Timothy C. Neugebauer

Parasitic capacitance cancellation in filter inductors

This paper introduces a technique for improving the high-frequency performance of filter inductors and common-mode chokes by cancelling out the effects of parasitic capacitance. This technique uses additional passive components to inject a compensation current that cancels the parasitic current, thereby improving high-frequency filtering performance. Two implementation approaches for this technique are introduced. The first implementation achieves cancellation using an additional small winding on the filter inductor and a small capacitor. This approach is effective where very high coupling of the windings can be achieved or where only moderate performance improvements are required. The second implementation utilizes a small radio frequency transformer in parallel with the filter inductor to inject cancellation currents from the compensation capacitor. This technique requires an additional component (the transformer), but can provide a high degree of cancellation. Experimental results confirm the theory in both implementations.

Inductance Compensation of Multiple Capacitors With Application to Common- and Differential-Mode Filters

Capacitor parasitic inductance often limits the high-frequency performance of electromagnetic interference (EMI) filters in both common-mode (CM) and differential-mode (DM) filtering domains. However, these limitations can be overcome through the use of specially-coupled magnetic windings that effectively nullify the capacitor parasitic inductance. This document explores the use of a single coupled magnetic winding to provide inductance compensation for multiple capacitors (e.g., both DM and CM capacitors) simultaneously, reducing the number of coils previously required. The substantial advantages of this method are illustrated both in a proof-of-concept test circuit and in an improved version of an existing EMI filter. The coupling between multiple inductance compensation windings in a single filter enclosure is also investigated

Design and evaluation of Feedforward Active ripple filters

An active ripple filter is an electronic circuit that cancels or suppresses the ripple current and electromagnetic interference generated by the power stage of a power converter, thus reducing the passive filtration requirements. This paper explores the design of feedforward active ripple filters for current ripple cancellation, including the design tradeoffs, advantages, and limitations of different implementation methods. The design and performance of an active filter using a novel Rogowski-coil current sensor is discussed in detail. Experimental results from a prototype converter system using this approach are presented, and quantitative comparisons are made between a hybrid passive/active filter and a purely passive filter. It is demonstrated that substantial improvements in filter mass and converter transient performance are achievable using this active ripple filtering method.

An active ripple filtering technique for improving common-mode inductor performance

Active ripple filtering is the replacement of large passive components in power filter circuits with smaller passive components and active control circuitry. This letter focuses on common-mode filters, where a large common-mode inductor (choke) is replaced by two smaller chokes and active op-amp control. The technique is appropriate when improved attenuation is required at relatively low frequencies and the high-frequency filtering requirements are easily met. Smaller chokes save significantly in material and winding costs. The technique is more advantageous if wire-wound chokes can be replaced by planar printed circuit board chokes. The use of the technique in an automotive electromagnetic interference (EMI) filter application is explored in detail.

Design and evaluation of an active ripple filter with Rogowski-coil current sensing

An active ripple filter is an electronic circuit which cancels or suppresses the ripple current and EMI generated by the power stage of a power converter, thus reducing the passive filtration requirements. This paper presents the design and evaluation of a feedforward active ripple filter which employs a Rogowski coil for ripple current sensing. The design of the active filter is discussed in detail, including the advantages, tradeoffs, and limitations of the approach. Experimental results from a prototype converter system using this approach are presented, and quantitative comparisons are made between a hybrid passive/active filter and a purely passive filter. It is demonstrated that substantial improvements in filter mass and converter transient performance can be achieved using the proposed active ripple filtering method.

A Fabrication Method for Integrated Filter Elements With Inductance Cancellation

This paper outlines a fabrication method for integrated filter elements. An integrated filter element is a three- (or more) terminal device comprising a capacitor and coupled air-core magnetic windings, in which the magnetic windings cancel the effects of capacitor parasitic inductance. This provides greatly enhanced filtration perfromance over a capacitor alone. Methods for designing and forming cancellation windings are described, along with means for repeatable interconnection with the capacitor and encapsulation of the filter element. The high performance and repeatability of filter elements fabricated with the proposed miethod are demionstrated with several examples

Filters with inductance cancellation using printed circuit board transformers

Capacitor parasitic inductance often limits the high-frequency performance of filters for power applications. However, these limitations can be overcome through the use of specially-coupled magnetic windings that effectively nullify the capacitor parasitic inductance. This paper explores the use of printed circuit board (PCB) transformers to realize parasitic inductance cancellation of filter capacitors. Design of such inductance cancellation transformers is explored, and applicable design rules are established and experimentally validated. The high performance of the proposed inductance cancellation technology is demonstrated in an EMI filter design.

Coupled-Magnetic Filters with Adaptive Inductance Cancellation

Conventional filter circuits suffer from a number of limitations, including performance degradation due to capacitor parasitic inductance and the size and cost of magnetic elements. Coupled-magnetic filters have been developed that provide increased filter order with a single magnetic component, but also suffer from parasitic inductance in the filter shunt path due to imperfectly-controlled coupling of the magnetics. In this paper, we introduce a new approach to coupled-magnetic filters that overcomes these limitations. Filter sensitivity to variations in coupling is overcome by adaptively tuning the coupling of the magnetic circuit with feedback based on the sensed filter output ripple. This active coupling control enables much greater robustness to manufacturing and environmental variations than are possible in the conventional coupled-magnetic approach, while preserving its advantages. Moreover, the proposed technique also adaptively cancels the deleterious effects of capacitor parasitic inductance, thereby providing much higher filter performance than is achievable in conventional designs. The new technique is experimentally demonstrated in a dc/dc power converter application and is shown to provide high performance

Computer-aided optimization of DC/DC converters for automotive applications

This paper investigates computer-aided optimization of DC/DC converters, with a focus on converters for dual-voltage automotive electrical systems. A new CAD optimization approach based on Monte Carlo search methods is introduced which allows the design space to be rapidly explored in an automated fashion and the most optimal designs and design approaches to be identified. The optimization approach also allows the effects of variations in design specifications on the cost, weight, and volume of an optimized converter to be readily determined.

A six-phase multilevel inverter for MEMS electrostatic induction micromotors

The construction of miniaturized rotating electric machines through microfabrication techniques is becoming a reality. Applications of such micromotors include miniaturized pumps, compressors, fans, coolers and turbogenerators. However, the characteristics of these devices make the design of power electronics for them challenging. These characteristics include high-voltage and high frequency operation, tightly constrained operating waveforms and timing, and capacitive input impedances. This paper explores the design of power electronics for microfabricated electrostatic induction machines. The authors describe the structure and operation of these machines, and establish the operating requirements of power converters for them. They provide a comparison of inverter topologies for this application, and propose an appropriate architecture. The design and experimental evaluation of a prototype six-phase, five-level inverter for this application is presented. The inverter operates at frequencies up to 2 MHz and at voltages up to 300 V, and meets the stringent waveform and timing constraints posed by this application.