Abstract:
A battery voltage measurement system is disclosed. The system includes a measurement unit, a calibration unit, and a control unit. The calibration unit is coupled between the measurement unit and a battery, for providing several test voltages to the measurement unit. The control unit is coupled to the calibration unit and the measurement unit, for controlling the calibration unit and for receiving an output voltage of the measurement unit. Under a calibration mode, the calibration unit outputs test voltages to the measurement unit, and the control unit calculates a calibration value according to a relation between the test voltages and the output voltage of the measurement unit. Under a measurement mode, the calibration unit transmits a battery voltage to the measurement unit, and the control unit calibrates the output voltage of the measurement unit according to the calibration value for acquiring accurate value of the battery voltage.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a measurement unit of a battery voltage; in particular, to a battery voltage measurement system with self-calibration capability. 
     2. Description of Related Art 
     Presently, the transportations use fossil fuels as a major power source. However, burning the fossil fuels may cause ecological environment problems and greenhouse effects. For reducing the dependency on fossil fuels, every country of the world is developing alternative energy for replacing fossil fuel. Because the electric car may be environmentally-friendly, many major vehicle manufacturers and countries invest a lot of resources in developing relative issues. Among the relative issues of the electric car, the battery and electric power management techniques may be the most important techniques. 
     The most significant capability of a high voltage battery management system is measuring the battery voltage, for avoiding the battery from overcharging or over-discharging. In order to measure the battery voltage precisely, the measurement circuit may include a microcontroller, an analog to digital converter, an operational amplifier, and a resistor for executing the measurement. However, the ageing and damaging problems, the ambient, and the work temperature may all influence the circuit characteristics of the electric components, and thus result in measurement errors. 
     Conventionally, the high voltage battery management system usually cannot determine the self-made measurement errors and do self calibration. The accuracy of voltage measurement which is done by the high voltage battery management system must be confirmed by external measurement devices, which causes extra costs and lowers usage convenience. 
     SUMMARY OF THE INVENTION 
     The object of the present invention is to disclose a battery voltage measurement system which has self-determining and self-calibrating capabilities. By providing fixed voltage for detection and software for control, the errors of battery voltage measurement lie within an allowable range. Therefore, the usage safety and lifespan of the series battery may be improved. 
     In order to achieve the aforementioned objects, according to an embodiment of the present invention, a battery voltage measurement system is disclosed. The battery voltage measurement system is applicable for measuring a battery voltage of a battery, and includes a measurement unit, a calibration unit, and a control unit. The measurement unit is used for measuring the battery voltage. The calibration unit is coupled between the battery and the measurement unit, for providing several test voltages to the measurement unit. The control unit is coupled to the measurement unit and the calibration unit, for controlling the calibration unit and for receiving an output voltage of the measurement unit. It is worth noting that the battery voltage measurement system has a calibration mode and a measurement mode. Under the calibration mode, the calibration unit outputs the test voltages to the measurement unit, and the control unit calculates a calibration value according to a relation between the test voltages and the output voltage of the measurement unit. Under the measurement mode, the calibration unit transmits the battery voltage to the measurement unit, and the control unit calibrates the output voltage of the measurement unit according to the calibration unit for acquiring the battery voltage correctly. 
     According to another embodiment of the present invention, a battery voltage measurement method is disclosed. The method includes a step of providing a plurality of test voltages to a measurement unit. The method also includes a step of calculating a calibration value according to a relation between the test voltages and an output voltage of the measurement unit. Moreover, the method further includes a step of transmitting a battery voltage to the measurement unit for measuring the battery voltage and calibrating the output voltage of the measurement unit according to the calibration value. 
     On the basis of the above, the battery voltage measurement system and method thereof according to the present invention may provide test voltages by themselves for determining whether the measurement circuits have an error or not, and may eliminating the error for acquiring precise battery voltage. 
     For further understanding of the present disclosure, reference is made to the following detailed description illustrating the embodiments and examples of the present disclosure. The description is only for illustrating the present disclosure, not for limiting the scope of the claim. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The drawings included herein provide further understanding of the present disclosure. A brief introduction of the drawings is as follows: 
         FIG. 1  shows a function block diagram of a battery voltage measurement system according to a first embodiment of the present invention; 
         FIG. 2  shows a circuit diagram of a battery voltage measurement system according to the first embodiment of the present invention; 
         FIG. 3  shows a schematic diagram of a measurement result according to the first embodiment of the present invention; 
         FIG. 4  shows a circuit diagram of a battery voltage measurement system according to a second embodiment of the present invention; and 
         FIG. 5  shows a flow chart of battery voltage measurement method according to an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The aforementioned illustrations and following detailed descriptions are exemplary for the purpose of further explaining the scope of the present invention. Other objectives and advantages related to the present invention will be illustrated in the subsequent descriptions and appended drawings. 
     First embodiment 
       FIG. 1  is a function block diagram of a battery voltage measurement system according to a first embodiment of the present invention. The battery voltage measurement system  100  includes a calibration unit  110 , a measurement unit  120 , and a control unit  130 . The calibration unit  110  is coupled between a series battery  101  and the measurement unit  120 , and the control unit  130  is coupled to the calibration unit  110  and the measurement unit  120 . The battery voltage measurement system  100  has a calibration mode and a measurement mode. 
     Under the calibration mode, the control unit  130  may enable the calibration unit  110  for outputting test voltages to an input end of the measurement unit  120 , and may obtain gain, linearity, and some circuit parameters of the measurement unit  120  according to a relation between the test voltages and an output voltage of the measurement unit  120 . The control unit  130  may further calculate a calibration value according to the parameters obtained under the calibration mode. Under the measurement mode, the calibration unit  110  may transmit the battery voltage of the series battery  101  to the measurement unit  120  for measuring. The control unit  130  may calibrate the output voltage of the measurement unit  120  according to the calibration value for deriving accurate value of the battery voltage. It is worth noting that the battery voltage may be the voltage of one single battery or several batteries in serial connection, and the embodiment is not restricted thereby. 
     The linearity or other circuit characteristics of the electric component may be influenced by the ageing and damaging problems of itself, the ambient, the work temperature, and some other factors, and may generate errors therefore. Thus, after executing the calibration mode, the battery voltage measurement system  100  may acquire the circuit characteristics of the measurement unit  120  again, for calibrating the output voltage of the measurement unit  120 . Therefore, the battery voltage measurement system  100  may obtain much more accurate battery voltage, and may eliminate the measurement errors caused by the circuit characteristic changes of the measurement unit  120 . 
     Please refer to  FIG. 1  and  FIG. 2  in the meantime.  FIG. 2  is a circuit diagram of the battery voltage measurement system  100  according to this embodiment. The calibration unit  110  includes an isolation unit  210  and a voltage generation unit  220 . The isolation unit  210  is coupled between the input end of the measurement unit  120  and the series battery  101 . Under the calibration mode, the isolation unit  210  may isolate the series battery  101  and the measurement unit  120  for preventing the measurement unit  120  from being influenced by the voltage of the series battery  101 . Under the measurement mode, the isolation unit  210  may transmit the battery voltage of the series battery  101  to the measurement unit  120  for measuring the magnitude of the battery voltage. The voltage generation unit  220  may generate test voltages VN and VP to the measurement unit  120  under the calibration mode. 
     The isolation unit  210  includes a first isolation circuit  211  and a second isolation circuit  212  which are coupled between respective two input ends of the measurement unit  120  and the series battery  101 . The first isolation circuit  211  includes resistors R 11 , R 12 , R 13 , an NPN transistor Q 1 , and a PMOS transistor Q 2 . A source node and a drain node of the PMOS transistor Q 2  are respectively connected to a positive end of a battery  11  and a first input end PIN 1  of the measurement unit  120 . The resistor R 12  is coupled between the source node and a gate node of the PMOS transistor Q 2 . The resistor R 13  is coupled between the gate node of the PMOS transistor Q 2  and a collector node of the NPN transistor Q 1 . A base node of the NPN transistor Q 1  is coupled to an enable signal VE through the resistor R 11 . The second isolation circuit includes resistors R 14 , R 15 , R 16 , an NPN transistor Q 3 , and a PMOS transistor Q 4 . The PMOS transistor Q 4  is coupled between a negative end of the battery  11  and a second input end of the measurement unit  120 . The remaining circuit connections are similar to their counterparts in the first isolation circuit  211 , thus the following disclosures may not go into details again. The control unit  130  may be connected to the base nodes of the NPN transistors Q 1  and Q 3  through the resistors R 11  and R 14  respectively, and may adjust the enable signal VE for turning on or off the PMOS transistors Q 2  and Q 4 . 
     When the enable signal VE is high, the PMOS transistors Q 2  and Q 4  may be turned on for transmitting the voltage difference between two ends of the battery  11  to the measurement unit  120 . On the other hand, when the enable signal VE is low, the PMOS transistors Q 2  and Q 4  may be turned off for isolating the battery  11  from the measurement unit  120 . The control unit  130  may output the enable signal VE to the isolation unit  210  according to the changes of the operation modes, for isolating the battery  11  and the measurement unit  120  under the calibration mode. 
     The voltage generation unit  220  includes an enable circuit  221 , a voltage generation circuit  222 , and an output isolation circuit  223 . The enable circuit  221  includes resistors R 17 , R 18 , R 19 , an NPN transistor Q 5 , and a PNP transistor Q 6 . An emitter node and a collector node of the PNP transistor Q 6  are coupled to the positive end of the battery  11  and the voltage generation circuit  222  respectively in order to transmit electric power to the voltage generation circuit  222  for generating the test voltages VP and VN. The resistor R 18  is coupled between the emitter node and a base node of the PNP transistor Q 6 . The resistor R 19  is coupled between the base node of the PNP transistor Q 6  and a collector node of the NPN transistor Q 5 . An emitter node of the NPN transistor Q 5  is coupled to a ground GND, and a base node of the NPN transistor Q 5  is coupled to a determination enabling signal DE. The control unit  130  may output the determination enabling signal DE to the NPN transistor Q 5  for controlling the PNP transistor Q 6 . 
     When the determination enabling signal DE is high, the PNP transistor Q 6  is turned on for transmitting the electric power of the series battery  101  to the voltage generation circuit  222 . On the other hand, when the determination enabling signal DE is low, the PNP transistor Q 6  is turned off for isolating the series battery  101  from the voltage generation circuit  222 . Under this situation, the voltage generation circuit  222  has no operation. 
     The voltage generation circuit  222  includes a resistor R 22 , a capacitor C 1 , and a plurality of bias generation circuits  231 ,  232 ,  233 , and a voltage division circuit  234 . The resistor R 22  is serially connected between the enabling circuit  221  and each of the bias voltage generation circuits  231 ,  232 , and  233 . The capacitor C 1  is coupled between the output end of each of the bias voltage generation circuits  231 ,  232 ,  233  and the ground GND. Each of the bias voltage generation circuit  231 ,  232 , and  233  includes standard voltage components and the NPN transistor. The bias voltage generation circuit  231  includes a resistor R 20 , a standard voltage component Z 1 , and an NPN transistor Q 7 . The standard voltage component Z 1  is coupled between one end of the resistor R 22  and a collector node of the NPN transistor Q 7 . An emitter node of the NPN transistor Q 7  is coupled to the ground GND, and a base node of the NPN transistor Q 7  is coupled to the control signal VC 1  through the resistor R 20 . The bias voltage generation circuit  232  includes a resistor R 21 , a standard voltage component Z 2 , and an NPN transistor Q 8 . The bias voltage generation circuit  233  includes a resistor R 23 , a standard voltage component Z 3 , and an NPN transistor Q 9 . The circuit structures of the bias voltage generation circuits  232  and  233  are similar to the circuit structure of the bias voltage generation circuit  231 , thus the following disclosures may not go into details again. The standard voltage component Z 1  may be a zener diode, but the scope of the present invention is not limited thereby. 
     The bias voltage generation circuits  231 ,  232 , and  233  are controlled by the control signals VC 1 , VC 2 , and VC 3  respectively. The control unit  130  may change the bias voltages generated by the bias voltage generation circuit  231 ,  232 , and  233  by adjusting the control signals VC 1 , VC 2 , and VC 3 . It is worth noting that there are three bias voltage generation circuits  231 ,  232 , and  233  in this embodiment, but the number of the bias voltage generation circuit is not limited thereby. 
     The voltage division circuit  234  is formed by several resistors R 24  to R 27  which are in serial connection, and is coupled between the bias voltage generation circuits  231  to  233  and the ground GND. 
     The output isolation circuit  223  includes two NMOS transistors Q 10  and Q 11  which are respectively coupled between one end of the resistor R 24  and the first input end PIN 1  of the measurement unit  120  and between another end of the resistor R 24  and the second input end of the measurement unit  120 . A gate node of the NMOS transistor is coupled to the output voltage VG of the enabling circuit  221  through the resistor R 28 . Thus when the enabling circuit  221  is active, its output voltage VG is high, which turns on the NMOS transistors Q 10  and Q 11  for outputting test voltages VP and VN. On the other hand, when the enabling circuit  221  is inactive, its output voltage is low, which turns off the NMOS transistors Q 10  and Q 11 . In other words, the output isolation circuit  223  is controlled by the output voltage VG of the enabling circuit  221 . When the determination enabling signal DE is active, the NMOS transistors Q 10  and Q 11  of the output isolation circuit  223  are turned on. When the determination enabling signal DE is inactive, the NMSO transistors Q 10  and Q 11  of the output isolation circuit  223  are turned off In this embodiment, the test voltages VP and VN may not be the voltages of the two ends of the resistor R 24 , they may be switched to different divisional voltage of different resistors. 
     It is worth noting that the major function of the voltage generation circuit  222  is to generate the test voltages, it may be implemented by several different circuit designs. For example, the circuit structures of the voltage generation circuit  222  may be implemented by simple resistors or digital to analog converters for generating analog voltages. The structure of the voltage generation circuit  222  is not restricted to the one shown in  FIG. 2 . 
     The measurement unit  120  includes an operational amplifier  251 , an analog to digital converter  252 , and resistors R 30 , R 31 , R 32 , and R 33 . The resistor R 30  is coupled between the first input end PIN 1  and a non-inverted input end of the operational amplifier  251 . The resistor R 31  is coupled between the non-inverted input end of the operation amplifier  251  and the ground GND. The resistor R 32  is coupled between an inverted input end of the operational amplifier  251  and the second input end PIN 2 . The resistor R 33  is coupled between the inverted input end and an output end of the operational amplifier  251 . The analog to digital converter  252  is coupled between the output end of the operational amplifier  251  and the control unit  130 , for converting the output voltage of the operational amplifier  251  into digital signals and transmitting the output voltage to the control unit  130 . The control unit  130  may be a micro controller, but the implementation of the control unit  130  is not restricted thereby. 
     In this embodiment, because there are three bias voltage generation circuits  231  to  233 , at least three sets of different test voltages VN and VP may be generated. Under the calibration mode, the control unit  130  may control the calibration unit  110  by adjusting the enabling signal VE, the determination enabling signal DE, and the control signals VC 1  to VC 3  for detecting the errors, gains, and circuit characteristics of the measurement unit  120 . For example, the control unit  130  may enable the control signals VC 1  to VC 3  in sequence for generating three sets of different test voltages VP and VN to the measurement unit  120 , and may acquire the gains and linearity of the measurement unit  120  according to the changes of the output voltage of the measurement unit  120 . 
     Please refer to  FIG. 3 .  FIG. 3  shows a schematic diagram of measurement results according to an embodiment of the present invention. Assuming that the voltage differences of the three sets of test voltages VP and VN are voltage VA, VB, and VC, and the output voltages of the measurement unit  120  are V 1 , V 2 , and V 3  respectively. As shown in  FIG. 3 , within the range from voltage VA to VC, the measurement unit  120  is not linear. The control unit  130  may calculate a calibration value according to a relation between three sets of the test voltages VP, VN and the output voltage of the measurement unit  120 . After that, under the measurement mode, the control unit  130  may calibrate the output voltage of the measurement unit  120  according to the calibration value, for obtaining accurate value of the battery voltage. 
     In addition, under the calibration mode, the control unit  130  may enable the determination enabling signal DE, for making the enabling circuit  221  transmit electric power to the voltage generation circuit  222  and generate test voltages VP and VN to the measurement unit  120  accordingly. The control unit  130  may simultaneously turn off the PMOS transistors Q 2  and Q 4  of the isolation unit  210  for isolating the series battery  101  and the measurement unit  120 . Under the measurement mode, the voltage generation unit  220  may not output the test voltages VP and VN, and the control unit  130  may simultaneously turn on the PMOS transistors Q 2  and Q 4  of the isolation unit  210  for transmitting the battery voltage of the battery  11  to the measurement unit  120 . 
     In other words, the battery voltage measurement system  100  may test circuit characteristics of the measurement unit  120  by itself, and then calibrate the output voltage of the measurement unit  120  according to the results of the test for improving the accuracy of the battery voltage measurement. The operations of the calibration may be executed and calculated by software, without adjusting hardware circuits. In addition, when the control unit  130  finds out that there is error generated by the measurement unit  120 , it may tell the user relative information by using the communication capability of the microprocessor. 
     It is worth noting that the enabling signal VE, the determination enabling signal DE, and the control signals VC 1  to VC 3  received by the calibration unit  110  may be transmitted from the control unit  130  or an outer system, thus the sources where the signals come from do not be limited by this embodiment. The battery voltage measurement system  100  may includes several sets of calibration units  110  and measurement units  120  in correspondence to other batteries of the series battery  101 . The number of sets of the calibration units  110  and the measurement units  120  are not restricted thereby. In addition, there may also have a plurality of isolation units  210  and voltage generation units  220  disposed in each calibration unit  110  for coupling to different batteries. On the basis of the aforementioned embodiments and descriptions, the person skilled in the art may derive other kinds of implementations within the scope of the present invention, and the following disclosures may not go into details again. 
     Second Embodiment 
     The first isolation circuit  211 , the second isolation circuit  212 , the enabling circuit  221 , and the output isolation circuit  223  in  FIG. 2  may be implemented by switches such as PMOS transistors, NMOS transistors, BJT transistors, or relays, and the types of switches are not restricted thereby. Please refer to  FIG. 4  which shows a circuit diagram of battery voltage measurement system according to a second embodiment of the present invention. The differences between  FIG. 4  and  FIG. 2  are that a switch  411  is used for replacing the first isolation circuit  211 , a switch  412  is used for replacing the second isolation circuit  212 , a switch  421  is used for replacing the enabling circuit  221 , and switches  423 ,  424  are used for replacing the output isolation circuit  223 . The remaining circuit structures and operation manners in  FIG. 4  are the same as their counterparts in  FIG. 2 , thus the following disclosures may not go into details again. 
     On the basis of the aforementioned embodiments, a battery voltage measurement method may be concluded. Please refer to  FIG. 2  and  FIG. 5 .  FIG. 5  shows a flow chart of the battery voltage measurement method according to an embodiment of the present invention. Firstly, the calibration unit  110  may provide several test voltages to the measurement unit  120  (step S 510 ). Then the control unit  130  may calculate a calibration value according to the relation between the test voltages and the output voltage of the measurement unit  120  (step S 520 ). After acquiring the calibration value, the calibration unit  110  may enter the measurement mode and transmits the battery voltage to the measurement unit  120  for measuring it, and under the measurement mode, the control unit  130  may calibrate the output voltage of the measurement unit  120  according to the calibration value for obtaining accurate value of the battery voltage (step S 530 ). Other details of the method are described in the first embodiment presented above. The person skilled in the art may know the implementation manners of the present invention according to the aforementioned descriptions and embodiments, thus the following disclosure may not go into details repeatedly. 
     In the embodiments described above, the PNP transistor may be an abbreviation of PNP bipolar junction transistor, the NPN transistor may be an abbreviation of NPN bipolar junction transistor, the NMOS transistor may be an abbreviation of N channel metal oxide semiconductor field effect transistor, and the PMOS transistor may be an abbreviation of P channel metal oxide semiconductor field effect transistor. 
     In addition, it is worth noting that the coupling connection between two of the aforementioned components may be a direct connection or an indirect connection which has the capability to transmit electric signals, and the present invention is not restricted thereby. The technique manners of the embodiments may be used independently or together, the number of the components may be increased, reduced, removed, adjusted, or replaced, and the scope of the present invention is not restricted thereby. The person skilled in the art may know the implementation manners of the present invention according to the aforementioned descriptions and embodiments, thus the following disclosure may not go into details repeatedly. 
     On the basis of the above, the battery voltage measurement system of the present invention may provide test voltages for testing the circuit characteristics of the measurement unit, and for eliminating the errors of the measurement unit. Therefore, according to the present invention, the measurement errors caused by component ageing, damaging, or the ambient may be reduced, and the accurate value of the battery voltage may be acquired. 
     Some modifications of these examples, as well as other possibilities will, on reading or having read this description, or having comprehended these examples, will occur to those skilled in the art. Such modifications and variations are comprehended within this disclosure as described here and claimed below. The description above illustrates only a relative few specific embodiments and examples of the present disclosure. The present disclosure, indeed, does include various modifications and variations made to the structures and operations described herein, which still fall within the scope of the present disclosure as defined in the following claims.