Active Filter Techniques for Reducing EMI Filter Capacitance

نویسنده

  • Arthur Smith
چکیده

Switching power converters are widely used due to their excellent efficiency, but they inherently generate ripple. Passive low-pass LC filters have been traditionally employed to meet ripple and EMI specifications [1]. These passive filters can contribute considerably to the volume and weight of a power converter. In particular, capacitors can become relatively large in order to meet strict ripple specifications. This is detrimental to cost and reliability of these passive EMI filters. For these reasons, capacitors in EMI filters can pose a considerable design challenge. Active circuit techniques can substantially reduce passive EMI filter capacitor requirements. This thesis investigates using active circuitry to mitigate the challenges of designing with large capacitors on three fronts: reducing capacitance in EMI filters, reducing damping capacitance, and reducing capacitance cost. A significant reduction of the passive EMI filter capacitor can be achieved by active ripple filters. This thesis investigates a hybrid passive/active filter topology that achieves ripple reduction by injecting a compensating voltage ripple across a series filter element. Both ripple feedforward and feedback are employed. The design of sensor, amplifier, and injector circuitry for this application is explored. The experimental results demonstrate the feasibility and high performance of the new approach, and illustrate its potential benefits. The damping capacitor can easily become the dominant capacitance of the system. By using signal-level transistors, the needed capacitance can be greatly reduced. A feedback system using current sense and current drive is explored in this thesis. Test results demonstrate an improvement by a factor of a thousand. Active techniques can also reduce the cost of capacitor in EMI filters, by enhancing the performance of low cost capacitors. This work applies active techniques to the input EMI filter of a commercial automotive motor drive system. Initial evaluation has demonstrated the feasibility of this approach. More work will be required to further evaluate the details of active filter system to this commercial application. Thesis Supervisor: David J. Perreault Title: Active Filter Techniques for Reducing EMI Filter Capacitance

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تاریخ انتشار 2014