Patent Application
20150003133
The present invention relates to a drive circuit of a semiconductor switching element in a power conversion circuit using a Schottky barrier diode of a wide-gap semiconductor.
Recently, silicon carbide (SiC), gallium nitride (GaN), or the like has been attracting attention as a wide-gap semiconductor material having larger band gap than silicon (Si). Since the wide-gap semiconductor material has about 10 times as much as dielectric breakdown electric field strength of Si, a thickness of a drift layer for securing a withstand voltage in a semiconductor element including the wide-gap semiconductor material as a base material can be about 1/10 of that of Si. Thus, it is possible to make an on-state voltage of a semiconductor element lower. Thus, even in a high withstand voltage region in which a bipolar element can only be used in a case of Si, a unipolar element can be used and high-speed switching becomes possible in a case of a wide-gap semiconductor element such as SiC.
In the following, SiC which represents the wide-gap semiconductor will be described. However, a different wide-gap semiconductor is in a similar manner.
To a power semiconductor module used in a power conversion circuit such as an inverter, a freewheel diode is connected in parallel with a semiconductor switching element. In a conventional power semiconductor module, an Si-PiN diode has been used as a freewheel diode. The Si-PiN diode is a bipolar-type semiconductor element and includes a structure in which when energization is performed with a large current in a forward bias, a voltage drop becomes low due to a conductivity modulation. However, the PiN diode has a characteristic in which a carrier remaining in the PiN diode due to a conductivity modulation generates a reverse recovery current during a process of a change from the forward bias state to a reverse bias state. In the PiN diode of Si, the remaining carrier has a long life, and thus, the reverse recovery current becomes large. Thus, due to the reverse recovery current, a loss during a semiconductor switching element being turned on (Eon) or a recovery loss generated when a diode performs reverse recovery (Err) becomes large.
Next, a terminal voltage and a current waveform of a diode during the generation of a reverse recovery current will be described.
On the other hand, a Schottky barrier diode (hereinafter, referred to as SBD) is a unipolar-type semiconductor element and a carrier is rarely generated therein by a conductivity modulation. Thus, when the Schottky barrier diode is used in an inverter circuit, a reverse recovery current is very small, and thus, a turn-on loss or a recovery loss can be made small. Conventional Si has low dielectric breakdown electric field strength. Thus, when an SBD is manufactured in a structure with a high withstand voltage, high resistance is generated during energization, and thus, a limit of a withstand voltage of an Si-SBD has been about 200 V. However, since SiC has 10 times as much as the dielectric breakdown electric field strength of Si, it has been known that it becomes possible to put an SBD with a high withstand voltage into a practical use and to reduce a loss during turn-on (Eon) or a recovery loss generated when a diode performs a reverse recovery (Err).
However, in a case where the SiC-SBD is applied to a circuit, when a semiconductor switching element of an own arm is turned on, a source voltage is applied to a terminal of a diode of an opposite arm. By junction capacitance of the diode and a parasitic inductance of a main circuit, a resonance current flows and a voltage oscillation or a voltage change rate during switching becomes larger than that of the PiN diode.
In an inverter in which the PiN diode is applied, as a method to reduce a surge voltage, there is a method to turn on, during a recovery period of a diode, a semiconductor switching element connected in parallel with the recovering diode and to short-circuit upper and lower arms momentarily. Thus, as a method to perform a short-circuit operation when a surge voltage is increased to a vicinity of a withstand voltage of an element, the following two methods are proposed.
In PTL 1, a method to perform a short-circuit by detecting a terminal voltage of a switching element and charging gate capacitance with a current source when the terminal voltage reaches a threshold is proposed.
In PTL 2, a method to perform a short-circuit by charging a gate of an IGBT during generation of recovery in an active clamp circuit which connects a Zener diode between a collector terminal and a gate terminal of the IGBT is proposed.
PTL 1: JP 2003-218675 A
PTL 2: JP 2005-328668 A
A voltage oscillation and a voltage change rate during switching are increased in an SiC-SBD, compared to those in a PiN diode. However, PTL 1 and PTL 2 of the conventional techniques are effective only when a surge voltage is increased to a vicinity of a withstand voltage of an element. When the SiC-SBD is applied, the voltage oscillation becomes large even when the surge voltage is small, and thus, it is hard to control the voltage oscillation.
The present invention has been made in consideration of the above problem, and a purpose of thereof is to provide a drive circuit of a semiconductor switching element, the drive circuit being capable of reducing a voltage oscillation securely when an SBD of a wide-gap semiconductor is applied to a power conversion circuit.
A drive circuit of a semiconductor switching element according to the present invention is configured to control a gate voltage of a semiconductor switching element in each of upper and lower arm circuits in each of which a Schottky barrier diode including a wide-gap semiconductor material as a base material is connected as a freewheel diode in parallel with the semiconductor switching element. To solve the above problem, the drive circuit includes a gate voltage increasing circuit configured to make, in a period since a gate voltage of the semiconductor switching element in one of the upper and lower arms starts being increased from a value in an off-state until the gate voltage reaches a value in an on-state, a gate voltage of the semiconductor switching element in the other one of the upper and lower arms change from a value in an off-state into a value larger than the value in the off-state and configured to control the value larger than the value in the off-state for a predetermined period of time.
By increasing, before a current starts flowing in a semiconductor switching element of one of upper and lower arms, a gate voltage of a semiconductor switching element in the other arm and by short-circuiting the upper and lower arms, it is possible to securely reduce a voltage oscillation in a power conversion circuit to which a Schottky barrier diode including a wide-gap semiconductor material as a base material is applied.
In the present power conversion circuit, as a switching element, an IGBT 2a and an IGBT 2b are connected to each other in series. A serially connected circuit of the IGBT 2a and the IGBT 2b configures a half-bridge circuit of one phase. Both ends of the serially connected circuit are connected to a DC power source 1 and a series connection point is connected to an AC output terminal 24. To the IGBT 2a and the IGBT 2b, as freewheel diodes, an SiC-SBD 3a and an SiC-SBD 3b are respectively connected in parallel. That is, an upper arm including a parallel circuit of the IGBT 2a and the SiC-SBD 3a and a lower arm including a parallel circuit of the IGBT 2b and the SiC-SBD 3b are connected in series. Both ends of the serially connected circuits of the upper and lower arms are connected to the DC power source 1 and the series connection point is connected to the AC output terminal 24. Here, the upper arm is connected between a high-voltage side of the DC power source 1 and the AC output terminal 24. The lower arm is connected to the AC output terminal 24 and a low-voltage side of the DC power source 1.
To the IGBT 2a and the IGBT 2b, a drive circuit 31a and a drive circuit 31b are respectively connected to control a gate voltage. The drive circuit 31a includes a gate circuit 4a to control a gate voltage of the IGBT 2a according to a switching control signal given to a gate control signal terminal 12a, and a gate voltage increasing circuit 11a to perform a short-circuit drive by increasing the gate voltage of the IGBT 2a according to a short-circuit control signal given to a short-circuit control signal terminal 25a. Similarly, the drive circuit 31b includes a gate circuit 4b to control a gate voltage of the IGBT 2b according to a switching control signal given to a gate control signal terminal 12b, and a gate voltage increasing circuit 11b to perform a short-circuit drive for a temporary arm short-circuit by increasing the gate voltage of the IGBT 2b according to a short-circuit control signal given to a short-circuit control signal terminal 25b.
The power conversion circuit of the present embodiment converts DC power of the DC power source 1 into AC power by performing on-off switching control on the IGBT 2a and the IGBT 2b respectively by the drive circuits 31a and 31b. The AC power is output from the AC output terminal 24 and is supplied to a load such as an induction motor or a permanent-magnetic motor which is connected to the AC output terminal 24. Note that in
Note that in
When the lower IGBT (2b) is turned on, a current flowing in the SiC-SBD 3a is decreased and a current starts flowing in the lower IGBT (2b) being turned on. Then, when the current flowing in the SiC-SBD 3a becomes zero, the SiC-SBD 3a is turned off (transitions from being on to being off). In a case of the SiC-SBD, a high recovery current such as that in the PiN diode does not flow. When being turned off, the SiC-SBD 3a operates as a capacitor by the junction capacitance 6a. Thus, by energy stored in the inductance 5 in
In the present embodiment, in a period since a gate-emitter voltage (hereinafter, referred to as “gate voltage”) of the lower IGBT (2b) starts changing into a value larger than a voltage in an off-state, that is, since the gate voltage starts being increased until the gate voltage reaches a gate voltage in an on-state, a gate voltage of the upper IGBT (2a) connected in parallel with the SiC-SBD 3a being turned off is controlled to a value larger than a voltage in an off-state by the gate voltage increasing circuit 11a. Specifically, in a case of
In the present embodiment, the gate voltage of the upper IGBT (2a) is controlled to a value larger than that in the off-state before a current start flowing in the lower IGBT (2b). Thus, when the displacement current starts flowing (t2), the gate voltage of the upper IGBT (2a) can be securely made equal to or higher than the threshold. Thus, a ringing oscillation can be controlled securely.
When the upper IGBT (2a) is turned on, a current by the energy stored in the inductance 5 starts flowing through the upper IGBT (2a). Here, since the upper IGBT (2a) operates as a resistance component, the ringing oscillation is controlled and a surge voltage and a noise level can be reduced. Then, when the gate voltage of the lower IGBT (2b) reaches a gate source voltage (t3), the gate voltage of the upper IGBT (2a) is controlled to the voltage in the off-state again. Thus, an increase in a power loss caused in the upper IGBT (2a) by a flow of a short-circuit current due to the turn-on of the upper IGBT (2a) and a turn-on loss in the lower IGBT (2b) can be controlled.
In the described embodiment, the upper IGBT (2a) is turned on by making the gate voltage equal to or higher than the threshold by the displacement current. However, a point when the displacement current starts flowing may be detected based on the voltage of the SiC-SBD 3a or the upper IGBT (2a) or the gate voltage of the lower IGBT (2b) and when the displacement current starts flowing, the gate voltage of the upper IGBT (2a) maybe set to a voltage value equal to or larger than the threshold (Vth) for a predetermined period of time by the gate voltage increasing circuit 11a.
Note that at least in a period in which the voltage of the SiC-SBD 3a and the upper IGBT (2a), that is, the voltage of the upper arm is increased, that is, in a recovery period after the current (return current) flowing in the SiC-SBD 3a is decreased and becomes zero, ringing can be reduced by turning on the IGBT 2a with the gate voltage of the IGBT 2a being equal to or higher than the threshold.
Next, an example of a detail circuit configuration of the drive circuit illustrated in
The drive circuit 31a in
When the switch for short-circuit control 42 is turned on, the gate circuit power supply in an off-state 44 and the power supply for a gate voltage increasing circuit 45 are connected in series and a current flows in the off-side gate resistance 47 and the resistance for a gate voltage increasing circuit 48. By the current, a voltage drop is caused in the off-side gate resistance 47 and a summed value of a terminal voltage of the off-side gate resistance 47 and a voltage of the gate circuit power supply in an off-state 44 is applied to a gate of the IGBT 2a. The gate voltage at this time becomes higher than the gate voltage in the off-state. Here, an increased amount of the gate voltage is set by a voltage division ratio between the off-side gate resistance 47 and the resistance for a gate voltage increasing circuit 48. In such a manner, the gate voltage increasing circuit 11a in the present embodiment applies, to the gate of the IGBT 2a, a positive voltage lower than the gate threshold voltage.
When the gate voltage of the IGBT 2a becomes higher than the gate voltage in the off-state, as described, the current by the energy stored in the inductance 5 flows as a short-circuit current in the IGBT 2a and the IGBT 2b of the upper and lower arms. Thus, ringing due to a resonance current by the inductance 5 and the capacitor 6a (junction capacitance of SiC-SBD 3a) can be reduced.
Then, by the short-circuit control signal given to the short-circuit control signal terminal 25a, the switch for short-circuit control 42 is turned off. Thus, the gate voltage of the IGBT 2a is controlled to the voltage in the off-state again. Thus, as described, an increase in a power loss in the IGBT 2a caused by the short-circuit current and a turn-on loss in the IGBT 2b can be controlled.
In the present embodiment, the gate circuit power supply in an on-state 43 and the power supply for a gate voltage increasing circuit 45 are provided separately, but may be a single power supply. Also, as the switches for a gate circuit 41a and 41b and the switch for short-circuit control 42, a semiconductor switching element such as an MOSFET can be applied.
In the present embodiment, by a one-shot circuit, a timing to make the gate voltage increasing circuit operate is controlled. For example, similarly to
As illustrated in
Thus, in the present embodiment illustrated in
According to the present embodiment, the gate voltage increasing circuit operates in a case where the switching current is equal to or larger than the threshold set in advance. Thus, it is possible to control a power loss in the gate voltage increasing circuit while controlling a peak value of the voltage change rate or the surge voltage and ringing effectively.
In the present embodiment, instead of the current sensor and the current detector in the embodiment in
According to the present embodiment, by a simple circuit configuration, it is possible to control a power loss in the gate voltage increasing circuit while controlling a peak value of a voltage change rate or a surge voltage and ringing effectively.
Note that, as the control circuit 100, a publicly-known pulse width modulation control circuit or the like can be used.
In the above, embodiments of the present invention have been described in detail but are not limited to the described embodiments. Various embodiments are possible within the technical spirit of the present invention. For example, as a semiconductor material to be abase material of an SBD, other than SiC, a wide-gap semiconductor, which has a band gap larger than that of Si, such as GaN or diamond can be applied. Also, as a semiconductor switching element which configures upper and lower arms of a power conversion circuit, other than an IGBT, a voltage-controlled semiconductor switching element such as a metal oxide semiconductor field effect transistor (MOSFET) or a static induction transistor (SIT) can be applied. Note that a semiconductor material to be a base material of the semiconductor switching element may be any of Si and wide-gap semiconductors.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2012-021464 | Feb 2012 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2013/051142 | 1/22/2013 | WO | 00 |
