JP2020195211A - Voltage converter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a voltage conversion device capable of effectively preventing a secondary functional failure of a voltage conversion unit. A voltage converter (DC-DC converter) 30 that controls a step-down of a voltage of a first battery 11 having a relatively high voltage with respect to a second battery 14 having a relatively low voltage is a secondary of a transformer 65. A rectifier circuit 66 having a first rectifier transistor 67 and a second rectifier transistor 68 connected to the side coil 65b, a fuse 71 capable of opening the rectifier circuit 66, and a current sensor 72 for detecting a short-circuit current flowing through the rectifier circuit 66. , An electronic control unit 28 and a gate drive unit 29. When the current sensor 72 detects a short-circuit current, the electronic control unit 28 and the gate drive unit 29 turn on one or both of the first rectifier transistor 67 and the second rectifier transistor 68 to cause the fuse 71 to open the rectifier circuit 66. [Selection diagram] Fig. 2

Description

The present invention relates to a voltage converter.

As this kind of technology, the vehicle-mounted DC-DC converter described in Patent Document 1 below is known. Such an in-vehicle DC-DC converter is configured by including two paired transistors in a circuit that rectifies the induced electromotive force of the secondary coil of the transformer.

Japanese Unexamined Patent Publication No. 2006-81263

By the way, in the DC-DC converter as described above, for example, when one transistor fails to open, both transistors are turned off to open the rectifier circuit. However, for example, when a transistor short-circuits, a short-circuit current flows in the transistor even if the short-circuited transistor is driven off, and this short-circuit current may cause a secondary malfunction of the DC-DC converter. ..

The voltage conversion device according to one aspect of the present invention is a voltage conversion device that controls a step-down of the voltage of a relatively high voltage primary power supply to a relatively low voltage secondary power supply. This voltage converter includes a rectifier circuit having a first rectifier transistor and a second rectifier transistor connected to the secondary coil of the transformer, a fuse capable of opening the rectifier circuit, and a first rectifier transistor or a second rectifier transistor. A voltage converter having a short circuit detection means for detecting a short circuit, and when the short circuit detection means detects a short circuit, one or both of the first rectifier transistor and the second rectifier transistor are turned on to cause the fuse to open the rectifier circuit. It includes a control unit.

According to the present invention, it is possible to provide a voltage conversion device capable of effectively preventing a secondary functional failure of the voltage conversion unit.

The circuit diagram which shows the main part structure of the vehicle which mounts the voltage conversion apparatus which concerns on embodiment of this invention. The circuit diagram which shows the main part structure of the DC-DC converter provided in the voltage conversion apparatus which concerns on this embodiment. The figure which shows an example of the flow of each current of a primary side and a secondary side when the transistor of a high side arm is on in the DC-DC converter which concerns on this embodiment. The figure which shows an example of the flow of each current of a primary side and a secondary side when the transistor of a low side arm is on in the DC-DC converter which concerns on this embodiment.

Hereinafter, an embodiment of the present invention will be described with reference to FIGS. 1 to 4. The voltage converter according to the embodiment of the present invention is connected to, for example, a power module that controls power transfer between the motor and the first battery (primary power supply), and is connected to a second battery (the voltage of the first battery). It is provided with a DC-DC converter (voltage conversion unit) that controls step-down to the secondary power supply).

The voltage converter and the power module are mounted on, for example, an electric vehicle. The electric vehicle is an electric vehicle, a hybrid vehicle, a fuel cell vehicle, or the like. An electric vehicle is a vehicle driven by a battery as a power source, a hybrid vehicle is a vehicle driven by a battery and an internal combustion engine as a power source, and a fuel cell vehicle is a vehicle driven by a fuel cell as a power source.

FIG. 1 is a circuit diagram showing a main configuration of a vehicle 10 equipped with a voltage conversion device 16 according to an embodiment of the present invention. As shown in FIG. 1, the vehicle 10 includes a first battery 11 having a relatively high voltage, a first motor 12 for driving a vehicle, a second motor 13 for power generation, and a second battery having a relatively low voltage. It includes a battery 14, auxiliary equipment 15, and a voltage conversion device 16.

The first battery 11 is, for example, a high-voltage battery that is a power source for the vehicle 10. The first battery 11 includes a battery case and a plurality of battery modules housed in the battery case. The battery module has a plurality of battery cells connected in series. The first battery 11 includes a positive electrode terminal PB and a negative electrode terminal NB connected to the first DC connector 16a of the voltage conversion device 16. The positive electrode terminal PB and the negative electrode terminal NB are connected to the positive electrode end and the negative electrode end of a plurality of battery modules connected in series in the battery case.

The first motor 12 generates a rotational driving force (power running operation) by the electric power supplied from the first battery 11. The second motor 13 is configured to generate generated electric power by the rotational driving force input to the rotating shaft, and for example, the rotational driving force of the internal combustion engine can be transmitted. The first and second motors 12 and 13 are, for example, three-phase alternating current (U-phase, V-phase, and W-phase) motors.

The first and second motors 12 and 13 include a rotor having a permanent magnet for a magnetic field and a stator having a three-phase stator winding for generating a rotating magnetic field that rotates the rotor. , So-called inner rotor type. The three-phase stator windings of the first motor 12 are connected to the first three-phase connector 16b of the voltage converter 16. The three-phase stator windings of the second motor 13 are connected to the second three-phase connector 16c of the voltage converter 16.

The second battery 14 is, for example, a low-voltage battery that drives auxiliary equipment such as an in-vehicle device of the vehicle 10. The second battery 14 is connected to the first battery 11 via a DC-DC converter 30 described later in the voltage converter 16. A voltage output from the DC-DC converter 30, that is, a voltage obtained by stepping down the output voltage of the first battery 11 is applied to the second battery 14.

Auxiliary equipment 15 is electrically connected to the second battery 14 via a cable and a fuse. The auxiliary equipment 15 is driven by the voltage output from the second battery 14, that is, the low operating voltage that operates the auxiliary equipment 15. Auxiliary equipment 15 is, for example, various electrical equipment.

The voltage converter 16 includes a power module 21, a reactor 22, a capacitor unit 23, a first current sensor 25, a second current sensor 26, a third current sensor 27, and an electronic control unit 28 (control unit). A gate drive unit 29 (control unit) and a DC-DC converter (power conversion unit) 30 are provided.

The power module 21 constitutes a first power conversion circuit unit 31, a second power conversion circuit unit 32, and a third power conversion circuit unit 33.

The first power conversion circuit unit 31 is connected to the three-phase stator winding of the first motor 12 by the first three-phase connector 16b. The first power conversion circuit unit 31 converts the DC power input from the first battery 11 via the third power conversion circuit unit 33 into three-phase AC power.

The second power conversion circuit unit 32 is connected to the three-phase stator winding of the second motor 13 by the second three-phase connector 16c. The second power conversion circuit unit 32 converts the three-phase AC power input from the second motor 13 into DC power. The DC power converted by the second power conversion circuit unit 32 can be supplied to at least one of the first battery 11 and the first power conversion circuit unit 31.

The first power conversion circuit unit 31 and the second power conversion circuit unit 32 include a bridge circuit formed by a plurality of switching elements connected by a bridge. For example, the switching element is a transistor such as an IGBT (Insulated Gate Bipolar Transistor) or a MOSFET (Metal Oxide Semi-conductor Field Effect Transistor).

For example, in each bridge circuit, a pair of high-side arm and low-side arm U-phase transistors UH and UL, a pair of high-side arm and low-side arm V-phase transistors VH and VL, and a pair of high-side arm and low-side The arm W-phase transistors WH and WL are bridge-connected.

Each bridge circuit includes a diode connected between the collector and the emitter of the above-mentioned transistors UH, UL, VH, VL, WH, and WL so as to be forward from the emitter to the collector.

In each transistor UH, VH, WH of the high side arm, a collector is connected to the positive electrode bus bar PI to form the high side arm. In each phase, each positive electrode bus bar PI of the high side arm is connected to the positive electrode bus bar 50p of the capacitor unit 23.

The emitters of each of the transistors UL, VL, and WL of the low side arm are connected to the negative electrode bus bar NI to form the low side arm. In each phase, each negative electrode bus bar NI of the low side arm is connected to the negative electrode bus bar 50n of the capacitor unit 23.

In each phase, the emitters of the high side arm transistors UH, VH, WH are connected to the collectors of the low side arm transistors UL, VL, WL at the connection point TI.

The first bus bar 51 forming the connection point TI in each phase of the first power conversion circuit unit 31 is connected to the first input / output terminal Q1. The first input / output terminal Q1 is connected to the first three-phase connector 16b. The connection point TI of each phase of the first power conversion circuit unit 31 is connected to the stator winding of each phase of the first motor 12 via the first bus bar 51, the first input / output terminal Q1 and the first three-phase connector 16b. It is connected.

The second bus bar 52 that forms the connection point TI in each phase of the second power conversion circuit unit 32 is connected to the second input / output terminal Q2. The second input / output terminal Q2 is connected to the second three-phase connector 16c. The connection point TI of each phase of the second power conversion circuit unit 32 is connected to the stator winding of each phase of the second motor 13 via the second bus bar 52, the second input / output terminal Q2, and the second three-phase connector 16c. It is connected.

The first power conversion circuit unit 31 and the second power conversion circuit unit 32 are each based on a gate signal which is a switching command input from the gate drive unit 29 to the gates of the transistors UH, VH, WH, UL, VL, and WL. Switches the phase transistor pair on (conducting) / off (disconnecting).

The first power conversion circuit unit 31 converts the DC power input from the first battery 11 via the third power conversion circuit unit 33 into three-phase AC power, and transfers the DC power to the three-phase stator winding of the first motor 12. The three-phase stator windings are energized with AC U-phase current, V-phase current, and W-phase current by sequentially commutating the energization of.

The second power conversion circuit unit 32 is driven by on (conducting) / off (disconnecting) the transistor pairs of each phase synchronized with the rotation of the second motor 13, and the three-phase stator winding of the second motor 13. The three-phase AC power output from is converted to DC power. The DC power converted from the three-phase AC power by the second power conversion circuit unit 32 can be supplied to the first battery 11 via the third power conversion circuit unit 33.

The third power conversion circuit unit 33 is a voltage control unit (VCU). The third power conversion circuit unit 33 includes a pair of high-side arm and low-side arm switching elements, and a reactor 22. For example, the third power conversion circuit unit 33 includes a first transistor S1 of the high side arm and a second transistor S2 of the low side arm. The third power conversion circuit unit 33 includes a diode connected between the collector and the emitter of the first transistor S1 and the second transistor S2 so as to be forward from the emitter toward the collector.

In the first transistor S1, a collector is connected to the positive electrode bus bar PV to form a high side arm. The positive electrode bus bar PV of the high side arm is connected to the positive electrode bus bar 50p of the capacitor unit 23.

In the second transistor S2, the emitter is connected to the negative electrode bus bar NV to form a low side arm. The negative electrode bus bar NV of the low side arm is connected to the negative electrode bus bar 50n of the capacitor unit 23. The negative electrode bus bar 50n of the capacitor unit 23 is connected to the negative electrode terminal NB of the first battery 11.

The emitter of the first transistor S1 of the high side arm is connected to the collector of the second transistor S2 of the low side arm. The connection point between the emitter of the first transistor S1 and the collector of the second transistor S2 is formed by the third bus bar 53. The third bus bar 53 is connected to the positive electrode terminal PB of the first battery 11 via the reactor 22.

Both ends of the reactor 22 are connected to a third bus bar 53 forming a connection point between the first transistor S1 and the second transistor S2, and a positive electrode terminal PB of the first battery 11. The reactor 22 includes a coil and a temperature sensor that detects the temperature of the coil. The temperature sensor is connected to the electronic control unit 28 by a signal line.

The third power conversion circuit unit 33 turns on (conducts) / turns off (cuts off) the transistor pair based on the gate signal which is a switching command input from the gate drive unit 29 to each gate of the first transistor S1 and the second transistor S2. ) Is switched.

The third power conversion circuit unit 33 has a first state in which the second transistor S2 is set to on (conduction) and the first transistor S1 is set to off (cutoff) at the time of boosting, and the second transistor S2 is turned off (cut off). And the second state in which the first transistor S1 is set to be on (conducting) are alternately switched.

In the first state, a current flows sequentially to the positive electrode terminal PB of the first battery 11, the reactor 22, the second transistor S2, and the negative electrode terminal NB of the first battery 11, and the reactor 22 is DC excited to accumulate magnetic energy. To.

In the second state, an electromotive voltage (induced voltage) is generated between both ends of the reactor 22 so as to prevent a change in magnetic flux due to the interruption of the current flowing through the reactor 22. The induced voltage due to the magnetic energy stored in the reactor 22 is superimposed on the battery voltage, and the boosted voltage higher than the voltage between the terminals of the first battery 11 is the positive bus bar PV and the negative bus bar NV of the third power conversion circuit unit 33. It is applied between.

The third power conversion circuit unit 33 alternately switches between the second state and the first state at the time of regeneration.

In the second state, a current flows sequentially to the positive electrode bus bar PV of the third power conversion circuit unit 33, the first transistor S1, the reactor 22, and the positive electrode terminal PB of the first battery 11, and the reactor 22 is DC excited to generate magnetic energy. Is accumulated.

In the first state, an electromotive voltage (induced voltage) is generated between both ends of the reactor 22 so as to prevent a change in magnetic flux due to the interruption of the current flowing through the reactor 22. The induced voltage due to the magnetic energy stored in the reactor 22 is stepped down, and the step-down voltage lower than the voltage between the positive electrode bus bar PV and the negative electrode bus bar NV of the third power conversion circuit unit 33 is lower than the voltage between the positive electrode terminal PB and the negative electrode of the first battery 11. It is applied between the terminal NB and the terminal NB.

The capacitor unit 23 includes a first smoothing capacitor 41 and a second smoothing capacitor 42.

The first smoothing capacitor 41 is connected between the positive electrode terminal PB and the negative electrode terminal NB of the first battery 11. The first smoothing capacitor 41 smoothes the voltage fluctuation generated by the on / off switching operation of the first transistor S1 and the second transistor S2 at the time of regeneration of the third power conversion circuit unit 33.

The second smoothing capacitor 42 is provided between the positive electrode bus bar PI and the negative electrode bus bar NI of the first power conversion circuit unit 31 and the second power conversion circuit unit 32, and the positive electrode bus bar PV and the negative electrode bus bar NV of the third power conversion circuit unit 33. It is connected in between.

Further, the second smoothing capacitor 42 is connected to a plurality of positive electrode bus bars PI and negative electrode bus bar NI, and positive electrode bus bar PV and negative electrode bus bar NV via a positive electrode bus bar 50p and a negative electrode bus bar 50n.

The second smoothing capacitor 42 is a voltage fluctuation generated by the on / off switching operation of the transistors UH, UL, VH, VL, WH, and WL of the first power conversion circuit unit 31 and the second power conversion circuit unit 32. To smooth.

Further, the second smoothing capacitor 42 smoothes the voltage fluctuation generated by the on / off switching operation of the first transistor S1 and the second transistor S2 when the third power conversion circuit unit 33 is boosted.

The first current sensor 25 forms a connection point TI for each phase of the first power conversion circuit unit 31 and is arranged on the first bus bar 51 connected to the first input / output terminal Q1, and is U-phase, V-phase, and W-phase. Detect each current of.

The second current sensor 26 forms a connection point TI for each phase of the second power conversion circuit unit 32 and is arranged on the second bus bar 52 connected to the second input / output terminal Q2, and is U-phase, V-phase, and W-phase. Detect each current of.

The third current sensor 27 is arranged on the third bus bar 53 which forms a connection point between the first transistor S1 and the second transistor S2 and is connected to the reactor 22, and detects the current flowing through the reactor 22.

The first current sensor 25, the second current sensor 26, and the third current sensor 27 are connected to the electronic control unit 28 by a signal line.

The electronic control unit 28 controls the operation of each of the first motor 12 and the second motor 13. For example, the electronic control unit 28 is a software functional unit that functions by executing a predetermined program by a processor such as a CPU (Central Processing Unit). The software function unit is an ECU (Electronic Control Unit) including a processor such as a CPU, a ROM (Read Only Memory) for storing a program, a RAM (Random Access Memory) for temporarily storing data, and an electronic circuit such as a timer. .. At least a part of the electronic control unit 28 may be an integrated circuit such as an LSI (Large Scale Integration).

For example, the electronic control unit 28 executes current feedback control using the current detection value of the first current sensor 25 and the current target value corresponding to the torque command value for the first motor 12, and inputs the current to the gate drive unit 29. Generate a control signal.

For example, the electronic control unit 28 executes current feedback control using the current detection value of the second current sensor 26 and the current target value corresponding to the regeneration command value for the second motor 13, and inputs the current to the gate drive unit 29. Generate a control signal.

The control signal is a signal indicating the timing for driving the transistors UH, VH, WH, UL, VL, and WL of the first power conversion circuit unit 31 and the second power conversion circuit unit 32 on (conducting) / off (disconnecting). is there. For example, the control signal is a pulse width modulated signal or the like.

The gate drive unit 29 actually performs each transistor UH, VH, WH, UL, VL, WL of each of the first power conversion circuit unit 31 and the second power conversion circuit unit 32 based on the control signal received from the electronic control unit 28. Generates a gate signal to drive on (conducting) / off (cutting off). For example, the gate drive unit 29 amplifies the control signal, shifts the level, and the like to generate the gate signal.

The gate drive unit 29 generates a gate signal for driving each of the first transistor S1 and the second transistor S2 of the third power conversion circuit unit 33 on (conducting) / off (disconnecting).

For example, the gate drive unit 29 generates a gate signal having a duty ratio according to a boost voltage command at the time of boosting of the third power conversion circuit unit 33 or a step-down voltage command at the time of regeneration of the third power conversion circuit unit 33. The duty ratio is, for example, the ratio of the on-time of each of the first transistor S1 and the second transistor S2.

The DC-DC converter 30 is controlled by an electronic control unit 28 and a gate drive unit 29. FIG. 2 is a circuit diagram showing a main configuration of a DC-DC converter 30 included in the voltage conversion device 16 according to the present embodiment.

As shown in FIG. 1, the DC-DC converter 30 is connected to the first DC connector 16a connected to the positive electrode terminal PB and the negative electrode terminal NB of the first battery 11 via the first positive electrode bus bar 60p1 and the first negative electrode bus bar 60n1. It is connected to the second DC connector 16d which is connected and connected to the positive electrode terminal and the negative electrode terminal of the second battery 14 via the second positive electrode bus bar 60p2 and the second negative electrode bus bar 60n2.

As shown in FIG. 2, the DC-DC converter 30 includes a first input capacitor 61, a second input capacitor 62, a bridge circuit 63, a current transformer 64, a transformer 65, a rectifier circuit 66, and an output capacitor 70. , A fuse 71 and a current sensor (short circuit detecting means) 72.

The first input capacitor 61 and the second input capacitor 62 are connected in series between the first positive electrode bus bar 60p1 and the first negative electrode bus bar 60n1. The connection points of the first input capacitor 61 and the second input capacitor 62 are connected to the current transformer 64.

The bridge circuit 63 is a so-called half-bridge circuit, and includes a pair of high-side arm and low-side arm switching elements. The switching element is, for example, a transistor such as a MOSFET. In the present embodiment, the bridge circuit 63 includes transistors QH and QL of the high side arm and the low side arm.

The drain of the transistor QH of the high side arm is connected to the first positive electrode bus bar 60p1. The source of the transistor QH of the high side arm is connected to the drain of the transistor QL of the low side arm. The source of the transistor QL of the low side arm is connected to the first negative electrode bus bar 60n1.

The connection point between the source of the transistor QH of the high side arm and the drain of the transistor QL of the low side arm in the bridge circuit 63 is connected to the first end of the primary coil 65a of the transformer 65. The bridge circuit 63 converts the DC power applied between the first positive electrode bus bar 60p1 and the first negative electrode bus bar 60n1 into AC power, and sequentially commutates the energization of the transformer 65 to the primary coil 65a. An alternating current is applied to the primary coil 65a.

The current transformer 64 is a current transformer for current detection. For example, the through-type current transformer 64 includes a hollow ring core, a primary conductor connected in series with a line through which the current to be measured flows and penetrating the ring core, and a secondary coil wound around the ring core. It includes a load resistor connected to the secondary coil. The primary conductor of the current transformer 64 is connected between the connection points of the first input capacitor 61 and the second input capacitor 62 and the second end of the primary coil 65a of the transformer 65. The current transformer 64 generates a voltage proportional to the input AC current flowing through the primary conductor in the load resistor.

The current transformer 64, for example, in connection with the overcurrent protection of the DC-DC converter 30, causes the drooping current on the secondary side (that is, the low voltage output side) to be on the primary side (that is, the high voltage input side). ) Is detected from the current. In the overcurrent protection of the DC-DC converter 30, the electronic control unit 28 has a current on the primary side (that is, a high voltage input side) converted by the current transformer 64, that is, a current on the primary side proportional to the output current. Based on the above, the overcurrent state (hanging point) of the output current is detected, and the switching of each transistor QH and QL is controlled so as to lower (hanging) the output voltage.

The transformer 65 includes a primary coil 65a and a secondary coil 65b.

The first end of the primary coil 65a is connected to the connection points of the transistors QH and QL of the high side arm and the low side arm of the bridge circuit 63. The second end of the primary coil 65a is connected to the connection points of the first input capacitor 61 and the second input capacitor 62 via the current transformer 64.

The secondary coil 65b is connected between the drain of the first rectifying transistor 67, which will be described later, and the drain of the second rectifying transistor 68, which will be described later. The intermediate tap of the secondary coil 65b is connected to the second positive electrode bus bar 60p2.

The transformer 65 generates an induced electromotive force in the secondary coil 65b by the AC power of the primary coil 65a, lowers the voltage applied to the primary coil 65a, and generates an induced voltage in the secondary coil 65b. Let me.

The rectifier circuit 66 includes a pair of a first rectifier transistor 67 and a second rectifier transistor 68, and rectifies the induced electromotive force of the secondary coil 65b of the transformer 65. In the present embodiment, the first rectifier transistor 67 and the second rectifier transistor 68 form a synchronous rectifier circuit using a MOSFET for synchronous rectification. That is, the rectifier circuit 66 of this embodiment is a synchronous rectifier circuit.

Further, in the MOSFET used for the first rectifying transistor 67 and the second rectifying transistor 68, in the present embodiment, internal parts such as a semiconductor and a material (for example, aluminum) constituting a current path are molded with a synthetic resin (for example, epoxy resin). It has a molded package structure.

The drains of the first rectifying transistor 67 and the second rectifying transistor 68 are connected to the second positive electrode bus bar 60p2 via the secondary coil 65b, and the source is connected to the second negative electrode bus bar 60n2.

The first rectifying transistor 67 and the second rectifying transistor 68 are switched by the electronic control unit 28 in synchronization with the switching of the transistors QH and QL of the primary side high side arm and the low side arm controlled by the electronic control unit 28. Be controlled.

For example, the electronic control unit 28 executes switching control of the first rectifying transistor 67 and the second rectifying transistor 68 in synchronization with the switching of the transistors QH and QL, and generates a control signal to be input to the gate drive unit 29.

The gate drive unit 29 generates a gate signal for actually driving the first rectifying transistor 67 and the second rectifying transistor 68 on (conducting) / off (cutting off) based on the control signal received from the electronic control unit 28.

A diode 69 is connected between the source and drain of the first rectifying transistor 67 and the second rectifying transistor 68, and the diode 69 is a so-called parasitic diode.

The output capacitor 70 is connected between the second positive electrode bus bar 60p2 and the second negative electrode bus bar 60n2. The output capacitor 70 smoothes the output voltage to the second battery 14.

A fuse 71 is connected in series with the second battery 14 between the connection point of the output capacitor 70 in the second positive electrode bus bar 60p2 and the second battery 14. The fuse 71 is provided so that the inside of the rectifier circuit 66 can be opened, and can cut off the current flowing in the rectifier circuit 66.

The fuse 71 is set so that the withstand capacity against current is lower than any component in the rectifier circuit 66 (for example, the first rectifier transistor 67 and the second rectifier transistor 68). For example, when a current exceeding the current (hereinafter, also referred to as “short-circuit current”) that flows when the first rectifier transistor 67 or the second rectifier transistor 68 is short-circuited due to a semiconductor failure, insulation failure, or the like flows through the fuse 71, it is built in. The alloy part to be blown is used.

For example, in the fuse 71, the cross-sectional area of the alloy part is set so that the alloy part is easily blown when a short-circuit current (for example, 1000 A) flows, and the alloy part is blown when a current equal to or larger than the short-circuit current flows. As described above, in the fuse 71 of the present embodiment, when a current equal to or larger than the short-circuit current flows, the time for the alloy component to blow is shortened as compared with the case where the short-circuit current simply flows.

The current sensor 72 is connected between the connection point of the output capacitor 70 in the second positive electrode bus bar 60p2 and the fuse 71. The current sensor 72 detects the current flowing in the rectifier circuit 66. For example, the current sensor 72 detects a short-circuit current flowing through the first rectifying transistor 67 or the second rectifying transistor 68.

The current sensor 72 is connected to the electronic control unit 28 by a signal line.

The electronic control unit 28 executes switching control of the first rectifying transistor 67 and the second rectifying transistor 68 based on the current detection value of the current sensor 72 in addition to the switching control synchronized with the switching of the transistors QH and QL described above. , Generates a control signal to be input to the gate drive unit 29.

The gate drive unit 29 includes a first gate drive unit 29a that generates a gate signal of the first rectifying transistor 67, and a second gate drive unit 29b that generates a gate signal of the second rectifying transistor 68. The first gate drive unit 29a and the second gate drive unit 29b actually generate gate signals for driving the first rectifier transistor 67 and the second rectifier transistor 68 on (conducting) / off (disconnecting), respectively.

For example, when the current sensor 72 detects a short-circuit current, the electronic control unit 28 executes switching control for on-driving at least one of the first rectifying transistor 67 and the second rectifying transistor 68 that has not failed. In the present embodiment, when the current sensor 72 detects a short-circuit current, the electronic control unit 28 executes switching control for turning on both the first rectifying transistor 67 and the second rectifying transistor 68.

Next, the operation of the DC-DC converter 30 controlled by the electronic control unit 28 and the gate drive unit 29 configured as described above will be described. FIG. 3 is a diagram showing an example of each current flow on the primary side and the secondary side when the transistor QH of the high side arm is on in the DC-DC converter 30 according to the present embodiment, and FIG. 4 is a diagram showing an example. It is a figure which shows an example of the flow of each current of the primary side and the secondary side when the transistor QL of a low side arm is on.

The DC-DC converter 30 turns on (conducts) / turns off (cuts off) each transistor QH, QL based on the gate signal input from the gate drive unit 29 to the gate of each transistor QH, QL of the high side arm and the low side arm. Switch.

Similarly, the DC-DC converter 30 rectifies the first and second gates from the first and second gate drive units 29a and 29b so as to synchronize with the on (conduction) / off (disconnection) switching of the transistors QH and QL. Based on the gate signal input to the gates of the transistors 67 and 68, the first and second rectifier transistors 67 and 68 are switched on (conducting) / off (disconnecting).

As shown in FIGS. 3 and 4, the DC-DC converter 30 has a first state in which the transistor QH of the high side arm is set to on (conduction) and the transistor QL of the low side arm is set to off (cutoff), and the transistor QH. Alternately switches between the second state, in which is set to off (block) and the transistor QL is set to on (conducting).

Then, the DC-DC converter 30 turns on the second rectifying transistor 68 (conducting) and turns off the first rectifying transistor 67 in the first state, and turns on the first rectifying transistor 67 in the second state. (Conduction) and the second rectifier transistor 68 are turned off (cut off).

In the first state, as shown in FIG. 3, the positive end of the first input capacitor 61, the transistor QH of the high side arm, the primary coil 65a of the transformer 65, and the current transformer 64 are sequentially arranged on the primary side. , A resonance current flows to the negative end of the first input capacitor 61. Then, on the secondary side, a current flows sequentially to the second rectifying transistor 68, the secondary coil 65b, the intermediate tap, and the fuse 71.

In the second state, as shown in FIG. 4, the positive end of the second input capacitor 62, the current transformer 64, the primary coil 65a of the transformer 65, and the transistor QL of the low side arm are sequentially arranged on the primary side. A resonance current flows to the negative end of the second input capacitor 62. Then, on the secondary side, a current flows sequentially to the first rectifying transistor 67, the secondary coil 65b, the intermediate tap, and the fuse 71.

By alternately switching between the first state and the second state set in this way, the battery voltage VB, which is the input voltage on the primary side, is stepped down, and the output voltage on the secondary side is applied to the second battery 14. be able to.

At this time, if either one of the first rectifying transistor 67 and the second rectifying transistor 68 is short-circuited due to a semiconductor failure, insulation failure, or the like, a short-circuit current flows through the short-circuited transistor. When the current sensor 72 detects the short-circuit current, the electronic control unit 28 executes on (conduction) control of the first rectifying transistor 67 and the second rectifying transistor 68, and generates an on control signal to be input to the gate drive unit 29.

In the gate drive unit 29, the first and second gate drive units 29a and 29b actually turn on (conduct) the first and second rectifier transistors 67 and 68 based on the on control signal received from the electronic control unit 28. A gate signal is generated to drive the first and second rectifying transistors 67 and 68 on (conducting).

When the first and second rectifying transistors 67 and 68 are driven on (conducting), a current also flows through the transistor that has not failed in the short circuit, and the current obtained by adding this current to the short circuit current, that is, the current equal to or greater than the short circuit current is the fuse. It flows to 71. As a result, the alloy component of the fuse 71 is blown, and the rectifier circuit 66 is opened.

According to this embodiment, the following effects can be obtained.
(1) A voltage conversion device 16 that controls step-down of the voltage of the relatively high voltage first battery 11 with respect to the relatively low voltage second battery 14. The voltage converter 16 includes a rectifier circuit 66 having a first rectifier transistor 67 and a second rectifier transistor 68 connected to the secondary side coil 65b of the transformer 65, a fuse 71 capable of opening the rectifier circuit 66, and a first rectifier. A DC-DC converter 30 having a short circuit detecting means for detecting a short circuit of the transistor 67 or the second rectifying transistor 68, and one of the first rectifying transistor 67 and the second rectifying transistor 68 or the second rectifying transistor 68 when the short circuit detecting means detects a short circuit. It includes an electronic control unit 28 and a gate drive unit 29 that drive both on and open the rectifier circuit 66 in the fuse 71.

With this configuration, for example, even when the first rectifying transistor 67 or the second rectifying transistor 68 is short-circuited, it is possible to effectively prevent the DC-DC converter 30 from having a secondary functional failure.

For example, when the first or second rectifying transistors 67 and 68 are short-circuited, a short-circuit current flows from the second battery 14 to the short-circuited first or second rectifying transistors 67 and 68. If a short-circuit current flows through the short-circuited first or second rectifying transistors 67 and 68, the current path in the first or second rectifying transistors 67 and 68 may generate abnormal heat.

When the current path generates abnormal heat, for example, when the first and second rectifying transistors 67 and 68 have a package structure, the synthetic resin that molds internal parts such as a semiconductor and the current path may be damaged by receiving heat. For example, if the current path is formed of aluminum and the synthetic resin is an epoxy resin, and the melting point of the aluminum is about 600 ° C. and the ignition point of the epoxy resin is about 530 degrees, the temperature of the current path rises until the ignition point of the synthetic resin is exceeded. There is a risk.

Due to such a temperature rise, the air or water contained in the synthetic resin and the package expands, and when the flame retardant is added to the synthetic resin, the flame retardant evaporates and the flame retardant also expands. As a result, the internal pressure of the molded package increases, and the package may burst. If the package ruptures, internal parts may scatter around the package, causing malfunction of the circuits and the like arranged around the package and functional failure such as poor insulation.

In the present embodiment, as described above, when the short circuit detecting means detects a short circuit, the first and second rectifying transistors 67 and 68 are driven on. Therefore, a current equal to or larger than the short-circuit current can flow through the fuse 71. In the fuse 71, the alloy parts are blown by a current equal to or larger than the short-circuit current, and the blow-off time is shortened in proportion to the magnitude of the current. Therefore, for example, the first and second rectifying transistors 67 and 68 are turned off to drive the short-circuit current. The blow time of the fuse 71 can be shortened as compared with the state in which only the current flows. As a result, bursting of the packages of the first and second rectifying transistors 67 and 68 can be suppressed. As a result, it is possible to prevent malfunction of the circuits and the like arranged around the first and second rectifying transistors 67 and 68 in the DC-DC converter 30 and functional failure such as poor insulation.

Further, for example, by increasing the cross-sectional area of the current paths of the first and second rectifying transistors 67 and 68, the withstand capacity of the current can be increased to suppress the temperature rise of the current path, and the damage to the package can be suppressed. Since the blowing time of the fuse 71 can be shortened by driving the first and second rectifying transistors 67 and 68 on, it is not necessary to increase the current withstand capacity of the first and second rectifying transistors 67 and 68. Therefore, it is possible to effectively prevent the DC-DC converter 30 from having a secondary functional failure without increasing the cost and size due to the increase in the withstand capacity of the current.

Further, for example, by providing two or more first and second rectifying transistors 67 and 68 in series, for example, when the first or second rectifying transistors 67 and 68 on the upstream side are short-circuited, the first or first rectifying transistor on the downstream side is short-circuited. 2 The rectifier circuit can be opened by driving the rectifier transistors 67 and 68 off. In the present embodiment, the fuse blowing time can be shortened by driving the first and second rectifying transistors 67 and 68 on, so that two or more first and second rectifying transistors 67 and 68 are connected in series. Without the provision, it is possible to effectively prevent the DC-DC converter 30 from having a secondary functional failure.

(2) One of the first rectifying transistor 67 and the second rectifying transistor 68, which are driven on when the short-circuit detecting means detects a short-circuit, is a transistor that has not failed. For example, the blow time of the fuse 71 can be shortened by driving on the first rectifying transistor 67 or the second rectifying transistor 68 that has not failed at least. As a result, even when the first rectifying transistor 67 or the second rectifying transistor 68 is short-circuited, it is possible to effectively prevent the DC-DC converter 30 from having a secondary functional failure.

(3) The first rectifying transistor 67 and the second rectifying transistor 68 are MOSFETs. Thereby, for example, even when a MOSFET is used for the first rectifying transistor 67 and the second rectifying transistor 68, the secondary functional failure of the DC-DC converter 30 due to a short-circuit failure of the MOSFET can be effectively prevented. Can be done.

(4) The short-circuit detecting means is a current sensor 72 that detects a short-circuit current flowing in the rectifier circuit 66. As a result, the short-circuit current can be easily detected with a simple configuration. As a result, it is possible to effectively prevent the secondary functional failure of the DC-DC converter 30 due to the failure of the first rectifying transistor 67 or the second rectifying transistor 68 without, for example, increasing the cost.

In the above embodiment, the rectifier circuit 66 has been described using a synchronous rectifier circuit using MOSFETs, but the present invention is not limited thereto. The rectifier circuit may be a circuit using a switching element such as a transistor.

In the above embodiment, the current sensor 72 has been described as the short circuit detecting means, but the present invention is not limited thereto. For example, the short circuit detecting means may be configured to use a voltage sensor that detects that the voltage has dropped due to the short circuit.

Further, in the above embodiment, the short circuit is detected by using the current sensor 72 that detects the current flowing through the rectifier circuit 66, but the present invention is not limited to this. For example, a current sensor may be arranged at a point where a current indirectly proportional to the short-circuit current flows, and a short-circuit may be detected by the current detected by the current sensor.

In the above embodiment, the voltage conversion device 16 including the DC-DC converter 30 mounted on the vehicle 10 has been described, but the present invention is not limited to this, and for example, the DC-DC converter mounted on another device is used. It can also be applied to a voltage converter equipped with a DC converter.

The above description is merely an example, and the present invention is not limited to the above-described embodiments as long as the features of the present invention are not impaired.

10 Vehicle, 11 1st battery, 12 1st motor, 13 2nd motor, 14 2nd battery, 16 Voltage converter, 28 Electronic control unit (control unit), 29 Gate drive unit (control unit), 30 DC-DC converter (Voltage converter), 65 transformer, 65b secondary coil, 66 rectifier circuit, 67 first rectifier transistor, 68 second rectifier transistor, 71 fuse, 72 current sensor (short circuit detection means)

Claims (4)

A voltage converter that controls step-down of the voltage of a relatively high voltage primary power supply to a relatively low voltage secondary power supply.
Detects a short circuit between a rectifier circuit having a first rectifier transistor and a second rectifier transistor connected to the secondary coil of the transformer, a fuse capable of opening the rectifier circuit, and the first rectifier transistor or the second rectifier transistor. A voltage converter having a short circuit detection means,
When the short-circuit detecting means detects a short-circuit, the fuse includes a control unit that turns on one or both of the first rectifier transistor and the second rectifier transistor to open the rectifier circuit to the fuse. Voltage converter. In the voltage conversion device according to claim 1,
A voltage conversion device, characterized in that one of the first rectifying transistor and the second rectifying transistor, which are driven on when the short-circuit detecting means detects a short-circuit, is a transistor that is not short-circuited. In the voltage converter according to claim 1 or 2.
A voltage conversion device characterized in that the first rectifying transistor and the second rectifying transistor are MOSFETs. In the voltage converter according to any one of claims 1 to 3,
A voltage conversion device, wherein the short-circuit detecting means is a current sensor that detects a short-circuit current flowing in the rectifier circuit.

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