JP2009081969A - Bidirectional switch - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a bidirectional switch which reduces a conduction loss and a switching loss, and is suitable for high-speed switching. <P>SOLUTION: A bidirectional switching circuit includes a semiconductor switching element such as for example, an IGBT or a GTO with a self-arc-extinguishing capacity, as a nonlinear switching element, and a semiconductor switching element such as for example, a MOSFET or a JFET with the self-arc-extinguishing capacity, as a linear switching element. The nonlinear switching element is turned on or off by a predetermined signal. In the former switching element, wherein a voltage produced at ON time and its flowing current have a nonlinear relation, and the element has one current flowing direction when the linear switching element is turned on or off by a predetermined signal, and in the latter switching element, a voltage produced at ON time and its flowing current have a linear relation. In the bidirectional switch, two sets of parallel circuits are connected in series, wherein the nonlinear switching element and the linear element are connected in antiparallel so that current flowing control directions of both switching elements may become reverse each other. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a bidirectional switch, and more particularly to a bidirectional switch using a semiconductor switching device suitable for application to a static power converter.

Conventionally, a power converter using a bidirectional switch that cuts off or conducts current flowing in both directions is known (see, for example, Patent Document 1). As shown in FIG. 3, the bidirectional switch used in this power conversion apparatus connects two IGBTs (Q1, Q2) in anti-series as semiconductor switching devices, respectively, and further adds 2 to each IGBT (Q1, Q2). Two diodes D1 and D2 are connected in antiparallel. That is, the bidirectional switch shown in FIG. 3A connects the emitters of the two IGBTs (Q1, Q2) to each other, and connects the emitters and collectors of the IGBTs (Q1, Q2) to the anodes of the diodes D1, D2, respectively. The cathode is connected in antiparallel. Here, for convenience of explanation, the collectors of the IGBTs (Q1, Q2) are assumed to be terminals a, b of the bidirectional switch, respectively.
Alternatively, as shown in FIG. 3B, this bidirectional switch connects the collectors of two IGBTs (Q1, Q2) to each other, and diodes D1, D2 are connected to the emitter and collector of the IGBT (Q1, Q2), respectively. The anode and cathode are connected in antiparallel.
The bidirectional switch shown in FIG. 3A configured as described above applies a control signal from a gate control circuit (not shown) to the gate of the IGBT (Q1) when current flows from the terminal a to the terminal b. ) Then, the current reaches the terminal b from the terminal a through the IGBT (Q1) and the diode D2. Conversely, when a current flows from terminal b to terminal a, a control signal is applied to the gate of IGBT (Q2) from gate control (not shown) to turn on IGBT (Q2). Then, the current reaches the terminal a from the terminal b through the IGBT (Q2) and the diode D1. Similarly, the bidirectional switch shown in FIG. 3B similarly operates as described above.

The bidirectional switch described above can also be configured using a semiconductor switching element such as GTO in addition to the IGBT, and is used in an AC power adjustment device, a matrix converter, and the like.
By the way, as shown in FIG. 4, the IGBT and GTO are in a non-linear relationship in which the relationship between the voltage generated at both ends of the device and the flowing current is not proportional (hereinafter, a semiconductor switching device having such characteristics is referred to as a non-linear switching device). Called). For example, a non-linear switching element has a characteristic that a voltage drop of about 0.7 V occurs at both ends even when a slight current flows. For IGBTs and GTOs having such characteristics, the MOSFET has a linear relationship in which the relationship between the voltage generated at both ends of the element and the flowing current is proportional as shown in FIG. 4 (hereinafter, such characteristics are provided). A semiconductor switching element is called a linear switching element).
Moreover, the relationship between the operating frequency (switching frequency) of these switching elements, the applied voltage of the switching elements, and the current that can flow is schematically shown in FIG. That is, although the MOSFET is not suitable for high voltage and large current applications, the operating frequency can be increased. On the other hand, IGBT and GTO cannot be made higher in operating frequency than MOSFET, but it can be seen that they are suitable for high voltage and large current applications.
Japanese Patent Laid-Open No. 11-252992

The conduction loss in the bidirectional switch described above is the product of the current flowing through the bidirectional switch and the voltage generated at both ends thereof. Therefore, the nonlinear switching element in which a relatively high voltage is generated even with a small current has a problem of large conduction loss at a small current.
IGBTs and GTOs are suitable for high-voltage and large-current applications as shown in FIG. 5 as compared to MOSFETs. However, as described above, the switching loss is large and a higher operating frequency is set. There is also a problem that it is not suitable for use.
Therefore, power converters using nonlinear switching elements such as IGBTs and GTOs are inefficient due to high losses at high frequencies and high frequency operations, and cooling components are increased in size, increased in equipment weight, and increased in cost. I couldn't deny that I was invited.
The bidirectional switch of the present invention has been made in order to solve the above-described problems, and an object thereof is a bidirectional switch suitable for reducing conduction loss and switching loss and increasing switching speed. Is to provide.

In order to achieve the above-described object, the bidirectional switch of the present invention is turned on or off by a predetermined signal, and the relationship between the voltage generated at both ends of the switch and the flowing current is not proportional to each other and is in a non-linear relationship. For example, a semiconductor switching element such as IGBT or GTO having a self-extinguishing capability as a nonlinear switching element having a flow direction, a voltage generated at both ends when turned on by a predetermined signal, and a current flowing therethrough A bidirectional switching circuit comprising a semiconductor switching element such as a MOSFET or JFET having a self-extinguishing capability as a linear switching element in a linear relationship in which the relationship of
This bidirectional switch is provided by connecting two sets of anti-parallel circuits connected in series so that the flow directions of the nonlinear switching element and the linear element are opposite to each other.
The bidirectional switch described above includes a body diode of a linear switching element (MOSFET or JFET) connected in reverse parallel to the other nonlinear switching element when one nonlinear switching element (IGBT or GTO) is in a flowing state. Current through. Therefore, the number of parts does not increase.
The bidirectional switch performs switching by the linear switching element when a voltage generated at both ends of the bidirectional switch is equal to or lower than a predetermined voltage value, while a voltage generated at both ends of the bidirectional switch has a predetermined voltage value. When exceeding, it is characterized by including a switching control unit that performs switching by the nonlinear switching element.

Therefore, the bidirectional switch described above uses a linear switching element (MOSFET or JFET) with low conduction loss when the voltage generated across the switch is equal to or lower than a predetermined voltage, while the voltage exceeds a predetermined voltage value. By using a non-linear switching element (IGBT or GTO) with low conduction loss, on / off control of the bidirectional switch can be performed to reduce conduction loss and switching loss.
Alternatively, the bidirectional switch performs switching by the linear switching element when the current flowing through the bidirectional switch is less than or equal to a predetermined current value, while the current flowing through the bidirectional switch exceeds a predetermined current value. The switching control part which switches by the said nonlinear switching element is provided.
Therefore, the above-described bidirectional switch uses a linear switching element (MOSFET or JFET) with a small conduction loss when the current flowing through the switch is small, while a nonlinear switching element (IGBT or GTO with a small conduction loss when the current flows is large. ) Can be used to turn on and off the bidirectional switch to reduce conduction loss and switching loss.
Further, the bidirectional switch configured as another aspect is switched by the linear switching element when a voltage generated at both ends of the bidirectional switch is a predetermined voltage value or less or a flowing current is a predetermined current value or less. A switching control unit that performs switching by the nonlinear switching element when a voltage generated at both ends of the bidirectional switch exceeds a predetermined voltage value and when a flowing current exceeds a predetermined current value. It is characterized by that.

Preferably, the switching control unit preferably provides a period during which both the nonlinear switching element and the linear switching element constituting the parallel circuit are simultaneously turned on or off.
More preferably, the switching control unit preferably turns on the linear switching element during a period in which a body diode of the linear switching element is conductive.
The bidirectional switch described above can further reduce the voltage drop during current flow, and effectively suppress conduction loss and switching loss.

As described above, according to the bidirectional switch of the present invention, when the voltage generated at both ends of the bidirectional switch is equal to or lower than a predetermined voltage, a linear switching element (MOSFET or JFET) with low conduction loss is used, while the voltage is When the voltage exceeds a predetermined voltage value, the on / off control of the bidirectional switch is performed using a non-linear switching element (IGBT or GTO) having a small conduction loss, so that the conduction loss and the switching loss can be reduced.
Also, the bidirectional switch of the present invention performs on / off control with a linear switching element that has low conduction loss when the current is small when the current flowing through the bidirectional switch is small. On the other hand, when the current is large, the conduction loss occurs when the current is large. Since on / off control is performed with a small number of nonlinear switching elements, conduction loss and switching loss can be reduced.
In addition, the bidirectional switch of the present invention uses a linear switching element (MOSFET or JFET) whose operating speed is higher than that of a nonlinear switching element (GTO or IGBT), so that the switching speed can be increased particularly in a low current region. It is.
Furthermore, the bidirectional switch according to the present invention reduces conduction loss and switching loss because, in a parallel circuit in which a non-linear switching element and a linear switching element are connected in anti-parallel, these switching elements are simultaneously turned on when current flows. be able to.

Alternatively, the bidirectional switch of the present invention can reduce conduction loss and switching loss because the linear switching element is turned on while the body diode of the linear switching element (MOSFET) is conductive.
Therefore, for example, an AC power adjustment device using the bidirectional switch of the present invention can achieve high efficiency, and in turn, a cooling component for cooling the bidirectional switch can be reduced in size, weight, and cost. In addition, there are significant practical effects such as higher performance associated with higher switching frequency.

Hereinafter, a bidirectional switch according to an embodiment of the present invention will be described with reference to the accompanying drawings. 1 and 2 are examples of embodiments for carrying out the present invention, and the present invention is not limited to these drawings.
FIG. 1 is a principle circuit diagram of an AC power adjusting device to which a bidirectional switch of the present invention is applied. The bidirectional switch shown in this figure uses an IGBT as a nonlinear switching element and a MOSFET as a linear switching element.
In FIG. 1, reference numeral 1 denotes an AC power supply. One end (terminal a) of the bidirectional switch SW <b> 1 is connected to one end of the AC power supply 1. As shown in FIG. 2A, the bidirectional switch SW1 has an antiparallel circuit formed by connecting MOSFETs (Q10, Q11) in antiparallel to each of the IGBTs (Q1, Q2). That is, the drain and source of MOSFET (Q10, Q11) are connected to the collector and emitter of IGBT (Q1, Q2), respectively. Two sets of these antiparallel circuits are connected in series to form a bidirectional switch. Incidentally, the MOSFETs (Q10, Q11) include body diodes BD10, BD11, respectively.
One end (terminal c) of another bidirectional switch SW2 is connected to the other end (terminal b) of this bidirectional switch. This bidirectional switch SW2 has the same configuration as the above-described bidirectional switch SW1. The other end (terminal d) of the bidirectional switch SW2 is connected to the other end of the AC power source 1.

One end of the reactor L is connected to the connection point of the two bidirectional switches SW1 and SW2, and the other end of the reactor L is between the terminal d of the bidirectional switch SW2 and the connection point of the AC power source 1. Capacitor C is connected in parallel to form a low pass filter. This low-pass filter plays a role of suppressing higher harmonic components than the switching frequency of the bidirectional switches SW1 and SW2. The alternating current whose harmonic components are suppressed by the low-pass filter is supplied to a load _RL connected in parallel with the capacitor C.
This AC power adjustment circuit is controlled by the switching control unit 20 to turn on and off the two bidirectional switches SW1 and SW2, and generates an AC voltage having an amplitude different from the amplitude of the AC power supply 1 and supplies the AC voltage to the load _RL. , AC power can be adjusted. The switching control unit 20 is supplied with a detection value from a sensor (not shown in FIG. 1) that detects a voltage generated in each bidirectional switch and / or a current flowing through these switches.
Schematically, the operation of the AC power adjustment device configured as described above will be described in more detail. In FIG. 1, when the terminal a side where the AC power source 1 and the bidirectional switch SW1 are connected is positive (plus), and the terminal d side of the AC power source 1 and the bidirectional switch SW2 is negative (minus), the switching control unit 20 (not shown) Turn on IGBT (Q1). Then, a current flows through a path of AC power source 1 → IGBT (Q1) → Body diode (BD11) of MOSFET (Q11) → reactor L → capacitor C and load R _L → AC power source 1.

Then, the switching control unit 20 turns on the IGBT (Q4) when turning off the IGBT (Q1). Then, current flows through the path of reactor L → capacitor C and load R _L → IGBT (Q4) → MOSFET (Q20) body diode (BD20) → reactor L.
Similarly, when the polarity of the AC power supply 1 is reversed, the switching control unit 20 controls the on / off of the IGBT (Q2) and the IGBT (Q3) as described above, so that both ends of the load R _L are controlled. Adjust the voltage.
Incidentally, the operation of this circuit is a circuit that is well known as an AC power adjusting device configured by using a diode instead of a MOSFET.
Thus, the bidirectional switch of the present invention can be configured with the same number of parts as the bidirectional switch configured by using the diode instead of the MOSFET, so that an increase in cost and the size of the apparatus can be minimized.
Next, another feature of the bidirectional switch of the present invention is that the switching controller 20 performs switching with a MOSFET that is a linear switching element when the voltage generated at both ends of the bidirectional switch is equal to or lower than a predetermined voltage value. When the voltage generated at both ends of the bidirectional switch exceeds a predetermined voltage value, switching is performed by the IGBT which is a nonlinear switching element.

That is, in the characteristic curve of the general MOSFET and IGBT shown in FIG. 4, when the current value I is equal to or lower than the point where these characteristic curves intersect, even if the current value is the same (current value I ₁ in this figure), the MOSFET The voltage is lower than the voltage of the IGBT (V _1a <V _1b ). In this case, the switching control unit turns on the MOSFET and reduces the conduction loss by causing a current to flow through the MOSFET.
When exceeding the current value I of the point of intersection is reverse to the characteristic curve (current value I ₂ in this figure), the voltage of the IGBT compared to the voltage of the MOSFET is low (V _2a <V _2b). In this case, the switching control unit 20 turns on the IGBT and reduces the conduction loss by passing a current through the IGBT.
Thus, the bidirectional switch of the present invention uses a linear switching element (MOSFET) with low conduction loss when the voltage generated across the bidirectional switch by the switching controller 20 is equal to or lower than the predetermined voltage, while the voltage is the predetermined voltage. When the value is exceeded, the on / off control of the bidirectional switch is performed using a nonlinear switching element (IGBT) with a small conduction loss, so that the conduction loss and the switching loss can be reduced.
Alternatively, when the current flowing through the bidirectional switch is less than or equal to a predetermined current value, the switching control unit 20 performs switching with a MOSFET that is a linear switching element, while the current flowing through the bidirectional switch (MOSFET) has a predetermined current value. When exceeding, you may control to switch by IGBT which is a nonlinear switching element.

As described above, when the switching control unit 20 controls the bidirectional switch of the present invention, when the current flowing through the bidirectional switch is small, such as when the load is light or the power supply voltage is low, the on / off of the linear switching element (MOSFET) is performed. On the other hand, when the heavy load or the power supply voltage is high and the current flowing through the bidirectional switch is large, the conduction loss can be reduced because the on / off control is performed by the nonlinear switching element (IGBT).
Furthermore, the switching control unit 20 of the present invention performs switching with a MOSFET that is a linear switching element when the voltage generated at both ends of the bidirectional switch is equal to or lower than a predetermined voltage value or when the flowing current is equal to or lower than the predetermined current value. Of course, when the voltage generated at both ends of the bidirectional switch exceeds a predetermined voltage value and when the flowing current exceeds the predetermined current value, control may be performed so that the IGBT which is a nonlinear switching element performs switching. Absent.
A MOSFET is a unipolar element and generally has a higher switching speed (operation speed) than a bipolar element such as an IGBT, and has a low switching loss per unit switching, and is suitable for high-frequency operation. Therefore, high-frequency switching can be performed by performing a switching operation using a MOSFET instead of an IGBT, so that higher-performance on / off control, that is, power control can be performed, and further, switching loss can be reduced.

Another feature of the bidirectional switch according to the present invention is that a period in which both the nonlinear switching element (IGBT) and the linear switching element (IGBT) constituting the parallel circuit are simultaneously turned on or off is provided.
That is, in the AC power adjustment device shown in FIG. 1, the switching control unit 20 is turned on the IGBT (Q1) of the bidirectional switch SW1 and is connected in parallel to the IGBT (Q1), unlike the above-described embodiment. A period for turning on the MOSFET (Q10) is also provided. Then, the current supplied from the AC power supply 1 flows through the IGBT (Q1) and the MOSFET (Q10), and flows into the body diode BD11.
However, when the switching control unit 20 turns on the IGBT (Q1) and the MOSFET (Q10) at the same time, the current flowing through each element is shunted so that the respective voltages are equal. Therefore, in the bidirectional switch of the present invention, when the current flowing through the bidirectional switch is small, the current flows predominantly on the MOSFET side, whereas when the current value is large, the current predominantly flows through the IGBT.
Thus, the bidirectional switch of the present invention has a period during which both the nonlinear switching element and the linear switching element are simultaneously turned on, so that the conduction loss can be further reduced and the control circuit can be simplified.

Next, another feature of the bidirectional switch of the present invention is that the linear switching element (MOSFET) is turned on during the period when the body diode of the linear switching element (MOSFET) is conductive (same as the synchronous rectification). principle).
By controlling in this way, the current flowing through the bidirectional switch flows not only through the body diode but also through the MOSFET, so that conduction loss and switching loss can be further reduced. Incidentally, in this case, the potential of the emitter of the IGBT (Q1) and the source of the MOSFET (Q10), and the potential of the emitter of the IGBT (Q2) and the source of the MOSFET (Q11) are the same potential. Therefore, it is possible to divert the power source driving the IGBT (Q1, Q2) without preparing a new insulated power source for driving the MOSFETs (Q10, Q11). Therefore, the bidirectional switch of the present invention can further reduce the conduction loss without increasing the number of parts.
Alternatively, the bidirectional switch described above includes a parallel circuit composed of IGBT (Q1) and MOSFET (Q10) and a parallel structure composed of IGBT (Q2) and MOSFET (Q11) as shown in FIG. The circuit may be replaced.
The bidirectional switch of the present invention is not limited to the above-described embodiment, and is extremely useful in practical use, for example, applicable to a matrix converter using the bidirectional switch.

The principle circuit diagram of the alternating current power regulating device to which the bidirectional switch of the present invention is applied. The circuit diagram which shows the structure of the bidirectional | two-way switch of this invention. The circuit diagram which shows the structure of the conventional bidirectional switch. The graph which shows the voltage-current characteristic of IGBT and MOSFET. The figure which shows the relationship between the operating frequency of various semiconductor switching elements, a voltage, and an electric current.

Explanation of symbols

1 AC Power Supply 20 Switching Control Unit BD10, BD11, BD12, BD13 Body Diode C Capacitor L Reactor Q1, Q2, Q3, Q4 IGBT
Q10, Q11, Q12, Q13 MOSFET
R _L load

Claims (6)

A non-linear switching element that is turned on or off by a predetermined signal and that has a non-linear relationship between a voltage generated at both ends thereof and a flowing current at the time of on, and has a single flow direction;
A bidirectional switching circuit comprising a linear switching element which is turned on or off by a predetermined signal and has a linear relationship between a voltage generated at both ends thereof and a flowing current at the time of turning on;
A bidirectional switch comprising two sets of anti-parallel circuits connected in series so that the flow directions of the nonlinear switching element and the linear element are opposite to each other.   2. The bidirectional switch according to claim 1, wherein when the voltage generated at both ends of the bidirectional switch is equal to or lower than a predetermined voltage value, switching is performed by the linear switching element, while the voltage is generated at both ends of the bidirectional switch. A bidirectional switch, comprising: a switching control unit that performs switching by the nonlinear switching element when a voltage exceeds a predetermined voltage value.   The bidirectional switch according to claim 1, wherein when the current flowing through the bidirectional switch is equal to or less than a predetermined current value, switching is performed by the linear switching element, while the current flowing through the bidirectional switch is predetermined. A bidirectional switch comprising a switching control unit that performs switching with the nonlinear switching element when a current value is exceeded.   2. The bidirectional switch according to claim 1, wherein when the voltage generated at both ends of the bidirectional switch is equal to or lower than a predetermined voltage value or the flowing current is equal to or lower than a predetermined current value, switching is performed by the linear switching element. On the other hand, a switching control unit that performs switching with the nonlinear switching element when a voltage generated at both ends of the bidirectional switch exceeds a predetermined voltage value and when a flowing current exceeds a predetermined current value is provided. Bi-directional switch characterized by.   5. The bidirectional switch according to claim 2, wherein the switching control unit provides a period in which both of the nonlinear switching element and the linear switching element configuring the parallel circuit are simultaneously turned on or off. 6. .   The bidirectional switch according to claim 2, wherein the switching control unit turns on the linear switching element during a period in which a body diode of the linear switching element is conductive.

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