JPH0917452A - Method and device that prevent over-discharge of battery - Google Patents

Abstract

PURPOSE: To protect a battery from overdischarging, and lengthen the working service life of the battery by comparing proportionally processed output voltage of respective cells of the battery with the reference voltage, and temporarily cutting off an electric current to be supplied to a load when the processed voltage is lower than the reference voltage. CONSTITUTION: An electric unit 11 contains a plurality, for example, four cells. An electric motor driver 12 controls a brushless DC motor 13 to be used to drive a motorcycle. First of all, voltage of four battery cells is processed for linear amplification and compensation by a battery voltage processing unit 14. Next, a compactor circuit 15 compares the output V1 to V4 with a designated threshold value, and checks whether or not either of these is lower than this threshold value. If it is lower than the threshold value, a prohibiting signal is sent to the driver 12, and electric power supply to the electric motor 13 is temporarily restricted.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to control of battery energy, and more particularly to a method and apparatus for preventing over-discharge of a battery of an electric vehicle. In this specification, the electric vehicle is used to include a motorcycle (motorcycle).

[0002]

2. Description of the Prior Art Ordinary lead-acid batteries usually have a low current and do not discharge too much (so-called deep discharge) so that the battery life is not affected by the way they are discharged. Can be used). However, the batteries used in electric vehicles have a wide operating range,
Battery life is quite short due to the high current and deep discharge required. Therefore, ordinary energy management methods cannot be applied to these batteries. Conventional energy management methods do not impose any restrictions on the cutoff point at which the battery stops discharging. Usually, it is until the battery voltage drops to a very low level, shutting down the power unit. The battery voltage at this point is usually much lower than the cut-off voltage, which adversely affects battery life. Therefore, there is a need for an energy management method that terminates battery discharge when it is detected that the battery voltage is below a specified cutoff point. Japanese Patent Application No. 83,106,489 of Sanyo Electric Co., Ltd. of Taiwan (Taiwan) discloses a circuit capable of preventing over-discharge of a lead-acid battery. However, this prior art method nevertheless has the drawback that even if the circuit passes the test in the laboratory setting, there are safety problems with using the circuit on an electric vehicle running on the road.

[0003]

SUMMARY OF THE INVENTION Accordingly, it is a primary object of the present invention to provide a method and apparatus for preventing battery over-discharge, which can protect the battery from over-discharge, thereby extending the service life of the battery. is there. Another object of the present invention is to provide a method and a device for preventing over-discharging of a battery, which can ensure safety of operation of a device having a battery by avoiding abrupt shutoff. According to the present invention, there is provided a method and apparatus for preventing over-discharge of a battery unit including a plurality of cells that achieves the above object. A method of preventing over-discharge of a battery unit according to the present invention includes (1) a step of obtaining an output voltage of each cell processed proportionally, and (2) a step of comparing each processed voltage with a reference voltage. And (3) generate an inhibit signal if one processed voltage is lower than the reference voltage, and temporarily interrupt the current supplied by the battery unit to the load if the inhibit signal is present, Fixed to reduce the average output current from the battery unit. As a result, the electric power is not suddenly cut off, the operation of the electric vehicle becomes safer, and the service life of the battery becomes longer.

An apparatus for preventing over-discharge of a battery unit of the present invention compares each processed voltage with a reference voltage with a battery voltage processing unit which obtains a proportionally processed output voltage of each cell of the unit. If one of the processed voltages is lower than the reference voltage, an inhibit signal is generated, and if the inhibit signal is present, the current supplied from the battery unit to the load is temporarily interrupted, thereby causing the battery unit to operate. And a comparator circuit that reduces the average output current from the. This device according to the invention for preventing over-discharge of batteries has many advantages. First, since it is possible to prohibit the discharge of a large current in the final stage of the operation of the battery, it is possible to avoid over-discharging which can shorten the service life of the battery.
Second, before the battery energy is almost exhausted, it is effective to allow the electric vehicle driver to drive the electric vehicle at a low speed to the nearest recharging station even in such a state. Energy management is possible. Thirdly, in the energy management of the present invention, the power supply is not suddenly cut off by any means,
It is possible to operate the electric vehicle in a state where safety is further guaranteed. Fourth, it does not require a complicated instrument such as a battery capacity display device, which reduces the manufacturing cost. Fifthly, it is possible to avoid the detrimental effect of the difference in capacity between the cells due to over-discharge, so that the service life of the battery unit as a whole can be extended.

The preferred embodiments of the present invention will now be described with reference to the accompanying drawings, which will provide a more complete understanding of the present invention.

[0006]

DETAILED DESCRIPTION OF THE INVENTION The purpose of the present invention is focused on how to prevent battery over-discharge (battery voltage is too low) and to give safety to electric vehicles. FIG. 1 is a graph showing the operating characteristics of a battery, in which the x-axis represents the output current (amperes) of the battery and the y-axis represents the battery voltage (volts), and each gradient represents the state of charge (SOC) under the same conditions. The graph shows the voltage-current characteristics of the battery when set to. Since the SOC value is constantly changing over time during use of the battery, the actual plot of the voltage-current characteristics of the battery is zigzag, as shown at A. When current is varied within the range I _a -I _b, the battery voltage is gradually decreased as the SOC value decreases, it varies with the output current. The battery voltage starts to decrease as the output current increases. Therefore, if it is desired not to reduce the battery voltage too much at the end of discharge, the best solution is to limit the battery output current so that the battery voltage rises to a higher level. Experiments have shown that batteries with low discharge current have a large capacity. Therefore, by limiting the maximum current output of the battery at the end of discharge, two benefits are obtained. That is, the battery is prevented from being over-discharged and the battery is kept in a large capacity state.

The present invention takes advantage of this discharge characteristic of the battery and applies a voltage-limited discharge method for energy management of the battery at the end of discharge. As shown in FIG. 2 (where I _C represents the average load current supplied by the battery in FIG. 2), the battery voltage after the operating voltage V _C has dropped below the level V _L is kept constant at V _L. This can be achieved by high frequency switching techniques for power devices. When the battery voltage drops below the limited voltage V _L , the power device connected in series with the load goes to the “off” state and the load current output goes to zero, thus increasing the battery voltage. When the battery voltage rises above the limited voltage V _L , the power unit is turned on again.
In this way, the output of the battery to the load is automatically limited and the output voltage of the battery does not fall below the limited voltage V _L , so that the life of the battery is maintained. Figure 3 is Chi
The operating speed and braking speed versus time of a Class B motorcycle (motorcycle) according to the Nese Nation Standard (CNS) 3105, D3029 are shown. Simulations and conversions were performed when the present invention was used in the class B motorcycle of FIG. FIG. 4 shows the voltage-time characteristic and the current-time characteristic of the battery used in the final stage of the operation of the motorcycle according to the voltage-limited discharge method of the present invention.

The x-axis of FIG. 3 represents time and the y-axis represents the speed of the motorcycle. Each cycle of the operation of the motorcycle has seven stages. That is, in step S1, the motorcycle is stopped, in step S2-1 the motorcycle is slowly accelerated, in step S2-2 the motorcycle is fully accelerated, in step S3 the motorcycle reaches the maximum speed, and in step S4. In step S5, the motorcycle is decelerated, in step S5 the motorcycle is maintained at a constant speed of 20 km / h, in step S6 the motorcycle is decelerated again,
In step S7, the motorcycle stops running. The corresponding voltage-time and current-time characteristics of the battery according to the invention used in a motorcycle for these operating phases are shown in FIG. The characteristic plots of each operation cycle have substantially the same shape. Cycle 1-4
Is in a normal state, and in cycle 5, the battery voltage drops to the limited voltage point when the maximum level current flows. In the conventional method, the power supply from the battery is cut off at this point. However, at this point the motorcycle is in a fully accelerated condition (at the point of maximum load), so if the power is cut off abruptly this unexpected condition for the driver will cause the motorcycle to crash. It can happen. According to the invention, the current output from the battery at this point is automatically limited as shown in FIG. As can be seen from FIG. 4, the maximum current level of the subsequent cycle is made lower than the maximum current level of the preceding cycle so that the battery voltage cannot go below the limit point. However, at this point the motorcycle is degrading its performance for acceleration, and it becomes even worse in response to decreasing battery capacity. The maximum speed of the motorcycle is clearly reduced as the operation progresses to cycle 10. With such a reduction in vehicle performance, the driver notices that the battery energy is almost exhausted. The driver can also take necessary measures before the battery energy is completely used up. Battery capacity can be increased because the current output is limited according to the characteristics of the battery, and the limited performance of the motorcycle reduces energy consumption. These two features allow the driver to extend the mileage of the motorcycle during the final stages of battery discharge, thus allowing the driver to drive the motorcycle to the nearest recharging station with low performance.

FIG. 5 is a block diagram of an apparatus according to the invention for energy management of an electric vehicle. In an electric vehicle such as an electric motorcycle, a battery unit 1
1 contains four 12V cells. The motor driver 12 controls the brushless DC motor 13 used to drive the motorcycle. First, the voltages of the four battery cells are processed by the battery voltage processing unit 14 for proportional amplification and compensation. The comparator circuit 15 then compares the outputs V1-V4 with a specified threshold value (this threshold value should not be lower than the cut-off point of the battery voltage), any of which is lower than this threshold value. Check if it is low. If it is low, a prohibition signal is sent to the driver 12 to temporarily limit the power supply to the electric motor 13. FIG. 6 is a detailed circuit diagram of the battery voltage processing unit 14 and the comparator circuit 15, and the contents thereof will be described below. In the circuit of the battery voltage processing unit 14, the output voltage of each cell of the battery unit 11 is the amplification circuit U.
1 and U4 to process the voltage level signals V1, V
2, V3 and V4. In the comparator circuit 15, four comparators are cascaded to the battery voltage processing unit 14, and each comparator compares four voltage level signals V1, V2, V3 and V4 with a reference voltage VR. The reference voltage VR can be adjusted in the range of 10.0 to 10.6 V by adjusting the resistance values of the resistors R21 and R22. If any one of the four signals V1, V2, V3 and V4 is lower than the reference voltage VR, the output of the corresponding comparator U2 goes from "high" to "low". 4 outputs of 4 comparators are AN
Since it is an input to the D gate, four signals V1,
If any one of V2, V3 and V4 is lower than the reference voltage VR, it causes the output of the AND gate (represented by "inhibit") to be "low". The low output of the AND gate serves as an inhibition signal to the motor driver 12. The inhibit signal temporarily stops the motor driver 12 from sending current to the load. This effect allows the average output current of the battery to be lowered, thus allowing the motorcycle to operate safely and to maintain the operating voltage of the battery to prolong the useful life of the battery.

The device and method for preventing over-discharge of a battery according to the present invention has many advantages. First, since it is possible to prohibit the discharge of a large current in the final stage of the operation of the battery, it is possible to avoid over-discharging which can shorten the service life of the battery. Second, before the battery energy is almost exhausted, effective energy management is required so that the driver of the electric vehicle can drive the electric vehicle at a low speed to the nearest recharging station even in such a state. To enable. Thirdly, in the energy management of the present invention, the electric power supply is not suddenly disconnected in any way, so that the electric vehicle can be operated in a state in which safety is further ensured. Fourth, it does not require a complicated instrument such as a battery capacity display device, which reduces the manufacturing cost. Fifthly, it is possible to avoid the detrimental effect of the difference in capacity between the cells due to over-discharge, so that the service life of the battery unit as a whole can be extended. The invention has been described with reference to its preferred embodiments. However, the present invention is not limited to the above embodiments, and various embodiments are possible within the scope of the claims.

[Brief description of the drawings]

FIG. 1 is a graph showing voltage-current characteristics of a battery during operation.

FIG. 2 is a graph showing a voltage-time characteristic and a current-time characteristic in a state of an average load current and a limited voltage, respectively.

FIG. 3 is a graph showing operating speed and braking speed vs. time characteristics of a class B motorcycle.

FIG. 4 is a plot showing voltage vs. time and current vs. time characteristics of a battery used at the end of operation.

FIG. 5 is a block diagram of a device for preventing over-discharge according to the present invention.

FIG. 6 is a detailed circuit diagram showing an embodiment of the device according to the present invention.

[Explanation of symbols]

 11 Battery Unit 12 Motor Driver 13 Brushless DC Motor 14 Battery Voltage Processing Unit 15 Comparator Circuit

Claims (4)

[Claims] 1. A method for preventing over-discharging of a battery unit comprising a plurality of cells: obtaining a proportionally processed output voltage of each cell; comparing each processed voltage with a reference voltage. And; and if one processed voltage is lower than the reference voltage, generate an inhibit signal and, if present, temporarily interrupt the current supplied to the load from the battery unit, thereby Decreasing the average output current from the battery unit; and a method of preventing over-discharge of the battery. 2. A device for preventing over-discharge of a battery unit consisting of a plurality of cells: a battery voltage processing unit for obtaining a proportionally processed output voltage of each cell of the unit;
Each processed voltage is compared with a reference voltage, and if one processed voltage is lower than the reference voltage, an inhibit signal is generated and, if present, the battery unit supplies the load to the load. A device for preventing over-discharge of a battery, which comprises: a comparator circuit for temporarily interrupting a current and thereby reducing an average output current from the battery unit. 3. The method according to claim 1, wherein the reference voltage is not only constant but can also be a function of the current specified for the battery unit within the safe operating range. 4. The device according to claim 2, wherein the output voltage processed in the battery voltage processing unit is obtained from a set of cells combined as a unit.