JP2008243398A - Fuel cell system, electronic device, and image forming device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel cell system in which a problem that a fuel cell stack is damaged due to lowering of an output voltage of a fuel cell stack when a generated power of the fuel cell stack is small and a necessary power required by an electronic device of a load is large can be solved and a necessary power can be stably supplied to the electronic device of a load. <P>SOLUTION: The fuel cell system is comprised of a fuel cell unit provided with a unit cell or a lamination of a plurality of the unit cells, a storing battery unit which is connected in parallel with the fuel cell stack and supplies power to a load unit, an output voltage detecting means to detect the output voltage of the fuel cell stack, and a controlling part to prevent and control lowering of the output voltage based on the detected result. When the output voltage of the fuel cell stack detected by the output voltage detecting means is higher than a predetermined voltage, the output voltage of the fuel cell stack is supplied to the load unit as it is, and when the detected voltage is lower, a power taken out from the fuel cell stack is controlled so that the predetermined voltage can be maintained. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a fuel cell system, an electronic apparatus, and an image forming apparatus, and more particularly to a control method for preventing a decrease in fuel cell output voltage of a power supply unit such as a copying machine or a printer, particularly a power supply unit using a fuel cell. .

  In recent years, with the advancement of electronic technology, portable electronic devices such as mobile phones, notebook PCs, mini PCs (= pocket PCs), portable audio devices, and PDAs are rapidly spreading. These portable electronic devices occupy a large number of systems that operate using a secondary battery as a power source, and these systems are accelerating their functions from the viewpoint of user convenience. As these systems become more sophisticated in the market, the power consumption of the system tends to increase. Furthermore, since the portable electronic device is required to be used for a long time, the capacity of the secondary battery as a power source is increasing. In such a situation, the fuel cell is attracting attention.

This fuel cell has a structure in which a fuel cell using liquid as a fuel has a structure in which an anode and a cathode are sandwiched between polymer electrolytes, and generates electricity by supplying fuel to the anode and supplying air to the cathode. It is. In this fuel cell, if the concentration of the fuel is too high, there is a problem that a “crossover phenomenon” occurs in which the fuel that has not reacted at the anode passes through the polymer electrolyte membrane and reacts at the cathode. Therefore, the concentration of diluted methanol needs to be about several percent. While generating several percent of diluted methanol, it is necessary to continue supplying fuel cells. However, this would make the fuel container very large. Therefore, as described in Patent Document 1, high-concentration (for example, 100%) fuel is put in the fuel container, an intermediate container is provided, and the intermediate container is diluted to a concentration of several percent. To supply fuel cells. The fuel diluted to several percent from the intermediate container is circulated to the fuel cells by a pump during power generation. Further, as in Patent Document 1, the intermediate container monitors the fuel concentration with a fuel concentration sensor (not shown), and a controller (not shown) supplies water with a pump when the concentration is higher than a preset value. On the other hand, when the concentration is low, the fuel is replenished with a pump so that the concentration is always constant.
JP 2004-227805 A

  However, even if the fuel concentration is increased by replenishing the fuel, there is a response delay of the fuel concentration sensor, so that overshoot or undershoot of the fuel concentration occurs. Also, since there is no cheap and small alcohol sensor, pay attention to the close relationship between the cell stack temperature and the power that can be output. By controlling it to be constant, the power that can be output without using an alcohol sensor can be controlled to be constant on average, but there is a time delay for the temperature to rise after refueling. After all, overshoot and undershoot of fuel concentration occur. For this reason, the output power fluctuates during overshoot or undershoot of the fuel concentration. In addition, because power is generated by a chemical reaction, the output power is large when the temperature during operation is high, the output power is small when the temperature is low, and the power required by the electronic equipment that is generally a load is not constant. For example, when the motor is started, a large amount of electric power is required.

  The present invention solves the problem that the output voltage of the fuel cell stack decreases and the fuel cell stack is damaged when the electric power required by the electronic device as a load is large when the generated power of the fuel cell stack is low In addition, an object of the present invention is to provide a fuel cell system, an electronic device, and an image forming apparatus that can stably supply necessary power to an electronic device as a load.

  In order to solve the above problems, the fuel cell system of the present invention has an ion conductive solid polymer electrolyte membrane sandwiched between two electrodes, a negative electrode and a positive electrode, and a low concentration liquid from a circulation tank is provided on the negative electrode. A fuel cell unit having a single cell in which fuel is circulated and an oxidant gas is supplied to the positive electrode or a cell stack in which two or more such single cells are stacked, and a load device connected in parallel to the fuel cell stack A storage battery for supplying power to the battery, output voltage detection means for detecting the output voltage of the fuel cell stack, and a control unit for performing output voltage drop prevention control based on the detection result. In the fuel cell system of the present invention, when the output voltage of the fuel cell stack detected by the output voltage detection means is higher than a predetermined voltage, the output voltage of the fuel cell stack is supplied to the load device as it is, When it is low, the electric power taken out from the fuel cell stack is controlled so as to maintain a predetermined voltage. Therefore, it is possible to prevent the fuel cell stack from being damaged due to a decrease in the output voltage of the fuel cell stack when the electric power required by the electronic device as a load is large when the generated power of the fuel cell stack is small. it can.

  The fuel cell system of the present invention will be described with reference to FIG. A resistance voltage dividing means connected in parallel to the fuel cell stack to resistively divide the output voltage of the fuel cell stack, and a current extracted from the cell stack according to the voltage after resistance division by the resistance voltage dividing means is controlled. An output voltage drop prevention control means comprising a circuit is provided. The output voltage drop prevention control is performed as follows. When the output voltage of the fuel cell stack detected by the output voltage detection means is about to fall below a predetermined voltage due to an increase in load, the output voltage drop prevention control means operates in a direction to limit the power taken out from the fuel cell stack. This prevents the output voltage from being lowered and maintains a predetermined voltage. Therefore, the output voltage of the fuel cell stack is prevented from being lowered and damaging the fuel cell stack even if the power required by the electronic equipment as a load increases when the power generated by the fuel cell stack is insufficient it can.

  Furthermore, the output voltage drop prevention control means is preferably analog control or digital control.

  Further, it is preferable to switch the output voltage drop prevention control means to analog control or digital control in accordance with the mode for maintaining the output voltage of the fuel cell stack.

  Further, a temperature sensor for detecting the temperature of the fuel cell stack is provided, and when the temperature of the fuel cell stack detected by the temperature sensor is lower than a predetermined temperature, the output voltage drop prevention control means is analog control, and when it is higher Digital control. Accordingly, it is possible to prevent damage to the fuel cell stack due to a decrease in the output voltage of the fuel cell stack when the temperature of the fuel cell stack becomes low.

  Also, a temperature sensor that detects the temperature of the control element that constitutes the output voltage drop prevention control means is provided, and when the temperature of the control element detected by the temperature sensor is lower than a predetermined temperature, the output voltage drop prevention control means is controlled by analog control. When it is high, digital control can be used to prevent destruction of the control element, and the necessary power can be stably supplied to the electronic device.

  Furthermore, when the state where the output voltage of the fuel cell stack is lower than a predetermined voltage continues for a certain time or longer, a connection means for disconnecting the fuel cell stack and the capacitor from the load device is provided as an abnormal state, and when the abnormal state is reached By detaching the fuel cell stack and the capacitor from the load device by means, it is possible to prevent the fuel cell stack and the capacitor from being damaged, and to avoid wasting unnecessary fuel.

  Another electronic device according to another invention is characterized by having the fuel cell system. Therefore, it is possible to provide an electronic device capable of realizing stable driving by supplying stable power.

  Furthermore, an image forming apparatus as another invention is characterized by having the fuel cell system. Therefore, a stable image forming operation can be realized by supplying stable power, and a highly reliable image forming apparatus can be provided.

  According to the fuel cell system of the present invention, when the output voltage of the fuel cell stack detected by the output voltage detection means is higher than a predetermined voltage, the output voltage of the fuel cell stack is supplied to the load device and is low. In this case, power supply to the load device is controlled so as to maintain a predetermined voltage. Therefore, the output voltage of the fuel cell stack is reduced to prevent the fuel cell stack from being damaged even if the electric power required by the electronic device as a load increases when the generated power of the fuel cell stack is low. be able to.

  In the fuel cell system of the present invention, an active direct methanol fuel cell (DMFC) will be described as an example. However, a fuel cell using a liquid such as ethanol or propanol as a fuel may be used. Further, the present invention is not limited to an active direct methanol fuel cell (DMFC), and may be a passive direct methanol fuel cell (DMFC).

  FIG. 1 is a block diagram showing the configuration of a fuel cell unit in the fuel cell system of the present invention. The fuel cell unit 100 shown in the figure includes a fuel tank 101 in which high-concentration methanol is stored, a fuel pump 102, a circulation tank 103, a fuel supply path 104, and methanol diluted in the circulation tank 103 in a cell stack. 105, the circulation pump 107 for pumping to the anode 106 side, the electrolyte membrane 108 and the cathode 109 of the cell stack 105, the blower 110, the discharge path 111, the condenser 112, and the fan 113 for sending air to the condenser 112, A water tank 114, a water pump 115, a temperature sensor 116 for detecting the temperature of the cell stack 105, a water level sensor 117 for monitoring the amount of diluted methanol in the circulation tank 103, and a control unit 118 for performing overall control. It is comprised including. Although the cell stack 105 is a single cell, since the output voltage of a single cell is less than 1 v, the cell stack 105 is actually used as a cell stack in which a plurality of cells are connected in series.

  The cell stack 105 includes an anode (fuel electrode) 106 having a catalyst for electrochemical oxidation of methanol (methanol oxidation electrode catalyst) and a cathode having a catalyst for selective electrochemical reduction of oxygen (oxygen reduction electrode catalyst). An electrolyte membrane 108 is sandwiched between the (air electrode) 109 and a conductive separator provided with a groove for flowing fuel outside the anode 106 and air is allowed to flow outside the cathode 109. It has a conductive separator provided with a groove. Further, methanol is stored in the fuel tank 101, and the methanol in the fuel tank 101 is sent to the circulation tank 103 by a fuel pump 102 connected to the fuel tank 101. In the circulation tank 103, methanol sent from the fuel tank 101 by the fuel pump 102 and water collected from the cell stack 105 are mixed. In order to supply the methanol aqueous solution in the circulation tank 103 to the anode 106 of the cell stack 105, a circulation pump 107 is disposed in the fuel supply path 104 connecting the circulation tank 103 and the anode 106.

  In the fuel cell unit 100 having such a configuration, in the cell stack 105 into which methanol as fuel and air are sent, electric power is generated between the anode 106 and the cathode 109, and carbon dioxide is present on the anode 106 side. Water is generated on the cathode 109 side. Carbon dioxide generated on the anode 106 side and water generated on the cathode 109 side are returned to the circulation tank 103. The water generated on the cathode 109 side returned to the circulation tank 103 is partly water vapor because of the high temperature inside the fuel cell, but when passing through the agglomerator 112, a fan is used in the condenser 112. The air is blown at 113 and cooled, and most of the air is separated into water and air and returned to the water tank 114. On the other hand, a part of the water vapor that has not been converted to water in the aggregator 112 is discharged from the circulation tank 103 together with carbon dioxide, and is discharged through the water tank 114. In this way, the aqueous methanol solution is supplied to the anode 106 of the cell stack 105 by the circulation pump 107, and the air is supplied to the cathode 109 by the blower 110, thereby generating power in the cell stack 105.

  Further, the amount of methanol diluted in the circulation tank 103 is monitored by the water level sensor 117, and when the amount of methanol diluted in the circulation tank 103 decreases, the water pump 115 operates and water is supplied from the water tank 114 to the circulation tank. 103. Further, the fuel concentration is monitored by a fuel concentration sensor (not shown), and the control unit 118 supplies water with the water pump 115 when the concentration is higher than a preset value, and conversely when the concentration is low. The fuel is replenished by the fuel pump 102 and is controlled so that the concentration is always constant.

  Further, since methanol is consumed by power generation and the concentration of diluted methanol gradually decreases, a methanol concentration sensor (not shown) is provided in the circulation tank 103 or in the middle of the circulation path of diluted methanol. Measure the methanol concentration regularly (for example, every minute), and when the concentration is lower than the target concentration, replenish with high-concentration methanol aqueous solution to keep the diluted methanol concentration constant and generate electric power that can generate electricity Is controlled to an average constant value.

  However, the output power of a fuel cell using liquid as fuel is very poor in response. The electric power required by the electronic device as a load is not constant. For example, even if a large electric power is suddenly required at the moment when the motor starts rotating, the output electric power of the fuel cell cannot follow. Further, since the fuel cell generates power by a chemical reaction, the output power is large when the temperature of the operating fuel cell is high, and the output power is small when the temperature is low. Even if the concentration is increased by replenishment, there is a response delay of each sensor, so that overshoot or undershoot of the fuel concentration occurs. Also, since there is no cheap and small alcohol sensor, pay attention to the close relationship between the cell stack temperature and the power that can be output. By controlling so that is constant, the output power can be controlled to be constant on average without using an alcohol sensor, but there is a time delay for the temperature to rise after refueling. Therefore, fuel concentration overshoot and undershoot also occur. For this reason, the output power fluctuates during overshoot or undershoot of the fuel concentration.

  In the present invention, as described above, the output voltage of the fuel cell stack is lowered and the fuel cell stack is damaged when the electric power required by the electronic device as the load is large when the generated power of the fuel cell stack is small. Therefore, a fuel cell system capable of supplying necessary electric power to an electronic device serving as a load is realized. In particular, when the temperature of the fuel cell stack is low, the generated power is extremely small. Therefore, if a large amount of electric power is taken out at this time, the output voltage of the fuel cell stack immediately decreases. It is desirable in terms of life to operate in a state where the voltage of each cell constituting the fuel cell stack is as high as possible. However, since power cannot be taken out so much, it is a compromise voltage considering the balance between the two. In addition, since the voltage of each cell varies, if the power is taken out too much, a cell with a low voltage will be applied with a voltage of the opposite polarity to the cell electrode, causing damage or significantly shortening the service life. Resulting in. The present invention for solving these problems will be described below with each embodiment.

  FIG. 2 is a schematic diagram showing the configuration of the fuel cell system according to the first embodiment of the present invention. The fuel cell system 10 of the present embodiment shown in the figure includes a fuel cell stack 11, a battery 12 connected in parallel to the fuel cell stack 11 and supplying power to the load device 200, and the fuel cell stack 11 Is mainly provided with a voltage drop prevention control circuit 13 for detecting the output voltage and preventing the drop of the output voltage. The output voltage of the fuel cell stack 11 does not drop below a predetermined voltage by taking out the output current from the fuel cell stack 11 via the voltage drop prevention control circuit 13 that performs the following control. In this way, the fuel cell stack is prevented from being damaged.

  Here, an outline of a method for limiting the electric power that passes when the output current from the fuel cell stack 11 is taken out via the control unit 118 of FIG. 1 will be broadly divided into two methods. . That is, it is an analog control method and a digital control method. The analog control method is electrically the same as taking out via a variable resistor. When the output voltage of the fuel cell stack 11 is lowered, the resistance value is increased, and when the output voltage is increased, the resistance value is decreased so that the output voltage of the fuel cell stack 11 does not fall below a certain value. At this time, in the resistor, electric power obtained by multiplying the square of the flowing current and the resistance value is lost as heat.

  On the other hand, the digital control method is electrically the same as taking out via a switch that is turned ON / OFF at high speed. That is, if the output voltage of the fuel cell stack 11 decreases, the ON / OFF time ratio increases so that the OFF time increases. If the output voltage increases, the ON / OFF time ratio increases. In this way, the output voltage of the fuel cell stack 11 is not lowered below a certain value. At this time, theoretically, no power loss occurs in the ON / OFF control.

  Next, operations common to the analog control method and the digital control method will be described below. Specifically, the output voltage of the fuel cell stack 11 is measured. If the voltage is higher than a predetermined voltage, the output power of the fuel cell stack 11 is used as it is, and the control unit 118 of FIG. Is supplied as power for driving the load device 200. If the measured output voltage of the fuel cell stack 11 is lower than a predetermined voltage, the output power of the fuel cell stack 11 is output until the output voltage of the fuel cell stack 11 reaches a predetermined voltage. 1 is supplied as a part of electric power for driving the control unit 118 of FIG. 1 and the load device 200 of FIG. 2 by limiting the power when passing through the control unit 118 of FIG. The voltage is prevented from dropping below a predetermined voltage. Although only a part of the electric power required by the control unit 118 in FIG. 1 and the load device 200 in FIG. 2 is supplied from the fuel cell stack 11, the shortage from the battery 12, such as a nickel metal hydride battery, a lithium ion battery, or a supercapacitor. Therefore, there is no problem in the operation of the control unit 118 and the load device 200.

  Note that the diode 14 in FIG. 2 causes the electric current in the fuel cell stack 11 if the current flows from the capacitor 12 to the fuel cell stack 11 when the power generation voltage of the fuel cell stack 11 is lower than the voltage of the capacitor. The decomposition not only generates hydrogen and oxygen, but also causes deterioration and destruction of the characteristics of the fuel cell stack 11, so that the fuel cell stack 11 can prevent the occurrence from the fuel cell stack 11 to the control unit 118 of FIG. 1 and the load device 200 of FIG. Continue to supply power. In addition, when the power generation voltage of the fuel cell stack 11 is higher than the voltage of the capacitor 12, the diode 15 continues to flow an unlimited charging current from the fuel cell stack 11 to the capacitor 12, the capacitor 12 is overcharged, and the capacitor 12 While the battery cell stack 11 is not broken, when the power cannot be supplied from the fuel cell stack 11 to the control unit 118 of FIG. 1 or the load device 200 of FIG. 2, the power is supplied from the battery 12 to the control unit 118 of FIG. 1 or the load device 200 of FIG. Continue to supply.

  Next, in the analog control method, as shown in FIG. 2, the output voltage of the fuel cell stack 11 is divided by two series resistors R1 and R2 inserted between the point A and the ground (GND). , Input to the + input terminal of the amplifier 16. The battery 12, such as a nickel metal hydride battery or a lithium ion battery, is connected in parallel to the input of the DC-DC converter 17. The output of the DC-DC converter 17 supplies power for driving the control unit 118 of FIG. 1 and the load device 200 of FIG. In addition, the voltage is divided by two series resistors R3 and R4 inserted between the grounds and input to the negative input terminal of the amplifier 16.

  In addition, since it is easier to understand by giving a specific number, it will be described below using a number, but is not limited to this number. For example, if the voltage of the capacitor 12 is 11V, the forward voltage drop of the diodes 14 and 14 is 0V, the output voltage of the DC-DC converter 17 is 5V, and the series resistors R3 and R4 are 2KΩ and 3KΩ, respectively, the −input terminal of the amplifier 16 3V is input to. Further, if the series resistors R1 and R2 are set to 7 KΩ and 3 KΩ, respectively, the same voltage as the −input terminal, 3 V is input to the + input terminal of the amplifier 16 when the voltage at the point A is 10 V. For example, even if power is supplied from the fuel cell stack 11 to the control unit, load device, etc., when there is a margin in power and the voltage at the point A is 12V, 3.6V is input to the + input terminal of the amplifier 16 To do. Regardless of the power generation status of the fuel cell stack 11, 3V is always input to the negative input terminal of the amplifier 16, so that the output of the amplifier 16 becomes H, the output of the inverter 18 becomes L, and the FET 19 is completely turned on. Therefore, the fuel cell stack 11 supplies all the electric power necessary for the control unit, the load device, and the like, which is electrically the same as that directly connected to the input of the DC-DC converter 17. At this time, since the voltage at the point A is 12V and the voltage of the battery 12 is 11V, when a charging circuit (not shown) is connected, a charging current flows into the battery 12, but no discharging current flows.

  As described above, during operation, if a large current instantaneously flows due to a temporary short circuit of the load or start-up of the motor, etc., or the voltage at point A is decreased due to a decrease in operating temperature or a control error in driving operation. The operation when the voltage drops is as follows. For example, when the voltage at the point A drops to 9V, 2.7V is input to the + input terminal of the amplifier 16. Since 3V is always input to the negative input terminal of the amplifier 16 regardless of the power generation state of the fuel cell stack 11, the output of the amplifier 16 becomes L, the output of the inverter 18 becomes H, and the FET 19 is completely set. Therefore, the output terminal of the fuel cell stack is completely disconnected from other circuits. When the output terminal of the fuel cell stack is electrically disconnected, no current is taken out from the fuel cell stack 11, so that the voltage at the point A starts to increase from 9V, and the voltage at the + input terminal and the −input terminal of the amplifier 16 Stop climbing when they are equal. The + input terminal of the amplifier 16 becomes 3V when the voltage at the point A becomes 10V because the resistors R1 and R2 are 7KΩ and 3KΩ, respectively. In other words, as long as the output terminal of the fuel cell stack 11 is in an open state and has a power generation capacity of 10 V or more, the voltage at the point A will not steadily drop below 10 V no matter how the load device side is overloaded. . At this time, since the voltage at the point A is 10V and the voltage of the battery 12 is 11V, even if a charging circuit (not shown) is connected to the battery 12, no charging current flows, but the power required by the control unit, load device, etc. All the batteries will be supplied.

  In the above control, the FET 19 increases the equivalent resistance value when the output voltage of the fuel cell stack 11 is low, such as a variable resistance, and decreases the equivalent resistance value when the output voltage is high. Since the voltage changes in an analog manner from ON to OFF and from OFF to ON so that the voltage does not drop below 10V, the power that is multiplied by the square of the current flowing through the FET 19 at that time and the equivalent resistance value of the FET at that time is lost as heat. Is called.

  FIG. 3 is a schematic diagram showing the configuration of the fuel cell system according to the second embodiment of the present invention. In the figure, the same reference numerals as those in FIG. 2 denote the same components. The fuel cell system 20 of the present embodiment shown in the figure is based on the digital control method described above. As shown in the figure, the output voltage of the fuel cell stack 11 is divided by two series resistors R1 and R2 inserted between the point A and the ground, and is input to the A / D input terminal of the microcomputer 21. . The battery 12, such as a nickel metal hydride battery or a lithium ion battery, is connected in parallel to the input of the DC-DC converter 17. The output of the DC-DC converter 17 supplies power for driving the control unit 118 of FIG. 1 and the load device 200 of FIG.

  Since it is easier to understand by giving specific numbers, explanations are given below using numbers, but are not limited to these numbers. For example, the voltage of the battery 12 is 11V, the forward voltage drop of the diodes 14 and 15 is 0V, and the output voltage of the DC-DC converter 17 is 5V. If the series resistors R1 and R2 are 7KΩ and 3KΩ, respectively, 3V is input to the A / D input terminal of the microcomputer 21 when the voltage at the point A is 10V. For example, the microcomputer 21 checks the voltage of the A / D input terminal every 1 msec. When the voltage is 3.0 V or less, the output terminal is set to H, and when the voltage of the A / D input terminal is 3.1 V or more, the output is output. When the terminal is set to L and the voltage of the A / D input terminal is more than 3.0V and less than 3.1V, a program for maintaining the state of the output terminal is incorporated in advance. For example, even if power is supplied from the fuel cell stack to the control unit, the load device, etc., when there is a margin in power and the voltage at point A is 12V, 3.6V is applied to the A / D input terminal of the microcomputer 21. input. The microcomputer 21 checks the voltage of the A / D input terminal every 1 msec and sets the output terminal to L because the input voltage is 3.1 V or higher. Since G of FET 19 becomes L and FET 19 is completely turned on, it is electrically the same as that directly connected to the input of the DC-DC converter 17, and the fuel cell stack 11 supplies the electric power required by the control unit, load device, etc. All will be supplied. At this time, since the voltage at the point A is 12V and the voltage of the battery 12 is 11V, when a charging circuit (not shown) is connected, a charging current flows into the battery 12, but no discharging current flows.

  During operation as described above, if a large current flows instantaneously for some reason, such as a temporary short circuit of the load or startup of a motor, or the voltage at point A decreases due to a decrease in operating temperature or a control error in driving operation. The operation is as follows. For example, when the voltage at point A drops to 9 V, 2.7 V is input to the A / D input terminal of the microcomputer 21. The microcomputer 21 checks the voltage of the A / D input terminal every 1 msec and sets the output terminal of the microcomputer 21 to H because the input voltage is 3.0V or less. Since G of the FET 19 becomes H and the FET 19 is completely turned off, the output terminal of the fuel cell stack 11 and the control unit, the load device and the like are completely electrically disconnected. When the output terminal of the fuel cell stack is electrically disconnected, no current is taken out from the fuel cell stack 11, so the voltage at point A starts to rise from 9V. The microcomputer 21 always checks the voltage of the A / D input terminal every 1 msec, and if it is checked, if the voltage of the A / D input terminal is 3.1 V or less, the state of the output terminal of the microcomputer 21 is not changed, that is, remains H. G becomes H and the FET is completely turned off, and the output terminal of the fuel cell stack, the control unit, the load device, and the like are maintained in an electrically completely disconnected state. If the voltage of the A / D input terminal exceeds 3.1 V when the voltage of the A / D input terminal is checked every 1 msec, the microcomputer 21 sets the output terminal to L. At this time, the voltage at point A is 10.33V. Since G of FET 19 becomes L and FET 19 is completely turned on, the output terminal of the fuel cell stack becomes electrically the same as that directly connected to the input of the DC-DC converter 17 and is required again by the control unit, load device, etc. The fuel cell stack 11 supplies all the electric power In other words, as long as the output terminal of the fuel cell stack 11 is in an open state and has a power generation capacity of 10 V or more, the voltage at the point A will not steadily drop below 10 V no matter how the load device side is overloaded. .

  At this time, since the voltage at point A is 10.33 V and the voltage of the battery 12 is 11 V, even if a charging circuit (not shown) is connected to the battery 12, no charging current flows, but it is necessary for the control circuit, the load device, etc. All the electric power is supplied from the battery. If the voltage at the point A exceeds 11V, the voltage of the battery 12 is 11V. If a charging circuit (not shown) is connected to the battery 12, a charging current starts to flow, and the power required by the control unit, load device, etc. All 12 will supply.

  In such a digital control method, the FET 19 is electrically the same as a switch that operates at high speed. If the output voltage of the fuel cell stack 11 decreases, the ON / OFF time ratio increases so that the OFF time increases. If the output voltage increases, the ON / OFF time ratio increases so that the ON time increases. The output voltage of the fuel cell stack 11 is controlled so as not to drop below 10V. At this time, current flows when ON, but the equivalent resistance of FET 19 is 0Ω, so there is no theoretical power loss. When OFF, the equivalent resistance of FET 19 is ∞Ω, but the current is 0A, so theoretically power loss. There is no power loss in theory.

  FIG. 4 is a schematic diagram showing the configuration of the fuel cell system according to the third embodiment of the present invention. In the figure, the same reference numerals as those in FIGS. 2 and 3 denote the same components. As described in the operations of the analog control method as in the first embodiment and the digital control method as in the second embodiment, the generated power further decreases after the voltage drops to a predetermined voltage. Although there are two methods for maintaining the voltage even when the load becomes heavy, the fuel cell system 30 of the present embodiment shown in FIG. 4 uses one of the control methods. Instead, the analog control method causes power loss in the FET, and the digital control method does not cause power loss in the FET. The microcomputer 21 is switched by a switch 31.

  FIG. 5 is a schematic diagram showing the configuration of a fuel cell system according to the fourth embodiment of the present invention. In the figure, the same reference numerals as those in FIG. 4 denote the same components. The fuel cell system 40 of the present embodiment shown in FIG. 5 is a method for controlling to maintain the voltage even when the generated power further decreases or the load becomes heavy when the voltage decreases to a predetermined voltage. Selection is made according to the temperature of the fuel cell stack 11 detected by the temperature sensor 41. Since the fuel cell stack 11 generates electric power through a chemical reaction, the chemical reaction becomes gentle and the electrical output decreases when the temperature is low. As an example, the fuel cell stack 11 that can obtain 30 W of output power at 60 ° C. can only obtain about 20 W of output power when operated at 50 ° C. When the fuel cell stack 11 is started after being left overnight, the temperature of the fuel cell stack 11 immediately after the start is slightly higher than room temperature, and the output power can hardly be taken out. Therefore, it is necessary to raise the temperature of the fuel cell stack 11 as soon as possible after startup. As such a method, it is known that the fuel supplied to the fuel cell stack 11 is heated by a heater or the concentration of the fuel supplied to the fuel cell stack 11 is increased to cause a crossover. The combined use of these components or the extraction of electric power from the fuel cell stack alone activates the chemical reaction in the fuel cell stack, so that the temperature rise can be accelerated.

  However, since electric power is taken out at a low temperature, a voltage drop is likely to occur and there is a high possibility of serious damage to the fuel cell stack. Therefore, after the output voltage of the fuel cell stack in the present embodiment has decreased to a predetermined voltage, the analog control method so as to maintain the voltage even if the generated power further decreases or the load becomes heavy, Alternatively, by performing either control of the digital control method, there is no possibility of damaging the output voltage drop of the fuel cell stack.

  Thus, both the analog control method and the digital control method have the same effect of preventing damage caused by the output voltage drop of the fuel cell stack. However, as described above, the digital control method consumes less power in the FET. Therefore, the effect of accelerating the temperature rise by activating the chemical reaction in the fuel cell stack by taking out electric power from the fuel cell stack cannot be expected so much. On the other hand, in the case of the analog control method, since the maximum power that can be placed in a range that does not cause damage due to a decrease in the output voltage of the fuel cell stack can be consumed by the FET, the chemical in the fuel cell stack can be obtained by extracting power from the fuel cell stack. The reaction can be activated to accelerate the temperature rise. On the other hand, after the temperature of the fuel cell stack reaches an operating temperature, for example, 60 ° C., it is not necessary to accelerate the temperature rise. Therefore, the digital control method is preferable in order to avoid wasteful power consumption. That is, the analog control method is performed when the temperature immediately after startup is low, for example, less than 50 ° C., and the control method is switched to the digital control method as shown in FIG.

  Thus, the temperature measurement of the fuel cell stack 11 by the temperature sensor 41 in the fourth embodiment is performed to determine whether the chemical reaction in the fuel cell stack 11 is active or not. That is, it may be anywhere as long as the temperature changes in relation to the chemical reaction in the fuel cell stack 11. The control method is switched by measuring the surface temperature of the fuel cell stack 11, the temperature between the fuel cell stacks 11, the internal temperature of the fuel cell stack 11, the temperature of the fuel circulating in the fuel cell stack, and the like. May be.

  FIG. 6 is a schematic diagram showing the configuration of a fuel cell system according to the fifth embodiment of the present invention. In the figure, the same reference numerals as those in FIG. 4 denote the same components. The fuel cell system 50 of the present embodiment shown in FIG. 6 has an analog control method that maintains the voltage even when the generated power further decreases or the load increases when the voltage decreases to a predetermined voltage, or A method for controlling either of the digital control methods is selected by detecting the temperature of a power control element such as the FET 19 constituting the control circuit by the temperature sensor 51. As described above, when the analog control method is selected by switching between the analog control method and the digital control method, or when the control is not switched and only the analog control method is selected, the analog control method is power. Is consumed by the power control element such as the FET 19, the temperature of the power control element such as the FET 19 rises. If this temperature becomes too high for some reason, such as a short circuit of the load device or a decrease in cooling capacity, the power control element such as the FET 19 will be destroyed. By detecting the temperature of the power control element such as the FET 19 and switching from the analog control method to the digital control method when the temperature reaches, for example, 100 ° C., theoretically there is no power consumption in the power control element such as the FET 19 in the digital control method. The temperature can be lowered. For example, when the temperature falls to 60 ° C., the digital control method may be returned to the analog control method. That is, the analog control method is performed when the temperature of the power control element such as the FET 19 is low, and the control method is switched to the digital control method as shown in FIG. 6 when the temperature approaches a dangerous temperature range. Note that the temperature measurement part may be other than the power control element, and may be a place where the temperature changes in relation to the temperature of the power control element, for example, a heat sink or a housing with the power control element attached.

  Here, the accumulator is a secondary battery or a supercapacitor, and after the output voltage of the fuel cell stack is lowered to a predetermined voltage, the voltage is maintained even if the generated power is further lowered or the load becomes heavy. To control. In the case of the circuit configuration as shown in FIG. 2, if the predetermined voltage is designed to be lower than the voltage of the battery, the fuel cell stack automatically gets out of the fuel cell stack at the moment when the output voltage of the fuel battery cell falls below the voltage of the battery. The power supply becomes zero and operates so as to supply all the power required by the circuit, auxiliary equipment, and load device from the capacitor.

  As described above, the fuel cell system of the present invention controls the output voltage of the fuel cell stack so that it does not drop below the set voltage. Even if a large current flows, the fuel cell stack is not damaged.

  However, if the abnormal condition continues, ignition and expansion of the damaged part may occur, which is dangerous. Therefore, in order to prevent such a danger, even if the danger is not reached, the power from the battery cell stack is not used effectively, so the state where the output voltage of the fuel battery cell stack is lower than a predetermined voltage is longer than a certain time. When the operation continues, the power control element is turned off and the fuel cell stack 11 is disconnected as in the fuel cell system 60 of the sixth embodiment as shown in FIG. 7 as an abnormal state, and the relay 61 is turned off and the battery is disconnected. Further, the drive of the blower, circulation pump, fuel pump, and water pump in FIG. 1 is stopped to stop the power generation of the fuel cell stack 11, thereby preventing danger and not consuming unnecessary fuel.

  Next, electronic devices, particularly those that repeatedly start and stop the motor, those that repeatedly turn on / off the incandescent lamp, for example, reciprocate the carriage, turn on / off the inkjet printer and the fixing heater that take out the paper from the cassette The power consumption of printers and copiers that form images using electrostatic latent images that are OFF controlled varies greatly. Controlling the output voltage of the fuel cell stack not to drop below the set voltage when the fuel cell stack output voltage is about to drop when the power consumption is increased to prevent the fuel cell stack from being damaged. . In particular, since the amount of power generated is extremely small immediately after the start of the fuel cell, if the load varies at this time, the output voltage drop of the fuel cell stack increases. However, it is a general user's mind to want to print out an image as soon as the fuel cell is started, but even in such a situation, the output voltage of the fuel cell stack of the present invention does not decrease below the set voltage. It is possible to prevent the fuel cell stack from being damaged by being controlled.

  FIG. 8 is a block diagram showing an example of an electrically coupled configuration of the fuel cell system of the present invention and an electronic device. In the figure, the same reference numerals as those in FIG. 2 denote the same components. The fuel cell system 10 is connected to a control circuit 300 of an electronic device. The battery 12 is installed in parallel with the DC-DC converter 17 so that its output current is connected in parallel to each electrode of the fuel cell stack of the fuel cell stack 11 and supplied to the DC-DC converter 17. However, there are times when the output current from the fuel cell stack 11 flows toward the power storage device 11 and is charged. For example, when the external device is an electronic device, the DC-DC converter 17 converts the input voltage into a voltage required by the electronic device. Further, when the external device is an electronic device and a large current is required for the control circuit 300, a necessary amount of current is supplied from the battery 12. Since the battery 12 is connected in parallel with the DC-DC converter 17 in this way, the fuel cell is not significantly affected by large power consumption fluctuations on the external device side. Therefore, the output voltage of the fuel cell is maintained almost constant.

  The electronic device control circuit 300 includes a CPU 301, a nonvolatile memory 302, a data receiving unit 303, a RAM / DMA controller 304, a RAM 305, a ROM 306, a timing control unit 307, an ink flow rate detection unit 308, a head controller 309, and a head driver 310. , A recording head 311, a carriage motor driver 312, a carriage motor 313, a line feed driver 314, and a line feed motor 315. The CPU 301 is for executing operation control and data processing of the ink jet printer. The ROM 306 stores a control program for the CPU 301 and various data for font processing. The RAM 305 temporarily stores various data including received image data. The data receiving unit 303 is for capturing image data sent from an external device such as a host computer. Further, the RAM / DMA controller 304 DMA-transfers the image data received by the data receiving unit 303 to the RAM 305 and controls access from the CPU 301 to the RAM 305. The non-volatile memory 302 stores printer-specific parameters, such as an EEPROM. The head driver 310 drives the recording head 311. The head controller 309 is for transferring image data to the head driver 310 and generating a heat pulse signal under the control of the CPU 301. The carriage motor driver 312, the carriage motor 313, and the timing control unit 307 are a control system that moves the recording head 311 by a control signal supplied from the CPU 301 and a recording timing pulse from an encoder or the like. The direction in which the recording head 311 moves is called the main scanning direction. The line feed motor driver 113 and the line feed motor 315 are control systems that convey a recording medium such as the recording paper 209 in accordance with a control signal supplied from the CPU 301. The direction in which this recording medium is conveyed is called the sub-scanning direction. Further, the ink flow rate detection unit 308 counts the number of ink droplets (dots) ejected for recording within a predetermined time from the recording signal sent to the recording head 311, and supplies it to the recording head 311 from the ink tank. It is a control circuit which detects the flow volume of the ink to be performed. For example, when the electronic device of the external device is an ink jet printer, the power consumption varies greatly depending on the difference between the two modes currently in continuous printing or standby. Further, there may be three modes in which the power is completely turned off, or the number of modes may be further increased when the electronic device is other than a printer.

Next, an example of an electronic device provided with the fuel cell system of the present invention will be described.
FIG. 9 is a schematic perspective view of an ink jet printer using the fuel cell system of the present invention as a power source. An ink jet printer 400 shown in FIG. 1 includes a fuel cell system and a printer unit that operates upon receiving power from the fuel cell system.

  Next, FIG. 10 is a perspective view showing the internal configuration of the printer unit. The printer section shown in the figure includes a line feed motor 401, a pressing member 402, a wire 403, an HP (position) sensor 404, a recording head cartridge 405, a carriage 406, a cable 407, a carriage motor 408, A recording sheet 409, a platen roller 410, a shaft 411, and a recording head 412 are included. The recording head cartridge 405 is a unit in which the recording head 412 and an ink tank as an ink supply source are integrated. The recording head cartridge 405 is fixed on the carriage 406 by a pressing member 402, and can reciprocate in the longitudinal direction along the shaft 411.

  Further, the ink droplets ejected from the recording head 412 reach the recording paper 409 whose recording surface is regulated by the platen roller 410 at a minute distance from the recording head 412 and form an image. A recording timing pulse corresponding to image data is supplied to the recording head 412 from an appropriate data supply source via a cable 407 and a terminal coupled thereto.

  Further, one to a plurality of recording head cartridges 405 (two in the illustrated example) can be provided depending on the ink color used. The carriage motor 408 is for causing the carriage 406 to scan along the shaft 411. The wire 403 is for transmitting the driving force of the motor 408 to the carriage 406. The line feed motor 401 is coupled to the platen roller 410 to convey the recording paper 409. The HP sensor 404 detects the position of the carriage 406.

Next, basic recording control for executing recording control of the ink jet printer according to the present embodiment will be described with reference to FIG.
First, image data input from the host computer by the data receiving unit 303 is temporarily stored in the RAM 305 via the RAM / DMA controller 304. The CPU 301 executes a control program stored in the ROM 306 and analyzes received commands, image data, and character codes. Thereafter, the input image data is converted into recording data by the CPU 301 and sequentially stored in the RAM 305. The reception command includes recording control information, and recording is performed with the number of recording passes corresponding to the recording control information. Next, the carriage motor 313 is driven by the carriage motor driver 312 when the development of the recording data for one line is completed or a recording command which is one of the received commands is input from the host computer. Then, in synchronization with the recording timing pulse output from the timing control unit 307, the recording data stored in the RAM 305 is transferred to the head driver 310 via the RAM / DMA controller 304 and the head controller 309. Then, a heat pulse signal is sent from the head controller 309 to the head driver 310, and ink droplets are ejected from the recording head 311.

  When the recording for one line is completed, the line feed motor 315 is driven to perform a line feed, and a series of procedures is completed. By repeating such a procedure over one page of the recording paper 409 in FIG. 10, the recording operation for one page is completed.

  Although an electronic printer has been described as an electronic device, the electronic device may be an electrophotographic image forming apparatus or other electronic devices.

  In addition, this invention is not limited to the said embodiment, It cannot be overemphasized that various deformation | transformation and substitution are possible if it is description in a claim.

It is a block diagram which shows the structure of the fuel cell unit in the fuel cell system of this invention. 1 is a schematic diagram showing a configuration of a fuel cell system according to a first embodiment of the present invention. It is the schematic which shows the structure of the fuel cell system which concerns on the 2nd Embodiment of this invention. It is the schematic which shows the structure of the fuel cell system which concerns on the 3rd Embodiment of this invention. It is the schematic which shows the structure of the fuel cell system which concerns on the 4th Embodiment of this invention. It is the schematic which shows the structure of the fuel cell system which concerns on the 5th Embodiment of this invention. It is the schematic which shows the structure of the fuel cell system which concerns on the 6th Embodiment of this invention. It is a block diagram which shows an example of the electrical coupling | bonding structure of the fuel cell system of this invention and an electronic device. 1 is a schematic perspective view of an ink jet printer using a fuel cell system of the present invention as a power source. It is a perspective view which shows the internal structure of a printer part.

Explanation of symbols

10, 20, 30, 40, 50, 60; fuel cell system,
11: Fuel cell stack, 12: Capacitor,
13, 22, 32, 42, 52, 62; voltage drop prevention control circuit,
14, 15; diode, 16; amplifier,
17; DC-DC converter, 18; inverter, 19; FET,
21; microcomputer, 31; switch, 41, 51; temperature sensor,
61; Relay, 100; Fuel cell unit, 200; Load device,
300; Control circuit 400; Inkjet printer.

Claims (10)

A single cell that has an ion conductive solid polymer electrolyte membrane sandwiched between two electrodes, a negative electrode and a positive electrode, circulates and supplies low concentration liquid fuel from a circulation tank to the negative electrode, and oxidant gas to the positive electrode Alternatively, a fuel cell unit having a cell stack in which two or more single cells are stacked, a capacitor connected in parallel to the fuel cell stack and supplying power to a load device, and an output voltage of the fuel cell stack In a fuel cell system having output voltage detection means for detecting and a control unit for performing overall control,
When the output voltage of the fuel cell stack detected by the output voltage detection means is higher than a predetermined voltage, the output voltage of the fuel cell stack is supplied to a load device, and when the output voltage is low, a predetermined voltage is supplied. A fuel cell system, wherein power supply from a fuel cell stack to a load device is controlled so as to be maintained. A single cell that has an ion conductive solid polymer electrolyte membrane sandwiched between two electrodes, a negative electrode and a positive electrode, circulates and supplies low concentration liquid fuel from a circulation tank to the negative electrode, and oxidant gas to the positive electrode Alternatively, a fuel cell unit having a cell stack in which two or more single cells are stacked, a capacitor connected in parallel to the fuel cell stack and supplying power to a load device, and an output voltage of the fuel cell stack In a fuel cell system having output voltage detection means for detecting and a control unit for performing overall control,
When the output voltage of the fuel cell stack detected by the output voltage detection means connected to the fuel cell stack is lower than a predetermined voltage, the current taken out from the fuel cell stack by the output voltage drop prevention control means is A fuel cell system that adjusts and maintains the output voltage of the fuel cell stack.   3. The fuel cell system according to claim 2, wherein the output voltage drop prevention control means is analog control.   3. The fuel cell system according to claim 2, wherein the output voltage drop prevention control means is digital control.   The fuel cell according to any one of claims 2 to 4, wherein the output voltage drop prevention control means is switched to analog control or digital control in accordance with a mode in which the output voltage of the fuel cell stack is maintained. system.   A temperature sensor for detecting the temperature of the fuel cell stack is provided, and when the temperature of the fuel cell stack detected by the temperature sensor is lower than a predetermined temperature, the output voltage drop prevention control means is set to analog control and is high 6. The fuel cell system according to claim 5, wherein time is digitally controlled.   A temperature sensor for detecting the temperature of the control element constituting the output voltage drop prevention control means is provided, and when the temperature of the control element detected by the temperature sensor is lower than a predetermined temperature, the output voltage drop prevention control means is provided. 6. The fuel cell system according to claim 5, wherein analog control is used, and digital control is used when the control is high.   When the state where the output voltage of the fuel cell stack is lower than a predetermined voltage continues for a certain time or longer, a connection means for disconnecting the fuel cell stack and the battery from the load device is provided as an abnormal state, 8. The fuel cell system according to claim 1, wherein the fuel cell stack and the battery are separated from the load device by the connecting means. 9.   An electronic apparatus comprising the fuel cell system according to claim 1.   An image forming apparatus comprising the fuel cell system according to claim 1.

Images