JPH11275714A - Power supply for electric vehicle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the capacity of a DC-to-DC converter and to prevent the charged state of sub-batteries from deteriorating by increasing the chances of fully charging them. SOLUTION: This power supply is provided with main batteries 3 for driving a drive motor 5, sub-batteries 8 for feeding power to low-voltage electric loads 9, and a DC-to-DC converter 7, which converts the voltage of the main batteries into voltages to be supplied to the sub-batteries and low-voltage electric loads. A current detector 10 detects the output current of the DCDC converter. As the output current increases, the output voltage of the DCDC converter is reduced continuously from a given maximum voltage capable of fully charging the sub-batteries to a given minimum voltage capable of operating the low- voltage electric loads. This design enables reduction in the capacity of the DCDC converter. When the output current of the DCDC converter becomes zero or small, its output voltage becomes high so that the sub-batteries are charged each time. Thus, a situation will not occur in which sub-batteries fall into an insufficiently charged state.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-voltage main battery capable of driving a drive motor, a sub-battery for supplying a general electric load of a vehicle, and a DC-DC converter for converting the voltage of the main battery to a low voltage. The present invention relates to a power supply device for an electric vehicle having:

[0002]

2. Description of the Related Art FIG. 6 is a diagram showing a block configuration of a power supply device for a conventional electric vehicle. In FIG. 6, 1 is a charger, 2 is a charge switch, 3 is a main battery, 4 is a power controller, 5 is a drive motor, 6 is a high-voltage electric load, 7
Is a DC-DC converter, 8 is an auxiliary battery, and 9 is a low voltage electric load.

[0003] The main battery 3 is a battery having a voltage (for example, 100 to 300 V) sufficient to drive the drive motor 5. The power controller 4 includes a circuit for transmitting the voltage of the main battery 3 to the drive motor 5 and the high-voltage electric load 6,
A controller for controlling the drive of the drive motor 5 and the like are included. The controller controls power supply to the drive motor 5 based on signals from various sensors (eg, an accelerator sensor). The high voltage electric load 6 is a load other than the drive motor 5 among loads to which the voltage of the main battery 3 is supplied, and examples of such loads include a power steering motor and an air conditioner motor.

[0004] The low-voltage electric load 9 is a general electric load mounted on other than the electric vehicle.
There are a lighting device, a control device, and the like. The low-voltage electric load 9 includes:
Power is supplied from the sub-battery 8 or the DC-DC converter 7. The DC-DC converter 7 is a converter that converts a high voltage of the main battery 3 into a low voltage, and its output voltage is a voltage that can fully charge the sub-battery 8 (hereinafter, referred to as a “fully chargeable voltage”). It is set to always output. For example, assuming that the low-voltage electric load 9 is a 24V load, the output voltage of the DC-DC converter 7 is always set to 28.5V. Therefore, the sub-battery 8 is always supplied with a fully charged voltage.

[0007] In FIG. 6, a portion on the right side of the position of the charging switch 2 is a vehicle, and a portion on the left side is a charging facility.
When the main battery 3 becomes exhausted, it goes to a charging facility, is connected to the charger 1, and is charged.

In the conventional example, the output voltage of the DC-DC converter 7 is always set to a fully chargeable voltage irrespective of the degree of consumption of the main battery 3. for that reason,
The output current of the DC-DC converter 7 is larger than when the voltage is lower than the fully chargeable voltage (however, the voltage at which the low-voltage electric load 9 can operate), and the capacity of the DC-DC converter 7 also increases. Had been lost. That is, DC-
Since the output of the DC converter 7 is set to be larger than necessary, there is a problem that the power of the main battery 3 is consumed extra and the power of the main battery 3 is not used effectively. Therefore, a proposal for improving this is made in Japanese Patent Laid-Open No. 7-79505.

In the technology disclosed in Japanese Patent Application Laid-Open No. 7-79505,
The output voltage of the DC-DC converter 7 can be set to a second set voltage (of course, a voltage that can operate a low-voltage electric load) lower than the fully chargeable voltage. The voltage is set to the second set voltage when the vehicle travels when the main battery 3 is consumed well, and is set to the fully chargeable voltage when the vehicle is stopped and charged to charge the main battery 3. Thus, the output of the DC-DC converter 7 is reduced, and the capacity thereof is also reduced.

[0008] Other conventional documents related to power supply devices for electric vehicles include, for example, Japanese Patent Application Laid-Open No. Hei 4-3258.
No. 01 publication.

[0009]

[Problems to be Solved] (Problems) However, the above-mentioned conventional technology (the technology of Japanese Patent Laid-Open No. 7-79505) has the following problems. The first problem is that the set value of the output voltage of the DC-DC converter is set to two, and the set value is simply switched between when the vehicle is running and when the vehicle is being charged. There was a problem that the output was still larger than necessary. The second problem is that there is little chance that the sub-battery is fully charged, and the state of charge of the sub-battery may be deteriorated.

(Explanation of Problems) First, the first problem will be described. Not all low-voltage electrical loads of a vehicle are activated when traveling. For example,
Radios may or may not be turned on, and lighting devices are not normally turned on during the day. However, JP-A-7-7
According to the technique disclosed in Japanese Patent Application Publication No. 9505, the output voltage of the DC-DC converter is set to the second set voltage at the time of traveling. Must be selected. However, as a practical matter, it is extremely rare that all low-voltage electrical loads are in operation, and the time during which all are operated is much shorter than the total operating time. The output voltage is adjusted to a second
Maintaining the set voltage is uneconomical in terms of energy savings.

Next, a second problem will be described. In the technology disclosed in Japanese Patent Application Laid-Open No. 7-79505, the output voltage of the DC-DC converter is set to a voltage that allows the sub-battery to be fully charged only when the main battery is charged.
Therefore, when the opportunity to fully charge the sub-battery is small and the main battery is not charged for a long time,
The state of charge of the sub battery deteriorates. An object of the present invention is to solve the above problems.

[0012]

According to the present invention, a main battery for driving a drive motor of an electric vehicle, an auxiliary battery for supplying power to a low-voltage electric load, and the main battery are provided. DC-D for converting the voltage of the sub-battery into a voltage to be supplied to the sub-battery and the low-voltage electric load
In a power supply device for an electric vehicle comprising a C-converter, a current detector for detecting an output current of the DC-DC converter, and as the output current detected by the current detector increases, the DC-DC A control unit for continuously reducing the output voltage of the converter from a predetermined maximum voltage to a predetermined minimum voltage.

Also, a detecting means for detecting that a special low-voltage electric load required to increase the applied voltage among the low-voltage electric loads is operated, and the detecting means detects the special low-voltage electric load. Means may be provided for making the detection signal from the current detector equivalent to the case of zero output current when the operation is detected.

(Summary of operation to be solved) The output current of the DC-DC converter is detected by a current detector. As the detected output current increases, the output voltage of the DC-DC converter is increased from a predetermined maximum voltage that can fully charge the sub-battery to a predetermined maximum voltage that can operate a low-voltage electrical load connected to the sub-battery. It drops continuously over a minimum voltage. This eliminates the need to increase the power output from the DC-DC converter more than necessary,
The capacity of the C-DC converter can be reduced.
When the output current of the DC-DC converter becomes zero or small, the output voltage is raised to a predetermined maximum voltage or a value close to the predetermined maximum voltage. At this time, the sub-battery is charged. For this reason, the sub-battery is less likely to be undercharged. Also, among the low-voltage electric loads, there are special low-voltage electric loads, such as headlights, which require a higher applied voltage at the time of operation, but when such a load is operated, there is a special case. DC
If a configuration for maximizing the output voltage of the DC converter is added, sufficient operation of the special low-voltage electric load as described above can be ensured.

[0015]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a diagram showing a block configuration of a power supply device for an electric vehicle according to the present invention. The symbol is FIG.
, 10 is a current detector, 11 is a lighting switch, 12 is another low-voltage electric load, and 13 is a headlight. The current detector 10 is for detecting the output current of the DC-DC converter 7, and the detection signal is DC-DC.
Sent to the DC converter 7 and used to control the output voltage of the DC-DC converter 7 (details of the control
FIG. 2).

The headlight 13 is one of the low-voltage electric loads 9, and among the low-voltage electric loads 9, as an example of a special low-voltage electric load in which it is desirable to increase the applied voltage when energizing, This is an example. When the headlights 13 are turned on, it is preferable that the power supply voltage be higher within a predetermined range in order to secure illuminance. When the lighting switch 11 is turned on, the headlight 13 is turned on.
Is detected, and the detection signal is supplied to the DC-DC
Send to converter 7. When there is a special low-voltage electric load other than the headlight 13, similar measures can be taken for the special low-voltage electric load.

FIG. 2 is a diagram showing a detailed circuit of the DC-DC converter according to the present invention. Reference numerals correspond to those in FIG. 1, 7-1 is a control unit, 20A and 20B are transistors, 21 is a transformer, 22 and 23 are diodes, 24 is a capacitor, 25A and 25B are comparators, and 26 is 3
Angular wave generation circuit, 27 is a smoothing circuit, 28 is a comparator,
29 is a sine wave generation circuit, 30 is a transistor, and 31 is an inversion circuit.

When the transistors 20A and 20B are turned on and off, an alternating current in which the input DC voltage is interrupted is generated and supplied to the primary side of the transformer 21. On the secondary side, an AC whose voltage is transformed (in the case of the present invention, stepped down) appears, is rectified by the diodes 22 and 23, is smoothed by the capacitor 24, and becomes the output voltage of the DC-DC converter 7. This voltage is supplied to the auxiliary battery 8 and the low-voltage electric load 9.
Is applied to

The output voltage of the DC-DC converter 7 varies depending on the duty ratio of the ON period of the transistors 20A and 20B (= the ratio of the ON period to the total period of the ON period and the OFF period). That is, when the ratio of the ON period is increased, the output voltage is increased. Transistor 20
The duty ratios of A and 20B are alternately controlled by the control unit 7-1. The control unit 7-1 includes the comparator 25
A, 25B, a triangular wave generation circuit 26, a smoothing circuit 27, a comparator 28, a sine wave generation circuit 29, and a transistor 30.

The current detector 10 is a DC-DC converter 7
Output current of the comparator 2
8 inverting input terminal (-). Transistor 3
0 indicates that the lighting switch 11 is turned on and the headlight 13
Is turned on when is turned on, and the inverting input terminal of the comparator 28 is set to the ground potential. That is, the headlight 13
When is turned on, the inverting input terminal is set to the ground potential regardless of the detection signal from the current detector 10. When the headlight 13 is not turned on, the transistor 3
0 is off and has no effect on the detection signal.

Non-inverting input terminal (+) of the comparator 28
, A sine wave output from the sine wave generation circuit 29 is input. FIG. 3 is a diagram illustrating the operation of such a comparator 28. FIG. 3A shows two inputs.
A is a non-inverting input (= sine wave voltage), and B and C are inverting inputs (= detection signal of the current detector 10; when the headlight 13 is turned on, the transistor 30 is turned on except for the ground potential.) is there. A is a sine wave generated from the sine wave generation circuit 29, and changes periodically with a constant amplitude. B is DC-D detected by the current detector 10
C is a detection signal when the output current of the C converter 7 is relatively large, and C is a detection signal when the output current is smaller. As the output current increases, the inverting input of FIG. 3A rises (however, since the output characteristics of the DC-DC converter 7 are as shown in FIG. 5 described later, the sine wave Up to one-half of.)

FIG. 3 (b) shows the output of the comparator 28 when the inverted input has a magnitude of B, and FIG. 3 (c) shows the output of the comparator 28 when the inverted input has a magnitude of C. ing. A high output is output while the non-inverting input is larger than the inverting input, and a low output is output during other periods.
As will be readily understood by comparing FIGS. 3B and 3C, when the output current of the DC-DC converter 7 is large (FIG. 3B), the high period is shorter. The output of the comparator 28 is smoothed by the smoothing circuit 27 and input to the non-inverting input terminals (+) of the comparators 25A and 25B.

The inverting input terminal (-) of the comparator 25A
, A triangular wave from the triangular wave generation circuit 26 is input, and a triangular wave from the triangular wave generation circuit 26 is inverted by an inversion circuit 31 to an inverting input terminal (−) of the comparator 25B. Is entered. FIG. 4 is a diagram illustrating the operation of the comparator 25A. FIG. 4A shows two inputs, where D is an inverted input (= triangular wave voltage), and E and F are non-inverted inputs (= output voltage of the smoothing circuit 27). As described above, the larger the output current detected by the current detector 10 is, the smaller the output voltage of the smoothing circuit 27 is. Therefore, the output current is higher when the non-inverting input is F than when the non-inverting input is E. Is big. That is, as the output current of the DC-DC converter 7 increases, the non-inverting input of FIG. 4A becomes smaller (however, if the maximum value of the duty ratio of the transistor 20A is to be set to 50%, Even at the minimum, the value of the non-inverting input should be kept at one half of the triangular wave voltage.)

FIG. 4 (b) shows the output of the comparator 25A when the non-inverting input is E, and FIG. 4 (c) shows the output of the comparator 25A when the non-inverting input is F.
A high output is output while the non-inverting input is larger than the inverting input, and a low output is output during other periods. As the non-inverting input becomes smaller (= as the output current of the DC-DC converter 7 increases), the period during which the output of the comparator 25A is high is shortened.

Since the transistor 20A is turned on while the high output of the comparator 25A is being input to the base of the transistor 20A, the on-period of the transistor 20A becomes shorter as the output current of the DC-DC converter 7 increases. Control. If the ON period is shortened, the output voltage of the DC-DC converter 7 decreases, so that the DC-DC converter 7 is controlled so that the output voltage decreases as the output current increases. The control of the transistor 20A has been described above, but the control of the transistor 20B is the same. However, since the control is alternately performed with the transistor 20A, the control timing is shifted by a half cycle of the control.

FIG. 5 is a diagram for explaining the output characteristics of the DC-DC converter. The horizontal axis represents the output current (I) of the DC-DC converter 7, and the vertical axis represents the output voltage (V) of the DC-DC converter 7. Curve A shows the DC-DC converter 7
Is an output characteristic curve. V _H is a voltage which is set as the maximum value of the output voltage (maximum voltage), V _L is the voltage that is set as a minimum voltage required for operating the low-voltage electric load 9 (basic voltage _VL ). The output voltage is reduced as the output current increases. Incidentally, when the output current I _1, the output voltage is set to V _1.

The maximum voltage V _H and the minimum voltage V _L are as follows. Since the maximum voltage V _H from the DC-DC converter 7 is nothing but a voltage that can fully charge the sub-battery 8, the maximum voltage V _H is a fully chargeable voltage and a low-voltage electric load. If 9 is a 24V load, it is set to, for example, 28.5V. On the other hand, a general low-voltage electric load 9 of a 24 V system usually has 2
Operation is sufficient if about 6.5 V, so that the minimum voltage V _L
Is set to 26.5 V, for example.

The output characteristic of the DC-DC converter 7 is shown in FIG.
When the low voltage electric load 9 is operated a lot (that is, during running), that is, when the current detected by the current detector 10 is large, the output of the DC-DC converter 7 The voltage is made small. Therefore, the power consumption is smaller than when the output voltage is maintained high without considering the magnitude of the current. Since the output voltage is low, the sub-battery 8 is not fully charged at this time.

On the other hand, when the current detected by the current detector 10 is small, the output voltage of the DC-DC converter 7 is increased, so that the sub-battery 8 is charged at this time. When the low-voltage electric load 9 is hardly operated (when the main battery 3 is being charged at the charging facility, or when the vehicle is stopped), the voltage _VH is output almost at the maximum.
At such time, the sub-battery 8 is fully charged. The power consumption in this case is also smaller than when charging is performed at the full chargeable voltage when the current to the low-voltage electric load 9 is large.

As described above, in any case, according to the present invention, the electric power supplied from the DC-DC converter 7 may be smaller than that of the prior art, so that the capacity of the DC-DC converter 7 can be reduced. . Since the power supplied from the DC-DC converter 7 is not increased more than necessary,
As a result, the energy of the main battery 3 is saved, and the traveling distance per charge of the main battery 3 is also increased.

By the way, when the low-voltage electric load 9 is operated like the headlight 13,
Although there is a special low-voltage electric load for which it is desired to increase the voltage within a predetermined range, when operating it, a configuration in which the voltage is increased as a special case may be added in response to the demand. . In FIG. 2, when the lighting switch 11 is turned on and the headlight 13 is turned on, a voltage is applied to the base of the transistor 30 through the lighting switch 11, and the transistor 30 is turned on. When the transistor 30 is turned on, the inverting input terminal (-) of the comparator 28 is set to the ground potential. If this is described using the detection signal from the current detector 10, this corresponds to the case where the output current becomes zero.

When the inverting input terminal of the comparator 28 is set to the ground potential, the high period of the output of the comparator 28 becomes longer, and the output of the smoothing circuit 27 becomes larger. Therefore, the high periods of the outputs of the comparators 25A and 25B become longer, and the ON periods of the transistors 20A and 20B become longer. As a result, the output voltage of the DC-DC converter 7 is increased as desired, and the illuminance of the headlight 13 is sufficiently ensured. Note that such special consideration for the special low-voltage electric load is not essential to the present invention, and may be omitted in some cases.

In the technology disclosed in Japanese Patent Application Laid-Open No. 7-79505, the output voltage of the DC-DC converter is set to a voltage at which full charge is possible when the main battery is charged. Was only fully charged,
According to the present invention, even when the main battery is not charged, D
If the output current from the C-DC converter is small, the voltage is almost set to a fully chargeable voltage, so that the battery is fully charged even when the main battery is not charged. As a result, the auxiliary battery is less likely to run out of the battery, and the vehicle is not prevented from running.

[0034]

As described above, the power supply device for an electric vehicle according to the present invention has the following effects. (Effect of Claim 1) The output current of the DC-DC converter is detected by a current detector, and as the output current increases, the output voltage of the DC-DC converter is increased to a predetermined maximum value at which the sub-battery can be fully charged. The power output from the DC-DC converter is unnecessarily large because the voltage is continuously reduced from the voltage limit to a predetermined minimum voltage at which the low-voltage electric load connected to the sub-battery can operate. And the capacity of the DC-DC converter can be reduced. Also, when the output current of the DC-DC converter becomes zero or small, the output voltage is raised, so that the sub-battery is charged at this time. For this reason, the sub-battery is less likely to be undercharged.

(Effect of Invention of Claim 2) In addition to the same effect as the invention of claim 1, the following effect is obtained. That is, among the low-voltage electric loads connected to the sub-battery,
There are special low-voltage electrical loads, such as headlights, that require a high applied voltage when operating, but when such loads are activated, the output voltage of the DC-DC converter is exceptionally maximized. Since the voltage is used, sufficient operation of the load as described above can be ensured.

[Brief description of the drawings]

FIG. 1 is a diagram showing a block configuration of a power supply device for an electric vehicle of the present invention.

FIG. 2 is a diagram showing a detailed circuit of a DC-DC converter according to the present invention.

FIG. 3 is a diagram for explaining the operation of a comparator 28;

FIG. 4 is a diagram illustrating an operation of a comparator 25A.

FIG. 5 is a diagram illustrating output characteristics of a DC-DC converter.

FIG. 6 is a diagram showing a block configuration of a conventional electric vehicle power supply device.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Charger, 2 ... Charge switch, 3 ... Main battery, 4 ...
Power controller, 5: drive motor, 6: high-voltage electric load, 7: DC-DC converter, 7-1: control unit, 8
... Auxiliary battery, 9 ... Low voltage electric load, 10 ... Current detector, 11 ... Lighting switch, 12 ... Other low voltage electric load,
13 ... headlights, 20A, 20B ... transistors,
Reference numeral 21: transformer, 22, 23: diode, 24: capacitor, 25A, 25B: comparator, 26: triangular wave generation circuit, 27: smoothing circuit, 28: comparator, 29
... Sine wave generating circuit, 30 ... Transistor, 31 ... Inverting circuit

Continued on the front page (51) Int.Cl. ⁶ Identification code FI H02M 3/28 H02M 3/28 H

Claims (2)

[Claims] 1. A main battery for driving a drive motor of an electric vehicle, a sub-battery for supplying a low-voltage electric load, and a voltage for supplying a voltage of the main battery to the sub-battery and the low-voltage electric load. DC-DC to convert to
In a power supply for an electric vehicle comprising a converter,
A current detector for detecting the output current of the DC-DC converter, and as the output current detected by the current detector increases, the output voltage of the DC-DC converter is increased from a predetermined maximum voltage to a predetermined voltage. A power supply device for an electric vehicle, comprising: a control unit for continuously reducing the voltage toward a minimum voltage. 2. Detecting means for detecting that a special low-voltage electric load of which the applied voltage is desired to be increased among the low-voltage electric loads is operated, and detecting the special low-voltage electric load by the detecting means. 2. A power supply device for an electric vehicle according to claim 1, further comprising means for making a detection signal from the current detector equivalent to a case where the output current is zero when the operation is detected.