Electric vehicle mounting plurality of drive batteries

Abstract

To prevent excess current or excess voltage from being applied to a motor 12 in use or other equipment 13 without requiring a large capacity of smoothing capacitor when switching battery packs to use in an electric vehicle mounting a plurality of driving battery packs 1, 11 while switching them.SOLUTION: An electric vehicle which mounts a plurality of driving battery packs and uses them while switching them has battery pack switching control means 20 controlling switching of battery packs to use for driving, of the driving battery packs. The battery pack switching control means is configured to switch battery packs to use while an electric vehicle is stopping.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to an electric vehicle equipped with a plurality of driving battery packs (battery packs), and more particularly to an electric vehicle in which the driving battery pack to be used can be switched during driving. [Background technology]

[0002] In order to extend the driving distance of an electric vehicle, various methods have been proposed for mounting a plurality of driving battery packs on the vehicle and switching between them. For example, Patent Document 1 proposes a configuration in which a vehicle mounted with a plurality of batteries is provided with a power supply switching means for selectively switching the power supply path to the motor drive unit and a detection means for detecting the remaining capacity of the plurality of batteries, and the degree of consumption of the plurality of batteries is determined based on a detection signal from the detection means, and when the remaining capacity of the battery in use becomes low, the battery being used is switched to another battery. Patent Document 2 proposes a configuration in which an electric vehicle is equipped with a plurality of batteries for supplying power to a motor for driving and a generator for charging the batteries, and the batteries for driving are selectively switched and used in sequence, and the battery not selected as the battery for driving is charged by the generator. Also proposed is a configuration in which the batteries are replaceable in an electric vehicle, a charged battery pack is mounted when the vehicle stops at a station, and the battery pack is switched as appropriate while the vehicle is driving, eliminating the need for time-consuming charging of the battery packs in the vehicle. In such a configuration, a system is being considered in which the weight of each replaceable battery pack is made light so that each individual battery pack can be carried and replaced by a person, and multiple replaceable battery packs are loaded onto a single vehicle and used in turn while the vehicle is operating. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2004-359032 [Patent Document 2] Patent Publication No. 2006-5996 Summary of the Invention [Problem to be solved by the invention]

[0004] In an electric vehicle equipped with multiple drive battery packs, the battery pack used to operate the motor and other devices is usually switched to a charged battery pack with a large remaining charge when the remaining charge of the battery in use, i.e., the SOC (State of Charge), drops. In this case, since the output voltage of the battery with a low SOC also drops, the moment the battery in use is switched to the charged battery with a high SOC, a voltage fluctuation occurs between the output terminals from the battery. In order to absorb such a fluctuation in the voltage between the output terminals, a smoothing capacitor is usually connected in parallel between the output terminals. However, if there is a fluctuation in the voltage between the output terminals while a significant current is flowing through the device connected between the output terminals, the current fluctuation corresponding to the voltage fluctuation will also be large, so a smoothing capacitor with a larger capacity is required to more reliably prevent the application of an overcurrent or overvoltage to the device in use. On the other hand, if the battery pack to be used is switched when no significant current is flowing through the device in use, there is almost no current fluctuation, and the application of an overcurrent or overvoltage to the device in use can be avoided, which is advantageous. Specifically, in the case of an electric vehicle, when the vehicle is stopped, the motor is stopped and no significant current flows through the motor, so it is preferable to perform the switching of battery packs while the vehicle is stopped.

[0005] Thus, the main object of the present invention is to prevent overcurrent or overvoltage from being applied to the motor or other equipment when switching between battery packs in an electric vehicle that is equipped with multiple drive battery packs and switches between them, without the need for a large-capacity smoothing capacitor. [Means for solving the problem]

[0006] According to the present invention, the above object is achieved by an electric vehicle that is loaded with a plurality of drive battery packs and switches between them, the electric vehicle having a battery pack switching control means that controls the switching of one of the drive battery packs to be used for drive, the battery pack switching control means being configured to execute the switching of the battery pack to be used while the electric vehicle is stopped.

[0007] In the above configuration, the "electric vehicle" may be any type of electric vehicle driven by a motor operated by battery power, and is configured to mount multiple battery packs at one time and use the multiple battery packs by switching them in sequence while the vehicle is in operation. The "battery pack" may be a device including multiple battery cells connected in series or parallel, a pair of input / output terminals to which the positive and negative electrodes of a cell group consisting of the multiple battery cells are connected, and a control means for monitoring the state of each battery cell and controlling whether or not it is charged or discharged, mounted on the vehicle and configured so that the cell group supplies power to the motor or receives power from the motor in a controlled manner and is charged by a charger. In the vehicle, the multiple battery packs mounted thereon are connected in parallel to the input / output terminals of the motor and other devices via circuit breakers, and the circuit breaker of only the battery pack being used permits conduction to the motor and other devices, and the circuit breakers of the other battery packs block conduction to the motor and other devices, so that only the selected battery packs among the multiple battery packs are in a use state. That is, the switching of the battery packs is achieved by controlling the state of each circuit breaker. The "battery pack switching control means" may be realized by a computer device that operates according to a program, and is specifically configured to control the state of the circuit breaker of each battery pack.

[0008] According to the above-mentioned configuration of the present invention, in a vehicle that switches between a plurality of battery packs and uses power from the battery packs to drive a motor, the switching of the battery pack to be used is performed while the vehicle is stopped, i.e., while the motor is stopped, thereby preventing the application of an overcurrent or overvoltage to the motor drive circuit, etc. Furthermore, with this configuration, the current flowing when the battery packs are switched is kept as small as possible, so that a smoothing capacitor with as small a capacity as possible can be used that is connected in parallel to the battery packs between the power input / output terminals of the motor and other devices in order to absorb voltage fluctuations when the battery packs are switched, and therefore it is possible to make the device smaller and less expensive.

[0009] In the above configuration, more specifically, the switching of battery packs may be performed by, when the SOC of a battery pack in use falls below a predetermined value which may be set as appropriate, switching the battery pack in use to a battery pack whose SOC exceeds a predetermined value which may be set as appropriate while the vehicle is stopped.

[0010] In addition, in a vehicle in which power is supplied from a battery pack via a voltage converter to various on-board devices, if an auxiliary battery (a battery capable of operating devices with relatively low power consumption, such as an on-board computer device) is installed, it is preferable that the operation of the voltage converter is also stopped when the battery pack is switched. This prevents the application of an overcurrent or overvoltage to the on-board devices when the battery pack is switched. On the other hand, if an auxiliary battery is not installed, the operation of the voltage converter may be maintained when the battery pack is switched to avoid a loss of power to the on-board computer device, etc., but it is preferable that the output voltage of the voltage converter is set low to avoid the effects of fluctuations (increases) in the output voltage of the battery pack, thereby preventing the application of an overcurrent or overvoltage to the on-board computer device, etc.

[0011] In the above configuration, the battery pack switching may be performed by a procedure in which only the charging of the battery pack that has been in use is prohibited, and the battery pack to be used is permitted to be discharged, and then the conduction of the battery pack to be used is started. This makes it possible to avoid a state in which the power supply is lost in the vehicle's power system when the battery pack is switched. This also prevents a state in which none of the battery packs is connected to the vehicle's power system when the battery pack is switched, and eliminates the need to use the power stored in the smoothing capacitor connected in parallel to the output terminal of the battery pack, so that the smoothing capacitor can have as small a capacity as possible. Effect of the Invention

[0012] Thus, according to the configuration of the present invention, as described above, the current and voltage applied to the motor or other devices during battery pack switching can be suppressed, and the motor or other devices can be protected from overcurrent or overvoltage. The configuration of the present invention may be applied to any type of electric vehicle equipped with a replaceable battery pack.

[0013] Other objects and advantages of the present invention will become apparent from the following description of preferred embodiments of the invention. [Brief description of the drawings]

[0014] [Figure 1] Fig. 1(A) is a schematic diagram of the configuration of a replaceable battery pack mounted on a vehicle of this embodiment. Fig. 1(B) is a schematic diagram of the configuration of a power system in the vehicle of this embodiment. Fig. 1(C) is a diagram showing an example of the circuit configuration of a breaker used in the battery pack. [Diagram 2] FIG. 2 is a diagram showing, in the form of a flowchart, the process of battery pack switching control in the vehicle of this embodiment when an auxiliary battery (sub-battery) is connected to the power system. [Diagram 3] FIG. 3 is a diagram showing, in the form of a flowchart, the process of battery pack switching control in the vehicle of this embodiment when the auxiliary battery is not connected to the power grid. [Explanation of symbols]

[0015] 1...replaceable battery pack, 2...battery cell, 3P...positive terminal, 3N...negative terminal, 4...control unit, 4a...communication terminal, 5...circuit breaker, 6...fuse, 7...current sensor, 8...temperature sensor, 10...vehicle power system, 11...on-board battery pack (stationary type), 11a...circuit breaker, 12...motor drive circuit and PCU (power control unit), 13...DC / DC converter (DCDC), 14...auxiliary battery (sub-battery), 15P...positive power line, 15N...negative power line, 20...control unit, 21...communication line BEST MODE FOR CARRYING OUT THEINVENTION

[0016] The present invention will now be described in detail with reference to some preferred embodiments thereof with reference to the accompanying drawings, in which like reference numerals indicate like parts.

[0017] Replaceable battery pack configuration In the vehicle of this embodiment, a plurality of battery packs are mounted as driving batteries, and each battery pack may be a replaceable battery pack as shown in Fig. 1. Specifically, a replaceable battery pack 1 includes a battery cell group in which a plurality of chargeable and dischargeable battery cells (secondary battery cells) 2 are connected in series or parallel, and various means for controlling the charging and discharging of the battery. More specifically, for example, the positive and negative electrodes of the battery cell group are connected to the positive terminal 3P and the negative terminal 3N, which are the output terminals of the battery pack, via a circuit breaker 5, and the control unit 4 is configured to determine whether or not to charge or discharge (conduction) the battery pack by controlling the state of the circuit breaker 5 based on communication with the power system of the vehicle in which the battery pack is incorporated via the communication terminal 4a, while referring to the voltage of each battery cell 2, the current flowing through the battery pack (current between the positive terminal 3P and the negative terminal 3N) detected by a current sensor 7, and the temperature of the battery cell group detected by a temperature sensor 8 that may be disposed at an appropriate interval near the battery cell group. The control unit 4 may be a microcomputer device of any type. In addition, a fuse 6 that cuts off the continuity when an overcurrent flows between the positive terminal 3P and the negative terminal 3N may be provided to protect the circuit.

[0018] In using the replaceable battery pack as illustrated in Fig. 1(A), for example, the replaceable battery pack is charged at any facility (such as a refilling station), and when the vehicle stops at the facility, the charged battery pack is loaded onto the vehicle, and when the battery pack used to drive the vehicle becomes low while the vehicle is in operation, the battery pack to be used is switched to the charged battery pack loaded onto the vehicle at the facility. This is advantageous because it eliminates the need to park the vehicle at a charging facility for a long time in order to charge the battery pack, which takes time. Since it is expected that a person will load the replaceable battery pack into the vehicle at the facility, it is being considered to form the battery pack into a weight and size that can be carried by a person.

[0019] Vehicle power system configuration In the power system of the vehicle to which this embodiment is applied, the power of the battery pack is basically used to operate the drive motor and other on-board devices, and in particular, in the case of this embodiment, a plurality of battery packs are connected in parallel via a circuit breaker so as to be selectively conducted to the devices to which the power is supplied. Specifically, for example, as shown in Fig. 1(B), in the power system 10 of the vehicle, a motor drive circuit and PCU 12 that drives the motor, and a direct current voltage converter (DCDC) 13 that converts the high voltage power of the battery pack into low voltage power and supplies the power to various on-board devices are connected between power lines 15P and 15N, and a plurality of battery packs, for example, an on-board battery pack 11 that may be stationary and a battery pack 1 that may be replaceable as described in Fig. 1(A), may be installed in a state that allows them to be connected in parallel. The in-vehicle battery pack 11 may include a battery cell group in which the secondary battery cells 2 are connected in series or parallel, and various means for controlling the charging and discharging of the battery, similar to the battery pack 1 (the circuit breaker 11a is external in the illustrated example, but may be built-in). The number of battery packs connected in parallel between the power lines 15P and 15N may be three or more, and a plurality of battery packs may be connected in series to each of the circuit lines connected in parallel between the power lines 15P and 15N. A control unit 20, which may be any type of computer device, is configured to monitor the states of the PCU 12, the DCDC 13, the circuit breaker 11a of the in-vehicle battery pack 11, and the replaceable battery pack 1, and to give control commands to each of them. The control unit 20 is operated by being supplied with power obtained by converting a high voltage from the battery pack to a low voltage by the DCDC 13. In addition to the battery packs 1 and 11, an auxiliary battery 14 (e.g., a 12V lead battery) capable of operating on-board auxiliary machinery (equipment with relatively low power consumption) may be provided so as to supply power to the control unit 20, DCDC 13, etc.

[0020] Circuit Breaker Configuration In the above configuration, the battery pack to be used to drive the motor is selected by selectively turning on the circuit breaker of each battery pack, as already mentioned. The circuit breaker used in this embodiment may typically be composed of a circuit breaker (discharge side) that allows current to flow from the battery side to the device side, and a circuit breaker (charge side) that allows current to flow from the device side to the battery side, as shown in FIG. 1(C). In operation, switch Q D When the is turned on, the diode D D and Switch Q D Current is allowed to flow to the device through switch Q C When the switch is turned on, the current flows from the device to the diode D C and Switch Q C This allows current to flow to the battery side through the switch Q, so that it is possible to selectively allow only charging, only discharging, or both charging and discharging currents to flow through each battery pack. C , Q D The ON / OFF state of is controlled by control commands from the control units 20 and 4.

[0021] Battery pack switching control (1) Overview In the vehicle of this embodiment, a plurality of battery packs mounted on the vehicle are switched to be connected to the motor and other devices in sequence to supply power to the motor and other devices. At that time, in response to a decrease in the remaining capacity of the battery pack in use, the battery pack connected to the motor and other devices is usually switched from a battery pack in use with a low SOC to a battery pack with a high SOC that is fully charged. In this regard, since the output voltage of the battery pack rises and falls corresponding to the high and low SOC, the voltage applied to the motor and other devices fluctuates on the upward side when the battery pack is switched. Therefore, in general, a smoothing capacitor (not shown) is connected in parallel to the power line (15P, 15N) between the battery pack side and the motor and other devices in order to absorb such voltage fluctuations and protect the motor and other devices from overvoltage and overcurrent. However, the larger the current when the battery pack is switched, the larger the amount of current fluctuation to be absorbed by the smoothing capacitor becomes, and a smoothing capacitor with a large capacity is required accordingly. On the other hand, if the battery pack switching is performed at a time when no significant current is flowing to the motor and other devices, large currents and voltages will not be applied to the devices even if there is a voltage fluctuation when the battery pack is switched, and the capacity of the smoothing capacitor can be kept smaller, achieving a smaller system size and lower cost. In the case of a vehicle, a state in which no significant current is flowing to the motor is when the vehicle is stopped, and a state in which no current is flowing to other devices is when the DCDC operation is stopped.

[0022] Thus, in this embodiment, the battery pack switching is performed when the vehicle is stopped. Preferably, when an auxiliary battery is present, the operation of the DCDC may be stopped when the battery pack is switched. When the battery pack is switched, the state of the circuit breaker of each battery pack may be switched so that power can always be supplied from one of the battery packs to the power lines and a situation in which the power supply is lost may be avoided.

[0023] (2) Battery pack switching process (when an auxiliary battery is present in the power grid) Specifically, the control unit 20 executes the battery pack switching process by referring to the vehicle's running conditions and the SOC of the battery pack. In this regard, if an auxiliary battery is present in the power system, power is supplied from the auxiliary battery to the control unit 20, so that the operation of the DCDC is stopped prior to the battery pack switching. The specific process may be as shown in FIG.

[0024] Referring to FIG. 2, in the process, first, the SOC of the battery in use (battery A) and the battery to be switched that has not yet been used (battery B) are confirmed (step 1). When the SOC of battery A falls below a reference value (switching reference value) at which battery switching is necessary and the SOC of battery B exceeds a value (switching sufficient value) indicating that the battery is sufficiently charged for future use (step 2), and further when the vehicle is stopped (step 3), the battery switching process is specifically initiated (when these conditions are not met simultaneously, battery pack switching is not executed).

[0025] In the battery switching process, first, the DCDC operation is instructed to stop charging and discharging of the battery pack by devices other than the motor (step 4), and when the stop of the DCDC is confirmed (step 5), the vehicle is prohibited from running (step 6). Then, for battery A, the charge side circuit breaker is turned off, and for battery B, both the charge side and discharge side circuit breakers are turned on (step 7). As a result, battery B is switched to a state in which it can be charged and discharged while maintaining a state in which battery A can only be discharged between the power lines. Therefore, even if the connection of battery B is not successful, the state in which power can be supplied by battery A is maintained, while charging from battery B to battery A can be prevented. After that, it is determined whether the voltage between the power lines (PN line voltage) has reached the output voltage of battery B (step 8). Here, if the output voltage of battery B is reflected between the power lines, it can be determined that the battery pack switching has been successful. In addition, there is a slight time delay (up to 100 ms) from the transmission of the control command to the circuit breaker in reflecting the output voltage of Battery B between the power lines, and if a change in voltage is observed before the expected delay time (predetermined time) has elapsed, the battery pack switching is successful. Thus, when the success of the battery pack switching is confirmed, the circuit breaker on the discharge side of Battery A is also shut off, which electrically disconnects Battery A from the power line (step 10), and an instruction is issued to resume the operation of the DCDC (step 11). Then, when the operation of the DCDC is confirmed (step 12), the vehicle is permitted to run, and a series of battery pack switching processes is completed (step).

[0026] In step 9 above, if no change in voltage is observed before a predetermined time has elapsed, it is determined that the connection of battery B has failed, and the circuit breaker of battery B is shut off on both the charging and discharging sides, and the circuit breaker of the charging side of battery A is restored to electrical continuity. This maintains the state in which power is input and output to battery A on the power line, and a power loss situation is avoided (step 14). However, since the remaining power of battery A is low, a warning of the remaining battery power is issued to the driver in any format at the same time as permission to travel is granted (step 15). Also, if the operation of the DCDC is not confirmed in step 12, a warning is issued together with permission to travel.

[0027] In the arrangement of FIG. 2 above, the auxiliary battery may be substituted with a capacitor.

[0028] (3) Battery pack switching process (when no auxiliary battery is present in the power grid) If there is no auxiliary battery in the power system, stopping the operation of the DCDC will result in no means of supplying power to the control unit 20, so the battery pack is switched while the DCDC is operating. In this regard, since the DCDC receives power from the battery pack, when the battery B is connected to the power line, the line voltage rises, and the output voltage of the DCDC may also rise accordingly. Therefore, in this embodiment, the set voltage of the DCDC output is reduced to a predetermined level that may be set appropriately (a method of suppressing the fluctuation of the DCDC output voltage due to the voltage fluctuation of the power line by increasing the operating frequency of the DCDC can be considered, but in that case, an increase in loss and an increase in heat and noise are caused, so it is preferable to adopt the reduction of the set voltage of the DCDC output as described above).

[0029] The process when the power grid does not have an auxiliary battery may be the same as the process in Fig. 2, except that the output voltage setting of the DCDC is reduced instead of stopping the operation of the DCDC. Referring to Fig. 3, specifically, in the process, instead of steps 4 and 5 in Fig. 2, an instruction to reduce the output voltage of the DCDC is executed (step 4a), and instead of steps 11 and 12 in Fig. 2, an instruction to restore the output voltage of the DCDC is executed (step 11a).

[0030] The above description has been given in relation to the embodiment of the present invention, but it will be apparent to those skilled in the art that many modifications and changes can be easily made thereto, and that the present invention is not limited to the embodiment exemplified above, but can be applied to various devices without departing from the concept of the present invention.

Claims

[Claim 1] An electric vehicle that is equipped with a plurality of drive battery packs and switches between them, the electric vehicle having a battery pack switching control means that controls the switching of a battery pack to be used for drive among the drive battery packs, the battery pack switching control means being configured to execute the switching of the battery pack to be used while the electric vehicle is stopped.

Images