JP2006278297A - Voltage transformer, fuel cell power generation system, and power generation method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a voltage transformer, a fuel cell power generation system, and a power generation method capable of starting the fuel cell in a short time without making the structure complicated and even at low temperatures. <P>SOLUTION: A DC-DC converter 5 (a first and a second voltage transforming circuits 51, 52) is provided adjacently at least at one side of a water tank 2 or a water passage WL. A water temperature detecting circuit 53 in the DC-DC converter 5 detects water temperatures in these parts. When the detected water temperature T is in lower water temperature state than a prescribed water temperature level (reference water temperature Tc), while keeping the increase of output current Iout in permitted state, these first and second voltage transforming circuits 51, 52 are mutually and periodically operated (alternately operated) so that only one voltage transforming circuit, out of the first and second voltage transforming circuits 51, 52, may be selectively operated. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a voltage conversion device, a fuel cell power generation system, and a power generation method that are suitably used in, for example, a fuel cell vehicle.

  In recent years, development of fuel cell vehicles using fuel cells as a power source has been actively conducted. This fuel cell generates power by reacting a fuel gas such as hydrogen with an oxidant gas such as oxygen. Further, the fuel gas and the oxidant gas are supplied to, for example, two electrodes arranged with an ion conductive membrane interposed in the fuel cell stack, for example.

  In general, each of the fuel gas and the oxidant gas is mixed with water vapor in order to prevent the reaction from occurring due to the deterioration of the ion conductive film. Thus, in a power generation system using a fuel cell, it is necessary to supply water. Therefore, in general, a water tank for humidifying these gases is provided, and water is supplied to the fuel cell stack.

  Here, when starting a fuel cell vehicle at a low temperature (for example, in a cold region or in winter), water in the water tank or the water path circulating between the water tank and the fuel cell stack is frozen. , You may not be able to generate electricity. In the past, moisture was defrosted using a heating means such as a heater. However, since it takes time to defrost, the fuel cell vehicle can be started until the fuel cell can generate power, that is, the fuel cell vehicle can be started. It took a long time to become.

  Therefore, in order to enable the fuel cell vehicle to start in a short time, for example, Patent Document 1 is provided with a spare tank having a small capacity and a heating function or a heat retaining function in addition to the water tank described above. In some cases, a technique has been disclosed in which moisture in a reserve tank is thawed by a heater and supplied to a fuel cell.

JP 2000-149970 A

  By the way, the heater as such a heating means generally generates heat by being driven by a DC-DC converter. In this DC-DC converter, a DC input voltage is converted into a pulse voltage by a switching circuit composed of a switching element, and then the pulse voltage is stepped down or boosted by a transformer, and the output voltage of the transformer is converted by a rectifier circuit, a smoothing circuit, or the like. It is a voltage conversion device having a function of converting again into a DC voltage.

  Here, in Patent Document 1, although the capacity of the spare tank is small, it must still be heated by a heater, and in order to be able to start in a short time, a large number of heaters are provided or the size is increased. Need to do. Therefore, it is necessary to increase the power by providing a large number of DC-DC converters or increasing the size thereof. Moreover, in the said patent document 1, it is necessary to provide the reserve tank provided with the heating function and the heat retention function newly.

  However, when a spare tank is newly provided or the heater is increased or increased in size (DC-DC converter is increased or increased in size), the weight of the entire vehicle increases and fuel consumption deteriorates. . In addition, the manufacturing cost increases due to an increase in the number of parts and an increase in the size of each part.

  Thus, with the conventional technology, it has been difficult to easily construct a fuel cell power generation system that can be started in a short time even at low temperatures.

  The present invention has been made in view of such problems, and an object of the present invention is to provide a voltage conversion device and a fuel cell power generation system capable of starting a fuel cell in a short time even at a low temperature without complicating the configuration. And providing a power generation method.

  The voltage converter of the present invention is a fuel cell power generation system configured to include a fuel cell, a water tank for storing water, and a water path for circulating water between the fuel cell and the water tank. Applied to convert the voltage supplied from the fuel cell, the temperature detecting means for detecting the temperature of water in at least one of the water tank and the water path, and at least one of which has a field effect transistor and A plurality of voltage conversion circuits configured to be adjacent to at least one of a water tank or a water path, each of which converts an input voltage supplied from a fuel cell into an output voltage of a different voltage, and are detected by temperature detection means. When the detected water temperature is higher than the predetermined reference water temperature, multiple voltage conversion circuits are operated in parallel, while the detected water temperature is lower than the reference water temperature. Controls multiple voltage conversion circuits so that some voltage conversion circuits, including voltage conversion circuits having field-effect transistors, are selectively operated among the multiple voltage conversion circuits during low water temperature conditions And a control circuit.

  In the voltage converter of the present invention, the temperature of water is detected in at least one of the water tank and the water path. Then, by comparing the obtained detected water temperature with a predetermined reference water temperature, it is determined whether these portions are in a high water temperature state or a low water temperature state. When the detected water temperature is a low water temperature state lower than the reference water temperature, some voltage conversion circuits of the plurality of voltage conversion circuits are selectively operated, and the circuit current is concentrated on the some voltage conversion circuits. . Since some of the voltage conversion circuits include a voltage conversion circuit having a field effect transistor, an increase in power loss due to current concentration occurs in the field effect transistor, thereby generating a heat generation amount in the element. Will also increase. Therefore, the amount of heat generated in the field effect transistors in the partial voltage conversion circuit is increased, and further, the partial voltage conversion circuit is adjacent to at least one of the water tank or the water path. The amount of heat conducted to the part increases, and the water temperature rises.

  In the voltage converter of the present invention, when the control circuit is in a low water temperature state, the output overcurrent droop point of the some voltage conversion circuits is larger than the output overcurrent droop point in the high water temperature state. It is possible to set it.

  In the voltage conversion device of the present invention, when the control circuit is in a low water temperature state, the voltage conversion circuits are connected to each other so that only one of the voltage conversion circuits is selectively operated. It is preferable to operate periodically. When configured in this way, the circuit current is always concentrated on only one voltage conversion circuit, and the degree of concentration increases, so the amount of increase in power loss in the field effect transistor operates two power conversion circuits simultaneously. The amount of heat generated in the element is further increased.

  In the voltage conversion device of the present invention, it is preferable that each of the plurality of voltage conversion circuits has the field effect transistor and is adjacent to at least one of the water tank or the water path. When configured in this manner, the ratio of field effect transistors increases in each voltage conversion circuit, so that the amount of increase in power loss as a whole increases and the amount of heat generated by the entire device also increases.

  In the voltage conversion device of the present invention, the voltage conversion circuit includes a switching element that generates an alternating voltage by switching an input voltage, a transformer that transforms the alternating voltage generated by the switching element, and the transformer. It is possible to include a rectifying element that rectifies the transformed AC voltage and an output circuit that generates an output voltage based on the rectifying element. In this case, at least one of the switching element or the rectifying element may be configured to be the above-mentioned field effect transistor, and it is preferable that both of them are field effect transistors. When configured in this manner, the ratio of field effect transistors increases in each voltage conversion circuit, so that the amount of increase in power loss as a whole increases and the amount of heat generated by the entire device also increases.

  In the voltage converter of the present invention, the temperature detecting means can be configured to include, for example, a thermistor.

  The fuel cell power generation system of the present invention includes a fuel cell, a water tank for storing water, a water path for circulating water between the fuel cell and the water tank, and water in at least one of the water tank and the water path. The temperature detection means for detecting the temperature and at least one of them has a field effect transistor and is arranged adjacent to at least one of the water tank or the water path, each of which receives the input voltage supplied from the fuel cell. A plurality of voltage conversion circuits that convert output voltages of different voltages and a plurality of voltage conversion circuits that operate in parallel when the detected water temperature detected by the temperature detection means is at a high water temperature higher than a predetermined reference water temperature, while the detected water temperature When the water temperature is lower than the reference water temperature, a voltage conversion circuit having a field effect transistor among the plurality of voltage conversion circuits As part of the voltage converter circuit operates selectively including one in which a control circuit for controlling the plurality of voltage conversion circuit.

  The power generation method of the present invention is applied to a fuel cell power generation system including a fuel cell, a water tank for storing water, and a water path for circulating water between the fuel cell and the water tank. And detecting a temperature of water in at least one of the water tank or the water path to obtain a detected water temperature, at least one of which has a field effect transistor and adjacent to at least one of the water tank or the water path. A plurality of voltage conversion circuits configured to convert the input voltage supplied from the fuel cell into an output voltage of a different voltage, and the detected water temperature is higher than a predetermined reference water temperature. While the plurality of voltage conversion circuits are operated in parallel when the detected water temperature is a low water temperature state lower than the reference water temperature, of the plurality of voltage conversion circuits, the field effect type Is obtained so as to selectively operate a portion of the voltage converter circuit including a voltage conversion circuit having a transistor.

  According to the voltage conversion device, the fuel cell power generation system, or the power generation method of the present invention, a part of the voltage conversion circuit including the voltage conversion circuit having the field effect transistor is adjacent to at least one of the water tank and the water path. In addition, the water temperature at these parts is detected, and when it is determined that the water temperature is low, the partial voltage conversion circuit is selectively operated. Since the water temperature can be increased by concentrating the temperature and increasing the amount of heat generated in the field-effect transistor, the fuel cell can be started at a low temperature in a short time without complicating the configuration. .

  Hereinafter, the best mode for carrying out the present invention (hereinafter simply referred to as an embodiment) will be described in detail with reference to the drawings.

  FIG. 1 shows the overall configuration of a fuel cell power generation system according to an embodiment of the present invention. In this fuel cell power generation system, power generated by the fuel cell 1 is supplied to the DC-DC converter 5 and the inverter 7 to drive the load of the DC-DC converter 5 and the motor 8. The power generation method according to an embodiment of the present invention is embodied by the fuel cell power generation system according to the present embodiment, and will be described below.

  This fuel cell power generation system includes a fuel cell 1, a water tank 2, a secondary battery 3, a DC-DC converter 4 (first DC-DC converter), and a DC-DC converter 5 (second DC- DC converter), a heater 61 that is a load of the DC-DC converter 5, an auxiliary battery 62 and an auxiliary machine 63, an inverter 7, and a motor 8.

The fuel cell 1 generates power based on a reaction between a fuel gas such as hydrogen (H ₂ ) (not shown) and an oxidant gas such as oxygen (O ₂ ) (not shown). Further, these fuel gas and oxidant gas are supplied to, for example, two electrodes arranged with an ion conductive membrane (not shown) sandwiched in a fuel cell stack (not shown). Further, water is supplied to the fuel cell 1 from the water tank 2 through the water path WL. The water supplied to the fuel cell 1 is used for humidifying the fuel gas and the oxidant gas and preventing the reaction from occurring due to the deterioration of the ion conductive membrane. The electric power generated by the fuel cell 1 in this way is supplied to the DC-DC converter 5 and the inverter 7.

  The secondary battery 3 is used when starting the fuel cell power generation system and functions as an auxiliary power source until the fuel cell 1 is started. The secondary battery 3 is composed of, for example, a lithium ion battery, a nickel metal hydride battery, or an electric double layer capacitor. The voltage supplied from the secondary battery 3 is converted and stabilized by the DC-DC converter 4 and supplied to the DC-DC converter 5 and the inverter 7. In this way, when starting the fuel cell power generation system, power is supplied from the secondary battery 3 to the DC-DC converter 5 and the inverter 7 via the DC-DC converter 4 instead of the fuel cell 1. .

  The inverter 7 converts the DC voltage supplied from the fuel cell 1 (or from the DC-DC converter 4 at the time of starting) into an AC voltage and supplies it to the motor 8. The motor 8 is driven by the AC voltage generated in this way. For example, when this fuel cell power generation system is applied to a fuel cell vehicle, a vehicle drive unit and a compressor for the fuel cell power generation system are driven.

  The DC-DC converter 5 converts the input DC voltage Vin supplied from the fuel cell 1 (or from the DC-DC converter 4 at start-up) via the input terminals T1 and T2 to a voltage different from the input DC voltage Vin. This is converted to an output DC voltage (output voltage) Vout to drive the heater 61, auxiliary battery 62 and auxiliary machine 63, which are loads. These loads are connected from the output terminals T3 and T4 of the DC-DC converter 5 through the output line LO and the ground line LG, respectively.

  The heater 61 is for heating the water in the water tank 2 or the water path WL to increase the water temperature at the time of starting at a low temperature (for example, in a cold region or in winter). It arrange | positions in the position which can conduct Q1 (it adjoins). The heater 61 is composed of, for example, a sheathed heater. The auxiliary battery 62 is a battery for storing the electric power supplied from the DC-DC converter 5 and driving the auxiliary machine 63 based on the electric power. Examples of the auxiliary machine 63 include an air conditioner, a headlight, a power window, a power steering, or a radio.

  Here, the DC-DC converter 5 also functions as a heating unit that heats the water in the water tank 2 and the water path WL at a low temperature together with the heater 61, and the heat Q2 generated in the DC-DC converter 5 is generated. It arrange | positions in the position which can conduct to at least one of the water tank 2 or the water path | route WL (it adjoins). Although details will be described later, by arranging in this way, the water temperature at these parts can be increased more quickly at low temperatures. The DC-DC converter 5 corresponds to a specific example of a “voltage converter” according to the present invention.

  FIG. 2 shows a circuit configuration of the DC-DC converter 5. The DC-DC converter 5 includes a first voltage conversion circuit 51 and a second voltage conversion circuit 52 connected in parallel between the input terminals T1 and T2 and the output terminals T3 and T4, respectively, and the first voltage. A first control IC 58 connected to the conversion circuit 51, a second control IC 59 connected to the second voltage conversion circuit 52, and a first overcurrent protection circuit 55 connected to the first control IC 58 A second overcurrent protection circuit 56 connected to the second control IC 59, a voltage conversion operation control circuit 57 connected to both the first and second voltage conversion circuits 55, 56, and the first And a reference voltage control circuit 54 connected to the second overcurrent protection circuits 55 and 56 and the voltage conversion operation control circuit 57, and a water temperature detection circuit 53 connected to the reference voltage control circuit 54. The input terminals T1 and T2 are connected to the fuel cell 1, the DC-DC converter 4 and the inverter 7 as described above, and the output terminal T3 is a heater 61 which is a load of the DC-DC converter 5 via the output line LO. Connected to the auxiliary battery 62 and the auxiliary machine 63, the output terminal T4 is connected to the above-described load via the ground line LG.

  Each of the first and second voltage conversion circuits 51 and 52 differs from the input DC voltage Vin supplied from the input terminals T1 and T2 with an output DC voltage (output that is lower in the example of FIG. 2). This is a circuit that converts the voltage into Vout, and constitutes the main function of the DC-DC converter 5. Here, the first and second voltage conversion circuits 51 and 52 are the “plurality of voltage conversion circuits”, “voltage conversion circuits including field effect transistors”, and “part of voltage conversion circuits” in the present invention. This corresponds to a specific example. Further, as will be described later, in these first and second voltage conversion circuits 51 and 52, the circuit current concentrates on one of them at a low temperature, and the voltage conversion operation is alternately performed. Such control of the first and second voltage conversion circuits 51 and 52 is performed by the water temperature detection circuit 53, the reference potential control circuit 54, the first and second overcurrent protection circuits 55 and 56, and the voltage conversion operation control circuit 57. , And the first and second control ICs 58 and 59. Hereinafter, first, the first voltage conversion circuit 51 and the second voltage conversion circuit 52 will be described in detail.

  First, the first voltage conversion circuit 51 will be described.

  The first voltage conversion circuit 51 includes a switching circuit 511 provided between the primary high voltage line H1 and the primary low voltage line L1, a primary winding CA1, and a secondary winding that is magnetically coupled thereto. A transformer 512 having lines CB1 and CC1, a rectifier circuit 513 provided on the secondary side of the transformer 512, and a smoothing circuit 514 connected to the rectifier circuit 513 are provided. The first voltage conversion circuit 51 further includes a current detection transformer 515 and a current-voltage conversion circuit 516 connected to the current detection transformer 515.

  The switching circuit 511 is a single-phase switching circuit that converts an input DC voltage Vin into a substantially rectangular wave-shaped single-phase AC voltage, and is a full bridge formed by connecting four switching elements (switching transistors S11 to S14) in a full bridge. Type switching circuit. Specifically, one ends of the switching transistors S11 and S12 (the source of the switching transistor S11 and the drain of the switching transistor S12) are connected to each other, and the one ends of the switching transistors S13 and S14 (the source of the switching transistor S13 and the switching transistor S14). Are connected to each other via the primary winding CA1 of the transformer 512. The other ends (drains) of the switching transistors S11 and S13 are connected to the input terminal T1 via the primary high voltage line H1, and the other ends (sources) of the switching transistors S12 and S14 are primary to each other. It is connected to the input terminal T2 via the side low voltage line L1. Further, switching signals LS11 to LS14 are supplied to the gates of the switching transistors S11 to S14 from a switching drive circuit 582 in a first control IC 58, which will be described later, and the switching operation is individually controlled. . Each of these switching transistors S11 to S14 is configured by a field effect transistor such as a MOS-FET (Metal Oxide Semiconductor-Field Effect Transistor). The switching transistors S11 to S14 correspond to specific examples of “switching element” and “field effect transistor” in the present invention.

  In the switching circuit 511, when the switching transistors S11 and S14 are turned on, the first voltage reaches the primary low voltage line L1 from the primary high voltage line H1 through the switching transistor S11, the primary winding CA1 and the switching transistor S14 in order. While the current flows through one current path, the switching transistors S12 and S13 are turned on, so that the primary low voltage passes through the switching transistor S13, the primary winding CA1 and the switching transistor S12 in order from the primary high voltage line H1. A current flows through the second current path that reaches the line L1.

  One end of the primary side winding CA1 of the transformer 512 is connected to one ends of the switching transistors S11 and S12, and the other end is connected to one ends of the switching transistors S13 and S14. Further, one ends (center taps) of the secondary windings CB1 and CC1 are connected to each other and led to the output terminal T3 via the choke coil 514L in the rectifier circuit 513 on the output line LO1, The other ends are respectively connected to one ends (drains) of rectifying transistors D11 and D12 in the rectifying circuit 513. That is, the first voltage conversion circuit 51 is a center tap type. The transformer 512 steps down or steps up (steps down in this example) the AC voltage converted by the switching circuit 511, and outputs AC voltages that are 180 degrees out of phase with each other from the other ends of the pair of secondary windings CB1 and CC1. It is designed to output. In this case, the degree of step-down or step-up is determined by the turn ratio between the primary side winding CA1 and the secondary side windings CB1 and CC1. The transformer 512 corresponds to a specific example of “transformer” in the present invention.

  The rectifier circuit 513 is a double-wave rectifier type composed of a pair of rectifier elements (rectifier transistors D11 and D12). Moreover, all of these rectifier elements are composed of field effect transistors such as MOS-FETs. Specifically, the drains of these field effect transistors are connected to the other ends of the secondary windings CB1 and CC1 to form the drains of the rectifying transistors D11 and D12. Are connected to each other on the ground line LG1 to constitute sources of the rectifying transistors D11 and D12. Further, switch signals LSD11 and LSD12 are respectively supplied to the gates of the rectifying transistors D11 and D12 from a switching drive circuit 582 in a first control IC 58 to be described later, and the switching operation is individually controlled so as to operate as a rectifying element. It has come to be. That is, this rectifier circuit 513 has a source common connection structure, and each DC half voltage period of the AC output voltage of the transformer 512 is individually rectified by the rectifying transistors D11 and D12 to obtain a DC voltage. ing. The rectifying transistors D11 and D12 correspond to specific examples of “rectifying element” and “field effect transistor” in the present invention.

  The smoothing circuit 514 includes a choke coil 514L and a smoothing capacitor 514C. The choke coil 514L is inserted and arranged in the output line LO1, one end of which is connected to one end (center tap) of the secondary windings CB1 and CC1, and the other end is connected to one end of the smoothing capacitor 514C and the output line LO1. To the output terminal T3. The smoothing capacitor 514C is connected between the other end of the choke coil 514L on the output line LO1 and the ground line LG1. An output terminal T4 is provided at the end of the output line LO1. With such a configuration, the smoothing circuit 514 smoothes the DC voltage rectified by the rectifying circuit 513 and generates an output DC voltage Vout. The rectifier circuit 513 and the smoothing circuit 514 correspond to a specific example of “output circuit” in the present invention.

  The current detection transformer 515 has a primary side winding CD1 inserted and arranged in the primary side low voltage line L1, and a secondary side winding CE1 whose one end is grounded and magnetically coupled to the primary side winding CD1. . With this configuration, the current detection transformer 56 detects the detection current I1 corresponding to the current flowing through the primary side low-voltage line L1 by the secondary winding CE1.

  The current-voltage conversion circuit 516 includes a rectifier diode D561D having an anode connected to one end (opposite the ground side) of the secondary winding CE1 of the current detection transformer 515, and the other end (ground) of the secondary winding CE1. Side) and the cathode of the rectifier diode D561D. With such a configuration, the current-voltage conversion circuit 516 rectifies the detection current I1 detected by the current detection transformer 515 by half-wave rectification by the rectifier diode 516D, and outputs the pulse-shaped detection voltage Vc1 obtained by this. It has become.

  Note that the arrangement of the current detection transformer 515 and the current-voltage conversion circuit 516 is not limited to that shown in FIG. 2, and may be inserted into the primary high-voltage line H1, for example, or the switching transistors S11, From one end of S12 (source of switching transistor S11 and drain of switching transistor S12) to one end of switching transistors S13 and S14 (source of switching transistor S13 and drain of switching transistor S14) via primary winding CA1. You may make it insert and arrange in a path | route. In the latter case, the current-voltage conversion circuit 516 may be configured by a so-called full-wave rectifier circuit. Further, the current detection transformer 515 and the current-voltage conversion circuit 516 may be inserted into the secondary side of the transformer 512, specifically, the ground line LG1 or the output line LO1, and in this case, the current-voltage conversion circuit 516 may be configured using a resistance or current sensor.

  Next, the second voltage conversion circuit 52 will be described. 2 that correspond to the components of the first voltage conversion circuit 51 among the components of the second voltage conversion circuit 52 shown in FIG. Or the code | symbol which added "1" is attached | subjected and description is abbreviate | omitted suitably.

  The second voltage conversion circuit 52 has a circuit configuration similar to that of the first voltage conversion circuit 51, and includes a switching circuit 521 provided between the primary high voltage line H2 and the primary low voltage line L2, and 1 A transformer 522 having a secondary winding CA2 and secondary windings CB2 and CC2 magnetically coupled thereto, a rectifier circuit 523 provided on the secondary side of the transformer 522, and a smoothing circuit connected to the rectifier circuit 523 524. The second voltage conversion circuit 52 further includes a current detection transformer 525 and a current-voltage conversion circuit 526 connected to the current detection transformer 525.

  The switching circuit 521, the transformer 522, the rectifier circuit 523, the smoothing circuit 524, the current detection transformer 525, and the current-voltage conversion circuit 526 are respectively the switching circuit 511, the transformer 512, the rectification circuit 513, and the smoothing circuit 514 in the first voltage conversion circuit. The current detection transformer 515 and the current-voltage conversion circuit 516 have the same configuration and function. For example, the switching circuit 521 is a full-bridge type switching circuit in which four switching transistors S21 to S24 are connected in a full-bridge connection, so that the input DC voltage Vin is converted into a substantially rectangular wave-shaped single-phase AC voltage. It has become. Further, the transformer 522 has a center tap type configuration, and the AC voltage converted by the switching circuit 521 is stepped down or stepped up (in this example, stepped down), and the phase is 180 degrees different from the secondary windings CB2 and CC2. AC voltage is output. The rectifier circuit 523 is a source common-connected double-wave rectifier type composed of a pair of rectifier elements (for example, rectifier transistors D21 and D22 configured by field effect transistors such as MOS-FETs), and a transformer 522. The rectifying transistors D21 and D22 individually rectify the half-wave periods of the AC output voltage of each of the AC output voltages based on switch signals LSD21 and LSD22 supplied from a switching drive circuit 592 in the second control IC 59, which will be described later. Get the voltage. The smoothing circuit 524 includes a choke coil 524L and a smoothing capacitor 524C, smoothes the DC voltage rectified by the rectifier circuit 523, and outputs the DC output voltage Vout between the output terminals T3 and T4. It has become. The current detection transformer 525 detects the detection current I2 corresponding to the current flowing in the primary low-voltage line L2 by the secondary winding CE2, and the current-voltage conversion circuit 526 includes a rectifier diode D562D and A resistor 516R is provided, and the detection current I2 is half-wave rectified by a rectifier diode 526D, and a DC detection voltage Vc2 obtained thereby is output.

  The switching transistors S21 to S24 correspond to specific examples of “switching element” and “field effect transistor” in the present invention, and the transformer 522 corresponds to a specific example of “transformer” in the present invention. The transistors D21 and D22 correspond to specific examples of “rectifier element” and “field effect transistor” in the present invention. The rectifier circuit 523 and the smoothing circuit 524 correspond to a specific example of “output circuit” in the present invention.

  Next, the water temperature detection circuit 53, the reference voltage control circuit 54, the first overcurrent protection circuit 55, the second overcurrent protection circuit 56, the voltage conversion operation control circuit 57, the first control IC 58 and the second control IC 59 Will be described in detail.

  The water temperature detection circuit 53 includes a thermistor 531 and a resistor 532. One end of the resistor 532 is connected to the power source Vcc, the other end is connected to one end of the thermistor 531 at the connection point P1, and the other end of the thermistor 531 is grounded. That is, the power supply voltage Vcc (divided voltage) divided by the resistor 532 and the thermistor 531 is applied to the connection point P1. Further, the thermistor 531 has a characteristic that its resistance value changes according to the temperature, and the voltage value at both ends thereof changes according to the temperature. Therefore, the water temperature detection circuit 53 detects the water temperature T by changing the potential at the connection point P2 according to the temperature of the water (water temperature T) in at least one of the water tank 2 and the water path WL. It is supposed to be. The thermistor 531 of the present embodiment is an NTC thermistor whose resistance value increases as the temperature decreases. The water temperature detection circuit 53 corresponds to a specific example of “temperature detection means” in the present invention.

  The reference voltage control circuit 54 includes a comparator 541 and resistors 542 to 544. The inverting input terminal of the comparator 541 is connected to the connection point P1, the reference voltage Ref1 is supplied to its non-inverting input terminal, and its output terminal is connected to the connection point P2. One end of the resistor 542 is connected to the power source Vcc, and the other end is connected to the connection point P2. One end of the resistor 543 is connected to the connection point P 2, and the other end is connected to the base of the NPN transistor 551 in the first overcurrent protection circuit 55. One end of the resistor 544 is connected to the connection point P <b> 2, and the other end is connected to the base of the NPN transistor 551 in the second overcurrent protection circuit 56. Further, the connection point P2 is connected to the input terminal Tin of the voltage conversion operation control circuit 57. With this configuration, the reference voltage control circuit 54 has the reference voltages V1 and V2 in the first and second overcurrent protection circuits 55 and 56 based on the potential at the connection point P1 supplied from the water temperature detection circuit 53. The input signal SIG0 (the potential at the connection point P2 = the output signal of the comparator 541) is supplied to the voltage conversion operation control circuit 57.

  The first overcurrent protection circuit 55 includes an NPN transistor 551, resistors 552 to 554, and a comparator 555. The base of the NPN transistor 551 is connected to the connection point P2 via the resistor 543 of the reference voltage control circuit 54, and its emitter is grounded. The resistors 552 and 553 are connected in parallel to each other, one end of each of the resistors 552 and 553 is connected to the connection point P31, the other end of the resistor 552 is connected to the collector of the NPN transistor 551, and the other end of the resistor 553 is connected. Grounded. One end of the resistor 554 is connected to the power source Vcc, and the other end is connected to the connection point P31. The non-inverting input terminal of the comparator 555 is connected to the connection point P31, the detection voltage Vc1 in the current-voltage conversion circuit 516 is supplied to the inverting input terminal, and the output terminal is a control pulse in the first control IC 58. The generation circuit 581 is connected.

  With such a configuration, the first overcurrent protection circuit 55 supplies the non-inverting input terminal of the comparator 555 based on the potential at the connection point P2 supplied from the reference voltage control circuit 54 (the output signal of the comparator 541). The reference voltage V1 is generated, and the comparator 555 compares the generated reference voltage V1 with the detection voltage Vc1 supplied from the current-voltage conversion circuit 516, and outputs the comparison to the first control IC 58. The signal Vs1 is output. Specifically, when the output signal of the comparator 541 is “L” level, the NPN transistor 551 is turned off, so that the reference voltage V1 is determined by the resistor 554 and the resistor 553 connected in series. On the other hand, when the output signal of the comparator 541 is at “H” level, the NPN transistor 551 is turned on, so that the reference voltage V1 is generated between the resistor 554 and the resistors 552 and 553 connected in parallel with each other. It is determined by series connection. When the reference voltage V1 set in this way is larger than the detection voltage Vc1 (rated voltage state), the comparator 555 outputs the output signal Vs1 of “H” level, while the reference voltage V1 is conversely When it is smaller than the detection voltage Vc1 (overvoltage state), the comparator 555 outputs an output signal Vs1 of “L” level. In this way, the first overcurrent protection circuit 55 compares the magnitudes of the potentials of the reference voltage V1 and the detection voltage Vc1, so that the first voltage conversion circuit 51 is in the rated voltage state or in the overvoltage state. The output signal Vs1 is output to the first control IC 58.

  The first control IC 58 includes a control pulse generation circuit 581 and a switching drive circuit 582. The control pulse generation circuit 581 sets the width (duty ratio) of the control pulse based on the output signal Vs1 output from the comparator 555 in the first overcurrent protection circuit 55, and the switching transistor S11 in the switching circuit 511. ~ S14 control pulses and control pulses for the rectifying transistors D11 and D12 in the rectifying circuit 513 are generated. Specifically, when the output signal Vs1 from the comparator 555 becomes “L” level (output overcurrent state), the pulse widths of the switching signals LS11 to LS14 and the switch signals LSD11 and LSD12 are reduced (the duty ratio is reduced). Make it smaller). The switching drive circuit 582 outputs switching signals LS11 to LS14 and switch signals LSD11 and LSD12 based on these generated control pulses, and actually drives the switching transistors S11 to S14 and the rectifying transistors D11 and D12, respectively. To do.

  The switching drive circuit 582 also has a function of controlling the voltage conversion operation of the first voltage conversion circuit 51 in accordance with a voltage conversion operation control signal Lon1 from the voltage conversion operation control circuit 57 described later. Specifically, when the voltage conversion control signal Lon1 is an “H” level signal, the first voltage conversion circuit 51 is operated. On the other hand, when the voltage conversion control signal Lon1 is an “L” level signal, the switching signals LS11˜ The voltage conversion operation of the first voltage conversion circuit 51 is stopped by setting the pulse width of the LS 14 and the switch signals LSD11 and LSD12 to 0 (duty ratio = 0).

  The second overcurrent protection circuit 56 has a circuit configuration similar to that of the first overcurrent protection circuit 55, and includes an NPN transistor 561, resistors 562 to 564, and a comparator 565. The second overcurrent protection circuit 56 also has a function similar to that of the first overcurrent protection circuit 55, and the potential of the connection point P2 supplied from the reference voltage control circuit 54 (of the comparator 541). The reference voltage V2 supplied to the non-inverting input terminal of the comparator 565 is generated based on the output signal), and the reference voltage V2 generated by the comparator 565 and the detection voltage Vc2 supplied from the current-voltage conversion circuit 526 are generated. Are compared, and an output signal Vs2 to the second control IC 59 is output. In this way, the second overcurrent protection circuit 56 compares the potential levels of the reference voltage V2 and the detection voltage Vc2, so that the second voltage conversion circuit 52 is in the rated voltage state or in the overvoltage state. The output signal Vs2 is output to the second control IC 59.

  The second control IC 59 has a circuit configuration similar to that of the first control IC 58 and includes a control pulse generation circuit 591 and a switching drive circuit 592. The second control IC 59 has the same function as the first control IC 58. Specifically, based on the output signal Vs2 output from the comparator 565 in the second overcurrent protection circuit 56, the control pulses of the switching transistors S21 to S24 in the switching circuit 521, and the rectification in the rectifier circuit 523. The control pulse widths (duty ratios) of the transistors D21 and D22 are set, and the switching signals LS21 to LS24 and the switch signals LSD21 and LSD22 are output based on these control pulses. The switching transistors S21 to S24 and the rectifying transistor, respectively. D12 and D22 are driven. Similarly to the first control IC 58, the voltage conversion operation of the second voltage conversion circuit 52 is controlled in accordance with a voltage conversion operation control signal Lon2 from the voltage conversion operation control circuit 57 described later. .

  The voltage conversion operation control circuit 57 is a circuit that controls the voltage conversion operations of the first voltage conversion circuit 51 and the second voltage conversion circuit 52. Specifically, it is always monitored whether the temperature of the first voltage conversion circuit 51 or the second voltage conversion circuit 52 is higher than a predetermined reference temperature, and when the temperature becomes higher than the predetermined reference temperature. The operation of the voltage conversion circuit is controlled to be stopped via the switching drive circuit 582 or the switching drive circuit 592.

  FIG. 3 shows a circuit configuration of the voltage conversion operation control circuit 57. The voltage conversion operation control circuit 57 includes a first temperature detection circuit 571, a second temperature detection circuit 572, a first overheat protection circuit 573 connected to the first temperature detection circuit 571, and a second temperature. A second overheat protection circuit 574 connected to the detection circuit 572 and a logic circuit 575 connected to the first and second overheat protection circuits 573 and 574 are included.

  The first temperature detection circuit 571 has the same circuit configuration and function as the water temperature detection circuit 53, and includes a thermistor 571T formed of an NTC thermistor and a resistor 571R. One end of the resistor 571R is connected to the power source Vcc, the other end is connected to one end of the thermistor 571T at the connection point P41, and the other end of the thermistor 571T is grounded. With such a configuration, the first temperature detection circuit 571 detects the temperature T1 by changing the potential at the connection point P41 in accordance with the temperature T1 of the first voltage conversion circuit 51.

  The second temperature detection circuit 572 also has the same circuit configuration and function as the water temperature detection circuit 53 and the first temperature detection circuit 571, and includes a thermistor 572T composed of an NTC thermistor and a resistor 572R. One end of the resistor 572R is connected to the power source Vcc, the other end is connected to one end of the thermistor 572T at the connection point P42, and the other end of the thermistor 572T is grounded. With this configuration, the second temperature detection circuit 572 detects the temperature T2 by changing the potential at the connection point P42 in accordance with the temperature T2 of the second voltage conversion circuit 52.

  The first overheat protection circuit 573 includes a comparator Com1 and a resistor 573R. The inverting input terminal of the comparator Com1 is connected to the connection point P41, the reference voltage Ref21 is supplied to its non-inverting input terminal, and its output terminal is connected to the connection point P51. One end of the resistor 573R is connected to the power source Vcc, and the other end is connected to the connection point P51. With this configuration, the first overheat protection circuit 573 has an input signal SIG1 (the potential of the connection point P51 = the output signal of the comparator Com1) based on the potential of the connection point P41 supplied from the first temperature detection circuit 571. ) Is supplied to the logic circuit 575.

  The second overheat protection circuit 574 has a circuit configuration and function similar to those of the first overheat protection circuit 573, and includes a comparator Com2 and a resistor 574R. The inverting input terminal of the comparator Com2 is connected to the connection point P42, the reference voltage Ref22 is supplied to its non-inverting input terminal, and its output terminal is connected to the connection point P52. One end of the resistor 574R is connected to the power source Vcc, and the other end is connected to the connection point P52. With such a configuration, the second overheat protection circuit 574 has an input signal SIG2 (the potential of the connection point P52 = the output signal of the comparator Com2) based on the potential of the connection point P42 supplied from the second temperature detection circuit 572. ) Is supplied to the logic circuit 575.

  The logic circuit 575 includes AND circuits AND1 to AND6 and OR circuits OR1 and OR2 connected to the output sides of the AND circuits AND1 to AND6. A negative logic input signal SIG1 is input from the first overheat protection circuit 573 to the first input terminal of the AND circuit AND1, and a negative logic input signal from the second overheat protection circuit 574 is input to the second input terminal thereof. SIG2 is input, a negative logic input signal SIG0 is input from the input terminal Tin to the third input terminal, and the output terminal is led to the first input terminal of the OR circuit OR1. A negative logic input signal SIG1 is input from the first overheat protection circuit 573 to the first input terminal of the AND circuit AND2, and a positive logic input signal from the second overheat protection circuit 574 is input to the second input terminal thereof. SIG2 is input, a negative logic input signal SIG0 is input from the input terminal Tin to the third input terminal, and the output terminal is led to the second input terminal of the OR circuit OR1. A negative logic input signal SIG1 is input from the first overheat protection circuit 573 to the first input terminal of the AND circuit AND3, and a negative logic input signal from the second overheat protection circuit 574 is input to the second input terminal thereof. SIG2 is input, a positive logic input signal SIG0 is input from the input terminal Tin to the third input terminal, and the output terminals are the third input terminal of the OR circuit OR1 and the first input terminal of the OR circuit OR2. Has been led to. A positive logic input signal SIG1 is input from the first overheat protection circuit 573 to the first input terminal of the AND circuit AND4, and a negative logic input signal from the second overheat protection circuit 574 is input to the second input terminal thereof. SIG2 is input, a negative logic input signal SIG0 is input from the input terminal Tin to the third input terminal, and the output terminal is led to the second input terminal of the OR circuit OR2. A positive logic input signal SIG1 is input from the first overheat protection circuit 573 to the first input terminal of the AND circuit AND5, and a negative logic input signal from the second overheat protection circuit 574 is input to the second input terminal thereof. SIG2 is input, a positive input signal SIG0 is input from the input terminal Tin to the third input terminal, and the output terminal is led to the third input terminal of the OR circuit OR1. A negative logic input signal SIG1 is input from the first overheat protection circuit 573 to the first input terminal of the AND circuit AND6, and a positive logic input signal from the second overheat protection circuit 574 is input to the second input terminal thereof. SIG2 is input, a positive input signal SIG0 is input from the input terminal Tin to the third input terminal, and the output terminal is led to the fourth input terminal of the OR circuit OR2. Further, the voltage conversion operation control signal Lon1 is led from the output terminal of the OR circuit OR1 to the output terminal Tout1, and the voltage conversion operation control signal Lon2 is led from the output terminal of the OR circuit OR2 to the output terminal Tout2. Yes.

  With this configuration, the logic circuit 575 forms a truth table 570 as shown in FIG. 4, and the voltage conversion operation control signals Lon1 and Lon2 are supplied to the switching drive circuits 582 and 592 based on the input signals SIG0 to SIG2, respectively. To supply. Here, as described above, the input signals SIG0 to SIG2 represent the water temperature T, the temperature T1 of the first voltage conversion circuit 51, and the temperature T2 of the second voltage conversion circuit 52, respectively. The signal indicates a low water temperature state or a normal temperature state, and the “H” level signal indicates a high water temperature state or a high temperature state. The voltage conversion operation control signals Lon1 and Lon2 are the control signal for the voltage conversion operation in the first voltage conversion circuit 51 and the control signal for the voltage conversion operation in the second voltage conversion circuit 52, respectively, as described above. The “L” level signal indicates a control signal to be operated, and the “H” level signal indicates a control signal to be stopped. The details of the truth table 570 will be described later.

  The reference voltage control circuit 54, the first and second overcurrent protection circuits 55 and 56, the voltage conversion operation control circuit 57, and the first and second control ICs 58 and 59 are the “control circuit” in the present invention. This corresponds to a specific example. Further, instead of (or in addition to) these circuits, for example, constituted by a microcomputer, the operations of the switching transistors S11 to S14 and S21 to S24 in the switching circuits 511 and 512, and the rectifier circuits 513 and 523 The operations of the rectifying transistors D11, D12, D21, and D22 may be controlled by software.

  Next, the operation of the fuel cell power generation system configured as described above will be described with reference to FIGS. 4 to 8 focusing on the operation of the DC-DC converter 5 which is a characteristic part thereof. FIG. 5 shows pulse waveforms of the reference voltages V1 and V2 generated by the first and second overcurrent protection circuits 55 and 56, respectively, and the detection voltages Vc1 and Vc2 supplied from the current-voltage conversion circuits 516 and 526. FIG. 6 shows the relationship between the output voltage Vout and the output current Iout, and FIG. 7 shows the output overcurrent drooping point Ip and the water tank 2 or the water path WL. This shows an example of the relationship with at least one water temperature T. FIG. 8 is a timing chart showing the operation of the DC-DC converter 5. (A) is the water temperature T, and (B) to (D) are inputs to the voltage conversion operation control circuit 57, respectively. Signals SIG0 to SIG2, (E) and (F) represent voltage conversion operation control signals Lon1 and Lon2 to the first and second voltage conversion circuits 51 and 52, respectively.

  First, referring to FIGS. 4 to 7, the water temperature (water temperature T) in at least one of the water tank 2 or the water path WL is set to a predetermined reference water temperature (reference water temperature Tc) set by the reference voltage control circuit 54. The operation when the water temperature is higher than) will be described.

  The electric power generated by the fuel cell 1 is supplied to the DC-DC converter 5 and the inverter 7. In the inverter 7, the supplied DC voltage is converted into an AC voltage and supplied to the motor 8. When the motor 8 is driven by this AC voltage, the load is driven using the power.

  On the other hand, in the DC-DC converter 5, the input DC voltage Vin supplied from the fuel cell 1 is different from that by the first and second voltage conversion circuits 51 and 52 (in the example of FIG. Is converted to an output DC voltage (output voltage) Vout which is a low voltage. Then, the auxiliary battery 62 and the auxiliary device 63 which are loads are driven by the output voltage Vout.

  Specifically, the DC-DC converter 5 performs the following voltage conversion operation.

  In the first voltage conversion circuit 51, in the switching circuit 511, the switching transistors S11 and S14 are in the on state and the switching transistors S12 and S13 are in the off state in response to the switching signals LS11 to LS14 supplied from the switching drive circuit 582. And the period in which the switching transistors S12 and S13 are on and the switching transistors S11 and S14 are off are alternately switched. With such a switching operation, the switching circuit 511 generates an AC pulse voltage based on the input DC voltage Vin and supplies the AC pulse voltage to the primary winding CA1 of the transformer 512. In the transformer 512, the pulse voltage is transformed, and the transformed pulse voltage is output from the secondary windings CB1 and CC1. The transformed pulse voltage is rectified by the rectifying transistors D11 and D12 of the rectifying circuit 513 in accordance with the switch signals LSD11 and LSD12 supplied from the switching drive circuit 582, and the choke coil 514L and the smoothing capacitor 514C of the smoothing circuit 514 are rectified. Thus, the rectified voltage waveform is smoothed. In this way, the output DC voltage Vout is supplied to and driven by the auxiliary battery 62 and the auxiliary 63.

  At this time, the output current Iout is always monitored indirectly as the detection current I1 by the current detection transformer 515, and the detection current I1 is converted into the detection voltage Vc1 by the current-voltage conversion circuit 516, and the first overcurrent protection is performed. It is output to the circuit 55. In the water temperature detection circuit 53, the potential at the connection point P1 is set according to the water temperature T of at least one of the water tank 2 and the water path WL. In the reference voltage control circuit 54, the reference voltage V1 supplied to the non-inverting input terminal of the comparator 555 in the first overcurrent protection circuit 55 is set based on the set potential of the connection point P1. The comparator 555 compares the potential of the reference voltage V1 set in this way with the potential of the detection voltage Vc1 output from the current-voltage conversion circuit 516.

  Here, in the water temperature detection circuit 53, since the water temperature T is in a high water temperature state, the voltage value at both ends of the thermistor 531 becomes small, and the potential at the connection point P1 becomes lower than the potential of the reference voltage Ref1. Is set. Therefore, since the output signal of the comparator 541 becomes “H” level and the NPN transistor 551 in the first overcurrent protection circuit 55 is turned on, the reference voltage V1 is in parallel with the resistor 554 as described above. It is determined by the series connection with the connected resistors 552 and 553.

  As a result of the comparison, as shown in FIG. 5, when the potential of the detection voltage Vc1 is lower than the reference potential V1H in this high water temperature state (pulse waveform PLS1 of the detection voltage), the output current Iout is Since the current is in the normal current state, the output signal Vs1 of the comparator 555 becomes the “H” level. At this time, the first control IC 58 outputs the switching signals LS11 to LS14 and the switch signals LSD11 and LSD12 having the control pulse width (duty ratio) for maintaining the normal current state, and maintains the normal current state. Thus, the operations of the switching transistors S11 to S14 and the rectifying transistors D11 and D12 are controlled.

  On the other hand, when the potential of the detection voltage Vc1 becomes higher than the reference potential V1H (pulse waveform PLS2 of the detection voltage: as indicated by the reference symbol P101 in FIG. 5, the respective potentials become the same potential and become higher. ), Since the output current Iout is in the output overcurrent state, the output signal Vs1 of the comparator 555 becomes the “L” level. At this time, the first control IC 58 sets the widths of the control pulses in the switching signals LS11 to LS14 and the switch signals LSD11 and LSD12 to be small (duty ratio is small). Therefore, as indicated by reference numeral P101 in the graph G1 in FIG. 6, the first voltage conversion circuit 51 enters the output overcurrent droop state at the output current IOH, and the value of the output voltage Vout falls below VOH and droops. Control is performed as follows. Note that this output overcurrent drooping point Ip (the output current: IOH at P101 in FIG. 6) is always the lower limit value IOH when the water temperature T is in a high water temperature state higher than the reference water temperature Tc, as shown in FIG. Set to

  On the other hand, in the second voltage conversion circuit 52, an output DC voltage (output voltage) Vout is generated based on the input DC voltage Vin by the same operation as that of the first voltage conversion circuit 51, and the auxiliary battery 62 and It is driven by being supplied to the auxiliary machine 63.

  Also in the second voltage conversion circuit 52, the output current Iout is always monitored indirectly as the detection current I2 by the current detection transformer 525, and the detection current I2 is changed to the detection voltage Vc2 by the current-voltage conversion circuit 526. The converted signal is output to the second overcurrent protection circuit 56. In the reference voltage control circuit 54, the reference voltage V2 to be supplied to the non-inverting input terminal of the comparator 565 in the second overcurrent protection circuit 56 is set based on the set potential of the connection point P1. The comparator 565 compares the potential of the reference voltage V2 set in this way with the potential of the detection voltage Vc2 output from the current-voltage conversion circuit 526.

  Here, in the high water temperature state, since the output signal of the comparator 541 becomes “H” level as described above, the NPN transistor 561 in the second overcurrent protection circuit 56 is also turned on, and the reference voltage V2 is It is determined by the series connection of the resistor 564 and the resistors 562 and 563 connected in parallel.

  In this way, in the second voltage conversion circuit 52, similarly to the first voltage conversion circuit 51, the control pulse widths (duty ratios) of the switching signals LS21 to LS24 and the switch signals LSD21 and LSD22 are controlled. The operations of the switching transistors S21 to S24 and the rectifying transistors D21 and D22 are controlled so as to maintain the normal current state. When the detected voltage Vc2 is higher than the reference potential V2H, the second control IC 59 reduces the width of the control pulse in the switching signals LS21 to LS24 and the switching signals LSD21 and LSD22 (duty ratio). Is set to be smaller). That is, the second voltage conversion circuit 52 is in an output overcurrent drooping state at the output current IOH, and control is performed such that the value of the output voltage Vout falls below VOH and droops.

  At this time, in the voltage conversion operation control circuit 57, the temperature T1 of the first voltage conversion circuit 51 and the temperature T2 of the second voltage conversion circuit 52 are always set by the first and second temperature detection circuits 571 and 572, respectively. Is being monitored. Specifically, the potentials of the connection points P41 and P42 are set according to these temperatures T1 and T2, respectively. In the first and second overheat protection circuits 573 and 574, input signals SIG1 and SIG2 output to the logic circuit 575 are set based on the set potentials of the connection points P41 and P42, respectively. Here, in the temperature detection circuits 571 and 572, as long as the temperatures T1 and T2 are in the normal temperature state, the voltage values at both ends of the thermistors 571T and 572T are reduced, and the potentials at the connection points P41 and P42 are the reference voltages Ref21 and Ref22, respectively. It is set to be lower than the potential. Therefore, in this case, the output signals (input signals SIG1 and SIG2) of the comparators Com1 and Com2 are both at the “L” level. As described above, since the output signal of the comparator 541 is at the “H” level in the high water temperature state, the input signal SIG0 input through the input terminal Tin is also at the “H” level.

  Therefore, in this case, as shown in the truth table 570 of FIG. 4, the voltage conversion operation control signals Lon1 and Lon2 to the first and second voltage conversion circuits 51 and 52 are both at the “H” level. The first voltage conversion circuit 51 and the second voltage conversion circuit 52 both perform a voltage conversion operation, that is, are in an operating state.

  On the other hand, when at least one of the temperatures T1 and T2 of the first and second voltage conversion circuits 51 and 52 is in a high temperature state, the voltage value at both ends of the thermistor 571T (or thermistor 572T) increases, and the connection point P41. (Or the connection point P42) is higher in potential than the reference voltage Ref21 (or reference voltage Ref22). Therefore, in this case, the input signal SIG1 (or SIG2) becomes the “H” level, and the voltage conversion operation control signal Lon1 (or the voltage conversion operation control signal Lon2) becomes the “L” level. Therefore, the first voltage conversion circuit 51 (Or the second voltage conversion circuit 52) does not perform the voltage conversion operation, that is, enters a stopped state. If the temperature T1 (or temperature T2) drops to the normal temperature state and the input signal SIG1 (or SIG2) becomes the “L” level after the stop state is made in this way, the first voltage conversion circuit. 51 (or the second voltage conversion circuit 52) returns to the operating state again.

  In this way, the voltage conversion operation control circuit 57 controls the voltage conversion operation in accordance with the temperatures T1 and T2 of the first and second voltage conversion circuits 51 and 52. As long as T1 and T2 are in the normal temperature state, both the first voltage conversion circuit 51 and the second voltage conversion circuit 52 perform the voltage conversion operation.

  Next, referring to FIGS. 4 to 8, when the water temperature T is in a low water temperature state lower than a predetermined reference water temperature (reference water temperature Tc), the fuel cell power generation system is started particularly in such a low water temperature state. The operation when doing this will be described.

  First, when the fuel cell power generation system is started, the secondary battery 3 functions as an auxiliary power source until the fuel cell 1 is started. Specifically, the voltage supplied from the secondary battery 3 is voltage-converted and stabilized by the DC-DC converter 4 and supplied to the DC-DC converter 5 and the inverter 7.

  In the DC-DC converter 5, the first voltage conversion circuit 51 and the second voltage conversion circuit 52 perform basically the same voltage conversion operation as that in the high water temperature state, and are supplied from the DC-DC converter 3. The input DC voltage Vin is converted into an output DC voltage (output voltage) Vout that is a different voltage (lower voltage in the example of FIG. 2). In addition to the auxiliary battery 62 and the auxiliary machine 63, the output voltage Vout also drives the heater 61 that is a load in the low water temperature state. By driving the heater 61 in this way, water in at least one of the water tank 2 or the water path WL is heated by the heat Q1 generated by the heater 61, and the water temperature T rises.

  Here, the DC-DC converter 5 differs from the high water temperature state in that the output overcurrent droop point Ip of the first and second voltage conversion circuits 51 and 52 is high as shown in FIGS. The temperature is larger than that in the water temperature state, and the first voltage conversion circuit 51 and the second voltage conversion circuit 52 are selectively operated alternately as shown in FIGS. 8 (E) and 8 (F). It is. As will be described in detail later, by operating in this way, in addition to the heater 61, the DC-DC converter 5 also functions as a heating means for water in at least one of the water tank 2 or the water path WL. ing. Specifically, in the low water temperature state, the DC-DC converter 5 performs the following operation.

  First, when the water temperature T is lowered, the resistance value of the thermistor 531 in the water temperature detecting means 53 increases, so that the voltage value at both ends of the water temperature detecting means 53 increases, and the potential at the connection point P1 is higher than the potential of the reference voltage Ref1. Become. Therefore, since the output signal of the comparator 541 becomes “L” level and the NPN transistors 551 and 561 are turned off, the reference voltage V1 is determined by the series connection of the resistor 554 and the resistor 553, and the reference voltage V2 is It is determined by the series connection of the resistor 564 and the resistor 563. Therefore, for example, as indicated by the arrow X1 in FIG. 5, the reference potentials V1 and V2 generated by the first and second overcurrent protection circuits 55 and 56 also rise from V1H and V2H to V1H and V2L, respectively. The criteria for determining whether or not an overcurrent state is present is relaxed compared to when the water temperature is high. Therefore, as indicated by reference numeral P102 in FIG. 5, the detection currents I1, I2 and the output current Iout are allowed to increase up to the current value corresponding to the potential of the pulse waveform PLS3 of the detection voltages Vc1, Vc2, and the graph of FIG. As indicated by the arrow X2 and the symbol P102 in G2 and the graph G3 in FIG. 7, the output overcurrent droop point Ip of the first and second voltage conversion circuits 51 and 52 also rises from IOH to IOL.

  At this time, in the voltage conversion operation control circuit 57, the output signal of the comparator 541 is at the “L” level, that is, the input signal SIG0 to the logic circuit 575 is at the “L” level (FIG. 8B). As can be seen from the truth table 570 of FIG. 4, at the start of the fuel cell power generation system, that is, in the initial state (timing t0 in FIG. 8; SIG0 = SIG1 = SIG2 = “L”), the voltage conversion operation control signal Lon1 is Since the Lon2 becomes the “L” level while the “H” level is set, the first voltage conversion circuit 51 is in the operating state, and the second voltage conversion circuit 52 is in the stop state (FIG. 8E, (F)).

  Thus, at the timing t0, the first voltage conversion circuit 51 operates in a state where the output overcurrent droop point Ip rises from IOH to IOL, while the second voltage conversion circuit 52 is stopped. . That is, only the first voltage conversion circuit 51 selectively operates in a state in which the increase in the output current Iout is allowed. Therefore, the circuit is connected to the first voltage conversion circuit 51 in the DC-DC converter 5. The current will be concentrated. Since the first voltage conversion circuit 51 includes field effect transistors (switching transistors S11 to S14 and rectifying transistors D11 and D12), the power loss Ploss caused by current concentration in these elements is reduced. An increase occurs, thereby increasing the amount of heat generated in the device. Specifically, for example, as summarized in Table 1 below, the power loss Ploss increases. Here, Table 1 shows the states of the first and second voltage conversion circuits 51 and 52 in the high water temperature state and the low water temperature state, the output current Iout, the power loss Ploss (FET) in the field effect transistor, and An example of the total value in the first and second voltage conversion circuits 51 and 52 is summarized. Regarding the power loss Ploss (FET), switching elements (switching transistors S11 to S14, S21 to S24) are included. And the case of the rectifier element (rectifier transistors D11, D12, D21, D22). In this example, in the high water temperature state, the first and second voltage conversion circuits 51 and 52 both output current Iout = 110A, and in the low water temperature state, the first and second voltage conversion circuits. One of 51 and 52 (voltage conversion circuit in the operating state) is assumed to have an output current Iout = 220A. Further, the power loss Ploss (FET) is shown as a ratio for each case.

  As can be seen from Table 1, in the high water temperature state, the first and second voltage conversion circuits 51 and 52 both have the output current Iout = 110A, and therefore the power loss Ploss (FET) is the switching element and the rectifying element. In either case, the first voltage conversion circuit: the second voltage conversion circuit: total = 1: 1: 2.

On the other hand, in the low water temperature state, the output current Iout of the voltage conversion circuit in the operating state as described above is 220A, and the output current Iout of the voltage conversion circuit in the stop state is 0A. Here, the power loss Ploss (FET) in the field effect transistor is expressed by the following formula (1) and formula (2) (formula (1); in the case of a switching element, formula (2); rectification In the case of an element), it increases in proportion to the square of the current flowing between its source and drain. Therefore, as shown in Table 1, in both cases of the switching element and the rectifying element, the first voltage conversion circuit: the second voltage conversion circuit: total = 4: 0: 4, and in the low water temperature state The calorific value increases twice as much as the calorific value in the high water temperature state.
Ploss (FET) ∝ (Iout / n) ² (1)
Ploss (FET) ∝ (Iout) ² (2)
Here, n is the number of turns N1 of the primary side winding CA1 (CA2) with respect to N2, assuming that the number of turns of the secondary side windings CB1 (CB2) and CC1 (CC2) is equal (= N2). The ratio (N1 / N2). Therefore, (Iout / n) represents the current flowing through the primary side, that is, the current flowing between the source and drain of the switching transistors S11 to S14 (S21 to S24).

  In this way, in the DC-DC converter 5, the field effect transistors (switching transistors S11 to S14 and rectifying transistors D11 and D12) in the first voltage conversion circuit in the operating state are in a high water temperature state. Further, since the DC-DC converter 5 (first voltage conversion circuit 51) is adjacent to at least one of the water tank 2 and the water path WL, the amount of heat Q2 conducted to these parts is increased. As shown in FIG. 8 (A), the water temperature gradually rises.

  Thereafter, the amount of heat generated in the first voltage conversion circuit 51 increases. Therefore, when the temperature T1 of the first voltage conversion circuit 51 becomes higher than a predetermined reference temperature at the timing t1, the above-described state occurs. As described above, the input signal SIG1 becomes “H” level, the voltage conversion operation control signal Lon1 becomes “L” level, and the voltage conversion operation control signal Lon2 becomes “H” level (FIG. 4). While the conversion circuit 51 is stopped, the second voltage conversion circuit 52 is changed from the stopped state to the operating state. In this way, at the timings t1 to t2, only the second voltage conversion circuit 52 selectively operates in a state where the increase in the output current Iout is allowed, and the second voltage conversion circuit 52 in the DC-DC converter 5 The circuit current is concentrated on the conversion circuit 52. Therefore, at the timings t1 to t2, the field effect transistors (switching transistors S21 to S24 and rectifiers) in the second voltage conversion circuit in the operating state are provided in the same manner as the first voltage conversion circuit 51 described above. In the transistors D21 and D22), the amount of heat generation is higher than that in the high water temperature state, and the DC-DC converter 5 (second voltage conversion circuit 52) is adjacent to at least one of the water tank 2 and the water path WL. Therefore, the amount of heat Q2 conducted to these parts also increases, and the water temperature further rises as shown in FIG. 8 (A).

  After that, as shown in FIG. 8, only the first voltage conversion circuit 51 is in the operating state again at the timing t2 to t3, and only the second voltage conversion circuit 52 is in the operating state at the timing t3 to t4. Only the first voltage conversion circuit 51 is in an operating state from t4 to t5, only the second voltage conversion circuit 52 is in an operating state from timing t5 to t6, and only the first voltage conversion circuit 51 is operating from timing t6 to t7. In the state, only the second voltage conversion circuit 52 is in the operating state from the timing t7 to t8, and only the first voltage conversion circuit 51 is in the operating state after the timing t8. These first and second voltage conversion circuits 51 and 5 are operated so that only one voltage conversion circuit of the circuits 51 and 52 selectively operates. There continue to cyclic operation (alternate operation) to each other, the water temperature T goes further increased. Note that the time interval at which such alternating operation is switched is gradually shortened because the water temperature T rises even when each voltage conversion circuit is stopped, and therefore the first and second voltage conversion circuits. This is because the temperatures T1 and T2 of 51 and 52 are again in an operating state before the temperatures T1 and T2 are completely lowered to the original temperatures.

  For example, when the water temperature T becomes higher than the predetermined reference water temperature Tc at the timing t9 and becomes a high water temperature state (FIG. 8A), the input signal SIG0 to the logic circuit 575 is at the “H” level as described above. (FIG. 8B), the input signals SIG1 and SIG2 are both “L” unless the temperatures T1 and T2 of the first and second voltage conversion circuits 51 and 52 are in a high temperature state (FIG. 8B). 8 (C), (D)) and the truth table 570 of FIG. 4, both the first and second voltage conversion circuits 51, 52 are in an operating state (FIGS. 8E, 8F). At this time, as described above, the output overcurrent droop point Ip decreases from IOL to IOH and returns to the original state (FIGS. 6 and 7). Further, as shown in the timings t10 to t11, for example, when the first voltage conversion circuit 51 is in a high temperature state (FIG. 8C), the first voltage is calculated according to the truth table 570 in FIG. The conversion circuit 51 is stopped (FIG. 8E).

  In this way, the amount of heat generated in the field effect transistor in the first voltage conversion circuit 51 or the second voltage conversion circuit 52 in the DC-DC converter 5 is increased, and the DC-DC converter 5 (first And the second voltage conversion circuit 51, 52) is adjacent to at least one of the water tank 2 or the water path WL, so that the water temperature T rises and the heating means is only the heater 61. In comparison, the fuel cell 1 can be easily started in a short time.

  As described above, in the present embodiment, the DC-DC converter 5 (first and second voltage conversion circuits 51 and 52) is adjacent to at least one of the water tank 2 or the water path WL, and the DC-DC. The water temperature detection circuit 53 in the converter 5 detects the water temperature at these parts, and when the detected water temperature T is in a low water temperature state lower than a predetermined reference water temperature (reference water temperature Tc), the output current Iout So that only one of the first and second voltage conversion circuits 51 and 52 selectively operates in a state in which the increase of the first and second voltage conversion circuits 51 and 52 is allowed. Since the circuit currents are concentrated on one voltage conversion circuit in the DC-DC converter 5, the electric fields in the voltage conversion circuit in the operating state are integrated. The water temperature T can be increased by increasing the amount of heat generated in the fruit type transistor as compared with that in the high water temperature state and also increasing the amount of heat Q2 to be conducted, so that the fuel cell can be operated at low temperatures without complicating the configuration. Can be started in a short time.

  Further, since the periodic operation (alternate operation) as described above is performed in the DC-DC converter 5 only at a low temperature, there is no need to change the rated power value, and a large number of such DC-DC converters may be provided. There is no need to increase the size. Also, it is not necessary to provide a large number of heaters 61 that are conventional heating means or to increase the size of the heaters. Therefore, there is no need to increase the number of parts, and thus the manufacturing cost is not increased and the overall weight is not increased. Therefore, the effects as described above can be obtained while maintaining the conventional configuration.

  While the present invention has been described with reference to the embodiment, the present invention is not limited to this embodiment, and various modifications can be made. That is, in the said embodiment, although the structure of the fuel cell electric power generation system and the DC-DC converter 5 was mentioned concretely and demonstrated, these structures are not limited to this, It is good also as another structure. For example, in the above-described embodiment, the case where there are two voltage conversion circuits has been described. However, the voltage conversion circuit may be configured by an arbitrary number of three or more.

  For example, in the above embodiment, when both the switching element and the rectifying element are configured by field effect transistors (switching transistors S11 to S14, S21 to S24 and rectifying transistors D11, D12, D21, and D22). Although the example has been described, at least one of these elements only needs to be configured by a field effect transistor. When configured in this way, the power loss in the element, that is, the amount of heat generated in the element is reduced as compared with the above embodiment, but the fuel cell 1 can be started more easily and in a shorter time than in the past. Is possible.

  In the above embodiment, an example in which the temperature detection means for the water temperature T is configured by the temperature detection circuit 53 including the thermistor 531 has been described. However, for example, it may be configured by a thermostat or the like. T may be configured to be detected either directly or indirectly.

  In the above embodiment, an example has been described in which both the first and second voltage conversion circuits 51 and 52 are configured to perform the selective operation as described above. The circuit does not need to perform such a selective operation, and at least one of the voltage conversion circuits including the field effect transistor and adjacent to at least one of the water paths WL performs such a selective operation. What is necessary is just to comprise.

  In the above embodiment, an example in which the first and second voltage conversion circuits 51 and 52 perform periodic operations (alternate operations) with each other has been described. (Alternate operation) is not necessary, and it may be configured such that only a specific voltage conversion circuit always performs a selective operation to concentrate the circuit current.

  Moreover, although the said embodiment has demonstrated the example in case both the 1st and 2nd voltage conversion circuits 51 and 52 are adjacent to at least one of the water tank 2 or the water path | route WL, the field effect is demonstrated. What is necessary is just to comprise so that at least one of the voltage conversion circuits which include a type transistor and performs the selective operation as described above may be adjacent to at least one of the water tank 2 or the water path WL.

  In the above-described embodiment, the first and second voltage conversion circuits 51 and 52 in the DC-DC converter 5 are both configured as a so-called full bridge type. It is possible to apply to various configurations such as a chopper type, a forward type, and a flyback type.

It is a functional block diagram showing the whole structure of the fuel cell power generation system which concerns on one embodiment of this invention. FIG. 3 is a circuit diagram illustrating a configuration of a second DC-DC converter illustrated in FIG. 1. FIG. 3 is a circuit diagram illustrating a configuration of a voltage conversion operation control circuit illustrated in FIG. 2. It is a specific figure showing the truth table of the logic circuit shown in FIG. It is a voltage vs. time characteristic diagram for explaining the relationship between the reference voltage and the pulse waveform of the detection voltage. FIG. 5 is a characteristic diagram of output voltage versus output current for explaining an output overcurrent droop point. It is a characteristic view of the output overcurrent droop point versus water temperature showing an example of a change mode of the output overcurrent droop point. It is a timing diagram for demonstrating operation | movement of a 2nd DC-DC converter.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Fuel cell, 2 ... Water tank, 3 ... Secondary battery, 4 ... 1st DC-DC converter, 5 ... 2nd DC-DC converter, 51 ... 1st voltage converter circuit, 52 ... 2nd Voltage conversion circuit, 511, 521 ... Switching circuit, 512, 522 ... Transformer, 513, 523 ... Rectifier circuit, 514, 524 ... Smoothing circuit, 515, 525 ... Current detection transformer, 516, 526 ... Current-voltage conversion circuit, 53 ... Water temperature detection circuit, 531 ... Thermistor, 54 ... Reference voltage control circuit, 541 ... Comparator, 55 ... First overcurrent detection circuit, 56 ... Second overcurrent detection circuit, 551, 561 ... NPN transistor, 555, 565 ... Comparator, 57 ... Voltage conversion operation control circuit, 570 ... Truth table, 571 ... First temperature detection circuit, 572 ... First overheat protection circuit, 573 ... Second temperature detection circuit, 5 4 ... 2nd overheat protection circuit, 571T, 573T ... thermistor, 575 ... logic circuit, 58 ... 1st control IC, 59 ... 2nd control IC, 581, 591 ... control pulse generation circuit, 582, 592 ... switching Drive circuit 61 ... Heater 62 ... Auxiliary battery 63 ... Auxiliary machine 7 ... Inverter 8 ... Motor, WL ... Water path, Vin ... Input DC voltage, Vout ... Output DC voltage (output voltage), Iout ... Output current, LO1, LO2, LO ... output line, LG1, LG2, LG ... ground line, Q1, Q2 ... heat, CL ... cold air, T1, T2 ... input terminal, T3, T4 ... output terminal, H1, H2 ... 1 Secondary side high pressure line, L1, L2 ... Primary side low pressure line, P1, P2, P31, P32, P41, P42, P51, P52 ... Connection point, S11-S14, S21-S24 ... Switching traffic Transistors, LS11 to LS14, LS21 to LS24... Switching signal, CA1, CA2... Primary side winding, CB1, CB2, CC1, CC2... Secondary side winding, D11, D12, D21, D22. , LSD12, LSD21, LSD22 ... switch signal, 514L, 524L ... choke coil, 514C, 524C ... smoothing capacitor, Com1, Com2 ... comparator, AND1-6 ... AND circuit, OR1, OR2 ... OR circuit, Ref1, Ref21, Ref22 , V1, V2, V1L, V2L, V1H, V2H ... reference voltage, VO ... rated output voltage, IOH ... rated output current, IOL, IOL1, IOL2 ... low temperature output current, Tc ... reference water temperature, Ip ... output overcurrent drooping Point, I1, I2 ... detection current, Vc1, Vc2 ... detection voltage, Vs1, Vs2... Comparator output signal, Lon1, Lon2... Voltage conversion operation control signal, SIG0 to SIG2... Input signal, Vcc... Power supply voltage, t0 to t11.

Claims (10)

The fuel cell is applied to a fuel cell power generation system including a fuel cell, a water tank that stores water, and a water path that circulates the water between the fuel cell and the water tank. A voltage conversion device that converts the voltage supplied from
Temperature detecting means for detecting the temperature of the water in at least one of the water tank or the water path;
At least one of them has a field effect transistor and is configured to be adjacent to at least one of the water tank or the water path, and each of the input voltages supplied from the fuel cell is changed to an output voltage of a different voltage. A plurality of voltage conversion circuits for conversion;
When the detected water temperature detected by the temperature detecting means is in a high water temperature state higher than a predetermined reference water temperature, the plurality of voltage conversion circuits are operated in parallel, while when the detected water temperature is in a low water temperature state lower than the reference water temperature. Control for controlling the plurality of voltage conversion circuits so that a part of the voltage conversion circuits including the voltage conversion circuit having the field effect transistor among the plurality of voltage conversion circuits is selectively operated. A voltage conversion device comprising: a circuit. The control circuit is set so that an output overcurrent droop point of the partial voltage conversion circuit is larger than an output overcurrent droop point in the high water temperature state in the low water temperature state. The voltage converter according to claim 1. The control circuit periodically operates the voltage conversion circuits so that only one voltage conversion circuit of the partial voltage conversion circuits selectively operates in the low water temperature state. The voltage converter according to claim 1 or 2. The plurality of voltage conversion circuits each include the field effect transistor and are adjacent to at least one of the water tank or the water path. The voltage converter according to item. The voltage conversion circuit includes:
A switching element that generates an alternating voltage by switching the input voltage;
A transformer for transforming an alternating voltage generated by the switching element;
5. An output circuit that includes a rectifying element that rectifies the AC voltage transformed by the transformer and generates the output voltage based on the rectifying element. 6. The voltage converter according to item. The voltage converter according to claim 5, wherein at least one of the switching element or the rectifying element is the field effect transistor. The voltage conversion device according to claim 6, wherein each of the switching element and the rectifying element is the field effect transistor. The voltage converter according to any one of claims 1 to 7, wherein the temperature detection unit includes a thermistor. A fuel cell;
A water tank for storing water;
A water path for circulating the water between the fuel cell and the water tank;
Temperature detecting means for detecting the temperature of the water in at least one of the water tank or the water path;
At least one of them has a field effect transistor and is configured to be adjacent to at least one of the water tank or the water path, and each of the input voltages supplied from the fuel cell is changed to an output voltage of a different voltage. A plurality of voltage conversion circuits for conversion;
When the detected water temperature detected by the temperature detecting means is in a high water temperature state higher than a predetermined reference water temperature, the plurality of voltage conversion circuits are operated in parallel, while when the detected water temperature is in a low water temperature state lower than the reference water temperature. Control for controlling the plurality of voltage conversion circuits so that a part of the voltage conversion circuits including the voltage conversion circuit having the field effect transistor among the plurality of voltage conversion circuits is selectively operated. A fuel cell power generation system comprising a circuit. A power generation method applied to a fuel cell power generation system configured to include a fuel cell, a water tank for storing water, and a water path for circulating the water between the fuel cell and the water tank. There,
Detecting the temperature of the water in at least one of the water tank or the water path to obtain a detected water temperature;
At least one of them has a field effect transistor and is configured to be adjacent to at least one of the water tank or the water path, and each of the input voltages supplied from the fuel cell is changed to an output voltage of a different voltage. Configure multiple voltage conversion circuits to convert,
When the detected water temperature is in a high water temperature state higher than a predetermined reference water temperature, the plurality of voltage conversion circuits are operated in parallel, while when the detected water temperature is in a low water temperature state lower than the reference water temperature, the plurality of voltage conversion circuits. Among them, a part of the voltage conversion circuit including the voltage conversion circuit having the field effect transistor is selectively operated.

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