JP2011004466A - Device for detecting capacitance drop of capacitor in resonance type converter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To detect the capacitance drop of a capacitor that absorbs a resonance current in a resonance type converter.SOLUTION: A device includes: a current detection unit 121 that detects the amount of current flowing between a DC power supply 11 and the capacitor C1; and a decision controller 20 that determines the capacitance of capacitor C1 decreases when the amount of current detected by the current detection unit 121 falls below a prescribed threshold.

Description

  The present invention relates to a technique for detecting a capacitance drop of a capacitor in a resonant converter.

  A DC-DC converter that boosts and / or steps down a direct current (DC) voltage is known as a voltage converter. The DC-DC converter is widely used in electric devices including electric circuits, such as personal computers, AV devices, mobile phones, and power supply systems. In recent years, there is an example in which a DC-DC converter is used in a power supply system of a vehicle such as a fuel cell vehicle, an electric vehicle, and a hybrid vehicle.

  The DC-DC converter can be configured by combining a switching element such as a transistor, a coil (reactor), a capacitor, and a diode, for example. As the DC-DC converter, a type called a resonant converter that realizes so-called soft switching is known. Soft switching uses a current resonance phenomenon to enable a switching operation with a voltage and / or current set to zero, thereby reducing power loss during switching.

International Publication No. WO2006 / 098376

  In a resonance type converter, a resonance current used for realizing soft switching may regenerate (reverse) to the input side. One example of such a factor is a reduction in the capacity of a capacitor that absorbs (buffers) the resonance current. That is, when a resonance current that cannot be absorbed by the capacitor is generated due to a decrease in the capacitance of the capacitor, the current can be regenerated to the input side. When the regeneration destination of the resonance current is a direct current power supply such as a fuel cell, the direct current power supply is reversely charged by the resonance current, and there is a possibility that performance degradation may occur.

  Accordingly, an object of the present invention is to enable detection of a decrease in the capacitance of a capacitor that absorbs a resonant converter resonant current. Another object of the present invention is to prevent the DC power supply from being reversely charged due to a resonance current that cannot be completely absorbed by the capacitor due to a decrease in the capacitance of the capacitor.

  In addition, the present invention is not limited to the above-described object, and other effects of the present invention can be achieved by the functions and effects derived from the respective configurations shown in the embodiments for carrying out the invention which will be described later. It can be positioned as one of

  One aspect of an apparatus for detecting a decrease in capacitor capacity of a resonant converter according to the present invention is a resonant type having a capacitor that is connected in parallel to a DC power source and absorbs a resonant current generated in a soft switching process based on a current resonant phenomenon. A device used for a converter, wherein a current detection unit that detects an amount of current flowing between the DC power supply and the capacitor, and the current amount detected by the current detection unit falls below a predetermined threshold, the capacitor And a determination control unit that determines that the capacity has decreased.

  Another aspect of the device for detecting a decrease in the capacitor capacity of the resonant converter of the present invention is a capacitor connected in parallel to a DC power source to absorb a resonance current generated in the process of soft switching based on a current resonance phenomenon. An apparatus used for a resonant converter having a current detection unit that detects an amount of current flowing between a connection point of the capacitor and the capacitor, and a current amount detected by the current detection unit has a predetermined threshold value And a determination control unit that determines that the capacity of the capacitor is reduced when the value is lower.

  Here, when the determination control unit determines that the capacitance of the capacitor has decreased, the determination control unit may perform OFF control of a switching element that causes the resonance current to flow through the capacitor in an ON state.

  Further, a current blocking circuit for blocking the resonance current toward the DC power supply and a bypass switch provided on an electric path for bypassing the current blocking circuit between the DC power supply and the connection point of the capacitor. In addition, the determination control unit performs ON control of the bypass switch while it is not determined that the capacity of the capacitor has decreased, and performs OFF control of the bypass switch when it is determined that the capacity of the capacitor has decreased. It may be.

  According to the present invention, it is possible to detect a decrease in the capacity of a capacitor that absorbs a resonant current in a resonant converter. As a result, it is possible to prevent the DC power source from being reversely charged due to the resonance current that cannot be completely absorbed by the capacitor due to the decrease in the capacitance, thereby preventing the performance deterioration of the DC power source.

It is a figure showing typically an example of composition of a power supply system concerning one embodiment and vehicles 1 carrying the power supply system concerned. FIG. 2 is a circuit diagram illustrating an example of an FC boost converter illustrated in FIG. 1. FIG. 3 is a diagram for explaining the operation (mode 1) of the FC boost converter illustrated in FIG. 2; It is a graph which shows the example of a time change of the electric current of the element in the FC boost converter of mode 1, or a voltage. FIG. 3 is a diagram for explaining the operation (mode 2) of the FC boost converter illustrated in FIG. 2; It is a graph which shows the example of a time change of the electric current or voltage of an element in the FC boost converter of mode 2. FIG. 3 is a partial equivalent circuit diagram of the FC boost converter illustrated in FIG. 2. It is a figure which shows an example of the time change of the electric current which flows into the A point in FIG. FIG. 3 is a diagram illustrating how a resonance current is regenerated to the power supply side in the FC boost converter illustrated in FIG. 2. FIG. 10 is a functional block diagram illustrating a modification of the ECU illustrated in FIGS. 2 and 9. It is a figure which shows the modification of the power supply system which illustrates an example in FIG.2 and FIG.9.

  Embodiments of the present invention will be described below with reference to the drawings. However, the embodiment described below is merely an example, and there is no intention to exclude various modifications and technical applications that are not explicitly described below. In other words, the present invention can be implemented with various modifications (combining the embodiments, etc.) without departing from the spirit of the present invention. In the following description of the drawings, the same or similar parts are denoted by the same or similar reference numerals. The drawings are schematic and do not necessarily match actual dimensions and ratios. In some cases, the dimensional relationships and ratios may be different between the drawings.

[1] Description of Embodiment FIG. 1 is a diagram schematically illustrating a configuration example of a power supply system 10 according to an embodiment and a vehicle 1 in which the power supply system 10 is mounted.

  The power supply system 10 is illustratively a fuel cell system having a fuel cell (FC) 11, and the vehicle 1 is a fuel cell vehicle as an example of an electrical device that uses the fuel cell system 10 as a source of driving power. . However, the vehicle 1 may be an electric vehicle or a hybrid vehicle.

  The vehicle 1 includes a motor 16 that drives the drive wheels 2, an electronic control unit (ECU) 20, an accelerator pedal sensor 21 that detects the opening of an accelerator pedal, and the like. The accelerator pedal sensor 21 is electrically connected to the electronic control unit 20. For example, the rotational speed of the motor 16 (drive wheel 2) is controlled by the ECU 20 according to the detected opening degree of the access pedal.

  In addition to the fuel cell (FC) 11, the fuel cell system 10 includes, as a non-limiting example, an FC boost converter 12, a battery 13, a battery boost converter 14, an inverter 15, and the like.

  The FC 11 is a device that generates electricity using an electrochemical reaction. Various types of fuel cells such as solid polymer type, phosphoric acid type, molten carbonate type, solid oxide type, and alkaline electrolyte type can be applied to FC11. The power generated by the FC 11 is used to drive the motor 16 that drives the drive wheels 2 of the vehicle 1 and to charge the battery 13.

  The battery 13 is a chargeable / dischargeable secondary battery, and various types of secondary batteries such as lithium ion, nickel hydride, and nickel cadmium can be applied. The battery 13 can supply electric power to various electric devices used when the vehicle 1 or the FC 11 is operated. The electrical equipment here includes, for example, lighting equipment for the vehicle 1, air conditioning equipment, a hydraulic pump, a pump for supplying fuel gas and reforming material of FC11, a heater for adjusting the temperature of the reformer, and the like.

  The FC 11 and the battery 13 are electrically connected in parallel to the inverter 15 as illustrated in FIG. An FC boost converter 12 is provided in the electrical path from the FC 11 to the inverter 15. The FC boost converter 12 is a DC-DC converter that boosts an input DC voltage, converts the DC voltage generated by the FC 11 into a predetermined DC voltage within a convertible range (for example, boosts it), and applies it to the inverter 15. Can do. Such boosting operation makes it possible to secure the driving power required to drive the motor 16 even when the output power of the FC 11 is low.

  On the other hand, the battery boost converter 14 is connected in parallel to the electrical path between the FC boost converter 12 and the inverter 15 in the electrical path from the battery 13 to the inverter 15. The converter 14 is also a DC-DC converter, and can convert the DC voltage applied from the battery 13 or the inverter 15 into a predetermined DC voltage within a convertible range.

  The converter 14 can be a step-up / step-down converter capable of both boosting and stepping down. For example, the converter 14 controls (boosts) the input DC voltage from the battery 13 and outputs it to the inverter 15 side. The input DC voltage can be controlled (stepped down) and output to the battery 13. Thereby, charging / discharging of the battery 13 is attained.

  Moreover, the converter 14 can control the terminal voltage of the inverter 15 by controlling the output voltage. This control controls the relative output voltage difference between the power supplies (FC 11 and battery 13) connected in parallel to the inverter 15, and makes it possible to properly use both powers.

  The inverter 15 receives DC voltage input from the FC 11 via the converter 12 and from the battery 13 via the converter 14, converts the input DC voltage into alternating current (AC) voltage, and drives the motor 16. Supply as voltage. At that time, the ECU 20 controls the operation (switching) of the inverter 15 so that an AC voltage corresponding to the required power is supplied to the motor 16.

  In addition to the control described above, the ECU 20 comprehensively controls the operation (operation) of the vehicle 1 and the fuel cell system 10. The ECU 20 can be exemplarily realized as a microcomputer including a CPU as an example of an arithmetic processing device, a RAM, a ROM as an example of a storage device, and the like. The ECU 20 is electrically connected to each element of the motor 16 and the fuel cell system 10 and various sensor groups, and appropriately receives various sensor values, performs arithmetic processing, transmits commands (control signals), and the like. In addition to the accelerator pedal sensor 21, the sensor group includes, for example, an SOC sensor that detects a state of charge (SOC) of the battery 13, a vehicle speed sensor that detects a vehicle speed (the number of rotations of the motor 16), and the like. Can be.

[2] Boost converter 12
Next, an example of an electric circuit diagram of the boost converter 12 is shown in FIG. The boost converter 12 shown in FIG. 2 exemplarily includes a main circuit 12a and an auxiliary circuit (snubber circuit) 12b.

  The main circuit 12a includes, for example, a switching circuit including a switching element (main switch) S1 and an antiparallel diode D4, a reactor (coil) L1, an (output) diode D5, an (input) capacitor C1, and an (output) capacitor. C3.

  The main circuit 12a periodically stores and switches the main switch S1 (ON / OFF), thereby accumulating the electric energy of the reactor L1 and releasing the accumulated energy corresponding to the amount of current (main current) flowing through the reactor L1. Is repeated periodically. The released electrical energy is superimposed on the output voltage of the FC 11 and output to the motor 16 side (inverter 15 side), which is an example of a load, via the diode D5. Thereby, the input voltage (output voltage of FC11) VL is boosted to a predetermined output voltage VH.

  Both ends of the input capacitor C1 are connected to the high potential side of FC11 and the low potential side of FC11 [for example, ground (GND)]. The input capacitor C1 reduces the ripple by smoothing the voltage (voltage before boosting) at both ends thereof. The voltage across the capacitor C1, which is the pre-boosting voltage VL, is equivalent to the output voltage of the FC11.

  One end of the reactor L1 is electrically connected to the positive electrode of the FC 11, and the other end of the reactor L1 is connected in series to the anode of the diode D5. One end of an output capacitor C3 is connected in parallel to the cathode of the diode D5. The cathode voltage of the output diode D5 is a boosted voltage VH supplied to the motor 16 side (inverter 15 side) which is an example of a load. The output capacitor C3 smoothes the boosted voltage VH to reduce fluctuations.

  As a non-limiting example, an insulated gate bipolar transistor (IGBT) can be applied to the main switch S1, and one pole (for example, collector) is connected in parallel to the electrical path between the reactor L1 and the output diode D5. In addition, the other pole (for example, an emitter) is connected to the negative electrode side (GND) of FC11.

  By applying a switch control signal such as a pulse width modulation (PWM) signal to the gate of the main switch S1, for example, ON / OFF of the main switch S1 is controlled. Further, by controlling the duty ratio of the switch control signal, the average amount of current flowing through the reactor L1 in the direction toward the output diode D5 can be controlled, and the boosting degree of the boost converter 12 can be controlled. The switch control signal is generated in the ECU 20, for example.

  An antiparallel diode D4 is connected between both poles of the main switch S1. The anti-parallel diode D4 allows current flow in the direction opposite to the current flow direction when the main switch S1 is ON.

  The auxiliary circuit 12b exemplarily includes a (regenerative) diode D3, a reactor (coil) L2, a (snubber backflow prevention) diode D2, a switch circuit including a switching element (auxiliary switch) S2 and an antiparallel diode D1, (Resonance) capacitor C2. By turning on the auxiliary switch S2, an LC resonance phenomenon is caused by the reactor L2 and the capacitor C2, and soft switching of the main switch S1 and the auxiliary switch S2 can be realized using the LC resonance phenomenon.

  Illustratively, the diode D3 is connected in parallel to the main switch S1 with its anode connected to the electrical path between the reactor L1 and the output diode D5. The cathode of the diode D3 is connected to one end of the capacitor C2, and the other end of the capacitor C2 is connected to the negative electrode side (GND) of the FC11. Further, one end of the reactor L2 is connected in parallel to the connection point between the cathode of the diode D3 and the capacitor C2, and the anode of the diode D2 is connected to the other end of the reactor L2.

  Furthermore, the cathode of the diode D2 is connected to one (for example, collector) of both electrodes of the auxiliary switch S2, and the other (for example, emitter) of both electrodes of the auxiliary switch S2 is connected to one end of the reactor L1 on the FC11 side. A diode D1 is connected in parallel between both electrodes of the auxiliary switch S2. The connection positions of the reactor L2 and the switch circuit including the auxiliary switch S2 and the diode D1 may be interchanged.

[3] Soft switching operation (modes 1 to 6)
In boost converter 12 configured as described above, one cycle of the boost operation based on the soft switching operation can be exemplarily represented by the following state transitions (modes 1 to 6).

  In an initial state in which both the main switch S1 and the auxiliary switch S2 are OFF, for example, a current flows along a path indicated by a dotted line in FIG. 3, and power is supplied to the inverter 15 (motor 16) side.

(Mode 1)
From the initial state, when the auxiliary switch S2 is turned on while the main switch S1 remains OFF, the charge accumulated in the output diode D5 flows to the input capacitor C1 via the diode D3, the reactor L2, and the auxiliary switch S2. Can be extinguished (soft turn-off). On the other hand, the current flowing from the FC11 side via the reactor L1 and the output diode D5 gradually shifts to the auxiliary circuit 12b side (diode D3). The arrow 100 in FIG. 3 expresses the state. Therefore, as shown by a solid line 200 in FIG. 2, a current flows back to the auxiliary circuit 12b through the path of the reactor L1, the diode D3, the reactor L2, the diode D2, and the auxiliary switch S2. Therefore, as illustrated in FIG. 4, in the period of mode 1 (period of time T0 to T1), the current flowing through the reactor L2 and the auxiliary switch S2 (L2 current) is the voltage across the reactor L2 (VH−VL). It increases according to the inductance value of the reactor L.

(Mode 2)
Thereafter, for example, as indicated by a solid line 300 in FIG. 5, the electric charge accumulated in the capacitor C2 is gradually discharged toward the reactor L2, and a current is formed by the reactor L2, the diode D2, the auxiliary switch S2, and the input capacitor C1. Through the electrical path. As a result, an LC resonance phenomenon occurs due to the reactor L2 capacitor C2, and the voltage across the capacitor C2 gradually decreases from positive to zero in a sinusoidal shape (see times T1 to T2 in FIG. 6). At the moment when the auxiliary switch S2 is turned on (time T1 in FIG. 6), the auxiliary switch S2 is zero current, and is turned on by soft switching.

(Mode 3)
The timing at which all the electric charges of the capacitor C2 are discharged, the voltage of the capacitor C2 becomes zero (see time T2 in FIG. 6), and the currents flowing through the reactor L1 and the reactor L2 (L1 current and L2 current) become the same (FIG. 6). At time T3), the main switch S1 is turned on. Then, the current flowing back through the auxiliary circuit 12b starts to flow through the main switch S1, and the current flowing through the main switch S1 (S1 current: see FIG. 6) gradually increases.

(Mode 4)
At this time, the main switch S1 is turned on from zero current and zero voltage. When the main switch S1 is ON, current flows through the paths of the main switches S1, FC11 and the reactor L1, and electric energy is gradually accumulated in the reactor L1. At this time, since no current flows through the auxiliary circuit 12b, the capacitor C2 is not charged, and the voltage of the capacitor C2 remains zero (see FIG. 6).

(Mode 5)
Thereafter, both the main switch S1 and the auxiliary switch S2 are turned off. Both switches S1 and S2 may be turned off simultaneously, or auxiliary switch S2 may be turned off first. At this time, since the voltage of the capacitor C2 is zero, the auxiliary switch S2 is turned off from zero current and zero voltage, and the main switch S1 is turned off from zero voltage. When the main switch S1 is turned off, the current flowing through the reactor L1 starts to flow through the path of the diode D3, the capacitors C2, FC11, and the reactor L1, and charging of the capacitor C2 starts. By charging the capacitor C2, the rate of voltage increase when the main switch S1 is turned off is suppressed, and it is possible to reduce the loss in the region where the tail current exists.

(Mode 6)
When the capacitor C2 is charged to the same voltage as the output voltage VH, the output diode D5 is turned ON, and the electric energy accumulated so far in the reactor L1 is supplied to the inverter 15 (motor 16) side. Thereafter, the auxiliary switch S2 is turned ON again, and the next cycle starts from mode 1.

[4] Capacitance drop determination of capacitor C1 In the soft switching operation as described above, in mode 2, the electric charge discharged from the capacitor C2 is the path 300 of the reactor L2, the diode D2, the auxiliary switch S2, and the capacitor C1 (see FIG. 5). ) Flows as an L2C2 resonance current. At this time, the L2C2 resonance current merges with the main current (L1 current) from the FC 11 flowing through the main circuit 12a at the connection point 120 between the reactor L1 of the main circuit 12a and the auxiliary switch S2 of the auxiliary circuit 12b. Flows in the opposite direction.

  FIG. 8 shows an example of a temporal change in the amount of current flowing through the point A shown in FIG. 7 when the current in the direction from the FC 11 toward the reactor L1 is positive and the current in the opposite direction is negative. In FIG. 8, the current in the negative region corresponds to the L2C2 resonance current I. The L2C2 resonance current I may be considered equivalent to the amount of current generated by the charge discharge of the capacitor C2.

The capacitance of the capacitor C2 C _2, the inductance value L ₂ of the reactor L2, the voltage applied to the capacitor C2 V, the current flowing through the reactor L2 and (L2 current) is represented respectively I, from the law of conservation of energy, the following Formula (1) is materialized.

Therefore, the current I can be obtained by the following equation (2).

When the voltage of the capacitor C2 is V = VH−VL, the expression (2) becomes the following expression (3).

ただし、例示的に、インピーダンスＺ_Aは、ＦＣ１１の内部インピーダンスと配線インピーダンスとを含み、インピーダンスＺ_Bは、コンデンサＣ１の内部インピーダンスと配線インピーダンスとを含む。 Here, for example, as shown in FIG. 7, assuming that the impedance values of the paths viewed from the high potential side of FC11 and capacitor C1 are Z _A and Z _B , respectively, the L2C2 resonance current I flowing back to the FC11 side is the respective impedance value. The current is divided according to the ratio of Z _A and Z _B. The shunt currents I _A and I _B can be expressed by the following equations (4) and (5), respectively.

However, for example, the impedance Z _A includes the internal impedance and the wiring impedance of the FC 11, and the impedance Z _B includes the internal impedance and the wiring impedance of the capacitor C1.

When the impedance value Z _{A of the} FC 11 is relatively larger than the impedance value Z _B of the capacitor C1, most of the L2C2 resonance current I can be absorbed (buffered) by the capacitor C1. If the capacity of the capacitor C1 is designed to a value that can absorb all of the L2C2 resonance current I, it is possible to avoid reverse charging of the FC11.

However, the capacitance of the capacitor C1 may be lower than the expected capacitance due to aging. When the capacitance of the capacitor C1 is represented by C ₁ and the voltage across the capacitor C1 is represented by Vc, the current I _C flowing through the capacitor C1 can be represented by the following equation (6).

Therefore, when Vc is constant and the capacitance of the capacitor C1 is reduced, the current (I _B ) flowing to the capacitor C1 is reduced, and the reduced current flows backward (regenerated) to the FC11 side (arrow 400 in FIG. 7). reference). In this case, the amount of current from FC11 toward reactor L1 is relatively reduced. If the FC11 is reversely charged by the regenerative current, there is a possibility that the performance of the FC11 is deteriorated.

  Therefore, in the present embodiment, for example, as shown in FIGS. 2 and 9, between the high potential side of the FC 11 and the input capacitor C1 (alternatively, it may be between the connection point of the capacitor C1 and the capacitor C1. ) Is detected (monitored). For the current detection (monitor), a current sensor 121 as an example of a current detection unit can be used.

  For example, a magnetic proportional sensor can be applied to the current sensor 121. The magnetic proportional current sensor indirectly measures the magnitude of the current by measuring the magnetic field when the current to be measured flows through the conductor. For example, a magnetic field corresponding to the current is converted into a voltage signal by the Hall element, the output voltage is amplified by an amplifier circuit, and the output voltage corresponding to the current is output as a sensor value.

  The current value (current sensor value) obtained by the current sensor 121 can be given to the ECU 20, for example. The ECU 20 is an example of a determination control unit, and can determine (detect) that the capacitance of the capacitor C1 has decreased when a certain amount of regenerative current is generated and the current sensor value falls below a predetermined threshold. When it is determined that the capacity of the capacitor C1 has decreased, the ECU 20 controls, for example, the auxiliary switch S2 to be turned off.

  Therefore, as shown in FIGS. 2 and 7, the ECU 20 illustratively has functions as a sampling processing unit 211 and a comparison / determination unit 212. The ECU 20 and the current sensor 121 function as an example of a circuit (device) that detects a decrease in the capacitance of the capacitor C1.

  The sampling processing unit 211 periodically samples the sensor value obtained by the current sensor 121. The sampling timing can be shortened within a range allowed in relation to the processing capability of the ECU 20. As the sampling period is set shorter, the determination accuracy in the comparison / determination unit 212 can be improved.

  The comparison / determination unit 212 uses the sensor value sampled by the sampling processing unit 211 (hereinafter, also referred to as “sampling value”) and a predetermined threshold value obtained based on the equation (4) or the equation (5). In comparison, it is determined whether or not the sampling value is below the threshold value. As a result of the determination, if the sampling value is below the threshold value, the comparison / determination unit 212 determines that the capacitance of the capacitor C1 has decreased (abnormal determination), and otherwise determines that it is normal.

  When it is determined that the capacity of the capacitor C1 has decreased, the comparison / determination unit 212 controls, for example, the auxiliary switch S2 to be OFF. Thereby, it is possible to avoid the L2C2 resonance current flowing through the auxiliary circuit 12b from flowing backward toward the FC11. Therefore, it is possible to prevent the FC11 from being reversely charged by the L2C2 resonance current, and to prevent performance degradation of the FC11.

  The abnormality determination by the comparison / determination unit 212 may be performed when a state below the threshold value continues for a predetermined time. Further, the determination result by the comparison / determination unit 212 can be presented from the ECU 20 to the driver or maintenance person of the vehicle 1, for example. As an example of the presentation mode, lighting of a predetermined alarm lamp provided in the vehicle 1, sound output from a speaker provided in the vehicle 1, and the like can be given.

  The threshold value can be stored in a memory such as a RAM in the ECU 20. Further, the abnormality determination in the comparison / determination unit 212 may be set so as to allow deviation from a threshold value within the error range. The permissible range can be determined according to system design requirements.

(Modification 1)
The ECU 20 may have a function as shown in FIG. 10, for example. That is, for example, the ECU 20 may have functions as the peak hold processing unit 222 and the comparison / determination unit 223 in addition to the sampling processing unit 211 described above.

  Here, the peak hold processing unit 222 holds the peak value of the current sensor value sampled by the sampling processing unit 211. The function of the peak hold processing unit 222 can be provided as a hardware peak hold circuit.

  Then, the comparison / determination unit 223 compares the sensor value held by the peak hold processing unit 222 with a predetermined threshold value, and determines that the capacitance of the capacitor C1 is reduced (abnormal) when the sensor value is below the threshold value. If not, it is determined as normal. The operation and control of the ECU 20 at the time of abnormality determination are the same as in the above-described embodiment.

  According to the first modification, the ECU 20 can compare the threshold value with the peak value of the current sensor value in the peak hold processing unit 222 as compared with the above-described embodiment, and thus simplify the comparison / determination process. And the processing load on the ECU 20 (CPU) can be reduced.

(Modification 2)
FIG. 11 is a circuit diagram focusing on the boost converter 12 according to the second modification. A regenerative current blocking circuit 12c and a bypass circuit 12d are provided between the FC 11 and the boost converter 12 shown in FIG.

  The regenerative current blocking circuit 12c has one end connected to the high potential side of the FC11 and the other end connected in series to the reactor L1 that is an element of the main circuit 12a, and backflow (regeneration) toward the high potential side of the FC11. It is a circuit that prevents the regenerative current. As the regenerative current blocking circuit 12c, for example, a diode D6 or a reactor L3 can be used. When the diode D6 is used, the anode is connected to the electric path on the high potential side of the FC 11 and the cathode is connected to the electric path on the reactor L1 side.

  For example, the bypass circuit 12d has one end connected to the high potential side of the FC 11 and the other end connected to the connection point of the input capacitor C1 connected to the electric path between the regenerative current blocking circuit 12c and the reactor L1. It is connected. The bypass circuit 12d can be ON / OFF controlled by, for example, the ECU 20, and can bypass the electric path that passes through the regenerative current blocking circuit 12c by being ON-controlled. For example, a relay switch can be used for the bypass circuit 12d.

  For example, the bypass circuit 12d is ON-controlled while the ECU 20 does not determine that the capacity of the capacitor C1 has decreased (bypass state). On the other hand, when it is determined that the capacitance of the capacitor C1 has decreased, the bypass circuit 12d is controlled to be OFF (non-bypass state).

  Thus, even if there is an L2C2 resonance current that cannot be completely absorbed by the capacitor C2 due to a decrease in the capacitance of the capacitor C1, the regeneration current blocking circuit 12c can prevent the resonance current from being regenerated to the FC11. Therefore, the FC11 can be prevented from being reversely charged by the L2C2 resonance current, and the performance degradation of the FC11 can be prevented.

  When the bypass circuit 12d is controlled to be OFF, the ECU 20 may control the auxiliary switch S2 to be OFF or may be maintained in an ON state. When the ON state is maintained, the soft switching by the auxiliary circuit 12b can be continued even if the capacitance of the capacitor C1 is reduced.

[6] Others The above-described embodiment is applied to a DC-DC converter (for example, another type of converter such as a step-down converter) having an electric path through which a resonance current flows in a direction opposite to the main current from the power supply side. May be. The above-described embodiment is not limited to the on-vehicle DC-DC converter, and may be applied to a DC-DC converter mounted on an electric device such as a personal computer, an audio visual (AV) device, or a portable terminal. .

1 Vehicle 2 Drive Wheel 10 Power Supply System (Fuel Cell System)
11 Fuel cell (FC) (DC power supply)
12 FC boost converter 12a Main circuit 12b Auxiliary circuit (snubber circuit)
12c Regenerative current blocking circuit 12d Bypass circuit 13 Battery 14 Battery boost converter 15 Inverter 16 Motor 20 Electronic control unit (ECU) (determination control unit)
21 Accelerator pedal sensor 120 Connection point 121 Current sensor (current detector)
211 Sampling processing unit 222 Peak hold processing unit 212,223 Comparison / determination unit C1 input capacitor C2 capacitor C3 output capacitor D1 to D6
L1, L2, L3 reactor (coil)
S1 Switching element (main switch)
S2 Switching element (auxiliary switch)

Claims (4)

A device used for a resonant converter having a capacitor connected in parallel to a DC power source and absorbing a resonant current generated in a soft switching process based on a current resonance phenomenon,
A current detector for detecting the amount of current flowing between the DC power supply and the capacitor;
A determination control unit that determines that the capacitance of the capacitor has decreased when the amount of current detected by the current detection unit falls below a predetermined threshold;
A device for detecting a decrease in the capacitance of a resonant converter. A device used for a resonant converter having a capacitor connected in parallel to a DC power source and absorbing a resonant current generated in a soft switching process based on a current resonance phenomenon,
A current detection unit that detects an amount of current flowing between the connection point of the capacitor and the capacitor;
A determination control unit that determines that the capacitance of the capacitor has decreased when the amount of current detected by the current detection unit falls below a predetermined threshold;
A device for detecting a decrease in capacitance of a capacitor. The determination control unit
The apparatus according to claim 1, wherein when it is determined that the capacity of the capacitor has decreased, the switching element that causes the resonance current to flow through the capacitor in an ON state is controlled to be OFF. A current blocking circuit for blocking the resonance current toward the DC power supply; and a bypass switch provided on an electric path for bypassing the current blocking circuit between the DC power supply and the connection point of the capacitor. ,
The determination control unit
The bypass switch is ON-controlled while it is not determined that the capacity of the capacitor is reduced, and the bypass switch is OFF-controlled when it is determined that the capacity of the capacitor is reduced. The device described in 1.

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