Driving 3.3kV IGBT Modules made Easy

The new 3.3kV dual-channel driver core 2SC0535T2A0-33 (2SC0535T in brief) from CONCEPT allows IGBT modules of the voltage class up to 3.3kV to be driven with full design flexibility in a wide range of applications such as traction, renewables, industry as well as HVDC and STATCOM.

The gate driver is a key component of power electronics systems. It connects the signal electronics with the high-voltage parts (e.g. IGBT modules) of the power converter. Properly designed gate drivers ensure safe driving of the IGBT modules in normal operation as well as in a fault condition such as system overload or IGBT short-circuit. High availability and reliability are mandatory, as the dysfunction of only a single gate driver in a power converter may lead to overall system failure or reduced performance.

On the other hand, the design cycles of power electronics systems are getting shorter and the pressure on the required flexibility and costs is steadily increasing. With the introduction of the brand-new 3.3kV dual-channel gate driver core 2SC0535T, CONCEPT has set itself the ambitious goal of providing easy ways of driving high-voltage IGBT modules up to 3.3kV with full flexibility, high reliability, high performance, reduced space requirements and low cost. This is made possible thanks to the uncompromising integration of CONCEPT’s SCALE-2 technology. The outstanding features of the 2SC0535T are described below.

Extended Ambient Temperature Range
Figure 1 shows a photograph of the 2SC0535T dual-channel driver core. With a footprint of only 59.2mmx76.5mm and a total height of 25mm, it can deliver a gate output power of up to 5W per channel with a gate current capability of ±35A over the full ambient temperature range from -55°C to 85°C. This makes it possible to drive 3.3kV IGBT modules at the high switching frequencies required in applications such as induction heating. Even 1.2kV or 1.7kV IGBT modules connected in series or in multilevel topologies can be driven with the minimum gate resistance, thus reducing switching losses and increasing the overall power converter efficiency. The negative temperature range has been extended from the industrial standard of -40°C to -55°C to even allow IGBT modules to be controlled at the extremely low temperatures required in certain traction applications.

Isolation up to 3.3kV and 50kV/μs
The driver isolation is designed to comply with the EN50178, EN50124-1 and IEC60077-1 standards in overvoltage category 2 and pollution degree 2, providing reinforced isolation between the primary and secondary sides. The related clearance and creepage distances given in Table 1 are dimensioned to fulfill these standards.

They allow the potential of 3.3kV IGBT modules at maximum DC link voltages to be fully exploited. Moreover, the total coupling capacitance in the range of 20pF between the primary side and each secondary side confers a dv/dt robustness of up to 50kV/μs thanks to the outstanding capability of the SCALE-2 technology. This guarantees that the signal information will be transferred reliably even at a high DC link voltage and with ultra-fast switching operations.

Monitoring Functions
The desaturation protection network with resistors as shown in Figs. 2 and 3 allows a robust design of the short-circuit protection function of the IGBT modules with short-circuit durations in the range of 5-10µs. The IGBT modules can be used with the maximum DC link voltage at double the nominal current without risking any false tripping of the desaturation protection function. If required, the threshold limit for desaturation protection can easily be increased by a simple resistive voltage divider (Rd in Figs. 2 and 3). Furthermore, the use of high-voltage diodes is completely avoided.

The patent pending circuits proposed in Figs. 2 and 3 also offer an important advantage. The transient voltage suppressor (TVS) chain is connected to the resistor network at node (1). This allows a high-ohmic resistor network Rvce1…Rvce3 to be used while keeping a constant voltage at (1) in the IGBT short-circuit condition over a wide range of the DC-link voltage, typically of 50% to 100% of its maximum value. The voltage at (1) is then basically determined by the clamping voltage of the TVS D1. This leads to an almost constant short-circuit duration, even at lower DC link voltages. If the connection between the resistor network and the TVS chain is removed, the short-circuit duration becomes higher as soon as the DC link voltage is reduced. As an alternative, the resistance value of the resistor network Rvce1…Rvce3 can be reduced in order to avoid higher IGBT short-circuit durations at lower DC link voltages, although this leads to high power losses in the resistor network and therefore a greatly increased space requirement.
Supply undervoltage monitoring is implemented on the driver primary side as well as on both secondary sides to avoid IGBT modules being driven with inadequate gate-emitter voltages.

In the failure condition (undervoltage monitoring or IGBT short-circuit), the corresponding driver channel is turned off and a fault feedback is transmitted immediately to the corresponding status output. The driver is then kept in the off-state during the blocking time, which is programmed with a resistor Rb at pin TB (see Figure 4) in a range between 10us and 130ms. The status signals SO1 and SO2 allow simple monitoring of the driver channels.

Advanced Active Clamping (AAC)
Active clamping is a widely used technique to reduce the collector-emitter voltage of the IGBT during the turn-off event. The IGBT is partially turned on as soon as its collector-emitter voltage exceeds a predefined threshold. The IGBT is then maintained in linear operation, thus reducing the fall rate of the collector current and therefore the collector-emitter overvoltage.

Basic active clamping topologies implement a single feedback path from the IGBT’s collector through TVS to the IGBT gate. The 2SC0535T supports SCALE-2 Advanced Active Clamping (AAC), where the feedback is also provided to the driver’s secondary side at pin ACL (see Figure 2): as soon as the voltage on the right side of the resistor R1 increases due to the active clamping activity, the turn-off MOSFET of the driver connected to GL is progressively switched off in order to improve the effectiveness of the active clamping and to reduce the losses in the TVS.

Dynamic Advanced Active Clamping (DA2C)
The maximum DC link voltage must be limited during operation as well as in the off-state condition when using AAC to avoid thermal overload or even static conduction of the TVS. The circuit of AAC in Figure 2 can be extended with a switch (e.g. IGBT or MOSFET) and one or more paralleled TVS as well as a small control circuit as shown in Figure 3 to address this drawback.

The resulting circuit, known as Dynamic Advanced Active Clamping (DA2C), allows the DC link voltage in the IGBT off-state to be further increased by opening Q1 in the IGBT off-state. Q1 is turned on as soon as the driver channel is turned on. It is kept in the on-state for about 15 to 20µs after IGBT turn-off thanks to a timer included in the control circuit, thus ensuring an adequate level of active clamping during the IGBT turn-off event.

In several traction, wind-turbine or solar-inverter applications, an extended range of the DC link voltage is required when all IGBT modules are in the off-state. In case of an inverter failure, all IGBTs are usually turned off to bring the system to a safe state. The energy stored in the inverter phase inductances is then fed into the DC link, leading to an immediate increase of its voltage.

Direct Paralleling
The turn-on and turn-off signal propagation delay is shorter than 100ns. The delay deviation in series production as well as the delay jitter are almost negligible. This timing precision allows direct paralleling of IGBT drivers for parallel-connected IGBT modules. Each IGBT module is then driven with its own 2SC0535T driver. This driving method has several advantages over the conventional approach, where one driver controls several parallel-connected IGBT modules.

Additional product features
The threshold levels of the input signals INA and INB are 2.6V for turn-on and 1.3V for turn-off. They allow the unrestricted use of an input signal logic level of between 3.3V and 15V. A simple resistive voltage divider can be used to increase the threshold levels and therefore the signal-to-noise ratio at the input if required (R1 and R2 in Figure 4).

The driving mode is selected with a resistor Rm at the MOD pin. In direct mode, both driver channels work fully independently. In half-bridge mode, only one driver channel is in the on-state while the other is in the off-state. At commutation, a programmable half-bridge dead time of 0.6µs to 4.1µs is programmable with the resistor Rm shown in Figure 4.

The DC/DC converter generates an unregulated isolated 25V supply voltage from the primary 15V supply voltage for each driver channel that can vary slightly depending on the driver load and temperature. The secondary voltage is divided into a regulated and stable +15V for the on-state gate-emitter voltage of the IGBT and an unregulated -10V for the off-state gate-emitter voltage. Thanks to the regulated +15V in the on-state, the gate-emitter voltage can be efficiently clamped with a Schottky diode to the +15V as shown in Figs. 2 and 3. This gate-emitter clamping method is considerably more effective than using transient voltage suppressors between the gate and emitter. The latter does not allow the gate-emitter voltage to be limited to 15V in the short-circuit condition, as some clamping voltage reserve must be included in view of the component tolerances and temperature dependence in order to avoid static conduction and therefore overload in the on-state.

Increased Reliability
2SC0535T drivers benefit from the high integration level of the SCALE-2 technology. This leads to a reduced board space optimized to comply with the given isolation standards. Moreover, it is well known that the reliability of a properly designed electronics system is directly related to the number and choice of the components used. Like all SCALE-2 drivers, 2SC0535T drivers feature a minimum number of carefully selected highly reliable components. This immediately results in an increased MTBF compared to the discrete solutions available on the market.

Optimum Space Requirement and Cost Performance
2SC0535T drivers allow the use of any IGBT module up to 3.3kV and offer full flexibility in terms of switching speed and features during the power converter design. The driver core can be assembled on a common printed circuit board, which is in any case needed to design additional electronics, thus saving space and costs.
Moreover, no fiber-optic interface is required, as the galvanic separation of the driving signals is realized with transformers, thus further reducing costs. A fiber-optic interface may still be used if required.

The pricing of the 2SC0535T is extremely competitive. With a target price of US$75 for two channels at quantities of 1000 items, the 2SC0535T sets a new benchmark for driving 3.3kV IGBT modules.

True Second Source
The recent events relating to the earthquake in Japan have shown how important second sources of critical components are. The primary-side LDI and secondary-side IGD ASICs have been developed on the basis of two semiconductor processes and can consequently be produced in two independent foundries. A third production site is currently being evaluated. The ASICs are packaged by two different companies.
The transformer production has also been released by two manufacturers. All other components of the driver have defined second sources. The printed circuit board can be assembled by two independent companies. Beyond that, CONCEPT invests considerable effort in maintaining safety stocks in order to ensure that even in the case of a component shortage on the global market, the gate drivers can continue to be manufactured and delivered to satisfy the customer demand at all times.

Applications
A wide range of applications such as traction, wind power, solar converters, induction heating and medium-voltage drives, as well as HVDC and STATCOM is made possible with 2SC0535T drivers. Any IGBT module of the voltage class up to 3.3kV can be safely driven in two-level topologies. Moreover, 2SC0535T drivers can be applied to three-level converters based on 1.2kV to 3.3kV IGBT modules. Even 1.2kV and 1.7kV IGBT modules can be connected directly in series under certain application conditions.

As already mentioned, the clearance and creepage distances were designed to fulfill the requirements of pollution degree 2 for 3.3kV IGBT modules. The design also complies with the requirements for pollution degree 3 for 1.7kV systems.
CONCEPT will soon provide basic boards to further facilitate the application of 2SC0535T drivers: they are assembled with all the components required to drive IGBT modules safely except for gate resistors, which must be determined by the user to adapt the basic board to the given application.

Summary
The 3.3kV dual-channel IGBT driver core 2SC0535T based on the SCALE-2 technology from CONCEPT sets a new standard in driver performance in terms of features, reliability, flexibility, space requirements and costs of driving IGBT modules of the voltage class up to 3.3kV in two-level and multilevel topologies.

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