrid vehicle travels from the electric vehicle travel mode. Shifting to over-de, the controller of the power supply system for a hybrid electric vehicle, characterized in that.

  In the present invention, “battery voltage of a composite battery” refers to “a voltage between terminals of a parallel connection battery (open circuit voltage)” that constitutes the composite battery, and “a direct connection of the parallel connection battery further connected in series. It includes the case of referring to the “voltage between terminals of the parallel connection battery (open circuit voltage)”, that is, “the voltage between terminals of the composite battery (open circuit voltage)”.

  According to the power supply system for a hybrid electric vehicle of the present invention, it has characteristics as a high capacity battery (high energy density type battery) capable of EV traveling for a long time, and easily makes a transition timing from the EV traveling mode to the HEV traveling mode. It is possible to obtain a state-of-charge vs. voltage characteristic that can be detected. In addition, according to the control device of the present invention, it is possible to detect the transition timing using an easily measured power supply voltage as an index. In addition, a transition from the EV traveling mode to the HEV traveling mode can be performed.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a block diagram showing an embodiment in which the present invention is applied to a motor drive power source of a plug-in hybrid electric vehicle, and FIG. 2 is a schematic diagram showing a drive system of the plug-in hybrid electric vehicle.

  This plug-in hybrid electric vehicle includes an engine 1 and a motor 10 as drive sources. That is, as shown in FIG. 2, the output shaft of the engine 1 is connected to the rotating shaft of the motor 10 via the electromagnetic clutch 14, and the output shaft of the motor 10 is connected to the axle 16 via the continuously variable transmission 15. ing.

  In order to drive the motor 10, a power system (power system) 50 for a hybrid electric vehicle including a composite battery 5 described later is provided and connected to the motor 10 via an inverter 9. The rotating shaft of the generator 1, which is a power generation and starting motor, is connected to the rotating shaft of the engine 1 via a drive belt 17. The generator 2 is electrically connected to the power supply system 50 via an inverter 9 and serves to convert the output of the engine 1 into electric power and to perform cranking at the start.

  The motor 10 and the generator 2 are composed of an AC machine such as a three-phase synchronous motor or a three-phase induction motor. However, the motor 10 and the generator 2 are not limited to the AC machine, and a DC motor can also be used. When using a DC motor, a DC / DC converter is used instead of the inverter 9.

  The composite battery 5 includes a parallel-connected battery 20 in which two types of secondary batteries (a first secondary battery 30 and a second secondary battery 40) having different charge state versus voltage characteristics are connected in parallel, or the parallel battery 20 The connection battery 20 is composed of a series-parallel connection battery further connected in series. In the case of this embodiment, as shown in FIG. 3, the composite battery 5 includes a plurality of parallel-connected batteries 20 in which a first secondary battery 30 and a second secondary battery 40 are connected in parallel. It consists of connected series-parallel connected batteries.

  Specifically, as shown in FIG. 4A, each parallel-connected battery 20 has a first charge state vs. voltage characteristic that has little or little tendency to decrease the open circuit voltage with respect to the decrease in the state of charge (SOC). The first secondary battery 30 having (curve A) and the second charge state versus voltage characteristic in which the open circuit voltage decreasing tendency with respect to the decrease in the state of charge (SOC) is larger than the first charge state versus voltage characteristic The second secondary battery 40 having (curve B) is connected in parallel, and as a whole, the tendency of the open circuit voltage to decrease with respect to the decrease in the state of charge (SOC) is at least half the state of charge (SOC 50%). ) Exceeds the first charge state section S1 until the first charge state section S1 is exceeded, and the third charge state increases in the second charge state section S2 from the end of the first charge state section S1 to the end of discharge (SOC 0%). And it is configured as a battery having a voltage characteristic (curve C).

  Here, SOC (%) is a value obtained by dividing the remaining capacity (Ah) of the battery by the full charge capacity (Ah) of the battery and multiplying by 100. It is an index that expresses what percentage of capacity it has.

As a specific example of the parallel-connected battery 20 having the above characteristics, in this embodiment, the positive electrode active material is LiMPO ₄ (where M is one or more elements selected from Fe, Mn, and Co), and the negative electrode active material is graphite. A first secondary battery 30 composed of at least one lithium ion battery (single cell) composed of carbonaceous material and a positive active material of LiMPO ₄ (where M is one or more selected from Fe, Mn, Co) Element) in which the negative electrode active material is connected in parallel with at least one second secondary battery 40 made of amorphous carbon made of amorphous carbon. FIG. 4A schematically shows the charge state vs. voltage characteristics of the parallel-connected battery 20.

LiMPO that has almost no potential dependence on the decrease in the state of charge (SOC) of the battery, except for both ends (the initial and final stages of discharge) of SOC 100% and SOC 0% on the horizontal axis indicating the remaining capacity of the battery, that is, the state of charge (SOC). _{When 4} is used for the positive electrode and graphite having a small potential dependency with respect to a decrease in the state of charge (SOC) of the battery is used for the negative electrode, a battery having a high energy density can be effectively constructed. On the other hand, even when the same LiMPO ₄ is used as the positive electrode, the use of amorphous carbon having a potential dependence on the decrease in the state of charge (SOC) of the battery as the negative electrode reduces the energy density, but the state of charge of the battery (SOC A battery having a voltage dependency with respect to a decrease in the above can be configured. Therefore, when the power supply system 50 is constructed using the parallel connection battery 20 in which these two types of secondary batteries are connected in parallel, or the composite battery 5 in which a plurality of these secondary batteries are connected in series, and EV travels from a fully charged state. Although the battery voltage dependency of the power supply capacity is very small, the voltage depends on the state of charge (SOC) of the battery when the state of charge (SOC) requiring the HEV mode is low, for example, when the SOC is 30% or less. Therefore, it becomes easy to detect the state of charge (SOC) or the remaining capacity of the battery using the battery voltage as an index, and it is possible to reliably detect the timing for switching from the EV traveling mode to the HEV traveling mode. Control in the driving mode is also simplified.

  As shown in FIG. 3, a positive electrode terminal 51 and a negative electrode terminal 52 are provided at both ends of the composite battery 5. In addition, battery expansion ports 21 are provided at both ends of each parallel connection battery 20 of the composite battery 5 so that the number of first secondary batteries 30 or second secondary batteries 40 connected in parallel can be increased. It has become.

  Furthermore, a cell controller 22 that detects the voltage (cell voltage) of each parallel connection battery 20 and controls charge / discharge of the cells is connected between the terminals of each parallel connection battery 20 of the composite battery 5. Here, the “cell voltage” means the voltage of the secondary battery as a single cell. In the present invention, since the secondary batteries of the single cell are connected in parallel, the cell voltage is between the terminals of the parallel-connected battery 20. Same as voltage. The cell controller 22 suppresses the balance of the cell voltage of each single cell of the composite battery 5 in which the parallel-connected batteries 20 are connected in series, that is, the voltage between the terminals of the parallel-connected battery 20, and may be overcharged / discharged. A circuit for determining whether or not.

  Returning to FIG. 1, the power supply system 50 includes the composite battery 5, a current detector 6 that detects a current of the composite battery 5, and a composite battery voltage detector 7 that detects a voltage between terminals of the composite battery 5. The voltage per unit (single cell) of the secondary battery constituting the parallel connection battery 20, that is, the cell voltage detector 8 for detecting the cell voltage. That is, the current detector 6 is inserted in series in the feeding path of the composite battery 5, the composite battery voltage detector 7 is connected to the positive terminal 51 and the negative terminal 52 of the composite battery 5, and the parallel-connected battery 20 is connected. The cell voltage detector 8 is connected to both ends of the. The cell voltage detector 8 is an extracted cell voltage detection function unit of the cell controller 22 described above.

  FIG. 4B is a diagram showing the relationship between the travel mode of the plug-in hybrid electric vehicle and the state of charge (SOC) of the parallel connection battery 20 of the composite battery 5.

  Each parallel-connected battery 20 of the composite battery 5 is first charged to 100% SOC after being charged from the outside, and then used as a motor driving power source for running in the EV running mode. This is shown as EV travel section M1 in FIG. 4 (b).

  The current and terminal voltage of the composite battery 5 in the electric vehicle running mode are detected by the current detector 6 and the composite battery voltage detector 7 and input to the battery controller 11. In addition, the current of the parallel connection battery 20 and the voltage between the terminals are detected by the current detection function unit and the voltage detection function unit (cell voltage detector 8) of the cell controller 22 and input to the battery controller 11.

  The battery controller 11 receives detection signals relating to current and voltage input from the current detector 6, the composite battery voltage detector 7, the cell voltage detector, and the like, and represents the battery state of the parallel-connected battery 20 from these values. Calculate the signal.

  In the case of this embodiment, the battery controller 11 is a signal representing the battery state of the parallel connection battery 20 based on the value of the cell voltage (voltage between terminals of the parallel connection battery 20) detected by the cell voltage detector 8. Is calculated, and the driving mode is shifted when a predetermined condition is satisfied.

  Further, based on the value of the voltage (voltage between terminals of the composite battery 5) detected by the composite battery voltage detector 7, a signal indicating the battery state for the parallel connection battery 20 is calculated, and a predetermined condition is satisfied. In the event of a failure, the driving mode can be changed. In this case, the inter-terminal voltage (cell voltage) per one parallel-connected battery 20 is calculated from the inter-terminal voltage of the composite battery 5 and the number of parallel-connected batteries 20 connected in series, and the parallel value is calculated from the value. The charge state vs. voltage characteristic (curve C) per unit of the connected battery 20 is estimated in comparison with known charge state vs. voltage characteristic data, and the result is output as a signal representing the battery state.

  In any case, the battery controller 11 starts the engine 1 and shifts to the hybrid travel mode when the detected or calculated cell voltage decreases to the predetermined travel mode transition voltage value Es. This running mode transition voltage value Es is a tendency of the open circuit voltage to decrease with respect to the decrease in the state of charge (SOC) on the third state of charge versus voltage characteristic (curve A in FIG. 4A) of the parallel-connected battery 20. Is set in the second charge state section S2, and the battery controller 11 serving as the transition control means determines that the engine 1 when the detected or calculated cell voltage reaches the mode transition voltage value Es. Is started to shift from the EV traveling mode to the HEV traveling mode. The engine 1 is started by receiving a signal indicating the battery state from the battery controller 11 and starting the generator 2, which is a starting motor, by the power generation controller 13 using the power from the composite battery 5. A display device 12 is connected to the battery controller 11.

  The battery controller 11 starts power generation by the generator 2 via the power generation controller 13 after shifting to the HEV travel mode. The electric power generated by the generator 2 is converted into DC power by the rectifier 3 and supplied to the composite battery 5.

  The vehicle controller 18 receives a signal indicating the battery state from the battery controller 11 as well as a vehicle signal indicating the driver's accelerator operation, brake operation, and the like, and controls the operation of the inverter 9.

According to the above-described hybrid electric vehicle power supply system, a lithium ion battery (LiFePO ₄ / graphite battery) in which the positive electrode active material is LiMPO ₄ and the negative electrode active material is graphitic carbon is used as the first secondary battery 30. In addition, a lithium ion battery (LiFePO ₄ / amorphous carbon battery) in which the positive electrode active material is LiMPO ₄ and the negative electrode active material is amorphous carbon is used as the second secondary battery 40, and both are connected in parallel. By configuring the connection battery 20 and using it as a power source for driving the motor, the following advantages can be obtained.

(1) LiFePO _{by 4} / graphitizing batteries connected in parallel LiFePO ₄ / amorphous carbon battery, LiFePO ₄ / graphite as compared with the case of the battery alone, time migration to migrate to the HEV from the EV traveling in plug-in hybrid vehicle, That is, the timing of applying the engine 1 can be easily and reliably detected only by monitoring a parameter that can be easily measured, such as a battery voltage. In other words, while using the positive electrode active material LiFePO ₄ having good durability but almost no potential dependence on the capacity, without significantly degrading the energy density of the battery, and without using an expensive and complicated control system, Only by monitoring the cell voltage, it is possible to detect the transition timing of the travel mode in which HEV travel starts from EV travel, and it is also possible to easily detect the state of charge (SOC) of the power battery during HEV travel.

  For this reason, since it is possible to easily prevent the battery from being excessively discharged by EV traveling with a simple device, it is possible to prevent a vehicle trouble and to make effective use of the entire capacity of the battery.

LiMPO ₄ (wherein M is one or more elements selected from Fe, Mn and Co) is used as the positive electrode active material. Among the elements M listed here, those made of Fe are particularly stable and durable. Can be used well.

(2) Furthermore, by combining a LiFePO ₄ / amorphous carbon battery with a graphite negative electrode battery, the energy density of the battery can be increased compared with the case of using only a LiFePO ₄ / amorphous carbon battery, and the EV travel distance can be increased. Since it can be made longer, it is economical and more favorable to the environment.

  The effects described in (1) and (2) above are particularly preferable when hard carbon is used as the amorphous carbon that is the negative electrode active material of the second secondary battery 40. Hard carbon is advantageous for rate characteristics at a large current because of its capacity, electrode reaction, and particularly easy diffusion of lithium ions inside the active material, even among amorphous carbon with a large capacity potential profile. .

  (3) In the hybrid electric vehicle power supply system of the present invention, the entire parallel-connected battery 20 is regarded as a single cell, and a single cell controller may be provided for this. Compared with the configuration in which the cell controller 22 is provided for each single cell, the number of power cell controllers 22 can be reduced.

For comparison, consider a composite battery configured as shown in FIG. This is because a first series battery formed by connecting a plurality of first secondary batteries 30 made of the above LiFePO ₄ / graphite battery in series and a second secondary battery 40 made of LiFePO ₄ / amorphous carbon battery. Are connected in parallel with each other to form a composite battery. In the case of such a configuration, as shown in FIG. 12, a cell controller 22 is provided for each single cell composed of one secondary battery.

  Therefore, when the composite battery 5 of FIG. 3 according to the embodiment of the present invention is compared with the composite battery having the configuration of FIG. 12, the number of cell controllers 22 may be half.

  (4) Furthermore, by increasing the capacity of the graphite negative electrode battery connected in parallel or connecting another graphite negative electrode battery in parallel using the battery expansion port 21, a vehicle having substantially the same configuration can be obtained. It is possible to configure plug-in hybrid vehicles having different EV travel distances.

  Examples of the present invention will be described below in comparison with comparative examples.

<Example 1>
Parallel LiFePO ₄ as the positive electrode active material, the first secondary battery 30 to the graphite negative active material, the LiFePO ₄ as a positive electrode active material, and a second secondary battery 40 to the hard carbon as a negative electrode active material A connected parallel connection battery 20 was created.

(Creation of positive electrode)
LiFePO ₄ (lithium iron phosphate) was prepared as a positive electrode active material by synthesis by the method of Deracourt et al. (Electrochemical Solid-State Letters, 9 (2006) A355.).

Next, LiFePO ₄ prepared above, acetylene black as a conductive additive, and PVdF (polyvinylidene fluoride) as a binder were mixed to prepare a positive electrode active material slurry. At that time, the composition ratio was adjusted to be positive electrode active material: acetylene black: PVdF = 86: 7: 7.

First, LiFePO ₄ , acetylene black and PVdF were weighed, and an appropriate amount of NMP (N-methyl-2-pyrrolidone) was added thereto, followed by thorough stirring and mixing with a homogenizer. Thereafter, using a die coater, a certain amount of this slurry was applied to both sides of a 20 μm thick aluminum foil as a current collector and dried. Thus, the positive electrode layer was formed on both surfaces of the aluminum foil. Then, at pressing by a roll press, the positive electrode layer portion such that the 100Mmx200mm, and cut out so as to lead a portion electrode layer is not present remains, was one LiFePO ₄ positive electrode. The coating conditions were adjusted so that the thickness of the positive electrode layer of this LiFePO ₄ positive electrode was 120 μm at the time of completion.

(Creation of negative electrode)
The negative electrode active material of the first secondary battery 30 is graphite having an average particle diameter of 20 μm, and the negative electrode active material of the second secondary battery 40 is hard carbon having an average particle diameter of 21 μm or hard having an average particle diameter of 5 μm. Carbon was used.

  The graphite negative electrode of the first secondary battery 30 was produced as follows, similarly to the case of the hard carbon negative electrode. In a homogenizer container, add a negative electrode active material made of graphite with an average particle diameter of 20 μm, acetylene black as a conductive additive, PVdF as a binder, and an appropriate amount of NMP as a slurry viscosity adjusting solvent, and stir and mix well. A negative electrode active material slurry was prepared. Next, this negative electrode active material slurry of graphite was applied to both sides of a copper foil as a current collector so that the mass of carbon per unit area was 1: 1, dried and pressed. .

  This negative electrode active material slurry was applied to both sides of a 15 μm thick copper foil as a current collector using a die coater and dried. As a result, a negative electrode layer made of graphite was formed on both sides of a copper foil as a current collector, and pressed to be 105 mm × 210 mm, and the lead portion where the negative electrode layer did not exist was cut out, leaving 1 A sheet of graphite negative electrode was obtained. The coating conditions were adjusted so that the thickness of the negative electrode layer of the graphite negative electrode was 80 μm when completed.

  The hard carbon negative electrode of the second secondary battery 40 was produced as follows. In a homogenizer container, a negative active material made of hard carbon having an average particle diameter of 21 μm or hard carbon having an average particle diameter of 5 μm, acetylene black as a conductive assistant, PVdF as a binder, an appropriate amount as a slurry viscosity adjusting solvent NMP was added and stirred and mixed well to prepare a negative electrode active material slurry. In this hard carbon negative electrode slurry, the mass ratio of negative electrode active material: acetylene black: PVdF was 88: 4: 8.

  This negative electrode active material slurry was applied to both sides of a 15 μm thick copper foil as a current collector using a die coater and dried. As in the case of the positive electrode, a negative electrode layer is formed on both sides of the current collector copper foil, pressed, and cut out to 105 mm × 210 mm, leaving a lead portion where the negative electrode layer is not present. Thus, one hard carbon negative electrode was obtained. The coating conditions were adjusted so that the thickness of the negative electrode layer of the hard carbon negative electrode was 80 μm at the time of completion.

(Electrolyte adjustment)
Ethylene carbonate (EC) and diethyl carbonate (DEC) were mixed at a volume ratio of 3: 7 to obtain a plasticizer (organic solvent) for the electrolytic solution. Subsequently, LiPF6 which is a lithium salt was added to this plasticizer so that it might become a density | concentration of 1M, and electrolyte solution was adjusted.

(Production of battery)
The production of the graphite negative electrode battery (first secondary battery 30) was performed as follows.

Each of the LiFePO ₄ positive electrode and graphite negative electrode cut out above was dried for 1 day in a 90 ° C. vacuum dryer. Six positive electrodes and seven graphite negative electrodes are alternately laminated so that a 25 μm thick polypropylene porous film is interposed between the positive electrode and the negative electrode, and the outermost side is the negative electrode. The negative electrode was bundled and the lead was welded. A positive electrode and negative electrode lead was drawn from this laminate, and was placed in an aluminum laminate film back, and the electrolyte was injected with a liquid injector, and sealed under reduced pressure to obtain a battery.

  In addition, the hard carbon negative electrode battery (second secondary battery 40) was produced as follows.

Each of the LiFePO ₄ positive electrode and hard carbon negative electrode cut out above was dried for one day in a 90 ° C. vacuum dryer and used. Six positive electrodes and seven negative electrodes are alternately laminated between the positive electrode and the negative electrode with a 25 μm-thick polypropylene porous film interposed between the positive electrode and the negative electrode. Bundled and welded the lead. A positive electrode and negative electrode lead was drawn out from the laminate, and placed in an aluminum laminate film back, and an electrolyte was injected with a liquid injector, and sealed under reduced pressure to obtain a battery.

(Parallel connection)
The above-mentioned two types of batteries, the graphite negative electrode battery (first secondary battery 30) and the hard carbon negative electrode battery (second secondary battery 40) were connected in parallel to constitute a parallel connection battery 20. After charging the parallel-connected battery 20 at a constant current-constant voltage up to 4 V at a current value of 0.3 C, a discharge curve after charging at a current value of 0.1 C was measured, and the charge state vs. voltage Characteristics (curve C1) were obtained. The relationship between the state of charge (SOC) of the parallel-connected battery 20 and the battery voltage (inter-terminal voltage) at this time is shown in FIG. In FIG. 5, the vertical axis represents the voltage across the terminals of the parallel-connected battery 20, but this reflects the open circuit voltage of each single cell.

  From FIG. 5, the decreasing tendency of the open circuit voltage with respect to the decrease in the state of charge (SOC) is almost or small in the first state of charge S1 up to SOC 35% exceeding at least half the state of charge (SOC 50%). It can be seen that the battery is configured as a battery having a third state of charge versus voltage characteristic (curve C) that increases in the second state of charge S2 from SOC over 0% to SOC 0% at the end of discharge.

  If the request is made to travel as long as possible in the HEV travel mode, the transition point to the HEV travel mode may be determined in the third charging state section S3 from about 35% SOC to about 10% SOC. When the third charge state section S3 is viewed using the voltage across the terminals of the parallel-connected battery 20 as an index, the mode transition voltage value Es is between 3.15V and 2.5V corresponding to the third charge state section S3. It will be good if it is decided to. Further, the charge state versus voltage characteristic (curve C1) of the parallel-connected battery 20 shown in FIG. 5 has a gentle slope, and the voltage range that can be selected as the mode transition voltage value Es is a range of 3.15V to 2.5V. Therefore, it is easy to determine a point to shift to the HEV traveling mode. If it is determined near the center of the voltage range, the mode transition voltage value Es is preferably determined in the range of 2.8V to 2.6V, and it can be seen that the battery capacity can be effectively used.

  In determining the third charge state section S3, the end of discharge (SOC 0%) is not used, and the previous SOC is about 10%. In order to prevent running, it is desirable to leave a spare capacity. Because. FIG. 4B shows the relationship between the EV travel section M1, the HEV travel section M2, and the spare section M3.

  Eight parallel-connected batteries 20 of Example 1 were connected in parallel, and 12 of them were further connected in series to constitute a composite battery 5 as a motor driving power source. In addition, one cell controller 22 is provided for each parallel-connected battery 20, and a battery expansion port 21 for further adding a graphite negative electrode battery is attached. When this composite battery 5 was used as a motor drive power source, as shown in Table 1, the engine start timing was easily detected and the battery energy density ratio was a high value of 1.21.

  Here, “energy density” is obtained by repeatedly charging and discharging a single cell, and dividing the product of the battery capacity (Ah) during discharge and the average voltage (V) during discharge by the mass (kg) of the cell. Mass energy density (Wh / kg). The battery energy density ratio in Table 1 is obtained as a comparative value when the energy density in the hard carbon negative electrode battery of Comparative Example 2 described later is 1.

<Example 2>
As Example 2, the positive electrode of the graphite negative electrode battery (first secondary battery 30) in Example 1 was changed to 8 sheets and the negative electrode was changed to 7 sheets, and the hard carbon negative battery (second secondary battery 40) was changed. In the same manner as in Example 1, except that the number of positive electrodes was changed to 4 and the number of negative electrodes was changed to 5, and the negative electrode mass ratio (graphite: hard carbon) was changed from 1: 1 to 2: 1 in Example 1. A connection battery 20 was produced. FIG. 6 shows the relationship between the battery charge state (SOC) of the parallel connection battery 20 and the battery voltage.

  As can be seen from FIG. 6, the charge state vs. voltage characteristics (curve C2) of the parallel connection battery 20 of Example 2 are compared with the charge state vs. voltage characteristics (FIG. 5) of the parallel connection battery 20 of Example 1. The second charge state section S2 in which the one charge state section S1 is longer and the voltage between the terminals falls to 3.15 V to 2.5 V becomes narrower and approaches a high capacity battery (high energy density type battery). However, this curve C2 also does not lose the characteristic of gradually falling in the relatively wide second charging state section S2, and the mode transition voltage value Es at the traveling mode transition point can be easily determined. Considering the slope of the curve C, the transition point to the HEV travel mode is determined in the third charge state section S3 from about SOC 17% to about SOC 5%. At this time, the voltage range in which the mode transition voltage value Es can be set does not change, and the mode transition voltage value Es may be determined in a wide range of 3.15 V to 2.5 V corresponding to the third charging state section S3. become. It can also be seen that when the mode transition voltage value Es is determined in the range of 2.8V to 2.6V near the center of the voltage range, the battery capacity can be effectively utilized.

  Eight parallel-connected batteries 20 of Example 2 were connected in parallel, and 12 of them were further connected in series to constitute a composite battery 5 as a motor driving power source. When this composite battery 5 was used as a motor drive power source, as shown in Table 1, the engine start timing was easily detected and the battery energy density ratio was a high value of 1.33.

<Example 3>
As Example 3, the positive electrode of the graphite negative electrode battery (first secondary battery 30) in Example 1 was changed to 8 sheets and the negative electrode was changed to 9 sheets, and the positive electrode of the hard carbon negative battery (second secondary battery 40). 2 and 3 negative electrodes, and the negative electrode mass ratio (graphite: hard carbon) was changed from 1: 1 to 4: 1 in Example 1, in the same manner as in Example 1, in a parallel connection battery. 20 was produced. FIG. 7 shows the relationship between the battery charge state (SOC) of the parallel connection battery 20 and the battery voltage.

  As can be seen from FIG. 7, the characteristic (curve C3) of the parallel connection battery 20 of Example 3 is longer in the first charge state section S1 than the characteristic of the parallel connection battery 20 of Example 2 (FIG. 6). And 2nd charge condition area S2 in which the voltage between terminals falls to 3.15V-2.5V becomes narrower, and approaches a high capacity | capacitance battery (high energy density type battery). However, this curve C3 also does not lose the characteristic of gently falling in the second charging state section S2, and the mode transition voltage value Es at the traveling mode transition point can be easily determined. Considering the slope of the curve C, the transition point to the HEV drive mode is determined in the third charging state section S3 from about SOC 15% to about SOC 5%. At this time, the voltage range in which the mode transition voltage value Es can be set does not change, and the mode transition voltage value Es may be determined in a wide range of 3.15 V to 2.5 V corresponding to the third charging state section S3. become. It can also be seen that when the mode transition voltage value Es is determined in the range of 2.8V to 2.6V near the center of the voltage range, the battery capacity can be effectively utilized.

  Eight parallel-connected batteries 20 of Example 3 were connected in parallel, and twelve of them were further connected in series to constitute a composite battery 5 as a motor driving power source. When this composite battery 5 was used as a power source for driving a motor, as shown in Table 1, the engine start timing was easily detected and the battery energy density ratio was a high value of 1.4.

<Comparative Example 1>
As Comparative Example 1, a power source battery as a motor driving power source was constituted only by the graphite negative electrode battery of Example 1 (first secondary battery 30). Here, the power supply battery was constituted only by a series connection battery in which secondary batteries (single cells) using 12 positive electrodes and 13 graphite negative electrodes were connected in series. There is no second secondary battery 40. Therefore, Comparative Example 1 is equivalent to the negative electrode mass ratio (graphite: hard carbon) changed from 1: 1 to 1: 0 in Example 1. FIG. 8 shows the relationship between the battery charge state (SOC) of the single battery and the battery voltage in the power supply battery of Comparative Example 1.

  As can be seen from FIG. 8, this graphite negative electrode battery exhibits characteristics as a high-capacity battery (high energy density type battery). However, since the fall is steep, the transition point of the running mode is detected from the change in battery voltage. It ’s difficult.

  When the power source battery of Comparative Example 1 was used as a motor driving power source, as shown in Table 1, the battery energy density ratio was a high value of 1.7, but it was difficult to detect the engine start timing. there were.

<Comparative example 2>
As Comparative Example 2, a power battery as a motor driving power source was constituted only by the hard carbon negative electrode battery (second secondary battery 40) of Example 1. Here, the power supply battery was constituted only by a series connection battery in which secondary batteries (unit cells) using 12 positive electrodes and 13 hard carbon negative electrodes were connected in series. There is no first secondary battery 30. Therefore, Comparative Example 2 is equivalent to the negative electrode mass ratio (graphite: hard carbon) changed from 1: 1 to 0: 1 in Example 1. FIG. 9 shows the relationship between the battery charge state (SOC) of the single battery and the battery voltage in the power source battery of Comparative Example 2.

  As can be seen from FIG. 9, this hard carbon negative battery has a gradual fall, so it is easy to detect the running mode transition point from the change in battery voltage, but the remaining capacity of the battery also decreases. Therefore, characteristics as a high capacity battery (high energy density type battery) are not ensured.

  When the power supply battery of Comparative Example 2 was used as a motor drive power supply, as shown in Table 1, the ease of engine start timing detection was good, but the battery energy density ratio was 1, which was a low value. It was.

  Table 1 summarizes the advantages and disadvantages of the parallel-connected batteries 20 of Examples 1 to 3 described above and the cells of the power batteries of Comparative Examples 1 and 2. In Table 1, the negative electrode mass ratio, the ease of detection of engine start timing based on the battery voltage, and the battery energy density ratio are based on the hard carbon negative battery of Comparative Example 2, and the relative values of the parallel-connected battery 20 or the single battery relative thereto. Evaluated.

As can be seen from Table 1, a second secondary battery 40 using LiFePO ₄ as a positive electrode active material and hard carbon as a negative electrode active material and a first secondary battery 30 using graphite carbon as a negative electrode active material are arranged in parallel. The composite battery 5 (Examples 1 to 3) including the parallel connection batteries 20 that are connected and further connected in series can easily and reliably detect the timing of entering the HEV travel mode from the EV travel mode. For this reason, since it is not necessary to switch the driving mode early because there is a problem due to excessive discharge or fear of this, the energy capacity of the battery can be used effectively. Moreover, since the graphite carbon negative electrode battery can be utilized in parallel with the hard carbon negative electrode battery, a power battery having excellent energy density and good controllability can be configured. By mounting this power supply battery, a plug-in hybrid electric vehicle with high performance and good controllability can be configured.

  Next, an example in which the composite battery 5 using the parallel connection battery 20 of Example 1 is applied to a motor driving power source of a plug-in hybrid electric vehicle will be described.

  Recently, a plug-in hybrid electric vehicle that travels by EV for a distance that can be traveled on a daily basis has attracted attention. On the other hand, looking at lithium ion batteries with high potential, in recent years, composite phosphorous oxides of transition metals and lithium have been developed as positive electrode materials having high chemical stability and excellent durability. When this type of positive electrode material and graphite negative electrode material are used to form a battery, the battery capacity voltage profile is flat and a battery having a high energy density can be formed. However, when a power source for a plug-in hybrid electric vehicle is used, a secondary battery In addition, a highly accurate ammeter is required to detect the state of charge (SOC), and an error in current integration is likely to occur. In particular, since the battery voltage changes abruptly only at the end of the discharge of the battery, the EV drive mode is set with complicated control and a sufficient capacity with a margin for setting the timing for shifting from the EV drive mode to the HEV drive mode. It is necessary to take measures such as giving up, leaving a problem in terms of effective use of the battery.

  Therefore, a specific example of control for easily shifting the running mode of the plug-in hybrid electric vehicle by using the composite battery 5 of Example 1 as a motor driving power source will be described with reference to FIGS. .

  FIG. 10 is a flowchart showing a procedure for charging the composite battery 5 formed by connecting the parallel connection batteries 20 of Example 1 in series and storing the remaining battery capacity (EN).

  First, it is confirmed that the battery temperature T is lower than the predetermined temperature T0, that is, T <T0 (S101). When the battery temperature T is equal to or higher than the predetermined temperature T0, the battery cooling fan is operated to cool to T <T0 (S102).

  Next, the composite battery 5 is charged while detecting the composite battery voltage (E) and maintaining T <T0 (S103 to S104). The inter-terminal voltage and current in the parallel-connected battery 20 at the time of charging, that is, the detection data of the time change of the cell voltage and cell current are stored in the memory, and the charging is terminated (S105 to S106).

  Thereafter, the state of charge (SOC) of the single cell, that is, the remaining battery capacity (EN) is calculated, the calculated remaining battery capacity data is written in the nonvolatile memory, and the charging process is terminated (S107 to S108). Here, when the remaining battery capacity (EN) is obtained, the charging energy is calculated from the current-voltage curve data at the time of charging, and is obtained from the capacity-voltage relationship of the cells stored in the memory and the cell voltage before charging. Add the remaining capacity before charging. Further, when calculating the charging energy, correction is made in consideration of the influence of the internal resistance of the cell.

  The composite battery 5 charged in this way is used as a motor driving power source.

  Next, a control method during travel of the plug-in hybrid electric vehicle using the composite battery 5 will be described based on the flowchart of FIG.

  The battery controller 11 detects the cell voltage (voltage between terminals of the parallel-connected battery 20) (E) by the cell voltage detector 8, while reading the known remaining capacity data (EN) and comparing the two. The remaining capacity of the battery is calculated, and the result is displayed on the display device 12 (S201 to S204).

  Alternatively, the composite battery voltage detector 7 detects the composite battery voltage and calculates the cell voltage (voltage between terminals of the parallel-connected battery 20) (E) from the composite battery voltage, while the known remaining capacity data (EN) Is read, the remaining capacity of the battery is calculated by comparing the two, and the result is displayed on the display device 12 (S201 to S204).

  The remaining capacity is stored in advance in the battery voltage and memory measured from the remaining capacity data when the battery is fully charged (SOC 100%) before the vehicle travels, and otherwise measured. It is calculated from a battery voltage-capacity relationship table.

  Next, it is determined whether the traveling mode is the urban area mode or the high speed mode (S205). In the urban area mode, there is a remaining battery capacity capable of running on an electric vehicle (EV running), that is, the cell voltage (E) is not lowered to the predetermined running mode transition voltage value Es described above. Confirm (S206). If it is confirmed (S206: YES), EV traveling is performed (S207).

  While the EV traveling is continued, the cell voltage (E) is always detected (S209), and whether or not the EV traveling is possible, that is, whether or not the cell voltage (E) is larger than the traveling mode transition voltage value Es. Is checked (S210). If the cell voltage (E) is greater than the travel mode transition voltage value Es (S210: YES), the process returns to step S207 to continue the EV travel (S207 to S210).

  As a result, the remaining capacity of the parallel-connected battery 20 decreases, the state of charge (SOC) enters a small region, and the cell voltage (E) reaches the travel mode transition voltage value Es. As a result, the determination in step S210 becomes NO (EV traveling is impossible), and the battery controller 11 starts the generator 2 as a starter motor via the power generation controller 13 and starts the engine 1 (S216). Thereafter, the vehicle is operated in the hybrid travel mode while charging the regenerative power (S217).

  On the other hand, if it is determined in step S205 that the travel mode is the high speed mode, the engine 1 is started, the regenerative electric power is turned off, and the vehicle is operated in the hybrid travel mode (S211). Then, the cell voltage (E) is monitored during operation in the high speed mode (S213), and whether or not the cell voltage (E) is higher than a predetermined voltage value Et (Et ≧ Es) (E> Et). Is determined (S214). If YES, the process returns to step S211, and the operation in the high-speed mode is continued. When the cell voltage (E) is reduced to the predetermined voltage value Et, charging by regenerative power is turned on (S215), and the process goes to step S216. move on. In addition, when stopping the driving | operation in high speed mode, it progresses to step S206 from step S212, and starts driving | running in a city area mode.

  The parallel-connected battery 20 of Example 1 has the charge state vs. voltage characteristics shown in FIG. 5, and the sloped portion where the voltage gently decreases with respect to the decrease in the state of charge (SOC) is a portion near the end of discharge. Therefore, if a mode transition point is set to a voltage value of 2.6 V or more and 2.8 V or less corresponding to approximately 20% of SOC at substantially the center of the inclined portion, this voltage value is set to the above-described steps S209 to S209. The mode transition point from the electric vehicle travel mode to the hybrid travel mode can be easily detected only by constantly monitoring in S210.

  The present invention is not limited to the above-described embodiment, and can be variously modified. For example, in the above-described embodiment, the voltage between the terminals is detected for one representative parallel-connected battery 20 among the plurality of parallel-connected batteries 20 constituting the composite battery 5, and the travel mode is determined from the change in the voltage value. The transition timing was detected. However, the present invention is not limited to this. That is, the voltage between terminals of each parallel connection battery 20 is detected for two or more parallel connection batteries 20 or for all parallel connection batteries 20 among the plurality of parallel connection batteries 20 constituting the composite battery 5. And it is also possible to detect the driving mode transition timing by comprehensively evaluating it.

  Moreover, in embodiment mentioned above, the voltage between terminals of the parallel connection battery 20 which comprises the composite battery 5 was detected, and driving mode transfer timing was detected from the change of the voltage value. However, the charge state vs. voltage characteristics regarding the tendency of the open circuit voltage to decrease with respect to the decrease in the state of charge (SOC) are as seen from the voltage across the terminals of the parallel connection battery 20 and as seen from the voltage across the terminals of the composite battery 5. There is a correlation, and it is almost proportional. Therefore, instead of the voltage detector that detects the inter-terminal voltage of the parallel-connected battery 20, the inter-terminal voltage of the composite battery 5 is detected by the composite battery voltage detector 7, and the detected voltage is the charge state in the composite battery 5. The battery controller 11 can also be configured to shift from the electric vehicle travel mode to the hybrid travel mode when a predetermined mode transition voltage value on the voltage characteristic is reached, thereby easily detecting the travel mode transition timing. be able to.

  Moreover, in the said embodiment, although the number of the 1st secondary battery 30 and the 2nd secondary battery 40 which comprise the said parallel connection battery 20 was mutually the same number, the 1st secondary battery 30 and the 2nd The number of parallel batteries may be different from that of the secondary battery 40. For example, as shown in FIG. 13A, a parallel connection battery 20 in which two first secondary batteries 30 and one second secondary battery 40 are connected in parallel, or FIG. 13B. As shown in FIG. 1, it is possible to configure a parallel connection battery 20 in which one first secondary battery 30 and two second secondary batteries 40 are connected in parallel. Of course, the number of the first secondary batteries 30 and the second secondary batteries 40 constituting the parallel connection battery 20 may be increased or decreased by the same number or different from each other.

  Moreover, in the said embodiment, although the number of the 1st secondary battery 30 and the 2nd secondary battery 40 in the parallel branch which comprises the said parallel connection battery 20 was made into the same number, the 1st secondary of the same kind As long as it is a combination of the battery 30 or the second secondary battery 40, a configuration in which a plurality of secondary batteries are connected in series or a configuration in which the batteries are connected in series and parallel can be used. As the former, for example, as shown in FIG. 14, a parallel-connected battery 20 in which two series first secondary batteries 30 and two series second secondary batteries 40 are connected in parallel is configured. Can do. Further, as the latter, for example, as shown in FIG. 15A, a series-parallel circuit in which one first secondary battery 30 and two parallel first secondary batteries 30 are connected in series is used. The parallel connection battery 20 can be configured by connecting in parallel a series circuit composed of the individual second secondary batteries 40. Further, as shown in FIG. 15B, a series circuit composed of two first secondary batteries 30 in series, one second secondary battery 40 and two second secondary batteries in parallel. The parallel-connected battery 20 can be configured by connecting in parallel a series-parallel circuit in which 40 is connected in series.

It is a block diagram which shows the control system of the hybrid electric vehicle concerning one Embodiment of this invention. FIG. 2 is a block diagram showing a drive system of the hybrid electric vehicle of FIG. 1. It is a figure which shows the structure of the power supply system concerning one Embodiment of this invention. It is a figure which shows the charge condition versus voltage characteristic of the parallel connection battery in the power supply system of FIG. It is a figure which shows the charge condition versus voltage characteristic of the parallel connection battery concerning Example 1 of this invention. It is a figure which shows the charge condition versus voltage characteristic of the parallel connection battery concerning Example 2 of this invention. It is a figure which shows the charge condition versus voltage characteristic of the parallel connection battery concerning Example 3 of this invention. It is a figure which shows the charge condition versus voltage characteristic of the graphite negative electrode battery concerning the comparative example 1. It is a figure which shows the charge condition versus voltage characteristic of the hard carbon negative electrode battery concerning the comparative example 2. FIG. 3 is a flowchart showing a procedure for charging a composite battery using the parallel connection battery of Example 1. It is the flowchart which showed the control procedure at the time of driving | running | working of the plug-in hybrid electric vehicle to which this invention is applied. It is the figure which showed the structure of the composite battery for a comparison with this invention. It is the figure which showed the modification circuit example of the parallel connection battery which comprises the power supply system for hybrid electric vehicles of this invention. It is the figure which showed the other modification circuit example of the parallel connection battery which comprises the power supply system for hybrid electric vehicles of this invention. It is the figure which showed another modified circuit example of the parallel connection battery which comprises the power supply system for hybrid electric vehicles of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Engine 2 Generator 3 Rectifier 5 Composite battery 6 Current detector 7 Composite battery voltage detector 8 Cell voltage detector 9 Inverter 10 Motor 11 Battery controller 12 Display device 13 Electric power generation controller 14 Electromagnetic clutch 15 Continuously variable transmission 16 Axle 17 Drive Belt 18 Vehicle controller 20 Parallel connection battery 21 Battery expansion port 22 Cell controller 30 First secondary battery 40 Second secondary battery 50 Power supply system 51 Positive terminal 52 Negative terminal

Claims (12)

As a power source for a hybrid electric vehicle, a composite battery comprising a parallel connection battery in which two types of secondary batteries having different charge state vs. voltage characteristics are connected in parallel, or a series / parallel connection battery in which this parallel connection battery is further connected in series, and ,
A voltage detector for detecting a battery voltage of the composite battery,
The parallel connection battery constituting the composite battery includes a first secondary battery having a first charge state-to-voltage characteristic with little or no decrease in open circuit voltage with respect to a decrease in charge state, and a decrease in charge state. And a second secondary battery having a second charge state-to-voltage characteristic that is greater than the first charge state-to-voltage characteristic. The decreasing tendency of the circuit voltage is hardly or small in the first charge state interval until it exceeds at least half of the charge state, and is large in the second charge state interval from the first charge state interval to the end of discharge. Configured as a battery having a third state of charge versus voltage characteristic,
A power supply system for a hybrid electric vehicle. The first secondary battery and the second secondary battery are respectively formed on a surface of a current collector, a positive electrode active material layer including a positive electrode active material, an electrolyte layer, and a current collector. A negative electrode active material layer containing a negative electrode active material and a secondary battery having at least one single battery layer laminated in this order,
The positive electrode active material layer and the negative electrode active material layer of the first secondary battery use the first positive electrode active material and the first negative electrode active material exhibiting the first charge state versus voltage characteristics,
Moreover, the active material property which exhibits the said 2nd charge state versus voltage characteristic is used for at least one of the positive electrode active material layer of the said 2nd secondary battery, and a negative electrode active material layer,
The power supply system for a hybrid electric vehicle according to claim 1.   3. The power system for a hybrid electric vehicle according to claim 2, wherein the active material property of the second secondary battery exhibiting the second charge state versus voltage characteristic is a second negative electrode active material. 4. . The first positive electrode active material is used for the positive electrode active material layer of the second secondary battery, and the second negative electrode active material is used for the negative electrode active material layer of the second secondary battery.
The power system for a hybrid electric vehicle according to claim 3. In the first secondary battery, LiMPO ₄ (wherein M is one or more elements selected from Fe, Mn, and Co) is used as the first positive electrode active material constituting the positive electrode active material layer. , Graphite carbon is used as the first negative electrode active material constituting the negative electrode active material layer,
In the second secondary battery, amorphous carbon is used as a second negative electrode active material constituting the negative electrode active material layer.
The power supply system for a hybrid electric vehicle according to claim 4. The power supply system for a hybrid electric vehicle according to claim 5, wherein M of the LiMPO ₄ is Fe.   The power system for a hybrid electric vehicle according to claim 5 or 6, wherein the amorphous carbon is hard carbon. A control device for a power system for a hybrid electric vehicle according to any one of claims 1 to 7,
Voltage detecting means for detecting a battery voltage during the electric vehicle running mode of the composite battery by the voltage detector;
Transition control means for starting the engine and transitioning to the hybrid travel mode when the battery voltage detected by the voltage detection means has decreased to a predetermined travel mode transition voltage value;
In the transition control means, the travel mode transition voltage value is set in a portion where the decrease tendency of the open circuit voltage with respect to the decrease in the charge state on the third charge state versus voltage characteristic of the parallel-connected battery is large. When the cell voltage determined from the battery voltage detected by the voltage detection means reaches the set mode transition voltage value, the electric vehicle travel mode is shifted to the hybrid travel mode.
A control device for a power supply system for a hybrid electric vehicle characterized by the above.   9. The control apparatus for a power system for a hybrid electric vehicle according to claim 8, wherein the battery voltage detected by the voltage detection means is a voltage between terminals of the parallel connection battery.   9. The control apparatus for a power system for a hybrid electric vehicle according to claim 8, wherein the battery voltage detected by the voltage detecting means is a voltage between terminals of the composite battery.   The predetermined travel mode transition voltage value is 2.5 V or more and 3.15 V or less per unit of the secondary battery constituting the parallel connection battery. Control device for a hybrid electric vehicle power system.   The predetermined travel mode transition voltage value is 2.6 V or more and 2.8 V or less per unit of the secondary battery constituting the parallel connection battery. Control device for a hybrid electric vehicle power system.

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