JP4587117B2 - Voltage converter - Google Patents

Description

  The present invention relates to a voltage conversion device, and more particularly to a bidirectional DC / DC converter.

In recent years, electric vehicles have been put into practical use as environmentally friendly vehicles. The electric system of an electric vehicle includes, for example, a power storage device that stores DC power, a traction inverter that converts DC voltage into AC voltage, a traction motor that is driven by AC power supplied from the traction inverter, and during power running A bidirectional converter is provided that boosts the output voltage of the power storage device and supplies DC power to the traction inverter, while charging the power storage device by reducing the DC voltage regenerated by the traction inverter during regenerative braking (patent) Reference 1).
JP 2003-333835 A

  However, since an IPM (Intelligent Power Module) used as an inverter has a temperature sensor arranged so as to detect the temperature of the switching element that increases heat loss when the IPM is used as an inverter, the IPM is DC When used as a DC / DC converter, the current path flowing through the switching element group differs between power running by a traction motor (load) (when the power storage device is discharged) and regenerative braking (when the power storage device is charged). The temperature indicated by does not necessarily detect the temperature of the switching element at which the heat loss increases. Therefore, if the passing power limit applied to the switching element group is the same during power running and regenerative braking, it is not possible to apply an appropriate passing power limit, and the DC / DC converter performance is maximized. I can't. In addition, for example, a switching element that is at a high temperature cannot be sufficiently protected, and the DC / DC converter may fail.

  Therefore, an object of the present invention is to provide a voltage conversion device that can maximize its capability by applying an appropriate passing power limit to the switching element group.

In order to solve the above problems, in the voltage converter of the present invention, the primary input / output terminal is connected to the first DC power supply, and the secondary input / output terminal can regenerate power with the second DC power supply. A voltage converter connected in parallel to a power load, wherein when the first DC power supply is discharged, the output voltage of the first DC power supply is boosted and supplied to the power load, while the first DC power supply When charging, the switching element group that steps down the output voltage of the second DC power supply or the DC voltage regenerated by the power load to charge the first DC power supply, and switching between discharging and charging of the first DC power supply e Bei a control device for changing the upper limit value of the electric power passing through the element group, H-bridge formed from the switching element group, and a switching element disposed on the upper arm, the switching element disposed on the lower arm side Configure the circuit, and on the upper arm side Temperature detecting means for detecting the temperature of either the switching element provided or the switching element disposed on the lower arm side, and the control device performs another operation based on the temperature of the switching element detected by the temperature detecting means. The temperature of the switching element is estimated, and the upper limit value of the passing power of the switching element group is changed. By optimizing the upper limit value of the passing power of the switching element during discharging and charging of the first DC power supply, the capability of the voltage conversion device can be maximized. Further, with this configuration, it is possible to appropriately manage the temperature of the voltage conversion device without installing temperature sensors in all the switching elements.

The voltage converter of the present invention can be used as an inverter or a DC / DC converter.

  In addition, the control device is configured such that the restriction start temperature of the upper limit value of the passing power of the switching element group is higher when discharging than the charging of the first DC power supply, or the limit rate of the upper limit value of the passing power is higher. You may control so that it may become small. When the voltage conversion device of the present invention is mounted on a vehicle, drivability can be improved by suppressing a decrease in motor output due to battery assist being restricted.

  Further, the control device may change the limit starting temperature of the upper limit value of the passing power of the switching element group or the limit rate of the upper limit value of the passing power based on the temperature of the switching element detected by the temperature detecting means.

  According to the present invention, the capability of the voltage converter can be maximized. Moreover, failure of the voltage converter can be suppressed.

Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.
FIG. 1 shows a main configuration of an electric system of a fuel cell electric vehicle 10 of the present embodiment. The fuel cell electric vehicle 10 includes a secondary battery (first DC power source) 11, a DC / DC converter (voltage converter) 12, a fuel cell (second DC power source) 13, a traction inverter 14, a traction motor 15, and A control device 16 is provided. The traction motor 15 is a power load that can regenerate power. The secondary battery 11 functions as a regenerative energy storage source at the time of brake regeneration and an energy buffer at the time of load fluctuation accompanying acceleration or deceleration of the vehicle. As the secondary battery 11, a power storage device such as a nickel / cadmium storage battery, a nickel / hydrogen storage battery, or a lithium secondary battery is suitable. Instead of the secondary battery 11, a power storage device such as a capacitor may be connected to the primary side of the DC / DC converter 12.

  The fuel cell 13 is a power generation device having a stack structure in which a plurality of cells are connected in series. The fuel cell 13 is preferably a solid polymer electrolyte type fuel cell. The polymer electrolyte fuel cell has the advantages of being able to start at room temperature, so the start-up time is short, high current density is obtained at room temperature, low-load operation is possible, and the size and weight can be reduced. It has excellent characteristics as a battery. However, not only the solid polymer electrolyte fuel cell but also an alkaline electrolyte fuel cell, an acidic electrolyte fuel cell, a molten salt electrolyte fuel cell, a solid electrolyte fuel cell, a phosphoric acid fuel cell, and the like can be used.

  The DC / DC converter (bidirectional DC / DC converter) 12 is connected to the secondary battery 11 on the primary side, and is connected in parallel to the traction inverter 14 and the fuel cell 13 on the secondary side. When the fuel cell electric vehicle 10 is powered by the traction motor 15, the DC / DC converter 12 boosts the output voltage of the secondary battery 11 and supplies DC power to the traction inverter 14, while the fuel cell electric vehicle 10 When regenerative braking is performed by the traction motor 15, the regenerated DC voltage is stepped down to charge the secondary battery 11. The DC / DC converter 12 also has a function of reducing the output voltage of the fuel cell 13 and charging the secondary battery 11 in order to store surplus generated power of the fuel cell 13. Power conversion (switching control) in the DC / DC converter 12 is controlled by the control device 16. The traction inverter 14 converts DC power supplied from either one or both of the secondary battery 11 and the fuel cell 13 into AC power (for example, three-phase AC). The traction inverter 14 includes, for example, a three-phase bridge circuit composed of six power transistors, converts DC power into AC power by the switching action of the power transistors, and supplies the AC power to the traction motor 15. The power transistor is controlled by the control device 16. The traction inverter 14 adjusts the amplitude and frequency of the three-phase alternating current necessary for adjusting the output torque and the rotational speed of the traction motor 15 to desired values in response to a request instruction from the control device 16, and 15 is supplied. The traction motor 15 is an electric motor for obtaining a driving force for traveling the vehicle, and is constituted by, for example, a three-phase synchronous motor.

  Based on the vehicle speed, the accelerator opening (acceleration request), and the like, the control device 16 obtains the required power of the entire system (the sum of vehicle travel power and auxiliary power). Next, the distribution of the output power of the fuel cell 13 and the secondary battery 11 is determined, and the reactant gas supply amount to the fuel cell 13 is adjusted so that the power generation amount of the fuel cell 13 matches the target power. The operation point (output voltage, output current) of the fuel cell 13 is adjusted by controlling the DC converter 12. Furthermore, the control device 16 controls the traction inverter 14 so as to obtain the target vehicle speed according to the accelerator opening, and adjusts the rotational speed and rotational torque of the traction motor 15.

FIG. 2 shows a circuit configuration of the DC / DC converter 12. The DC / DC converter 12 includes an H bridge circuit including NPN transistors Tr1 and Tr3 disposed on the upper arm side and NPN transistors Tr2 and Tr4 disposed on the lower arm side. Between the emitters and collectors of the NPN transistors Tr1 to Tr4, diodes D1 to D4 that flow current from the emitter side to the collector side are connected. An inductance L is connected between a connection point between the NPN transistors Tr1 and Tr2 and a connection point between the NPN transistors Tr3 and Tr4. The DC / DC converter 12 is an IPM that can be used as an inverter. For convenience of explanation, only four NPN transistors Tr1 to Tr4 as switching elements are shown, but actually six are arranged. Temperature sensors S1 and S2 for detecting the temperatures of the NPN transistors Tr2 and Tr4 are arranged on the lower arm side of the H bridge circuit. Since the NPN transistors Tr2 and Tr4 are switching elements having the largest heat loss when using a voltage converter that can be used as an inverter or a DC / DC converter as an inverter, the temperature sensors S1 and S2 are arranged on the lower arm side Is installed. The detected temperatures of the temperature sensors S1, S2 are output to the control device 16. The control device 16 performs switching control of each switching element to control power conversion in the DC / DC converter 12, and estimates the temperatures of the NPN transistors Tr1 and Tr3 based on the detected temperatures of the temperature sensors S1 and S2. The passing power of each switching element is limited. When the detected temperatures of the temperature sensors S1 and S2 exceed a predetermined threshold temperature, the control device 16 performs self-protection of the DC / DC converter 12 so that the switching element is not damaged.

  The primary side input / output terminal of the DC / DC converter 12 is connected to the secondary battery 11. The DC voltage output from the secondary battery 11 is smoothed by the capacitor C 1 and supplied to the DC / DC converter 12. On the other hand, the input / output terminal on the secondary side of the DC / DC converter 12 is connected to the secondary side 17. The secondary side 17 is a general term for the fuel cell 13, the traction inverter 14, and the traction motor 15 described above. The DC voltage output from the secondary side 17 is smoothed by the capacitor C <b> 2 and supplied to the DC / DC converter 12.

  When the fuel cell electric vehicle 10 is powered by not only the fuel cell 13 but also the secondary battery 11, as shown by the one-dot chain line in the figure, it passes through the NPN transistors Tr 1 and Tr 4. Current flows. Since the voltage on the secondary side is higher than the voltage on the primary side, during power running, the heat loss of the NPN transistor Tr4 is larger than the heat loss of the NPN transistor Tr1, and the temperature of the NPN transistor Tr4 is higher than the switching element. The highest temperature is shown. Since the temperature of the NPN transistor Tr4 can be directly detected by the temperature sensor S2, the passing power of the switching element may be limited based on the detected temperature of the temperature sensor S2. However, if the switching power limit of the switching element is strictly enforced during power running (the start temperature of the pass power limit is set lower or the limit rate of the pass power limit is increased), the battery assist amount is limited. Motor output will be reduced, and drivability will be affected. Therefore, it is preferable that the passing power limitation of the switching element during power running is performed gently (the start temperature of the passing power limitation is set higher or the limiting rate of the passing power limitation is reduced). Here, the limiting rate of the passing power limit refers to the degree of reduction (or reduction) of the upper limit value of the passing power of the switching element.

On the other hand, when the fuel cell electric vehicle 10 is regeneratively braked, a current flows through the NPN transistors Tr3 and Tr2 as indicated by a two-dot chain line in the figure. Since the secondary side voltage is higher than the primary side voltage, the heat loss of the NPN transistor Tr3 is larger than the heat loss of the NPN transistor Tr2 during regenerative braking, and the temperature of the NPN transistor Tr3 is the switching element. The highest temperature is shown. However, although the temperature sensor S1 can detect the temperature of the NPN transistor Tr2, it cannot detect the temperature of the NPN transistor Tr3. The reason for this is that, as described above, the temperature sensors S1 and S2 are installed at the switching element temperature at which the element temperature becomes maximum when a voltage converter that can be used as an inverter or a DC / DC converter is used as an inverter. This is because it is selected so that it can be detected. Therefore, the control device 16 estimates the temperature of the NPN transistor Tr3 based on the temperature detected by the temperature sensor S1, and strictly restricts the passing power of the switching element. More specifically, in consideration of the fact that the temperature of the NPN transistor Tr3 is higher than the detected temperature indicated by the temperature sensor S1, the threshold temperature for performing the pass power limitation is set lower. The threshold temperature should be set to a level in which the correlation between the temperature of the NPN transistor Tr3 and the temperature of the NPN transistor Tr2 is measured in advance so that the NPN transistor Tr3 is not overheated.

  If the passing power of the switching element during regenerative braking is strictly limited, the amount of regenerative power that can be stored in the secondary battery 11 is reduced, but a deceleration force corresponding to the amount of depression of the hydraulic brake can be obtained. Does not affect the performance.

  According to the present embodiment, it is possible to optimize the passing power limit of the switching element during power running and regenerative braking, so that the capability of the DC / DC converter 12 can be maximized. Also, even if temperature sensors are not installed in all switching elements, the temperature of other switching elements is estimated from the temperature of some switching elements and the passing power is limited, so that appropriate temperature management becomes possible. . In addition, the effect on drivability can be reduced by gently performing the passing power limitation of the switching element during power running.

It is a principal lineblock diagram of the electric system of the fuel cell electric vehicle of this embodiment. It is a circuit diagram of the bidirectional DC / DC converter of this embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Fuel cell electric vehicle 11 ... Secondary battery 12 ... DC / DC converter 13 ... Fuel cell 14 ... Traction inverter 15 ... Traction motor 16 ... Controller 17 ... Secondary side Tr1-Tr4 ... Transistor D1-D4 ... Diode L ... Inductance S1-S2 ... Temperature sensor

Claims (3)

A primary side input / output terminal is connected to a first DC power source, and a secondary side input / output terminal is a voltage converter connected in parallel to a second DC power source and a power load capable of power regeneration,
When the first DC power supply is discharged, the output voltage of the first DC power supply is boosted and supplied to the power load, while when the first DC power supply is charged, the output of the second DC power supply is output. A switching element group that steps down a voltage or a DC voltage regenerated by the power load to charge the first DC power supply;
E Bei a control device for changing the upper limit of the passing electric power of the switching element group at the time of charging and during discharging of the first DC power supply,
The switching element group constitutes an H bridge circuit composed of a switching element arranged on the upper arm side and a switching element arranged on the lower arm side,
Temperature detection means for detecting the temperature of either the switching element disposed on the upper arm side or the switching element disposed on the lower arm side;
The said control apparatus is a voltage converter which estimates the temperature of another switching element based on the temperature of the said switching element which the said temperature detection means detected, and changes the upper limit of the passing electric power of the said switching element group . The voltage conversion device according to claim 1,
The control device is configured such that the restriction start temperature of the upper limit value of the passing power of the switching element group is higher during discharging than the charging time of the first DC power supply, or the upper limit value of the passing power is limited. Is a voltage conversion device that controls so as to be small. The voltage conversion device according to claim 1 or 2 ,
The control device changes a limit start temperature of the upper limit value of the passing power of the switching element group or a limit rate of the upper limit value of the passing power based on the temperature of the switching element detected by the temperature detecting unit. .

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