Richard M. Bass

Averaged modeling of PWM converters operating in discontinuous conduction mode

Various aspects of averaged modeling of hard-switching pulse-width modulated (PWM) converters operating in the discontinuous conduction mode (DCM) are studied. A more streamlined modeling procedure is proposed which serves as a general framework for comparing different models. A duty ratio constraint that defines the diode conduction interval is identified to be the key to accurate prediction of high-frequency behavior. A new duty-ratio constraint is proposed that leads to full-order averaged models of DCM converters. Numerical analyses and experimental measurements confirm that the new models correctly predict the small-signal responses up to one third of the switching frequency and are more accurate than all previous models. Moreover, new analytical results are included to show the origin of the high-frequency pole in DCM operation and to explain why the full-order model is capable of accurately predicting it. Averaged circuit counterparts of the new models are developed in the form of averaged switch models to facilitate circuit simulation.

Modeling of PWM converters in discontinuous conduction mode. A reexamination

Six existing methods for modeling PWM converters in discontinuous conduction mode (DCM) are reviewed. They are classified as either reduced-order or full-order model methods, and the methods in each group are shown to produce exactly the same averaged models. Using the concept of duty-ratio constraints, a new method is presented that leads to either the conventional reduced-order model or a new full-order model, depending on how the duty-ratio constraint is derived. With a boost converter as an example, the new full-order averaged model is shown to be more accurate than previously published models.

Analysis of the class AD audio amplifier including hysteresis effects

Combinations of analog and switching techniques have led to the development of audio power amplifiers capable of producing low distortion with high efficiency. The high efficiency is achieved with a combination of an inverter and an analog amplifier, where the inverter provides the power, and the analog amplifier acts as an active filter to correct distortion. In this paper, a full analysis of the system is presented using the hysteresis describing function approach to model the inverter. The set of equations obtained allows the description of the nonlinear behavior of the system, such as the limit cycle of the output voltage and its dependency on the hysteresis. The theoretical development also provides the relation between the switching frequency and the system parameters. The derived equations are verified and compared using PSpice simulations.

Analysis of charge pumps using charge balance

A simple, generalized method for steady-state analysis of charge pumps or switched-capacitor power supplies, which is intuitive yet accurate, is presented. Second order effects that were previously not considered are included. The analysis is compared with simulations and shown to be accurate. The significance of the equations for analyzing charge pumps is also discussed.

Residential harmonic loads and EV charging

The market penetration of large single-phase residential harmonic loads, including electric vehicle (EV) battery chargers of 6.6 kW, is a potential power quality and power delivery concern for electric power providers and consumers. Charging systems with high harmonic current distortion can potentially result in secondary distribution line and transformer de-rating or quality of service consequences. This paper reports on the main findings of a project that examined the secondary (customer-side) distribution harmonic impacts of residential harmonic loads, with and without EV charging. Simulations as well as actual field test site data, to determine the impact of residential single phase loads and EV charging systems on the secondary of the distribution transformer, show that-commercial EV chargers engineered to National Electric Vehicle Infrastructure Working Council (IWC) guidelines based upon IEC 1000-3-4 do not give rise to excessive voltage THD on the secondary of the transformer-the rise in voltage THD due to EV charging is less than 0.8% in all three field test sites and should not be a cause for concern. Load management strategies like off-peak charging should be encouraged to minimize the impacts on the distribution system.

Autonomous control technique for high-performance switches

A method for creating high-performance switch modules from power transistors and simple control circuits is presented. The method is based on switching function principles by which any type of switch can be represented by an ideal switch in combination with basic logic elements. These high-performance modules can be configured to emulate diodes, thyristors, special resonant devices, or nearly any other switch type. The control is autonomous-it depends on the terminal behavior and external gate signals and requires no additional information from the application circuit. Experimental examples of several switch modules in low-voltage power converters are given. The experimental modules use power MOSFETs and give performance similar to that of synchronous rectifiers but with much greater flexibility. An example is noted in which a module configured to emulate a silicon controlled rectifier (SCR) shows voltage drops below 0.25 V at several amperes of forward current. >

Comparison of VSI and CSI topologies for single-phase active power filters

This paper explores design considerations and relative merits of the voltage-source inverter (VSI) and current-source inverter (CSI) topologies for single-phase active power filter applications. While the VSI has largely overtaken the CSI as the inverter of choice for many applications, the CSI is shown to have certain advantages for single-phase active power filtering.

Control structure optimization of a boost converter: an LQR approach

This paper investigates the interaction between the power stage and the controller of a boost converter and suggests a new method for simultaneously designing the power stage and controller. The controller is formulated as a linear quadratic regulator and the associated cost function is minimized through changes in the power stage parameters. It is found that better performance can be achieved than with a traditional two-step design process where the power stage and controller are designed sequentially. Optimization and simulation results for a boost converter are presented to illustrate the design process and benefits.

Large-signal averaging methods under large ripple conditions [for power convertors]

The accuracy of the averaging approximation is known to deteriorate as the ripple magnitudes of power converters] increase. This paper describes and compares the application of two large-ripple averaging methods, the multi-frequency averaging (MFA) method and Krylov-Bogoliubov-Mitropolsky (KBM) method.

Large signal design alternatives for switching power converter control

Three theoretical design constraints based on the state-space geometry of the large-signal switching model are introduced. Experimental confirmation of the theoretical results is reported. The relation to small-signal analysis and design is explored.<<ETX>>