JP2011019337A - Converter control apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a converter control apparatus capable of sufficiently exhibiting operation performance of a soft switching converter by taking countermeasures against low temperature.SOLUTION: A controller detects the temperature Tev of an EV element, on the basis of a signal transmitted from a temperature sensor (step S1). If it is determined that the temperature Tev of the EV element is lower than a switching threshold temperature Tth1, the controller starts hard switch control, while always turning off a second switch element of an auxiliary circuit (step S2→step S3). Meanwhile, when determining that the temperature Tev of the EV element is not less than the switching threshold temperature Tth1 (NO in step S2), the controller starts soft switching control (step S4).

Description

  The present invention relates to a converter control device that controls an output voltage of a fuel cell.

  In fuel cell systems mounted on automobiles, various hybrid fuel cell systems with fuel cells and batteries as power sources have been proposed in order to respond to sudden load changes exceeding the power generation capacity of fuel cells. Has been.

  In the hybrid fuel cell system, the output voltage of the fuel cell and the output voltage of the battery are controlled by a DC / DC converter. As a DC / DC converter that performs such control, a type that performs voltage conversion by causing a switching element such as a power transistor, IGBT, or FET to perform PWM operation is widely used. DC / DC converters are required to have further lower loss, higher efficiency, and lower noise in accordance with power saving, downsizing, and higher performance of electronic devices, and in particular, switching loss and switching surge associated with PWM operation. Reduction is desired.

  One of the techniques for reducing such switching loss and switching surge is soft switching technique. Here, soft switching is a switching method for realizing ZVS (Zero Voltage Switching) or ZCS (Zero Current Switching), and has low switching loss and stress applied to the power semiconductor device. On the other hand, a switching method in which the voltage / current is directly turned on / off by the switching function of the power semiconductor device is called hard switching. In the following description, a method in which both or one of ZVS / ZCS is realized is called soft switching, and the other is called hard switching.

  Soft switching is realized by, for example, a step-up / step-down DC / DC converter (main boost circuit) including an inductor, a switching element, a diode, etc., and an auxiliary circuit for reducing switching loss (so-called soft switching converter). (See, for example, Patent Document 1).

JP 2005-102438 A

FIG. 18 is a diagram illustrating the relationship between the withstand voltage of the elements constituting the soft switching converter and the element temperature, and FIG. 19 is a diagram illustrating the relationship between the boost voltage and the temperature of the soft switching converter.
As shown in FIG. 18, the lower the element temperature, the lower the breakdown voltage of the elements constituting the soft switching converter. For this reason, the boost voltage of the soft switching converter (that is, the output voltage of the soft switch converter) is also set for each element temperature range so as not to exceed the breakdown voltage of the element (see FIG. 19).

However, from the viewpoint of the operating efficiency of the soft switching converter, it is preferable to operate the soft switch converter by lowering the boost voltage (in other words, to use the soft switching converter in a state where the operating performance is lowered). Absent.
At present, the boosted voltage is switched in accordance with the rise of the element temperature due to the use of the soft switching converter without taking any measures against the temperature rise (for example, the boosted voltage Vu2 → the boosted voltage Vu1 shown in FIG. 19). There was a problem that the operation performance of the soft switching converter could not be fully utilized.

  The present invention has been made in view of the circumstances described above, and an object of the present invention is to provide a converter control device that can fully utilize the operation performance of a soft switching converter by performing a low-temperature countermeasure process.

In order to solve the above problems, a converter control device according to the present invention is a soft switching converter control device including a main booster circuit and an auxiliary circuit for controlling the output of a fuel cell, and constitutes the soft switching converter. Switching between a temperature sensor for detecting a related temperature of the element, hard switching using the main booster circuit, and soft switching using the main booster circuit and the auxiliary circuit, and the related temperature is equal to or lower than a set threshold value And a switching switching means for switching to the hard switching, and a switching control means for performing switching control of the hard switching and the soft switching.

  According to such a configuration, when the related temperature of the elements constituting the soft switching converter is equal to or lower than a set threshold (for example, −2 ° C. or the like), the soft switching converter control is switched from soft switching to hard switching as low temperature countermeasure control. . By such switching, although the operating performance of the soft switching converter temporarily falls, the switching loss can be increased and the element temperature can be raised rapidly, so that the operating performance of the soft switching converter can be fully utilized. .

  Here, in the above configuration, in the state where the switching control of the hard switching is performed for the soft switch converter, the reaction gas supplied to the fuel cell is less than that during normal power generation, and the A judgment means for judging whether or not low-efficiency power generation with a large power loss as compared with normal power generation is performed, and when a positive judgment result is obtained by the judgment means, the output power of the fuel cell is An embodiment further comprising operating point control means for controlling the operating operating point of the fuel cell so as to reduce the output current of the fuel cell by a predetermined amount while keeping the fuel cell constant.

  In the above configuration, the determination unit determines whether low-efficiency power generation is performed for the fuel cell and whether the element temperature of the elements constituting the soft switch converter is equal to or higher than a specified temperature. Is preferred.

  Furthermore, in the above configuration, the main booster circuit includes a main coil having one end connected to a high potential side terminal of the fuel cell, and a first diode having a cathode connected to the other end of the main coil. A main switch having one end connected to the other end of the main coil and the other end connected to a low potential side terminal of the fuel cell, an anode of the first diode, and a low potential side terminal of the fuel cell A smoothing capacitor connected to the main switch, the auxiliary circuit connected in parallel to the main switch constituting the main booster circuit, and connected in parallel to the main switch, and the high potential of the fuel cell An aspect including a first series connection body in which a clamp diode and a snubber capacitor are connected in series, which are connected to the terminal on the side and the terminal on the low potential side, is preferable.

  Further, in the above configuration, the auxiliary circuit includes a diode, an auxiliary coil, and the auxiliary switch connected between a connection portion of the clamp diode and the snubber capacitor and one end of the main coil. An embodiment further comprising a second series connection body connected in series is also preferable.

  According to the present invention, it is possible to sufficiently utilize the operation performance of the soft switching converter by performing the low temperature countermeasure process.

It is a system configuration figure of the FCHV system concerning this embodiment. It is a figure which shows the circuit structure of the multiphase FC soft switching converter which concerns on the same embodiment. It is a figure which shows the circuit structure for 1 phase of the FC soft switching converter which concerns on the same embodiment. It is a flowchart which shows the soft switching process which concerns on the same embodiment. FIG. 6 is a diagram showing an operation in mode 1. FIG. 6 is a diagram illustrating an operation in mode 2. FIG. 6 is a diagram illustrating an operation in mode 3. FIG. 10 is a diagram illustrating an operation in mode 4. FIG. 10 is a diagram illustrating an operation in mode 5. FIG. 10 is a diagram illustrating an operation in mode 6. It is the figure which illustrated the relationship between the voltage Vc of the snubber capacitor | condenser C2 of mode 5, the voltage Ve concerning 1st switching element S1, and the electric current Ie which flows through 1st switching element S1. It is a figure which shows the voltage and electric current behavior in the transition process from mode 2 to mode 3. It is a flowchart which shows a switching switching control process. It is a flowchart which shows an element destruction prevention control process. It is a figure which shows the relationship between FC electric current and FC voltage. It is a figure which shows the relationship between FC electric current, FC voltage, and FC power. It is the figure which illustrated other composition of an auxiliary circuit. It is the figure which illustrated the relationship between the proof pressure of the element which comprises a soft switching converter, and element temperature. It is the figure which showed the boost voltage and temperature relationship of a soft switching converter.

A. Embodiments Hereinafter, embodiments according to the present invention will be described with reference to the drawings. FIG. 1 shows a configuration of an FCHV system mounted on a vehicle according to the present embodiment. In the following description, a fuel cell vehicle (FCHV) is assumed as an example of the vehicle, but the present invention can also be applied to an electric vehicle. Further, the present invention can be applied not only to vehicles but also to various moving bodies (for example, ships, airplanes, robots, etc.), stationary power sources, and portable fuel cell systems.

A-1. Overall System Configuration The FCHV system 100 includes an FC converter 2500 between the fuel cell 110 and the inverter 140, and a DC / DC converter (hereinafter referred to as a battery converter) 180 between the battery 120 and the inverter 140. .

  The fuel cell 110 is a solid polymer electrolyte cell stack in which a plurality of unit cells are stacked in series. The fuel cell 110 is provided with a voltage sensor V0 for detecting the output voltage Vfcmes of the fuel cell 110 and a current sensor I0 for detecting the output current Ifcmes. In the fuel cell 110, the oxidation reaction of the formula (1) occurs in the anode electrode, the reduction reaction of the formula (2) occurs in the cathode electrode, and the electromotive reaction of the formula (3) occurs in the fuel cell 110 as a whole.

H ₂ → 2H ⁺ + 2e ⁻ (1)
(1/2) O ₂ + 2H ⁺ + 2e ⁻ → H ₂ O (2)
H ₂ + (1/2) O ₂ → H ₂ O (3)

  The unit cell has a structure in which a MEA in which a polymer electrolyte membrane or the like is sandwiched between two electrodes, a fuel electrode and an air electrode, is sandwiched between separators for supplying fuel gas and oxidizing gas. The anode electrode is provided with an anode electrode catalyst layer on the porous support layer, and the cathode electrode is provided with a cathode electrode catalyst layer on the porous support layer.

  The fuel cell 110 is provided with a system for supplying fuel gas to the anode electrode, a system for supplying oxidizing gas to the cathode electrode, and a system for supplying coolant (all not shown). By controlling the supply amount of the fuel gas and the supply amount of the oxidizing gas according to the signal, it is possible to generate desired power.

  The FC converter 2500 plays a role of controlling the output voltage Vfcmes of the fuel cell 110, and converts the output voltage Vfcmes input to the primary side (input side: fuel cell 110 side) into a voltage value different from the primary side ( Step-up or step-down) and output to the secondary side (output side: inverter 140 side). Conversely, the voltage input to the secondary side is converted to a voltage different from the secondary side and output to the primary side. A bidirectional voltage converter. The FC converter 2500 controls the output voltage Vfcmes of the fuel cell 110 to be a voltage corresponding to the target output.

  The battery 120 is connected in parallel to the fuel cell 110 with respect to the load 130, and stores a surplus power storage source, a regenerative energy storage source during regenerative braking, and an energy buffer when the load fluctuates due to acceleration or deceleration of the fuel cell vehicle. Function as. As the battery 120, for example, a secondary battery such as a nickel / cadmium storage battery, a nickel / hydrogen storage battery, or a lithium secondary battery is used.

  The battery converter 180 plays a role of controlling the input voltage of the inverter 140 and has a circuit configuration similar to that of the FC converter 2500, for example. Note that a step-up converter may be employed as the battery converter 180, but a step-up / step-down converter capable of step-up and step-down operations may be employed instead, and the input voltage of the inverter 140 can be controlled. Any configuration can be adopted.

  The inverter 140 is, for example, a PWM inverter driven by a pulse width modulation method, and converts DC power output from the fuel cell 110 or the battery 120 into three-phase AC power in accordance with a control command from the controller 160, thereby obtaining a traction motor. The rotational torque of 131 is controlled.

  The traction motor 131 is the main power of the vehicle, and generates regenerative power during deceleration. The differential 132 is a reduction device that reduces the high-speed rotation of the traction motor 131 to a predetermined number of rotations and rotates the shaft on which the tire 133 is provided. The shaft is provided with a wheel speed sensor (not shown) and the like, thereby detecting the vehicle speed of the vehicle. In the present embodiment, all devices (including the traction motor 131 and the differential 132) that can operate by receiving power supplied from the fuel cell 110 are collectively referred to as a load 130.

  The controller 160 is a computer system for controlling the FCHV system 100 and includes, for example, a CPU, a RAM, a ROM, and the like. The controller 160 inputs various signals (for example, a signal representing the accelerator opening, a signal representing the vehicle speed, a signal representing the output current and output terminal voltage of the fuel cell 110) supplied from the sensor group 170, and the load. The required power of 130 (that is, the required power of the entire system) is obtained.

  The required power of the load 130 is, for example, the total value of the vehicle running power and the auxiliary machine power. Auxiliary power is the power consumed by in-vehicle accessories (humidifiers, air compressors, hydrogen pumps, cooling water circulation pumps, etc.), and equipment required for vehicle travel (transmissions, wheel control devices, steering devices, and suspensions) Power consumed by devices, etc., and power consumed by devices (air conditioners, lighting fixtures, audio, etc.) disposed in the passenger space.

Then, the controller (converter control device) 160 determines the distribution of output power between the fuel cell 110 and the battery 120 and calculates a power generation command value. When the controller 160 obtains the required power for the fuel cell 110 and the battery 120, the controller 160 controls the operations of the FC converter 2500 and the battery converter 180 so that the required power is obtained.

  The FC cooling mechanism 210 is a mechanism that cools the fuel cell 110 by circulating a cooling medium (for example, cooling water) through the cooling flow path, and includes a cooling pump, a radiator, a switching valve, and the like. The FC cooling mechanism 210 is provided with a temperature sensor 231 that detects the temperature of the cooling medium (reflecting the FC temperature).

  The EV cooling mechanism 220 is a mechanism that cools devices (hereinafter, EV devices) such as the FC converter 2500 and the battery converter 180 by circulating a cooling medium (for example, cooling water) in the cooling flow path, and includes a cooling pump, a radiator, It is configured with a switching valve. Similarly to the FC cooling mechanism 210, the EV cooling mechanism 220 is also provided with a temperature sensor 232 that detects the temperature of the cooling medium (reflecting the temperature of the elements constituting the EV device).

A-2. Configuration of FC Converter As shown in FIG. 1, the FC converter 2500 has a circuit configuration as a three-phase resonant converter composed of a U phase, a V phase, and a W phase. The circuit configuration of the three-phase resonant converter combines an inverter-like circuit part that once converts an input DC voltage into AC, and a part that rectifies the AC again to convert it to a different DC voltage. In the present embodiment, a multi-phase soft switching converter (hereinafter referred to as a multi-phase FC soft switching converter) provided with a freewheel circuit (details will be described later) is employed as the FC converter 2500.

A-2-1. 2 is a diagram showing a circuit configuration of a multi-phase FC soft switching converter 2500 mounted on the FCHV system 100, and FIG. 3 is a diagram of the multi-phase FC soft switching converter 2500. It is a figure which shows the circuit structure for 1 phase.

  In the following description, the U-phase, V-phase, and W-phase FC soft switching converters constituting the multi-phase FC soft switching converter 2500 are referred to as FC soft switching converters 250a, 25b, and 250c, respectively, and need not be particularly distinguished. In some cases, it is simply called FC soft switching converter 250. Further, the voltage before boosting input to the FC soft switching converter 250 is called a converter input voltage Vin, and the voltage after boosting output from the FC soft switching converter 250 is called a converter output voltage Vout.

As shown in FIG. 3, each FC soft switching converter 250 includes a main boosting circuit 22a for performing a boosting operation, an auxiliary circuit 22b for performing a soft switching operation, and a freewheel circuit 22c. .
The main booster circuit 22a switches the energy stored in the coil L1 to the load 130 via the diode D5 by the switching operation of the switching circuit including the first switching element S1 made of IGBT (Insulated Gate Bipolar Transistor) and the diode D4. The output voltage of the fuel cell 110 is boosted by releasing.

  More specifically, one end of the coil L1 is connected to the high potential side terminal of the fuel cell 110, one pole of the first switching element S1 is connected to the other end of the coil L1, and the other end of the first switching element S1. Is connected to the low potential side terminal of the fuel cell 110. The cathode terminal of the diode D5 is connected to the other end of the coil L1, and the capacitor C3 functioning as a smoothing capacitor is connected between the anode terminal of the diode D5 and the other end of the first switching element S1. . The main booster circuit 22a is provided with a smoothing capacitor C1 on the fuel cell 110 side, which makes it possible to reduce the ripple of the output current of the fuel cell 110. A voltage sensor Sv1 that detects the voltage across the first switching element S1 is provided.

  Here, the voltage VH applied to the capacitor C3 becomes the converter output voltage Vout of the FC soft switching converter 150, and the voltage VL applied to the smoothing capacitor C1 is the output voltage of the fuel cell 110 and the converter input voltage of the FC soft switching converter 150. Vin.

  The auxiliary circuit 22b includes a first series connection body including a clamp diode D3 connected in parallel to the first switching element S1 and a snubber capacitor C2 connected in series to the clamp diode D3. In the first series connection body, the cathode terminal of the clamp diode D3 is connected to the other end of the coil L1, and the anode terminal of the clamp diode D3 is connected to one end of the snubber capacitor C2. Further, the other end of the snubber capacitor C2 is connected to a terminal on the low potential side of the fuel cell 110. A voltage sensor Sv2 that detects the voltage across the snubber capacitor C2 is provided.

Further, the auxiliary circuit 22b includes a diode D2, a second switching element S2, a diode D1, and a second series connection body configured by an auxiliary coil L2 common to each phase.
In the second series connection body, the anode terminal of the diode D2 is connected to the connection portion between the diode D3 of the first series connection body and the snubber capacitor C2. Furthermore, the cathode terminal of the diode D2 is connected to the pole at one end of the second switching element (auxiliary switch) S2. Moreover, the pole of the other end of the second switching element S2 is connected to a connection site between the auxiliary coil L2 and the freewheel circuit 22c. The anode terminal of the freewheel diode D6 is connected to the low potential side of the fuel cell 110, while the cathode terminal of the freewheel diode D6 is connected to the auxiliary coil L2. This free wheel circuit 22c includes a common free wheel diode D6 for each phase, and even if the second switching element S2 has an open failure while the auxiliary coil L2 is energized, the second switching element S2 is provided. This is a circuit for realizing a fail-safe function provided in order to prevent the occurrence of a surge voltage that would break down. Note that the present invention can also be applied to a configuration that does not include the freewheel circuit 22c.

  In the FC soft switching converter 250 configured as described above, the controller 160 adjusts the switching duty ratio of the first switching element S1 of each phase, whereby the boost ratio by the FC soft switching converter 250, that is, the converter input voltage Vin is adjusted. The ratio of the converter output voltage Vout is controlled. Also, soft switching is realized by interposing the switching operation of the second switching element S2 of the auxiliary circuit 12b in the switching operation of the first switching element S1.

On the other hand, in the FC soft switching converter 250, if the auxiliary circuit 12b is not functioned (that is, the second switching element S2 of the auxiliary circuit 12b is always turned off), hard switching is realized. As is well known, since hard switching has a larger switching loss than soft switching, hard switching is not usually performed.
However, as explained in the section of the problem to be solved by the invention, when the element temperature is low, such as at a low temperature start, the breakdown voltage becomes low. Therefore, the FC soft switching converter 250 is used with the operation performance lowered. There is a problem of having to.

  Therefore, in the present embodiment, as the low-temperature countermeasure control, the control of the FC soft switching converter 250 is switched from the soft switching control to the hard switching control, thereby increasing the switching loss and thereby rapidly increasing the element temperature. It is possible to make full use of the operation performance of the soft switching converter.

  Here, the outline of the switching control of the FC soft switching converter 250 will be described. When performing hard switching control, the second switching element S2 of the auxiliary circuit 12b is always turned off, while when performing soft switching control. The soft switching process shown below is executed, thereby enabling switching between hard switching and soft switching.

  Next, the soft switching operation by the FC soft switching converter 250 will be described with reference to FIG. FIG. 4 is a flowchart showing one cycle of processing (hereinafter referred to as soft switching processing) of the FC soft switching converter 25 through the soft switching operation. The controller 160 sequentially executes steps S101 to S106 shown in FIG. Form one cycle. In the following description, modes representing the current and voltage states of the FC soft switching converter 25 are expressed as modes 1 to 6, respectively, and the states are shown in FIGS. 5 to 10, the current flowing through the circuit is indicated by an arrow.

<Soft switching operation>
First, the initial state in which the soft switching process shown in FIG. 4 is performed is a state where power required for the load 130 is supplied from the fuel cell 110, that is, both the first switching element S1 and the second switching element S2 are turned off. Thus, a current is supplied to the load 130 via the coil L1 and the diode D5.

(Mode 1; see FIG. 5)
In step S101, the first switching element S1 is kept turned off while the second switching element S2 is turned on. When such a switching operation is performed, the current flowing to the load 130 side through the coil L1, the diode D3, the second switching element S2, and the auxiliary coil L2 due to the potential difference between the output voltage VH of the FC soft switching converter 150 and the input voltage VL. Then, it gradually shifts to the auxiliary circuit 12b side. In FIG. 5, the state of current transfer from the load 130 side to the auxiliary circuit 12b side is indicated by a white arrow.

Further, when the second switching element S2 is turned on, current circulation occurs in the direction of the arrow Dm11 shown in FIG. Here, the current change rate of the second switching element S2 increases according to the voltage across the auxiliary coil L2 (VH−VL) and the inductance of the auxiliary coil L2, but the current flowing through the second switching element S2 is the auxiliary coil L2. As a result, soft turn-off of the current (see arrow Dm12 shown in FIG. 5) flowing to the load 130 side via the diode D5 is realized.
Here, the transition completion time tmode1 from mode 1 to mode 2 is represented by the following equation (4).
Ip; phase current L2id; inductance of auxiliary coil L2

(Mode 2; see FIG. 6)
When the transition completion time has elapsed and the process proceeds to step S102, the current flowing through the diode D5 becomes zero, and the current flows into the auxiliary circuit 12b via the coil L1 and the diode D5 (see arrow Dm21 shown in FIG. 6). Instead, due to the potential difference between the snubber capacitor C2 and the voltage VL of the fuel cell 110, the charge charged in the snubber capacitor C2 flows toward the auxiliary circuit 12b (see arrow Dm22 shown in FIG. 6). The voltage applied to the first switching element S1 is determined according to the capacitance of the snubber capacitor C2.

Here, FIG. 12 is a diagram showing the voltage / current behavior in the transition process from mode 2 to mode 3, wherein the voltage of the fuel cell 110 is a thick solid line, the voltage of the snubber capacitor C2 is a thin solid line, and the current of the snubber capacitor C2 is shown. It is indicated by a broken line.
After energization of the path Dm21 shown in FIG. 6 is started (see (A) in FIG. 12), the path Dm22 shown in FIG. 6 is caused by the potential difference between the voltage VH of the snubber capacitor C2 and the voltage VL of the fuel cell 110. Energization, that is, energization of the auxiliary coil L2 is started (see (B) shown in FIG. 12). Here, as shown in FIG. 12, the current of the snubber capacitor C <b> 2 continues to rise until the voltage of the snubber capacitor C <b> 2 reaches the voltage VL of the battery 110.

More specifically, although the electric charge accumulated in the snubber capacitor C2 begins to be regenerated on the power source side due to the potential difference between the voltage VH of the snubber capacitor C2 and the voltage VL of the fuel cell 110 (arrow Dm22 shown in FIG. 6), the original potential difference is ( VH−VL), the flow of electric charge (discharge) accumulated in the snubber capacitor C2 stops when it reaches the power supply voltage (that is, the voltage VL of the fuel cell 110) (timing Tt1 shown in FIG. 12). Due to the characteristic of the auxiliary coil L2 (that is, the characteristic that the current is to continue to flow), the charge continues to flow even if the voltage of the snubber capacitor C2 becomes VL or less (see (C) in FIG. 12). At this time, if the following expression (4) ′ is satisfied, all the charges of the snubber capacitor C2 flow (discharge).
Left side; right side of energy stored in auxiliary coil L2; energy remaining in snubber capacitor C2

  When the electric charge accumulated in the snubber capacitor C2 is exhausted, a free wheel operation is performed along the path Dm23 shown in FIG. 6 and energization is continued (see (D) shown in FIG. 12). Thereby, all the energy accumulated in the auxiliary coil L2 is released. Since the anode of the diode D2 is connected to one end of the auxiliary coil L2, the LC resonance stops at a half wave. For this reason, the snubber capacitor C2 holds 0 V after discharging.

Here, the transition completion time tmode2 from mode 2 to mode 3 is expressed by the following equation (5).
C2d: capacitance of capacitor C2

(Mode 3; see FIG. 7)
When the operation of flowing a current through the path Dm22 shown in FIG. 6 is completed and the electric charge of the snubber capacitor C2 is completely discharged or reaches the minimum voltage (MIN voltage), the first switching element S1 is turned on, and the process proceeds to step S103. In a state where the voltage of the snubber capacitor C2 becomes zero, the voltage applied to the first switching element S1 is also zero, so that ZVS (Zero Voltage Switching) is realized. In such a state, the current Il1 flowing in the coil L1 is the sum of the current Idm31 flowing on the auxiliary circuit 12b side indicated by the arrow Dm31 and the current Idm32 flowing through the first switching element S1 indicated by the arrow Dm32 (the following equation (6) reference).

Here, the current Idm31 flowing through the first switching element S1 is determined according to the decreasing rate of the current Idm31 flowing through the auxiliary circuit 12b. The current change rate of the current Idm31 flowing to the auxiliary circuit 12b side is expressed by the following equation (7). That is, the current Idm31 flowing to the auxiliary circuit 12b side decreases at the change rate of the following equation (7), so the first switching Even if the element S1 is turned on, the current flowing through the first switching element S1 does not suddenly rise, and ZCS (Zero Current Switching) is realized.

(Mode 4; see FIG. 8)
In step S104, the state of step S103 continues, increasing the amount of current flowing into the coil L1 and gradually increasing the energy stored in the coil L1 (see arrow Dm42 in FIG. 8). Here, since the auxiliary circuit 12b includes the diode D2, no reverse current flows through the auxiliary coil L2, and the snubber capacitor C2 is not charged via the second switching element S2. At this time, since the first switching element S1 is turned on, the snubber capacitor C2 is not charged via the diode D3. Therefore, the current of the coil L1 is equal to the current of the first switching element S1, and the energy stored in the coil L1 is gradually increased. Here, the turn-on time Ts1 of the first switching element S1 is approximately represented by the following formula (8).
Tcon; control period The control period means a time period of the soft switching process when a series of processes from step S101 to step S106 is defined as one period (one cycle).

(Mode 5; see FIG. 9)
When desired energy is stored in the coil L1 in step S104, the first switching element S12 is turned off, and a current flows through a path indicated by an arrow Dm51 in FIG. Here, FIG. 11 is a diagram illustrating the relationship among the voltage Vc of the snubber capacitor C2, the voltage Ve applied to the first switching element S1, and the current Ie flowing through the first switching element S1 in mode 5. When the above switching operation is performed, the charge is removed from the snubber capacitor C2, which is in a low voltage state in mode 2, so that the voltage Vc of the snubber capacitor C2 becomes the converter output voltage of the FC soft switching converter 150. Rise toward VH. At this time, the rising speed of the voltage Ve applied to the first switching element S1 is suppressed by charging the snubber capacitor C2 (that is, the rise of the voltage is slowed down), and switching loss at the time of turn-off (see α shown in FIG. 11). It is possible to perform a ZVS operation for reducing the above.

(Mode 6; see FIG. 10)
When the snubber capacitor C2 is charged to the voltage VH, the energy stored in the coil L1 is released to the load 130 side (see arrow Dm61 shown in FIG. 10). Here, the turn-off time Ts2 of the first switching element S1 is approximately represented by the following formula (9).

  By performing the soft switching process described above, the switching loss of the FC soft switching converter 150 can be suppressed as much as possible, and the output voltage of the fuel cell 110 can be increased to a desired voltage and supplied to the load 130. It becomes.

A-2-2. Switching Operation of Switching Control FIG. 13 is a flowchart showing a switching switching control process executed by the controller 160.
The controller 160 detects the temperature (element related temperature; hereinafter, EV element temperature) Tev of the elements constituting the EV cooling mechanism 220 based on the sensing signal sent from the temperature sensor 232 installed in the EV cooling mechanism 220 ( Step S1).

  Controller 160 compares EV element temperature Tev with switching threshold temperature Tth1 stored in a memory (not shown), and determines whether EV element temperature Tev is lower than switching threshold temperature Tth1 (step S2). Here, the switching threshold temperature Tth1 is a threshold temperature (for example, −2 ° C. or the like) for determining switching between the hard switching control and the soft switching control for the FC soft switching converter 250, and can be obtained in advance by experiments or the like. . The switching threshold temperature Tth1 may be a fixed value, but may be configured so that it can be set and changed as appropriate during maintenance work.

  When the controller (switching switching control means, switching control means) 160 determines that the EV element temperature Tev is lower than the switching threshold temperature Tth1 (step S2; YES), the second switching element S2 of the auxiliary circuit 12b is always turned off. Hard switch control is started (step S3), and the process is terminated.

  On the other hand, when the controller (switching switching control means, switching control means) 160 determines that the EV element temperature Tev is equal to or higher than the switching threshold temperature Tth1 (step S2; NO), the switching described with reference to FIGS. By performing the process, soft switching control is started (step S4), and the process is terminated.

<The problem of abnormal overheating of the element due to hard switching control>
As described above, by switching the control of the FC soft switching converter 250 from the soft switching control to the hard switching control, it is possible to increase the switching loss and thereby quickly increase the element temperature (that is, rapidly increase the temperature). It becomes.
However, from another viewpoint, when switching loss is increased, each element constituting the FC soft switching converter 250 (hereinafter collectively referred to as “IMP element”) is overheated, and there is no limitation. Otherwise, there is a risk that the element will be destroyed due to abnormal overheating of the IPM element.

Therefore, in the present embodiment, when a certain condition is satisfied, the operating point of the fuel cell 110 is changed so that the element temperature of the IPM element falls below the heat resistant temperature (load factor restriction start temperature) Tls. Implement control.
Here, the case of satisfying a certain condition means that the fuel cell 110 is rapidly warming up due to low-efficiency power generation, and the control for changing the operation point of the fuel cell 110 is the FC current on the equal power line. This is control (element destruction prevention control) that reduces the loss generated in the IMP element by reducing the current (passing current) flowing through the FC soft switching converter 250 while satisfying the required power by lowering the FC voltage and increasing the FC voltage. .

The details of the element destruction prevention control will be described below with reference to FIG. FIG. 14 is a flowchart showing an element destruction prevention control process executed by the controller 160 in the hard switching control.
The controller 160 detects the EV element temperature Tev based on a sensing signal sent from the temperature sensor 232 installed in the EV cooling mechanism 220, and the element temperature Tev is stored in a memory (not shown). It is determined whether or not Tth2 has been exceeded (step S10).

  Here, the element destruction prevention threshold temperature Tth2 is a threshold temperature (for example, 105 ° C. or the like) for determining whether or not element destruction prevention control is necessary, and can be obtained in advance through experiments or the like. The element destruction prevention threshold temperature Tth2 is set lower than the load factor restriction start temperature Tls (for example, 120 ° C.) (Tth2 <Tls). The element destruction prevention threshold temperature Tth2 may be a fixed value, but may be configured so that it can be set and changed as appropriate during maintenance work.

  When the controller 160 determines that the EV element temperature Tev does not exceed the element destruction prevention threshold temperature Tth2 (step S20; NO), the controller 160 ends the process without executing the following steps.

  On the other hand, when the controller (determination means) 160 determines that the EV element temperature Tev exceeds the element destruction prevention threshold temperature Tth2 (step S20; YES), it determines whether or not the fuel cell 110 is performing low-efficiency power generation. (Step S30). If it is determined that the fuel cell 110 is not operating at a low efficiency (step S30; NO), the process is terminated without executing the following steps. Here, the low-efficiency power generation of the fuel cell 110 means that the reaction gas (for example, the oxidizing gas supplied to the cathode) supplied to the fuel cell 110 is less than that during normal power generation and compared to normal power generation. This refers to power generation with large power loss (details will be described later).

  Whether or not the low-efficiency power generation is being performed is determined by, for example, the FC temperature detected by the temperature sensor 231 being lower than a threshold temperature (for example, 0 ° C.) and the stoichiometric ratio of the oxidizing gas supplied to the fuel cell 110. Is below a threshold value (for example, about 1.2), it is determined that the power generation is low efficiency. Of course, the determination method of whether or not the low-efficiency power generation is being performed is not limited to this. For example, it may be determined whether or not the low-efficiency power generation is being performed based on the values of the FC voltage and the FC current. Hereinafter, the difference between low-efficiency power generation and normal power generation will be described in detail.

<Difference between low-efficiency power generation and normal power generation>
FIG. 15 is a diagram showing the relationship between the output current (FC current) and the output voltage (FC voltage) of the fuel cell, in which the case of normal power generation is shown by a solid line, and the case of low efficiency power generation is shown by a dotted line . The horizontal axis represents the FC current, and the vertical axis represents the FC voltage.

  Here, when performing low-efficiency power generation, for example, while operating the fuel cell 110 in a state where the air stoichiometric ratio is reduced to around 1.0 (theoretical value) (see the dotted line portion in FIG. 15), normal power generation is performed. For example, the fuel cell 40 is operated in a state where the air stoichiometric ratio is set to 2.0 or more (theoretical value) (see the solid line portion in FIG. 15). By performing low-efficiency power generation, the power loss is larger than that of normal power generation, so that rapid warm-up is possible.

  Here, FIG. 16 is a diagram showing the relationship between the output current (FC current), output voltage (FC voltage), and output power (FC power) of the fuel cell 110 during low-efficiency power generation, and the left horizontal axis represents the FC current. The right horizontal axis represents FC power, and the axis represents FC voltage.

In the present embodiment, if it is determined that it is necessary to prevent element destruction due to abnormal overheating of the EV element during low-efficiency power generation, the FC current is reduced on the equal power line l so that the FC voltage is increased. Move (change) the operating point. As a result, while satisfying the required power, the current passing through the FC soft switch converter 250 can be reduced to reduce the power loss, and finally the IMP element can be prevented from being destroyed.
Before changing operating point After changing operating point (I1, V1) → (I2, V2)
(I1> I2, V1 <V2)

  Specifically, when the controller (operating point control means) 160 determines in step S30 shown in FIG. 14 that the fuel cell 110 is generating low efficiency (step S30; YES), the FC current is calculated on the equal power line. The operation point of the fuel cell 110 is moved (changed) so as to decrease the fixed amount ΔI (= I2−I1) and increase the FC voltage, and the process is terminated. As a result, while satisfying the required power, the current passing through the FC soft switch converter 250 can be reduced to reduce the power loss, and finally the IMP element can be prevented from being destroyed. Here, the reduction amount ΔI (= I2−I1) of the FC current is obtained in advance by an experiment or the like to obtain the reduction amount of the power loss necessary for preventing the element destruction, so that the reduction of the obtained power loss can be obtained. Should be set. Of course, the FC current decrease amount ΔI may be a fixed value, but may be configured so as to be appropriately set / changed during maintenance work.

B. In the present embodiment described above, as the second series connection body included in the auxiliary circuit 22b, the anode terminal of the diode D2 is connected to the connection portion between the diode D3 and the snubber capacitor C2 of the first series connection body, and the diode D2 The cathode terminal is connected to the pole of one end of the second switching element (auxiliary switch) S2 (see FIG. 3). Regarding the circuit topology of this second series connection body, the coil L2, the diode D2, A mode in which the series order of the switching circuits by the second switching element S2 or the like is appropriately changed can also be adopted. Specifically, as shown in FIG. 16, the order of the switching circuit including the coil L2 and the second switching element S2 may be changed while the free wheel circuit 22c is excluded.

DESCRIPTION OF SYMBOLS 100 ... FCHV system, 110 ... Fuel cell, 120 ... Battery, 130 ... Load, 140 ... Inverter, 2500 ... FC converter, 160 ... Controller, 170 ... Sensor group, 180 ... Battery converter, 210 ... FC cooling mechanism, 220 ... EV Cooling mechanism, 231, 232 ... temperature sensor, 250 ... FC soft switching converter, 22a ... main booster circuit, 22b ... auxiliary circuit, 22c ... freewheel circuit, S1, S2 ... switching element, C1, C3 ... smoothing capacitor, C2 ... Snubber capacitors, L1, L2, ... coils, D1, D2, D3, D4, D5 ... diodes, D6 ... freewheeling diodes.

Claims (5)

A control device for a soft switching converter having a main booster circuit and an auxiliary circuit for controlling the output of a fuel cell,
A temperature sensor for detecting a related temperature of an element constituting the soft switching converter;
Switching switching means for switching between hard switching using the main boosting circuit and soft switching using the main boosting circuit and the auxiliary circuit, and switching to the hard switching when the related temperature is equal to or lower than a set threshold. When,
A control device for a soft switching converter, comprising switching control means for performing switching control of the hard switching and the soft switching. In the state where the switching control of the hard switching is performed for the soft switch converter, the reaction gas supplied to the fuel cell is less than that during normal power generation, and the power loss is larger than that in the normal power generation. A determination means for determining whether low-efficiency power generation is being performed;
When a positive determination result is obtained by the determination means, the operation of the fuel cell is performed so as to reduce the output current of the fuel cell by a predetermined amount while keeping the output power of the fuel cell constant. The control device for a soft switching converter according to claim 1, further comprising operating point control means for controlling the point.   3. The soft switching converter according to claim 2, wherein the determination unit determines whether low-efficiency power generation is performed for the fuel cell and an element temperature of an element constituting the soft switch converter is equal to or higher than a specified temperature. Control device. The main booster circuit
A main coil having one end connected to a terminal on the high potential side of the fuel cell;
A first diode having a cathode connected to the other end of the main coil;
A main switch having one end connected to the other end of the main coil and the other end connected to a terminal on the low potential side of the fuel cell;
A smoothing capacitor connected to the anode of the first diode and a terminal on the low potential side of the fuel cell;
The auxiliary circuit is
An auxiliary switch connected in parallel to the main switch constituting the main booster circuit;
A first series connection body connected in parallel to the main switch and connected to a high potential side terminal and a low potential side terminal of the fuel cell, in which a clamp diode and a snubber capacitor are connected in series; The control apparatus of the soft switching converter of Claims 1-3. The auxiliary circuit is
And further comprising a second series connection body connected between a connection portion of the clamp diode and the snubber capacitor and one end of the main coil, wherein the diode, the auxiliary coil, and the auxiliary switch are connected in series. Item 5. The soft switching converter control device according to Item 4.