WO2010143028A1

WO2010143028A1 - Converter control device and converter control method

Info

Publication number: WO2010143028A1
Application number: PCT/IB2010/000842
Authority: WO
Inventors: Nobuyuki Kitamura; Takahiro Umehara
Original assignee: Toyota Jidosha Kabushiki Kaisha
Priority date: 2009-06-11
Filing date: 2010-04-15
Publication date: 2010-12-16
Also published as: JP2010288366A

Abstract

A reactor current detecting unit detects reactor currents at the time points of valleys and peaks of a triangular wave (that is, inflection points of the triangular wave) supplied from an oscillating unit, and outputs the reactor currents to a mean reactor current deriving unit. The mean reactor current deriving unit averages pairs of the reactor current detected at the time point of the valley of the triangular wave and the reactor current detected at the time point of the peak of the triangular wave, supplied from the reactor current detecting unit, to derive mean reactor currents.

Description

CONVERTER CONTROL DEVICE AND CONVERTER CONTROL METHOD

BACKGROUND OF THE INVENTION

1. Field of the Invention

[0001] The invention relates to a converter control device and a converter control method.

2. Description of the Related Art

[0002] In a fuel cell system mounted on an automobile, or the like, in order to take measures against steep variations in load, which exceed the power generation capacity of a fuel cell, various hybrid fuel cell systems equipped with both fuel cell and battery as a power source are suggested.

[0003] In a hybrid fuel cell system, an output voltage, or the like, of a fuel cell is controlled by a DC-DC converter. In generally, a DC-DC converter, which carries out such control converts a voltage by causing a switching element, such as a power transistor, an insulated gate bipolar transistor (IGBT) and an FET, to perform PWM operation, is used. In a typical DC-DC converter, a duty command for driving a switching element is derived through feedback proportional integral (PI) control that uses the value of electric current flowing through a reactor (reactor current) or the value of output voltage (for example, see Japanese Patent Application Publication No. 2005-176567 (JP-A-2005-176567)).

[0004] Incidentally, such a DC-DC converter includes a current sensor for detecting a reactor current, and a response delay occurs in the current sensor. Therefore, in the above described current control method, a response delay of the current sensor is anticipated to uniformly determine the timing at which the reactor current is detected. However, a response delay of the current sensor has an individual difference, so, for example, in a multi-phase DC-DC converter formed of multiple phases, there is a problem that it is difficult to accurately detect a reactor current because of a difference in response delay among the current sensors of the respective phases.

SUMMARY OF THE INVENTION

[0005] The invention provides a converter control device and converter control method that further accurately detect a reactor current irrespective of an individual difference in response delay of a current sensor that detects the reactor current.

[0006] A first aspect of the invention relates to a converter control device for controlling a converter that includes a reactor connected to a fuel cell and a switch for controlling a reactor current flowing through the reactor. The converter control device includes: an oscillator that generates a triangular wave having a predetermined frequency; a gate signal generating circuit that generates a gate signal for switching on/off of the switch in synchronization with the triangular wave; a current sensor that detects the reactor current; and a reactor current deriving unit that derives a mean value between a reactor current detected at the time point of a peak of the triangular wave and a reactor current detected at the time point of a valley of the triangular wave.

[0007] With the above configuration, a reactor current is detected at the time point of the valley of the triangular wave, while a reactor current is detected at the time point of the peak of the triangular wave, and a pair of these reactor currents are averaged (see FIG. 4, and the like). Thus, even when there are variations in response delay of the current sensor (for example, individual difference of the current sensor, or the like), the influence of the variations may be suppressed, and, as a result, it is possible to detect a reactor current with high accuracy.

[0008] In the above configuration, the gate signal generating circuit may generate a gate signal for switching the switch from off to on at substantially a middle point from valley to peak of the triangular wave, and may generate a gate signal for switching the switch from on to off at substantially a middle point from peak to valley of the triangular wave.

[0009] In addition, in the above configuration, a first terminal of the reactor may be connected to a high-potential terminal of the fuel cell, a first terminal of the switch may be connected to a second terminal of the reactor, and a second terminal of the switch may be connected to a low-potential terminal of the fuel cell, the converter may be a soft switching converter, wherein the converter may include a main step-up circuit that includes a first diode, of which a cathode is connected to the second terminal of the reactor, and a smoothing capacitor that is provided between an anode of the first diode and the second terminal of the switch; and an auxiliary circuit that includes a first serially connected element and a second serially connected element, wherein the first serially connected element having a second diode and a snubber capacitor is connected in parallel with the switch and is connected to the second terminal of the reactor and the low-potential terminal of the fuel cell, and wherein the second serially connected element having a third diode, an auxiliary reactor and an auxiliary switch is connected between the first terminal of the reactor and a connecting portion of the second diode and the snubber capacitor.

[0010] A second aspect of the invention relates to a converter control method for controlling a converter that includes a reactor connected to a fuel cell and a switch for controlling a reactor current flowing through the reactor. The converter control method includes: generating a triangular wave having a predetermined frequency; generating a gate signal for switching on/off of the switch in synchronization with the triangular wave; and detecting a reactor current at the time point of a peak of the triangular wave and a reactor current at the time point of a valley of the triangular wave to derive a mean value between the reactor current at the time point of the peak of the triangular wave and the reactor current at the time point of the valley of the triangular wave.

[0011] According to the aspects of the invention, it is possible to further accurately detect a reactor current irrespective of an individual difference in response delay of a current sensor that detects the reactor current.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] The foregoing and further objects, features and advantages of the invention will become apparent from the following description of example embodiments with reference to the accompanying drawings, wherein like numerals are used to represent like elements and wherein:

FIG. 1 is a view that shows the configuration of a hybrid fuel cell system according to a first embodiment;

FIG. 2 is a view that shows the circuit configuration of each phase converter according to the first embodiment;

FIG. 3 is a. functional block diagram that shows a reactor current deriving function according to the first embodiment;

FIG. 4 is a timing chart that shows the relationship among a triangular wave, a gate signal, a reactor current and an output signal of a current sensor according to the first embodiment;

FIG. 5 is a timing chart that shows the relationship among a triangular wave, a gate signal, a reactor current and an output signal of a current sensor according to a related art;

FIG. 6 is a view that shows the circuit configuration of a multi-phase FC soft switching converter according to a second embodiment; and

FIG. 7 is a view that shows the circuit configuration of one phase of the multi-phase FC soft switching converter according to the second embodiment.

DETAILED DESCRIPTION OF EMBODIMENTS

[0013] Hereinafter, a first embodiment according to the invention will be described with reference to the accompanying drawings. FIG. 1 shows the configuration of an FCHV system mounted on a vehicle according to the present embodiment. Note that, in the following description, it is assumed that a fuel cell vehicle (fuel cell hybrid vehicle (FCHV)) is an example of the vehicle; instead, the aspect of the invention may also be applied to an electric vehicle, or the like. In addition, the aspect of the invention may also be applied to not only vehicles but also various mobile units (for example, a ship, an airplane, a robot, or the like), a stationary power source, and a portable fuel cell system.

[0014] The FCHV system 100 includes an FC converter 2500 between a fuel cell 110 and an inverter 140, and also includes a DC-DC converter (hereinafter, battery converter) 180 between a battery 120 and the inverter 140.

[0015] The fuel cell 110 is a solid polymer electrolyte cell stack formed of a plurality of serially stacked unit cells. A voltage sensor VO and a current sensor 10 are installed in the fuel cell 110. The voltage sensor VO detects the output voltage Vfcmes of the fuel cell 110. The current sensor 10 detects the output current Ifcmes of the fuel cell 110. In the fuel cell 110, an oxidation reaction expressed by equation (1) occurs in an anode, a reduction reaction expressed by equation (2) occurs in a cathode, and an electromotive reaction expressed by equation (3) occurs in the fuel cell 110 as a whole. H₂ → 2H⁺ + 2e^~ (1) (l/2)O₂ + 2H⁺ + 2e^" → H₂O (2) H₂ + (l/2)O₂ → H₂O (3)

[0016] Each unit cell has a structure such that an MEA is sandwiched by separators that respectively supply fuel gas and oxidation gas. The MEA is formed so that a polymer electrolyte membrane, or the like, is sandwiched by two electrodes, that is, a fuel electrode and an air electrode. The anode includes an anode catalyst layer on a porous support layer. The cathode includes a cathode catalyst layer on a porous support layer.

[0017] The fuel cell 110 includes a line that supplies fuel gas to the anode, a line that supplies oxidation gas to the cathode and a line that provides coolant (all of them are not shown). The fuel cell 110 is able to generate desired electric power by controlling the supply of fuel gas and the supply of oxidation gas in accordance with a control signal from a controller 160.

[0018] The FC converter 2500 serves to control the output voltage Vfcmes of the fuel cell 110. As shown in FIG. 1, the FC converter (multi-phase DC-DC converter) 2500 according to the present embodiment has a configuration such that three phases of a U-phase converter 20a, a V-phase converter 20b and a W-phase converter 20c are connected in parallel with one another. The FC converter 2500 undergoes switching control over driving phases, such as one-phase driving, two-phase driving and three-phase driving. For example, in accordance with electric power required by a load, only the U-phase is used in the one-phase driving, the U-phase and the V-phase are used in the two-phase driving, and the U-phase, the V-phase and the W-phase are used in the three-phase driving. Note that, in the following description, when it is not particularly necessary to differentiate among the U-phase converter 20a, the V-phase converter 20b and the W-phase converter 20c, they are simply referred to as phase converters 20.

[0019] The FC converter 2500 is used to execute control so that the output voltage Vfcmes of the fuel cell 110 becomes a voltage corresponding to a target output. Here, as shown in FIG. 1, the input current Ifcmes of the FC converter 2500 is detected by the current sensor 2510, and the input voltage Vfcmes is detected by the voltage sensor 2520. In addition, electric current flowing through the reactor of each phase (hereinafter, reactor current) is detected by a corresponding one of current sensors 2610a to 2610c. Specifically, the U-phase reactor current is detected by the current sensor 2610a, the V-phase reactor current is detected by the current sensor 2610b, and the W-phase reactor current is detected by the current sensor 2610c. Note that, when it is not necessary to particularly differentiate among the U-phase current sensor 2610a, the V-phase current sensor 2610b and the W-phase current sensor 2610c, they are simply referred to as current sensors 2610.

[0020] FIG. 2 is a configuration diagram of a load driving circuit that is an extracted circuit of each phase converter 20 (that is, one-phase of the FC converter 2500). Note that, in the following description, a voltage that has not yet been stepped up and that is input to each phase converter 20 is called input voltage Vin, and a voltage that has been stepped up and that is output from each phase converter 20 is called output voltage Vout.

[0021] As shown in FIG. 2, each phase converter 20 includes a reactor Ll, a rectifier diode Dl, and a switching element SWl formed of an insulated gate bipolar transistor (IGBT), or the like. One end of the reactor Ll is connected to an output end (not shown) of the fuel cell 110, and the other end of the reactor Ll is connected to the collector of the switching element SWl. Here, electric current that flows through the reactor Ll is detected by the current sensor 2610 that detects the reactor current of each phase as described above. The switching element SWl is connected between the power supply line and grounding line of the inverter 140. Specifically, the collector of the switching element SWl is connected to the power supply line, and the emitter of the switching element SWl is connected to the grounding line. In the above configuration, as the switch SWl is turned on, electric current flows from the fuel cell 110 through the reactor Ll to the switch SWl, and then the reactor Ll is direct-current energized to store magnetic energy.

[0022] Subsequently, as the switch SWl is turned off, an induced voltage caused by the magnetic energy stored in the reactor Ll is superimposed on the voltage (input voltage Vin) of the fuel cell 110. Thus, an operating voltage (output voltage Vout) higher than the input voltage Vin is output from the reactor Ll', and output current is output via the diode Dl. The controller 160 appropriately changes the duty ratio (which will be _.described later) of on/off of the switch SWl to obtain the desired output voltage Vout.

[0023] Referring back to FIG. 1, the battery 120 is connected to the load 130 in parallel with the fuel cell 110. The battery 120 functions as a redundant electric power storage source, a regenerative energy storage source during regenerative braking, and an energy buffer at the time of fluctuations in load resulting from acceleration or deceleration of a fuel cell vehicle. The battery 120 is, for example, a secondary battery, such as a nickel-cadmium battery, a nickel-hydrogen battery and a lithium secondary battery.

[0024] The battery converter 180 serves to control the input voltage of the inverter 140. The battery converter 180, for example, has a circuit configuration similar to that of the FC converter 2500. Note that a step-up converter may be employed as the battery converter 180; instead, a step-up/down converter that is able to perform both step-up operation and step-down operation may be employed, or any configuration that is able to control the input voltage of the inverter 140 may be employed.

[0025] The inverter 140 is, for example, a PWM inverter that is driven by pulse width modulation. In accordance with a control command from the controller 160, the inverter 140 converts direct-current electric power output from the fuel cell 110 or the battery 120 into three-phase alternating-current electric power to control the rotational torque of a traction motor 131.

[0026] The traction motor 131 is a main power source of the vehicle, and is configured to generate regenerative electric power during deceleration. A differential 132 is a reduction gear. The differential 132 reduces the highspeed rotation of the traction motor 131 to a predetermined rotational speed to rotate shafts provided with tires 133. ^ Awheel speed sensor, or the like, (not shown) is provided for each shaft. By so doing, the vehicle speed, or the like, of the vehicle is detected. Note that, in the present embodiment, all the devices (including the traction motor 131 and the differential 132) that are operable with electric power supplied from the fuel cell 110 are collectively termed the load 130.

[0027] The controller 160 is a computer system for controlling the FCHV system 100. The controller 160, for example, includes a CPU, a RAM, a ROM, and the like. The controller 160 inputs various signals (for example, a signal that indicates an accelerator operation amount, a signal that indicates a vehicle speed, a signal that indicates the output current or output terminal voltage of the fuel cell 110, and the like) supplied from sensors 170 to calculate a required electric power of the load 130 (that is, a required electric power of the overall system).

[0028] The required electric power of the load 130 is, for example, the total value of a vehicle driving power and an auxiliary machine power. The auxiliary machine power, for example, includes electric power consumed by in-vehicle auxiliary machines (a humidifier, an air compressor, a hydrogen pump, a coolant circulation pump, and the like), electric power consumed by devices (a transmission, a wheel controller, a steering system, a suspension, and the like) required for vehicle driving, and electric power consumed by devices (an air conditioner, a lighting fixture, an audio, and the like) arranged in a vehicle cabin.

[0029] Then, the controller (converter control device) 160 determines the distribution of the output power of the fuel cell 110 and the output power of the battery 120, and then determines a power generation command value. As the controller 160 calculates electric power required for the fuel cell 110 and electric power required for the battery 120, the controller 160 controls the operation of the FC converter 2500 and the operation of the battery converter 180 so as to obtain these required electric powers.

[0030] FIG. 3 is a block diagram that shows a reactor current deriving function implemented by the controller 160, and the like. FIG. 4 is a timing chart that shows the relationship among a triangular wave, a gate signal, a reactor current and an output signal of a current sensor according to the present embodiment.

[0031] An oscillating unit (oscillator) 210 generates a reference triangular wave having a predetermined frequency, and then outputs the triangular wave to a gate signal generating circuit 220, a reactor current detecting unit 230, and the like. The gate signal generating circuit (generating circuit) 220 generates a gate signal so as to attain electric current that exhibits a variation similar to the triangular wave. More specifically, as shown in FIG. 4, the gate signal generating circuit 220 carries out timer interrupt at substantially a middle point from valley to peak of the triangular wave supplied from the oscillating unit 210 to generate a gate signal (gate on signal) for switching the switch SWl from off to on, while the gate signal generating circuit 220 carries out timer interrupt at substantially a middle point from peak to valley of the triangular wave supplied from the oscillating unit 210 to generate a gate signal (gate off signal) for switching the switch SWl from on to off.

[0032] The reactor current detecting unit (current detecting unit) 230 detects reactor currents at the time points of valleys and peaks of the triangular wave (that is, inflection points of the triangular wave) supplied from the oscillating unit 210, and outputs the detected reactor currents to a mean reactor current deriving unit 240. Note that, in FIG. 4, reactor currents detected at the time points of the valleys of the triangular wave are denoted by I_da-i to Id_a-k (k ≥ 2), and reactor currents detected at the time points of the peaks of the triangular wave are denoted by I_mo-1 to I_mo-k-

[0033] The mean reactor current deriving unit (reactor current deriving unit) 240 averages pairs of reactor current I_da and reactor current I_m0 (for example, the reactor current Id_a-i and the reactor current I_mo-1) to derive mean reactor currents I_ave-i to I_ave-k- The reactor currents Id_a are detected at the time points of valleys of the triangular wave by the reactor current detecting unit 230. The reactor currents I_m0 are detected at the time points of peaks of the triangular wave by the current detecting unit 230. Note that the thus detected reactor currents are used for feedback control, feedforward control, or the like.

[0034] Here, FIG. 5 is a timing chart that shows the relationship among a triangular wave, a gate signal, a reactor current and an output signal of a current sensor according to a related art. As shown in FIG. 5, there is a response delay d due to the current sensor 2610 between the reactor current and the output signal of the current sensor 2610.

[0035] In the related art, in order to obtain the mean value of the reactor currents, the response delay d of the current sensor 2610 is anticipated to read the output signal of the current sensor 2610 at a timing earlier by the response delay; however, in this configuration, there is a problem that it is impossible to handle variations in the response delay of the current sensor (for example, individual difference of the current sensor, and the like) and, therefore, it is difficult to accurately detect reactor currents (here, the mean value of reactor currents).

[0036] In contrast, as shown in FIG. 4, the reactor currents I_da are detected at the time points of the valleys of the triangular wave, while the reactor currents I_mo are detected at the time points of the peaks of the triangular wave, and the pairs of these reactor currents (for example, the reactor current I_d3-1 and the reactor current I_mo-i) are averaged. Thus, even when there are variations in the response delay of the current sensor (for example, individual difference of the current sensor, or the like), the influence of the variations may be suppressed, and, as a result, it is possible to detect a reactor current with high accuracy.

[0037] In the above described embodiment, it is assumed that the switching element, such as IGBT, is caused to perform PWM operation as the DC-DC converter to convert voltage; however, the aspect of the invention is not limited to this configuration. As is generally known, the DC-DC converter is desired to further reduce a loss, improve efficiency and reduce noise with a reduction in power, a decrease in size and improvement in performance of electronic devices. Particularly, it is desired to reduce a switching loss and a switching surge attended with PWM operation.

[0038] One of techniques for reducing such a switching loss and a switching surge is a soft switching technique. Here, soft switching is a switching mode for implementing zero voltage switching (ZVS) or zero current switching (ZCS). The soft switching is, for example, implemented by a so-called soft switching converter in which an auxiliary circuit for reducing a switching loss is added to a typical step-up/down DC-DC converter that includes an inductor, a switching element and a diode. In a second embodiment, a case where a multi-phase soft switching converter (hereinafter, multi-phase FC soft switching converter) is employed as a DC-DC converter that controls the voltage of the fuel cell 110 will be described.

[0039] FIG. 6 is a view that shows the circuit configuration of a multi-phase FC soft switching converter 250. The multi-phase FC soft switching converter 250 includes not only a U-phase converter 150a, a V-phase converter 150b and a W-phase converter 150c but also a freewheel circuit 32c (here, a freewheel diode D6). Note that, in the following description, when it is not necessary to specifically differentiate among one-phase converters that constitute the multi-phase FC soft switching converter 250, they are simply referred to as FC soft switching converters 150. In addition, a voltage that has not been stepped up and that is input to the FC soft switching converter 150 is termed converter input voltage Vin, and a voltage that has been stepped up and that is output from the FC soft switching converter 150 is termed converter output voltage Vout.

[0040] FIG. 7 is a view that shows the circuit configuration of one-phase (for example, U-phase) converter that constitutes the multi-phase FC soft switching converter 250. The FC soft switching converter 150 includes a main step-up circuit 12a for carrying out step-up operation and an auxiliary circuit 12b for carrying out soft switching operation. The main step-up circuit 12a releases energy stored in the reactor Ll to a load 13 via a diode D5 through switching operation of a switching circuit to step up the output voltage of the fuel cell 22. The switching circuit is formed of a main switch Sl, formed of IGBT₅ or the like, and a diode D4.

[0041] More specifically, one end of the reactor Ll is connected to the high-potential terminal of the fuel cell 22, one end electrode of the main switch Sl is connected to the other end of the reactor Ll, and the other end electrode of the main switch Sl is connected to the low-potential terminal of the fuel cell 22. In addition, the cathode terminal of the diode D5 is connected to the other end of the reactor Ll, and, furthermore, a capacitor C3 that functions as a smoothing capacitor is connected between the anode terminal of the diode D5 and the other end of the main switch Sl. A smoothing capacitor Cl is provided for the main step-up circuit 12a at a side adjacent to the fuel cell 22. By so doing, it is possible to reduce a ripple of the output current of the fuel cell 22.

[0042] Here, the current sensor 2610 is provided between the high-potential terminal of the fuel cell 110 and the reactor Ll. The current sensor 2610 detects electric current flowing through the reactor Ll (that is, reactor current). In addition, a voltage VH applied to the capacitor C3 is the converter output voltage Vout of the FC softswitching converter 150, and a voltage VL applied to the smoothing capacitor Cl is the output voltage of the fuel cell 22 and is the converter input voltage Vin of the FC soft switching converter 150.

[0043] The auxiliary circuit 12b includes a first serially connected element that is connected in parallel with the main switch Sl. The first serially connected element includes a diode D3 and a snubber capacitor C2. The snubber capacitor C2 is serially connected to the diode D3. In the first serially connected element, the cathode terminal of the diode D3 is connected to the other end of the reactor Ll, and the anode terminal of the diode D3 is connected to one end of the snubber capacitor C2. Furthermore, the other end of the snubber capacitor C2 is connected to the low-potential terminal of the fuel cell 22.

[0044] Furthermore, the auxiliary circuit 12b includes a second serially connected element. In the second serially connected element, a diode D2, a switching •circuit, and a coil L2 are serially connected. The switching circuit is formed of an auxiliary switch S2 and a diode Dl. The coil L2 is an induction element. In the second serially connected element, the anode terminal of the diode D2 is connected to a connecting portion of the diode D3 and snubber capacitor C2 of the first serially connected element. Furthermore, the cathode terminal of the diode D2 is connected to one end of the auxiliary switch S2. In addition, the other end of the auxiliary switch S2 is connected to one end of the coil L2 common to the phases, and the other end of the coil L2 is connected to the high-potential terminal of the fuel cell 22.

[0045] In the thus configured FC soft switching converter 150, the controller 160 regulates the switching duty ratio of the main switch Sl to control the step-up ratio of the FC soft switching converter 150, that is, the ratio of the converter output voltage Vout to the converter input voltage Vin. In addition, switching operation of the auxiliary switch S2 of the auxiliary circuit 12b intervenes in the switching operation of the main switch Sl to implement soft switching.

[0046] As in the case of the above described first embodiment, in the present embodiment, the controller 160 detects reactor currents Ida flowing through the reactor Ll at the time points of the valleys of the triangular wave, and detects reactor currents I_mo flowing through the reactor Ll at the time points of the peaks of the triangular wave, and then averages the pairs of these reactor currents (for example, the reactor current Id_a-i and the reactor current I_m0-1). Thus, it is possible to detect a reactor current with high accuracy.

[0047] Note that in the above described embodiments, a controller for a multi-phase converter having a plurality of phases is illustrated; however, the aspect of the invention is not limited to the above configuration. The aspect of the invention may also be similarly applied to a controller for a single-phase converter.

Claims

CLAIMS:

1. A converter control device for controlling a converter that includes a reactor connected to a fuel cell and a switch for controlling a reactor current flowing through the reactor, comprising: an oscillator that generates a triangular wave having a predetermined frequency; a gate signal generating circuit that generates a gate signal for switching on/off of the switch in synchronization with the triangular wave; a current sensor that detects the reactor current; and a reactor current deriving unit that derives a mean value between a reactor current detected at the time point of a peak of the triangular wave and a reactor current detected at the time point of a valley of the triangular wave.

2. The converter control device according to claim 1, wherein the gate signal generating circuit generates a gate signal for switching the switch from off to on at substantially a middle point from valley to peak of the triangular wave, and generates a gate signal for switching the switch from on to off at substantially a middle point from peak to valley of the triangular wave.

3. The converter control device according to claim 1 or 2, wherein: a first terminal of the reactor is connected to a high-potential terminal of the fuel cell; a first terminal of the switch is connected to a second terminal of the reactor, and a second terminal of the switch is connected to a low-potential terminal of the fuel cell; the converter is a soft switching converter, wherein the converter includes: a main step-up circuit that includes a first diode, of which a cathode is connected to the second terminal of the reactor, and a smoothing capacitor that is provided between an anode of the first diode and the second terminal of the switch; and an auxiliary circuit that includes a first serially connected element and a second serially connected element, wherein the first serially connected element having a second diode and a snubber capacitor is connected in parallel with the switch and is connected to the second terminal of the reactor and the low-potential terminal of the fuel cell, and wherein the second serially connected element having a third diode, an auxiliary reactor and an auxiliary switch is connected between the first terminal of the reactor and a connecting portion of the second diode and the snubber capacitor.

4. A converter control method for controlling a converter that includes a reactor connected to a fuel cell and a switch for controlling a reactor current flowing through the reactor, comprising: generating a triangular wave having a predetermined frequency; generating a gate signal for switching on/off of the switch in synchronization with the triangular wave; and detecting a reactor current at the time point of a peak of the triangular wave and a reactor current at the time point of a valley of the triangular wave to derive a mean value between the reactor current at the time point of the peak of the triangular wave and the reactor current at the time point of the valley of the triangular wave.