8 CONDUCTED EMISSION COMPLIANCE www.vicorpower.com Issue 3 2024 Power Electronics Europe www.power-mag.com MHz switching frequency-based devices enable miniaturization of the DC-DC converter and EMI filters Achieving EMI conducted emission compliance for automobiles with a single stage filter. By Nicola Rosano, Sr. Strategic FA/System Engineer at Vicor When it comes to electric vehicles (EVs), all OEMs want to design lighter, smaller and more affordable solutions. Additionally, utilities, regulatory agencies and OEM’s are seeking to leverage a vehicle to grid (V2G) connection to enable energy, period exchange with the distribution network From a power electronics perspective, this pursuit entails power conversion circuitry with greater power densities and the ability to meet the requirements for connecting the vehicle to the grid. With respect to DC-DC power converters, one notable way to miniaturize the system and increase overall power density is through higher-frequency switching. Yet, despite the potential benefits of systems with switching frequencies over 1.3MHz, technical challenges have kept many designers to working at lower frequencies, such as 100kHz or below. Imagine having a DC-DC power conversion solutions that harness the benefits of high-frequency switching without incurring conventional shortcomings. That could go a long way toward achieving smaller and lightweight EV power design goals of the OEM while adding V2G capability. The benefits of high-frequency DC-DC power conversion In the pursuit of lighter, smaller and more affordable automotive systems, highfrequency power conversion offers a promising solution. The primary benefit of moving to higherfrequency power conversion systems is a reduction in component size in both the physical device and the supporting input and output EMI filters. Some of the most space-consuming components in the converter itself are the passives, such as inductors and capacitors. Inductors and capacitors store and release energy in each switching cycle to smooth out current and voltage waveforms, respectively. When the converter’s switching frequency is higher, these components store less energy per cycle, allowing for smaller-value components allowing a decrease in the overall system size and enabling more power-dense systems for the same power level target. Beyond the converter, the associated input EMI filters are a major space consumer related to DC-DC conversion. DC-DC converters generate EMI due to the rapid switching of currents and voltages, which can create noise at the switching frequency and its harmonics. To mitigate this noise, EMI filters are employed at the input with cutoff frequencies typically dependent by the power stage requirements. (Figure 1) These filters also rely on passive components where size is directly correlated to switching frequency. By shifting the converter’s switching frequency to the MHz order, the desired EMI filter cutoff frequency can be increased. At higher cutoff frequencies, designers can make the passive components in the EMI filter much smaller, decreasing overall system size and weight while increasing system power density. Not only does switching to higherfrequency DC-DC conversion reduce component size and weight, but it also enables systems with improved transient responses. In DC-DC converters, the control loop bandwidth is typically a fraction of the switching frequency. Higher switching frequencies enable higher control loop bandwidth, allowing the feedback loop to react more rapidly to disturbances. A higher bandwidth allows the converter to correct output deviations quicker, ensuring that the output voltage remains stable even with sudden load or input voltage changes. Figure 1: An active EMI filter (labeled QPI) is often employed at the input of a DC-DC converter, with its cutoff frequency determined by the switching frequency of the converter.
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