What impact do inverter di/dt spikes have on EMC?

In inverters, di/dt spikes have a significant negative impact on EMC, mainly manifested in radiated emissions and conducted interference. Rapidly changing current (di/dt) induces a high voltage (V=L*di/dt) in an inductive circuit. This induced voltage superimposed on the switching waveform forms ringing and spikes, becoming a rich source of high-frequency noise. Di/dt spikes exacerbate magnetic field radiation in the power circuit (DC bus, IGBT, capacitors), making the circuit essentially a magnetic field antenna. Simultaneously, spike currents can couple to nearby sensitive signal lines or control lines, causing malfunctions. It also causes high-frequency oscillations in the DC bus voltage, increasing input conducted noise.

To reduce the impact of di/dt, the design should minimize parasitic inductance in the power circuit; using multilayer busbar technology is one of the most effective methods. Connecting a small inductor in series with the IGBT emitter or using a saturated magnetic ring can limit the rate of current rise. Optimizing the layout and selection of the DC bus capacitors provides a low-inductance high-frequency current path. Using a current probe to measure the switching current waveform allows for the evaluation of the di/dt ratio and optimization of the drive resistor. Eintec Electronics' low-inductance bus capacitor and multilayer busbar design solutions can help engineers effectively manage the EMC challenges posed by di/dt.