Patent Description:
Hybrid-electric and all-electric aircraft are increasingly becoming more relevant in the aerospace industry. To optimize the design of the new air vehicles, high voltage and high current electrical systems are being introduced into new models. Various voltages are being proposed for future aircraft ranging from <NUM> V AC to <NUM> V DC and above. Wide band gap (WBG) semiconductor materials (e.g., silicon carbide and gallium nitride) enable power electronics to operate at these higher voltages as well as at higher temperatures and frequencies making power electronics made from these materials significantly more powerful and energy-efficient than those made from conventional semi-conductor materials. Fast switching transients of WBG power devices (e.g., converters) helps to achieve low switching losses, however, at the same time, these transients introduce electromagnetic interference (EMI) and/or electromagnetic compatibility (EMC) issues with WBG power devices as well as introduce the possibility of false turn-ons of the devices.

In <CIT> there is disclosed a drive circuit for a voltage-controlled type semiconductor device which comprises an ON gate drive circuit for supplying an ON control signal to a control electrode of the semi-conductor device which performs a current switching, an OFF gate drive circuit for supplying an OFF control signal to the control electrode of the semi-conductor device, a high voltage power source for supplying a control current of a predetermined current increase rate to the control electrode of the semiconductor device through at least one of the ON gate drive circuit and OFF gate drive circuit, a low voltage power source for supplying to the control electrode a control current to hold the semiconductor device in a normal state, and a switch for supplying an output of the high voltage power source to the control electrode in an earlier portion of a turn ON or a turn OFF period, and an output of the low voltage power source to the control electrode in a normally ON or a normally OFF state.

The present invention is a gate drive circuit of a wide band gap (WBG) power device in the form of an insulated gate bipolar transistor (IGBT). The gate drive circuit includes a buffer, a di/dt sensing network, a turn-on circuit portion, and a turn-off circuit portion. The buffer is coupled via a first current path to a gate of the IGBT and is capable of being supplied with a turn-on command and a turn-off command. Upon being supplied with the turn-on command, the buffer supplies a first current via the first current path to the gate of the IGBT. Upon being supplied with a turn-off command, the buffer ceases the supply of the first current. The di/dt sensing network receives a feedback control signal representative of a voltage measurement across a parasitic inductance that exists between a Kelvin emitter and a power emitter of the IGBT. The turn-on circuit portion, upon the buffer being supplied with the turn-on command and the di/dt sensing network receiving a feedback control signal representative of zero volts measured across the parasitic inductance, supplies a second current via a second current path to the gate of the IGBT in addition to the first current supplied by the buffer. The turn-off circuit portion, upon the buffer receiving the turn-off command and the di/dt sensing network receiving a feedback control signal representative of zero volts measured across the parasitic inductance, discharges a gate capacitance of the IGBT through both the first current path and a third current path.

Non-limiting and non-exhaustive examples are described in the present disclosure with reference to the following Figures.

Additionally, examples set forth in this disclosure are not intended to be limiting and merely set forth some of the possible embodiments for the appended claims.

Whenever appropriate, terms used in the singular will also include the plural and vice versa. The use of "a" herein means "one or more" unless otherwise stated or where the use of "one or more" is clearly inappropriate. The use of "or" means "and/or" unless stated otherwise. The use of "comprise," "comprises," "comprising," "include," "includes," and "including" are interchangeable and not intended to be limiting. For example, the term "including" shall mean "including but not limited to. " The term "such as" is also not intended to be limiting.

Gate drivers serve as the interface between a low power input and a power device. Gate drivers operate to produce a high current drive input for the gate of a high power transistor. As an interface element, the operation of a gate driver can have a significant effect on the operation of its associated power device. Accordingly, design features of the gate drivers need to reflect desired operation of the associated power device.

<FIG> depicts a prior art configuration of a conventional gate drive circuit that is recommended by several power semiconductor device manufacturers. As shown, a first gate drive circuit <NUM> supplies the input to the gate of a conventional upper switch <NUM> of a phase leg of a power converter while a second gate drive circuit <NUM> supplies the input to the gate of a conventional lower switch <NUM> of the phase leg of the power converter. The gate drive circuits <NUM>, <NUM> operate with fixed gate voltages and resistors, which must be designed to accommodate tradeoffs between switching behaviors, such as switching speed, switching loss, crosstalk suppression and switch stress.

Gate driver designs used to address these switching behaviors in conventional power devices can generally be grouped into three broad control categories comprising gate drivers with passive control, gate drivers with open-loop control and gate drivers with closed-loop control.

Passive control gate drivers for conventional power devices generally consist of a switchable voltage source and a gate resistor (or a combination of gate resistors); no feedback signals are monitored to make adjustments within the circuit. Passive gate drivers are a widely used approach.

Open-loop control gate drivers for conventional power devices use an open-loop control approach that employs switchable (or adjustable) gate resistors along with gate current source/sink or gate voltage to control current slopes or voltage slopes during switching transients of the conventional power device. Passive or active components can be added to the open-loop gate driver circuit to meet design criteria. The main strategies for open-loop control include controlling gate voltage, gate current and gate loop impedance. As with passive gate drivers, open-loop gate drivers utilize no feedback signals.

Closed-loop control gate drivers for conventional power devices utilize both drain-source voltage (Vds) and drain current (Id) as feedback signals to measure dVds/dt and dld/dt and compare them to a desired voltage slope and a desired current slope, respectively. In order to achieve separate gate control during different switching subintervals, a feedback control with sensors to identify the subintervals is used. The feedback control is implemented with high bandwidth analog circuits with small signal transistors or with a digital approach, such as a field programmable gate array (FPGA) with high-speed high-resolution digital-to-analog (D/A) and analog-to-digital (A/D) conversion. Thus, switching loss and electromagnetic interface (EMI) can be controlled in a closed-loop gate driver with significantly more complexity.

As with conventional power devices, design criteria considerations for a gate driver of a wide band gap (WBG) power device (e.g., silicon carbide power devices or gallium nitride power devices) include switching characteristics of the WBG power device and a control scheme to manage those characteristics. More specifically, design considerations of the gate driver for WBG power devices of the present invention include, but are not limited to, safe switching operation of the WBG power device, preventing shoot-through occurrence in the WBG power device, reducing switching losses, controlling switching speed and time, and improving electromagnetic interference (EMI) of the WBG power converter.

Further, in order to fully utilize the high switching speed capability and behavior of WBG power devices, a first gate driver of the present invention is specifically designed to best serve the upper WBG power device in a phase-leg configuration of a converter and a second gate driver of the present invention is specifically designed to best serve the lower WBG power device in the phase-leg configuration of the converter.

Switching behavior during turn-on and turn-off transients in a WBG power device, particularly a silicon carbide (SiC) power device, can be divided into four subintervals: switching delay subinterval, current commutation subinterval (i.e., di/dt transient), voltage commutation subinterval (i.e., dv/dt transient), and finally the ensuing ringing subinterval. Among them, di/dt, dv/dt, and ringing subintervals have a significant impact on switching speed, switching losses, and switch stresses. Specifically, during the turn-on transient, the excellent reverse recovery characteristics of SiC power devices result in negligible reverse recovery loss even given the high di/dt induced reverse recovery of the power device's internal antiparallel diode. Also, the modest transconductance and large internal gate resistance due to the small chip size of SiC power devices as compared to their Si counterparts limit the di/dt as well. Thus, unlike the design criterion of active gate drives for Si power devices, fast gate drives for SiC power devices no longer need to limit the switching device di/dt. However, high dv/dt induced crosstalk is critical for SiC power devices on account of the low threshold voltage and the large internal gate resistance. Therefore, the gate driver of SiC power devices should have the capability of crosstalk suppression; otherwise, SiC's switching speed has to be sacrificed to avoid the potential hazard of shoot-through failure induced by crosstalk. During the turn-off transient due to the low negative allowable maximum gate voltage, the spurious gate voltage triggered by crosstalk can easily exceed the gate voltage rating of SiC power devices. Hence, similar to the turn-on transient, crosstalk mitigation during the turn-off transient is necessary for the gate drive design.

In view of the design considerations discussed herein, <FIG> illustrates a gate driver circuit <NUM> for WBG power devices designed for fast switching and crosstalk suppression. As shown, a first gate drive circuit <NUM> supplies the input to the gate of a WBG power device upper switch <NUM> of a phase leg of a power converter while a second drive circuit <NUM> supplies the input to the gate of a WBG power device lower switch <NUM> of the phase leg of the power converter. Compared with conventional gate driver circuit <NUM> (S1 H and S2H) or <NUM> (S1 L and S2 L) of <FIG>, the gate driver circuits for WBG power devices additionally include two auxiliary transistors and two diodes. For example, the gate driver circuit <NUM> includes auxiliary transistors Sa1 H and Sa2 H with diodes DaH and Doff H while the gate driver circuit <NUM> includes auxiliary transistors Sa1 L and Sa2 L with diodes DaL and Doff L.

<FIG> illustrates the logic signals for the WBG power devices <NUM>, <NUM> and their respective gate drive circuits <NUM>, <NUM>. Note that the delay time between the main driving signal and the auxiliary signal in <FIG> is preferably set as the switching time. As shown, the gate driver circuit <NUM>, <NUM>, each of which includes a turn-on section and a turn-off section, is based on di/dt feedback control that focuses on reducing the switching loss, delay, and total switching time, while maintaining the switching stress and EMI noise level during both turn-on and turn-off transients.

A block diagram of the turn-on section <NUM> of each gate driver <NUM>, <NUM> of <FIG> is illustrated in <FIG>. As illustrated, a WBG power device <NUM> (e.g., IGBT) is coupled to the turn-on section <NUM> that includes a conventional totem pole gate drive structure (e.g., buffer <NUM>) along with a di/dt sensing network <NUM>, a logic circuit <NUM>, a level shifter <NUM>, a source follower <NUM> and a gate charger <NUM>. The di/dt sensing network <NUM> is used to detect the different turn on phases. The feedback control signal is obtained using the measurement of voltage across the parasitic inductance LEe between a Kelvin emitter e2 and a power emitter E2 of the power device <NUM>.

<FIG> illustrates the circuit implementation of the turn-on section <NUM> of the gate driver (e.g., gate driver <NUM> or gate driver <NUM>). In operation, when the turn-on command Vin is applied at the turn-on delay stage, the voltage across parasitic inductance LEe is zero since no current is flowing through the IGBT. At this instant, the output of the AND logic gate is high, which activates the level shifter's small-signal MOSFET M1, and, subsequently, the source follower MOSFET M3 and gate charger MOSFET M2 are turned on. Hence, the IGBT gate emitter capacitance Cge is now charged by the conventional gate current ig1 together with an additional current ig2.

A block diagram of the turn-off section <NUM> of each gate driver <NUM>, <NUM> of <FIG> is illustrated in <FIG>. As illustrated, a WBG power device <NUM> (e.g., IGBT) is coupled to the turn-off section <NUM> that includes a conventional totem pole gate driver structure (e.g., buffer <NUM>) along with a di/dt sensing network <NUM>, a logic circuit <NUM>, a level shifter <NUM> and a gate discharger <NUM>. The functionality of the turn-off section <NUM> is similar to the functionality of the turn-on section <NUM> with the exception that there is no source follower or gate charger, and the gate discharger <NUM> is controlled to remove current from gate capacitance during a certain period of the turn-off transient.

<FIG> illustrates the circuit implementation of the turn-off section <NUM> of the gate driver (e.g., gate driver <NUM> or gate driver <NUM>). In operation, when the turn-off command Vin is applied to the gate driver, the voltage across parasitic inductance LEe stays zero during both the turn-off delay stage and the voltage rising stage since no current is flowing through the IGBT. The output of the NOR logic gate is high, which activates the paralleled level shifter small-signal MOSFETs, and the gate discharger. The IGBT gate-emitter capacitance is then effectively discharged by the conventional gate current ig1 together with an additional current ig3. The higher total gate current charges the Miller capacitor more rapidly, and thus results in a shorter voltage tail duration and lower turn-off switching loss.

Claim 1:
A gate drive circuit for a wide band gap (WBG) power device in the form of an insulated gate bipolar transistor (IGBT), comprising:
a buffer (<NUM>) coupled via a first current path to a gate (g2) of the IGBT (<NUM>), the buffer capable of being supplied with a turn-on command and a turn-off command, the buffer supplying a first current (ig1) via the first current path to the gate of the IGBT upon being supplied with the turn-on command and stopping supply of the first current upon being supplied with the turn-off command;
a di/dt sensing network (<NUM>) receiving a feedback control signal (E2) representative of a voltage measurement across a parasitic inductance (Lee) that exists between a Kelvin emitter and a power emitter of the IGBT (<NUM>);
a turn-on circuit portion that, upon the buffer (<NUM>) being supplied with the turn-on command and the di/dt sensing network (<NUM>) receiving a feedback control signal representative of zero volts measured across the parasitic inductance, supplies a second current (ig2) via a second current path to the gate of the IGBT (<NUM>) in addition to the first current supplied by the buffer; and
a turn-off circuit portion, upon the buffer (<NUM>) receiving the turn-off command and the di/dt sensing network (<NUM>) receiving a feedback control signal representative of zero volts measured across the parasitic inductance, discharges a gate capacitance of the IGBT (<NUM>) through both the first current path and a third current path (ig3).