JP2009165245A - Fuel cell system and dc-dc converter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress switching loss as much as possible in a voltage step-up converter such as a DC-DC converter for stepping up the output voltage from a DC power supply unit such as a fuel cell. <P>SOLUTION: The fuel cell system is provided with a main voltage step-up section for causing a main switch means S1 to perform a switching operation for a main coil L1 connected to a terminal of a high potential side of the fuel cell so that the output voltage of the fuel cell can be stepped up; and an auxiliary voltage step-up section having a snubber capacitor C2 connected in parallel to the main switch means S1 and capable of adjusting a voltage applied to the main switch means S1, and adjusting an applied voltage of the snubber capacitor C2 in response to the voltage step-up operation of the main voltage step-up section. When the output voltage is stepped up by the voltage step-up section via a switching operation of the main switch means S1, the main switch means S1 removes charges accumulated on the snubber capacitor C2 before performing a predetermined switching operation. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a fuel cell system that supplies electric power from a fuel cell that generates electric power by an electrochemical reaction to a drive motor.

  In recent years, a fuel cell has attracted attention as a power source excellent in operating efficiency and environmental performance. The fuel cell controls the supply amount of fuel gas and outputs electric power according to the request from the drive motor, but due to the delay in response of the gas supply amount, the responsiveness of the output power may be low, A secondary battery may be mounted for compensation. This secondary battery stores the regenerative energy generated when the drive motor decelerates and the electric power generated by the fuel cell, compensates for a decrease in the responsiveness of the fuel cell, and increases the output of the entire fuel cell system. For this purpose, the stored energy is discharged.

  Here, in a fuel cell system in which a fuel cell and a secondary battery are connected in parallel to constitute a power source, the output voltage of the fuel cell and the output voltage of the secondary battery are converted by a DC-DC converter, We plan to use it together. A snubber capacitor is provided in parallel with the switch element in order to reduce a loss caused by the switching operation of the switch element included in the DC-DC converter, that is, a so-called switching loss (see, for example, Patent Document 1). In this technique, the charge stored in the snubber capacitor is recovered by the switching operation of another switch element, thereby reducing the switching loss in the DC-DC converter.

Patent Document 2 also discloses a technique related to a so-called soft switch for reducing switching loss in a DC-DC converter. In this technique, when soft switching is performed, the resonance action with the resonance inductance is used for charging and discharging the buffer capacitor. As a result, noise and heat are suppressed during voltage boosting.
JP 2001-224165 A JP 2003-33013 A JP 2007-184243 A

  In a DC-DC converter that boosts an output voltage from a DC power source such as a fuel cell, a desired voltage can be applied to a load by a combination of a switching operation by a switch element and a coil. However, in the switching operation by this switch element, there is a possibility that the voltage conversion efficiency of the DC-DC converter is lowered due to switching loss.

  Therefore, so-called soft switch control is useful in which a buffer capacitor is provided in parallel with the switch element so as not to generate a spike voltage during a switching operation, and a sudden rise in voltage is avoided. However, even when this soft switch control is executed, some voltage may be applied to the switch element, and if a switching operation is performed at that time and current flows into the switch element, the occurrence of switching loss is inevitable. .

  The present invention has been made in view of the above problems, and an object of the present invention is to suppress switching loss as much as possible in a boost converter such as a DC-DC converter that boosts an output voltage from a DC power source such as a fuel cell. And

  In the present invention, in order to solve the above-mentioned problem, a snubber capacitor for performing so-called soft switch control is provided in parallel with the switch element, and the electric charge accumulated in the snubber capacitor is removed before the switching operation by the switch element. It was decided to. As a result, the switching operation is performed in a state where the voltage applied to the switch element is extremely low, and as a result, the switching loss can be kept low.

  Therefore, in detail, the present invention relates to a fuel cell that is a DC power supply, a booster that boosts the output voltage of the fuel cell and applies the boosted voltage to a load, and a booster that controls voltage boosting by the booster Control means, wherein the boosting unit performs switching operation by main switch means on the main coil connected to the high potential side terminal of the fuel cell, A main booster that boosts the output voltage of the fuel cell; and a snubber capacitor that is connected in parallel to the main switch means and can adjust a voltage applied to the main switch means; and boosts by the main booster An auxiliary boosting unit that adjusts an applied voltage of the snubber capacitor according to an operation, and the boosting control unit outputs power from the boosting unit via a switching operation of the main switch unit. When boosting is performed, the main switching means for removing charges accumulated in the snubber capacitor prior to performing a predetermined switching operation.

  In the fuel cell system, the DC voltage output from the fuel cell is boosted by the booster, and the boosted voltage is applied to the load. Thereby, an arbitrary voltage up to a relatively high voltage can be applied to the load, and various effects can be given to driving the load. Here, the booster has a main booster and an auxiliary booster, and the main booster boosts the output voltage of the fuel cell by the action of the main coil and the main switch means.

  When the voltage is boosted by the main booster, the auxiliary booster adjusts the applied voltage of the snubber capacitor in accordance with the boosting operation of the main booster. Since the snubber capacitor of the auxiliary booster is connected in parallel to the main switch means, the voltage applied to the main switch means is prevented from changing suddenly even if the switching operation of the main switch means is performed. Therefore, the spike voltage is less likely to occur. Therefore, in boosting the output voltage of the fuel cell in the auxiliary boosting unit, the voltage applied to the main switch means via the applied voltage of the snubber capacitor is appropriately adjusted, so that when boosting the voltage by the boosting unit. The switching loss can be reduced.

  Here, the step-up control means removes the charge of the snubber capacitor before the main switch means performs a predetermined switching operation in the voltage step-up control via the step-up part having the main step-up part and the auxiliary step-up part. The predetermined switching operation is a switching operation in which a current flows into the switch means by the switching operation of the main switch means, and is one of the switching operations when the voltage boosting by the boosting unit is performed. .

  Accordingly, in the state where the voltage applied to the main switch means is lowered due to the removal of the charge of the snubber capacitor by the boost control means, preferably the voltage applied to the main switch means is zero when the charge of the snubber capacitor is completely removed. In this state, a predetermined switching operation of the main switch means is performed. As a result, it is possible to further reduce the switching loss due to the switching operation of the main switch means in the voltage boosting by the boosting unit.

Here, in the fuel cell system, the boost control means includes first boosting means for storing electric power from the fuel cell in the main coil by the first switching operation of the main switch means, and the main switch means. And a second booster that supplies the power stored by the first booster to the load through the snubber capacitor by a second switching operation. In this case, the predetermined switching The operation may be the first switching operation.

  As described above, the boost control unit controls the voltage boost by the boost unit. Therefore, the voltage boosting is performed by first storing the electric power from the fuel cell in the main coil by the first boosting unit, and then boosting the load side by taking into consideration the characteristics of the snubber capacitor described above by the second boosting unit. A voltage is applied. The functions of the first and second boosting means are exhibited by the switching operation of the main switch means (the former is the first switching operation and the latter is the second switching operation). That is, the control of the boosting unit by the boosting control means is performed through the control of the switching operation of the main switch means.

  Here, the first switching operation in the first step-up means is a switching operation for storing electric power in the main coil. Therefore, current may flow into the main switch means by this first switching operation. Therefore, the boost control means performs the above-described snubber capacitor charge removal before the first switching operation is performed, so that the switching operation of the main switch means during the processing by the first boosting means, that is, the first switching operation. It is possible to reliably reduce the switching loss due to.

  In the fuel cell system described above, the main boosting unit has one end connected to the terminal on the high potential side of the fuel cell, and one pole connected to the other end of the main coil. The main switch means for switching, the other pole being connected to the terminal on the low potential side of the fuel cell, the first diode having the cathode terminal connected to the other end of the main coil, and the first diode And a smoothing capacitor provided between the anode terminal and the other pole of the main switch means. The auxiliary boosting unit is provided in parallel with the main switch means, and is connected between the other end of the main coil and a terminal on the low potential side of the fuel cell, and the snubber capacitor. And an inductive element connected between a connection portion between the second diode and the snubber capacitor in the first series connection body and one end of the main coil. You may make it have a 2nd serial connection body containing the auxiliary | assistant coil, the 3rd diode, and the auxiliary switch means which performs switching. At this time, the step-up control means may remove the electric charge stored in the snubber capacitor according to the resonance action of the auxiliary coil and the snubber capacitor by the switching operation of the auxiliary switch means.

  That is, the snubber capacitor in the auxiliary boosting unit suppresses a rapid increase in the voltage applied to the main switch means and further suppresses the switching loss of the main switch means, and the snubber capacitor and the second series connection body. The auxiliary coil is caused to resonate to remove electric charges in the snubber capacitor. Thereby, quick charge removal from the snubber capacitor becomes possible.

  Here, in the fuel cell system described above, the auxiliary boosting unit has a plurality of removing means for removing the electric charge stored in the snubber capacitor, and the boosting unit uses the switching operation of the main switch unit. When the output voltage is boosted, the boost control unit selects a removing unit used for removing the charge of the snubber capacitor from the plurality of removing units based on an electrical state in the boosting unit. May be.

That is, the fuel cell system according to the present invention is provided with a plurality of removing means for removing the charge of the snubber capacitor. In other words, the switching loss of the main switch means is allowed based on the electrical condition of the boosting unit. In order to remove the electric charge of the snubber capacitor as much as possible to suppress it as much as possible, a necessary removing means is selected based on the electrical condition of the booster related to the electric charge removal of the snubber capacitor. . As a result, a removing means according to the need for charge removal is used, and therefore it is possible to completely remove the charge of the snubber capacitor.

  As an example of a plurality of removing means, an auxiliary boosting unit of the fuel cell system is provided in parallel to the auxiliary switch means of the second series connection body, and a predetermined location of the second series connection body There may be mentioned a case where the fuel cell further includes second auxiliary switch means connected to a terminal on the low potential side of the fuel cell. At this time, the boost control means may select at least one of the auxiliary switch means and the second auxiliary switch means for removing the charge of the snubber capacitor. In the present invention, either one or both of the auxiliary switch means and the second auxiliary switch means are selected. However, when both are selected, the auxiliary switch means and the second auxiliary switch means are not necessarily switched simultaneously. There is no need to let them. The timing of switching between the two may be any timing suitable for removing the charge of the snubber capacitor. In this regard, even if the number of removing means is three or more, the charge removing by each removing means is similarly performed at a timing suitable for the charge removal of the snubber capacitor.

  The technical idea of the present invention disclosed in the fuel cell system described above can also be applied to a DC-DC converter that boosts the output voltage of a DC power supply and applies the boosted voltage to a load. That is, the DC-DC converter includes a main boosting unit that boosts the output voltage of the DC power supply by performing a switching operation by the main switch means on the main coil connected to the high potential side terminal of the DC power supply. And a snubber capacitor connected in parallel to the main switch means and capable of adjusting a voltage applied to the main switch means, and an applied voltage of the snubber capacitor according to a boosting operation by the main boosting unit When the boosting of the output voltage of the DC power source is performed through the auxiliary boosting unit that is adjusted and the switching operation of the main switch means, the snubber capacitor is charged before the main switch means performs a predetermined switching operation. Boosting control means for removing the generated charges.

  In the DC-DC converter, the step-up control means includes a first step-up means for storing power from the DC power source in the main coil by a first switching operation of the main switch means, and the main switch means. Second boosting means for supplying the electric power stored by the first boosting means to the load through the snubber capacitor by the second switching operation, and the predetermined switching operation is It may be a switching operation.

  In the above-described DC-DC converter, similarly to the fuel cell system described above, it is possible to suppress the switching loss of the main switch means at the time of voltage boost as much as possible.

  According to the fuel cell system of the present invention, switching loss can be suppressed as much as possible in a boost converter such as a DC-DC converter that boosts an output voltage from a DC power source such as a fuel cell.

  An embodiment of a fuel cell system 10 according to the present invention will be described in detail based on the drawings. The fuel cell system 10 according to the present embodiment supplies power to a drive motor 16 that is a drive device of a vehicle 1 that is a moving body. It can also be applied to objects that do not move but need to be supplied with power.

  FIG. 1 schematically shows a schematic configuration of a fuel cell system 10 according to the present invention and a mobile vehicle 1 that uses electric power supplied from the fuel cell system 10 as a drive source. The vehicle 1 is self-propelled and movable when the drive wheels 2 are driven by a drive motor (hereinafter simply referred to as “motor”) 16. The motor 16 is a so-called three-phase AC motor and receives supply of AC power from the inverter 15. Further, DC power is supplied to the inverter 15 from a fuel cell (hereinafter also referred to as “FC”) 11 which is a main power source of the fuel cell system 10 and a battery 13 which is a secondary battery. 15 is converted to alternating current.

  Here, the fuel cell 11 generates power by an electrochemical reaction between hydrogen gas stored in the hydrogen tank 17 and oxygen in the air pumped by the compressor 18, and the fuel cell 11 and the inverter 15 An FC boost converter 12, which is a boost DC-DC converter, is electrically connected between them. As a result, the output voltage from the fuel cell 11 is boosted to an arbitrary voltage within a range controllable by the FC boost converter 12 and applied to the inverter 15. In addition, the terminal voltage of the fuel cell 11 can be controlled by the boosting operation of the FC boost converter 12. The detailed configuration of the FC boost converter 12 will be described later. The battery 13 is a chargeable / dischargeable power storage device, and is a boost type battery booster so that the inverter 15 is in parallel with the FC boost converter 12 between the battery 13 and the inverter 15. Converter 14 is electrically connected. As a result, the output voltage from the battery 13 is boosted to an arbitrary voltage within a range controllable by the battery boost converter 14 and applied to the inverter 15. Further, the terminal voltage of the inverter 15 can be controlled by the boosting operation of the battery boosting converter 14. As shown in FIG. 1, in the fuel cell system 10, a step-up / step-down converter capable of a step-up operation and a step-down operation can be employed instead of the step-up type battery step-up converter 14. In the following embodiments, the description will be given mainly assuming that the battery boost converter 14 is a boost converter. However, there is no intention to limit the use of the step-up / step-down converter, and appropriate adjustments are made in the use. . Then, by adopting the buck-boost converter, the facts that should be further noted will be appropriately disclosed.

  Further, the vehicle 1 is provided with an electronic control unit (hereinafter referred to as “ECU”) 20, and is electrically connected to each of the above-described control objects, thereby generating power for the fuel cell 11, driving the motor 16, and the like. Will be controlled. For example, the vehicle 1 is provided with an accelerator pedal that receives an acceleration request from the user, the opening degree thereof is detected by the accelerator pedal sensor 21, and the detection signal is electrically transmitted to the ECU 20. The ECU 20 is also electrically connected to an encoder that detects the number of rotations of the motor 16, whereby the number of rotations of the motor 16 is detected by the ECU 20. The ECU 20 can perform various controls based on these detection values and the like.

  In the fuel cell system 10 configured as described above, the accelerator pedal opening degree that the user of the vehicle 1 has stepped on is detected by the accelerator pedal sensor 21, and the ECU 20 is based on the accelerator opening degree and the rotational speed of the motor 16. The power generation amount of the fuel cell 11 and the charge / discharge amount from the battery 13 are appropriately controlled. Here, in order to improve the fuel consumption of the vehicle 1 which is a moving body, the motor 16 is a PM motor with a high voltage and low current specification. Accordingly, since the motor 16 can exhibit a high torque at a low current, it is possible to reduce heat generation in the windings and other wirings inside the motor, and to reduce the rated output of the inverter 15. It becomes possible. Specifically, in the motor 16, the counter electromotive voltage is set to be relatively high in order to enable a relatively large torque output at a low current, while the motor 16 has a high rotational speed against the high counter electromotive voltage. The supply voltage from the fuel cell system 10 is set high so that it can be driven. At this time, the FC boost converter 12 is provided between the fuel cell 11 and the inverter 15, and the battery boost converter 14 is also provided between the battery 13 and the inverter 15, thereby increasing the supply voltage to the inverter 15. It is done. Again, a step-up / step-down converter may be employed in place of the battery boost converter 14.

  In this way, by configuring the fuel cell system 10 to include the FC boost converter 12, the motor 16 is driven by the boost operation of the FC boost converter 12 even if the output voltage (terminal voltage) of the fuel cell 11 itself is low. Therefore, it is possible to reduce the size of the fuel cell 11 by reducing the number of stacked cells. As a result, the weight of the vehicle 1 can be reduced, and the fuel consumption can be further improved.

  Here, in the fuel cell system 10, a fuel cell 11 that can generate power is a main power source for the motor 16. Therefore, in order to improve the efficiency of the fuel cell system 10, reducing the power loss in the FC boost converter 12 interposed between the fuel cell 11 and the inverter 15 will greatly contribute to improving the efficiency of the entire system. Conceivable. Of course, the same applies in principle to the battery boost converter 14 between the battery 13 and the inverter 15.

  Here, the characteristics of the electric circuit of the FC boost converter 12 will be described with reference to FIG. FIG. 2 is a diagram showing the electrical configuration of the fuel cell system 10 with the FC boost converter 12 as the center, but the description of the battery 13 and the battery boost converter 14 is omitted for ease of explanation.

  The FC boost converter 12 includes a main boost circuit 12a for performing a boost operation as a DC-DC converter, and an auxiliary circuit 12b for performing a soft switching operation to be described later. The main booster circuit 12a releases the energy stored in the coil L1 to the motor 16 side (inverter 15 side) via the diode D5 by the switching operation of the switching circuit composed of the switching element S1 and the diode D4. The output voltage of the battery 11 is boosted. Specifically, one end of the coil L1 is connected to the terminal on the high potential side of the fuel cell 11. The pole at one end of the switch element S1 is connected to the other end of the coil L1, and the pole at the other end of the switch element S1 is connected to a terminal on the low potential side of the fuel cell. The cathode terminal of the diode D5 is connected to the other end of the coil L1, and the capacitor C3 is connected between the anode terminal of the diode D5 and the other end of the switch element S1. In the main booster circuit 12a, the capacitor C3 functions as a smoothing capacitor for the boost voltage. The main booster circuit 12a is also provided with a smoothing capacitor C1 on the fuel cell 11 side, which makes it possible to reduce the ripple of the output current of the fuel cell 11. The voltage VH applied to the smoothing capacitor C3 becomes the outlet voltage of the FC boost converter 12. In FIG. 2, the power supply voltage of the fuel cell 11 is indicated by VL, which is a voltage applied to the smoothing capacitor C <b> 1 and an inlet voltage of the FC boost converter 12.

Next, the auxiliary circuit 12b includes a first series connection including a diode D3 connected in parallel to the switch element S1 and a snubber capacitor C2 connected in series thereto. In the first series connection body, the cathode terminal of the diode D3 is connected to the other end of the coil L1, and the anode terminal thereof is connected to one end of the snubber capacitor C2. Furthermore, the other end of the snubber capacitor C2 is connected to a low potential side terminal of the fuel cell 11. Further, the auxiliary circuit 12b includes a second series connection body in which a coil L2, which is an inductive element, a diode D2, and a switching circuit composed of the switch element S2 and the diode D1 are connected in series. In this second series connection body, one end of the coil L2 is connected to a connection site between the diode D3 and the snubber capacitor C2 of the first series connection body. Further, the cathode terminal of the diode D2 is connected to the other end of the coil L2, and the anode terminal thereof is connected to the pole of one end of the switch element S2. The other end of the switch element S2 is connected to one end side of the coil L1. In addition, about the circuit topology of this 2nd series connection body, the form which replaced suitably the series order of the switching circuit by the coil L2, the diode D2, switch element S2, etc. can also be employ | adopted. In particular, instead of the state shown in FIG. 2, the order of the switching circuit including the coil L2 and the switch element S2 is changed, so that the coil L1 and the coil L2 can be integrated in an actual mounting circuit, and the modularization of the semiconductor element is easy It becomes.

  The FC boost converter 12 configured as described above adjusts the switching duty ratio of the switch element S1, thereby increasing the boost ratio by the FC boost converter 12, that is, the output voltage of the fuel cell 11 input to the FC boost converter 12. The ratio of the output voltage of the FC boost converter 12 applied to the inverter 15 is controlled. Further, by interposing the switching operation of the switching element S2 of the auxiliary circuit 12b in the switching operation of the switching element S1, so-called soft switching described later is realized, and the switching loss in the FC boost converter 12 can be greatly reduced. It becomes.

  Next, soft switching in the FC boost converter 12 will be described based on FIGS. 3 and 4A to 4F. FIG. 3 is a flowchart of one cycle processing (hereinafter referred to as “soft switching processing”) for boosting in the FC boost converter 12 via the soft switching operation. In the soft switching process, each process of S101 to S106 is sequentially performed by the ECU 20 to form one cycle. The mode in which the current and voltage flow in the FC boost converter 12 by each process is expressed as mode 1 to mode 6, respectively. The state is shown in FIGS. The soft switching process in the FC boost converter 12 will be described below based on these drawings. In FIGS. 4A to 4F, reference numerals of the main booster circuit 12a and the auxiliary circuit 12b are omitted for the sake of brevity, but each circuit is cited in the description of each mode. There is a case. In each figure, a thick arrow indicates a current flowing through the circuit.

  The initial state in which the soft switching process shown in FIG. 3 is performed is a state where electric power is supplied from the fuel cell 11 to the inverter 15 and the motor 16, that is, when both the switch elements S1 and S2 are turned off, the coil L1 In this state, current flows to the inverter 15 side via the diode D5. Therefore, when one cycle of the soft switching process is completed, the same state as the initial state is reached.

  In the soft switching process, first, in S101, the current / voltage state of mode 1 shown in FIG. 4A is formed. Specifically, the switch element S1 turns on the switch element S2 in a turn-off state. In this way, due to the potential difference between the outlet voltage VH and the inlet voltage VL of the FC boost converter 12, the current flowing to the inverter 15 side via the coil L1 and the diode D5 gradually shifts to the auxiliary circuit 12b side. . In FIG. 4A, the state of the current transition is indicated by a white arrow.

  Next, in S102, when the state of S101 continues for a predetermined time, the current flowing through the diode D5 becomes zero, and instead, the electric charge stored in the snubber capacitor C2 due to the potential difference between the snubber capacitor C2 and the voltage VL of the fuel cell 11. Flows into the auxiliary circuit 12b (mode 2 state shown in FIG. 4B). The snubber capacitor C2 has a function of determining a voltage applied to the switch element S1. When the switch element S1 is turned on, the electric charge of the snubber capacitor C2 that affects the voltage applied to the switch element S1 flows into the auxiliary circuit 12b in mode 2, so that the voltage applied to the snubber capacitor C2 decreases. . At this time, the current continues to flow until the voltage of the snubber capacitor C2 becomes zero due to the half-wave resonance of the coil L2 and the snubber capacitor C2. As a result, it is possible to reduce the applied voltage when the switch element S1 is turned on in S103 described later.

Further, in S103, when the electric charge of the snubber capacitor C2 is completely discharged, the switch element S1 is further turned on, and the mode 3 current / voltage state shown in FIG. 4C is formed. That is, when the voltage of the snubber capacitor C2 is zero, the voltage applied to the switch element S1 is also zero, and the switch element S1 is turned on in that state to bring the switch element S1 to the zero voltage state. Therefore, the switching loss in the switch element S1 can theoretically be zero.

  In S104, the state of S103 continues, increasing the amount of current flowing into the coil L1, and gradually increasing the energy stored in the coil L1. This state is the current / voltage state of mode 4 shown in FIG. 4D. Thereafter, when desired energy is stored in the coil L1, the switch elements S1 and S2 are turned off in S105. Then, the electric charge is extracted in the mode 2 and the snubber capacitor C2 in the low voltage state is charged, and reaches the same voltage as the outlet voltage VH of the FC boost converter 12. This state is the current / voltage state of mode 5 shown in FIG. 4E. When the snubber capacitor C2 is charged to the voltage VH, the energy stored in the coil L1 in S106 is released to the inverter 15 side. This state is the current / voltage state of mode 6 shown in FIG. 4F. When this mode 5 is performed, the voltage applied to the switch element S1 is delayed by the snubber capacitor C2, so that the switching loss due to the tail current in the switch element S1 can be further reduced.

  As described above, the soft switching process is performed with the processes of S101 to S106 as one cycle, so that the switching loss in the FC boost converter 12 is suppressed as much as possible, and the output voltage of the fuel cell 11 is boosted to the inverter 15. Supply becomes possible. As a result, it is possible to efficiently drive the motor 16 which is a high voltage low current motor.

  Here, in the fuel cell system 10, in addition to the soft switching process, the intermittent operation control of the FC boost converter 12 is performed, thereby improving the system efficiency. For the sake of brevity, paying attention to the relationship between the fuel cell 11 and the inverter 15 and the motor 16, the power from the fuel cell 11, which is the main power source for the motor 16, is connected to the inverter 15 side via the FC boost converter 12. Supplied to. The voltage to be applied to the inverter 15 when the fuel cell 11 as the main power source drives the motor 16 must be a voltage that can sufficiently resist the counter electromotive force of the motor 16. Therefore, in the conventional fuel cell system not provided with the FC boost converter 12, as shown in FIG. 5, the fuel cell indicated by LV1 is applied in the speed range (0 to VSmax) that the vehicle 1 can take. The voltage must always exceed the voltage that is necessary for driving the motor and should be applied to the inverter 15 (hereinafter referred to as “motor required voltage”). Therefore, a voltage that greatly exceeds the voltage to be applied to the inverter is applied to the inverter, and the switching loss of the inverter is increased. And especially in the area | region where the speed of the vehicle 1 is low, the switching loss of an inverter may become remarkable.

  Here, since the FC boost converter 12 is provided in the fuel cell system 10 according to the present invention, the voltage from the fuel cell 11 can be boosted and applied to the inverter 15. However, in the boosting operation by the FC boost converter 12, some switching loss occurs due to the switching element, so that the boosting operation is a cause of reducing the efficiency of the system. On the other hand, as described above, since the motor 16 is a high-voltage, low-current motor, the back electromotive voltage generated with the increase in the number of rotations increases, and the boosting operation by the FC boost converter 12 is indispensable. Become.

Therefore, the correlation between the output voltage from the fuel cell 11 and the required motor voltage to be applied to the inverter 15 is indicated by LV1 and LV2 in FIG. As indicated by LV <b> 2 in FIG. 6, the counter electromotive voltage of the motor 16 increases as the speed of the vehicle 1 increases. Therefore, the required motor voltage also increases as the vehicle speed increases. Here, in the correlation between the output voltage LV1 of the fuel cell 11 and the required motor voltage LV2, the fuel 1 is set so that the speed VS0 of the vehicle 1 when the two intersect each other is a speed that substantially covers the normal operation of the vehicle 1 by the user. The voltage characteristic of the battery 11 and the voltage characteristic of the motor 16 may be determined. In the present embodiment, VS0 is set to 110 km / h from the vehicle driving regulations and the tendency of the user's normal operation. Then, the maximum output during driving of the motor 16 that enables the vehicle 1 to travel at the speed VS0 is calculated, and the voltage (motor required voltage) to be applied to the inverter 15 so that the maximum output can be exhibited. ) Is derived. Then, the design of the fuel cell 11 (for example, in a fuel cell formed by stacking a plurality of cells) so that the required motor voltage can be directly output from the fuel cell 11 without going through the FC boost converter 12. The number of stacked cells is adjusted).

  In the fuel cell system 10 including the fuel cell 11 designed in this way, the output voltage from the fuel cell 11 is higher than the motor required voltage for driving the motor 16 until the speed of the vehicle 1 reaches VS0. Therefore, even if the motor 16 is a high voltage low current specification motor, the motor 16 can be driven by the direct output voltage from the fuel cell 11 without the boost operation of the FC boost converter 12. Become. In other words, under this condition, the driving operation of the motor 16 can be ensured by stopping the switching operation by the FC boost converter 12 and applying the output voltage from the fuel cell 11 to the inverter 15. Thereby, the switching loss in the FC boost converter 12 can be completely eliminated. Furthermore, since the voltage applied to the inverter 15 does not become excessively high because the FC boost converter 12 is stopped, that is, the voltage difference between LV1 and LV2 can be suppressed to be smaller than in the state shown in FIG. The switching loss in the inverter 15 can be kept low.

  On the other hand, when the vehicle speed of the vehicle 1 is equal to or higher than VS0, the required motor voltage for driving the motor 16 becomes higher than the output voltage from the fuel cell 11, so that the boost operation by the FC boost converter 12 is necessary. It becomes. In this case, the switching loss in the FC boost converter 12 can be suppressed as much as possible by performing the above-described soft switching processing.

  Up to the above, only the correlation between the fuel cell 11 and the motor 16 has been focused on for the sake of simplicity of explanation. However, in the fuel cell system 1, as shown in FIG. It is also possible to supply power. When power is supplied from the battery 13, the output voltage from the battery 13 is boosted by the battery boost converter 14 and then applied to the inverter 15. Here, since the battery boost converter 14 is a so-called boost converter, in order to supply power from the battery 13 to the inverter 15, the outlet voltage of the battery boost converter 14 (the voltage on the inverter 15 side, the FC boost converter 12 Is equal to or higher than the inlet voltage (battery 13 side voltage).

Therefore, the correlation between the output voltage of the battery 13 and the output voltage of the fuel cell 11 will be described with reference to FIGS. 7A and 7B. In both figures, the IV characteristic of the battery 13 (indicated by the dotted line LBT in the figure) and the IV characteristic of the fuel cell 11 (indicated by the solid line LFC in the figure) are shown. 7A, in the region where the IV characteristic LFC of the fuel cell 11 is higher than the IV characteristic LBT of the battery 13, even if the FC boost converter 12 is stopped, the output voltage of the battery 13 is the outlet voltage of the FC boost converter 12. Since the battery boost converter 14 is in a lower state, the battery boost converter 14 can perform a boost operation, and power can be supplied from the battery 13 to the motor 16. Therefore, in this state, operation stop of the FC boost converter 12 is allowed. On the other hand, in the region where the IV characteristic LBT of the battery 13 is higher than the IV characteristic LFC of the fuel cell 11, when the FC boost converter 12 is stopped, the output voltage of the battery 13 becomes higher than the outlet voltage of the FC boost converter 12. Therefore, the output distribution control of the fuel cell 11 and the battery 13 by the boost operation of the battery boost converter 14 becomes impossible. Therefore, the operation stop of the FC boost converter 12 is not allowed in this state.

  That is, when boosting the output voltage from the battery 13 by the battery boost converter 14 and applying the voltage to the motor 16, the outlet voltage of the FC boost converter 12 is the output voltage of the battery 13 (the inlet of the battery boost converter 14). Therefore, there is a case where the operation of the FC boost converter 12 is not permitted to be stopped. For example, as shown in FIG. 7A, when the IV characteristic LFC of the fuel cell 11 is lower than the IV characteristic LBT of the battery 13 in a relatively low current region, in order to ensure the boost operation of the battery boost converter 14, Stopping the operation of the FC boost converter 12 is not allowed, and as a result, the possibility of reducing the switching loss described above is lowered. On the other hand, for example, as shown in FIG. 7B, when the IV characteristic LFC of the fuel cell 11 is always above the IV characteristic LBT of the battery 13, from the viewpoint of ensuring the boost operation of the battery boost converter 14, the FC boost converter Twelve operation stops are not limited.

  The operation limitation of the FC boost converter 12 related to ensuring the boost operation of the battery boost converter 14 up to the above is that the battery boost converter 14 included in the fuel cell system 10 shown in FIG. Due to the fact that there is no converter). Therefore, in the fuel cell system 10, when the step-up / step-down converter capable of the boosting operation and the step-down operation is adopted instead of the battery boosting converter 14, the FC boosting converter 12 is not restricted by the above-described operation restriction. Output voltages from the fuel cell 11 and the battery 13 can be selectively applied to the motor 16.

  As described above, in this embodiment, the necessary IV characteristics of the battery 13 and the IV characteristics of the fuel cell 11 are determined based on the assumed driving of the vehicle 1, and the correlation between both IV characteristics and the output voltage of the fuel cell 11 are determined. From the relationship with the required motor voltage, a control region for the boosting operation of the FC boost converter 12 as shown in the maps of FIGS. 8A and 8B was defined. Hereinafter, the boosting operation of the FC boost converter 12 will be described in detail.

  8A and 8B show the processing executed in the FC boost converter 12 in association with the operation region formed with the inlet voltage of the FC boost converter 12 as the horizontal axis and the outlet voltage as the vertical axis. It is a map. 8A is a map when the battery boost converter 14 included in the fuel cell system 10 is a boost converter, and FIG. 8B is a step-up / step-down converter instead of the boost battery boost converter 14. It is a map when adopting. First, the map shown in FIG. 8A will be described. Here, the map includes a straight line LR1 which means that the boost ratio by the FC boost converter 12 is 1, that is, the ratio of the inlet voltage to the outlet voltage is 1: 1, and the boost ratio is A straight line LR2 that means a value in the vicinity of 2 (in the figure, the boost ratio is simply indicated as “2”), a straight line LR3 that means that the boost ratio is 10, and the FC boost converter 12 A straight line LR4 indicating the highest output voltage is described. The straight line LR2 will be described later with reference to FIGS. 9, 10A, and 10B. A straight line LR3 indicates the maximum boost ratio by the FC boost converter 12. Therefore, it can be seen that the operation range of the FC boost converter 12 is a region surrounded by the straight lines LR1, LR3, and LR4.

Here, in the assumed speed range of the vehicle 1, when the load applied to the motor 16 is the lowest, that is, when the load about the frictional resistance of the road is applied (in the figure, load factor = R / L (Road Load)) FC boosting The relationship between the inlet voltage of converter 12 and its outlet voltage is indicated by a one-dot chain line LL1. On the other hand, in the same way, in the assumed speed range of the vehicle 1, when the load applied to the motor 16 is the highest, that is, when the accelerator opening of the vehicle 1 is 100% (in the figure, the load factor = 100%), the FC boosting The relationship between the inlet voltage of converter 12 and its outlet voltage is indicated by a one-dot chain line LL2. Therefore, the fuel cell system 10 mounted on the vehicle 1 causes the FC boost converter 12 to perform the boosting operation indicated by the region sandwiched between the alternate long and short dash lines LL1 and LL2 from the viewpoint of driving the vehicle 1. become.

In the map shown in FIG. 8A, the operation region of the FC boost converter 12 is divided into four regions RC1 to RC4. In these areas, characteristic operations relating to the operation of the FC boost converter 12 are performed, and the operation of the FC boost converter 12 in each area will be described below. First, a region RC1 is defined as a region below the straight line LR1 indicating the step-up ratio 1. In this region RC1, the step-up ratio required for driving the motor 16 is 1 or less (actually, since the FC boost converter 12 is a step-up converter, the step-up ratio is set to 1 or less, that is, step-down) Note that it is possible to stop the FC boost converter 12 and apply the output voltage of the fuel cell 11 directly to the inverter 15 as a result. Therefore, the output voltage of the fuel cell 11 serving as the inlet voltage of the FC boost converter 12 is a range between the maximum voltage Vfcmax of the fuel cell 11 and the Vfcb having the same value as the open circuit voltage (OCV) of the battery 13. In the region RC1 defined by being surrounded by the straight line LR1 and the one-dot chain line LL1, the boosting operation of the FC boost converter 12 is completely stopped. As a result, switching loss in the FC boost converter 12 can be suppressed. As described above, the operation stop of the FC boost converter 12 is restricted with the voltage Vfcb as a boundary, because the battery boost converter 14 is a boost converter as described above, so as to ensure the boost operation.

  Next, the region RC2 will be described. This region is defined as a region where the inlet voltage of the FC boost converter 12 is equal to or lower than the above Vfcb, and the outlet voltage of the FC boost converter 12 is equal to or lower than the OCV of the battery 13, that is, equal to or lower than the voltage equal to Vfcb. . That is, in this region RC2, if the boost operation of the FC boost converter 12 is not performed, the outlet voltage of the battery boost converter 14 becomes lower than the inlet voltage, and the boost operation of the battery boost converter 14 becomes impossible. Even if the boosting operation of the FC boosting converter 12 is performed, the boosting operation of the battery boosting converter 14 is similarly impossible because the boosting ratio is low.

  In the region RC2 defined in this way, the FC boost converter 12 is stopped so that the switching loss does not occur, similarly to the region RC1. Then, the terminal voltage of the fuel cell 11 is controlled to the lowest voltage that can be controlled by the battery boost converter 14. In the figure, when an ideal boost converter is used, the voltage Vfcb is set on the assumption that the voltage is equal to the OCV of the battery 13. This state is continued as long as the discharge power of the battery 13 permits.

  This region RC2 is a transitional region that is interposed when the operation region of the FC boost converter 12 shifts from the region RC1 to a region RC3 described later while the driving state of the motor 16 changes. Therefore, when the battery boost converter 14 is a boost converter, the IV characteristics of the fuel cell 11 and the battery 13 described with reference to FIGS. 7A and 7B are set so that the transient region RC2 becomes as small as possible. It is preferable to appropriately adjust the correlation with the IV characteristics.

Here, regarding the region below the straight line LR1, the map shown in FIG. 8B, that is, the map when the step-up / step-down converter is employed instead of the battery boost converter 14 in the fuel cell system 10 will be described. In this case, since the output voltage of the battery 13 can be stepped down by the step-up / step-down converter, the operation stop of the FC boost converter 12 is not restricted by the voltage Vfcb as described above. Therefore, as shown in FIG. 8B, in the region below the straight line LR1, it becomes easy to stop the operation of the FC boost converter 12 without restriction and improve the efficiency of the system. Therefore, this results in FIG.
In B, there is no region corresponding to the region RC2. Here, the description of the map shown below applies to FIGS. 8A and 8B in common, and therefore the description will be given collectively.

  In the operation region other than the regions RC1 and RC2 described above, the FC boost converter 12 is driven and the output voltage of the fuel cell 11 is boosted. In this step-up operation, the switching loss in the FC step-up converter 12 is suppressed as much as possible by executing the soft switching processing described based on FIGS. Here, the operation region in which the soft switching process is performed is divided into a semi-soft switch region RC3 and a soft switch region RC4 by a straight line LR2. Hereinafter, the semi-soft switch region RC3 and the soft switch region RC4 will be described in detail.

  First, the technical significance of the straight line LR2 will be described. As described above, the straight line LR2 is a straight line that means that the boost ratio by the FC boost converter 12 becomes a value in the vicinity of 2. The electrical structure of the FC boost converter 12 according to the present invention is as shown in FIG. 2, but in the operation of mode 2 in the above-described series of soft switching processes, the coil L2 of the auxiliary circuit 12b and the snubber capacitor C2 are used. The snubber capacitor C2 is discharged using half-wave resonance. If only the part actually operating in the FC boost converter 12 is extracted in the operation of mode 2, the circuit configuration shown in FIG. 9 is obtained.

  In the circuit configuration shown in FIG. 9, unless the electric charge charged in the snubber capacitor C2 is completely discharged, the switch element S1 is in a state where a voltage is applied to the switch element S1 in the subsequent operation of mode 3. As a result, a current is generated due to the turn-on, resulting in a switching loss. Therefore, it is understood that it is important to completely discharge the electric charge of the snubber capacitor C2 in this mode 2. For this purpose, the energy stored in the coil L2 at the time of operation of mode 1 is transferred to the snubber capacitor C2. Must be greater than the energy stored. In other words, the outlet voltage VH of the FC boost converter 12 must be higher than the inlet voltage VL by a predetermined amount or more.

  Therefore, the relationship between the ratio VH / VL between the outlet voltage and the inlet voltage and the voltage remaining in the snubber capacitor C2 during the discharge will be described with reference to FIGS. 10A and 10B. 10A shows the voltage transition of the snubber capacitor C2 when the ratio VH / VL exceeds 2, and FIG. 10B shows the voltage transition of the snubber capacitor C2 when the ratio VH / VL is less than 2. In the case shown in FIG. 10A, the value of VH−VL becomes larger than VL. Therefore, when half-wave resonance occurs, the voltage of the snubber capacitor C2 becomes zero due to the action of the diode D2. On the other hand, in the case shown in FIG. 10B, since the value of VH−VL is smaller than VL, even if half-wave resonance occurs, the voltage of the snubber capacitor C2 remains above a certain value. Therefore, in such a case, even if the soft switching process is performed, some switching loss occurs. As described above, the straight line LR2 exists as a reference for determining whether or not the switching loss can be effectively suppressed by the soft switching process.

  Theoretically, if the ratio VH / VL is twice or more, the voltage of the snubber capacitor C2 after discharge becomes zero, but in reality, energy loss occurs in the diode and the wiring, so the ratio VH / VL The value of VL is preferably more than twice (for example, 2.3). Then, in the operation region sandwiched between the alternate long and short dash lines LL1 and LL2, the region excluding the regions RC1 and RC2 is divided into two by the straight line LR2, and the region located below the straight line LR2 is subjected to the soft switching process. The quasi-soft switch region RC3 in which it is difficult to efficiently suppress the switching loss even if the switching is performed, and the region located above the straight line LR2 is the soft switch region RC4 in which the switching loss is efficiently suppressed by the soft switching process. And

  As described above, the operation region of the FC boost converter 12 can be divided into predetermined regions RC1 to RC4. However, as described above, the switching loss of the FC boost converter 12 cannot be sufficiently suppressed in the semi-soft switch region RC3. Therefore, from the viewpoint of improving the efficiency of the fuel cell system 10, it is preferable to avoid as much as possible that the FC boost converter 12 performs a boost operation in this region. Therefore, an example of control of the FC boost converter 12 for promoting the efficiency of the fuel cell system 10 will be described with reference to FIG. The FC boost converter control shown in FIG. 11 is executed when the electric power generated by the fuel cell 11 is supplied to the motor 16 by the ECU 20. The boosting operation in the semi-soft switch region RC3 is preferably avoided as much as possible for the better efficiency of the fuel cell system 10, as described above, but the fuel cell system according to the present invention. 10 does not completely exclude the step-up operation, and the step-up operation may be used as necessary.

  First, in S201, the maximum torque that the motor 16 can output at maximum corresponding to the actual rotational speed of the motor 16 detected by the encoder is calculated. Specifically, the ECU 20 has a map in which the rotation speed of the motor 16 is associated with the maximum torque corresponding thereto, and the maximum torque of the motor 16 is obtained by accessing the map according to the detected rotation speed. Calculated. When the process of S201 ends, the process proceeds to S202.

In S202, the required torque requested to be output to the motor 16 is calculated based on the opening of the accelerator pedal detected by the accelerator pedal sensor 21. If it is defined that the fully open of the accelerator pedal requires the maximum torque at the current rotational speed of the motor 16, the required torque according to the following formula, assuming that the coefficient when fully opened is 100% and the coefficient when fully closed is 0%. Is calculated. When the process of S202 ends, the process proceeds to S203.
(Required torque) = (Maximum torque) x (Coefficient according to accelerator pedal opening)

In S203, based on the calculation results in S201 and S202, a required output that is an output required for the motor 16 is calculated according to the following equation. When the process of S203 ends, the process proceeds to S204.
(Request output) = (Request torque) x (Motor speed)

  In S204, the required motor voltage (Vmot), which is a voltage to be applied to the inverter 15, so that necessary power is supplied to the motor 16 based on the required output calculated in S203 and the rotation speed of the motor 16. Calculated. Specifically, the ECU 20 has a motor required voltage map in which the function F formed by the rotation speed (rpm) of the motor 16 and the required output (P) and the motor required voltage are associated with each other. The required voltage of the motor is calculated by accessing this map according to the number of rotations and the required output. The required motor voltage map can be determined in advance by experiments or the like. As an example, the required voltage value should be higher because the counter electromotive voltage increases as the rotational speed of the motor 16 increases. Since the required voltage value should be increased in order to achieve its output with less current as the value of becomes higher, these points are reflected in the correlation between the function F and the required motor voltage. When the process of S204 ends, the process proceeds to S205.

  In S205, the output voltage (Vfc) of the fuel cell 11 that is generating electric power is detected according to the accelerator pedal opening detected by the accelerator pedal sensor 21. This detection is performed via a voltage sensor (not shown). When the processing of S205 ends, the process proceeds to S206. In S206, the required motor voltage calculated in S204 is divided by the output voltage of the fuel cell 11 detected in S205 to calculate a temporary boost ratio Rt (= Vmot / Vfc). When the process of S206 ends, the process proceeds to S207.

In S207, it is determined whether or not the FC boost converter 12 can be stopped.
That is, it is determined whether the operation region of the FC boost converter 12 belongs to either the region RC1 or RC2. Specifically, when the provisional boost ratio calculated in S206 is less than 1 and the output voltage of the fuel cell 11 is between Vfcmax and Vfcb, the operation region of the FC boost converter 12 is RC1, and the fuel When the output voltage of the battery 11 is equal to or lower than Vfcb and the outlet side voltage of the FC boost converter 12 is equal to or lower than the voltage equal to Vfcb, it is determined that the operation region of the FC boost converter 12 is RC2. The values of Vfcb and Vfcmax may be determined in advance according to the actual specifications of the fuel cell 11 and the battery 13. Further, the voltage on the outlet side of the FC boost converter 12 is detected via a voltage sensor (not shown).

  If the determination in step S207 is affirmative, the process proceeds to step S208, where the FC boost converter 12 is stopped and the output voltage from the fuel cell 11 is directly applied to the inverter 15. Thereby, the switching loss in the FC boost converter 12 can be suppressed. As described above, when the operation region of the FC boost converter 12 belongs to RC1, application after boosting from the battery 13 to the inverter 15 is possible, but when the operation region belongs to RC2, the battery boosting operation is possible. The terminal voltage of the fuel cell 11 is controlled to the lowest voltage that can be controlled by the converter 14. On the other hand, if a negative determination is made in S207, the process proceeds to S209.

  In S209, it is determined whether or not the provisional boost ratio Rt calculated in S206 exceeds 2. That is, it is determined whether the operation region of the FC boost converter 12 is in the soft switch region RC4 or the semi-soft switch region RC3. If an affirmative determination is made in S209, it means that the operation region of the FC boost converter 12 is in the soft switch region RC4, so that the process proceeds to S210, and the target output voltage of the FC boost converter 12 becomes the motor required voltage Vmot. The soft switching process indicated by 3 is executed. Note that the duty ratio of the switch element S1 is determined according to the provisional boost ratio Rt. On the other hand, if a negative determination is made in S209, it means that the operation region of the FC boost converter 12 is in the semi-soft switch region RC3. In this case, the process proceeds to S211.

  In S211, in addition to the voltage boost based on the temporary boost ratio Rt calculated in S206 in the fuel cell system 10, further additional voltage boost (hereinafter simply referred to as “additional voltage boost”) is allowed. Is determined. In other words, the negative determination in S209 means that the operation region of the FC boost converter 12 is currently in the quasi-soft switch region RC3, so that the operation region can be shifted to the soft switch region RC4. It is determined whether or not. That is, when an additional voltage boost is performed to shift the operation region from the quasi-soft switch region RC3 to the soft switch region RC4, the voltage applied to the inverter 15 becomes higher than the necessary motor required voltage. As a result, although the switching loss in the inverter 15 becomes large, when the decrease in the switching loss of the FC boost converter 12 is compared with the increase in the switching loss of the inverter 15, the former decrease may be large. It is possible that this additional voltage boost is very useful in terms of system efficiency. Therefore, in S211, it is determined whether or not this additional voltage boost is allowed. If an affirmative determination is made in S211, the operation proceeds to S212, and an additional boost ratio Ra for additional voltage boost is determined. This additional boost ratio Ra is necessary for the final boost ratio by the FC boost converter 12 (boost ratio by Rt × Ra) to exceed the boost ratio determined by the straight line LR2 (for example, boost ratio 2). This is an additional step-up ratio. Then, after the process of S212, the process proceeds to S213, in which the target output voltage of the FC boost converter 12 becomes a voltage calculated by multiplying the output voltage Vfc of the fuel cell 11 by the boost ratio Rt and the additional boost ratio Ra. The soft switching process indicated by 3 is executed. The duty ratio of the switch element S1 is determined according to the product of the temporary boost ratio Rt and the additional boost ratio Ra.

Thus, when the negative determination is made in S209, the FC boost converter 12 is inherently
The operation region is the quasi-soft switch region RC3, and as described above, it is difficult to sufficiently suppress the switching loss even if the soft switching process is performed in that state. In this case, by considering the additional boosting ratio Ra in the boosting ratio by the FC boosting converter 12, the operating region of the FC boosting converter 12 is softened by raising the voltage further than the voltage that is essentially required to drive the motor 16. The switch area RC4. As a result, switching loss can be effectively suppressed.

  On the other hand, if a negative determination is made in S211, the process proceeds to S214, and the soft switching process is performed in a state where the operation region of the FC boost converter 12 is RC3. When the fuel cell 11 is in a state where the additional voltage boosting is not allowed, that is, in a state where the switching loss in the inverter 15 becomes significant by additionally boosting the voltage as described above, the processing of S212 and S213 is performed. I will not.

  According to the FC boost converter control shown in FIG. 11, the boost operation of the FC boost converter 12 can be stopped as much as possible on the assumption that the drive of the motor 16 is ensured, thereby suppressing the switching loss. it can. Further, even when the FC boost converter 12 is boosted, the soft switching process is performed after setting the operation region to the soft switch region RC4 as much as possible. Therefore, the switching loss of the FC boost converter 12 is minimized. Can be suppressed.

<Modification>
As described in the above embodiment, in the process S205 in the FC boost converter control shown in FIG. 11, the output voltage of the fuel cell 11 that is generating electric power according to the accelerator pedal opening detected by the accelerator pedal sensor 21 is detected. Is done. In this modification, for detection of the output voltage of the fuel cell 11, the output voltage of the fuel cell 11 is calculated based on the output of the fuel cell 11 (hereinafter referred to as FC output). Here, the FC output is calculated according to the following equation (1).
(FC output) = (Request output) + (Auxiliary machine request output) + (Battery charge (discharge) output) (1)

  The auxiliary machine required output is an output required for auxiliary machines such as the hydrogen tank 17 and the compressor 18, the battery charge output is an output required for the battery 13 at the time of charging, and the battery discharge output is at the time of discharging. Is the output of the battery 13 in FIG. If the remaining power storage amount of the battery 13 is less than the SOC threshold, the battery charge output is included in the above equation (1) to calculate the FC output. If the remaining power storage amount of the battery 13 is equal to or greater than the SOC threshold value, the battery discharge output is added to the above (1) as a minus amount to calculate the FC output. Then, the output voltage of the fuel cell 11 is calculated based on the FC output calculated by the above equation (1). Specifically, the ECU 20 has an IP characteristic MAP in which the FC output and the output current of the fuel cell 11 are associated, and an IV characteristic map in which the output current of the fuel cell 11 and the output voltage of the fuel cell 11 are associated. These maps are accessed according to the FC output, and the output voltage of the fuel cell 11 is calculated. According to this modification, the output required for the auxiliary machine and the remaining power storage amount of the battery 13 are calculated by calculating the FC output in consideration of the output required for the auxiliary machine and the remaining power storage amount of the battery 13. In consideration of the above, the output voltage of the fuel cell 11 can be calculated.

Moreover, you may deform | transform said Formula (1) like Formula (2) shown below.
(FC output) = (Request output) + (Auxiliary machine request output) + (Battery charge (discharge) output) + (F
Switching loss of C boost converter 12) + (switching loss of battery boost converter 14) (2)
By modifying in this way, the switching loss of the FC boost converter 12 and the switching loss of the battery boost converter 14 are further added, and the FC output is calculated, whereby the switching loss of the FC boost converter 12 and the battery boost converter are calculated. The output voltage of the fuel cell 11 can be calculated in consideration of the 14 switching losses.

  The switching loss of the FC boost converter 12 is calculated by providing a current sensor and a voltage sensor at the inlet / outlet of the FC boost converter 12 and measuring the current and voltage on the inlet / outlet side of the FC boost converter 12. Further, the switching loss of the battery boost converter 14 is calculated by providing a current sensor and a voltage sensor at the inlet / outlet of the battery boost converter 14 and measuring the current and voltage on the inlet / outlet side of the battery boost converter 14. Here, when both the FC boost converter 12 and the battery boost converter 14 are performing a boost operation, the FC output is calculated in consideration of the switching loss of the FC boost converter 12 and the switching loss of the battery boost converter 14. On the other hand, when only the battery boost converter 14 is performing a boost operation, the FC output is calculated taking into account only the switching loss of the battery boost converter 14.

  In addition, it is preferable to consider the driving efficiency of the motor 16 for voltage application to the inverter 15 for driving the motor 16. For example, as described in the above embodiment, when the FC boost converter 12 is not stopped when power is supplied from the fuel cell 11 to the motor 16, the voltage applied to the inverter 15 is boosted by the FC boost converter 12. In this modification, the voltage applied to the inverter 15 is associated with the efficiency characteristics of the load including the inverter 15 and the motor 16 and the voltage applied to the inverter 15 based on the required torque and the rotation speed of the motor 16. Determine from the map. Then, by the boosting operation of the FC boost converter 12, the output voltage of the fuel cell 11 is boosted to the determined voltage and applied to the inverter 15. For example, the efficiency characteristic of the inverter 15 is the conversion efficiency of the inverter 15 with respect to the voltage applied to the inverter 15, and the efficiency characteristic of the motor 16 is the driving efficiency of the motor 16 with respect to the voltage applied to the motor 16.

  In this modification, the load efficiency characteristic is determined, and the load efficiency characteristic region as shown in FIGS. 12A, 12B, and 12C is defined from the relationship between the required torque and the rotation speed of the motor 16. 12A, 12B, and 12C are maps that display the load efficiency characteristic region in stages according to the level of efficiency, with the required torque on the vertical axis and the rotation speed of the motor 16 on the horizontal axis. FIG. 12A is a map displaying a region of the efficiency characteristic of the load when the voltage applied to the inverter 15 is high. FIG. 12B is a map displaying a region of load efficiency characteristics when the voltage applied to the inverter 15 is medium. FIG. 12C is a map that displays the region of the efficiency characteristic of the load when the voltage applied to the inverter 15 is low. The point A in FIGS. 12A, 12B and 12C is determined based on the required torque T1 and the rotational speed R1 of the motor 16, and the point B corresponds to the required torque T2 and the rotational speed R2 of the motor 16. Based on the decision.

  Point A in FIG. 12C is included in the region where the efficiency characteristic of the load is high efficiency, but point A in FIGS. 12A and 12B is not included in the region where the efficiency characteristic of the load is high efficiency. Therefore, it can be understood that the load efficiency characteristic is high when the voltage applied to the inverter 15 is low at the required torque T1 and the rotation speed R1 of the motor 16. Point B in FIG. 12B is included in the region where the load efficiency characteristic is high efficiency, but point B in FIGS. 12A and 12C is not included in the region where the load efficiency characteristic is high efficiency. Therefore, it can be understood that the load efficiency characteristic is high when the voltage applied to the inverter 15 is medium at the required torque T2 and the rotation speed R2 of the motor 16. In this modification, the ECU 20 has the map as described above, and the optimum voltage can be applied to the inverter 15 by determining the voltage to be applied to the inverter 15 from the viewpoint of the efficiency characteristic of the load.

  A second embodiment of the fuel cell system according to the present invention will be described with reference to FIGS. The difference between the fuel cell system according to the present embodiment and the fuel cell system according to the first embodiment described above is the auxiliary circuit 12b in the FC boost converter 12 and the related technology. Therefore, in the present embodiment, description will be made by paying attention to the difference.

  FIG. 13 is a diagram showing the electrical configuration of the fuel cell system 10 with the FC boost converter 12 as the center, as in FIG. Here, the auxiliary circuit 12b of the FC boost converter 12 shown in FIG. 13 is further provided with a switching circuit including a switch element S3 and a diode D6. Specifically, one end of the switch element S3 is connected to the anode terminal side of the diode D2, and the other end of the switch element S3 is connected to the low potential side terminal of the fuel cell 11. This switch element S3 supports the discharge of the charge stored in the snubber capacitor C2 in the mode 2 operation in the previous soft switching process. In this embodiment, a new soft switching process including the switching operation of the switch element S3 will be described with reference to FIGS.

  FIG. 14 is a flowchart showing the flow of the soft switching process in the FC boost converter 12 as in FIG. The difference from the soft switching process shown in FIG. 3 is that the process shown in FIG. 14 is a new process by the switching operation of the switch element S3 between the processes of S102 and S103, that is, between the operations of mode 2 and mode 3. S301 is set. Therefore, this difference will be described with emphasis, and other processes will be denoted by the same reference numerals as those in FIG. 3 and detailed description thereof will be omitted.

  Here, when the mode 2 operation is performed by the process of S102, in the FC boost converter 12, the switch element S3 is in a turn-off state. In order to clearly show the effect of the switching operation of the switch element S3, the relationship between the outlet voltage VH of the FC boost converter 12 and the inlet voltage VL is expressed by a ratio VH / V that is a parameter representing the electrical state of the FC boost converter 12. For VL, the ratio is set to be less than 2. In this case, due to the half-wave resonance of the coil L2 and the snubber capacitor C2, the charge of the snubber capacitor C2 is released, but the voltage of the snubber capacitor C2 does not become zero as shown in FIG. 10B.

  Here, in the present embodiment, the switch element S3 is turned on by the process of S301 at the timing when the voltage fluctuation of the snubber capacitor C2 due to the half-wave resonance becomes the bottom value. Then, as shown in FIG. 15, since the electric charge that could not be removed by the half-wave resonance in the snubber capacitor C2 is dispersed in the auxiliary circuit 12b via the switch element S3, the voltage of the snubber capacitor C2 is further reduced. Can be made. As a result, in the process of S103 after S301, when the switch element S1 is turned on, the voltage applied to the switch element S1 can be reduced as much as possible, thereby suppressing the switching loss more surely. it can. Incidentally, in the relationship between the outlet voltage VH of the FC boost converter 12 and its inlet voltage VL, if the ratio VH / VL exceeds a predetermined value (in this embodiment, exceeds 2), the charge of the snubber capacitor C2 is in mode 2. Since it is completely removed by the operation, the process of S301 is not necessarily performed.

  A third embodiment of the fuel cell system according to the present invention will be described with reference to FIG. FIG. 16 is a flowchart regarding control of the FC boost converter 12 when starting to supply power to the motor 16 from a state where the fuel cell system 10 is stopped. Therefore, the start-up FC boost converter control shown in FIG. 16 is a control performed by the ECU 20 before the FC boost converter control shown in FIG. 11, and is different from the FC boost converter 12 disclosed in the above embodiments. Can be applied.

  First, in S401, before power is supplied from the fuel cell 11 to the motor 16, the boost ratio in the FC boost converter 12 is set to 2. That is, when the fuel cell 11 is started, the operation range of the FC boost converter 12 is set to the soft switch region RC4 by setting the boost ratio in the FC boost converter 12 to 2 regardless of the operating state of the motor 16. Will be. Thereafter, power supply from the fuel cell 11 to the motor 16 is started in S402, and soft switching processing for boosting operation by the FC boost converter 12 is executed in S403.

  Further, in S404, it is determined whether or not the output voltage of the fuel cell 11 has reached a predetermined output voltage necessary for driving the motor 16. If an affirmative determination is made in S404, it means that the start-up process of the fuel cell 11 has been completed, and therefore, the FC boost converter control for driving the motor 16 is performed thereafter. On the other hand, if a negative determination is made in S404, it means that the start-up process of the fuel cell 11 has not ended, and therefore the processes after S403 are repeated again.

  As described above, in the start-up FC boost converter control according to this embodiment, the boost ratio in the FC boost converter 12 is set to 2 regardless of the operation state of the motor 16 until the start-up process of the fuel cell 11 is completed. The Normally, when the fuel cell 11 is started, since the value of the ratio VH / VL does not exceed a predetermined threshold value (2 in the present embodiment), the switch element S1 with the voltage of the snubber capacitor C2 set to zero. Cannot be turned on, and the effect of reducing the switching loss by the soft switching process cannot be enjoyed. Therefore, particularly when the fuel cell 11 is started by the processing of S401, the boosting ratio is forcibly set to 2 and the operation region of the FC boost converter 12 is set to the soft switch region RC4. Efficiency can be improved.

<Other examples>
Note that the above circuit has an element for suppressing regenerative power on the electric circuit flowing from the snubber capacitor C2 to the fuel cell 11 so that the regenerative power stored in the snubber capacitor C2 is not input to the fuel cell 11 during soft switching. Alternatively, the regenerative power stored in the snubber capacitor C <b> 2 may flow to the battery 13. As a method for suppressing the regenerative power flowing to the fuel cell 11, for example, a smoothing capacitor, a zener diode, or a varistor with one end grounded may be provided on the electric path flowing from the snubber capacitor C2 to the fuel cell 11. It can suppress that the voltage of an electric circuit becomes more than a regulation voltage. It is also useful to provide a diode for preventing regenerative power from flowing backward from the snubber capacitor C2 to the fuel cell 11. And as a method of making regenerative electric power flow to battery 13, the method of making the circuit structure which connects the downstream of switch element S2 to battery 13 instead of fuel cell 11 is mentioned, for example.

  Further, as described in the above embodiment, when power is supplied from the fuel cell 11 to the load including the inverter 15 and the motor 16 through the FC boost converter 12, power loss in the FC boost converter 12 occurs. This power loss includes iron loss or switching loss that is less dependent on the amount of power to be converted. For this reason, the reduction in power efficiency is particularly noticeable in a low load region where the output power is small. Therefore, in the low load region, the FC boost converter 12 is stopped and the power of the fuel cell 11 is supplied to the load without conversion (through mode, bypass mode), or power is loaded from the battery 13 through the battery boost converter 14. There is a strong demand for supply.

Here, a through mode and a bypass mode in a general converter will be briefly described with reference to FIGS. 17A to 17D. In addition, the thick line arrow in each figure shows the flow of the electric current in each converter. FIG. 17A shows that the converter is a step-up converter (the above-mentioned F
The C boost converter 12 is this type of converter. It is a figure which shows the mode of the through mode when it is. By setting the switch element for boosting to the turn-off state, the voltage on the primary side can be applied to the secondary side as it is. FIG. 17B is a diagram showing a state of a bypass mode in a converter in which the converter is a boost converter, and a bypass diode is connected in parallel to a series body of a boost coil and a diode. is there. By turning off the switch element for boosting, the voltage on the primary side can be bypassed and applied to the secondary side. FIG. 17C is a diagram illustrating a through mode when the converter is a half-bridge type converter. Of the two switching elements for boosting, the upper side in the figure is turned on and the lower side is turned off, so that the primary voltage can be applied to the secondary side as it is. FIG. 17D is a diagram showing a through mode when the converter is a full-bridge converter. Of the four switch elements for boosting, the upper two in the figure are turned on and the lower two are turned off, so that the primary voltage can be applied to the secondary as it is. . Although the configurations shown in FIGS. 17B to 17D are different from the converter of the FC boost converter 12 described above, if the FC boost converter 12 adopts these configurations, the switch elements are controlled as shown in the drawings. Thus, the through mode and the bypass mode are realized.

  On the other hand, the fuel cell 11 is required to avoid the sintering phenomenon of the catalyst in order to improve durability. The sintering phenomenon is a phenomenon in which the Pt catalyst on the electrode of the fuel cell 11 aggregates, and is assumed to be induced by an oxidation-reduction reaction against water (and against protons) on the surface of the Pt catalyst. Furthermore, it is known that such a redox reaction is caused at a relatively high potential in which the terminal voltage of the fuel cell 11 is close to the open circuit voltage (OCV).

  By the way, when the fuel cell 11 becomes lightly loaded, the terminal voltage of the fuel cell 11 approaches the open circuit voltage (OCV) according to the IV characteristics of the fuel cell 11. However, as described above, when the FC boost converter 12 is stopped, the terminal voltage of the fuel cell 11 cannot be controlled, and it becomes difficult to avoid deterioration of the catalyst due to the reaction.

  Therefore, when the FC boost converter 12 is stopped, the terminal of the fuel cell 11 is controlled by controlling the voltage on the output side of the FC boost converter 12 by the battery boost converter 14 provided in parallel with the FC boost converter 12. What is necessary is just to control a voltage. That is, the ECU 20 monitors the terminal voltage of the fuel cell 11 and controls the output voltage of the battery boost converter 14 so that the terminal voltage is less than a reference value for avoiding sintering. This reference value may be set as an experimental value or an experience value, for example.

  On the other hand, when the terminal voltage of the battery 13 is high and the required voltage of the inverter 15 is low and the boost ratio of the battery boost converter 14 cannot be 1 or more, the battery boost converter 14 must be stopped. In such a case, in order to avoid the sintering phenomenon, the FC boost converter 12 does not stop, and the terminal voltage of the fuel cell 11 may be controlled by the FC boost converter 12 based on the required voltage of the inverter 15.

  In any case, in order to control the terminal voltage of the fuel cell 11 below the reference value, it is necessary to draw current from the fuel cell 11 and consume power. The electric power in this case is normally consumed by a load including the inverter 15 and the motor 16. However, surplus power is stored in the battery 13 when the SOC of the battery 13 is low and power can be stored in the battery 13, and power that cannot be stored in the battery 13 is consumed by auxiliary equipment (air conditioner, lighting, pump, etc.). do it.

The fuel cell system 10 is also a system that shuts off the output of the fuel cell 11 when the vehicle 1 collides. Specifically, a relay circuit for turning on / off the electrical connection between the inverter 15 and the battery boost converter 14 is provided on the downstream side of the FC boost converter 12 of the fuel cell system 10. As is apparent from the configuration described above, the fuel cell system 10 has a relatively small amount of current flowing downstream of the FC boost converter 12. For this reason, the fuel cell system 10 is a system that employs a smaller (low current) relay circuit than the relay circuit provided immediately after the fuel cell in the same type of existing relay circuit. ing.

  The ECU 20 of the fuel cell system 10 constantly monitors the presence or absence of a collision based on the output of a collision detection sensor provided in the vehicle 1 and controls the relay circuit when it detects a collision. , The unit that cuts off the electrical connection between the FC boost converter 12 and the inverter 15 and the battery boost converter 14.

It is a figure which shows schematic structure of the fuel cell system based on the Example of this invention. It is a figure which shows the electric circuit structure of the fuel cell system shown in FIG. 1, Comprising: It is a 1st figure which shows the electric circuit structure of FC boost converter especially. 3 is a flowchart showing a flow of soft switching processing for voltage boosting performed by the FC boost converter shown in FIG. 2. FIG. 4 is a diagram schematically showing a current flow in the FC boost converter when the mode 1 operation of the soft switching process shown in FIG. 3 is performed. FIG. 4 is a diagram schematically showing a current flow in the FC boost converter when the mode 2 operation of the soft switching process shown in FIG. 3 is performed. FIG. 4 is a diagram schematically showing a current flow in the FC boost converter when the mode 3 operation of the soft switching process shown in FIG. 3 is performed. FIG. 4 is a diagram schematically showing a current flow in the FC boost converter when the mode 4 operation of the soft switching process shown in FIG. 3 is performed. FIG. 4 is a diagram schematically showing a current flow in the FC boost converter when the mode 5 operation of the soft switching process shown in FIG. 3 is performed. FIG. 4 is a diagram schematically showing a current flow in the FC boost converter when the mode 6 operation of the soft switching process shown in FIG. 3 is performed. It is a figure which shows the correlation with the output voltage of a fuel cell and the motor required voltage for a motor drive set with the conventional fuel cell system. It is a figure which shows the correlation with the output voltage of a fuel cell and the motor required voltage for a motor drive set with the fuel cell system which concerns on the Example of this invention. It is a 1st figure which shows the correlation of IV characteristic of a fuel cell, and IV characteristic of a battery set with the fuel cell system which concerns on the Example of this invention. It is a 2nd figure which shows the correlation with IV characteristic of a fuel cell, and IV characteristic of a battery set with the fuel cell system which concerns on the Example of this invention. In the fuel cell according to the embodiment of the present invention, the processing executed in the FC boost converter is associated with the operation region formed with the inlet voltage of the FC boost converter as the horizontal axis and the outlet voltage as the vertical axis. It is the displayed first map. In the fuel cell according to the embodiment of the present invention, the processing executed in the FC boost converter is associated with the operation region formed with the inlet voltage of the FC boost converter as the horizontal axis and the outlet voltage as the vertical axis. It is the displayed second map. FIG. 4 is a diagram excerpting and describing only the part actually operating in the FC boost converter for the convenience of explanation when the operation of mode 2 of the soft switching process shown in FIG. 3 is performed. The ratio VH / VL between the outlet voltage of the FC boost converter according to the embodiment of the present invention and the inlet voltage, and the voltage remaining in the snubber capacitor at the time of discharge when the mode 2 operation of the soft switching process shown in FIG. 3 is performed It is a 1st figure which shows the correlation. The ratio VH / VL between the outlet voltage of the FC boost converter according to the embodiment of the present invention and the inlet voltage, and the voltage remaining in the snubber capacitor at the time of discharge when the mode 2 operation of the soft switching process shown in FIG. 3 is performed It is a 2nd figure which shows correlation with. 4 is a flowchart showing a flow of control performed by the FC boost converter in order to promote efficiency of the fuel cell system according to the embodiment of the present invention. In the fuel cell system which concerns on the Example of this invention, it is the map which displayed the area | region of the efficiency characteristic of the load in case the voltage applied to an inverter is high. In the fuel cell system which concerns on the Example of this invention, it is the map which displayed the area | region of the efficiency characteristic of the load in case the voltage applied to an inverter is medium. In the fuel cell system which concerns on the Example of this invention, it is the map which displayed the area | region of the efficiency characteristic of the load in case the voltage applied to an inverter is low. It is a figure which shows the electric circuit structure of the fuel cell system shown in FIG. 1, Comprising: It is a 2nd figure which shows the electric circuit structure of FC boost converter especially. It is a flowchart which shows the flow of the soft switching process for the voltage boosting performed with the FC boost converter shown in FIG. The ratio VH / VL between the outlet voltage of the FC boost converter according to the embodiment of the present invention and the inlet voltage, and the voltage remaining in the snubber capacitor during discharge when the mode 2 operation of the soft switching process shown in FIG. 14 is performed It is a figure which shows correlation with. It is a flowchart regarding control of the FC boost converter at the time of starting in order to supply electric power to a motor from the state which the fuel cell system based on the Example of this invention stopped. It is a 1st figure which shows typically the through mode in a converter. It is a figure which shows typically the bypass mode in a converter. It is a 2nd figure which shows typically the through mode in a converter. It is a 3rd figure which shows typically the through mode in a converter.

Explanation of symbols

1 .... Vehicle 10 .... Fuel cell system 11 .... Fuel cell (FC)
12 .... FC boost converter 12a ... Main boost circuit 12b ... Auxiliary circuit 13 ... Battery 14 ... Battery boost converter 15 ... Inverter 16 ... Motor 20 .... ECU
21 ... Accelerator pedal sensor S1, S2, S3 ... Switch elements C1, C3 ... Smoothing capacitor C2 ... Snubber capacitors L1, L2, L3 ... Coils D1, D2, D3 , D4, D5... Diode

Claims (7)

A fuel cell that is a DC power source;
Boosting the output voltage of the fuel cell and applying the boosted voltage to a load;
Boost control means for controlling voltage boost by the boost unit;
A fuel cell system comprising:
The boosting unit includes:
A main boosting unit that boosts the output voltage of the fuel cell by performing a switching operation with the main switch means on the main coil connected to the high potential side terminal of the fuel cell;
A snubber capacitor connected in parallel to the main switch means and capable of adjusting a voltage applied to the main switch means; and an applied voltage of the snubber capacitor is adjusted according to a boosting operation by the main boosting unit; An auxiliary boosting unit,
When the output voltage is boosted by the boosting unit through the switching operation of the main switch unit, the boosting control unit stores the charge stored in the snubber capacitor before the main switch unit performs a predetermined switching operation. Remove,
Fuel cell system. The boost control means includes:
First boosting means for accumulating electric power from the fuel cell in the main coil by a first switching operation of the main switch means;
Second boosting means for supplying the power stored by the first boosting means to the load through the snubber capacitor by the second switching operation of the main switch means;
Have
The predetermined switching operation is the first switching operation.
The fuel cell system according to claim 1. The main boosting unit includes:
The main coil having one end connected to a terminal on the high potential side of the fuel cell;
The main switch means for switching, wherein one pole is connected to the other end of the main coil and the other pole is connected to a terminal on the low potential side of the fuel cell;
A first diode having a cathode terminal connected to the other end of the main coil;
A smoothing capacitor provided between the anode terminal of the first diode and the other pole of the main switch means;
The auxiliary booster is
A first series connection including a second diode and the snubber capacitor provided in parallel to the main switch means and connected between the other end of the main coil and a low potential side terminal of the fuel cell. Body,
An auxiliary coil which is an inductive element connected between the connection part of the second diode and the snubber capacitor in the first series connection body and one end of the main coil and an auxiliary diode which performs switching. A second series connection including switch means,
The step-up control means removes the electric charge stored in the snubber capacitor according to the resonance action of the auxiliary coil and the snubber capacitor by the switching operation of the auxiliary switch means.
The fuel cell system according to claim 1 or 2. The auxiliary boosting unit has a plurality of removing means for removing the electric charge stored in the snubber capacitor,
When the output voltage is boosted by the boosting unit via the switching operation of the main switch unit, the boosting control unit is configured to select the snubber capacitor among the plurality of removing units based on an electrical state in the boosting unit. Select the removal means used for the charge removal of
The fuel cell system according to any one of claims 1 to 3. The auxiliary booster is provided in parallel to the auxiliary switch means of the second series connection body, and is connected between a predetermined location of the second series connection body and a terminal on the low potential side of the fuel cell. A second auxiliary switch means,
The step-up control means selects at least one of the auxiliary switch means and the second auxiliary switch means for charge removal of the snubber capacitor;
The fuel cell system according to claim 4. A DC-DC converter that boosts the output voltage of a DC power supply and applies the boosted voltage to a load,
A main booster that boosts the output voltage of the DC power supply by performing a switching operation with the main switch means on the main coil connected to the high potential side terminal of the DC power supply,
A snubber capacitor connected in parallel to the main switch means and capable of adjusting a voltage applied to the main switch means; and an applied voltage of the snubber capacitor is adjusted according to a boosting operation by the main boosting unit; An auxiliary boosting unit,
When the output voltage of the DC power supply is boosted via the switching operation of the main switch means, the boost control means removes the charge stored in the snubber capacitor before the main switch means performs a predetermined switching operation. When,
DC-DC converter provided with. The boost control means includes:
First boosting means for storing power from the DC power source in the main coil by the first switching operation of the main switch means;
Second boosting means for supplying the power stored by the first boosting means to the load through the snubber capacitor by the second switching operation of the main switch means;
Have
The predetermined switching operation is the first switching operation.
The DC-DC converter according to claim 6.

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