Digital Active CM EMI Suppression of a DC-DC Converter with Synthesized Switching-Slope Dependent Cancellation Pulses

The common mode EMI of power electronic systems can often be seen as a sequence of short, periodic disturbance pulses caused by the switching actions of the power transistors. To reduce passive filter components, these individual pulses can be suppressed by injecting appropriate cancellation signals with active EMI filters. By using digitally synthesized cancellation pulses generated by an FPGA with a digital-analog converter (DAC), high EMI suppression can be achieved. These cancellation pulses can be generated with an adaptive finite impulse response (FIR) filter, which takes the PWM signals of the system as input and recreates step responses as fitting cancellation pulses. When asymmetric disturbance pulses occur, multiple FIR filters must be used, as the turn-on transient might cause different waveforms than the turn-off of the same transistor. This paper presents a possible implementation for multiple filters. Additionally, the FIR filter is substituted by another signal generation technique using other storage options available on the FPGA, saving valuable FPGA resources and allowing for much longer cancellation pulses. For demonstration, the extended algorithm is applied to the common mode EMI of a DC-DC converter showing long and asymmetric disturbance pulses. The EMI suppression is evaluated in the test setup with an EMI test receiver, showing high broadband EMI suppression in the considered frequency range of 150 kHz to 30 MHz.