Abstract:
A multiplex voltage measurement apparatus configured to detect the breakage of a line coupling a voltage detection terminal and an electric leakage detection circuit includes a multiplex voltage measurement section and an electric leakage detection circuit. The multiplex voltage measurement section is configured to measure the voltage of each of N serially connected voltage sources via (N+1) voltage detection terminals coupled to a capacitor. The electric leakage detection circuit is configured to measure an insulation impedance between the voltage sources and a chassis. A sample switch in the leakage detection circuit prevents the formation of a loop connecting the electric leakage detection circuit to the voltage measurement section in the event of a disconnection between a voltage detection terminal and the multiplex voltage measurement section, allowing the detection of such a disconnection.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a multiplex voltage measurement apparatus, and specifically to a multiplex voltage measurement apparatus for measuring a voltage of each of serially connected N voltage sources. 
     2. Description of the Related Art 
     A high-power electric source of several hundred voltages for an electric vehicle is formed by a number of secondary battery cells, such as nickel-hydrogen storage cells, which are serially connected to each other. Each of the serially connected battery cells should be monitored for its capacity for the purpose of charge/discharge control. In particular, a battery formed by 240 serially connected cells produces a total voltage of 288 V. In such a battery, it is physically difficult to monitor each cell. In Japanese Laid-Open Publication No. 8-140204, for example, the voltage is measured for each of 24 modules each including 10 cells. 
     In an electric vehicle, high-voltage systems are electrically insulated from a chassis in order to avoid hazardous conditions. On the other hand, since a processor for charge/discharge control uses a potential of the chassis as a reference potential, the voltage of a battery should be insulatively measured. In the battery disclosed in Japanese Laid-Open Publication No. 8-140204, an insulation circuit unit including an operational amplifier, an AD converter, a photocoupler, a power supply, etc., is provided for each module. The structure of such a battery is enormously complicated. 
     As means of insulatively measuring the output voltage of a sensor or the like, a flying capacitor is known. FIG. 3 shows a structure of a multiplex voltage measurement apparatus  400 . In this example, the number of voltage sources (N) is 5. 
     Serially-connected voltage sources V 1 -V 5  are connected to a capacitor  3  through voltage detection terminals T 1 -T 6 , and through a first multiplexer  1  formed by switches S 1 , S 3 , and S 5  and a second multiplexer  2  formed by switches S 2 , S 4 , and S 6 . The capacitor  3  is connected to a voltage measurement circuit  6  through a first sample switch  4  formed by switches  4   a  and  4   b  and a polarity correction circuit  5 . 
     FIG. 4 is a timing chart for opening/closure of the respective switches S 1 -S 6 , and  4   a  and  4   b.  An operation of the multiplex voltage measurement apparatus  400  is now described with reference to FIG. 4 in conjunction with FIG.  3 . 
     Prior to measuring the voltages of the voltage sources V 1 -V 5 , the switches S 1 -S 6 , and  4   a  and  4   b  are all opened (OFF). During period P 1 , first of all. the switches S 1  and S 2  are closed (ON), whereby the voltage of the voltage source V 1  is applied to the capacitor  3 , and a charge is stored in the capacitor  3 . After being kept closed (ON) for a predetermined time period, the switches S 1  and S 2  are turned off. Then, after a predetermined time has elapsed since the switches S 1  and S 2  were turned off, the first sample switch  4  (switches  4   a  and  4   b ) is turned on, whereby the charged voltage in the capacitor  3 , i.e., the voltage of the voltage source V 1 , is transferred to the polarity correction circuit  5  and the voltage measurement circuit  6 . 
     As a matter of course, a driving circuit of each switch and a contact point of the switch are kept separated. The first multiplexer  1  is not closed while the first sample switch  4  is closed, and the second multiplexer  2  is not closed while the first sample switch  4  is closed. Therefore, the voltage of the voltage source V 1  is insulatively measured, i.e., when the voltage of the voltage source V 1  is measured, the voltage source V 1  and the capacitor  3  are insulated. 
     During period P 2 , the switches S 2  and S 3  and the switches  4   a  and  4   b  are similarly turned on and off, and. during period P 3 , the switches S 3  and S 4  and the switches  4   a  and  4   b  are similarly turned on and off. In this way, as shown in FIG. 4, the multiplex voltage measurement apparatus  400  operates in a multiplex manner. 
     It should be noted in FIG. 3 that the voltage value of an odd-numbered voltage source is inverted by the polarity correction circuit  5  so as to have the same polarity as that of the voltage value of an even-numbered voltage source before it is transmitted to the voltage measurement circuit  6 . An example of the polarity correction circuit  5  is shown in FIG.  5 . 
     The polarity correction circuit  5  shown in FIG. 5 is a well-known absolute-value circuit. The polarity correction circuit  5  changes the polarity of a voltage to be input to an AD converter of the voltage measurement circuit  6  such that all of the voltages to be input to the AD converter have the same polarity. The polarity correction circuit  5  is effective for a unipolar voltage source such as a battery. It should be noted that the polarity correction circuit  5  is not limited to such an analog circuit, but may be a digital circuit which is independent of a polarity output bit of a bipolar input-type AD converter. 
     Referring again to FIG. 3, the multiplex voltage measurement apparatus  400  further includes an electric leakage detection circuit  7 . The electric leakage detection circuit  7  includes a second capacitor  10 , amplifiers  11  and  12 , a signal generation circuit  13 , and a level comparison circuit  14 . The electric leakage detection circuit  7  compares output levels of the amplifier  12  and the signal generation circuit  13 , thereby measuring the insulation impedance between the N voltage sources and the chassis. 
     However, in the conventional multiplex voltage measurement apparatus  400  having the above-described structure, if a line between the voltage detection terminal T 6  and the switch S 6  which is connected to the electric leakage detection circuit  7  is disconnected at position  15  (shown by “x” in FIG.  6 ), a loop L (represented by a line with arrows in FIG. 6) is formed. As a result, an electric charge is stored in the first capacitor  3 , which should not be generated when the switches S 1 -S 6  are open, and accordingly, a voltage is generated therein. Therefore, breakage of the line connected to the voltage detection terminal T 6 , e.g., disconnection at position. 15 , cannot be detected. 
     SUMMARY OF THE INVENTION 
     According to one aspect of the present invention, a multiplex voltage measurement apparatus includes a multiplex voltage measurement section for measuring a voltage of each of N serially connected voltage sources and an electric leakage detection circuit for measuring an insulation impedance between the N voltage sources and a chassis, the multiplex voltage measurement section including, (N+1) voltage detection terminals connected to the N voltage sources, a first capacitor having a first terminal and a second terminal, a first multiplexer for selectively connecting any of odd-numbered voltage detection terminals among the (N+1) voltage detection terminals to the first terminal of the first capacitor, a second multiplexer for selectively connecting any of even-numbered voltage detection terminals among the (N+1) voltage detection terminals to the second terminal of the first capacitor, a voltage measurement circuit for measuring the voltage between the first terminal and the second terminal of the first capacitor, a first sample switch for connecting the first terminal and the second terminal of the first capacitor to the voltage measurement circuit, and a polarity correction circuit for changing the polarity of voltages of the N voltage sources such that the voltages of the odd-numbered voltage sources among the N voltage sources and the voltages of the even-numbered voltage sources among the N voltage sources have the same polarity, wherein the multiplex voltage measurement section measures the voltages of the N voltage sources by repeating a process in which the first and second multiplexers select one of the N voltage sources, and the first and second multiplexers are opened while the first sample switch is closed, and the electric leakage detection circuit including a second capacitor connected to one end of the N voltage sources, a signal generator for supplying a signal through the second capacitor to the one end of the N voltage sources, a level comparison circuit for comparing a signal level of the signal generator and a signal level of the second capacitor, and a second sample switch provided between the signal generator and the one end of the N voltage sources. 
     In one embodiment of the present invention, the second sample switch is provided between the second capacitor and the one end of each of the N voltage sources. 
     In another embodiment of the present invention, the second sample switch is provided between the second capacitor and the signal generator. 
     In still another embodiment of the present invention, the second sample switch is opened only when the multiplex voltage measurement circuit measures one of the N voltage sources which is located at the one end of the N voltage sources. 
     According to the present invention, in order to eliminate the above-described problem in the conventional voltage measurement apparatus, a second sample switch is provided for opening/closing a line between the signal generator  13  of the electric leakage detection circuit  7  and one end of the N voltage sources in the conventional multiplex voltage measurement apparatus  400  shown in FIG.  6 . 
     The second sample switch is opened only when measuring one of the N voltage sources which is located at the one end of the N voltage sources. Otherwise, the second sample switch is closed. 
     With such an arrangement, even when the line between the voltage detection terminal T 6  and the switch S 6  is disconnected, the loop L described above is not formed, and an electric charge is not stored in the first capacitor  3 . Therefore, the disconnection of the line between the voltage detection terminal T 6  and the switch S 6  can be easily detected. It should be noted that the voltage sources except for the first and last voltage sources of the serially connected N voltage sources are not connected to the electric leakage detection circuit, and thus, the loop L is not formed with respect to these voltage sources. 
     Furthermore, the second sample switch may be provided between the second capacitor  10  and one end of the N voltage sources, or between the second capacitor  10  and the signal generator  13 . In either case, the same effects can be obtained. 
     Thus, the invention described herein makes possible the advantage of providing a multiplex voltage measurement apparatus which can detect breakage of a line which is provided between a voltage detection terminal and a switch corresponding thereto and which is connected to an electric leakage detection circuit. 
     This and other advantages of the present invention will become apparent to those skilled in the art upon reading and understanding the following detailed description with reference to the accompanying figures. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a structure of a multiplex voltage measurement apparatus  100  according to embodiment 1 of the present invention. 
     FIG. 2 shows a structure of a multiplex voltage measurement apparatus  100 A according to embodiment 2 of the present invention. 
     FIG. 3 shows a structure of a conventional multiplex voltage measurement apparatus  400 . 
     FIG. 4 is a timing chart for illustrating an operation of the conventional multiplex voltage measurement apparatus  400 . 
     FIG. 5 shows a structure of a polarity correction circuit  5 . 
     FIG. 6 illustrates an operation of the conventional multiplex voltage measurement apparatus  400  when a line breakage occurred. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Hereinafter, embodiments of the present invention will be described with reference to FIGS. 1 and 2. 
     (Embodiment 1) 
     A multiplex voltage measurement apparatus  100  according to embodiment 1 of the present invention is described with reference to FIG.  1 . In FIG. 1, like elements are indicated by like reference numerals used to describe the multiplex voltage measurement apparatus  400  of FIG. 3, and detailed descriptions thereof are omitted. Reference numeral  8  denotes a leakage resistance between a chassis (not shown) and a battery. 
     The multiplex voltage measurement apparatus  100  includes a multiplex voltage measurement section  200  for measuring the voltage of each of five serially-connected voltage sources V 1 -V 5 , and an electric leakage detection circuit  300  for measuring the insulation impedance between the five voltage sources and the chassis. 
     The multiplex voltage measurement section  200  includes: six voltage detection terminals T 1 -T 6  connected to the five voltage sources V 1 -V 5 ; a first capacitor  3  having a first terminal  3 A and a second terminal  3 B; a first multiplexer  1  formed by switches S 1 , S 3 , and S 5  for selectively connecting any of the odd-numbered voltage detection terminals T 1 , T 3 , and T 5  to the first terminal  3 A of the capacitor  3 ; a second multiplexer  2  formed by switches S 2 , S 4 , and S 6  for selectively connecting any of the even-numbered voltage detection terminals T 2 , T 4 , and T 6  to the second terminal  3 B of the capacitor  3 ; a polarity correction circuit  5  and a voltage measurement circuit  6  for measuring the voltage between the first terminal  3 A and the second terminal  3 B, and a first sample switch  4  formed by switches  4   a  and  4   b  for connecting the first terminal  3 A and the second terminal  3 B of the first capacitor  3  to the polarity correction circuit  5  and the voltage measurement circuit  6 . The polarity correction circuit  5  changes the polarity of a voltage to be input to the voltage measurement circuit  6  such that the voltages derived from the odd-numbered voltage sources V 1 , V 3 , and V 5  and the voltages derived from the even-numbered voltage sources V 2 , V 4 , and V 6  have the same polarity. 
     In the multiplex voltage measurement section  200 , the first multiplexer  1  and the second multiplexer  2  select one of the voltage sources V 1 -V 5  while the first sample switch  4  is open. Then, the first multiplexer  1  and the second multiplexer  2  are opened, and the first sample switch  4  is then closed. Such a process is repeated, whereby the voltages of the respective voltage sources V 1 -V 5  are measured. 
     For example, in the case of measuring the voltage of the voltage source V 1 , the switches S 1  and S 2  are closed (ON) while the first sample switch  4  is open (OFF) (see period P 1  in FIG.  4 ). Meanwhile, the switches S 3 , S 4 , S 5 , and S 6  are open (OFF). 
     When the switches S 1  and S 2  are closed, the voltage of the voltage source V 1  is applied to the capacitor  3 , and an electric charge is stored in the capacitor  3 . After being kept closed (ON) for a predetermined time period, the switches S 1  and S 2  are turned off. Then, after a predetermined time has elapsed since the switches S 1  and S 2  were turned off, the first sample switch  4  (switches  4   a  and  4   b ) is turned on, whereby the charged voltage in the capacitor  3 , i.e., the voltage of the voltage source V 1 , is applied to the polarity correction circuit  5 . The polarity correction circuit  5  generates based on the voltage of the voltage source V 1  a signal which has the same polarity as that of the voltage of the voltage source V 1 , and transmits this signal to the voltage measurement circuit  6 , which measures the voltage of the voltage source V 1  based on the signal received from the polarity correction circuit  5 . This process is repeatedly and sequentially performed for the voltage sources V 1 -V 5 , whereby the voltages of the voltage sources V 1 -V 5  are measured. 
     The electric leakage detection circuit  300  includes: a second capacitor  10  connected to a line between the voltage source V 5  and the voltage detection terminal T 6 : a signal generator  13  for supplying a signal to the voltage source V 5  through the second capacitor  10 ; a level comparison circuit  14  for comparing signal levels of the second capacitor  10  and the signal generator  13 ; and a second sample switch  15   a  provided between the voltage source V 5  and the second capacitor  10 . 
     In this example, the multiplex voltage measurement section  200  includes five voltage sources V 1 -V 5  and six voltage detectionterminals T 1 -T 6 , but the number of voltage sources and the number of voltage detection terminals are not limited thereto. The present invention can be practiced so long as N voltage sources and (N+1) voltage detection terminals are provided. 
     In the multiplex voltage measurement apparatus  100  of FIG. 1, when the voltage of the voltage source V 5  is measured while the second sample switch  15   a  of the electric leakage detection circuit  300  is open, the switches S 5  and S 6  are closed, whereby the capacitor  3  is charged with the voltage of the voltage source V 5 . Then, the switches S 5  and S 6  are opened, and the first sample switch  4  is closed, whereby the voltage of the voltage source V 5  is measured by the voltage measurement circuit  6 . 
     In the above structure, if a line between the voltage detection terminal T 6  and the switch S 6  is disconnected at position  15  (shown by “x” in FIG.  1 ), the capacitor  3  is not charged with the voltage of the voltage source V 5 . Accordingly, the voltage between the first terminal  3 A and the second terminal  3 B of the capacitor  3  decreases to 0 V. Therefore, the disconnection at position  15  can be detected. 
     However, if the second sample switch  15   a  is closed, an output of the electric leakage detection circuit  300  flows in the following order: the electric leakage detection circuit  300 →the switch S 6 →the first capacitor  3 →the voltage source V 5 →leakage resistance  8 →the electric leakage detection circuit  300 , whereby the same loop as the loop L of FIG. 6 is formed. In such a case, the voltage between the first terminal  3 A and the second terminal  3 B of the capacitor  3  does not decrease to a small value, such as 0 V. Accordingly, an incorrect value is measured as the voltage of the voltage source V 5 , and the disconnection at position  15  cannot be detected. 
     According to this embodiment, in order to avoid such a malfunction, the second sample switch  15   a  is opened simultaneously with the closure of the switches S 5  and S 6 , whereby the above loop is not formed. With such an arrangement, when the line between the voltage detection terminal T 6  and the switch S 6  is disconnected at position  15 , the voltage value between the first terminal  3 A and the second terminal  3 B of the capacitor  3  decreases to 0 V and, therefore, the disconnection of the line between the voltage detection terminal T 6  and the switch S 6  can be detected. 
     (Embodiment 2) 
     A multiplex voltage measurement apparatus  100 A according to embodiment 2 of the present invention is described with reference to FIG.  2 . In FIG. 2, like elements are indicated by like reference numerals used to describe the multiplex voltage measurement apparatus  100  of FIG. 1, and detailed descriptions thereof are omitted. 
     In the multiplex voltage measurement apparatus  100 A according to embodiment 2 of the present invention, especially in the electric leakage detection circuit  300 A, the second sample switch  15   b  is provided between the second capacitor  10  and the signal generator  13  in place of the second sample switch  15   a  provided between the voltage source V 5  and the second capacitor  10 . Effects obtained by this structure are completely the same as those obtained by the electric leakage detection circuit  300  of the multiplex voltage measurement apparatus  100  according to embodiment 1. 
     As described hereinabove, according to the present invention, there can be provided a multiplex voltage measurement apparatus which can detect breakage of a line which is provided between a voltage detection terminal and a switch corresponding thereto and which is connected to an electric leakage detection circuit. 
     Various other modifications will be apparent to and can be readily made by those skilled in the art without departing from the scope and spirit of this invention. Accordingly, it is not intended that the scope of the claims appended hereto be limited to the description as set forth herein, but rather that the claims be broadly construed.