Switching device, power conversion device, and switching device control method

Abstract

In a switching device (1), a first switching element (104) and a second switching element (105) switch, in accordance with the inversion of the polarity of AC power, switching operations between a first input terminal (101) and a second input terminal (102) to which the AC power is inputted. A first input unit (22) and a second input unit (32) cause a first control signal and a second control signal corresponding to a first operation and a second operation of the switching operations to be inputted from a first signal source (21) and a second signal source (31) to the first switching element (104) and the second switching element (105). First changing units (221, 222) and second changing units (321, 322) respectively switch the impedance states of the first input unit (22) and the second input unit (32) in accordance with the polarity of the AC power.

Description

Switching device, power conversion device, and method for controlling switching device

[0001] The present invention relates to a switching device, a power conversion device, and a method for controlling a switching device.

[0002] Patent Document 1 describes a power conversion device in which the gates and emitters of multiple semiconductor elements connected in parallel to a main circuit bus are connected to terminals of a control device for each semiconductor element, and each semiconductor element is controlled to be turned on and off by a gate signal from the control device. Within the control device of this power conversion circuit, each gate connection terminal and each emitter connection terminal are connected at connection points within the control device. Components for preventing common-mode currents are connected to the wiring between the gate connection terminal and emitter connection terminal of each semiconductor element and each connection point within the control device.

[0003] JP 2008-178261 A

[0004] In Patent Document 1, there is a concern that the accuracy of the switching operation of each semiconductor element may be reduced due to the influence on the gate signal of common mode current prevention components connected to the wiring that supplies the gate signal to each semiconductor element of the control device.

[0005] An object of the present invention is to suppress the influence of measures against the generation of common mode current due to switching operations on control signals for switching elements.

[0006] A switching device according to one aspect of the present invention, which solves the above-mentioned problems, switches the direction of current flowing between a first input terminal and a second input terminal to which AC power is input, by switching operation of a switching element. The switching device includes a first switching element, a second switching element, a first input unit, a second input unit, a first change unit, and a second change unit. The first switching element and the second switching element are connected in series and connected between the first input terminal and the second input terminal. The first switching element and the second switching element switch their switching operation between a first operation and a second operation in response to the polarity of the AC power reversing between the first polarity and the second polarity. The first switching element and the second switching element switch their switching operation so as to perform mutually opposite operations. The first input unit inputs a first control signal corresponding to the first operation from a first signal source to a control terminal of the first switching element. The second input unit inputs a second control signal corresponding to the first operation from a second signal source to a control terminal of the second switching element. The first changer sets the first input unit to a low impedance state when the AC power has a first polarity and to a high impedance state when the AC power has a second polarity, the second changer sets the second input unit to a low impedance state when the AC power has the second polarity and to a high impedance state when the AC power has the first polarity.

[0007] According to the present invention, it is possible to suppress the influence of measures against the generation of common mode current due to switching operations on the control signal of the switching element.

[0008] FIG. 1 is a diagram showing the configuration of a switching device according to a first embodiment of the present invention. FIG. 2 is a diagram showing the operating states of a first change unit and a second change unit when AC power has a first polarity. FIG. 3 is a diagram showing the operating states of the first change unit and the second change unit when AC power has a second polarity. FIG. 4 is a diagram showing the configuration of a power conversion device according to an embodiment of the present invention. FIG. 5 is a diagram showing the configurations of a first control circuit and a second control circuit of a switching device according to a second embodiment of the present invention. FIG. 6 is a diagram showing the configurations of a third input unit and a fourth input unit of a switching device according to the second embodiment of the present invention. FIG. 7 is a diagram showing the configurations of a third input unit and a fourth input unit of a switching device according to a third embodiment of the present invention.

[0009] Hereinafter, an embodiment of the present invention and its modifications will be described with reference to the drawings. In the description of the drawings, the same parts are given the same reference numerals and the description thereof will be omitted.

[0010] (First Embodiment of Switching Device) Fig. 1 is a diagram showing the configuration of a switching device according to a first embodiment of the present invention. The switching device 1 of the first embodiment switches the direction of current flowing between a first input terminal 101 and a second input terminal 102, to which AC power is input from an AC power supply (not shown), by the switching operation of a switching element. The switching device 1 has a first switching element 104, a second switching element 105, and a control circuit 201 for controlling them.

[0011] In this embodiment, the first switching element 104 and the second switching element 105 are implemented as four-terminal packaged MOSFETs (Metal Oxide Semiconductor Field Effect Transistors). The first switching element 104 and the second switching element 105 are configured as a series circuit in which the source terminals are connected to each other to form a common source terminal 103. The four-terminal packaged MOSFET has a driver source terminal for a gate driver in addition to the three terminals of a normal MOSFET (drain, source, and gate). The driver source terminal is a terminal Kelvin-connected to the source terminal. The four-terminal packaged MOSFET can be configured as a transistor using a wide bandgap semiconductor with a large bandgap, such as SiC (silicon carbide) or GaN (gallium nitride).

[0012] The potential of the source terminal of a MOSFET fluctuates during switching operation due to the influence of package inductance present in the MOSFET's bonding wires, etc. For example, when a MOSFET is turned off, the voltage generated across the package inductance acts to maintain the potential of the gate terminal for a long time even after the input of a control signal to the MOSFET's gate terminal has ended. This action slows the decrease in the MOSFET's gate-source current, delaying the MOSFET's turn-off. When a MOSFET is turned on, the voltage generated across the package inductance slows the increase in the gate-source current of a MOSFET whose gate terminal receives a control signal, delaying the MOSFET's turn-on. The driver source terminal of a four-terminal packaged MOSFET is less affected by package inductance, and therefore its potential fluctuates less during switching operation than the source terminal. Using four-terminal packaged MOSFETs for the first switching element 104 and the second switching element 105 allows the first switching element 104 and the second switching element 105 to perform high-speed switching operations.

[0013] The first switching element 104 switches its switching operation between a first operation and a second operation under the control of the control circuit 201 in response to the polarity of the AC power input to the first input terminal 101 and the second input terminal 102 being reversed between a first polarity and a second polarity. The second switching element 105 switches its switching operation between the first operation and the second operation under the control of the control circuit 201 in response to the polarity of the AC power being reversed between the first polarity and the second polarity, so as to be the opposite operation to that of the first switching element 104. The first operation is a switching operation in which the on / off state of the switching element is switched at a frequency higher than the frequency of the AC power during a fixed period in which the polarity of the AC power is not reversed. The second operation is a switching operation in which the on / off state of the switching element is fixed during a fixed period in which the polarity of the AC power is fixed. In this embodiment, the first polarity of the AC power is defined as a polarity in which the first input terminal 101 is at a positive potential and the second input terminal 102 is at a negative potential, and the second polarity of the AC power is defined as a polarity in which the first input terminal 101 is at a negative potential and the second input terminal 102 is at a positive potential.

[0014] The control circuit 201 includes a first control circuit 202 for the first switching element 104 and a second control circuit 203 for the second switching element 105. The first control circuit 202 includes a first signal source 21 and a first input unit 22, and the second control circuit 203 includes a second signal source 31 and a second input unit 32. The first signal source 21 and the second signal source 31 are connected to a reference point 204. The first signal source 21 and the second signal source 31 output a first control signal and a second control signal, respectively. The first control signal and the second control signal are pulse signals with the potential of the reference point 204 as a reference potential. The first signal source 21 and the second signal source 31 output pulse signals at a frequency higher than the frequency of the AC power input to the first input terminal 101 and the second input terminal 102, respectively. The pulse period of the first control signal and the pulse period of the second control signal are synchronized.

[0015] The first signal source 21 is connected to the gate terminal, which is the control terminal, of the first switching element 104 via the first input unit 22 by a first wiring 205. The first wiring 205 is a transmission path for transmitting a pulse signal output by the first signal source 21 as a first control signal from the first input unit 22 to the gate terminal of the first switching element 104. The second signal source 31 is connected to the gate terminal, which is the control terminal of the second switching element 105 via the second input unit 32 by a second wiring 206. The second wiring 206 is a transmission path for transmitting a pulse signal output by the second signal source 31 as a second control signal from the second input unit 32 to the gate terminal of the second switching element 105. The reference point 204 is connected to the drive source terminal of the first switching element 104 via the first input unit 22 by a third wiring 207. The third wiring 207 is a path connecting the drive source terminal of the first switching element 104 to the reference point 204. The reference point 204 is connected to the drive source terminal of the second switching element 105 via the second input unit 32 by a fourth wiring 208. The fourth wiring 208 is a path connecting the drive source terminal of the first switching element 104 to the reference point 204. The first switching element 104 and the second switching element 105 are each Kelvin-connected by their drive source terminals to the reference point 204 to which the first signal source 21 and the second signal source 31 are connected.

[0016] 2 is a diagram showing the operating states of the first change unit of the first input unit 22 and the second change unit of the second input unit 32 when AC power input to the first input terminal 101 and the second input terminal 102 has a first polarity. The first input unit 22 has, as the first change unit, a first switch 221 and a second switch 222 that open and close in conjunction with each other. The first switch 221 opens and closes the first wiring 205. The second switch 222 opens and closes the third wiring 207. The second input unit 32 has, as the second change unit, a third switch 321 and a fourth switch 322 that open and close in conjunction with each other. The third switch 321 opens and closes the second wiring 206. The fourth switch 322 opens and closes the fourth wiring 208.

[0017] The first switch 221 and the second switch 222 are opened and closed in cooperation to switch the first input unit 22 between a low impedance state and a high impedance state in which the impedance is higher than the low impedance state. The third switch 321 and the fourth switch 322 are opened and closed in cooperation to switch the second input unit 32 between a low impedance state and a high impedance state.

[0018] The first switch 221 and the second switch 222 close the first wiring 205 and the third wiring 207 when AC power input to the first input terminal 101 and the second input terminal 102 has a first polarity. When the first switch 221 and the second switch 222 close the first wiring 205 and the third wiring 207, the first input unit 22 enters a low impedance state. When the AC power input to the first input terminal 101 and the second input terminal 102 has the first polarity, the third switch 321 and the fourth switch 322 open the second wiring 206 and the fourth wiring 208. When the third switch 321 and the fourth switch 322 open the second wiring 206 and the fourth wiring 208, the second input unit 32 enters a high impedance state in which the impedance is higher than the low impedance state.

[0019] 3 is a diagram showing the operating states of the first change unit of the first input unit 22 and the second change unit of the second input unit 32 when AC power input to the first input terminal 101 and the second input terminal 102 has a second polarity. The first switch 221 and the second switch 222 open the first wiring 205 and the third wiring 207 when AC power input to the first input terminal 101 and the second input terminal 102 has the second polarity. When the first switch 221 and the second switch 222 open the first wiring 205 and the third wiring 207, the first input unit 22 enters a high impedance state. The third switch 321 and the fourth switch 322 close the second wiring 206 and the fourth wiring 208 when AC power input to the first input terminal 101 and the second input terminal 102 has the second polarity. When the third switch 321 and the fourth switch 322 close the second wiring 206 and the fourth wiring 208, the second input section 32 is in a low impedance state.

[0020] When in a low impedance state, the first input unit 22 inputs a first control signal from the first signal source 21 to the gate terminal of the first switching element 104 via the first wiring 205, causing the first switching element 104 to perform a switching operation in a first operation corresponding to the first control signal. When in a low impedance state, the first input unit 22 connects the driver source terminal of the first switching element 104 to the reference point 204 via the third wiring 207, causing the first switching element 104 to perform a high-speed switching operation. When in a high impedance state, the first input unit 22 substantially cuts off the connection between the first switching element 104 and the first signal source 21 and the reference point 204. Due to this cutoff, when the first input unit 22 is in the high impedance state, the first control signal is not input to the gate terminal of the first switching element 104, and the first switching element 104 performs a switching operation in a second operation in which the on / off state is fixed.

[0021] When in a low impedance state, the second input unit 32 inputs the second control signal from the second signal source 31 to the gate terminal of the second switching element 105 via the second wiring 206, causing the second switching element 105 to perform a switching operation in a first operation corresponding to the second control signal. When in a low impedance state, the second input unit 32 connects the driver source terminal of the second switching element 105 to the reference point 204 via the fourth wiring 205, causing the second switching element 105 to perform a high-speed switching operation. When in a high impedance state, the second input unit 32 essentially cuts off the connection between the second switching element 105 and the second signal source 31 and the reference point 204. Due to this cutoff, when the second input unit 32 is in a high impedance state, the second control signal is not input to the gate terminal of the second switching element 105, and the second switching element 105 performs a switching operation in a second operation in which the on / off state is fixed.

[0022] In the switching device 1 of this embodiment, when AC power input to the first input terminal 101 and the second input terminal 102 has a first polarity, the first input section 22 is in a low impedance state and the second input section 32 is in a high impedance state. At this time, the first switching element 104 is enabled for high-speed switching due to connection of the driver source terminal to the reference point 204, and performs a first switching operation in response to the input of a first control signal. The second switching element 105 is disconnected from the second signal source 31 and the reference point 204 and performs a second switching operation in which its on / off state is fixed. Due to this switching operation, current flows between the first input terminal 101 and the second input terminal 102 from the first input terminal 101 at a positive potential to the second input terminal 102 at a negative potential. Noise current generated by the switching operation of the first switching element 104 does not flow through the second wiring 206 and the fourth wiring 208, which are substantially disconnected by the second input section 32 in the high impedance state. Therefore, the noise current is prevented from flowing in opposite directions through the first wiring 205 or the third wiring 207 and the second wiring 206 or the fourth wiring 208 to become a common mode current.

[0023] When AC power input to the first input terminal 101 and the second input terminal 102 has a second polarity, the first input section 22 enters a high impedance state and the second input section 32 enters a low impedance state. At this time, the first switching element 104 is disconnected from the first signal source 21 and the reference point 204 and performs a second switching operation with a fixed on / off state. The second switching element 105 enters a state where high-speed switching is possible due to the connection of the driver source terminal to the reference point 204, and performs a first switching operation in response to the input of a second control signal. Due to this switching operation, current flows between the first input terminal 101 and the second input terminal 102 from the second input terminal 102 at a positive potential to the first input terminal 101 at a negative potential. Noise current generated by the switching of the second switching element 105 does not flow through the first wiring 205 and the third wiring 207, which are substantially disconnected by the first input section 22 in the high impedance state. This prevents the noise current from becoming a common-mode current.

[0024] In this embodiment, the first or second control signal is input to the control terminal of the switching element that performs the first operation, either the first switching element 104 or the second switching element 105, by the input part in the low impedance state, either the first input part 22 or the second input part 32. Therefore, the path of the common mode current is substantially blocked without affecting the input of the control signal to the control terminal of the switching element that performs the first operation, and it is possible to prevent measures against the generation of common mode current due to switching operation from affecting the control signal.

[0025] In this embodiment, the switching operation of the first switching element 104 and the second switching element 105 is switched every time the polarity of the AC power input to the first input terminal 101 and the second input terminal 102 is reversed. This switching switches the switching element that performs the switching operation in the first operation and the switching element that performs the switching operation in the second operation. This switching causes the series circuit of the first switching element 104 and the second switching element 105 to function as a bidirectional switch that switches the direction of the current flowing between the first input terminal 101 and the second input terminal 102 every time the polarity of the AC power is reversed. In this bidirectional switch, measures to prevent the generation of common-mode current due to switching of the first switching element 104 and the second switching element 105 can be suppressed from affecting the control signal.

[0026] Between the gate terminals of the first switching element 104 and the second switching element 105, there is a path that passes through the first wiring 205, the first signal source 21, the reference point 204, the second signal source 31, and the second wiring 206. Between the driver source terminals of the first switching element 104 and the second switching element 105, there is also a path that passes through the third wiring 207, the reference point 204, and the fourth wiring 208. A noise current generated by the switching operation of the first switching element 104 or the second switching element 105 flows into the wiring with the lower impedance of the two paths described above. If the path into which the noise current has flowed has an impedance state that allows current to flow, the direction of the noise current is opposite on the first switching element 104 side and the second switching element 105 side across the reference point 204, and therefore a common mode current is generated. The change unit on one of the switching elements corresponding to the polarity of the AC power input between the first input terminal 101 and the second input terminal 102 opens both switches on the two paths, putting the input unit corresponding to the polarity of the AC power into a high impedance state and blocking the noise current. Even when MOSFETs in a four-terminal package are used for the first switching element 104 and the second switching element 105, the path of the common mode current can be substantially blocked without affecting the control signal input to the gate terminal, which is the control terminal of the MOSFET performing the first operation. This blocking can prevent measures to prevent the generation of common mode current due to switching operation from affecting the control signal.

[0027] The noise current can be blocked on the first switching element 104 side and the second switching element 105 side by, for example, arranging a common mode choke (CMC) coil (not shown) on the first wiring 205 to the fourth wiring 208. Alternatively, the noise current can be blocked by arranging an isolator (not shown) on the first wiring 205 to the fourth wiring 208 instead of a CMC coil to provide a physical insulating portion midway between the first wiring 205 to the fourth wiring 208.

[0028] However, when the first switching element 104 and the second switching element 105 are switched at high speed, the ringing frequency band of the noise current becomes high. Therefore, when a CMC coil is provided, the self-resonant frequency of the CMC coil must be set to be equal to or higher than the ringing frequency band so that the CMC coil exhibits inductive characteristics and functions as an inductor even in the ringing frequency band. Increasing the self-resonant frequency of the CMC coil requires increasing the distance between the coil lines to reduce the stray capacitance between the lines, which inevitably increases the size of the switching device 1 due to the larger CMC coil.

[0029] When an isolator is used, the resolution of photoelectric conversion limits the frequency of the electrical signal that the isolator can reproduce. If the ringing frequency band of the noise signal exceeds the limit frequency that the isolator can reproduce, using the isolator reduces the controllability of the switching operation of the switching device 1.

[0030] The switching device 1 of this embodiment can deal with the generation of common mode currents by using a method that can suppress the effect on the control signal of the switching element, without using a CMC coil or an isolator, which would increase the size of the device or reduce the controllability of the switching operation.

[0031] (Embodiment of Power Conversion Device Using Switching Device) Fig. 4 is a diagram showing the configuration of a power conversion device according to one embodiment of the present invention. Fig. 4 shows, as an example of the power conversion device, an inverter device that generates high-frequency AC power from AC power of an AC power supply. The power conversion device may be a device other than an inverter device, as long as it is necessary to switch the direction of current flowing between a first input terminal and a second input terminal to which AC power is input in response to a reversal of the polarity of the AC power.

[0032] The switching device 1 of the first embodiment can be used as a bidirectional switch in the inverter device 2 of Fig. 4, for example. The inverter device 2 has the switching device 1 of the first embodiment, a first choke inductor 12, a second choke inductor 13, and a first LC resonant circuit 14 and a second LC resonant circuit 15. The first choke inductor 12 and the second choke inductor 13 have the same inductance value, and the first LC resonant circuit 14 and the second LC resonant circuit 15 have the same values ​​for the coils and capacitors that make up each circuit.

[0033] The first switching element 104 and the second switching element 105 of the switching device 1 each have a shunt capacitor 106 connected in parallel between the drain terminal and the source terminal. The shunt capacitors 106 of the first switching element 104 and the second switching element 105 have the same capacitance value. The first choke inductor 12 and the second choke inductor 13 are connected to the first input terminal 101 and the second input terminal 102 of the switching device 1, respectively. AC power from the AC power supply 11 passes through the first choke inductor 12 or the second choke inductor 13 and is input between the first input terminal 101 and the second input terminal 102. The first LC resonant circuit 14 and the second LC resonant circuit 15 are connected to the first input terminal 101 and the second input terminal 102, respectively, and are further connected to the supply target 2.

[0034] In the inverter device 2 of this embodiment, a high-frequency resonant current is generated in the first LC resonant circuit 14 and the second LC resonant circuit 15 by the switching operation of the first switching element 104 and the second switching element 105, and high-frequency AC current is generated from the AC power of the AC power supply 11. The high-frequency AC power generated by the inverter device 2 is supplied to the supply target 3. The switching device 1 causes the first switching element 104 or the second switching element 105, which performs a switching operation in the first operation, to perform a switching operation at the resonant frequency of the first LC resonant circuit 14 and the second LC resonant circuit 15. By having the switching device 1 perform this operation, the inverter device 2 of this embodiment having the above-mentioned configuration can form a class E circuit without using a rectifier circuit and generate high-frequency AC current from the AC power of the AC power supply 11 with high efficiency.

[0035] In this embodiment, the choke inductor through which AC power input between the first input terminal 101 and the second input terminal 102 passes includes a first choke inductor 12 on the first input terminal 101 side and a second choke inductor 13 on the second input terminal 102 side. Also, in this embodiment, the LC resonant circuit connected to the supply target 3 includes a first LC resonant circuit 14 on the first input terminal 101 side and a second LC resonant circuit 15 on the second input terminal 102 side. Of these, either the first choke inductor 12 and first LC resonant circuit 14 on the first input terminal 101 side or the second choke inductor 13 and second LC resonant circuit 15 on the second input terminal 102 side may be omitted. In this embodiment, a choke inductor and an LC resonant circuit each composed of elements of the same value are provided on the first input terminal 101 side and the second input terminal 102 side, resulting in a circuit configuration in which the positive and negative polarity sides of the inverter device 2 are symmetrical. By providing the inverter device 2 with such a symmetrical circuit configuration, it is possible to reduce electromagnetic noise in the entire circuit of the inverter device 2.

[0036] In the inverter device 2 of this embodiment, in the switching device 1 used as a bidirectional switch, it is possible to take measures against the occurrence of common mode current by using a method that can suppress the influence on the control signal of the switching element without using a CMC coil or an isolator.

[0037] (Second embodiment of switching device) Figure 5 is a diagram showing the configuration of a first control circuit 202 and a second control circuit 203 of a switching device according to a second embodiment of the present invention. The configuration of parts of the switching device of this embodiment that are not shown in Figure 5 are the same as the configuration of the switching device 1 of the first embodiment shown in Figure 1.

[0038] 5 , in the switching device according to the second embodiment, a third input unit 23 is added to the first control circuit 202 of the switching device 1 according to the first embodiment, and a fourth input unit 33 is added to the second control circuit 203. The third input unit 23 is arranged closer to the first switching element 104 than the first input unit 22 on the first wiring 205 and the third wiring 207. The fourth input unit 33 is arranged closer to the second switching element 105 than the second drive unit 32 on the second wiring 206 and the fourth wiring 208.

[0039] The third input unit 23 inputs a third control signal corresponding to the second operation to the gate terminal of the first switching element 104 without passing through the first input unit 22 when the AC power of the AC power supply 11 input between the first input terminal 101 and the second input terminal 102 has the second polarity. The fourth input unit 33 inputs a fourth control signal corresponding to the second operation to the gate terminal of the second switching element 105 without passing through the second input unit 32 when the AC power of the AC power supply 11 input between the first input terminal 101 and the second input terminal 102 has the first polarity.

[0040] FIG. 6 is a diagram showing the configurations of the third input unit 23 and the fourth input unit 33. The third input unit 23 has a third input terminal 24 provided as a first connection point on the first wiring 205, and a fifth switch 26 provided between the third input terminal 24 and a power supply 25. In this embodiment, the third input unit 23 further includes the power supply 25 and an operational amplifier 27, which uses the power supply 25 as a positive power supply and the potential of the reference point 204 appearing on the third wiring 207 as a negative power supply. The operational amplifier 27 amplifies a control signal transmitted to the gate terminal of the first switching element 104 via the first wiring 205. The power supply 25 and the operational amplifier 27 may be provided outside the third input unit 23. The fifth switch 26 is turned on when the AC power of the AC power supply 11 input between the first input terminal 101 and the second input terminal 102 has a first polarity, and is turned off when the AC power of the AC power supply 11 has a second polarity. When the fifth switch 26 is turned on, it connects the third input terminal 24 of the third input unit 23 to the power supply 25, and causes the above-mentioned third control signal to appear at the third input terminal 24 due to the potential of the power supply 25. When the fifth switch 26 is turned off, it disconnects the third input terminal 24 of the third input unit 23 from the power supply 25, and stops the appearance of the third control signal at the third input terminal 24.

[0041] The fourth input unit 33 has a fourth input terminal 34 provided as a second connection point on the second wiring 206, and a sixth switch 36 provided between the fourth input terminal 34 and a power supply 35. In this embodiment, the fourth input unit 33 further includes the power supply 35 and an operational amplifier 37 that uses the power supply 35 as a positive power supply and the potential of the reference point 204 appearing on the fourth wiring 208 as a negative power supply. The operational amplifier 37 amplifies a control signal transmitted to the gate terminal of the second switching element 105 via the second wiring 206. The power supply 35 and the operational amplifier 37 may be provided outside the fourth input unit 33. The sixth switch 36 is turned on when the AC power of the AC power supply 11 input between the first input terminal 101 and the second input terminal 102 has the second polarity, and is turned off when the AC power of the AC power supply 11 has the first polarity. When the sixth switch 36 is turned on, it connects the fourth input terminal 34 of the fourth input unit 33 to the power supply 35, and causes the aforementioned fourth control signal to appear at the fourth input terminal 34 due to the potential of the power supply 35. When the sixth switch 36 is turned off, it disconnects the fourth input terminal 34 of the fourth input unit 33 from the power supply 35, and stops the appearance of the fourth control signal at the fourth input terminal 34.

[0042] The first switch 221 and the second switch 222 of the first input unit 22 and the third switch 321 and the fourth switch 322 of the second input unit 32 are all turned off in FIG. 6 , but they are turned on or off in accordance with the polarity of the AC power of the AC power supply 11, as in the first embodiment.

[0043] The operational amplifier 27 amplifies the first control signal from the first signal source 21 while the fifth switch 26 is off, and amplifies the third control signal appearing at the third input terminal 24 in place of the first control signal while the fifth switch 26 is on. The operational amplifier 37 amplifies the first control signal from the second signal source 31 while the sixth switch 36 is off, and amplifies the fourth control signal appearing at the fourth input terminal 34 in place of the first control signal while the sixth switch 36 is on.

[0044] Even in the switching device of the second embodiment having the first control circuit 202 and the second control circuit 203 configured as described above, it is possible to take measures against the occurrence of common mode current by using a method that can suppress the influence on the control signal of the switching element without using a CMC coil or an isolator.

[0045] In this embodiment, the third input unit 23 or the fourth input unit 33 inputs the third control signal or the fourth control signal to the gate terminal of the first switching element 104 or the second switching element 105 that performs switching operation in the second operation, without passing through the first input unit 22 or the second input unit 32. The first input unit 22 or the second input unit 32, which is in a low impedance state, inputs the first control signal or the second control signal to the gate terminal of the second switching element 105 or the first switching element 104 that performs switching operation in the first operation. In this embodiment, by controlling the switching device to perform the above-mentioned operation, it is possible to execute the control method for the switching device according to the embodiment of the present invention. In this embodiment, even if the first input unit 22 or the second input unit 32 is in a high impedance state, the corresponding first switching element 104 or the second switching element 105 can be switched in the second operation by inputting the third control signal or the fourth control signal.

[0046] The switching device of the second embodiment can be used as a bidirectional switch in the inverter device 2 of Fig. 4 in place of the switching device 1 of the first embodiment. Even in an inverter device using the switching device of the second embodiment, in the switching device used as a bidirectional switch, it is possible to take measures against the occurrence of common mode current by a method that can suppress the influence on the control signal of the switching element without using a CMC coil or an isolator.

[0047] (Third Embodiment of Switching Device) FIG. 7 is a diagram showing the configuration of a first control circuit 202 and a second control circuit 203 of a switching device according to a third embodiment of the present invention. The configuration of parts of the switching device according to this embodiment that are not shown in FIG. 7 are the same as the configuration of the switching device 1 according to the first embodiment shown in FIG. 1. In the switching device according to this embodiment, a first stabilizing load 28 is added to the third input unit 23 of the switching device according to the second embodiment, and a second stabilizing load 38 is added to the fourth input unit 33. The first stabilizing load 28 is connected to the third input terminal 24 on the first wiring 205 and the third wiring 207. The first stabilizing load 28 stabilizes the potential of the third input terminal 24 connected to the power supply 25 relative to the potential of the reference point 204 to which the third wiring 207 is connected while the fifth switch 26 of the third input unit 23 is on. The second stabilizing load 38 is connected to the fourth input terminal 34 on the second wiring 206 and the fourth wiring 208. The second stabilizing load 38 stabilizes the potential of the fourth input terminal 34 connected to the power supply 35 relative to the potential of the reference point 204 to which the fourth wiring 208 is connected while the sixth switch 36 of the fourth input section 33 is on.

[0048] In this embodiment, the first stabilizing load 28 and the second stabilizing load 38 prevent the third control signal and the fourth control signal appearing at the third input terminal 24 while the fifth switch 26 is on and the fourth input terminal 34 while the sixth switch 36 is on from becoming unstable. Since the potentials of the third control signal and the fourth control signal are stabilized, it is possible to stabilize the switching operation by the second operation of the first switching element 104, whose gate terminal receives the third control signal, and the second switching element 105, whose gate terminal receives the fourth control signal.

[0049] The switching device of the third embodiment can be used as a bidirectional switch in the inverter device 2 of Fig. 4 in place of the switching device 1 of the first embodiment. Even in an inverter device using the switching device of the third embodiment, in the switching device used as a bidirectional switch, it is possible to take measures against the occurrence of common mode current by a method that can suppress the influence on the control signal of the switching element without using a CMC coil or an isolator.

[0050] The above-described embodiment is merely an example of the present invention, and therefore the present invention is not limited to the above-described embodiment, and various modifications can be made to the design and other aspects of the present invention without departing from the technical concept of the present invention.

[0051] 1 Switching device, 2 Inverter device (power conversion device), 3 Supply target, 11 AC power supply, 12 First choke inductor (choke inductor), 13 Second choke inductor (choke inductor), 14 First LC resonant circuit (LC resonant circuit), 15 Second LC resonant circuit (LC resonant circuit), 21 First signal source, 22 First input section, 23 Third input section, 24 Third input terminal (first connection point), 25, 35 Power supply, 26 Fifth switch, 28 First stabilizing load, 31 Second signal source, 32 Second input section, 33 Fourth input section, 34 Fourth input terminal (second connection point), 36 Sixth switch, 38 Second stabilizing load, 101 First input terminal, 102 Second input terminal, 104 First switching element (switching element), 105 Second switching element (switching element), 106 Shunt capacitor, 204 Reference point, 205 First wiring (transmission path of first control signal), 206 Second wiring (transmission path of second control signal), 207 third wiring (path connecting the driver source terminal of the first switching element to the reference point), 208 fourth wiring (path connecting the driver source terminal of the second switching element to the reference point), 221 first switch (first change unit), 222 second switch (first change unit), 321 third switch (second change unit), 322 fourth switch (second change unit).

Claims

A switching device that switches a direction of a current flowing between a first input terminal and a second input terminal to which AC power is input by a switching operation of a switching element, a first switching element connected between the first input terminal and the second input terminal, and switching a switching operation between a first operation and a second operation in response to a polarity of the AC power being inverted between a first polarity and a second polarity; a second switching element connected between the first input terminal and the second input terminal and connected in series with the first switching element, the second switching element switching its switching operation between the first operation and the second operation in response to a reversal of the polarity of the AC power, so as to perform an operation opposite to that of the first switching element; a first input unit that inputs a first control signal corresponding to the first operation from a first signal source to a control terminal of the first switching element; a second input unit that inputs a second control signal corresponding to the first operation from a second signal source to a control terminal of the second switching element; a first change unit that sets the first input unit to a low impedance state when the AC power has the first polarity and sets the first input unit to a high impedance state having an impedance higher than that of the low impedance state when the AC power has the second polarity; a second change unit that sets the second input unit to the low impedance state when the AC power has the second polarity and sets the second input unit to the high impedance state when the AC power has the first polarity; A switching device comprising:

2. The switching device according to claim 1, wherein the first operation is a switching operation in which an on / off state of the switching element is switched at a frequency higher than a frequency of the AC power during a fixed period in which the polarity of the AC power is not reversed, and the second operation is a switching operation in which the on / off state of the switching element is fixed during the fixed period.

3. The switching device according to claim 1, wherein each of the first switching element and the second switching element is a MOSFET (Metal Oxide Semiconductor Field Effect Transistor) in a four-terminal package having a driver source terminal Kelvin-connected to a reference point to which the first signal source and the second signal source are connected, the driver source terminal of the first switching element being connected to the reference point via the first input section, and the driver source terminal of the second switching element being connected to the reference point via the second input section. 　 the first change unit includes a first switch that opens and closes a transmission path of the first control signal from the first input unit to the control terminal of the first switching element, and a second switch that opens and closes a path connecting the driver source terminal of the first switching element to the reference point; the first change unit switches the impedance of the first input unit between the high impedance state and the low impedance state by opening and closing the first switch and the second switch in conjunction with each other; the second change unit includes a third switch that opens and closes the transmission path of the second control signal from the second input unit to the control terminal of the second switching element, and a fourth switch that opens and closes the path connecting the driver source terminal of the second switching element to the reference point in conjunction with the third switch; and the second change unit switches the impedance of the second input unit between the high impedance state and the low impedance state by opening and closing the third switch and the fourth switch in conjunction with each other.

5. The switching device according to claim 1, further comprising: a third input unit that, when the AC power has the second polarity, inputs a third control signal corresponding to the second operation to a control terminal of the first switching element without passing through the first input unit; and a fourth input unit that, when the AC power has the first polarity, inputs a fourth control signal corresponding to the second operation to a control terminal of the second switching element without passing through the second input unit.

6. The switching device according to claim 5, wherein the third input section includes a fifth switch that connects the third input section to a power supply when the AC power has the second polarity and that disconnects the third input section from the power supply when the AC power has the first polarity, and the fourth input section includes a sixth switch that connects the fourth input section to a power supply when the AC power has the first polarity and that disconnects the fourth input section from the power supply when the AC power has the second polarity.

7. The switching device according to claim 6, wherein the third input section has a first stabilizing load connected to a first connection point of the third input section, which is connected to a power supply by the fifth switch, and stabilizes the potential of the first connection point relative to the potential of a reference point to which the first signal source and the second signal source are connected; and the fourth input section has a second stabilizing load connected to a second connection point of the fourth input section, which is connected to a power supply by the sixth switch, and stabilizes the potential of the second connection point relative to the potential of the reference point.

8. A power conversion device comprising the switching device according to claim 1, wherein the power conversion device generates high-frequency AC current from AC power input between a first input terminal and a second input terminal, through which the switching device switches the direction of current flow, by switching operations of a first switching element and a second switching element of the switching device.

9. The power conversion device according to claim 8, further comprising: a choke inductor connected to at least one of the first input terminal and the second input terminal and through which the AC power passes; an LC resonant circuit connected between the one of the first input terminal and the second input terminal and an object to which the high-frequency AC current is supplied; and a shunt capacitor connected in parallel with the switching device.

10. The power conversion device according to claim 9, wherein the choke inductor includes a first choke inductor and a second choke inductor connected to the first input terminal and the second input terminal, respectively, and the LC resonant circuit includes a first LC resonant circuit and a second LC resonant circuit connected to the first input terminal and the second input terminal, respectively, and the supply target. 　 A control method for a switching device having a series circuit of a first switching element and a second switching element connected between a first input terminal and a second input terminal to which AC power is input, wherein the first switching element and the second switching element each switch a switching operation between a first operation and a second operation in response to a polarity of the AC power being reversed between a first polarity and a second polarity, thereby switching a direction of a current flowing between the first input terminal and the second input terminal, when the AC power has the first polarity, a first input unit that inputs a first control signal corresponding to the first operation to a control terminal of the first switching element is set to a high impedance state, and a second input unit that inputs a second control signal corresponding to the first operation to a control terminal of the second switching element is set to a low impedance state having an impedance lower than the high impedance state, so that a third control signal corresponding to the second operation is input to the control terminal of the first switching element without passing through the first input unit; when the AC power has the second polarity, the first input unit is set to the low impedance state and the second input unit is set to the high impedance state, and a fourth control signal corresponding to the second operation is input to the control terminal of the second switching element without passing through the second input unit; A method for controlling a switching device.

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