Leo F. Casey

A high-frequency, low volume, point-of-load power supply for distributed power systems

A resonant version of the DC-DC forward converter is presented in which both the primary-side switch and the secondary-side diode are either on or off at the same time. Such a topology is capable of operation in the 10-MHz range, and can be used for very-low volume point-of-load conversion in distributed power systems. This type of converter takes advantage of a very low transformer leakage inductance to achieve zero-voltage switching of all its power semiconductor devices. Its resonant ring is also independent of load current. A 50-W prototype operating at 3.6 MHz is presented along with a discussion of the changes necessary to achieve 10 MHz. >

Analysis of Instability in Electrical Machines

While there exist numerous studies of electromechanical instabilities of specific electrical machines in constant or periodic speed operation, a broader perspective is not commonly offered. In contrast, a general machine model is used here to present essential and common features of these stability analyses. Fundamental issues are illuminated at this level of generality before specialization to the details of a specific machine. To begin, Park-transformable machines in constant-speed operation are considered. The local dynamics of these machines are linear and time-invariant. For such machines it is shown that instability may be analyzed in a useful way via systematically obtained reduced-order models. This is illustrated by significantly expanding an earlier study of a hybrid stepping motor. The more general situation in which the linearized models that govern local behavior are periodically varying is considered next. Classical Floquet theory is reviewed to provide the tools needed for stability analysis in this situation.

Comparison of the square-wave and quasi-resonant topologies

The waveforms of a square-wave and a quasi-resonant dc-dc converter are examined in detail so that a comparison between the switching and conduction losses for each topology can be made. Using data from commercially available semiconductor devices, conservative estimates are then given for the switching frequency at which the resonant approach becomes advantageous. The effect of an isolation transformer on this comparison is also addressed.

A high frequency, low volume, point-of-load power supply for distributed power systems

A resonant version of the dc-dc forward converter is presented in this paper. It is a topology capable of operation in the 10 MHz range, and it can be used for very low volume, point-of-load conversion in distributed power systems. In comparison to other resonant topologies, this converter takes advantage of a very low transformer leakage inductance to achieve zero-voltage switching of all its power semiconductor devices. Its resonant ring is also independent of load current. A 50 watt prototype operating at 3.6 MHz and a discussion of the component work necessary to reach 10 MHz are presented.

Issues regarding the capacitance of 1-10 MHz transformers

Capacitive modeling issues are addressed, particularly with respect to minimizing leakage inductance. Reasonable assumptions about the winding configuration and the distribution of voltage around it are made. The total electrical energy stored in the winding when a voltage is applied is then calculated and partitioned into the differential and common-mode parts. A description of how the common-mode current flows is discussed, and the tradeoff between leakage inductance and capacitance is quantified. Some experimental results are provided.<<ETX>>

Copper-based hybrid fabrication of a 50 W, 5 MHz 40 V-5 V DC/DC converter

A prototype 50 W, 40 V to 5 V DC/DC converter operating at 5 MHz and constructed with chip and wire hybrid techniques on a ceramic substrate with copper thick-film conductors is presented. A brief discussion of the thick-film process is given to point out the special issues concerning copper-based conductor systems. Some of the specific trade-offs that arise with regard to the construction of a power circuit with hybrid techniques are discussed. A method by which transformers may be fabricated to have very little leakage inductance, both internally and in their connection to rectifiers, is then described. The performance of a power circuit, the dual resonant forward converter is presented. >

CMOS drive and control circuitry for 1-10 MHz power conversion

The design, implementation, and experimental evaluation of CMOS subcircuits that can be combined to implement integrated control and drive for 1-10 MHz power circuits are presented. The approach taken is to develop controller/driver ICs for a specific prototype power converter. By maximizing the performance of the different subcircuits in successive design iterations, the fundamental questions about the viability of CMOS technology for high-frequency controller/driver applications can be answered. The ability of CMOS to satisfactorily perform at these high frequencies is documented. >

Feedback controller design for servo systems with dominant mechanical resonances

An estimator-based linear discrete-time controller for a high-performance two-axis miniature wheelchair drive is presented. This drive has a dominant resonance at approximately half the Nyquist frequency of the controller. The controller actively damps this resonance while simultaneously achieving a higher closed-loop bandwidth than in conventional designs. The controller design methodology is based on linear-quadratic-Gaussian (LQG) optimal control. Transformations are presented that simplify the implementation of the resulting fourth-order state estimator and linear control law. The drive is implemented with incremental-position encoders, a microprocessor, switching converters and a pair of motors.<<ETX>>