Power converter

Abstract

To provide a power conversion device capable of reducing losses while maintaining switching speed.SOLUTION: A power conversion device includes: a switching element 11ul through which a main current Is flows when a gate voltage Vg is applied to a gate; a wiring 12ul having an inductance component Ls through which the main current Is flows; a transformer 30 including an inductor 31 and an inductor 32 connected in series and connected in parallel to the wiring 12ul; an input terminal 13a to which an external command voltage Vref is applied for driving the switching element 11ul; and a gate resistor 33 provided between the input terminal 13a and the gate, and a connection point CP between the inductor 31 and the inductor 32 is connected to a control reference potential and the polarity of the inductor 31 is in the same direction as the polarity of the inductor 32.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present disclosure relates to a power conversion device.

Background Art

[0002] In order to achieve both reduction of switching loss and reduction of surge voltage or surge current, active gate control for controlling the gate voltage is known. For example, Patent Document 1 describes a circuit configuration in which the voltage applied to the emitter inductance is divided by a resistor voltage divider circuit, and the divided voltage is applied to the gate drive circuit.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the circuit configuration described in Patent Document 1, a resistor voltage divider circuit is provided in the path through which the gate current flows. Therefore, loss occurs in the resistor voltage divider circuit. On the other hand, increasing the resistance value of the resistor included in the resistor voltage divider circuit reduces the gate current, so that the loss in the resistor voltage divider circuit can be reduced. However, reducing the gate current decreases the switching speed.

[0005] The present disclosure describes a power conversion device capable of reducing loss while maintaining the switching speed.

Means for Solving the Problems

[0006] A power conversion device according to one aspect of the present disclosure comprises a switching element having a control terminal and a first current terminal and a second current terminal through which a main current flows, wherein a main current flows when a voltage is applied to the control terminal; wiring through which the main current flows, the wiring having an inductance component; a transformer connected in parallel with the wiring, including a first inductor and a second inductor connected in series; an input terminal to which a command voltage for driving the switching element is applied; and a resistor provided between the input terminal and the control terminal. The connection point between the first inductor and the second inductor is connected to a control reference potential. The polarity of the first inductor is in the same direction as the polarity of the second inductor.

[0007] In this power converter, a transformer is connected in parallel with the wiring through which the main current flows. Therefore, when the main current flows, a back electromotive force (EMF) is generated in the inductance component of the wiring, and the same back EMF is generated in the transformer. The transformer includes a first inductor and a second inductor connected in series, so the back EMF is divided based on the turns ratio of the first and second inductors. The connection point between the first and second inductors is connected to a control reference potential, so the voltage generated in the first inductor is applied to the control reference potential, thereby adjusting the voltage applied to the control terminals. In this way, a voltage divider circuit is formed by the first and second inductors, so losses in the voltage divider circuit can be reduced without reducing the current flowing to the control terminals of the switching element. As a result, it is possible to reduce losses while maintaining the switching speed.

[0008] The inductance of the transformer may be greater than the inductance component of the wiring. In this case, the main current flows mainly through the wiring, and a relatively small current flows through the transformer. Therefore, the transformer can be made smaller. [Effects of the Invention]

[0009] According to this disclosure, it is possible to reduce losses while maintaining the switching speed. [Brief explanation of the drawing]

[0010] [Figure 1] Figure 1 shows the circuit configuration of a power conversion device according to one embodiment. [Figure 2] Figure 2 is a schematic circuit diagram showing the switching element and driver circuit shown in Figure 1. [Figure 3] Figure 3 is a diagram illustrating the operation during turn-off. [Figure 4] Figure 4 is a diagram illustrating the operation when the turn is switched on. [Figure 5] Figure 5(a) shows an example of the implementation of a switching element and a transformer. Figure 5(b) is a circuit diagram of the switching element shown in Figure 5(a). [Modes for carrying out the invention]

[0011] A power conversion device according to one embodiment will be described in detail below with reference to the attached drawings. In the description of the drawings, the same reference numerals are used for the same or equivalent elements, and redundant explanations are omitted.

[0012] The circuit configuration of a power converter according to one embodiment will be described with reference to Figure 1. Figure 1 is a diagram showing the circuit configuration of a power converter according to one embodiment. The power converter 1 shown in Figure 1 is an inverter device that converts DC power supplied from an external power source 2 into AC power that can drive a motor 3. The power converter 1 is mounted, for example, on a vehicle.

[0013] External power supply 2 is a DC power supply, such as a storage battery. Power converter 1 has input terminals 1a and 1b. Input terminal 1a is connected to the positive terminal of external power supply 2, and input terminal 1b is connected to the negative terminal of external power supply 2 and the reference potential V0.

[0014] Motor 3 has three phases of coils 3u, 3v, and 3w. Coils 3u, 3v, and 3w are connected, for example, in a Y-connection. Motor 3 rotates when current flows through coils 3u, 3v, and 3w in a predetermined pattern. The connection configuration of coils 3u, 3v, and 3w is not limited to a Y-connection; a delta connection may also be used.

[0015] The power conversion device 1 includes switching elements 11uh, 11ul, 11vh, 11vl, 11wh, 11wl (hereinafter referred to as "switching elements 11uh to 11wl"), freewheeling diodes Duh, Dul, Dvh, Dvl, Dwh, Dwl (hereinafter referred to as "freewheeling diodes Duh to Dwl"), driver circuits 13uh, 13ul, 13vh, 13vl, 13wh, 13wl (hereinafter referred to as "driver circuits 13uh to 13wl"), a capacitor 14, and a control device 15.

[0016] Each of the switching elements 11uh to 11wl has a control terminal, a first current terminal, and a second current terminal. In this embodiment, n-channel metal oxide semiconductor field-effect transistors (MOSFETs) are exemplified as each of the switching elements 11uh to 11wl. In this case, the control terminal is the gate, the first current terminal is the drain, and the second current terminal is the source. Each of the switching elements 11uh to 11wl may be a p-channel MOSFET. Each of the switching elements 11uh to 11wl may be an insulated gate bipolar transistor (IGBT). In this case, the control terminal is the gate, the first current terminal is the collector, and the second current terminal is the emitter. Each of the switching elements 11uh to 11wl may be a GaNHEMT.

[0017] The switching element 11uh is the switching element of the upper arm of the U phase. The switching element 11ul is the switching element of the lower arm of the U phase. The switching element 11uh and the switching element 11ul are connected in series between the input terminal 1a and the input terminal 1b. Specifically, the drain of the switching element 11uh is connected to the input terminal 1a. The source of the switching element 11uh and the drain of the switching element 11ul are connected to each other and are connected to the coil 3u. The source of the switching element 11ul is connected to the input terminal 1b.

[0018] The switching element 11vh is the switching element of the upper arm of the V phase. The switching element 11vl is the switching element of the lower arm of the V phase. The switching element 11vh and the switching element 11vl are connected in series between the input terminal 1a and the input terminal 1b. Specifically, the drain of the switching element 11vh is connected to the input terminal 1a. The source of the switching element 11vh and the drain of the switching element 11vl are connected to each other and are connected to the coil 3v. The source of the switching element 11vl is connected to the input terminal 1b.

[0019] The switching element 11wh is the switching element of the upper arm of the W phase. The switching element 11wl is the switching element of the lower arm of the W phase. The switching element 11wh and the switching element 11wl are connected in series between the input terminal 1a and the input terminal 1b. Specifically, the drain of the switching element 11wh is connected to the input terminal 1a. The source of the switching element 11wh and the drain of the switching element 11wl are connected to each other and are connected to the coil 3w. The source of the switching element 11wl is connected to the input terminal 1b.

[0020] A gate voltage Vg is applied to the gates of the switching elements 11uh to 11wl from the driver circuits 13uh to 13wl respectively. When the gate voltage Vg is applied to the gate, a main current (source current) Is flows between the drain and the source of each switching element. Specifically, when the gate-source voltage becomes greater than the threshold voltage of the switching element, the switching element turns on, and a main current Is corresponding to the difference between the gate-source voltage and the threshold voltage flows between the drain and the source.

[0021] The freewheeling diodes Duh to Dwl are freewheeling diodes connected in parallel to the switching elements 11uh to 11wl respectively. The cathode of each freewheeling diode is connected to the drain of the corresponding switching drive element. The anode of each freewheeling diode is connected to the source of the corresponding switching element.

[0022] Each of the driver circuits 13uh to 13wl is an active gate driver circuit that changes the gate voltage Vg based on an external command voltage Vref (command voltage; see Figure 2) input from the control device 15 and a back electromotive voltage Vss (see Figure 2). The details of the driver circuit will be described later.

[0023] The capacitor 14 is charged by the external power supply 2 and is used to suppress voltage fluctuations generated when the power conversion device 1 operates. The capacitor 14 is connected in parallel with the external power supply 2. Specifically, one end of the capacitor 14 is connected to the input terminal 1a, and the other end of the capacitor 14 is connected to the input terminal 1b. As the capacitor 14, for example, a capacitor bank including a plurality of electrolytic capacitors is used.

[0024] The control device 15 is a circuit that generates an external command voltage Vref for driving the switching elements 11uh to 11wl. Based on an external command (for example, a requested rotational speed), the control device 15 determines the target current flowing through the motor 3 and derives the external command voltage Vref required for that target current to flow. In this embodiment, the control device 15 derives an external command voltage Vref for each switching element and supplies the external command voltage Vref to each of the driver circuits 13uh to 13wl.

[0025] Next, the driver circuits 13uh to 13wl will be described in detail with reference to Figure 2. Figure 2 is a schematic circuit diagram showing the switching elements and driver circuits shown in Figure 1. Here, each of the driver circuits 13uh to 13wl has basically the same configuration. Therefore, driver circuit 13ul will be described in detail.

[0026] As shown in Figure 2, the power converter 1 further includes a wiring 12ul through which the main current Is flows. The wiring 12ul connects the source of the switching element 11ul to the reference potential V0 (input terminal 1b). The wiring 12ul has an inductance component Ls (stray inductance).

[0027] The driver circuit 13ul includes an input terminal 13a, a transformer 30, and a gate resistor 33 (resistor). An external command voltage Vref for driving the switching element 11ul is applied to the input terminal 13a.

[0028] Transformer 30 is connected in parallel with wiring 12ul. The inductance (impedance) of transformer 30 is greater than the inductance component Ls (impedance) of wiring 12ul. The inductance of transformer 30 is set to, for example, about 100 times the inductance component Ls of wiring 12ul. Therefore, most of the main current Is flows through wiring 12ul, and almost no current flows through transformer 30.

[0029] The transformer 30 includes an inductor 31 (first inductor) and an inductor 32 (second inductor). Inductors 31 and 32 are magnetically coupled. Specifically, inductors 31 and 32 are wound around a core made of magnetic material. Inductor 31 is the primary side of the transformer 30, and inductor 32 is the secondary side of the transformer. The turns ratio between inductor 31 and inductor 32 is 1:n (where n is a positive value).

[0030] Inductors 31 and 32 are connected in series. Specifically, one end of inductor 31 is connected to the source of the switching element 11ul, and the other end of inductor 31 is connected to one end of inductor 32. The connection point CP between inductor 31 and inductor 32 is connected to the control reference potential. The other end of inductor 32 is connected to the reference potential V0 via the input terminal 1b. The polarity of inductor 31 is in the same direction as the polarity of inductor 32.

[0031] The gate resistor 33 is provided between the input terminal 13a and the gate of the switching element 11ul. Specifically, one end of the gate resistor 33 is connected to the input terminal 13a, and the other end of the gate resistor 33 is connected to the gate of the switching element 11ul.

[0032] Next, the operation of the switching element during turn-on and turn-off will be explained with further reference to Figures 3 and 4. Figure 3 is a diagram illustrating the operation during turn-off. Figure 4 is a diagram illustrating the operation during turn-on. Since the operation of all switching elements 11uh to 11wl is basically the same, the operation of switching element 11ul during turn-off and turn-on will be explained here.

[0033] As shown in Figure 3, when the external command voltage Vref is changed to zero, the gate voltage Vg of the switching element 11ul begins to decrease, and the switching element 11ul starts to turn off. Then, as the main current Is flowing through the wiring 12ul decreases, a negative back electromotive force Vss (=Ls × dIs / dt) is generated by the inductance component Ls of the wiring 12ul. Since the transformer 30 is connected in parallel with the wiring 12ul (inductance component Ls), a back electromotive force Vss is also generated in the transformer 30.

[0034] Inductors 31 and 32 are magnetically coupled, and their turns ratio is 1:n. Therefore, a voltage equal to 1 / (1+n) times the back electromotive force Vss (=Vss / (1+n)) is generated across inductor 31. The connection point CP between inductors 31 and 32 is connected to the control reference potential. Therefore, the voltage Va at one end of the gate resistor 33 is the external command voltage Vref minus a voltage equal to 1 / (1+n) times the back electromotive force Vss (=Vref-Vss / (1+n)). Here, since the back electromotive force Vss is a negative value, the voltage Va is the external command voltage Vref plus 1 / (1+n) times the absolute value of the back electromotive force Vss (=Vref+|Vss| / (1+n)). Consequently, while the main current Is continues to decrease, the voltage Va is greater than the external command voltage Vref, which slows down the rate at which the gate voltage Vg decreases, and thus slows down the turn-off speed. As a result, voltage surges in the drain-source voltage Vds of the switching element 11ul are suppressed.

[0035] As shown in Figure 4, when the external command voltage Vref is changed from zero to a predetermined value, the gate voltage Vg of the switching element 11ul begins to rise, and the switching element 11ul starts to turn on. Then, when the main current Is begins to flow through the wiring 12ul, a positive back electromotive force Vss (=Ls × dIs / dt) is generated by the inductance component Ls of the wiring 12ul. Since the transformer 30 is connected in parallel with the wiring 12ul (inductance component Ls), a back electromotive force Vss is also generated in the transformer 30.

[0036] Inductors 31 and 32 are magnetically coupled, and their turns ratio is 1:n. Therefore, a voltage equal to 1 / (1+n) times the back electromotive force Vss (=Vss / (1+n)) is generated across inductor 31. The connection point CP between inductors 31 and 32 is connected to the control reference potential. As a result, the voltage Va at one end of the gate resistor 33 is obtained by subtracting 1 / (1+n) times the back electromotive force Vss from the external command voltage Vref. Consequently, while the main current Is continues to increase, the voltage Va is smaller than the external command voltage Vref, which slows down the rate of increase of the gate voltage Vg and consequently slows down the turn-on speed. As a result, current surges in the main current Is are suppressed.

[0037] Then, when the main current Is exceeds its peak and begins to decrease, the sign of the back electromotive force Vss reverses, generating a negative back electromotive force Vss. As a result, the voltage Va becomes greater than the external command voltage Vref, increasing the rate at which the gate voltage Vg rises, and thus increasing the turn-on speed. Consequently, the turn-on time is shortened.

[0038] Next, we will explain implementation examples of the switching element and transformer with reference to Figures 5(a) and 5(b). Figure 5(a) is a diagram showing an implementation example of the switching element and transformer. Figure 5(b) is a circuit diagram of the switching element shown in Figure 5(a).

[0039] As shown in Figure 5(b), component C11 is used as the switching element. Component C11 is a four-terminal package having a drain T1, a power source T2, a driver source T3, and a gate T4. The power source T2 is a terminal through which a large current flows. The driver source T3 is a terminal for the control reference potential. Component C11 includes the switching element 11 and a freewheeling diode D.

[0040] As shown in Figure 5(a), component C11 is mounted on the circuit board 10. Wiring patterns P1 to P4 are formed on the circuit board 10. Wiring pattern P1 is connected to the drain T1. Wiring pattern P2 is connected to the power source T2. Wiring pattern P3 is connected to the driver source T3, and wiring pattern P4 is connected to the gate T4. The transformer 30 is mounted spanning wiring patterns P2 and P3. In other words, the transformer 30 is mounted such that one end of inductor 31 is connected to wiring pattern P3, the other end of inductor 31 is connected to one end of inductor 32, and the other end of inductor 32 is connected to wiring pattern P2.

[0041] In this implementation example, the internal wiring portion of component C11 is used as the inductance component Ls, thus simplifying the implementation.

[0042] In the power converter 1 described above, a transformer 30 is connected in parallel with the wiring 12ul through which the main current Is flows. Therefore, when the main current Is flows, a back electromotive force Vss is generated in the inductance component Ls of the wiring 12ul, and the same back electromotive force Vss is generated in the transformer 30. Since the transformer 30 includes inductors 31 and 32 connected in series, the back electromotive force Vss is divided based on the turns ratio of inductors 31 and 32. The connection point CP between inductors 31 and 32 is connected to a control reference potential, so the voltage generated in inductor 31 is applied to the control reference potential, thereby adjusting the gate voltage Vg applied to the gate of the switching element 11ul. In this way, a voltage divider circuit is formed by inductors 31 and 32, so that losses in the voltage divider circuit can be reduced without reducing the gate current of the switching element 11ul. From the above, it can be seen that the power converter 1 makes it possible to reduce losses while maintaining the switching speed.

[0043] Since the inductance of transformer 30 is greater than the inductance component Ls of wiring 12ul, the main current Is flows mainly through wiring 12ul, and a relatively small current flows through inductor 31. Therefore, transformer 30 can be miniaturized, and costs can be reduced.

[0044] By changing the turns ratio between inductor 31 and inductor 32, the magnitude of the voltage generated in inductor 31 can be adjusted. Therefore, since the amount of increase or decrease relative to the external command voltage Vref can be changed, it becomes possible to adjust the voltage surge amount and the current surge amount.

[0045] Furthermore, the driver circuits other than driver circuit 13ul have the same circuit configuration as driver circuit 13ul. Therefore, the same effects as driver circuit 13ul can be obtained with these driver circuits as well.

[0046] Although one embodiment of the present disclosure has been described in detail above, the power conversion device according to the present disclosure is not limited to the above embodiment.

[0047] Component C11 may be a 3-terminal packaged product or a module. [Explanation of Symbols]

[0048] 1...Power converter, 11uh, 11ul, 11vh, 11vl, 11wh, 11wl...Switching element, 12ul...Wiring, 13a...Input terminal, 30...Transformer, 31...Inductor (first inductor), 32...Inductor (second inductor), 33...Gate resistor (resistor), CP...Connection point, Is...Main current, Ls...Inductance component, Vg...Gate voltage, Vref...External command voltage (command voltage).

Claims

1. A switching element having a control terminal and a first current terminal and a second current terminal through which a main current flows, wherein the main current flows when a voltage is applied to the control terminal, The wiring through which the main current flows includes a wiring having an inductance component, A transformer is connected in parallel with the wiring, and includes a first inductor and a second inductor connected in series. An input terminal to which a command voltage for driving the switching element is applied, A resistor is provided between the input terminal and the control terminal, Equipped with, The connection point between the first inductor and the second inductor is connected to a control reference potential. A power conversion device in which the polarity of the first inductor is in the same direction as the polarity of the second inductor.

2. The power conversion device according to claim 1, wherein the inductance of the transformer is greater than the inductance component of the wiring.

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