Influence of IGBT-module switching characteristics to radio frequency noise

The presented paper investigates the relationship between high frequency oscillations created in power modules and their radio frequency noise emission. It is shown that high frequency oscillations with slew rates comparable or higher than the ones generated by the used semiconductors leads to significant higher noise emission in the radio frequency range. During turn on of the IGBT a high frequency oscillation is created between the stray inductances of the DC-Link and the reverse capacitances of the blocking freewheeling diodes. The DC-Link stray inductances are charged by the reverse recovery current of the freewheeling diode. When the reverse recovery current peak is passed the diode begins to block and the energy stored in the inductances oscillates to the reverse capacitance of the diode. The quality of the oscillation is mainly influenced by the tailing of the diodes reverse recovery current. At the investigated three phase, 600V, 200A power module the observed turn on resonance frequency is 33MHz. The crucial characteristic of this phenomenon is that the noise emission is not only higher at the resonance but for all frequency above, too. By reducing the module inductances the resonances are shifted to higher frequencies but measurements show that the emitted spectrum stays the same. To reduce the module inductances do not solve the problem. The results of the investigation enable the design of power modules with reduced radiated emissions.