Parallel-connected IGBTs are conventionally driven by a common driver, with individual gate and emitter resistors for each IGBT. An alternative approach to driving parallel-connected IGBT modules is to use an individual driver for each module. Figure 1 shows the difference between conventional parallel connection of IGBT modules with a common driver core and direct paralleling of SCALE-2 driver cores.
Direct paralleling of gate drivers has become possible with the SCALE-2 technology from CONCEPT as the signal propagation delays (typically 80ns ±4ns) and the delay jitter (typically <±1-3ns) are very small with narrow tolerances for SCALE-2 drivers with a transformer interface. The following SCALE-2 driver cores with a transformer interface can therefore be directly paralleled without producing an excessive current imbalance in paralleled IGBT modules:
2SD300C17 is not suitable for direct paralleling.
This application note describes the advantage of direct paralleling in brief and explains how to use SCALE-2 driver cores in direct paralleling operation.
When driving parallel-connected IGBT modules, it is important to ensure their symmetrical operation. Measurements in half-bridge topologies have shown that symmetrical operation of these modules can be reached when using a properly designed converter. The following points must especially be considered:
- The converter should be constructed as symmetrically as possible with respect to the paralleled IGBT modules in order to ensure symmetrical operation. In particular, the DC-link stray inductance of each paralleled IGBT module should be similar (Ls1 ≈ Ls2, Ls5 ≈ Ls6 in Fig. 2).
- It is important – except for the load terminals (Ls5 and Ls6) – to have a low-inductance connection between all paralleled IGBT modules (Ls4 small). Furthermore, it is also advantageous to minimize stray inductances Ls1, Ls2 and Ls3 in order to reduce the collector-emitter overvoltage at turn off.
In any case it is recommended to measure the collector emitter voltage as well as the collector current of all paralleled IGBT modules to check the symmetry.