Battery power circuit and automobile battery power circuit
A load is connected to a first battery group. The first battery group and a second battery group are connected in series to each other. A bidirectional DC/DC converter for electric power migration between the first battery group and the second battery group is provided.
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This is a divisional of application Ser. No. 10/434,281 filed May 9, 2003. The entire disclosure of the prior application, application Ser. No. 10/434,281, is hereby incorporated by reference.
BACKGROUND OF THE INVENTIONThe present invention relates to a battery power circuit for use in a motorcar or the like, which circuit outputs a plurality of voltage levels.
First, the operation will be described with reference to
However, most of electric components mounted on motorcars are formed of 14 V systems. Therefore, a battery whose rated voltage is 12V is required unless all the electric components are replaced by 42V systems. Not to say, in the present circumstances where there are few electric components supporting 42V systems and these electric components are expensive (due to the problem of quantity), it can be foreseen that electric components support 14V systems fundamentally, and hence it can be foreseen that the 14V load has a high capacity.
Therefore, a high-capacity stationary battery 100 is charged with a voltage of 12 V using the output of the battery group 200 through the DC/DC converter 300 so as to operate electric components. In addition, when electric components of 14V systems are used stationarily during driving or the like, the electric components have to be operated directly from the DC/DC converter 300. To this end, the DC/DC converter 300 has to have a high capacity.
Thus, even if a battery group having a rated voltage of 36 V is provided for attaining the idle stop operation, the power circuit will be expensive because the high-capacity DC/DC converter 300 or the high-capacity stationary battery 100 is required. Since the high-capacity DC/DC converter 300 generates a great deal of heat, accessories for cooling are required to thereby cause further increase in cost.
In addition, it is also generally known that greater power is required for starting the engine 7 at the time of initial start-up of the engine 7 (start-up in the state where the temperature of the engine 7 is low, for example, when driving is started initially). In order to use the electric motor 6 to perform initial start-up, it is necessary to supply a higher current to the electric motor 6. To this end, the power conversion circuit 5 has to have large-current specifications. Thus, the power conversion circuit 5 becomes expensive.
As a solution to this problem, there is proposed a system in which initial start-up is performed by the rotation of a cell motor based on key operation while only the idle stop operation is performed by an electric motor. By this system, the power conversion circuit does not have to have large-current specifications. However, at the time of initial start-up in such a configuration, it is necessary to supply a large quantity of charges to the cell motor. Thus, a high-capacity stationary battery is still essential. Therefore, even if electric components of 14V systems are reduced in the future, a high-capacity stationary battery still has to remain. This causes a great obstacle to reduction in cost.
In a related-art power circuit for an electric motorcar, a high-capacity DC/DC converter is required for obtaining 12 V from 36 V as described above. Accessories associated with the DC/DC converter are expensive, and the high-capacity 12V stationary battery 100 is also expensive and becomes an obstacle to miniaturization.
SUMMARY OF THE INVENTIONIt is therefore an object of the invention to provide a battery power circuit in which a DC/DC converter or a battery is made low in capacity and small in size.
A battery power circuit according to the invention includes a first battery group connected to a load, a second battery group connected in series with the first battery group, and a DC/DC converter for electric power migration between the first battery group and the second battery group.
In addition, charging capacity of the first battery group may be different from charging capacity of the second battery group.
In addition, the first battery group may be constituted by one battery having a rated voltage of 12 V while the second battery group is constituted by two batteries having a rated voltage of 12 V and connected in series.
In addition, the DC/DC converter may include a series body of a switch and a reactor connected between one end of a series body of the first battery group and the second battery group and a connection point where the first battery group and the second battery group are connected in series, and a diode connected between a connection point of the switch and the reactor and the other end of the series body of the battery groups.
In addition, the DC/DC converter may be a bidirectional DC/DC converter for bidirectional electric power migration between the first battery group and the second battery group.
Further, the bidirectional DC/DC converter may include a series body of a first switch and a second switch connected to opposite ends of a series body of the first battery group and the second battery group, and a reactor connected between a connection point of the first battery group and the second battery group and a connection point of the first switch and the second switch.
In addition, a control unit may be provided for making control to prevent the first switch and the second switch from being turned on simultaneously.
In addition, the second battery group may be constituted by capacitors.
In addition, an automobile battery power circuit according to the invention includes an electric motor whose power is transmitted to an engine, and a power conversion circuit connected between a series body of a first battery group and a second battery group and the electric motor. The electric motor generates electricity in response to the power from the engine and charges the series body of the battery groups through the power conversion circuit.
Further, the electric motor may be an electric motor for restarting the engine which is stopped in accordance with temporary stop during driving.
In addition, a cell motor for starting the engine only by a key operation at an early stage of start of driving may be connected as the load.
In addition, electric power maybe supplied from the first battery group to the second battery group through the bidirectional DC/DC converter while the engine is restarted by the electric motor.
In addition, electric power may be supplied from the series body of the first battery group and the second battery group to the electric motor through the power conversion circuit while the engine is started by the cell motor.
BRIEF DESCRIPTION OF THE DRAWINGS
During the stationary operation of the engine 7, the electric motor 6 rotates to also serve as a generator. Thus, the battery group 1 and the battery group 21-2n are charged in series by generated energy through the power conversion circuit 5. In addition, the voltage between the opposite ends of the battery group 1 and the battery group 21-2n is stepped down to 12 V and supplied to the load 4 through the DC/DC converter 3. In addition, electric power is also supplied from the battery group 1 to the load 4 directly in parallel. In addition, at the time of initial start-up or at the time of restart in the idle stop operation, the electric motor 6 is rotated directly from the series circuit of the battery group 1 and the battery group 21-2n through the electric conversion circuit 5, so that the engine 7 is started through the power transmitter 8.
In Embodiment 1 of the invention, the electric power supply to the load 4 is divided into two systems. That is, one is the system owing to the electric power directly charged into the battery group 1 through the power conversion circuit 5, and the other is the system owing to the electric power stepped down from the battery group 2 through the DC/DC converter 3. Here, the ratio of the electric power owing to the DC/DC converter 3 can be obtained easily from the following idea. That is, assume that the voltage of the battery group 1 and the voltage of the battery group 2 are balanced, that is, the charge quantity of charge into each battery group is equal to the charge quantity of discharge from the battery group. In this case, the charge quantity supplied from the DC/DC converter 3 becomes equal to the charge quantity directly supplied from the battery group 1 to the load 4. Accordingly, the electric power Px owing to the DC/DC converter 3 has the following relationship to electric power consumption Po in the load 4.
Px/Po=E2/(E1+E2)
where Ei designates the voltage of a battery group i. Thus, Px becomes smaller than Po, and the capacity of the DC/DC converter 3 can be reduced correspondingly in comparison with that in the related art. In addition, the loss is reduced so that accessories such as a cooler can be miniaturized. As a result, the automobile battery power circuit itself can be reduced in cost and in size.
Incidentally, various systems can be considered about the configuration of the DC/DC converter. Fundamentally, any system will show similar effect if it can transmit the electric power of the battery group 2 to the battery group 1.
Embodiment 6
Incidentally, the bidirectional DC/DC converter 30 does not operate during the operation of the cell motor 10 in
Incidentally,
Thus, according to Embodiment 7, the batteries of the power circuit can be reduced in capacity so that the circuit can be reduced in cost and in size. In addition, the current flowing into the battery group 2 becomes so small that there is no problem even if high-impedance batteries are used for the battery group 2.
Incidentally, though not shown in the drawings, the battery group 2 may be substituted by capacitors. Further, effect similar to that in Embodiment 4 can be obtained when a diode is connected in parallel with the opposite ends of the capacitors. Furthermore, when the battery group 2 is substituted by capacitors, the voltage of the capacitors can be set desirably within a range not higher than the withstand voltage of the capacitors or the power conversion circuit 5. Thus, by adjusting the capacitor voltage at the time of restart or initial start-up, a desired output can be extracted from this power circuit without increasing the output of the bidirectional DC/DC converter 30 so much. When the output of the bidirectional DC/DC converter 30 and the withstand voltage of the capacitors are selected, this power circuit can be designed to have an optimal and small size.
In addition, when the power conversion circuit 5 according to the invention is used, and the cell motor 10 or the bidirectional DC/DC converter 30 is provided, the motorcar can start to move only if the battery group 1 is charged in advance. Accordingly, externally charging terminals may be provided in the battery group 1.
Embodiment 8
The pattern A shows the case where batteries having a rated voltage of 12 V are arranged in three-series.
The pattern B shows the case where batteries having a rated voltage of 12 V are arranged in three-series, and the battery group 1 has a higher capacity than any other. This pattern is effective in a power circuit in which the load 4 has a high capacity or the cell motor 10 for initial start-up is provided.
The pattern C shows the case where the battery group 1 has a lower capacity than any other. This pattern is effective in a system in which mounting with electric components of 42V systems is advanced, and the cell motor 10 is not provided. By reducing the capacity of the battery group 1 for electric components of 14V systems, the power circuit can be reduced in cost and in size.
In addition, not to say, the invention is applicable not only to an automobile battery system but also to a battery system having any purpose if it is an apparatus including batteries having two kinds of voltages, for example, to a microcomputer power supply system having outputs of 5 V and 12 V.
A battery power circuit according to the invention includes a first battery group connected to a load, a second battery group connected in series with the first battery group, and a DC/DC converter for electric power migration between the first battery group and the second battery group. Thus, the DC/DC converter can be designed to have a low capacity and a small size.
In addition, charging capacity of the first battery group is made different from charging capacity of the second battery group. Thus, further miniaturization can be attained.
In addition, the first battery group is constituted by one battery having a rated voltage of 12 V while the second battery group is constituted by two batteries having a rated voltage of 12 V and connected in series. Thus, a power circuit suitable to an automobile battery power circuit is provided
In addition, the DC/DC converter includes a series body of a switch and a reactor connected between one end of a series body of the first battery group and the second battery group and a connection point where the first battery group and the second battery group are connected in series, and a diode connected between a connection point of the switch and the reactor and the other end of the series body of the battery groups. Thus, the DC/DC converter has a simple configuration with a reduced number of parts, so that further miniaturization can be attained.
In addition, the DC/DC converter is made a bidirectional DC/DC converter for bidirectional electric power migration between the first battery group and the second battery group. Thus, the DC/DC converter has a low capacity and a small size. In addition, even if a part of the battery groups discharges for some reason, the part of the battery groups can be charged by the other high-capacity battery groups. Thus, the reliability is improved.
Further, the bidirectional DC/DC converter includes a series body of a first switch and a second switch connected to opposite ends of a series body of the first battery group and the second battery group, and a reactor connected between a connection point of the first battery group and the second battery group and a connection point of the first switch and the second switch. Thus, the DC/DC converter is miniaturized.
In addition, a control unit is provided for making control to prevent the first switch and the second switch from being turned on simultaneously. Thus, the reliability is improved.
In addition, the second battery group is constituted by capacitors. Thus, miniaturization can be attained.
In addition, an automobile battery power circuit according to the invention includes any one of the aforementioned battery power circuits, an electric motor whose power is transmitted to an engine, and a power conversion circuit connected between a series body of a first battery group and a second battery group and the electric motor. The electric motor generates electricity in response to the power from the engine and charges the series body of the battery groups through the power conversion circuit. Thus, the battery groups can be reduced in capacity.
Further, the electric motor is made an electric motor for restarting the engine which is stopped in accordance with temporary stop during driving. Thus, the battery groups can be further reduced in capacity.
In addition, a cell motor for starting the engine only by a key operation at an early stage of start of driving is connected as the load. Thus, the battery groups can be reduced in capacity.
In addition, electric power is supplied from the first battery group to the second battery group through the bidirectional DC/DC converter while the engine is restarted by the electric motor. Thus, the battery groups can be further reduced in capacity.
In addition, electric power is supplied from the series body of the first battery group and the second battery group to the electric motor through the power conversion circuit while the engine is started by the cell motor. Thus, the battery groups can be further reduced in capacity.
Claims
1. A battery power circuit comprising:
- a first battery group connected to a load;
- a second battery group connected in series with said first battery group; and
- a bidirectional DC/DC converter for electric power migration between said first battery group and said second battery group,
- wherein a charging capacity of said first battery group is different from a charging capacity of said second battery group.
2. A battery power circuit comprising:
- a first battery group connected to a load;
- a second battery group connected in series with said first battery group; and
- a bidirectional DC/DC converter for electric power migration between said first battery group and said second battery group
- wherein,
- said second battery group is constituted by capacitors.
3. The battery power circuit according to claim 1, wherein said first battery group has a higher charging capacity than said second battery group.
4. The battery power circuit according to claim 2, wherein a diode is connected in parallel to opposite ends of a group of said capacitors.
Type: Application
Filed: Nov 8, 2005
Publication Date: Mar 16, 2006
Applicant:
Inventors: Akihiko Iwata (Tokyo), Toshiyuki Kikunaga (Tokyo)
Application Number: 11/268,472
International Classification: H02J 7/00 (20060101);