Discharge device and power conversion device

Abstract

To make it possible to suppress change in a discharge current due to temperature change in a discharge device and a power conversion device in which a current adjustment unit having a transistor adjusts magnitude of the discharge current of a discharge unit.SOLUTION: A discharge device 5 connected in parallel to a smoothing capacitor 4 and configured to discharge electric charges accumulated in the smoothing capacitor 4 as a discharge current includes: a discharge unit 5a through which the discharge current flows; and a discharge current adjustment unit 5b configured to adjust magnitude of the discharge current flowing through the discharge unit 5b. The discharge unit 5a and the discharge current adjustment unit 5b are connected in parallel to the smoothing capacitor 4. The discharge current adjustment unit 5b includes a second discharge current adjustment unit semiconductor switch 5b5 and a second zener diode 5b6 located on a lower potential side than the second discharge current adjustment unit semiconductor switch 5b5 and connected in series with the second discharge current adjustment unit semiconductor switch 5b5.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a discharge device and a power conversion device. [Background technology]

[0002] For example, Patent Document 1 discloses a discharge device that can be miniaturized. This discharge device is for discharging the charge of a smoothing capacitor provided in a drive device for a motor that rotates the wheels of a vehicle, and includes a discharge circuit component connected in parallel with the smoothing capacitor and a current adjustment circuit component that adjusts the current of the discharge circuit component, with the discharge circuit component and the current adjustment circuit component configured as a set, and multiple sets connected in series. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2018-160954 Summary of the Invention [Problem to be solved by the invention]

[0004] The discharge device of Patent Document 1 described above can be said to include a discharge section in which multiple discharge circuit components are connected in series, and a discharge current adjustment section in which multiple current adjustment circuit components are connected in series. The current adjustment components included in the discharge current adjustment section include a transistor. The voltage between the input and output terminals of a transistor changes depending on temperature. Therefore, in the discharge device of Patent Document 1, the discharge current changes depending on temperature.

[0005] The present invention has been made in consideration of the above-mentioned problems, and aims to make it possible to suppress changes in discharge current due to temperature changes in discharge devices and power conversion devices in which a current adjustment unit having a transistor adjusts the magnitude of the discharge current of a discharge unit. [Means for solving the problem]

[0006] The present invention employs the following configuration as a means for solving the above problems.

[0007] A first aspect of the present invention is a discharge device that is connected in parallel to a capacitance element and discharges charge accumulated in the capacitance element as a discharge current, and includes a discharge section through which the discharge current flows and a discharge current adjustment section that adjusts the magnitude of the discharge current flowing in the discharge section, wherein the discharge section and the discharge current adjustment section are connected in parallel to the capacitance element, and the discharge current adjustment section has a discharge current adjustment transistor and a Zener diode that is located on a lower potential side than the discharge current adjustment transistor and is connected in series with the discharge current adjustment transistor.

[0008] A second aspect of the present invention is a power conversion device that performs power conversion between a battery and a load, and employs a configuration including the above-mentioned capacitive element and the discharge device according to the first aspect. [Effects of the Invention]

[0009] According to the present invention, the discharge current adjustment unit has a Zener diode connected in series to a discharge current adjustment transistor. The discharge current adjustment transistor and the Zener diode have opposite temperature characteristics. That is, when the voltage across the discharge current adjustment transistor decreases due to a rise in temperature, the voltage across the Zener diode increases. On the other hand, when the voltage across the discharge current adjustment transistor increases due to a drop in temperature, the voltage across the Zener diode decreases. Therefore, according to the present invention, the discharge current adjustment transistor and the Zener diode can suppress changes in the discharge current due to temperature. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a schematic configuration diagram of a vehicle equipped with a discharge device according to a first embodiment of the present invention. [Figure 2] 1 is a circuit diagram of a discharge device according to a first embodiment of the present invention. [Figure 3] FIG. 6 is a circuit diagram of a discharge device according to a second embodiment of the present invention. [Figure 4] FIG. 10 is a circuit diagram of a discharge device according to a third embodiment of the present invention. [Figure 5] FIG. 10 is a circuit diagram of an oscillation circuit included in a discharge device according to a third embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0011] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a discharge device and a power conversion device according to the present invention will be described below with reference to the drawings.

[0012] (First embodiment) 1 is a schematic configuration diagram of a vehicle 100 equipped with a discharge device 5 of this embodiment. The vehicle 100 is, for example, an electric vehicle or a hybrid vehicle. As shown in FIG. 1, the vehicle 100 includes, for example, a high-voltage battery HB (battery), a low-voltage battery LB (battery), a motor M (load), and a power conversion device 1.

[0013] The high-voltage battery HB is a secondary battery such as a lithium-ion battery, and outputs relatively high-voltage DC power of, for example, several hundred volts. This high-voltage battery HB is a battery that outputs driving power to be supplied to the motor M, and is what is known as a driving battery. The low-voltage battery LB is a secondary battery such as a lead-acid battery, and outputs relatively low-voltage DC power of, for example, about 12 V. This low-voltage battery LB is a battery that outputs auxiliary power to be supplied to auxiliary devices (not shown), and is what is known as an auxiliary device battery.

[0014] The motor M generates rotational power by receiving driving power from the high-voltage battery HB via the power conversion device 1. The rotational power generated by the motor M is transmitted to the drive wheels of the vehicle 100 via a transmission mechanism (not shown).

[0015] The power conversion device 1 is a device that performs power conversion between batteries (high-voltage battery HB and low-voltage battery LB) and the motor M. For example, the power conversion device 1 converts DC power to AC power, AC power to DC power, and voltage. Specifically, the power conversion device 1 boosts the drive power output from the high-voltage battery HB and converts it to AC, and supplies it to the motor M. The power conversion device 1 also converts regenerative power output from the motor M to DC, reduces the voltage, and supplies it to the high-voltage battery HB. Furthermore, the power conversion device 1 reduces the voltage of the drive power output from the high-voltage battery HB to generate power for auxiliary devices, and supplies it to the low-voltage battery LB.

[0016] 1, the power conversion device 1 includes a step-up / step-down converter 2, an inverter 3, a smoothing capacitor 4, a discharge device 5, and a DC-DC converter 6. The step-up / step-down converter 2, the inverter 3, and the DC-DC converter 6 constitute a power conversion circuit H that performs power conversion.

[0017] The buck-boost converter 2 is a circuit including a reactor and a capacitor, and it boosts or lowers the voltage of electric power. Specifically, the buck-boost converter 2 has a pair of primary-side input / output terminals and a pair of secondary-side input / output terminals. It selectively performs a boost process, boosting battery power at the primary-side input / output terminals and outputting it to the secondary-side input / output terminals, or a buck process, lowering regenerative power at the secondary-side input / output terminals and outputting it to the primary-side input / output terminals. That is, the buck-boost converter 2 boosts the drive power supplied from the high-voltage battery HB and outputs it to the inverter 3. The buck-boost converter 2 also lowers the regenerative power supplied from the inverter 3 and outputs it to the high-voltage battery HB. As shown in FIG. 1 , the buck-boost converter 2 is connected to the inverter 3 by a high-potential wiring 7 and a low-potential wiring 8. The high-potential wiring 7 connects the high-voltage end, which is one of the secondary-side input / output terminals of the buck-boost converter 2, to the inverter 3. The low-potential wiring 8 connects the low-voltage end, which is the other of the secondary-side input / output terminals of the buck-boost converter 2, to the inverter 3.

[0018] The inverter 3 converts DC power to AC power or AC power to DC power. For example, the inverter 3 converts DC driving power supplied from the step-up / step-down converter 2 into three-phase AC power and outputs it to the motor M. The inverter 3 also converts regenerative AC power supplied from the motor M into DC power and outputs it to the high-voltage battery HB.

[0019] Furthermore, the step-up / step-down converter 2 and the inverter 3 include a plurality of semiconductor power devices. Each semiconductor power device includes a power transistor. These semiconductor power transistors include semiconductor elements and are mounted on an insulated circuit board. For example, one semiconductor power device includes two power transistors. However, a semiconductor power device having a single power transistor may also be included. For example, each power transistor includes a plurality of semiconductor elements formed of, for example, SiC (silicon carbide). Note that the power transistor may include semiconductor elements formed of other materials such as Si (silicon) or GaN (gallium nitride).

[0020] As shown in Fig. 1 , the smoothing capacitor 4 is a capacitance element provided between the buck-boost converter 2 and the inverter 3. That is, one end of the smoothing capacitor 4 is connected to one of the secondary-side input / output terminals of the buck-boost converter 2, and the other end is connected to the other of the secondary-side input / output terminals of the buck-boost converter 2. In this embodiment, one end of the smoothing capacitor 4 is connected to the high-voltage end of the buck-boost converter 2 via a high-potential wiring 7. Moreover, the other end of the smoothing capacitor 4 is connected to the low-voltage end, which is the other of the secondary-side input / output terminals of the buck-boost converter 2, via a low-potential wiring 8.

[0021] Such a smoothing capacitor 4 smoothes ripples in the boost power output from the secondary-side input / output terminals of the boost / buck converter 2. Furthermore, this smoothing capacitor 4 charges or discharges electric charge using the boost power output from the secondary-side input / output terminals of the boost / buck converter 2 and the regenerative power input from the inverter 3 so that the high-voltage end has a higher potential than the low-voltage end. Note that it is also possible to adopt a configuration in which the smoothing capacitor 4 is provided but the boost / buck converter 2 is not provided.

[0022] The discharge device 5 is connected to the high-voltage end of the buck-boost converter via a high-potential wiring 7. The discharge device 5 is also connected to the low-voltage end of the buck-boost converter via a low-potential wiring 8. The discharge device 5 is connected in parallel to the smoothing capacitor 4 connected to the inverter 3, and is provided between the buck-boost converter 2 and the inverter 3. The discharge device 5 is a discharge circuit that forcibly discharges the smoothing capacitor 4 that has accumulated charge using the boosted power of the buck-boost converter 2 or the regenerative power of the inverter 3. In other words, the discharge device 5 discharges the charge accumulated in the smoothing capacitor 4 as a discharge current.

[0023] The voltage across the terminals of the smoothing capacitor 4 is applied to the discharge device 5 as a discharge voltage. This discharge device 5 generates a discharge current according to the discharge voltage and its own internal resistance (discharge resistance). The discharge device 5 constantly discharges the power stored in the smoothing capacitor 4, and when the power supply from the high-voltage battery HB is stopped by a contactor (not shown), the discharge device 5 reduces the voltage of the smoothing capacitor 4. The discharge device 5 will be described in detail later.

[0024] The DC-DC converter 6 steps down the drive power output from the high-voltage battery HB and converts it into power for the auxiliary devices. The DC-DC converter 6 converts the DC drive power into DC power for the auxiliary devices.

[0025] Next, the discharge device 5 will be described in detail. FIG. 2 is a circuit diagram of the discharge device 5. As shown in FIG. 2, the discharge device 5 includes a discharge unit 5a, a discharge current adjustment unit 5b, and a midpoint connection line 5c. The discharge unit 5a is a circuit that conducts a discharge current, through which the discharge current flows and converts the discharge current into thermal energy. The discharge current adjustment unit 5b is a circuit that adjusts the magnitude of the discharge current flowing to the discharge unit 5a. As shown in FIG. 2, the discharge unit 5a and the discharge current adjustment unit 5b are connected in parallel to the smoothing capacitor 4.

[0026] The high-potential end of the discharge unit 5a is connected to the high-potential wiring 7, and the low-potential end is connected to the low-potential wiring 8. The discharge unit 5a has a first discharge unit semiconductor switch 5a1, a first discharge unit resistor 5a2, a second discharge unit semiconductor switch 5a3, and a second discharge unit resistor 5a4. In other words, the discharge unit 5a has a plurality of semiconductor switches and a plurality of resistors. The number of semiconductor switches and resistors included in the discharge unit 5a is not limited. In other words, the discharge unit 5a may have a single semiconductor switch and a single resistor, or three or more.

[0027] As shown in FIG. 2, the semiconductor switch 5a1 for the first discharge section, the resistor 5a2 for the first discharge section, the semiconductor switch 5a3 for the second discharge section, and the resistor 5a4 for the second discharge section are arranged in series in this order from the high potential wiring 7 to the low potential wiring 8.

[0028] In this embodiment, the first discharge unit semiconductor switch 5a1 and the second discharge unit semiconductor switch 5a3 use metal oxide semiconductor field effect transistors (MOSFETs), which have higher withstand voltage performance than bipolar transistors. However, the first discharge unit semiconductor switch 5a1 and the second discharge unit semiconductor switch 5a3 are not limited to metal oxide semiconductor field effect transistors.

[0029] The drain terminal of the first discharge unit semiconductor switch 5a1, which is the input terminal for the discharge current (the high potential terminal of the discharge unit 5a), is connected to one end of the smoothing capacitor 4 via the high potential wiring 7. The source terminal of the first discharge unit semiconductor switch 5a1, which is the output terminal for the discharge current, is connected to one end of the first discharge unit resistor 5a2. The gate terminal of the first discharge unit semiconductor switch 5a1, which is the control terminal, is connected to a discharge unit semiconductor switch connection line 5b7, which will be described later. When a voltage is applied to the gate terminal, the first discharge unit semiconductor switch 5a1 becomes conductive, allowing a discharge current to flow from the drain terminal to the source terminal.

[0030] One end of the first discharge section resistor 5a2 is connected to the source terminal (output terminal) of the first discharge section semiconductor switch 5a1, and the other end of the first discharge section resistor 5a2 is connected to the drain terminal, which is the input terminal, of the second discharge section semiconductor switch 5a3.

[0031] The drain terminal of the second discharge unit semiconductor switch 5a3, which is the input terminal for the discharge current, is connected to the other terminal of the first discharge unit resistor 5a2. The source terminal of the second discharge unit semiconductor switch 5a3, which is the output terminal for the discharge current, is connected to one terminal of the second discharge unit resistor 5a4. The gate terminal of the second discharge unit semiconductor switch 5a3, which is the control terminal, is connected to a discharge unit semiconductor switch connection line 5b7, which will be described later. When a voltage is applied to the gate terminal, the second discharge unit semiconductor switch 5a3 is brought into a conductive state in which a discharge current flows from the drain terminal to the source terminal.

[0032] One end of the second discharge section resistor 5a4 is connected to the source terminal (output end) of the second discharge section semiconductor switch 5a3. The other end (low potential end of the discharge section 5a) of the second discharge section resistor 5a4 is connected to the other end of the smoothing capacitor 4 via the low potential wiring 8.

[0033] The discharge unit 5a also includes a discharge current adjuster semiconductor switch connection line 5a5. A discharge current adjuster semiconductor switch connection line 5a5 is provided for each semiconductor switch (described later) included in the discharge current adjuster 5b. In this embodiment, since the discharge current adjuster 5b has two semiconductor switches, two discharge current adjuster semiconductor switch connection lines 5a5 are also provided. One discharge current adjuster semiconductor switch connection line 5a5 is connected to the midpoint between the source terminal of the first discharge unit semiconductor switch 5a1 and one end of the first discharge unit resistor 5a2. The other discharge current adjuster semiconductor switch connection line 5a5 is connected to the midpoint between the source terminal of the second discharge unit semiconductor switch 5a3 and one end of the second discharge unit resistor 5a4.

[0034] In the discharge unit 5a, when a discharge current is conducted, the first discharge unit semiconductor switch 5a1 and the second discharge unit semiconductor switch 5a3 in particular generate heat and discharge by converting the discharge current into thermal energy. In other words, the discharge unit 5a consumes the charge accumulated in the smoothing capacitor 4 by converting the electrical energy of the discharge current into thermal energy.

[0035] The high-potential end of the discharge current adjustment unit 5b is connected to the high-potential wiring 7, and the low-potential end is connected to the low-potential wiring 8. The discharge current adjustment unit 5b has a first discharge current adjustment unit resistor 5b1, a first discharge current adjustment unit semiconductor switch 5b2, a first Zener diode 5b3, a second discharge current adjustment unit resistor 5b4, a second discharge current adjustment unit semiconductor switch 5b5, and a second Zener diode 5b6. That is, the discharge current adjustment unit 5b has a plurality of semiconductor switches, a plurality of resistors, and a plurality of Zener diodes. The number of semiconductor switches and resistors included in the discharge current adjustment unit 5b is not limited. That is, the discharge current adjustment unit 5b may have a single semiconductor switch and a single resistor, or three or more of each.

[0036] As shown in FIG. 2, the resistor 5b1 for the first discharge current adjustment unit, the semiconductor switch 5b2 for the first discharge current adjustment unit, the first Zener diode 5b3, the resistor 5b4 for the second discharge current adjustment unit, the semiconductor switch 5b5 for the second discharge current adjustment unit, and the second Zener diode 5b6 are arranged in series in this order from the high potential wiring 7 toward the low potential wiring 8.

[0037] In this embodiment, the first discharge current adjustment unit semiconductor switch 5b2 and the second discharge current adjustment unit semiconductor switch 5b5 are NPN bipolar transistors, but are not limited to bipolar transistors.

[0038] One end (high potential end of the discharge current adjustment unit 5b) of the first discharge current adjustment unit resistor 5b1 is connected to one end of the smoothing capacitor 4 via the high potential wiring 7. The other end of the first discharge current adjustment unit resistor 5b1 is connected to the collector terminal which is the input end of the first discharge current adjustment unit semiconductor switch 5b2.

[0039] The first discharge current adjustment unit semiconductor switch 5b2 has a collector terminal, which is an input terminal, connected to the other terminal of the first discharge current adjustment unit resistor 5b1. The first discharge current adjustment unit semiconductor switch 5b2 has an emitter terminal, which is an output terminal, connected to the cathode terminal of the first Zener diode 5b3. The first discharge current adjustment unit semiconductor switch 5b2 has a base terminal, which is a control terminal, connected to the discharge current adjustment unit semiconductor switch connection line 5a5. When a voltage is applied to the base terminal, the first discharge current adjustment unit semiconductor switch 5b2 is brought into a conductive state in which a current flows from the collector terminal to the emitter terminal.

[0040] The cathode terminal of the first Zener diode 5b3 is connected to the emitter terminal of the semiconductor switch 5b2 for the first discharge current adjustment unit. The anode terminal of the first Zener diode 5b3 is connected to one end of the resistor 5b4 for the second discharge current adjustment unit. The first Zener diode 5b3 is not necessarily provided.

[0041] One end of the second discharge current adjustment resistor 5b4 is connected to the anode terminal of the first Zener diode 5b3, and the other end of the second discharge current adjustment resistor 5b4 is connected to the collector terminal, which is the input terminal, of the second discharge current adjustment semiconductor switch 5b5.

[0042] The second discharge current adjustment unit semiconductor switch 5b5 has a collector terminal, which is an input terminal, connected to the other terminal of the second discharge current adjustment unit resistor 5b4. The second discharge current adjustment unit semiconductor switch 5b5 has an emitter terminal, which is an output terminal, connected to the cathode terminal of the second Zener diode 5b6. The second discharge current adjustment unit semiconductor switch 5b5 has a base terminal, which is a control terminal, connected to the discharge current adjustment unit semiconductor switch connection line 5a5. When a voltage is applied to the base terminal, the second discharge current adjustment unit semiconductor switch 5b5 is brought into a conductive state in which a current flows from the collector terminal to the emitter terminal.

[0043] The second Zener diode 5b6 has a cathode terminal connected to the emitter terminal of the second discharge current adjustment unit semiconductor switch 5b5, and an anode terminal (low potential end of the discharge current adjustment unit 5b) connected to the other end of the smoothing capacitor 4 via the low potential wiring 8.

[0044] The discharge current adjustment unit 5b also includes a discharge unit semiconductor switch connection line 5b7. A discharge unit semiconductor switch connection line 5b7 is provided for each semiconductor switch included in the discharge unit 5a. In this embodiment, since the discharge unit 5a has two semiconductor switches, two discharge unit semiconductor switch connection lines 5b7 are also provided. One discharge unit semiconductor switch connection line 5b7 is connected to the midpoint between the other end of the first discharge current adjustment unit resistor 5b1 and the collector terminal of the first discharge current adjustment unit semiconductor switch 5b2. The other discharge unit semiconductor switch connection line 5b7 is connected to the midpoint between the other end of the second discharge current adjustment unit resistor 5b4 and the collector terminal of the second discharge current adjustment unit semiconductor switch 5b5.

[0045] In this way, the discharge current adjustment unit 5b has the second Zener diode 5b6 located at a lower potential side than the second discharge current adjustment unit semiconductor switch 5b5. The second Zener diode 5b6 is also connected in series with the second discharge current adjustment unit semiconductor switch 5b5.

[0046] The midpoint connection line 5c is a wiring that connects the discharge unit 5a and the discharge current adjustment unit 5b. As shown in Fig. 2, one end of the midpoint connection line 5c is connected to the midpoint between the other end of the first Zener diode 5b3 and the collector terminal of the second discharge current adjustment unit resistor 5b4. The other end of the midpoint connection line 5c is connected to the midpoint between the other end of the first discharge unit resistor 5a2 and the drain terminal of the second discharge unit semiconductor switch 5a3.

[0047] Here, a description will be given of the operation of the discharge device 5. It is assumed that a voltage equal to or greater than the breakdown voltage is applied to the first Zener diode 5b3 and the second Zener diode 5b6.

[0048] In the discharge device 5 of this embodiment, a portion of the power stored in the smoothing capacitor 4 is supplied as a discharge current. When the first discharge unit semiconductor switch 5a1, the second discharge unit semiconductor switch 5a3, the first discharge current adjustment unit semiconductor switch 5b2, and the second discharge current adjustment unit semiconductor switch 5b5 are all in a non-conductive state, and charge is stored in the smoothing capacitor 4 and the voltage between the terminals increases, the voltage applied to the gate terminal of the first discharge unit semiconductor switch 5a1 increases. When the voltage applied to the gate terminal of the first discharge unit semiconductor switch 5a1 increases, the first discharge unit semiconductor switch 5a1 becomes conductive, and a discharge current flows through the first discharge unit semiconductor switch 5a1.

[0049] When the discharge current flows through the first discharge unit semiconductor switch 5a1, the first discharge unit resistor 5a2 is also energized. As a result, a voltage difference occurs between the base terminal and the emitter terminal of the first discharge current adjustment unit semiconductor switch 5b2 due to a voltage drop across the first discharge unit resistor 5a2. When a voltage difference occurs between the base terminal and the emitter terminal of the first discharge current adjustment unit semiconductor switch 5b2, the first discharge current adjustment unit semiconductor switch 5b2 becomes conductive.

[0050] The discharge current output from first discharge section resistor 5a2 is supplied to both second discharge section semiconductor switch 5a3 and second discharge current adjustment section resistor 5b4. When the discharge current flows through second discharge section semiconductor switch 5a3, current is also passed through second discharge section resistor 5a4. As a result, a voltage difference occurs between the base terminal and emitter terminal of second discharge current adjustment section semiconductor switch 5b5 due to a voltage drop across second discharge section resistor 5a4.

[0051] When a voltage difference occurs between the base terminal and emitter terminal of the second discharge current adjustment unit semiconductor switch 5b5 due to a voltage drop caused by the second discharge unit resistor 5a4, the second discharge current adjustment unit semiconductor switch 5b5 becomes conductive.

[0052] Here, when the semiconductor switch 5b5 for the second discharge current adjustment unit is turned on, the voltage applied to the gate terminal of the semiconductor switch 5b5 for the second discharge current adjustment unit decreases, so that the current flowing through the semiconductor switch 5b5 for the second discharge current adjustment unit decreases, and the discharge current flowing through the resistor 5a4 for the second discharge unit also decreases.

[0053] On the other hand, when the discharge current flowing through second discharge unit semiconductor switch 5a3 decreases, the voltage difference between the base terminal and the emitter terminal of second discharge current adjustment unit semiconductor switch 5b5 decreases, the current flowing through second discharge current adjustment unit semiconductor switch 5b5 decreases, the gate voltage of second discharge unit semiconductor switch 5a3 increases, and the discharge current flowing through second discharge unit semiconductor switch 5a3 increases.

[0054] By repeating such operations of second discharge unit semiconductor switch 5a3 and second discharge current adjustment unit semiconductor switch 5b5, the discharge current flowing through second discharge unit resistor 5a4 becomes constant. As a result, second discharge unit resistor 5a4 conducts a constant discharge current regardless of the voltage of smoothing capacitor 4.

[0055] The discharge device 5 of this embodiment as described above is connected in parallel to the smoothing capacitor 4 and discharges the charge accumulated in the smoothing capacitor 4 as a discharge current. The discharge device 5 of this embodiment includes a discharge unit 5a and a discharge current adjustment unit 5b. A discharge current flows through the discharge unit 5a. The discharge current adjustment unit 5b adjusts the magnitude of the discharge current flowing through the discharge unit 5a. In the discharge device 5 of this embodiment, the discharge unit 5a and the discharge current adjustment unit 5b are connected in parallel to the smoothing capacitor 4. The discharge current adjustment unit 5b includes a second discharge current adjustment unit semiconductor switch 5b5 and a second Zener diode 5b6. The second Zener diode 5b6 is located at a lower potential than the second discharge current adjustment unit semiconductor switch 5b5 and is connected in series with the second discharge current adjustment unit semiconductor switch 5b5.

[0056] According to the discharge device 5 of this embodiment, the discharge current adjustment unit 5b includes a second Zener diode 5b6 connected in series with the second discharge current adjustment unit semiconductor switch 5b5. The second discharge current adjustment unit semiconductor switch 5b5 and the second Zener diode 5b6 have opposite temperature characteristics. That is, when the inter-terminal voltage between the base and emitter of the second discharge current adjustment unit semiconductor switch 5b5 decreases due to a rise in temperature, the inter-terminal voltage of the second Zener diode 5b6 increases. On the other hand, when the inter-terminal voltage between the base and emitter of the second discharge current adjustment unit semiconductor switch 5b5 increases due to a drop in temperature, the inter-terminal voltage of the second Zener diode 5b6 decreases. Therefore, according to the discharge device 5 of this embodiment, the second discharge current adjustment unit semiconductor switch 5b5 and the second Zener diode 5b6 can suppress changes in the discharge current due to temperature.

[0057] Furthermore, according to the discharge device 5 of this embodiment, the provision of the second Zener diode 5b6 makes it possible to increase the resistance value of the second discharge section resistor 5a4 compared to a case in which the second Zener diode 5b6 is not provided, thereby reducing the voltage applied to the second discharge section semiconductor switch 5a3 and suppressing heat generation from the second discharge section semiconductor switch 5a3.

[0058] The power conversion device 1 of this embodiment performs power conversion between batteries (high-voltage battery HB and low-voltage battery LB) and the motor M. The power conversion device 1 of this embodiment also includes a smoothing capacitor 4 and a discharge device 5 of this embodiment. Since the power conversion device 1 of this embodiment includes the discharge device 5, it is possible to suppress changes in discharge current due to temperature.

[0059] (Second embodiment) Next, a second embodiment of the present invention will be described. In the description of this embodiment, the description of the same parts as those in the first embodiment will be omitted or simplified.

[0060] Fig. 3 is a circuit diagram of a discharge device 5A of this embodiment. As shown in Fig. 3, in the discharge device 5A of this embodiment, the discharge current adjustment unit 5b has a bypass semiconductor switch 5b8 (switching element) and a switch control unit 5b9.

[0061] The bypass semiconductor switch 5b8 is a switching element connected in parallel to the second Zener diode 5b6. Under the control of the switch control unit 5b9, the bypass semiconductor switch 5b8 switches between a state in which a current passes through the second Zener diode 5b6 and a state in which a current bypasses the second Zener diode 5b6.

[0062] In the discharge device 5A of this embodiment, a metal oxide semiconductor field effect transistor (MOSFET) is used as the bypass semiconductor switch 5b8, but the first discharge unit semiconductor switch 5a1 and the second discharge unit semiconductor switch 5a3 are not limited to metal oxide semiconductor field effect transistors.

[0063] The drain terminal, which is the input terminal of the bypass semiconductor switch 5b8, is connected to the cathode terminal of the second Zener diode 5b6. The source terminal, which is the output terminal of the bypass semiconductor switch 5b8, is connected to the anode terminal of the second Zener diode 5b6. The gate terminal, which is the control terminal of the bypass semiconductor switch 5b8, is connected to the switch control unit 5b9. When a voltage is applied to the gate terminal from the switch control unit 5b9, the bypass semiconductor switch 5b8 enters a conductive state in which a current flows from the drain terminal to the source terminal.

[0064] In this embodiment, two each of the first discharge current adjustment unit resistors 5b1 and the second discharge current adjustment unit resistors 5b4 are connected in series. A diode 5d is provided in the middle of the midpoint connection line 5c. The diode 5d is arranged so that its cathode terminal faces the discharge unit 5a and its anode faces the discharge current adjustment unit 5b. As shown in FIG. 3, the discharge current adjustment unit 5b has a control unit connection line 5b10 that connects the midpoint of the two second discharge current adjustment unit resistors 5b4 and the switch control unit 5b9.

[0065] The switch control unit 5b9 is connected to the control unit connection line 5b10 and the low potential wiring 8, and controls the switch control unit 5b9 in accordance with the magnitude of the current flowing from the control unit connection line 5b10 to the low potential wiring 8. In other words, the switch control unit 5b9 is connected to the high potential side of the semiconductor switch 5b5 for the second discharge current adjustment unit.

[0066] The switch control unit 5b9 controls the bypass semiconductor switch 5b8 to a conducting state when the current flowing from the control unit connection line 5b10 to the low potential wiring 8 is large (when the magnitude of the current flowing to the high potential side of the second discharge current adjustment unit semiconductor switch 5b5 exceeds a predetermined threshold). Also, the switch control unit 5b9 controls the bypass semiconductor switch 5b8 to a non-conducting state when the current flowing from the control unit connection line 5b10 to the low potential wiring 8 is small (when the magnitude of the current flowing to the high potential side of the second discharge current adjustment unit semiconductor switch 5b5 does not exceed the threshold). An oscillator circuit, a microcomputer, or the like, which will be described later, can be used as this switch control unit 5b9.

[0067] According to the discharge device 5A of this embodiment, when the inter-terminal voltage of the smoothing capacitor 4 is high, the current flowing from the control unit connection line 5b10 to the low potential wiring 8 increases, and the bypass semiconductor switch 5b8 is turned on. As a result, the discharge current flowing through the second discharge unit resistor 5a4 is determined by the inter-terminal voltage between the base and emitter of the second discharge current adjustment unit semiconductor switch 5b5.

[0068] On the other hand, according to the discharge device 5A of the present embodiment, when the voltage across the smoothing capacitor 4 is low, the current flowing from the control unit connection line 5b10 to the low potential wiring 8 decreases, and the bypass semiconductor switch 5b8 is brought into a non-conductive state. As a result, the discharge current flowing through the second discharge unit resistor 5a4 is determined by the sum of the voltage across the base and emitter of the second discharge current adjustment unit semiconductor switch 5b5 and the voltage across the second Zener diode 5b6.

[0069] Therefore, according to the discharge device 5A of the present embodiment, when the voltage across the terminals of the smoothing capacitor 4 is high, the discharge current flowing through the second discharge unit resistor 5a4 can be reduced to suppress heat generation in the first discharge unit semiconductor switch 5a1 and the second discharge unit semiconductor switch 5a3. On the other hand, according to the discharge device 5A of the present embodiment, when the voltage across the terminals of the smoothing capacitor 4 is low, the discharge current flowing through the first discharge unit semiconductor switch 5a1 and the second discharge unit semiconductor switch 5a3 can be increased to shorten the discharge period of the smoothing capacitor 4.

[0070] (Third embodiment) Next, a third embodiment of the present invention will be described. In the description of this embodiment, the description of the same parts as those in the second embodiment will be omitted or simplified.

[0071] Fig. 4 is a circuit diagram of a discharge device 5B of this embodiment. As shown in Fig. 4, in the discharge device 5B of this embodiment, a discharge current adjuster 5b has an oscillator circuit 5b11 as a switch controller 5b9.

[0072] 5 is a circuit diagram of the oscillator circuit 5b11. The oscillator circuit 5b11 is a multivibrator oscillator circuit, and as shown in this figure, includes a first oscillator circuit Zener diode 10, a first resistor 11, a first semiconductor switch 12, a second resistor 13, a third resistor 14, a second semiconductor switch 15, a fourth resistor 16, a first capacitor 17, a second capacitor 18, a bypass semiconductor switch connection line 19, and a second oscillator circuit Zener diode 20.

[0073] In this embodiment, NPN-type bipolar transistors are used as the first semiconductor switch 12 and the second semiconductor switch 15. However, the first semiconductor switch 12 and the second semiconductor switch 15 are not limited to bipolar transistors.

[0074] The first oscillation circuit Zener diode 10 has a cathode terminal connected to the control unit connection line 5b10 and an anode terminal connected to the first resistor 11. One end of the first resistor 11 is connected to the first oscillation circuit Zener diode 10 and the other end is connected to the collector terminal of the first semiconductor switch 12. The first semiconductor switch 12 has a collector terminal connected to the first resistor 11, an emitter terminal connected to the frame ground, and a base terminal connected to the other end of the second capacitor 18. The second resistor 13 has one end connected to the collector terminal of the first semiconductor switch 12 and the other end connected to the base terminal of the first semiconductor switch 12.

[0075] The third resistor 14 has one end connected to the control unit connection line 5b10 and the other end connected to the collector terminal of the second semiconductor switch 15. The second semiconductor switch 15 has a collector terminal connected to the third resistor 14, an emitter terminal connected to the frame ground, and a base terminal connected to the other end of the first capacitor 17. The fourth resistor 16 has one end connected to the collector terminal of the second semiconductor switch 15 and the other end connected to the base terminal of the second semiconductor switch 15.

[0076] The first capacitor 17 has one end connected to the other end of the first resistor 11 and the other end connected to the base terminal of the second semiconductor switch 15. The second capacitor 18 has one end connected to the other end of the third resistor 14 and the other end connected to the base terminal of the first semiconductor switch 12.

[0077] The bypass semiconductor switch connecting line 19 is a wiring that connects the gate terminal of the bypass semiconductor switch 5b8 shown in Fig. 4 to the other end of the third resistor 14. The Zener diode 20 for the second oscillation circuit has a cathode terminal connected to an intermediate portion of the bypass semiconductor switch connecting line 19 and an anode terminal connected to the frame ground.

[0078] In such an oscillator circuit 5b11, the period during which the bypass semiconductor switch connection line 19 is energized per unit time when the current flowing from the control unit connection line 5b10 to the frame ground is small (when the terminal voltage of the smoothing capacitor 4 is low) can be made longer than when the current flowing from the control unit connection line 5b10 to the frame ground is small (when the terminal voltage of the smoothing capacitor 4 is low).

[0079] Therefore, according to the discharge device 5B of this embodiment, when the voltage across the terminals of the smoothing capacitor 4 is high, the average value of the discharge current flowing through the second discharge resistor 5a4 per unit time can be reduced, thereby suppressing heat generation in the first discharge unit semiconductor switch 5a1 and the second discharge unit semiconductor switch 5a3. On the other hand, according to the discharge device 5B of this embodiment, when the voltage across the terminals of the smoothing capacitor 4 is low, the average value of the discharge current flowing through the first discharge unit semiconductor switch 5a1 and the second discharge unit semiconductor switch 5a3 per unit time can be increased, thereby shortening the discharge period of the smoothing capacitor 4.

[0080] As described above, in the discharging device 5B of the present embodiment, the oscillator circuit 5b11 shortens the period of time in which the current is applied per unit time when the voltage of the smoothing capacitor 4 is higher than a predetermined reference value, compared to when the voltage of the smoothing capacitor 4 is lower than the reference value. Therefore, as described above, heat generation in the first discharge unit semiconductor switch 5a1 and the second discharge unit semiconductor switch 5a3 is suppressed when the voltage between the terminals of the smoothing capacitor 4 is high, and the discharge period of the smoothing capacitor 4 can be shortened when the voltage between the terminals of the smoothing capacitor 4 is low.

[0081] In addition, the configuration of the oscillator circuit is not limited to the above configuration, as long as the period of time during which the smoothing capacitor 4 is in a conducting state per unit time can be shortened when the voltage of the smoothing capacitor 4 is higher than a predetermined reference value compared to when the voltage of the smoothing capacitor 4 is lower than the reference value.

[0082] While the preferred embodiments of the present invention have been described above with reference to the accompanying drawings, it goes without saying that the present invention is not limited to the above-described embodiments. The shapes and combinations of the components shown in the above-described embodiments are merely examples, and various modifications can be made based on design requirements, etc., without departing from the spirit of the present invention.

[0083] The above embodiment can also be described as follows, for example:

[0084] [Appendix 1] A discharge device connected in parallel to a capacitance element to discharge electric charges accumulated in the capacitance element as a discharge current, a discharge section through which the discharge current flows; a discharge current adjusting unit that adjusts the magnitude of the discharge current flowing in the discharge unit; Equipped with the discharge unit and the discharge current adjustment unit are connected in parallel to the capacitance element, The discharge current adjusting unit is a discharge current adjusting transistor; a Zener diode located on a lower potential side than the discharge current adjusting transistor and connected in series with the discharge current adjusting transistor; have A discharge device characterized by:

[0085] [Appendix 2] The discharge current adjusting unit is a switching element connected in parallel to the Zener diode; a switching element control unit that controls the switching element; 2. The discharge device according to claim 1, comprising:

[0086] [Appendix 3] The switching element control unit connected to the high potential side of the discharge current adjusting transistor, When the magnitude of the current flowing through the high potential side of the discharge current adjusting transistor exceeds a predetermined threshold, the switching element is brought into a conducting state; When the magnitude of the current flowing on the high potential side of the discharge current adjusting transistor does not exceed the threshold value, the switching element is brought into a non-conducting state. 3. The discharge device according to claim 2.

[0087] [Appendix 4] The discharge device according to claim 3, wherein the switching element control unit shortens the period of time in which the capacitance element is in the conducting state per unit time when the voltage of the capacitance element is higher than a predetermined reference value compared to when the voltage of the capacitance element is lower than the reference value.

[0088] [Appendix 5] A power conversion device that performs power conversion between a battery and a load, The capacitive element; A discharge device according to any one of Supplementary Notes 1 to 4. Equipped with A power conversion device characterized by: [Explanation of symbols]

[0089] 1...power conversion device, 4...smoothing capacitor (capacitive element), 5...discharge device, 5a...discharge section, 5A...discharge device, 5a1...semiconductor switch for first discharge section, 5a2...resistor for first discharge section, 5a3...semiconductor switch for second discharge section, 5a4...resistor for second discharge section, 5a5...semiconductor switch connection line for discharge current adjustment section, 5b...discharge current adjustment section, 5B...discharge device, 5b1...resistor for first discharge current adjustment section, 5b2...semiconductor switch for first discharge current adjustment section, 5b3...first Zener diode, 5b4...resistor for second discharge current adjustment section, 5b5...second discharge current Semiconductor switch for adjustment unit (transistor for adjusting discharge current), 5b6...second Zener diode (Zener diode), 5b7...semiconductor switch connection line for discharge unit, 5b8...bypass semiconductor switch (switching element), 5b9...switch control unit (switching element control unit), 5b10...control unit connection line, 5b11...oscillator circuit, 5c...midpoint connection line, 5d...diode, 6...DC-DC converter, 7...high-potential wiring, 8...low-potential wiring, HB...high-voltage battery (battery), LB...low-voltage battery (battery), M...motor (load)

Claims

1. A discharge device connected in parallel to a capacitance element to discharge electric charges accumulated in the capacitance element as a discharge current, a discharge section through which the discharge current flows; a discharge current adjusting unit that adjusts the magnitude of the discharge current flowing in the discharge unit; Equipped with the discharge unit and the discharge current adjustment unit are connected in parallel to the capacitance element, The discharge current adjusting unit a discharge current adjusting transistor; a Zener diode located on a lower potential side than the discharge current adjusting transistor and connected in series with the discharge current adjusting transistor; have A discharge device characterized by:

2. The discharge current adjusting unit a switching element connected in parallel to the Zener diode; a switching element control unit that controls the switching element; 2. The discharge device according to claim 1, further comprising:

3. The switching element control unit connected to the high potential side of the discharge current adjusting transistor, When the magnitude of the current flowing through the high potential side of the discharge current adjusting transistor exceeds a predetermined threshold, the switching element is brought into a conducting state; When the magnitude of the current flowing on the high potential side of the discharge current adjusting transistor does not exceed the threshold value, the switching element is brought into a non-conducting state.

3. The discharge device according to claim 2.

4. The discharge device according to claim 3, characterized in that the switching element control unit shortens the period of time in which the current is applied per unit time when the voltage of the capacitance element is higher than a predetermined reference value compared to when the voltage of the capacitance element is lower than the reference value.

5. A power conversion device that performs power conversion between a battery and a load, the capacitive element; The discharge device according to any one of claims 1 to 4. Equipped with A power conversion device characterized by:

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