WO2015107584A1

WO2015107584A1 - Power supply apparatus of vehicle

Info

Publication number: WO2015107584A1
Application number: PCT/JP2014/005840
Authority: WO
Inventors: Hideki Kamatani; Suguru KUMAZAWA; Ryoji Sato
Original assignee: Toyota Jidosha Kabushiki Kaisha
Priority date: 2014-01-15
Filing date: 2014-11-20
Publication date: 2015-07-23
Also published as: JP2015133862A

Abstract

A power supply apparatus of a vehicle includes: a battery (150); a converter (200) stepping up a voltage (VB) of the battery (150) and supplying the stepped-up voltage to inverters (210, 220) of the vehicle; and a control device (500) controlling the converter (200) in a continuous voltage step-up mode and an intermittent voltage step-up mode. In the continuous voltage step-up mode the converter (200) is continuously operated. In the intermittent voltage step-up mode the converter (200) is intermittently operated. The control device (500) controls the converter (200) so that discharge power from the battery (150) does not exceed a discharge power upper limit (Wout). The control device (500) suppresses an operation of the converter (200) in the intermittent voltage step-up mode to a greater extent as the discharge power upper limit (Wout) is smaller.

Description

POWER SUPPLY APPARATUS OF VEHICLE

The present invention relates to a power supply apparatus of a vehicle.

A battery mounted on a hybrid vehicle may be degraded if the battery is charged with large electric power or discharges large electric power. Thus, in order to protect the battery, generally a discharge power upper limit Wout is set to thereby limit discharge power from the battery and a charge power upper limit Win is also set to thereby limit charge power to the battery. An example of such a hybrid vehicle is disclosed in Japanese Patent Laying-Open No. 2010-98882 (PTL 1). A control system of this vehicle limits an upper limit of a system voltage, depending on a discharge power upper limit Wout or charge power upper limit Win of a battery.

[PTL 1] Japanese Patent Laying-Open No. 2010-98882
[PTL 2] Japanese Patent Laying-Open No. 2011-15603

In the case where electric current consumption of a motor generator is small, intermittent voltage step-up control may be performed by intermittently operating and stopping a voltage step-up converter to thereby reduce an electric power loss due to switching of the voltage step-up converter. In the case where this control is performed, current flowing through the voltage step-up converter (step-up current) and current flowing from/into a battery (battery current) are also quickly switched between a state of being flown and a state of not being flown. Depending on the configuration of an ECU (Electronic Control Unit) which performs vehicle control, data of electric current used for the control may be measured in slow cycles, resulting in a failure to be able to precisely observe changes of the electric current.

In order to limit the charge/discharge power of the battery for the sake of battery protection during intermittent voltage step-up control, the step-up current has to be limited. During intermittent voltage step-up control, however, changes of the step-up current cannot precisely be observed, resulting in deterioration of the controllability of the step-up current.

A discharge power upper limit Wout and a charge power upper limit Win of a battery (hereinafter also referred to collectively as power upper limit) can be set depending on the SOC (State Of Charge) or the temperature of the battery. For example, in the case where the battery has a low temperature or a high temperature, the power upper limit is set smaller relative to the case where the battery temperature is a normal temperature. In the case where the power upper limit is small as mentioned above, it may be impossible to control the step-up current so that the charge/discharge power during intermittent voltage step-up control is less than the power upper limit. Consequently, the battery may be degraded and the battery performance may be deteriorated.

An object of the present invention is to provide a power supply apparatus of a vehicle that is capable of ensuring an effect of reducing an electric power loss by the intermittent voltage step-up control and still capable of suppressing deterioration of the battery performance.

A power supply apparatus of a vehicle according to an aspect of the present invention includes: a power storage device; a voltage step-up converter stepping up a voltage of the power storage device and supplying the stepped-up voltage to an electrical load of the vehicle; and a control device controlling the voltage step-up converter in a continuous voltage step-up mode and an intermittent voltage step-up mode. In the continuous voltage step-up mode the converter is continuously operated. In the intermittent voltage step-up mode the converter is intermittently operated. The control device controls the voltage step-up converter so that discharge power from the power storage device does not exceed a discharge power upper limit, and suppresses an operation of the voltage step-up converter in the intermittent voltage step-up mode to a greater extent as the discharge power upper limit is smaller.

Under control in the intermittent voltage step-up mode, the controllability of the step-up current is deteriorated. Therefore, if the discharge power upper limit is small, the discharge power from the battery may exceed the discharge power upper limit. According to the above-described features, the operation in the intermittent voltage step-up mode is suppressed to a greater extent as the discharge power upper limit is smaller. The discharge power can thus be prevented from exceeding the discharge power upper limit. Accordingly, the performance deterioration of the power storage device can be suppressed.

Preferably, in a case where the discharge power upper limit is smaller than a predetermined threshold value, the control device inhibits the operation of the voltage step-up converter in the intermittent voltage step-up mode.

According to the above-described features, the operation in the intermittent voltage step-up mode is inhibited and an operation in the continuous voltage step-up mode is performed instead. Under control in the continuous voltage step-up mode, the controllability of the step-up current is not deteriorated and therefore the discharge power can more reliably be prevented from exceeding the discharge power upper limit. Accordingly, the performance deterioration of the power storage device can be suppressed.

Preferably, in a case where the discharge power upper limit is smaller than a predetermined threshold value, the control device sets smaller a rate at which the voltage of the power storage device is stepped up in the intermittent voltage step-up mode, relative to a case where the discharge power upper limit is equal to or larger than the predetermined threshold value.

According to the above-described features, the intermittent voltage step-up control is continued and therefore a power loss of the voltage step-up converter can be reduced. Further, the rate at which the voltage of the power storage device is stepped up in the intermittent voltage step-up mode is set smaller to thereby reduce the maximum value of the step-up current. The maximum value of the discharge power can thus be reduced. Therefore, the discharge power can be prevented from momentarily exceeding the discharge power upper limit. Accordingly, the performance deterioration of the power storage device can be suppressed.

Preferably, the predetermined threshold value is determined based on through current flowing through the voltage step-up converter in the intermittent voltage step-up mode.

The discharge power increases with an increase of the through current. Therefore, according to the above-described features, an appropriate threshold value on which the magnitude of the discharge power is reflected can be determined. Thus, the discharge power can more reliably be prevented from exceeding the discharge power upper limit. Accordingly, the performance deterioration of the power storage device can be suppressed.

Preferably, the predetermined threshold value is determined based on discharge power from the power storage device when the through current is at its maximum.

When the through current is at its maximum, the discharge power is at its maximum. According to the above-described features, a sufficiently large threshold value which corresponds to the maximum value of the discharge power is determined. Thus, a range in which the intermittent voltage step-up control is inhibited is made sufficiently broad, and therefore, the discharge power can more reliably be prevented from exceeding the discharge power upper limit. Accordingly, the performance deterioration of the power storage device can be suppressed.

Preferably, in a case where the discharge power upper limit is smaller than a first threshold value and equal to or larger than a second threshold value which is smaller than the first threshold value, the control device sets smaller a rate at which the voltage of the power storage device is stepped up in the intermittent voltage step-up mode, relative to a case where the discharge power upper limit is equal to or larger than the first threshold value. In a case where the discharge power upper limit is smaller than the second threshold value, the control device inhibits the operation of the voltage step-up converter in the intermittent voltage step-up mode.

According to the above-described features, in the case where the discharge power upper limit is smaller than the first threshold value and equal to or larger than the second threshold value, a power loss of the voltage step-up converter can be reduced by the intermittent voltage step-up control while preventing the discharge power from exceeding the discharge power upper limit. In contrast, in the case where the discharge power upper limit is smaller than the second threshold value, the discharge power can more reliably be prevented from exceeding the discharge power upper limit. Accordingly, the performance deterioration of the power storage device can be suppressed.

Preferably, the first and second threshold values are determined based on through current flowing through the voltage step-up converter in the intermittent voltage step-up mode.

Preferably, the first and second threshold values are determined based on discharge power from the power storage device when the through current is at its maximum.

In accordance with the present invention, an effect of reducing an electric power loss by the intermittent voltage step-up control can be ensured and deterioration of the battery performance can still be suppressed.

Fig. 1 is a block diagram for illustrating an example configuration of a hybrid vehicle shown as a typical example of the electrically powered vehicle according to first to fourth embodiments of the present invention. Fig. 2 is a circuit diagram illustrating an example configuration of an electrical system of the hybrid vehicle shown in Fig. 1. Fig. 3 is a waveform diagram for illustrating reactor current IL in the case where a converter 200 is controlled in an intermittent voltage step-up mode. Fig. 4 is a conceptual diagram showing a limitation on discharge power upper limit Wout with respect to the SOC of a battery 150 in the first embodiment. Fig. 5 is a conceptual diagram showing a limitation on discharge power upper limit Wout with respect to temperature TB of battery 150 in the first embodiment. Fig. 6 is a flowchart showing a procedure of voltage step-up control by converter 200. Fig. 7 is a flowchart showing details of step ST25 in the flowchart of Fig. 6. Fig. 8 is a waveform diagram for illustrating operations in a continuous voltage step-up mode and an intermittent voltage step-up mode. Fig. 9 is a conceptual diagram showing a limitation on discharge power upper limit Wout with respect to the SOC of battery 150 in the second embodiment. Fig. 10 is a conceptual diagram showing a limitation on discharge power upper limit Wout with respect to temperature TB of battery 150 in the second embodiment. Fig. 11 is a diagram for comparison of reactor current IL depending on a recovery rate when battery 150 discharges. Fig. 12 is a flowchart showing details of step ST25 in the flowchart of Fig. 6. Fig. 13 is a waveform diagram for illustrating reactor current IL in the case where converter 200 is controlled in an intermittent voltage step-down mode. Fig. 14 is a conceptual diagram showing a limitation on charge power upper limit Win with respect to the SOC of battery 150 in the third embodiment. Fig. 15 is a conceptual diagram showing a limitation on charge power upper limit Win with respect to temperature TB of battery 150 in the third embodiment. Fig. 16 is a flowchart showing a procedure of voltage step-down control by converter 200. Fig. 17 is a flowchart showing details of step ST25 in the flowchart of Fig. 16. Fig. 18 is a waveform diagram for illustrating operations in a continuous voltage step-down mode and an intermittent voltage step-down mode. Fig. 19 is a conceptual diagram showing a limitation on charge power upper limit Win with respect to the SOC of battery 150 in the fourth embodiment. Fig. 20 is a conceptual diagram showing a limitation on charge power upper limit Win with respect to temperature TB of battery 150 in the fourth embodiment. Fig. 21 is a diagram for comparison of reactor current IL depending on a recovery rate when battery 150 is charged. Fig. 22 is a flowchart showing details of step ST25 in the flowchart of Fig. 16 in the fourth embodiment.

Embodiments of the present invention will hereinafter be described in detail with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference characters, and a description thereof will not be repeated.

<Configuration Common to Embodiments>
Fig. 1 is a block diagram for illustrating an example configuration of a hybrid vehicle shown as a typical example of the electrically powered vehicle according to first to fourth embodiments of the present invention.

Referring to Fig. 1, the hybrid vehicle includes an engine 100, a first MG (Motor Generator) 110, a second MG 120, a power split device 130, a reduction gear 140, a battery 150, drive wheels 160, and a control device 500. Control device 500 is configured to include a PM (Power Management) - ECU (Electronic Control Unit) 170 and an MG - ECU 172.

The hybrid vehicle is caused to run by a drive force from at least one of engine 100 and second MG 120. Engine 100, first MG 110, and second MG 120 are coupled to each other through power split device 130.

Power split device 130 is typically configured as a planetary gear mechanism. Power split device 130 includes a sun gear 131 which is an externally-toothed gear, a ring gear 132 which is an internally-toothed gear arranged concentrically with sun gear 131, a plurality of pinion gears 133 meshing with sun gear 131 and with ring gear 132, and a carrier 134. Carrier 134 is configured to hold a plurality of pinion gears 133 so that they can rotate on respective axes and also revolve.

Power split device 130 splits motive power generated by engine 100 into two paths. One is a path for driving drive wheels 160 through reduction gear 140. The other is a path for generating electric power by driving first MG 110.

First MG 110 and second MG 120 are each typically a three-phase AC rotating electric machine configured in the form of a permanent-magnet motor.

First MG 110 mainly operates as "electric generator" and is capable of generating electric power from a drive force which is supplied from engine 100 and split by power split device 130. The electric power generated by first MG 110 is used differently depending on the condition in which the vehicle is running and the condition of the SOC (State Of Charge) of battery 150. Regarding this electric power, its voltage is thereafter adjusted by a converter, which will be described later herein, and stored in battery 150. In the case for example where engine 100 is motored when the engine is started, first MG 110 can also operate as an electric motor as a result of torque control.

Second MG 120 mainly operates as "electric motor" and is driven by means of at least one of the electric power stored in battery 150 and the electric power generated by first MG 110. The motive power generated by second MG 120 is transmitted to a driveshaft 135 and further transmitted through reduction gear 140 to drive wheels 160. Thus, second MG 120 assists engine 100 or causes the vehicle to run by the drive force from second MG 120.

When the hybrid vehicle is regeneratively braked, second MG 120 is driven by drive wheels 160 through reduction gear 140. In this case, second MG 120 operates as an electric generator. Thus, second MG 120 serves as a regenerative brake converting braking energy into electric power. The electric power generated by second MG 120 is stored in battery 150.

Battery 150 is a battery pack made up of a plurality of battery modules connected in series, the battery modules each being made up of a plurality of battery cells integrated into the battery module. The voltage of battery 150 is approximately 200 V for example. Battery 150 can be charged with electric power generated by first MG 110 or second MG 120. The temperature, the voltage, and the current of battery 150 are detected by a battery sensor 152. A temperature sensor, a voltage sensor, and a current sensor are herein collectively referred to as battery sensor 152.

PM-ECU 170 and MG-ECU 172 are each configured to have a CPU (Central Processing Unit) and a memory (not shown) incorporated therein, and configured to perform operations based on values detected respectively by the sensors, through software processing in accordance with a map and a program stored in the memory. Alternatively, at least a part of PM-ECU 170 and MG-ECU 172 may be configured to perform a predetermined mathematical operation and/or a predetermined logical operation through hardware processing by a dedicated electronic circuit or the like.

Engine 100 is controlled in accordance with an operational command value from PM-ECU 170. First MG 110, second MG 120, converter 200, and

inverters

210, 220 are controlled by MG-ECU 172. PM-ECU 170 and MG-ECU 172 are connected to each other so that they can bidirectionally communicate with each other.

Although PM-ECU 170 and MG-ECU 172 are configured as separate ECUs in the present embodiment, a single ECU incorporating respective functions of these ECUs may be provided.

Fig. 2 is a circuit diagram illustrating an example configuration of an electrical system of the hybrid vehicle shown in Fig. 1.

Referring to Fig. 2, the electrical system of the hybrid vehicle includes converter 200 (voltage step-up converter), inverter 210 associated with first MG 110, inverter 220 associated with second MG 120, an SMR (System Main Relay) 230, and capacitors C1, C2.

Converter 200 includes two power semiconductor switching elements Q1, Q2 (also referred to simply as "switching element" hereinafter) connected in series, diodes D1, D2 provided in association with switching elements Q1, Q2, respectively, and a reactor L.

Switching elements Q1, Q2 are connected in series between a positive line PL2 and a ground line GL which is connected to a negative electrode of battery 150. The collector of switching element Q1 is connected to positive line PL2 and the emitter of switching element Q2 is connected to ground line GL. Diodes D1, D2 are connected in anti-parallel with switching elements Q1, Q2, respectively. Switching element Q1 and diode D1 constitute an upper arm of converter 200 and switching element Q2 and diode D2 constitute a lower arm of converter 200.

As power semiconductor switching elements Q1, Q2, any of IGBT (Insulated Gate Bipolar Transistor), power MOS (Metal Oxide Semiconductor) transistor, power bipolar transistor and the like can appropriately be used. ON/OFF of each of switching elements Q1, Q2 is controlled by a switching control signal from MG-ECU 172.

Reactor L has one end connected to a positive line PL1 which is connected to a positive electrode of battery 150, and the other end connected to a connection node of switching elements Q1, Q2, namely a connection point between the emitter of switching element Q1 and the collector of switching element Q2.

Capacitor C2 is connected between positive line PL2 and ground line GL. Capacitor C2 smoothes an AC component of a voltage variation between positive line PL2 and ground line GL. Capacitor C1 is connected between positive line PL1 and ground line GL. Capacitor C1 smoothes an AC component of a voltage variation between positive line PL1 and ground line GL.

Further, an air conditioner (A/C) 240 is connected between positive line PL1 and ground line GL. Although not shown, an auxiliary machine other than air conditioner 240 may also be connected between positive line PL1 and ground line GL. Current supplied to air conditioner 240 and current supplied to the auxiliary machine are collectively expressed as auxiliary current Idc.

Current IL flowing in reactor L (hereinafter reactor current) is detected by a current sensor SEIL. It should be noted that the direction of reactor current IL flowing from battery 150 to the connection point between the emitter of switching element Q1 and the collector of switching element Q2 is defined as positive direction. A voltage sensor 180 detects a voltage across terminals of capacitor C2 that is an output voltage of converter 200, namely detects a voltage VH (system voltage) between positive line PL2 and ground line GL, and outputs the detected value to MG-ECU 172.

Converter 200, inverter 210, and inverter 220 are electrically connected to each other through positive line PL2 and ground line GL.

In a voltage step-up operation, converter 200 steps up a DC voltage VB (voltage across the opposite terminals of capacitor C1) that is supplied from battery 150, and supplies system voltage VH generated by the voltage step-up to

inverters

210, 220. More specifically, in response to a switching control signal from MG-ECU 172, an ON period of switching element Q1 and an ON period of switching element Q2 are alternated, and a voltage step-up ratio is determined depending on a ratio between these ON periods.

In a voltage step-down operation, converter 200 steps down system voltage VH which is supplied through capacitor C2 from

inverters

210, 220 to charge battery 150 with the voltage. More specifically, in response to a switching control signal from MG-ECU 172, a period in which only switching element Q1 is ON and a period in which both switching elements Q1, Q2 are OFF are alternated, and a voltage step-down ratio is determined depending on the duty ratio of the ON period.

When the voltage step-up/step-down operation of converter 200 is stopped, switching element Q1 is fixed in an ON state and switching element Q2 is fixed in an OFF state.

Inverter 210 is configured in the form of a common three-phase inverter, and includes a U phase arm 15, a V phase arm 16, and a W phase arm 17. Arms 15 to 17 include switching elements Q3 to Q8 and anti-parallel diodes D3 to D8.

When the vehicle is running, inverter 210 controls current or voltage of each phase coil of first MG 110 so that first MG 110 operates in accordance with an operational command value (typically torque command value) which is set for generating a drive force (vehicle drive torque, electric power generation torque, or the like) required for the vehicle to run. Namely, inverter 210 performs bidirectional DC/AC power conversion between positive line PL2 and first MG 110.

Inverter 220 is configured in the form of a common three-phase inverter, like inverter 210. When the vehicle is running, inverter 220 controls current or voltage of each phase coil of second MG 120 so that second MG 120 operates in accordance with an operational command value (typically torque command value) which is set for generating a drive force (vehicle drive torque, regenerative braking torque, or the like) required for the vehicle to run. Namely, inverter 220 performs bidirectional DC/AC power conversion between positive line PL2 and second MG 120.

PM-ECU 170 calculates a torque command value TR1 for first MG 110 and a torque command value TR2 for second MG 120, based on an accelerator pedal position Acc and a speed V of the hybrid vehicle.

MG-ECU 172 calculates an optimum value (target value) of output voltage (system voltage) VH of converter 200, namely a command voltage VH*, based on torque command value TR1 for first MG 110 and torque command value TR2 for second MG 120 that are calculated by PM-ECU 170 as well as a motor rotational speed MRN1 of first MG 110 and a motor rotational speed MRN2 of second MG 120. MG-ECU 172 calculates, based on output voltage VH of converter 200 that is detected by voltage sensor 180 and command voltage VH*, a duty ratio for controlling output voltage VH so that voltage VH is equal to command voltage VH*, and accordingly controls converter 200.

MG-ECU 172 controls converter 200 by setting the converter in one of a continuous voltage step-up mode and an intermittent voltage step-up mode. The continuous voltage step-up mode is a mode in which converter 200 performs a voltage step-up operation without stopping. The intermittent voltage step-up mode is a mode in which converter 200 intermittently repeats a voltage step-up operation and stoppage of the voltage step-up operation. When converter 200 performs the voltage step-up operation, switching elements Q1, Q2 are switched between an ON state and an OFF state. When converter 200 stops the voltage step-up operation, switching element Q1 is fixed in the ON state and switching element Q2 is fixed in the OFF state.

The fact that converter 200 does not step up the voltage in the continuous voltage step-up mode and the fact that converter 200 stops voltage step-up in the intermittent voltage step-up mode are different from each other in terms of the following respect.

In the continuous voltage step-up mode, the voltage of battery 150 is supplied to

inverters

210, 220 through converter 200. Therefore, in the case where converter 200 does not step up the voltage in the continuous voltage step-up mode, the voltage of battery 150 is supplied as it is through converter 200 (duty ratio is 1) to

inverters

210, 220 without being stepping up.

In contrast, when converter 200 stops voltage step-up in the intermittent voltage step-up mode, the voltage of battery 150 is not supplied through converter 200 to

inverters

210, 220.

Instead of the continuous voltage step-up mode and the intermittent voltage step-up mode, a continuous voltage step-down mode and an intermittent voltage step-down mode may be provided. Namely, MG-ECU 172 sets converter 200 in one of the continuous voltage step-down mode and the intermittent voltage step-down mode. In the continuous voltage step-down mode, converter 200 performs a voltage step-down operation without stopping. In the intermittent voltage step-down mode, converter 200 intermittently repeats a voltage step-down operation and stoppage of the voltage step-down operation. When converter 200 performs the voltage step-down operation, a period in which only switching element Q1 is ON and a period in which both switching elements Q1, Q2 are OFF are alternated. When converter 200 stops the voltage step-down operation, switching element Q1 is fixed in an ON state and switching element Q2 is fixed in an OFF state.

<First Embodiment>
Referring to Fig. 2, control device 500 sets discharge power upper limit Wout (Wout >= 0 (Wout is equal to or greater than 0)) representing an upper limit of discharge power from battery 150. Whenever battery 150 discharges, control device 500 calculates the discharge power from battery 150 and discharge power upper limit Wout, and controls converter 200 so that the discharge power does not exceed discharge power upper limit Wout even for a moment. More specifically, based on reactor current IL detected by current sensor SEIL, control device 500 adjusts the ratio between an ON period of switching element Q1 and an ON period of switching element Q2.

Fig. 3 is a waveform diagram for illustrating reactor current IL in the case where converter 200 is controlled in the intermittent voltage step-up mode. Referring to Fig. 3, while the intermittent voltage step-up control is performed, reactor current IL varies in very short cycles (3 to 5 ms for example). In order to accurately observe the current, it is necessary that the time intervals at which the current is measured are sufficiently shorter than the intervals at which the current varies.

If the time intervals at which the current is measured are to be shortened, it is necessary to use a high-speed CPU or increase the communication frequency, which causes an increase in cost. In view of this, for PM-ECU 170 in the present embodiment, a CPU having control cycles longer than the cycles in which reactor current IL varies is used. By way of example, the period of the control cycle of the CPU of PM-ECU 170 is approximately 8 ms. Meanwhile, converter 200 is controlled by MG-ECU 172 so that the period of the cycle in which reactor current IL varies is approximately 5 ms.

Therefore, under the control in the intermittent voltage step-up mode, the precision with which reactor current IL is measured is lower relative to the control in the continuous voltage step-up mode. Consequently, under the intermittent voltage step-up control, there is a possibility that converter 200 cannot be controlled so that the discharge power from battery 150 does not exceed discharge power upper limit Wout. In such a case, battery 150 may be degraded and the performance of battery 150 may be deteriorated.

How to set discharge power upper limit Wout is now described. In the present embodiment, control device 500 can set discharge power upper limit Wout depending on the SOC and/or temperature TB of battery 150.

It should be noted that control device 500 can calculate an estimate value of the SOC of battery 150 based on a detection signal from battery sensor 152. Since a known method can be used as the method of estimating the SOC, the detailed description thereof is not herein repeated. Further, control device 500 can obtain temperature TB of battery 150 from battery sensor 152.

Fig. 4 is a conceptual diagram showing a limitation on discharge power upper limit Wout with respect to the SOC of battery 150 in the first embodiment. Referring to Fig. 4, the horizontal axis represents the SOC of battery 150 and the vertical axis represents discharge power upper limit Wout.

For a low SOC range (range where SOC < S1), discharge power upper limit Wout is set smaller as compared with a range (range where SOC >= S1) other than the low SOC range. It should be noted that Wout = 0 means that discharging of battery 150 is inhibited.

Further, in the present embodiment, whether to permit or inhibit the control in the intermittent voltage step-up mode is determined based on discharge power upper limit Wout. Then, a threshold value KWO1 is defined for discharge power upper limit Wout.

In the case where discharge power upper limit Wout is equal to or more than threshold value KWO1, the control in the intermittent voltage step-up mode is permitted. In contrast, in the case where discharge power upper limit Wout is less than threshold value KWO1, the control in the intermittent voltage step-up mode is inhibited. Namely the control in the continuous voltage step-up mode is performed.

Fig. 5 is a conceptual diagram showing a limitation on discharge power upper limit Wout with respect to temperature TB of battery 150 in the first embodiment. The horizontal axis in Fig. 5 represents temperature TB of battery 150.

Particularly in the case where battery 150 is configured in the form of a secondary battery, the internal resistance of battery 150 is higher at a low temperature and a high temperature. Therefore, for a low temperature range (range where TB < T1) and a high temperature range (range where TB > T2), discharge power upper limit Wout is limited relative to a normal temperature range (range where T1 <= TB <= T2 (TB is equal to or more than T1 and is equal to or less than T2)).

Further, similarly to the limitation with respect to the SOC shown in Fig. 4, the control in the intermittent voltage step-up mode is permitted in the case where discharge power upper limit Wout is equal to or more than threshold value KWO1. In contrast, in the case where discharge power upper limit Wout is less than threshold value KWO1, the control in the intermittent voltage step-up mode is inhibited. Namely the control in the continuous voltage step-up mode is performed.

Although discharge power upper limit Wout can be set based on one of the SOC and the temperature of battery 150, both the SOC and the temperature can also be used to set discharge power upper limit Wout. In the case where both the SOC and the temperature are used, a smaller one of the value of discharge power upper limit Wout corresponding to the SOC at a certain time (see Fig. 4) and the value of discharge power upper limit Wout corresponding to temperature TB at this time (see Fig. 5) can be used.

Fig. 6 is a flowchart showing a procedure of voltage step-up control by converter 200. Fig. 7 is a flowchart showing details of step ST25 in the flowchart of Fig. 6. Fig. 8 is a waveform diagram for illustrating operations in a continuous voltage step-up mode and an intermittent voltage step-up mode.

Fig. 8 (a) is a chart showing output voltage (system voltage) VH of converter 200 in the continuous voltage step-up mode and the intermittent voltage step-up mode. Fig. 8 (b) is a chart showing reactor current IL in the continuous voltage step-up mode and the intermittent voltage step-up mode. Although reactor current IL is actually caused to vary by switching of converter 200, Fig. 8 (b) shows the reactor current whose varying component due to switching is smoothed. Fig. 8 (c) is a chart showing a voltage step-up power loss LP due to switching in the continuous voltage step-up mode and the intermittent voltage step-up mode.

Referring to Figs. 2 and 6, in step ST10, control device 500 sets converter 200 in the continuous voltage step-up mode. Converter 200 performs the voltage step-up operation without stopping the voltage step-up operation.

After this, when an average ILM of reactor current IL in a predetermined period in the past is less than a threshold value TH1 in step ST20, control device 500 causes the process to proceed to step ST25. In step ST25, control device 500 checks discharge power upper limit Wout in order to determine whether to permit the converter 200 to be set in the intermittent voltage step-up mode or not.

Referring to Figs. 2 and 7, in response to the start of the process of step ST25, control device 500 determines whether or not discharge power upper limit Wout is less than threshold value KWO1 in step ST100.

In the case where discharge power upper limit Wout is equal to or more than threshold value KWO1 in step ST100 (NO in step ST100), control device 500 causes the process to proceed to step ST120. In step ST120, control device 500 determines to permit the intermittent voltage step-up mode, and causes the process to proceed to step ST30 in the flowchart of Fig. 6. In this case, converter 200 is set in the intermittent voltage step-up mode to operate.

In contrast, in the case where discharge power upper limit Wout is less than threshold value KWO1 in step ST100 (YES in step ST100), control device 500 causes the process to proceed to step ST110. In step ST110, control device 500 determines to inhibit the intermittent voltage step-up mode, and causes the process to return to step ST10 in the flowchart of Fig. 6. In this case, converter 200 is set in the continuous voltage step-up mode to operate.

In step ST30, control device 500 sets converter 200 in the intermittent voltage step-up mode. In the case where the converter is set in the intermittent voltage step-up mode, control device 500 first causes the voltage step-up operation of converter 200 to be stopped (see time (1) in Fig. 8 for example).

When the voltage step-up operation of converter 200 is stopped, current is not output from battery 150. Therefore, reactor current IL is zero and voltage step-up power loss LP is zero. While the voltage step-up operation of converter 200 is stopped, first MG 110 and/or second MG 120 are/is driven with electric power stored in capacitor C2. As electrical charge is discharged from capacitor C2, system voltage VH is decreased.

After this, when a deviation |VH*-VH| between system voltage VH and command voltage VH* is equal to or more than a limit value dVH in step ST40, control device 500 causes the process to proceed to step ST50. In step ST50, control device 500 causes converter 200 to restart the voltage step-up operation (see time (2) in Fig. 8 for example).

When the voltage step-up operation by converter 200 is restarted, battery 150 supplies current (recovery current) which is necessary to drive first MG 110 and/or second MG 120 while charging capacitor C2. Therefore, reactor current IL is increased and voltage step-up power loss LP is increased.

After this, when system voltage VH is equal to command voltage VH* in step ST60, control device 500 causes the process to proceed to step ST70. In step ST70, control device 500 causes the voltage step-up operation by converter 200 to be stopped (see time (3) in Fig. 8 for example). Following step ST70, the process is performed again from step ST40.

When average ILM of reactor current IL in a predetermined period in the past is larger than a threshold value TH2 in step ST80, control device 500 causes the process to proceed to step ST90 to set converter 200 in the continuous voltage step-up mode. Converter 200 performs the voltage step-up operation without stopping (see time (4) in Fig. 8 for example). At time (4) in Fig. 8, it is shown that command voltage VH* has been increased and reactor current IL begins to increase. After step ST90, the series of the process steps shown in Fig. 6 is repeated in the case where a predetermined condition is met.

Fig. 8 (c) shows by what amount voltage step-up power loss LP is reduced in a set of one period in which voltage step-up is stopped and one subsequent period in which voltage step-up is performed, in the intermittent voltage step-up mode. An area P3 of a region enclosed by a line which represents a reference power loss BS and a line which represents voltage step-up power loss LP and is located higher than the line of reference power loss BS is the sum of voltage step-up power losses LP larger than the voltage step-up power loss in the continuous voltage step-up mode. An area P0 of a region enclosed by the line which represents reference power loss BS and the line which represents voltage step-up power loss LP and is located lower than the line of reference power loss BS is the sum of voltage step-up power losses LP smaller than the voltage step-up power loss in the continuous voltage step-up mode. A value P1 determined by subtracting P2 (=P3) from P0 is the sum of reductions of the voltage step-up power loss, relative to the voltage step-up power loss in the continuous voltage step-up mode, achieved by the operation in the intermittent voltage step-up mode in the set of one period in which voltage step-up is stopped and one subsequent period in which voltage step-up is performed.

As shown in Fig. 8 (c), the converter 200 can be set in the intermittent voltage step-up mode to thereby reduce the voltage step-up power loss. A longer period in which the voltage step-up is stopped produces a greater effect of reducing the loss.

Thus, according to the first embodiment, in the case where discharge power upper limit Wout is equal to or more than threshold value KWO1, control device 500 can reduce an electric power loss of converter 200 by the intermittent voltage step-up control. In contrast, in the case where discharge power upper limit Wout is less than threshold value KWO1, control device 500 inhibits the operation of converter 200 in the intermittent voltage step-up mode. Namely, in the case where discharge power upper limit Wout is less than threshold value KWO1, converter 200 is controlled in the continuous voltage step-up mode. Since the controllability of reactor current IL is not deteriorated in the continuous voltage step-up mode, the discharge power from battery 150 can reliably be prevented from exceeding discharge power upper limit Wout.

<Second Embodiment>
Although the above description of the first embodiment concerns the control under which the intermittent voltage step-up control is inhibited, the intermittent voltage step-up control can also be suppressed by other control methods. In a second embodiment, the rate at which the battery voltage is stepped up is limited. More specifically, based on discharge power upper limit Wout, an increase per unit time (hereinafter also referred to as recovery rate) of output voltage (system voltage) VH from the converter is changed.

A hybrid vehicle and its electrical system in the second embodiment have respective configurations equivalent to the configurations shown in Figs. 1 and 2, respectively. Therefore, the description thereof will not be repeated.

Fig. 9 is a conceptual diagram showing a limitation on discharge power upper limit Wout with respect to the SOC of battery 150 in the second embodiment. Fig. 9 is comparable to Fig. 4.

For discharge power upper limit Wout in the second embodiment, a threshold value KWO2 (second threshold value) is defined in addition to threshold value KWO1 (first threshold value). It should be noted that threshold value KWO2 is smaller than threshold value KWO1.

In the case where discharge power upper limit Wout is less than threshold value KWO2, the control in the intermittent voltage step-up mode is inhibited. Namely, the control in the continuous voltage step-up mode is performed.

In contrast, in the case where discharge power upper limit Wout is equal to or more than threshold value KWO2, the control in the intermittent voltage step-up mode is permitted. It should be noted that when discharge power upper limit Wout is equal to or more than threshold value KWO1, a recovery rate RTFD is set. In contrast, when discharge power upper limit Wout is equal to or more than threshold value KWO2 and less than threshold value KWO1, a recovery rate RTSD slower than recovery rate RTFD is set. These recovery rates RTFD, RTSD will be detailed later herein.

Fig. 10 is a conceptual diagram showing a limitation on discharge power upper limit Wout with respect to temperature TB of battery 150 in the second embodiment. Fig. 10 is comparable to Fig. 5.

Similarly to the limitation with respect to the SOC shown in Fig. 9, in the case where discharge power upper limit Wout is less than threshold value KWO2, the control in the intermittent voltage step-up mode is inhibited and the control in the continuous voltage step-up mode is performed.

In contrast, when discharge power upper limit Wout is equal to or more than threshold value KWO2, the control in the intermittent voltage step-up mode is permitted. It should be noted that in contrast to the fact that recovery rate RTFD is set when discharge power upper limit Wout is equal to or more than threshold value KWO1, recovery rate RTSD is set for the temperature range where discharge power upper limit Wout is equal to or more than threshold value KWO2 and less than threshold value KWO1.

Fig. 11 is a diagram for comparison of reactor current IL depending on the recovery rate when battery 150 discharges. Referring to Fig. 11, the horizontal axis is time axis and the vertical axis represents system voltage VH or reactor current IL.

Fig. 11 (a) is a chart showing system voltage VH and reactor current IL in the continuous voltage step-up mode. Fig. 11 (b) is a chart showing system voltage VH and reactor current IL in the case where the recovery rate is relatively slow (in the case of recovery rate RTSD) in the intermittent voltage step-up mode. Fig. 11 (c) is a chart showing system voltage VH and reactor current IL in the case where the recovery rate is relatively fast (in the case of recovery rate RTFD) in the intermittent voltage step-up mode.

As described above in connection with Figs. 9 and 10, the recovery rate is set slower as discharge power upper limit Wout is smaller in the second embodiment. Slowdown of the recovery rate slows down the rate at which electrical charge to be stored in capacitor C2 is output from converter 200. Therefore, as shown in Fig. 11 (b) and Fig. 11 (c), the maximum value of reactor current IL decreases. Since the discharge power from battery 150 increases in proportion to reactor current IL, the maximum value of reactor current IL can be limited to thereby limit the maximum value of the discharge power. In this way, the discharge power can be prevented from momentarily exceeding discharge power upper limit Wout.

Next, a procedure of voltage step-up control in the second embodiment will be described. It should be noted that a flowchart and a waveform diagram for the overall voltage step-up control in the second embodiment are equivalent to the flowchart (see Fig. 6) and the waveform diagram (see Fig. 8) in the first embodiment, respectively. Therefore, the detailed description thereof will not be repeated.

Fig. 12 is a flowchart in the second embodiment showing details of step ST25 in the flowchart of Fig. 6. Referring to Figs. 2 and 12, in response to the start of the process of step ST25, control device 500 determines whether or not discharge power upper limit Wout is less than threshold value KWO1 in step ST100.

In the case where discharge power upper limit Wout is equal to or more than threshold value KWO1 in step ST100 (NO in step ST100), control device 500 causes the process to proceed to step ST120. In step ST120, control device 500 determines to permit the intermittent voltage step-up mode, and causes the process to proceed to step ST30 in the flowchart of Fig. 6. In this case, converter 200 is set in the intermittent voltage step-up mode and relatively fast recovery rate RTFD is set.

In contrast, in the case where discharge power upper limit Wout is less than threshold value KWO1 in step ST100 (YES in step ST100), control device 500 causes the process to proceed to step ST105.

In the case where discharge power upper limit Wout is equal to or more than threshold value KWO2 in step ST105 (namely KWO2 <= Wout < KWO1 (Wout is equal to or more than KWO2 and less than KWO1), NO in step ST105), control device 500 causes the process to proceed to step ST115. In step ST115, control device 500 determines to permit the intermittent voltage step-up mode, and causes the process to proceed to step ST30 in the flowchart of Fig. 6. In this case, converter 200 is set in the intermittent voltage step-up mode and relatively slow recovery rate RTSD is set.

In contrast, in the case where discharge power upper limit Wout is less than threshold value KWO2 in step ST105 (YES in step ST105), control device 500 causes the process to proceed to step ST110. In step ST110, control device 500 determines to inhibit the intermittent voltage step-up mode, and causes the process to return to step ST10 in the flowchart of Fig. 6. In this case, converter 200 is set in the continuous voltage step-up mode to operate.

Namely, in the case where discharge power upper limit Wout is larger than threshold value KWO1, control device 500 permits the intermittent voltage step-up control. In this case, relatively fast recovery rate RTFD is set. In contrast, in the case where discharge power upper limit Wout is smaller and equal to or more than threshold value KWO2 and less than threshold value KWO1, control device 500 permits the intermittent voltage step-up control and also sets recovery rate RTSD which is slower than recovery rate RTFD. Further, in the case where discharge power upper limit Wout is still smaller and less than threshold value KWO2, control device 500 inhibits the intermittent voltage step-up control. In this way, control device 500 suppresses the operation of converter 200 in the intermittent voltage step-up mode, as discharge power upper limit Wout is smaller.

In the first embodiment as well, the inhibition of the intermittent voltage step-up control may be replaced with a permission of the intermittent voltage step-up control and a limitation on the recovery rate. Namely, referring to Figs. 4 and 5, control device 500 may set the recovery rate (rate at which voltage VB of battery 150 is stepped up) smaller in the case where discharge power upper limit Wout is less than threshold value KWO1, relative to the case where discharge power upper limit Wout is equal to or more than threshold value KWO1.

Discharge power upper limit Wout is essentially set on the precondition that the intermittent voltage step-up control is not performed. As described above, when the intermittent voltage step-up control is performed, the controllability of reactor current IL is deteriorated, which may cause the discharge power to exceed discharge power upper limit Wout. It is therefore necessary to define threshold values KWO1, KWO2 for suppressing the intermittent voltage step-up control.

According to the inventors of the prevent invention, threshold value KWO1 is preferably determined based on reactor current IL when the recovery rate is RTFD. Likewise, threshold value KWO2 is preferably determined based on reactor current IL when the recovery rate is RTSD.

The discharge power increases with an increase of reactor current IL. In view of this, threshold values KWO1, KWO2 are determined based on reactor current IL. Accordingly, appropriate threshold values on which the magnitude of the discharge power is reflected can be determined. Thus, the discharge power can more reliably be prevented from exceeding discharge power upper limit Wout under the intermittent voltage step-up control.

Further, according to the inventors of the present invention, threshold values KWO1, KWO2 are more preferably determined based on the maximum discharge power that can occur under the intermittent voltage step-up control as shown in Fig. 9. In other words, threshold value KWO1 is determined based on the discharge power at the time when reactor current IL reaches its maximum value in the case of recovery rate RTFD (the time when reactor current IL reaches its maximum value ILF in Fig. 11 (c)). Likewise, threshold value KWO2 is determined based on the discharge power at the time when reactor current IL reaches its maximum value in the case of recovery rate RTSD (the time when reactor current IL reaches its maximum value ILS in Fig. 11 (b)). This is for the reason that the discharge power reaches its maximum value when reactor current IL is at its maximum.

Threshold values KWO1, KWO2 are defined to be larger than the maximum value of the discharge power. Thus, a range in which the intermittent voltage step-up control is inhibited is made sufficiently broad. Accordingly, the discharge power can still more reliably be prevented from exceeding discharge power upper limit Wout.

Although the method of determining threshold values KWO1, KWO2 is applied as well to temperature TB, Fig. 10 does not show the two arrows representing the maximum value of the discharge power (see Fig. 9), for the sake of avoiding complication of the drawing. The method of determining threshold value KWO1 is applied as well to the first embodiment (see Figs. 4 and 5). It should be noted that the method of determining threshold values KWO1, KWO2 is not limited to the above-described one.

The condition on which a limitation is imposed on discharge power upper limit Wout is not limited to the SOC (see Fig. 4 or 9) or the temperature (see Fig. 5 or 10) of the battery. In the case where discharge power upper limit Wout is determined based on other conditions, the control shown by the flowcharts of Figs. 6, 7, and 12 is also applicable.

Referring again to Fig. 2, the first and second embodiments are outlined. A power supply apparatus of a vehicle includes: battery 150; converter 200 stepping up voltage VB of battery 150 and supplying the stepped-up voltage to

inverters

210, 220 of the vehicle; and control device 500 controlling converter 200 in a continuous voltage step-up mode and an intermittent voltage step-up mode. In the continuous voltage step-up mode converter 200 is continuously operated. In the intermittent voltage step-up mode converter 200 is intermittently operated. Control device 500 controls converter 200 so that discharge power from battery 150 does not exceed discharge power upper limit Wout. Control device 500 suppresses an operation of converter 200 in the intermittent voltage step-up mode to a greater extent as discharge power upper limit Wout is smaller.

Preferably, in a case where discharge power upper limit Wout is smaller than predetermined threshold value KWO1, control device 500 inhibits the operation of converter 200 in the intermittent voltage step-up mode.

Preferably, in a case where discharge power upper limit Wout is smaller than predetermined threshold value KWO2, control device 500 sets smaller the recovery rate (rate at which voltage VB of battery 150 is stepped up) in the intermittent voltage step-up mode, relative to a case where discharge power upper limit Wout is equal to or larger than threshold value KWO2.

Preferably, in a case where discharge power upper limit Wout is smaller than threshold value KWO1 and equal to or larger than threshold value KWO2 which is smaller than threshold value KWO1, control device 500 sets smaller the recovery rate in the intermittent voltage step-up mode, relative to a case where discharge power upper limit Wout is equal to or larger than threshold value KWO1. In a case where discharge power upper limit Wout is smaller than threshold value KWO2, control device 500 inhibits the operation of converter 200 in the intermittent voltage step-up mode.

Preferably, threshold values KWO1, KWO2 are determined based on reactor current IL (through current) flowing through converter 200 in the intermittent voltage step-up mode.

Preferably, threshold values KWO1, KWO2 are determined based on discharge power from battery 150 when reactor current IL is at its maximum.

<Third Embodiment>
In the electrical system shown in Fig. 2, converter 200 steps up voltage VB of battery 150 to system voltage VH to supply it to

inverters

210, 220 during a power-running operation. In contrast, converter 200 steps down system voltage VH from

inverters

210, 220 to voltage VB to charge battery 150 during a regenerative operation. In a third embodiment, control similar to the control in the first embodiment is applied to the converter which steps down the voltage for charging the battery.

A hybrid vehicle and its electrical system in the third embodiment have respective configurations equivalent to the configurations shown in Figs. 1 and 2, respectively. Therefore, the description thereof will not be repeated.

Referring to Fig. 2, control device 500 sets charge power upper limit Win (Win >= 0) representing an upper limit of charge power to battery 150. Whenever battery 150 is charged, control device 500 calculates the charge power to battery 150 and charge power upper limit Win, and controls converter 200 so that the charge power does not exceed charge power upper limit Win even for a moment. More specifically, based on reactor current IL detected by current sensor SEIL, control device 500 adjusts the ratio between an ON period of switching element Q1 and an ON period of switching element Q2.

Fig. 13 is a waveform diagram for illustrating reactor current IL in the case where converter 200 is controlled in the intermittent voltage step-down mode. It should be noted that the direction of reactor current IL flowing to battery 150 from the connection point between the emitter of switching element Q1 and the collector of switching element Q2 is defined as negative direction (see Fig. 2).

Referring to Fig. 13, while the intermittent voltage step-down control is performed, reactor current IL varies in very short cycles (3 to 5 ms for example). In order to accurately observe the current, it is necessary that the time intervals at which the current is measured are sufficiently shorter than the intervals at which the current varies.

If the time intervals at which the current is measured are to be shortened, it is necessary to use a high-speed CPU or increase the communication frequency, which causes an increase in cost. In view of this, for PM-ECU 170 in the present embodiment, a CPU having control cycles longer than the cycles in which reactor current IL varies is used. By way of example, converter 200 is controlled by MG-ECU 172 so that the period of the cycle in which reactor current IL varies is approximately 5 ms. Meanwhile, the period of the control cycle of the CPU of PM-ECU 170 is approximately 8 ms.

Therefore, under the control in the intermittent voltage step-down mode, the precision with which reactor current IL is measured is lower relative to the control in the continuous voltage step-down mode. Consequently, under the intermittent voltage step-down control, there is a possibility that converter 200 cannot be controlled so that the charge power to battery 150 does not exceed charge power upper limit Win. In such a case, battery 150 may be degraded and the performance of battery 150 may be deteriorated.

How to set charge power upper limit Win is now described. In the present embodiment, control device 500 can set charge power upper limit Win depending on the SOC and/or temperature TB of battery 150.

Fig. 14 is a conceptual diagram showing a limitation on charge power upper limit Win with respect to the SOC of battery 150 in the third embodiment. Referring to Fig. 14, the horizontal axis represents the SOC of battery 150 and the vertical axis represents charge power upper limit Win.

For a high SOC range (range where SOC > S2), charge power upper limit Win is set smaller as compared with a range (range where SOC <= S2) other than the high SOC range. It should be noted that Win = 0 means that charging of battery 150 is inhibited.

Further, in the present embodiment, whether to permit or inhibit the control in the intermittent voltage step-down mode is determined based on charge power upper limit Win. Then, a threshold value KWI1 is defined for charge power upper limit Win.

In the case where charge power upper limit Win is equal to or more than threshold value KWI1, the control in the intermittent voltage step-down mode is permitted. In contrast, in the case where charge power upper limit Win is less than threshold value KWI1, the control in the intermittent voltage step-down mode is inhibited. Namely the control in the continuous voltage step-down mode is performed.

Fig. 15 is a conceptual diagram showing a limitation on charge power upper limit Win with respect to temperature TB of battery 150 in the third embodiment. The horizontal axis in Fig. 15 represents temperature TB of battery 150.

Particularly in the case where battery 150 is configured in the form of a secondary battery, the internal resistance of battery 150 is higher at a low temperature and a high temperature. Therefore, for a low temperature range (range where TB < T1) and a high temperature range (range where TB > T2), charge power upper limit Win is limited relative to a normal temperature range (range where T1 <= TB <= T2).

Further, similarly to the limitation with respect to the SOC shown in Fig. 14, the control in the intermittent voltage step-down mode is permitted in the case where charge power upper limit Win is equal to or more than threshold value KWI1. In contrast, in the case where charge power upper limit Win is less than threshold value KWI1, the control in the intermittent voltage step-down mode is inhibited. Namely the control in the continuous voltage step-down mode is performed.

Although charge power upper limit Win can be set based on one of the SOC and the temperature of battery 150, both the SOC and the temperature can also be used to set charge power upper limit Win. In the case where both the SOC and the temperature are used, a smaller one of the value of charge power upper limit Win corresponding to the SOC at a certain time (see Fig. 14) and the value of charge power upper limit Win corresponding to temperature TB at this time (see Fig. 15) can be used.

Fig. 16 is a flowchart showing a procedure of voltage step-down control by converter 200. Fig. 17 is a flowchart showing details of step ST25 in the flowchart of Fig. 16. Fig. 18 is a waveform diagram for illustrating operations in a continuous voltage step-down mode and an intermittent voltage step-down mode.

Fig. 18 (a) is a chart showing input voltage (system voltage) VH to converter 200 in the continuous voltage step-down mode and the intermittent voltage step-down mode. Fig. 18 (b) is a chart showing reactor current IL in the continuous voltage step-down mode and the intermittent voltage step-down mode. Although reactor current IL is actually caused to vary by switching of converter 200, Fig. 18 (b) shows the reactor current whose varying component due to switching is smoothed. Fig. 18 (c) is a chart showing a voltage step-down power loss LP due to switching in the continuous voltage step-down mode and the intermittent voltage step-down mode.

Referring to Figs. 2 and 16, in step ST10, control device 500 sets converter 200 in the continuous voltage step-down mode. Converter 200 performs the voltage step-down operation without stopping the voltage step-down operation.

After this, when an average ILM of reactor current IL in a predetermined period in the past is larger than a threshold value TH1 in step ST20, control device 500 causes the process to proceed to step ST25. In step ST25, control device 500 checks charge power upper limit Win in order to determine whether to permit the converter 200 to be set in the intermittent voltage step-down mode or not.

Referring to Figs. 2 and 17, in response to the start of the process of step ST25, control device 500 determines whether or not charge power upper limit Win is less than threshold value KWI1 in step ST100.

In the case where charge power upper limit Win is equal to or more than threshold value KWI1 in step ST100 (NO in step ST100), control device 500 causes the process to proceed to step ST120. In step ST120, control device 500 determines to permit the intermittent voltage step-down mode, and causes the process to proceed to step ST30 in the flowchart of Fig. 16. In this case, converter 200 is set in the intermittent voltage step-down mode to operate.

In contrast, in the case where charge power upper limit Win is less than threshold value KWI1 in step ST100 (YES in step ST100), control device 500 causes the process to proceed to step ST110. In step ST110, control device 500 determines to inhibit the intermittent voltage step-down mode, and causes the process to return to step ST10 in the flowchart of Fig. 16. In this case, converter 200 is set in the continuous voltage step-down mode to operate.

In step ST30, control device 500 sets converter 200 in the intermittent voltage step-down mode. In the case where the converter is set in the intermittent voltage step-down mode, control device 500 first causes the voltage step-down operation of converter 200 to be stopped (see time (1) in Fig. 18 for example).

When the voltage step-down operation of converter 200 is stopped, current is not output from converter 200 to battery 150. Therefore, reactor current IL is zero and voltage step-down power loss LP is zero. While the voltage step-down operation of converter 200 is stopped, power is stored in capacitor C2 by inverter 210 receiving AC power from first MG 110 and/or inverter 220 receiving AC power from second MG 120. As charge is stored in capacitor C2, system voltage VH is increased.

After this, when a deviation |VH*-VH| between system voltage VH and command voltage VH* is equal to or more than a limit value dVH in step ST40, control device 500 causes the process to proceed to step ST50. In step ST50, control device 500 causes converter 200 to restart the voltage step-down operation (see time (2) in Fig. 18 for example).

When the voltage step-down operation by converter 200 is restarted, current (recovery current) is supplied to converter 200 while capacitor C2 discharges. Therefore, reactor current IL is increased in the negative direction and voltage step-down power loss LP is increased.

After this, when system voltage VH is equal to command voltage VH* in step ST60, control device 500 causes the process to proceed to step ST70. In step ST70, control device 500 causes the voltage step-down operation by converter 200 to be stopped (see time (3) in Fig. 18 for example). Following step ST70, the process is performed again from step ST40.

When average ILM of reactor current IL in a predetermined period in the past is less than a threshold value TH2 in step ST80, control device 500 causes the process to proceed to step ST90 to set converter 200 in the continuous voltage step-down mode. Converter 200 performs the voltage step-down operation without stopping (see time (4) in Fig. 18 for example). At time (4) in Fig. 18, it is shown that command voltage VH* has been decreased and reactor current IL begins to decrease. After step ST90, the series of the process steps shown in Fig. 16 is repeated in the case where a predetermined condition is met.

Fig. 18 (c) shows by what amount voltage step-down power loss LP is reduced in a set of one period in which voltage step-down is stopped and one subsequent period in which voltage step-down is performed, in the intermittent voltage step-down mode. An area P3 of a region enclosed by a line which represents a reference power loss BS and a line which represents voltage step-down power loss LP and is located higher than the line of reference power loss BS is the sum of voltage step-down power losses LP larger than the voltage step-down power loss in the continuous voltage step-down mode. An area P0 of a region enclosed by the line which represents reference power loss BS and the line which represents voltage step-down power loss LP and is located lower than the line of reference power loss BS is the sum of voltage step-down power losses LP smaller than the voltage step-down power loss in the continuous voltage step-down mode. A value P1 determined by subtracting P2 (=P3) from P0 is the sum of reductions of the voltage step-down power loss, relative to the voltage step-down power loss in the continuous voltage step-down mode, achieved by the operation in the intermittent voltage step-down mode in the set of one period in which voltage step-down is stopped and one subsequent period in which voltage step-down is performed.

As shown in Fig. 18 (c), the converter 200 can be set in the intermittent voltage step-down mode to thereby reduce the voltage step-down power loss. A longer period in which the voltage step-down is stopped produces a greater effect of reducing the loss.

Thus, according to the third embodiment, in the case where charge power upper limit Win is equal to or more than threshold value KWI1, control device 500 can reduce an electric power loss of converter 200 by the intermittent voltage step-down control. In contrast, in the case where charge power upper limit Win is less than threshold value KWI1, control device 500 inhibits the operation of converter 200 in the intermittent voltage step-down mode. Namely, in the case where charge power upper limit Win is less than threshold value KWI1, converter 200 is controlled in the continuous voltage step-down mode. Since the controllability of reactor current IL is not deteriorated in the continuous voltage step-down mode, the charge power to battery 150 can reliably be prevented from exceeding charge power upper limit Win.

<Fourth Embodiment>
Although the above description of the third embodiment concerns the control under which the intermittent voltage step-down control is inhibited, the intermittent voltage step-down control can also be suppressed by other control methods. In a fourth embodiment, the rate at which the voltage from the inverter is stepped down is limited. More specifically, based on charge power upper limit Win, a decrease per unit time (hereinafter also referred to as recovery rate) of input voltage (system voltage) VH from the inverter is changed.

A hybrid vehicle and its electrical system in the fourth embodiment have respective configurations equivalent to the configurations shown in Figs. 1 and 2, respectively. Therefore, the description thereof will not be repeated.

Fig. 19 is a conceptual diagram showing a limitation on charge power upper limit Win with respect to the SOC of battery 150 in the fourth embodiment. Fig. 19 is comparable to Fig. 14.

For charge power upper limit Win in the fourth embodiment, a threshold value KWI2 is defined in addition to threshold value KWI1. It should be noted that threshold value KWI2 is smaller than threshold value KWI1.

In the case where charge power upper limit Win is less than threshold value KWI2, the control in the intermittent voltage step-down mode is inhibited. Namely, the control in the continuous voltage step-down mode is performed.

In contrast, in the case where charge power upper limit Win is equal to or more than threshold value KWI2, the control in the intermittent voltage step-down mode is permitted. It should be noted that when charge power upper limit Win is equal to or more than threshold value KWI1, a recovery rate RTFC is set. In contrast, when charge power upper limit Win is equal to or more than threshold value KWI2 and less than threshold value KWI1, a recovery rate RTSC slower than recovery rate RTFC is set. These recovery rates RTFC, RTSC will be detailed later herein.

Fig. 20 is a conceptual diagram showing a limitation on charge power upper limit Win with respect to temperature TB of battery 150 in the fourth embodiment. Fig. 20 is comparable to Fig. 15.

Similarly to the limitation with respect to the SOC shown in Fig. 19, in the case where charge power upper limit Win is less than threshold value KWI2, the control in the intermittent voltage step-down mode is inhibited and the control in the continuous voltage step-down mode is performed.

In contrast, in the case where charge power upper limit Win is equal to or more than threshold value KWI2, the control in the intermittent voltage step-down mode is permitted. It should be noted that in contrast to the fact that recovery rate RTFC is set when charge power upper limit Win is equal to or more than threshold value KWI1, recovery rate RTSC is set when charge power upper limit Win is equal to or more than threshold value KWI2 and less than threshold value KWI1.

Fig. 21 is a diagram for comparison of reactor current IL depending on the recovery rate when battery 150 is charged. Referring to Fig. 21, the horizontal axis is time axis and the vertical axis represents system voltage VH or reactor current IL.

Fig. 21 (a) is a chart showing system voltage VH and reactor current IL in the continuous voltage step-down mode. Fig. 21 (b) is a chart showing system voltage VH and reactor current IL in the case where the recovery rate is relatively slow (in the case of recovery rate RTSC) in the intermittent voltage step-down mode. Fig. 21 (c) is a chart showing system voltage VH and reactor current IL in the case where the recovery rate is relatively fast (in the case of recovery rate RTFC) in the intermittent voltage step-down mode.

As described above in connection with Figs. 19 and 20, the recovery rate is set slower as charge power upper limit Win is smaller in the fourth embodiment. Slowdown of the recovery rate causes the maximum value of reactor current IL to decrease as shown in Fig. 21 (b) and Fig. 21 (c). Since the charge power to battery 150 increases in proportion to reactor current IL, the maximum value of reactor current IL can be limited to thereby limit the maximum value of the charge power. In this way, the charge power can be prevented from momentarily exceeding charge power upper limit Win.

Next, a procedure of voltage step-down control in the fourth embodiment will be described. It should be noted that a flowchart and a waveform diagram for the overall voltage step-down control in the fourth embodiment are equivalent to the flowchart (see Fig. 16) and the waveform diagram (see Fig. 18) in the third embodiment, respectively. Therefore, the detailed description thereof will not be repeated.

Fig. 22 is a flowchart in the fourth embodiment showing details of step ST25 in the flowchart of Fig. 16. Referring to Figs. 2 and 22, in response to the start of the process of step ST25, control device 500 determines whether or not charge power upper limit Win is less than threshold value KWI1 in step ST100.

In the case where charge power upper limit Win is equal to or more than threshold value KWI1 in step ST100 (NO in step ST100), control device 500 causes the process to proceed to step ST120. In step ST120, control device 500 determines to permit the intermittent voltage step-down mode, and causes the process to proceed to step ST30 in the flowchart of Fig. 16. In this case, converter 200 is set in the intermittent voltage step-down mode and relatively fast recovery rate RTFC is set.

In contrast, in the case where charge power upper limit Win is less than threshold value KWI1 in step ST100 (YES in step ST100), control device 500 causes the process to proceed to step ST105.

In the case where charge power upper limit Win is equal to or more than threshold value KWI2 in step ST105 (namely KWI2 <= Win < KWI1, NO in step ST105), control device 500 causes the process to proceed to step ST115. In step ST115, control device 500 determines to permit the intermittent voltage step-down mode, and causes the process to proceed to step ST30 in the flowchart of Fig. 16. In this case, converter 200 is set in the intermittent voltage step-down mode and relatively slow recovery rate RTSC is set.

In contrast, in the case where charge power upper limit Win is less than threshold value KWI2 in step ST105 (YES in step ST105), control device 500 causes the process to proceed to step ST110. In step ST110, control device 500 determines to inhibit the intermittent voltage step-down mode, and causes the process to return to step ST10 in the flowchart of Fig. 16. In this case, converter 200 is set in the continuous voltage step-down mode to operate.

Namely, in the case where charge power upper limit Win is larger than threshold value KWI1, control device 500 permits the intermittent voltage step-down control. In this case, relatively fast recovery rate RTFC is set. In contrast, in the case where charge power upper limit Win is smaller and equal to or more than threshold value KWI2 and less than threshold value KWI1, control device 500 permits the intermittent voltage step-down control and also sets recovery rate RTSC which is slower than recovery rate RTFC. Further, in the case where charge power upper limit Win is still smaller and less than threshold value KWI2, control device 500 inhibits the intermittent voltage step-down control. In this way, control device 500 suppresses the operation of converter 200 in the intermittent voltage step-down mode, as charge power upper limit Win is smaller.

In the third embodiment as well, the inhibition of the intermittent voltage step-down control may be replaced with a permission of the intermittent voltage step-down control and a limitation on the recovery rate. Namely, referring to Figs. 14 and 15, control device 500 may set the recovery rate (speed at which input voltage VH from

inverters

210, 220 is stepped down) smaller in the case where charge power upper limit Win is less than threshold value KWI1, relative to the case where charge power upper limit Win is equal to or more than threshold value KWI1.

Charge power upper limit Win is essentially set on the precondition that the intermittent voltage step-down control is not performed. As described above, when the intermittent voltage step-down control is performed, the controllability of reactor current IL is deteriorated, which may cause the charge power to exceed charge power upper limit Win. It is therefore necessary to define threshold values KWI1, KWI2 for suppressing the intermittent voltage step-down control.

According to the inventors of the prevent invention, threshold value KWI1 is preferably determined based on reactor current IL when the recovery rate is RTFC. Likewise, threshold value KWI2 is preferably determined based on reactor current IL when the recovery rate is RTSC.

The charge power increases with an increase of reactor current IL in the negative direction. In view of this, threshold values KWI1, KWI2 are determined based on reactor current IL. Accordingly, appropriate threshold values on which the magnitude of the charge power is reflected can be determined. Thus, the charge power can more reliably be prevented from exceeding charge power upper limit Win under the intermittent voltage step-down control.

Further, according to the inventors of the present invention, threshold values KWI1, KWI2 are more preferably determined based on the maximum charge power that can occur under the intermittent voltage step-down control as shown in Fig. 19. In other words, threshold value KWI1 is determined based on the charge power at the time when reactor current IL reaches its maximum value in the case of recovery rate RTFC (the time when reactor current IL reaches its maximum value ILF in Fig. 21 (c)). Likewise, threshold value KWI2 is determined based on the charge power at the time when reactor current IL reaches its maximum value in the case of recovery rate RTSC (the time when reactor current IL reaches its maximum value ILS in Fig. 21 (b)). This is for the reason that the charge power reaches its maximum value when reactor current IL is at its maximum.

Threshold values KWI1, KWI2 are defined to be larger than the maximum value of the charge power. Thus, a range in which the intermittent voltage step-down control is inhibited is made sufficiently broad. Accordingly, the charge power can still more reliably be prevented from exceeding charge power upper limit Win.

Although the method of determining threshold values KWI1, KWI2 is applied as well to temperature TB, Fig. 20 does not show the two arrows representing the maximum value of the charge power (see Fig. 19), for the sake of avoiding complication of the drawing. The method of determining threshold value KWI1 is applied as well to the third embodiment (see Figs. 14 and 15). It should be noted that the method of determining threshold values KWI1, KWI2 is not limited to the above-described one.

The condition on which a limitation is imposed on charge power upper limit Win is not limited to the SOC (see Fig. 14 or 19) or the temperature (see Fig. 15 or 20) of the battery. In the case where charge power upper limit Win is determined based on other conditions, the control shown by the flowcharts of Figs. 16, 17, and 22 is also applicable.

Finally, referring again to Fig. 2, the third and fourth embodiments are outlined. A power supply apparatus of a vehicle includes: battery 150; converter 200 stepping down voltage VH from

inverters

210, 220 of the vehicle and supplying the stepped-down voltage to battery 150; and control device 500 controlling converter 200 in a continuous voltage step-down mode and an intermittent voltage step-down mode. In the continuous voltage step-up mode converter 200 is continuously operated. In the intermittent voltage step-up mode converter 200 is intermittently operated. Control device 500 controls converter 200 so that charge power to battery 150 does not exceed charge power upper limit Win. Control device 500 suppresses an operation of converter 200 in the intermittent voltage step-down mode to a greater extent as charge power upper limit Win is smaller.

Preferably, in a case where charge power upper limit Win is smaller than predetermined threshold value KWI1, control device 500 inhibits the operation of converter 200 in the intermittent voltage step-down mode.

Preferably, in a case where charge power upper limit Win is smaller than predetermined threshold value KWI1, control device 500 sets smaller the recovery rate (rate at which input voltage VH from

inverters

210, 220 is stepped down) in the intermittent voltage step-down mode, relative to a case where charge power upper limit Win is equal to or larger than threshold value KWI1.

Preferably, in a case where charge power upper limit Win is smaller than threshold value KWI1 and equal to or larger than threshold value KWI2 which is smaller than threshold value KWI1, control device 500 sets smaller the recovery rate in the intermittent voltage step-down mode, relative to a case where charge power upper limit Win is equal to or larger than threshold value KWI1. In a case where charge power upper limit Win is smaller than threshold value KWI2, control device 500 inhibits the operation of converter 200 in the intermittent voltage step-down mode.

Preferably, threshold values KWI1, KWI2 are determined based on reactor current IL (through current) flowing through converter 200 in the intermittent voltage step-down mode.

Preferably, threshold values KWI1, KWI2 are determined based on charge power to battery 150 when reactor current IL is at its maximum.

While the first to fourth embodiments have been described in terms of the hybrid vehicle, the above-described control is applicable to any vehicle in which a battery is charged and discharged. Therefore, control like the above-described one is also applicable for example to electric vehicle or fuel cell vehicle.

It should be construed that the embodiments disclosed herein are given by way of illustration in all respects, not by way of limitation. It is intended that the scope of the present invention is defined by claims, not by the description above, and encompasses all modifications and variations equivalent in meaning and scope to the claims.

100 engine; 110 first MG; 120 second MG; 112, 122 neutral point; 130 power split device; 131 sun gear; 132 ring gear; 133 pinion gear; 134 carrier; 135 ring gear shaft (driveshaft); 140 reduction gear; 150 battery; 152 battery sensor; 160 drive wheel; 170 PM-ECU; 172 MG-ECU; 180 voltage sensor; 200 converter; 210, 220 inverter; 230 SMR; 240 air conditioner; 500 control device; PL1, PL2 positive line; GL ground line; Q1-Q8 switching element; D1-D8 diode; C1, C2 capacitor; L reactor.

Claims

A power supply apparatus of a vehicle, comprising:
a power storage device;
a voltage step-up converter stepping up a voltage of said power storage device and supplying the stepped-up voltage to an electrical load of the vehicle; and
a control device controlling said voltage step-up converter in a continuous voltage step-up mode and an intermittent voltage step-up mode, in said continuous voltage step-up mode said voltage step-up converter being continuously operated, in said intermittent voltage step-up mode said voltage step-up converter being intermittently operated,
said control device controlling said voltage step-up converter so that discharge power from said power storage device does not exceed a discharge power upper limit, and suppressing an operation of said voltage step-up converter in said intermittent voltage step-up mode to a greater extent as said discharge power upper limit is smaller.
The power supply apparatus of a vehicle according to claim 1, wherein in a case where said discharge power upper limit is smaller than a predetermined threshold value, said control device inhibits the operation of said voltage step-up converter in said intermittent voltage step-up mode.
The power supply apparatus of a vehicle according to claim 1, wherein in a case where said discharge power upper limit is smaller than a predetermined threshold value, said control device sets smaller a rate at which the voltage of said power storage device is stepped up in said intermittent voltage step-up mode, relative to a case where said discharge power upper limit is equal to or larger than said predetermined threshold value.
The power supply apparatus of a vehicle according to claim 2 or 3, wherein said predetermined threshold value is determined based on through current flowing through said voltage step-up converter in said intermittent voltage step-up mode.
The power supply apparatus of a vehicle according to claim 4, wherein said predetermined threshold value is determined based on discharge power from said power storage device when said through current is at its maximum.
The power supply apparatus of a vehicle according to claim 1, wherein
in a case where said discharge power upper limit is smaller than a first threshold value and equal to or larger than a second threshold value which is smaller than said first threshold value, said control device sets smaller a rate at which the voltage of said power storage device is stepped up in said intermittent voltage step-up mode, relative to a case where said discharge power upper limit is equal to or larger than said first threshold value, and
in a case where said discharge power upper limit is smaller than said second threshold value, said control device inhibits the operation of said voltage step-up converter in said intermittent voltage step-up mode.
The power supply apparatus of a vehicle according to claim 6, wherein said first and second threshold values are determined based on through current flowing through said voltage step-up converter in said intermittent voltage step-up mode.
The power supply apparatus of a vehicle according to claim 7, wherein said first and second threshold values are determined based on discharge power from said power storage device when said through current is at its maximum.