Control device of an electrically powered vehicle

Abstract

An electrically powered vehicle control device that controls an electrically powered vehicle that includes a motor (106) that transmits driving power to wheels, an inverter (102) that drives the motor (106), and a battery (103) that supplies power to the inverter (102), the control device further including: a battery storage amount estimating means (110) for estimating a storage amount of the battery (103); and a motor rotation speed detecting means (109) for detecting a rotation speed of the motor (106), wherein output terminals of the inverter (102) are short-circuited so that a three-phase short circuit is applied when the rotational speed of the motor (106) reaches or exceeds a predetermined first rotational speed while the storage amount estimated by the battery storage amount estimating means (110) is equal to or greater than a predetermined amount, and wherein the three-phase short circuit is stopped when the rotation speed of the motor (106) is greater than a second predetermined rotation speed found by subtracting a predetermined value from the first predetermined rotation speed.

Description

Technical FieldThe present invention relates to an electrically driven vehicle control device that controls an electrically driven vehicle including a motor that is driven via an inverter using a battery as a power supply, and more particularly to an electrically driven vehicle control device that prevents overcharging of a battery.Prior ArtHybrid electric powered vehicles using an engine and an engine mounted thereon or electric cars driven by an engine alone are increasing in an effort to reduce CO 2- emissions. These electrically powered vehicles using an internal combustion engine mounted thereon include an inverter for driving the motor and a battery serving as a power supply in addition to the motor.In these electrically powered vehicles, the battery is charged by regenerative power generation with the aim of extending a travel distance or with the aim of suppressing an increase in power consumption by the internal combustion engine for power generation. In regenerative power generation, power consumed other than heat generated in braking is extracted as electric power. The costs incurred or the fuel consumed with this power generation is thus zero. It is therefore desirable to store the power generated by the regenerative power generation in the battery as much as possible.On the other hand, many of the batteries mounted on the electrically driven vehicle have a property that the life becomes shorter when they are charged with an overcurrent or overcharged. Thus, when the batteries are charged, processing is necessary to protect the batteries from overcharge or the like.To solve these problems, JP 3 751 736 B2 discloses a technique according to which an SOC (State of Charge)) detection means for detecting an SOC of the battery (hereinafter also referred to as a storage amount / storage amount) is provided. In a braking mode in which the regenerative power generation is performed, the regenerative power generation is stopped when the SOC of the battery is near a full charge, and the mode is switched to counter-current braking. In contrast to regenerative power generation in which the battery is charged with power generated by the motor, battery power is consumed by the counter-current braking because the motor is driven by power supply, thus there is no risk of overcharging of the battery. In this way, the technique disclosed in JP 3 751 736 B2 prevents overcharging of the battery by regenerative power generation.Also, JP 2003-164 002 A discloses a technique according to which an SOC detection means for detecting an SOC of the battery is provided. If it is determined that the battery cannot be charged (e.g., when an SOC is near full charge), a three-phase short circuit is applied through short circuit input terminals of the motor. By applying the three-phase short circuit, current generated by the motor is consumed in the motor and is not charged to the battery. Thus, there is no risk of overcharging the battery. By configuring in this manner, overcharging of the battery by regenerative power generation is prevented. Specifically, JP 2003-164 002 A discloses a control device including a motor driving wheels of a vehicle, an inverter driving the motor and a battery supplying power to the inverter, and a means for estimating the SOC of the battery and a means for detecting the rotational speed of the motor. The output terminals of the inverter are shorted in three phases depending on the rotational speed when the battery is fully or nearly fully charged.Further, JP H09-47 055 A (PTL 3) discloses a technique according to which overcharging is prevented by applying a three-phase short circuit when a synchronous generator is in low-field control, that is, when an inductive voltage generated by the motor is large compared to a voltage across the battery. If an inductive voltage generated by the motor is large compared to a voltage across the battery, an amount of current to be generated cannot be controlled by the inverter. Thus, overcharging is prevented by applying a three-phase short circuit.FR 2 934 529 A1 describes an electric braking method for a vehicle, in particular a hybrid motor vehicle, equipped with a drive train comprising at least one electric motor connected to an electric accumulator via a speed regulator, said speed regulator using said electric motor to put said electric motor in a short-circuit or partial short-circuit state to generate an additional engine brake when at least one parameter of the state of said electric accumulator indicates that it is in a state that no longer allows to accept an electric load.JP 2010-207 053 A discloses a motor controller for an electric vehicle, which is equipped with a motor torque calculator for controlling motor torque so that the actual rotation speed of the motor reaches the target rotation speed of the motor; an inverter three-phase output unit that makes a three-phase short circuit to a motor generator to reduce the motor rotation speed; An integrated controller to reduce the number of motor revolutions by the three-phase short circuit at the three-phase output unit when shifting a gear from low to high, to interrupt the three-phase short circuit when the number of motor revolutions reaches the number of revolutions, to stop the three-phase short circuit set higher than the target number of motor revolutions, and to perform feedback control for the number of revolutions so that the actual number of motor revolutions reaches the target number of motor revolutions by the motor torque calculator.JP 2007-221 885 A discloses a charging controller in an electric vehicle in which a limit value for the discharge power is set according to the temperature characteristics so that the discharge restriction is enhanced as the battery temperature rises.JP 2009-81 958 A discloses that the MPU of a charge / discharge control device calculates the calorific value of each individual cell after elapse of a predetermined period of time based on the charge / discharge current flowing through a battery pack, estimates the temperature of each individual cell after elapse of a predetermined period of time from the temperature of the individual cell detected at a temperature detection section based on the thus calculated calorific value and the predetermined specific heat and the weight of the individual cell, and determines whether or not the estimated temperature exceeds a predetermined value, and further suppresses a calculated allowable current when it is determined that the predetermined value is exceeded.US 2006 / 0 152 196 A discloses a method for controlling the battery current limiting, which controls maximum charging and discharging current values as a function of the state of charge of the battery. The current limiting control method integrates the charge and discharge current of the battery to calculate a first state of charge, determines first charge and discharge current limit value candidates from this first state of charge, calculates a second state of charge based on the battery voltage, and determines second charge and discharge current limit value candidates from this second state of charge. Further, the method uses the smaller one of the first and second charge and discharge current limit value candidates as charge and discharge current limit values for charging and discharging the battery. DE 11 2006 000 511 T5 discloses a fault determination device which determines whether a fault is present in a drive circuit which, using a plurality of switching elements which constitute a drive device, drives an electrical device which, in operation, generates a counterelectromotive force.DE 10 2008 048 463 A1 describes a method for regulating the temperature of an electric drive system, in which temperature states at predetermined points in the electric drive system are monitored and a maximum permissible torque of the electric drive system is attenuated on the basis of the monitored temperature states.US 2009 / 0 243 554 A1 describes a method for protecting a battery for a hybrid vehicle, in which the counter electromotive voltage of a motor is limited by limiting the motor rotational speed when it is determined that there is the risk of overcharging of the battery in the event of a failure of a component connected to the motor controller, such as a motor controller, a battery controller, etc., whereby the battery is protected from the risk of overcharging and the safety of the battery is ensured.Results of the InventionTechnical ProblemWhen a rotation speed of the motor is increased, a power generation voltage (inductive voltage) of the motor is also increased proportionally. If the motor is driven by a power supply, it is necessary to apply a voltage greater than the inductive voltage through the inverter. However, because a voltage applicable from the inverter is limited by a voltage across the battery, a rotation speed of the motor allowed by the power supply is limited.On the other hand, there is a need for an electrically driven vehicle driven by a motor to power-drive the motor until the motor rotates at high speed, and this need is satisfied by a low-flux control or a step-up DC-DC converter. The weak flux control controls the motor to be driven by a power supply until rotating at high speed by decreasing an inductance voltage of the motor by changing current history phases, and the step-up DC-DC converter drives the motor by a power supply until rotating at high speed by stepping up a voltage across the battery. Configured in this manner, if the low-flux control or step-up of the battery voltage is stopped while the motor is driven at high speed, an inductance voltage of the motor becomes high with respect to an electromotive voltage of the battery (equivalent to an open circuit voltage of the battery).As described above, when a rotation speed of the motor increases and a power generation voltage becomes larger than an electromotive voltage of the battery, a current generated by the motor is charged to the battery by passing through a commutation diode of the inverter. In a region where a power generation voltage of the motor becomes larger than an electromotive voltage of the battery, the inverter operates equivalently to a full-wave rectifying circuit, and the motor cannot be driven by a power supply or regeneration by switching the inverter (charging of the battery is performed even when an attempt is made to drive by a power supply or regeneration). In a state where the inverter functions as a full-wave rectifying circuit and driving is performed neither by power supply nor by regeneration as described above, there is a problem that charging of the battery from the motor cannot be stopped by applying reverse braking as by the technique disclosed in PTL 1, and the battery is overcharged.FIG. 12 is a view showing a relationship between a motor rotation speed and a braking torque when a three-phase short circuit is applied through short-circuit input terminals of the motor (in the case of a three-phase motor, three input terminals are short-circuited). As shown in FIG. 12, it is known that the braking torque during a three-phase short circuit becomes smaller in inverse proportion to the motor rotation speed from a certain rotation speed or more.For example, assuming the case that the technique disclosed in PTL 2 is applied to an electrically driven vehicle in which the motor and the drive wheels are connected by a single speed reducer, according to the technique disclosed in PTL 2, a three-phase short circuit is applied regardless of a rotation speed of the motor when the battery cannot be charged. Thus, the motor rotation speed decreases due to the three-phase short circuit, and the braking torque of the motor abruptly increases in response to an increase in the motor rotation speed. Accordingly, the driver needs to reduce a depression amount of the brake pedal in response to a drop in the engine rotation speed. This results in a problem that the driver feels uncomfortable.Assuming the case that the technique disclosed in PTL 3 is applied to a control device in the electrically driven vehicle, a three-phase short circuit is applied while an inductive voltage of the motor is large compared to the voltage across the battery. Thus, even when the SOC of the battery is low and there is a good capacity for overcharging, the charging of the battery is stopped. This results in a problem that the regenerative power cannot be used.The invention has been made in view of the foregoing circumstances, and it is an object to provide a control device of an electrically driven vehicle capable of preventing overcharging of the battery even when a motor rotation speed is high and an inductive voltage of the motor is greater than a voltage across the battery without making driving uncomfortable.Solution of the ProblemIn order to solve the above problems, an electrically driven vehicle control device of the invention is an electrically driven vehicle control device that controls an electrically driven vehicle including a motor that transmits a driving force to wheels, an inverter that drives the motor, and a battery that supplies power to the inverter. The control device includes a battery storage amount estimating means for estimating a storage amount of the battery and a rotational speed detecting means for detecting a rotational speed of the motor. Output terminals of the inverter are short-circuited when the rotational speed of the motor reaches or exceeds a predetermined rotational speed while the storage amount estimated by the battery storage amount estimating means is equal to or greater than a predetermined amount.Advantageous Effects of the InventionAccording to the electrically driven vehicle control device of the invention, it becomes possible to provide an electrically driven vehicle control device capable of preventing overcharging of the battery even when the motor rotates at high speed and a voltage generated by the motor becomes equal to or greater than a voltage across the battery, so that the life of the battery is not shortened.The foregoing and other objects, features, aspects and advantages of the present invention will become apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.BRIEF DESCRIPTION OF THE DRAWINGSFIG. 1 is a view showing a configuration of a control device of an electrically driven vehicle according to a first embodiment of the invention. FIG. 2 is a flowchart showing an operation of the control device of an electrically driven vehicle according to the first embodiment of the invention. FIG. 3 is a diagram showing a relationship between a battery temperature and a first predetermined rotation speed of a motor. FIG. 4 is a diagram showing a relationship between a stator temperature and a rotor temperature of the motor. FIG. 5 is a timing chart including an operation of an electrically driven vehicle including the control device when the rotor temperature is low. FIG. 6 is a time chart showing an operation of the electrically driven vehicle including the control device when the rotor temperature is high. FIG. 7 is a view showing a configuration of a control device of an electrically driven vehicle according to a second embodiment of the invention. FIG. 8 is a block diagram of a charge current estimating means used in the electrically driven vehicle control device according to the second embodiment of the present invention. FIG. 9 is a block diagram of charging current limit value setting means used in the electrically driven vehicle control device according to the second embodiment of the invention. FIG. 10 is a flowchart showing an operation of the control device of an electrically driven vehicle according to the second embodiment of the invention. FIG. 11 is a time chart showing an operation of the electrically driven vehicle including the control device. FIG. 12 is a view showing a relationship between a motor rotation speed and a braking torque when a three-phase short circuit is applied.DESCRIPTION OF EMBODIMENTSFirst EmbodimentFIG. 1 is a view showing a configuration of an electrically driven vehicle control device of the first embodiment.Referring to FIG. 1, a controller 101 calculates a driving torque of a motor based on information such as a depression amount to an unillustrated accelerator pedal and a brake pedal, and drives an inverter (inverter) 102 to drive the motor with the calculated driving torque. A battery 103 supplies power to a step-up DC-DC converter 104 and the inverter 102. The step-up DC-DC converter 104 supplies a current to the inverter 102 by stepping up a voltage across the battery 103. A connection device (hereinafter referred to as a contactor) 105 formed of a contactor or a relay device is provided between the battery 103 and the step-up DC-DC converter 104. It is configured such that the battery 103 is disconnected from the step-up DC-DC converter 104 and the inverter 102 when the contactor 105 is turned off.The inverter 102 is formed of six switching elements, for example, IGBTs (Insulated Gate Bipolar Transistors), and converts direct current output from the step-up DC-DC converter 104 into three-phase alternating current.Reference numeral 106 denotes a motor. An output shaft of the motor 106 meshes with a final drive gear (not shown) so that a driving force is transmitted to the wheels.A configuration of the control device 101 will now be described. The control device 101 includes a microcomputer 107, control means 108, motor rotation speed detection means 109, battery storage amount estimation means 110, contactor operation means 111, battery temperature measurement means 112, and temperature estimation means 113.The microcomputer 107 determines a torque at which the motor 106 is driven based on information about the accelerator pedal, not shown, and a brake pedal, and gives a command to the inverter control means 108. The inverter control means 108 determines an operation of the switching elements of the inverter 102 to follow a motor torque specified by the microcomputer 107.The motor rotation speed detection means 109 calculates a rotation speed of the motor 106 by differentiating angle information obtained from an angle sensor, for example, a resolver.The battery storage amount estimating means 110 estimates a storage amount (storage amount) of the battery 103. The battery storage amount estimating means 110 sets an initial value of the storage amount in advance by measuring an open circuit voltage (OCV) of the battery 103 while the contactor 105 is turned off, and then acquires a storage amount by summing a current value input to the battery 103 and output from the battery 103.The contactor operation means 111 turns off the contactor 105 if there is an OFF command for the contactor 105 from the microcomputer 107.The battery temperature measurement means 112 measures a temperature of the battery 103. A temperature sensor such as a thermistor is provided for each cell, and a maximum value among these temperature sensors is used as the battery temperature.The rotor temperature estimating means 113 estimates a rotor temperature of the motor 103. A temperature sensor such as a thermistor is provided, for example, inside a stator winding of the motor 106, and the rotor temperature estimating means 113 may estimate the rotor temperature using a value of the temperature by referring to a map or by applying a filter to a value of the temperature sensor.The motor rotation speed detecting means 109, the inverter control means 108, the battery storage amount estimating means 110, the contactor operation means 111, the battery temperature measuring means 112 and the rotor temperature estimating means 113 are shown separately from the microcomputer 107. These means may be internal processing of the microcomputer 107.The electric-powered vehicle control device of the first embodiment is configured as described above, and its operation will be described next. FIG. 2 is a flowchart showing an operation of the electric-powered vehicle control device of the first embodiment. Processing shown in this flowchart is performed by the microcomputer 107 with a constant period of 10 msec, for example.First, in step 201, it is determined whether a storage amount of the battery 103 estimated by the battery storage amount estimating means 110 is equal to or larger than a predetermined storage amount (storage amount). When the storage amount of the battery 103 is equal to or larger than the predetermined storage amount, the process proceeds to step 202, otherwise, the process proceeds to step 212. The storage amount used in this determination is a storage amount just below overcharge set to 80%. It is desirable to have a second predetermined storage amount of, for example, about 75%, so that this determination is a hysteresis determination.In step 202, a first predetermined rotational speed and a second predetermined rotational speed of the motor are determined based on the battery temperature determined by the battery temperature measuring means 112. Herein, the first predetermined rotational speed is calculated with reference to a map shown in FIG. 3 indicating a relationship between the battery temperature and the first rotational speed of the motor 106. The second predetermined rotational speed is a value found by subtracting a predetermined value from the first predetermined rotational speed. The predetermined value to be subtracted is set so that the determination is a hysteresis determination to prevent ON and OFF determinations from being repeated for a three-phase short circuit described below. It proceeds to step 203 when the first predetermined rotational speed and the second predetermined rotational speed of the motor 106 are determined.In step 203, it is confirmed whether there is a state in which the contactor 106 is ON and a three-phase short circuit is not applied. If a three-phase short is not applied and the contactor is ON, the method continues with step 204; otherwise, the method continues with step 206.In step 204, it is determined whether a rotation speed of the motor 106 is equal to or greater than a first predetermined rotation speed. If this determination is true, that is, if the rotational speed of the motor 106 is equal to or greater than the first predetermined rotational speed, the process proceeds to step 205. If the determination is false, the flow proceeds to step 213.In step 205, the microcomputer 107 stops a torque command according to an operation state of the driver, which is normal control, and commands the inverter control means 108 to apply a three-phase short circuit. The inverter control means 108 then switches the switching elements ON or OFF so that the three output terminals of the inverter 102 are short-circuited. When the processing in step 205 ends, the process proceeds to END.By applying the three-phase short circuit only when the motor 106 rotates at equal to or greater than the first predetermined rotation speed, a three-phase short circuit is applied only while the motor 106 rotates at low speed, during which the braking torque becomes large. Thus, it becomes possible to provide a control device of an electric motor that makes drivability uncomfortable.Subsequently, in step 213, power supply driving is permitted and regenerative power generation is prohibited. In this state, power supply driving is performed as the driver desires while the accelerator pedal is depressed and the vehicle is steadily accelerating or running. While the accelerator pedal is being raised and the vehicle is decelerating, all the switching elements of the inverter 102 are turned off and current is not generated by the motor 106. When the processing in step 213 ends, the process proceeds to END.In step 206, it is determined whether the rotational speed of the motor 106 is greater than the second predetermined rotational speed. If this determination is true, that is, if it is determined that the rotation speed of the motor 106 is greater than the second predetermined rotation speed in a range in which the inverter 102 operates as a full wave rectifier, the process proceeds to step 208; otherwise, the process proceeds to step 207.In step 207, a command to stop the three-phase short circuit is provided. Further, power supply driving is allowed and regenerative power generation is prevented as in step 213. When the contactor 105 is OFF, the contactor 105 is also turned on. When step 207 ends, the process continues to end.In step 208, it is confirmed whether the rotor temperature estimated by the rotor temperature estimating means 113 is a predetermined temperature. If the rotor temperature is equal to or greater than a predetermined temperature, the process proceeds to step 209; otherwise, the process proceeds to END. The predetermined temperature used in this determination is set to a temperature so as not to cause irreversible demagnetization of the permanent magnets used in the motor when the three-phase short circuit is applied.In step 209, it is determined whether a delay time since the application of the three-phase short circuit exceeds a predetermined time. When the delay time is equal to or longer than the predetermined time, the process proceeds to step 210, and proceeds to END. The predetermined time is set to a time required for a flowing current to become zero when a three-phase short circuit is applied while the current flows from the inverter 102 to the battery 103.In step 210, an OFF signal is outputted to the contactor control means 111 to turn off the contactor 105. The process then continues with step 211. In step 211, the three-phase short circuit applied is stopped and the process proceeds to END.In this way, the current flowing from the inverter 102 to the battery 103 becomes zero after the three-phase short circuit is applied. It thus becomes possible to turn off the contactor 105 without causing a surge of current which otherwise occurs when the contactor is turned off.By turning off the contactor 105 in a state where the rotor temperature of the motor 106 is high, by disconnecting the battery 103 from the inverter 102, it also becomes possible to prevent demagnetization of the motor 106 while preventing overcharging of the battery 103.If the three-phase short circuit is applied, the three-phase short circuit is stopped in step 212 and the microcomputer 107 commands the inverter control means 108 that motor torque corresponding to the operation of the driver can be outputted. When the contactor 105 is turned off, the contactor 105 is also turned on. If a three-phase short circuit is not applied, that is, if a torque command corresponding to an operation of the driver is outputted, the process proceeds to END.FIG. 3 is a diagram showing a relationship between the battery temperature and the first predetermined rotational speed of the motor. In the figure, the battery temperature and the first predetermined rotational speed of the motor 106 have a relationship expressed by a linear function. However, the relationship is not necessarily expressed by a linear function. The relationship is determined based on an electromagnetic voltage (voltage across the terminals when the battery terminals are opened, that is, an open circuit voltage)) and an inductive voltage of the motor 106 in a state in which the battery 103 is charged to an extent over which the battery 103 is overcharged.It is known that an electromotive voltage at which the battery 103 is overcharged varies with the battery temperature, and there is a characteristic that the battery 103 is damaged when the battery 103 is charged with a high voltage when the battery temperature is low. Accordingly, the map of FIG. 3 is calculated by recording a rotation speed of the motor 106 at which an inductive voltage of the motor 106 becomes equal to or greater than an electromotive voltage at which the battery 103 is overcharged at each battery temperature. It is possible to adopt a method in which the map is calculated in advance and the first predetermined rotational speed is calculated based on the battery temperature. However, the computations can be made online. As described, by changing the first predetermined rotational speed in response to the battery temperature, it is possible to provide an electrically driven vehicle control device capable of preventing the overcharging reliably even when the battery temperature varies.FIG. 4 is a diagram showing a relationship between the stator temperature and the rotor temperature of the motor 105. In the figure, the relationship between the stator temperature and the rotor temperature is a relationship expressed by a linear function. However, the relationship is not necessarily the relationship shown in the figure. The map is generated by driving the motor alone in advance and using a relationship between the rotor temperature and the stator temperature at the time of this driving.FIG. 5 is a time chart showing an operation of an electrically driven vehicle corresponding to the control device 101 when the rotor temperature is low.Referring to FIG. 5, A is a map indicating a vehicle speed of the electrically driven vehicle. In the electrically powered vehicle of this embodiment, since the motor 106 having the wheels is connected to a final drive gear having a fixed gear ratio, the rotational speed of the motor 106 and the vehicle speed exhibit waveforms having a ratio of 1:1.B is a map indicating the rotation speed of the motor 106, and C is a map indicating a bus voltage of the inverter 102. A bus voltage of the inverter 102 fluctuates with an operation state of the step-up DC-DC converter 104.D is a map indicating a battery current. The battery current is a current flowing between the battery 103 and the step-up DC-DC converter 104, which are shown on the plus side when discharging from the battery 103 and on the minus side when charging the battery 103.E is a map indicating a motor current effective value, and represents an effective value of a three-phase AC waveform given from the inverter 102 to the motor 106.F is a map indicating a storage amount of the battery 103 calculated by the battery storage amount estimating means 110.G is a diagram indicating a state of the contactor 105. In this figure, the contactor 105 is constantly turned on, and therefore the battery 103 and the step-up DC-DC converter 104 are connected.Referring to the figure, a period from the time t 0 to t 1 is a portion in which the motor 106 is driven at a high speed by step-up a voltage across the battery 103 by the step-up DC-DC converter 104. In this time, power supply driving is performed by extracting power from the battery 103.At time t 1, the step-up DC-DC converter 104 stops the step-up operation. At this time, the motor 106 is driven at a high speed, and an inductive voltage of the motor 106 is larger than an electromotive voltage of the battery 103.A period from times t 1 to t 2 is a portion in which an inductive voltage of the motor 106 is larger than an electromotive voltage of the battery 103. In this section, the inverter 102 functions as a full-wave rectifying circuit and charges the battery 103. A storage amount of the battery 103 increases because it is charged.At time t 2, a storage amount of the battery 103 reaches a predetermined storage amount (e.g., 80%), and a three-phase short circuit is applied to the inverter 102. A three-phase short circuit may be applied by turning on the IGBTs on the low side and turning off the IGBTs on the high side.In a portion from times t 2 to t 3, the inverter 102 is three-phase short-circuited. While the inverter 102 is three-phase short-circuited, its bus voltage C coincides with an electromotive voltage of the battery 103. The base current D also becomes zero and is not charged to the battery 103.In this way, by applying a three-phase short circuit in a range where the rotation speed of the motor is high and the inductive voltage thereof exceeds an electromotive voltage of the battery 103, it becomes possible to stop charging of the battery 103, which in turn can prevent overcharging of the battery 103.The three-phase short-circuit voltage is stopped at time t 3 because the motor rotation speed B becomes lower than the second predetermined rotation speed. By setting the first predetermined rotational speed and the second predetermined rotational speed in this manner, it becomes possible to provide an electrically driven vehicle control device in which a three-phase short circuit is not applied and is frequently stopped.At and after time t 3, the motor is driven in response to a driver's operation with the accelerator pedal or a brake pedal.FIG. 6 is a time chart showing an operation of an electrically driven vehicle including the control device 101 when the rotor temperature is high.Referring to FIG. 6, H to N correspond to A to G of FIG. 5, P represents the rotor temperature which is a value estimated by the rotor temperature estimating means 114. In the time chart of FIG. 6, the rotor temperature P is a temperature greater than the predetermined temperature.With respect to the figure, the operations are the same as those in FIG. 5 until time t2. At time t 3, contactor 105 is turned OFF by contactor operation means 111 because the delay time since the application of the three-phase short at time t 2 exceeds the predetermined time.In this embodiment, the step-up DC-DC converter 104 and the inverter 102 are connected only to the battery 103. However, if current is supplied to electrical components of the vehicle from a step-up DC-DC converter, it is preferred that the step-up DC-DC converter is also turned off.The three-phase short circuit is stopped at time t 4. The contactor 105 is turned off from times t 4 to t 5, and the battery 103 and the step-up DC-DC converter 104 are disconnected. Thus, the inverter bus voltage J is zero. In addition, because the three-phase short circuit is stopped, the motor current effective value is also zero in this range.By turning off the contactor 105 after the battery current K is set to zero by applying the three-phase short circuit, it becomes possible to prevent damage to the battery caused by surge current that otherwise occurs when the contactor 105 is turned off. By turning off the contactor 105 and stopping the three-phase short circuit while the rotor temperature P is high, it also becomes possible to provide an electrically-driven vehicle control device capable of preventing overcharging of the battery 103 while preventing demagnetization of the vehicle.At and after time t 5, the motor 106 is driven in response to a driver's operation in the same manner as at and after time t 3 of FIG. 5.Second EmbodimentA control device of an electrically driven vehicle according to a second embodiment of the invention will now be described.FIG. 7 is a view showing a configuration of the electric-powered vehicle control device of the second embodiment. In the figure, the same or equivalent parts as those of FIG. 1 are denoted by the same reference numerals, and description will be omitted.Referring to FIG. 7, a control device 701 is substantially the same configuration as that of the first embodiment of the above-described control device 101, and includes a microcomputer 702, inverter control means 108, motor rotation speed detection means 109, battery storage amount estimation means 110, contactor operation means 111, battery temperature measurement means 112, and rotor temperature estimation means 113. It should be noted that the microcomputer 702 is different from the microcomputer 107 of the first embodiment in that it includes a charge current estimating means 703 and an upper limit value setting means 704.The charge current estimating means 703 estimates a charge current to be charged to the battery 103 based on the storage amount estimated by the battery storage amount estimating means 110 and the motor rotation speed detected by the motor rotation speed detecting means 109. The upper limit value setting means 704 sets an upper limit value of a charging current on the basis of the temperature of the battery 103 measured by the battery temperature measuring means 112 and the storage amount of the battery 103.FIG. 8 is a block diagram of the charge current estimating means 703. The charging current estimating means 703 includes an inductive voltage calculating means 801, an impedance calculating means 802, a battery electromotive voltage calculating means 803, and a charging current calculating means 804.The inductive voltage calculation means 801 calculates an inductive current on the basis of the rotational speed of the motor 106. Because an inductive voltage in a permanent magnet synchronous motor can be calculated as: (rotational speed of the motor) x (permanent magnet flux), this calculation is used herein. Since the permanent magnetic flux also changes with the rotor temperature, correction is performed according to a value of the rotor temperature estimating means 113.The impedance calculation means 802 calculates an impedance of the inverter 102, the motor 106, and the battery 103. Factors that determine the impedance of the inverter 102, the motor 106, and the battery 103 include a resistance in a current-carrying path for the inverter 102, and a resistance component and an inductance component of the coil for the motor 106. The factors also include an internal resistance of the battery 103 to the battery 103.From these factors, the impedance calculation means 802 calculates an impedance Rz in accordance with a following equation: wherein R1 is the internal resistance of the battery 103, R2 is the resistance in the current carrying path of the inverter 102, R3 is the coil resistance of the motor 106, L is the coil resistance of the motor, and W is the rotation speed of the motor 106.The internal resistance R1 of the battery 103 can be found, for example, through steps (1) to (4) as follows:(1) an electromotive voltage of the battery 103 is calculated based on the storage amount of the battery 103;(2) an amount of current when the current flows to the inverter 102 and a voltage across the terminals of the battery 103 are measured;(3) a storage drop amount is calculated as a difference between the electromotive voltage calculated in (1) and the voltage across the terminals of the battery 103 obtained in (2); and(4) the internal resistance is calculated by Ohm's law using the amount of current of the battery 103 obtained in (2) and the storage decrease amount calculated in (3):The battery electromotive voltage calculation means 803 calculates an electromotive voltage of the battery 103 based on the storage amount of the battery 103. The electromotive voltage of the battery 103 varies with characteristics of the battery 103. Thus, a map is generated by measuring a relationship between a storage amount and an electromotive voltage of the battery 103 in advance, and an electromotive voltage across the battery 103 is calculated by referring to the map when the control is performed.The charging current calculation means 804 calculates a charging current in accordance with an equation below using the inductive voltage V 1 calculated by the inductive voltage calculation means 801, the impedance Rz calculated by the impedance calculation means 802, and the battery electromotive voltage V 2 calculated by the battery electromotive voltage calculation means 803, and outputs the calculation result as an estimated value.FIG. 9 is a block diagram of the upper limit value setting means 704. The upper limit value setting means 704 is constituted of a first upper limit value calculating means 901 for calculating a charging current upper limit value determined by a charging amount of the battery 103, a second upper limit value calculating means 902 for calculating a charging current upper limit value determined by the battery temperature, and a minimum value calculating means 903.Each of the first upper limit value calculation means 901 and the second upper limit value calculation means 902 calculates the charge current upper limit value using a map generated in advance by measuring, for example, the characteristics of the battery 103. The minimum value calculation means 903 outputs the charging current upper limit value calculated by the first upper limit value calculation means 901 and / or the charging current upper limit value calculated by the second upper limit value calculation means 902, which is also smaller and smaller (i.e., which is also the more strict limitation).This embodiment adopts, as the charge current upper limit value setting means 704, a method by which the limit values are calculated based on the storage amount and the battery temperature of the battery 103, and whichever is the more strict limit is outputted. Alternatively, the upper limit value may be calculated using, for example, a two-input map of the storage amount and a battery temperature of the battery 103.The electrically driven vehicle control device of the second embodiment is configured as described above, and an operation thereof will be described next. FIG. 10 is a flowchart showing an operation of the electrically driven vehicle control device of the second embodiment.First, in step 1001, the upper limit value setting means 704 calculates an upper limit value of the charging current. In step 1002, the charging current estimating means 703 estimates a charging current.In step 1003, it is determined whether the estimated charging current has a value equal to or greater than the upper limit value. If this determination is true, that is, if the charging current has a value equal to or greater than the upper limit value, the process proceeds to step 1004. If the determination is false, the process proceeds to step 1005.In step 1004, a three-phase short circuit is applied because there is a possibility that the charging current to the battery 103 becomes an over-current. In step 1005, regenerative power generation is permitted without applying a three-phase short circuit because the charging current to the battery 103 becomes an over-current.FIG. 11 is a time chart showing an operation of an electrically driven vehicle including a control device 701.In FIG. 11, Q is a map indicating a vehicle speed, and R is a map indicating a rotation speed of the motor 106. S is a diagram indicating a bus voltage of the inverter 102. The bus voltage of the inverter 102 becomes large in voltage across the battery 103 by step-up the voltage of the battery using the step-up DC-DC converter 104. In the figure, an alternate long and short dash line represents an inductance voltage of the motor 106, and a dash line represents an electric power voltage of the battery 103.T is a map showing a current of the battery 103. The current of the battery 103 is a current flowing between the battery 103 and the step-up DC-DC converter 104 shown on the positive side when discharging from the battery 103 and on the negative side when charging the battery 103.U is a map indicating the charging current value estimated by the charging current estimated value and the charging current upper limit value calculated by the charging current upper limit value setting means 704. V is a map indicating a state whether or not the three-phase short circuit is applied.Referring to the map, in a period from the times t 0 to t 1, the motor 105 accelerates and the bus voltage of the inverter 102 increases in the electromotive voltage of the battery 103 by boosting the voltage of the battery 103 using the boost DC-DC converter 104. At this time, a current T of the battery 103 is discharged from the battery 103 and a three-phase short circuit is not applied.At time t 1, the step-up DC-DC converter 104 stops the operation, and the bus voltage S of the inverter 102 becomes a value substantially equal to the value of the electromotive voltage of the battery 103. By stopping the step-up DC-DC converter 104, the bus voltage of the inverter 102 becomes small compared to an inductive voltage of the motor 106. The charge current estimation value increases at this time in a charging direction and takes a value angreater than the charge current upper limit value set in accordance with a state of the battery 103. More specifically, a three-phase short circuit is applied at time point 1 because it is determined that the battery 103 is charged with an excessively large current.The three-phase short circuit is applied to the inverter 102 from times t 1 to t 2. Thus, the current T of the battery 103 becomes zero. In this range, a braking force is also generated due to the three-phase short circuit, and the vehicle speed Q, the motor rotation speed R, and the motor inductive voltage drop.Time t 2 is a time point at which the charge current estimation value falls below the charge current upper limit value, and the three-phase short circuit is stopped at time t 2. The battery 103 is charged at and after the time point t 2 because the three-phase short circuit is stopped.By calculating the charge current upper limit value and the charge current estimation value and applying a three-phase short circuit only in a limited case where the charge current limit value becomes larger than the charge current upper limit value, it is possible to stop charging only when the battery 103 is charged with an excessively large current. It is thus possible to charge the battery with regenerative power while preventing deterioration of the battery 103 by the charging with an overcurrent.The embodiments describe a case where the electrically driven vehicle is an electric car driven by an engine alone. However, the same advantages can be obtained when the electrically driven vehicle is a hybrid car driven by an internal combustion engine and the engine.

Claims

An electrically driven vehicle control device that controls an electrically driven vehicle including a motor (106) that transmits a driving force to wheels, an inverter (102) that drives the motor (106), and a battery (103) that supplies power to the inverter (102), the control device further including: a battery storage amount estimation means (110) for estimating a storage amount of the battery (103); A motor rotation speed detecting means (109) for detecting a rotation speed of the motor (106), wherein output terminals of the inverter (102) are short-circuited so that a three-phase short circuit is applied when the rotation speed of the motor (106) reaches or exceeds a predetermined first rotation speed while the storage amount estimated by the battery storage amount estimating means (110) is equal to or greater than a predetermined amount, and wherein the three-phase short circuit is stopped when the rotation speed of the motor (106) is greater than a second predetermined rotation speed found by subtracting a predetermined value from the first predetermined rotation speed.An electric-powered vehicle control apparatus according to claim 1, characterized in that said control apparatus includes: battery temperature measurement means (112) for measuring a temperature of said battery (103), wherein said predetermined rotational speed is changed in response to the temperature of said battery (103).The control device of an electric powered vehicle according to claim 1, characterized in that the control device includes: charging current estimating means (703) for estimating a current value to be charged to the battery (103) based on the rotation speed of the motor (106) and the storage amount of the battery (103); battery temperature measuring means (112) for measuring a temperature of the battery (103); An upper limit value setting means (704) for setting an upper limit value of the current to be charged to the battery (103) based on the storage amount of the battery (103) and the temperature of the battery (103), wherein the output terminals of the inverter (102) are short-circuited when a value of the charging current estimated by the charging current estimating means (703) is larger than the upper limit value set by the upper limit value setting means (704).The electric-powered vehicle control device according to claim 3, characterized in that: the predetermined rotational speed is changed in response to the temperature of the battery (103).The control device of an electrically powered vehicle according to any one of claims 1 to 4, characterized in that the control device includes: a connection device (105) that turns on and off connection of the battery (103) and the inverter (102), wherein the connection device (105) is turned off after a lapse of a predetermined time since the output terminals of the inverter (102) are short-circuited.An electric-powered vehicle control apparatus according to claim 5, characterized in that said control apparatus includes: rotor temperature estimating means (113) for estimating a rotor temperature of said motor (106), said connecting device (105) being turned off when said rotor temperature is equal to or greater than a predetermined temperature.

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