JP2011170992A - Voltage monitoring system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress deterioration of accuracy of voltage detection due to temperature dependency of components with a simpler configuration in a voltage monitoring system of a fuel cell. <P>SOLUTION: The voltage monitoring system 20 of a fuel cell stack FC where a plurality of fuel cells FC1-FC4 are layered includes: a voltage transmission circuit 30 that is provided in each of the fuel cells FC1-FC4 and outputs each of the voltages of the fuel cells FC1-FC4; a minimum value detection circuit 50 that collects voltages of the fuel cells FC1-FC4 output by the voltage transmission circuit 30 and detects a minimum value out of the output voltages via diodes D51-D54; and an output circuit 70 that outputs a detection result of the minimum value detection circuit 50 via a diode D72 disposed in the direction opposite to the diodes D51-D54. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a voltage monitoring technique for a fuel cell stack in which a plurality of fuel cells are stacked.

  Since the actual output of a single cell is less than 1V, the fuel cell is generally configured as a fuel cell stack in which a plurality of single cells are connected in series to ensure the necessary high voltage as a whole. In such a fuel cell stack, if an abnormality occurs even in a single cell, it is necessary to limit the output of the entire stack or stop the operation. For this reason, a voltage monitoring system that monitors the voltage of a single cell constituting the fuel cell stack has been proposed in order to suitably control the fuel cell stack (for example, Patent Document 1 below).

  In such a voltage monitoring system, the voltage value to be detected may be affected by the environmental temperature due to the temperature dependence of the constituent members, and the detection accuracy may deteriorate. For this reason, a technique has been proposed in which a temperature sensor is provided to perform temperature compensation according to the detected temperature. For example, in Patent Document 3 below, temperature compensation of the on-resistance of the field effect transistor is performed according to the temperature detected by the temperature sensor. However, the method using the temperature sensor requires not only the installation of the temperature sensor but also a temperature compensation calculation according to the detected temperature, which leads to a complicated apparatus and high cost.

JP 2008-103201 A JP 2002-184443 A JP 2002-151163 A

  In view of the above-described problems, the problem to be solved by the present invention is to suppress deterioration in voltage detection accuracy due to temperature dependence of components in a fuel cell voltage monitoring system with a simple configuration.

  The present invention has been made to solve the above-described problems, and can be realized as the following forms or application examples.

Application Example 1 A voltage monitoring system for a fuel cell stack in which a plurality of fuel cells are stacked,
A voltage transmission means provided for each of the plurality of fuel cells, each voltage of the fuel cell being individually taken out from the fuel cell and output;
Detecting means for collecting the voltages of the plurality of fuel cells output by the voltage transmission means, and detecting at least one of the minimum value and the maximum value of the output voltages via a first diode;
A voltage monitoring system comprising: output means for outputting a detection result of the detection means via a second diode provided in a direction opposite to the first diode.

  The voltage monitoring system having such a configuration takes out and collects the voltages of each of the fuel cells individually, detects at least one of the minimum value and the maximum value via the first diode, and is opposite to the first diode. Is output via a second diode provided in the direction of. Here, in the first diode and the second diode, a voltage drop is caused by the forward voltage. This forward voltage has a temperature dependency that decreases as the temperature increases. However, the forward voltage is provided in the opposite direction to the first diode and the second diode. Since the voltage is generated in the reverse direction, at least a part of the fluctuation of the forward voltage due to the temperature dependency can be canceled out between the first diode and the second diode. Therefore, it is possible to suppress the deterioration of the voltage detection accuracy due to the temperature dependence of the diode. In addition, since the detection result is only output via the second diode provided in the direction opposite to the first diode included in the detection means, the configuration is simple.

Application Example 2 In the voltage monitoring system according to Application Example 1, the first diode and the second diode have substantially the same temperature dependence characteristics of forward voltage.

  In the voltage monitoring system having such a configuration, since the temperature dependence characteristics of the forward voltage are substantially the same between the first diode and the second diode, the fluctuation of the forward voltage due to the temperature dependence is reduced with respect to the first diode and the second diode. Can almost cancel each other out. Therefore, the temperature dependence of the diode can be almost eliminated for the entire system, and highly accurate voltage detection can be performed.

Application Example 3 An application in which the output unit includes a buffer circuit that is interposed between the detection unit and the second diode and suppresses an influence on the detection unit from the output stage side of the detection unit. The voltage monitoring system according to Example 1 or Application Example 2.

  In the voltage monitoring system having such a configuration, since the buffer circuit is interposed between the detection means and the second diode, the influence on the detection means from the output stage side of the detection means can be suppressed, and the accuracy is high. Voltage detection can be performed.

Application Example 4 In the voltage monitoring system according to Application Example 3, the output unit is interposed between the buffer circuit and the second diode, and the detection result is output via the buffer circuit. A voltage monitoring system comprising: a transformer for input; and a switch circuit connected to a winding on the input side of the transformer and outputting the detection result to the transformer as an AC voltage.

  Since the voltage monitoring system having such a configuration can output the detection result to the second diode as an AC voltage via the transformer by turning the switch circuit ON / OFF, it is insulated from the high-pressure fuel cell side. Since the detection result can be output to the low pressure side in the state, safety can be improved.

Application Example 5 In the voltage monitoring system according to any one of Application Examples 1 to 4, the voltage transmission means is a differential amplifier connected to the anode side and the cathode side of the plurality of fuel cells. And the detecting means includes the first diode provided in the same direction for each output of the differential amplifier, and a voltage monitor including a capacitor interposed between the first diode and the ground. system.

  In the voltage monitoring system having such a configuration, since the detection means includes a differential amplifier, a diode, and a capacitor, the configuration of the voltage monitoring system can be simplified. Moreover, since it can comprise using a general purpose component, manufacture is easy and can reduce cost.

It is explanatory drawing which shows schematic structure of the voltage monitoring system 20 as 1st Example. It is explanatory drawing which shows schematic structure of the voltage monitoring system 120 as a 2nd Example. It is explanatory drawing which shows schematic structure of the voltage transmission circuit 230 as a 3rd Example. It is explanatory drawing which shows schematic structure of the voltage monitoring system 320 as a 4th Example. It is explanatory drawing which shows schematic structure of the voltage monitoring system 420 as a 5th Example.

A. First embodiment:
A schematic configuration of a voltage monitoring system 20 as an embodiment of the present invention is shown in FIG. The voltage monitoring system 20 is a system that monitors the voltage of the fuel cell stack FC in which a plurality of fuel cells are stacked. A fuel cell here is what is called a single cell which is the minimum unit of electric power generation. The fuel cell in this example is a solid polymer type fuel cell, and is provided with a cathode electrode and an anode electrode on the surface of an electrolyte membrane that is a thin film of a solid polymer material showing good proton conductivity in a wet state. A gas diffusion layer, a channel member, and a separator are laminated on both surfaces of the electrolyte membrane / electrode assembly (not shown). The fuel cell stack FC is sandwiched between terminals, insulators, and end plates arranged at both ends in the stacking direction, and is connected to a fuel gas, oxidizing gas, and cooling water supply / discharge system (not shown). The rated output of the fuel cell stack FC is 300 V in this embodiment. However, the rated output may be set as appropriate, and the number of fuel cells constituting the fuel cell stack FC may be two or more.

  As shown in FIG. 1, the voltage monitoring system 20 includes a voltage transmission circuit 30, a minimum value detection circuit 50, and an output circuit 70. The voltage transmission circuit 30 is configured by the same circuit connected to each of the fuel cells FC1 to FC4 constituting the fuel cell stack FC. When viewed from the fuel cells FC1 to FC4, the voltage transmission circuit 30 is connected to both input terminals of the operational amplifiers 31 to 34. The operational amplifiers 31 to 34 are differential amplifiers, and are voltages obtained by amplifying the voltages of the fuel cells FC1 to FC4 connected to both input terminals with a predetermined gain (in this case, the gain is set to 1, so the fuel cells FC1 to FC1). The voltage of FC4 itself is isolated from the actual potential and output.

  Since the fuel cells FC1 to FC4 are stacked and electrically connected in series, the cathode voltage of each fuel cell corresponds to the number of fuel cells stacked up to that fuel cell with respect to the ground level. It is raised to the specified potential. Since differential amplifiers are used as the operational amplifiers 31 to 34, the output voltages of the operational amplifiers 31 to 34 are values representing the voltages of the fuel cells FC1 to FC4 with respect to the ground level. In the present embodiment, the power supply 36 provided independently of the fuel cell stack FC is used as the power supply for the operational amplifiers 31 to 34.

  The minimum value detection circuit 50 is a circuit that detects the minimum value of the output voltages of the fuel cells FC1 to FC4, and includes diodes D51 to D54, a capacitor C56, a power source 57, and a resistor R58, as shown in FIG. ing. All the outputs of the operational amplifiers 31 to 34 described above are connected to diodes D51 to D54 in the reverse direction. For this reason, the output of each operational amplifier 31-34 is what is called a wired OR connection. That is, the outputs of the operational amplifiers 31 to 34 have no influence on the outputs of the other operational amplifiers 31 to 34. A capacitor C56, one end of which is connected to the ground, is connected to the outputs of the wired OR connected operational amplifiers 31 to 34, and a predetermined positive power source 57 is further connected via a pull-up resistor R58. . This voltage is set to a sufficiently large value with respect to the assumed output of the operational amplifiers 31 to 34.

The minimum value detection operation of the minimum value detection circuit 50 will be described. The minimum value detection operation is an operation for detecting the minimum value among the voltages of the fuel cells FC1 to FC4. In order to simplify the description, the following operation will be described assuming that the voltage drop of the diodes D51 to D54 is 0 volts.
(1) If the operational amplifiers 31 to 34 are not operating and the outputs of the operational amplifiers 31 to 34 are in a high impedance state, no current flows into the outputs of the operational amplifiers 31 to 34, so the capacitor C56 is charged. Thus, the voltage at the terminal TE1 becomes equal to the voltage of the positive power supply 57 connected via the pull-up resistor R58.

  (2) Next, when the operational amplifiers 31 to 34 are operated at a predetermined timing and the output voltages of the fuel cells FC1 to FC4 are detected and output by the operational amplifiers 31 to 34 as differential amplifiers, the diodes D51 to D54 are output. As a result, current flows through the terminal TE1, and the voltage at the terminal TE1 of the capacitor C56 decreases. This operation continues until the voltage at the terminal TE1 becomes the lowest voltage Vmin1 among the outputs of the connected operational amplifiers 31-34. When the voltage at the terminal TE1 coincides with the voltage Vmin1, the other operational amplifiers 31 to 34 (operational amplifiers other than the operational amplifier that outputs the voltage Vmin1) are higher than the voltage at the terminal TE1, so that current flows through the diodes D51 to D54. There is nothing.

  (3) If the voltage of one of the fuel cells further decreases and the lowest voltage among the outputs of the connected operational amplifiers 31 to 34 becomes Vmin2 (Vmin1> Vmin2), the voltage at the terminal TE1 of the capacitor C56 The current flows into the operational amplifiers 31 to 34 that output the lower voltage via the diodes D51 to D54, and the voltage at the terminal TE1 of the capacitor C56 decreases. This operation continues until the voltage at the terminal TE1 becomes the voltage Vmin2. When the voltage at the terminal TE1 matches the voltage Vmin2, the other operational amplifiers 31 to 34 are higher than the voltage at the terminal TE1, so that no current flows through the diodes D51 to D54.

  (4) On the contrary, when the voltage of the fuel cell, which has been the minimum voltage until then, becomes high and the lowest voltage among the outputs of the connected operational amplifiers 31 to 34 becomes Vmin3 (Vmin1 <Vmin3), Since 34 is higher than the voltage of the terminal TE1, no current flows through the diodes D51 to D54. Therefore, the capacitor C56 is gradually charged by the power source 57. This charging is continued until the voltage at the terminal TE1 of the capacitor C56 reaches the voltage Vmin3. When the voltage at the terminal TE1 exceeds the voltage Vmin3, a current flows through the diodes D51 to D54, and the voltage at the terminal TE1 of the capacitor C56 decreases.

  Actually, in any of the cases (2) to (4) described above, since the forward voltage Vf (Forword Voltage) exists in the diode (usually about 0.7 volts in the case of a silicon diode), the terminal TE1 The voltage becomes higher than the minimum value of the output voltage of the operational amplifiers 31 to 34 by this forward voltage Vf. Since the forward voltage Vf of each diode is known, each fuel is detected by detecting the voltage at the terminal TE1. It is easy to detect the minimum voltage of the batteries FC1 to FC4. In this way, the capacitor C56 holds the minimum output of the operational amplifiers 31 to 34, that is, the voltage corresponding to the minimum voltage of the fuel cells FC1 to FC4.

  The forward voltage Vf described above has temperature dependence. When the environmental temperature increases by 1 ° C., the forward voltage Vf decreases by, for example, 2.0 mV. In this case, if the environmental temperature can change from 0 ° C. to 50 ° C., the fluctuation range of the forward voltage Vf at that time is 0.1 V (= 2.0 mV / ° C. × 50 ° C.). For this reason, in the present embodiment, diodes D51 to D54 are used whose temperature dependence characteristics of the forward voltage Vf are substantially equal. Here, the fact that the temperature-dependent characteristics are substantially equal means that variation between individuals is allowed, and this corresponds to the case where the temperature-dependent characteristics are treated as equal in design. For example, it can be said that the temperature-dependent characteristics are substantially equal if the variation in the forward voltage Vf between individuals according to changes in the environmental temperature is within 10%. As described above, the diodes having the same temperature dependence characteristics may be selected by measuring the temperature dependence characteristics of the respective diodes when the voltage monitoring system 20 is manufactured, and selecting a diode whose fluctuation range falls within a predetermined range. Alternatively, diodes manufactured from the same semiconductor lot may be selected. In this way, the characteristics of the diodes manufactured from the same semiconductor lot are close, so there is a high possibility that the fluctuation range will be within the predetermined range, and measurement can be omitted or the number of diodes to be measured can be reduced. The manufacturing process can be simplified.

  The minimum value held by the capacitor C56 of the minimum value detection circuit 50 in this way is output to the output circuit 70. As shown in FIG. 1, the output circuit 70 includes a buffer circuit 71 and a diode D72. When viewed from the minimum value detection circuit 50, the output circuit 70 has a buffer circuit 71 and a diode D72 connected in series in the order of the buffer circuit 71 and the diode D72 with respect to the output of the minimum value detection circuit 50. The buffer circuit 71 suppresses the influence of the buffer circuit 71 from the output stage side to the input stage side. In this embodiment, the buffer circuit 71 is a voltage follower, and outputs the input voltage value itself from the minimum value detection circuit 50 to the diode D72 side. In this way, if the output of the minimum value detection circuit 50 is output to the diode D72 side via the buffer circuit 71, the voltage value held by the capacitor C56 is not affected by the diode D72 side. The detection accuracy of the minimum value in the circuit 50 can be improved. However, the buffer circuit 71 is not essential.

  The diode D72 is provided in the forward direction with respect to the output of the buffer circuit 71. That is, the diode D72 is provided in the opposite direction so that the current flow direction when viewed from the voltage transmission circuit 30 side is reversed as compared with the diodes D51 to D54 constituting the minimum value detection circuit 50. Yes. In the present embodiment, a diode D72 having a temperature dependent characteristic of the forward voltage Vf substantially equal to that of the diodes D51 to D54 is used.

  The output of the diode D72 is output to an MCU (not shown) in this embodiment. In this embodiment, the MCU is a microcomputer specialized for AD conversion. The MCU AD-converts the input minimum value and outputs it to a CPU (not shown) that controls the operation of the fuel cell stack FC, and generates power from the fuel cell stack FC based on the minimum voltages of the fuel cells FC1 to FC4. Used for condition monitoring. Note that the minimum value may be directly input to the CPU without going through the MCU.

  The voltage monitoring system 20 having such a configuration individually collects and collects the voltages of the fuel cells FC1 to FC4, detects their minimum values via the diodes D51 to D54, and is in the direction opposite to the diodes D51 to D54. Is output via a diode D72 provided in the circuit. Here, the forward voltage Vf of the diodes D51 to D54 and the diode D72 has temperature dependence, but is provided in the opposite direction to the diodes D51 to D54 and the diode D72. In the diodes D51 to D54 and the diode D72, Since the forward voltage Vf is generated in the reverse direction, fluctuations in the forward voltage Vf due to temperature dependence can be canceled out between the diodes D51 to D54 and the diode D72. Therefore, it is possible to suppress the deterioration of the voltage detection accuracy due to the temperature dependence of the diode. In addition, the configuration is simple because only the detection result of the minimum value detection circuit 50 is output via the diode D72 provided in the opposite direction to the diodes D51 to D54.

  In addition, since the temperature monitoring characteristics of the forward voltage Vf in the voltage monitoring system 20 are substantially the same between the diodes D51 to D54 and the diode D72, fluctuations in the forward voltage Vf due to the temperature dependence are detected by the diodes D51 to D54 and the diode D72. Can almost cancel each other out. Therefore, the temperature dependence of the diode can be almost eliminated in the entire voltage monitoring system 20, and highly accurate voltage detection can be performed.

  Further, since the voltage monitoring system 20 cancels the forward voltage Vf with the diodes D51 to D54 and the diode D72 provided in opposite directions, the minimum value output from the voltage monitoring system 20 is the fuel cell FC1 to FC1. It becomes equal to the minimum value of FC4, it is not necessary to correct the forward voltage Vf, and the configuration can be simplified.

B. Second embodiment:
A voltage monitoring system 120 as a second embodiment of the present invention will be described with reference to FIG. In FIG. 2, the same components as those in the first embodiment are denoted by the same reference numerals as those in FIG. Hereinafter, the voltage monitoring system 120 will be described only with respect to differences from the first embodiment, and description of common points will be omitted. The voltage monitoring system 120 includes a voltage transmission circuit 30, a minimum value detection circuit 50, and an output circuit 170, as illustrated. The configurations of the voltage transmission circuit 30 and the minimum value detection circuit 50 are the same as in the first embodiment. The output circuit 170 includes a buffer circuit 71, a transformer 173, a switch SW174, and a diode D72. The output circuit 170 is different from the first embodiment in that a transformer 173 and a switch SW174 are interposed between the buffer circuit 71 and the diode D72.

  The transformer 173 has an input side winding connected to the minimum value detection circuit 50 and the ground, and an output side winding connected to the diode D72 and the ground. This ground is the ground of the MCU that outputs the output voltage of the diode D72. Further, a switch SW174 is interposed between the input side winding and the ground. The switch SW174 is a relay that switches ON / OFF of the conductive state between the input side winding of the transformer 173 and the ground.

  When the switch SW174 is turned on, power corresponding to the output of the minimum value detection circuit 50 flows into the input winding of the transformer 173 via the buffer circuit 71. Since the current change is extremely large, a positive output voltage corresponding to the input voltage appears at both ends of the output side winding of the transformer 173 according to the mutual inductance between the input and output of the transformer 173. When the switch SW174 is turned off, no current flows into the input winding. Since this change in current is extremely large, a negative output voltage corresponding to the input voltage appears at both ends of the output side winding of the transformer 173 due to the back electromotive force. That is, by repeatedly turning ON / OFF the switch SW174, the transformer 173 converts the input voltage from the minimum value detection circuit 50 into an AC voltage and outputs it. In this embodiment, the numbers of turns of the input side winding and the output side winding are equal. Therefore, the maximum amplitude of the AC signal converted to AC voltage is equal to the output of the minimum value detection circuit 50.

  The output of the transformer 173 converted into an AC voltage in this way is half-wave rectified by a forward diode D72 and output to an MCU (not shown). Therefore, if the maximum amplitude is detected, the MCU can know the minimum value of the output voltage of the fuel cells FC1 to FC4.

  Since the voltage monitoring system 20 having such a configuration repeats ON / OFF of the switch SW174, the output of the buffer circuit 71 is converted into an AC voltage by the transformer 173 and output to the diode D72, so that the minimum voltage of the fuel cells FC1 to FC4 Can be output. Since the input stage and the output stage of the transformer 173 are insulated from each other, the detection result of the minimum value detection circuit 50 can be outputted to the low-pressure side while being insulated from the high-pressure fuel cell stack FC side by the transformer 173. Can be increased.

C. Third embodiment:
A third embodiment of the present invention will be described. The voltage monitoring system according to the third embodiment differs from the voltage monitoring system 20 according to the first embodiment described above only in the configuration of the voltage transmission circuit. Hereinafter, the voltage monitoring system as the third embodiment will be described only with respect to differences from the first embodiment, and description of common points will be omitted. FIG. 3 is an explanatory diagram showing the configuration of the voltage transmission circuit 230 as the third embodiment. The voltage transmission circuit 230 includes resistors R231 to R234 and current sensors 241 to 244. That is, the voltage transmission circuit 230 includes resistors R231 to R234 and current sensors 241 to 244 in place of the operational amplifiers 31 to 34 of the voltage transmission circuit 30 as the first embodiment. Different.

  A resistor R231 and a current sensor 241 are connected in series between the anode and cathode of the fuel cell FC1. Similarly, for the fuel cells FC2 to FC4, resistors R232 to R234 and current sensors 242 to 244 are connected in series.

  The current sensors 241 to 244 are non-contact type DC current sensors, and have the same value as the output voltage of the fuel cells FC1 to FC4 according to the current flowing through the resistors R231 to 234 in a state insulated from the fuel cells FC1 to FC4. Is output. In this embodiment, Hall element type magnetic sensors are used for the current sensors 241 to 244. The voltage transmission circuit 230 having such a configuration can perform the minimum value detection operation based on the same principle as in the first embodiment. As a result, the same effects as in the first embodiment can be obtained.

  The above-described current sensors 241 to 244 only have to have the above-described functions. For example, various magnetic sensors and current sensors such as a mag-amp type and a magnetic multivibrator type can be used. Note that a current transformer can also be used as the current sensors 241 to 244 if the fuel cells FC1 to FC4 need only be output when there is a sudden change in output.

D. Fourth embodiment:
A voltage monitoring system 320 as a fourth embodiment of the present invention will be described with reference to FIG. In FIG. 4, the same reference numerals as those in FIG. 1 are assigned to the same configurations as those in the first embodiment. Hereinafter, the voltage monitoring system 320 will be described only with respect to differences from the first embodiment, and description of common points will be omitted. As illustrated, the voltage monitoring system 320 according to the fourth embodiment includes switch circuits 311 to 314, a transformer 330, a minimum value detection circuit 350, and an output circuit 70.

  Each of the switch circuits 311 to 314 is basically the same circuit. When viewed from the fuel cells FC1 to FC4, capacitors C301 to C304 are interposed between the anode and the cathode, and the switches SW321 to SW321 are parallel to this. SW324 and windings 341 to 344 are connected in series. In this way, one switch circuit 311 to 314 is provided for each of the fuel cells FC1 to FC4 constituting the fuel cell stack FC.

  The switches SW321 to SW324 are relays that receive signals from a CPU (not shown) and switch ON / OFF of the conduction state between the anode side and the cathode side of the fuel cells FC1 to FC4. The transformer 330 is a transformer having the windings 341 to 344 as input side windings and the winding 346 as output side windings. When the switches SW321 to SW324 are all OFF, the capacitors C301 to C304 are charged by the fuel cells FC1 to FC4. The capacitors C301 to C304 do not consume power once they are charged. In this state, when any one of the switches SW321 to SW324 is turned on, the power stored in the capacitor corresponding to the switch that is turned on among the capacitors C301 to C304 is transferred to the input side winding of the transformer 330. Flows in. Since the change in current is extremely large, an output voltage corresponding to the input voltage appears at both ends of the winding 346 that is the output side winding of the transformer 330 according to the mutual inductance between the input and output of the transformer 330. If any one of the switches SW321 to SW324 is turned on, current flows also from the corresponding fuel cells FC1 to FC4. However, since the fuel cells FC1 to FC4 have internal resistance, a large rush occurs in a short time. Current cannot flow. For this reason, inrush current is passed through the windings 341 to 344 which are the input side windings of the transformer 330 using the capacitors C301 to C304. Such capacitors C301 to C304 are so-called speed-up capacitors. The switch circuits 311 to 314 and the transformer 330 correspond to the voltage transmission circuit 30 of the first embodiment.

  The minimum value detection circuit 350 is a circuit common to the fuel cells FC1 to FC4, and includes capacitors C351 and C352, a diode D353, and a switch SW354. One end of the winding 346 is connected to the input terminal of the buffer circuit 71 constituting the output circuit 70, the other end is connected to the ground, and a capacitor C351 and a capacitor C352 are connected to both ends of the winding 346. Each is installed in parallel. In addition, a diode D353 and a switch SW354 are interposed between the capacitor C351 and the capacitor C352. The diode D353 is provided in the reverse direction when viewed from the transformer 330 side.

  The operation of the minimum value detection circuit 350 will be described. First, a predetermined initial voltage V0 is applied to the capacitor C352 in advance with the switch SW354 turned off. Here, the initial voltage V0 is a voltage that is assumed to be surely higher than the minimum value of the voltages of the fuel cells FC1 to FC4. In this embodiment, a configuration is adopted in which application is performed from a positive power source (not shown).

  Then, the switch SW321 of the switch circuit 311 is turned on with the switches SW322 to SW324 of the switch circuits 312 to 314 being turned off. Then, the voltage V1 of the fuel cell FC1 is input to the transformer 330, and the output V1 is held by the capacitor C351. Thereafter, the switch SW354 is turned on. Then, if the voltage V1 is equal to or higher than the voltage V0, the diode D353 is reverse-biased, so that the capacitor C352 still holds V0. On the other hand, if the voltage V1 is smaller than the voltage V0, the diode D353 is forward-biased, and the charges of the capacitor C351 and the capacitor C352 are leveled through the diode D353. By repeating ON / OFF of the switch SW321 in such a state, when the voltage V1 is smaller than the voltage V0, the voltage V1 is finally held in the capacitor C352. Note that since a counter electromotive force is generated when the switch SW321 is turned off, it is necessary to turn off the switch SW354 in advance each time.

  If such an operation is also performed for the switch circuits 312 to 314, the minimum voltage Vmin that is the minimum value of the voltages of the fuel cells FC1 to FC4 is finally held in the capacitor C352. The minimum voltage Vmin thus detected is output to the output circuit 70. The configuration of the output circuit 70 is the same as that of the first embodiment.

  In the voltage monitoring system 320 having such a configuration, the diode D353 that constitutes the minimum value detection circuit 350 and the diode D72 that constitutes the output circuit 70 are provided in opposite directions. Can play. Further, since the input stage and the output stage of the transformer 330 are insulated from each other, the detection result of the minimum value detection circuit 350 can be outputted to the low pressure side while being insulated from the high pressure fuel cell stack FC side by the transformer 330. Can increase the sex.

E. Example 5:
A voltage monitoring system 420 as a fifth embodiment of the present invention will be described with reference to FIG. The voltage monitoring system 420 is different from the first embodiment in that the maximum value of the output voltage of the fuel cells FC1 to FC4 is detected. In FIG. 5, the same components as those in the first embodiment are denoted by the same reference numerals as those in FIG. Hereinafter, the voltage monitoring system 420 will be described only with respect to differences from the first embodiment, and description of common points will be omitted. The voltage monitoring system 420 includes a voltage transmission circuit 30, a maximum value detection circuit 450, and an output circuit 470, as illustrated. The configuration of the voltage transmission circuit 30 is the same as that of the first embodiment.

  The maximum value detection circuit 450 is a circuit that detects the maximum value among the outputs of the fuel cells FC1 to FC4, and includes diodes D451 to D454, a capacitor C456, and a resistor R458. All outputs of the operational amplifiers 31 to 34 of the voltage transmission circuit 30 are connected to forward diodes D451 to D454. A capacitor C456 having one end connected to the ground is connected to the outputs of the operational amplifiers 31 to 34. The resistor R458 is a so-called pull-down resistor, and discharges the electric charge accumulated in the capacitor C456. If there is no output from the operational amplifiers 31 to 34, the voltage at the terminal TE2 of the capacitor C456 is made zero.

The maximum value detection operation of the maximum value detection circuit 450 will be described. The maximum value detection operation is an operation for detecting the maximum value among the voltages of the fuel cells FC1 to FC4. In order to simplify the description, the following operation will be described assuming that the voltage drop of the diodes D451 to D454 is 0 volts.
(1) When the operational amplifiers 31 to 34 are operated at a predetermined timing, and the output voltages of the fuel cells FC1 to FC4 are detected and output by the operational amplifiers 31 to 34 that are differential amplifiers, they are passed through the diodes D451 to D454. Current flows in and the voltage at the terminal TE2 of the capacitor C456 increases. This operation continues until the voltage at the terminal TE2 reaches the highest voltage Vmax1 among the outputs of the connected operational amplifiers 31 to 34. When the voltage at the terminal TE2 coincides with the voltage Vmax1, since the other operational amplifiers 31 to 34 (op-amps other than the operational amplifier that outputs the voltage Vmax1) are lower than the voltage at the terminal TE2, a current flows through the diodes D451 to D454. There is nothing.

  (2) If the voltage of any one of the fuel cells further rises and the highest voltage among the outputs of the connected operational amplifiers 31 to 34 becomes Vmax2 (Vmax1 <Vmax2), the voltage from the terminal TE2 of the capacitor C456 Current flows from the operational amplifiers 31 to 34 that output a higher voltage via the diodes D451 to D454, and the voltage at the terminal TE2 of the capacitor C456 increases. This operation continues until the voltage at the terminal TE2 becomes the voltage Vmax2.

  (3) Conversely, when the voltage of the fuel cell that has been the maximum voltage until then becomes low and the highest voltage among the outputs of the connected operational amplifiers 31 to 34 becomes Vmax3 (Vmax1> Vmax3), the capacitor C456 Since the voltage at the terminal TE2 is lower than the outputs of the operational amplifiers 31 to 34, no current flows from the operational amplifiers 31 to 34 to the capacitor C456. As a result, the capacitor C456 is discharged through the resistor R458 until the voltage changes from Vmax1 to Vmax3.

  Actually, in any of the cases (1) to (3) described above, since the forward voltage Vf exists in the diode, the voltage at the terminal TE2 is higher than the maximum value of the output voltage of the operational amplifiers 31 to 34. Although the voltage decreases by the voltage Vf, the forward voltage Vf of each diode is known, so that it is easy to detect the maximum voltage of each of the fuel cells FC1 to FC4 by detecting the voltage at the terminal TE2. In this way, the capacitor C456 holds the maximum output of the operational amplifiers 31 to 34, that is, the voltage corresponding to the maximum voltage of the fuel cells FC1 to FC4. Here, diodes D451 to D454 having the same temperature dependence characteristic of the forward voltage Vf are used for the same reason as in the first embodiment.

  The maximum value held by the capacitor C456 of the maximum value detection circuit 450 in this way is output to the output circuit 470. The output circuit 470 includes a buffer circuit 71 and a diode D472 as shown in FIG. The difference from the output circuit 70 of the first embodiment is that the direction of the diode D472 is provided in the opposite direction to the diode D72 of the first embodiment. That is, the diode D472 is provided in the opposite direction so that the current flow direction when viewed from the voltage transmission circuit 30 side is reversed as compared with the diodes D451 to D454 constituting the maximum value detection circuit 450. Yes. In the present embodiment, a diode D472 having a temperature dependent characteristic of the forward voltage Vf substantially equal to that of the diodes D451 to D454 is used.

  In the voltage monitoring system 420 having such a configuration, the diodes D451 to D454 that constitute the maximum value detection circuit 450 and the diode D472 that constitutes the output circuit 470 are provided in opposite directions, and thus the same as in the first embodiment. There is an effect. Also in the fifth embodiment, the configuration of the second embodiment can be applied.

  Thus, the voltage monitoring system 20 of the present invention is not limited to the one that detects the minimum value of the fuel cells FC1 to FC4, but can be applied to one that detects the maximum value. The configuration for detecting the maximum value is not limited to the above example. For example, the configuration of the voltage transmission circuit 230 shown as the third embodiment may be applied instead of the voltage transmission circuit 30 of the fifth embodiment. . Alternatively, in the voltage monitoring system 320 shown as the fourth embodiment, the directions of the diode D353 and the diode D72 may be provided in opposite directions. The voltage monitoring system 20 may be configured to detect both the maximum value and the minimum value. In this case, for example, the input of the maximum value detection circuit 450 shown in the fifth embodiment is connected between the operational amplifiers 31 to 34 of the voltage monitoring system 20 shown in the first embodiment and the diodes D51 to D54. Alternatively, the output circuit 470 may be connected to the output stage of the maximum value detection circuit 450 so that the maximum value and the minimum value are output to the MCU at the same time.

F. Modifications:
A modification of the above embodiment will be described.
F-1. Modification 1:
In the above-described embodiment, the diode provided in the minimum value detection circuit or the maximum value detection circuit (for example, the diodes D51 to D54 in the first example) and the diode provided in the output circuit (for example, the diode in the first example) D72) has a configuration in which the temperature dependence characteristics of the forward voltage Vf are substantially equal, but it is not necessarily required to have a configuration in which the temperature dependence characteristics are substantially equal. For example, in the first embodiment, the minimum voltage of the fuel cells FC1 to FC4 is Vmin, the forward voltage Vf at the ambient temperature T of the diodes D51 to D54 and the diode D72 is Vf0, the forward voltage Vf of the diodes D51 to D54 is Vf0 + α, and the diode D72. When the forward voltage Vf of the diode D72 is Vf0 + β (α, β are the amount of change in the forward voltage Vf depending on the change in the environmental temperature), the output Vout of the diode D72 is expressed as Vmin + (α−β) by the following equation (1). Therefore, if the changes α and β are in a relationship satisfying −α <α−β <α, that is, 2α <β <0 or 0 <β <2α, compared with the configuration without the diode D72. This is because the temperature dependency of the diodes D51 to D54 is reduced. Normally, it is unlikely that the amount of change in the forward voltage Vf depending on the temperature of the diode will cause a difference of more than twice, so the diodes D51 to D54 and the diode D72 are selected without considering the temperature dependence characteristics. However, α and β satisfy the relationship of the following equation (1). Further, in the following equation (1), the forward voltages Vf at the environmental temperature T of the diodes D51 to D54 and the diode D72 are Vf0 equal to each other, but even if these values are different, the difference is known. It is easy to detect the minimum voltage of the fuel cells FC1 to FC4.
Vout = Vmin + (Vf0 + α) − (Vf0 + β)
= Vmin + (α−β) (1)

F-2. Modification 2:
In the above-described embodiment, the buffer circuit 71 is configured to output the input voltage itself, that is, configured to have a gain of 1. However, the configuration is not necessarily limited to this configuration. For example, when the temperature dependence characteristics of the forward voltage Vf of the diodes D51 to D54 and the diode D72 are substantially equal and the fluctuation amounts α and β described in the first modification satisfy the relationship of 1.5α = β, the buffer circuit 71 If the gain is 1.5, as in the first embodiment, fluctuations in the forward voltage Vf due to temperature dependence can be almost canceled out between the diodes D51 to D54 and the diode D72. Of course, the deterioration of the voltage detection accuracy due to the temperature dependency of the diode can be suppressed to a certain extent without matching the relationship between the fluctuation amounts α and β and the gain of the buffer circuit 71 in this way. Therefore, the buffer circuit 71 is not limited to the voltage follower, and may be any circuit as long as the input impedance is high enough that the output of the minimum value detection circuit or the maximum value output circuit is not affected by the output stage side. Or a collector grounding circuit.

  In the third embodiment described above, the transformer 173 has a configuration in which the number of turns of the input-side winding and the number of turns of the output-side winding are the same. However, the configuration is not limited thereto. Similar to the buffer circuit 71 described above, if the relationship between the fluctuation amounts α and β and the turn ratio are matched, almost all of the fluctuations in the forward voltage Vf due to the temperature dependence are eliminated by the diodes D51 to D54 and the diode D72. This is because the deterioration of the voltage detection accuracy due to the temperature dependence of the diode can be suppressed to a certain extent without achieving such matching.

F-3. Modification 3:
In the above-described embodiment, all the fuel cells FC1 to FC4 constituting the fuel cell stack FC are connected to one voltage monitoring system (here, one set of voltage transmission circuit, minimum value (or maximum value) detection circuit, and output circuit). In the case where there are a large number of fuel cells constituting the fuel cell stack FC, a large number of fuel cells are divided into a predetermined number of groups, and a voltage monitoring system is provided for each group. Thus, the minimum value or the maximum value for each group may be output to the MCU or the like. In such a case, as described in the second embodiment, if the winding on the output side of the transformer 173 is connected to a ground such as an MCU, the output of a plurality of groups can be received by one MCU. Alternatively, by collecting outputs from a plurality of voltage monitoring systems provided for each group and further providing a voltage monitoring system that outputs a minimum value and a maximum value, the voltage monitoring system is provided in multiple stages, and the fuel cell The minimum value and maximum value of the entire stack FC may be output to the MCU or the like.

  Thus, when the number of fuel cells constituting the fuel cell stack FC is large, the circuit board of the voltage monitoring system becomes large, and the environmental temperature distribution may be biased depending on the location on the circuit board. In such a case, if temperature compensation is performed using a temperature sensor, it is necessary to provide temperature sensors at a plurality of locations, resulting in an increase in cost. On the other hand, according to the voltage monitoring system of the present invention, if the diode that constitutes the minimum value detection circuit and the diode that constitutes the output circuit are provided close to each other in the above-mentioned group unit, the environmental temperature distribution is biased. It is possible to cope with this, and the cost can be reduced.

  As mentioned above, although embodiment of this invention was described, elements other than the element described in the independent claim among the components of this invention in embodiment mentioned above are additional elements, and are suitably abbreviate | omitted or combined. Is possible. In addition, the present invention is not limited to such an embodiment, and it is needless to say that the present invention can be implemented in various modes without departing from the gist of the present invention. For example, the present invention is not limited to the polymer electrolyte fuel cell shown in the embodiments, but can be applied to various fuel cells such as a direct methanol fuel cell and a phosphoric acid fuel cell. Alternatively, the circuit configuration in the voltage monitoring system of the present invention is not limited to the above-described embodiment, and can be realized by replacing with an equivalent circuit having an equivalent function. The present invention can also be realized as a method for suppressing deterioration in voltage detection accuracy due to temperature dependence of components in a voltage monitoring system.

20, 120, 320, 420 ... voltage monitoring system 30, 230 ... voltage transmission circuit 31-34 ... operational amplifier 36 ... power supply 50, 350 ... minimum value detection circuit 57 ... power supply 70, 170, 470 ... output circuit 71 ... buffer circuit 173 ... Transformers 241 to 244 ... Current sensors 311 to 314 ... Switch circuits 330 ... Transformers 341 to 344,346 ... Windings 450 ... Maximum value detection circuits D51 to D54, D72, D353, D451 to D454, D472 ... Diodes SW174, SW321 SW324, SW354 ... switch R58, R231-R234, R458 ... resistor C56, C301-C304, C351, C352, C456 ... capacitor FC ... fuel cell stack FC1-FC4 ... fuel cells TE1, TE2 ... terminals

Claims (5)

A voltage monitoring system for a fuel cell stack in which a plurality of fuel cells are stacked,
A voltage transmission means provided for each of the plurality of fuel cells, each voltage of the fuel cell being individually taken out from the fuel cell and output;
Detecting means for collecting the voltages of the plurality of fuel cells output by the voltage transmission means, and detecting at least one of the minimum value and the maximum value of the output voltages via a first diode;
A voltage monitoring system comprising: output means for outputting a detection result of the detection means via a second diode provided in a direction opposite to the first diode.   The voltage monitoring system according to claim 1, wherein the first diode and the second diode have substantially the same temperature dependency characteristic of a forward voltage.   2. The output means according to claim 1, further comprising a buffer circuit interposed between the detection means and the second diode and suppressing an influence on the detection means from the output stage side of the detection means. 2. The voltage monitoring system according to 2. The voltage monitoring system according to claim 3,
The output means includes
A transformer that is interposed between the buffer circuit and the second diode and inputs the detection result via the buffer circuit;
A voltage monitoring system comprising: a switch circuit connected to a winding on the input side of the transformer and outputting the detection result to the transformer as an AC voltage. A voltage monitoring system according to any one of claims 1 to 4,
The voltage transmission means is a differential amplifier connected to the anode side and the cathode side of the plurality of fuel cells,
The voltage monitoring system, wherein the detection means includes the first diode provided in the same direction for each output of the differential amplifier, and a capacitor interposed between the first diode and the ground.

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