HOW2POWER TODAY

ISSUE: January 2012

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IN THIS ISSUE:

» From the Editor’s Desk

» Predictive Energy Balancing Enhances Control
   of Power Converters

» Voltage-Mode Control Scheme Improves Buck
   Converter Performance At High Frequencies

» System-On-Chip Architecture Raises Performance
   Of Microstepping Motor Driver Designs

» Current-Loop Control In Switching Converters
   Part 5: Refined Model

» Powering The Digital Media World:
   CES 2012 Signals Emergence Of Solar Inverters
   For Consumer Products

» Special Guest Commentary:
   Debunking Solar Power Myths: Misconceptions
   About Solar System Metrics Could
   Hamper Solar Success

» New Power Products

» What's New at H2P

New control techniques clear a path for higher performance in power supplies and motor drives. Some involve a refinement of existing methods to address some pressing design goals, while others take a novel approach aimed more at solving fundamental challenges in power conversion. An example of the latter may be found in Tom Lawson’s article on Predictive Energy Balancing, a control technique his company developed to overcome an inherent conflict in the design of PWM-controlled power supplies, which is how to achieve both stability and agility without compromise. Meanwhile, two other articles in this issue discuss refinements of voltage-mode control to benefit point-of-load regulators and microstepping motor drives. One control method pursues jitter-free operation in a synchronous buck converter running at high frequency and narrow duty cycle, while the other aims for high microstepping resolution with extremely low torque ripple. Moving away from control techniques, we also have the latest installment in Dennis Feucht’s series on modeling of current-mode control. Here, the author brings the discussion to a climax by unveiling his refined, unified model. In addition to the design articles, a commentary by Richard Leverton explores the fundamental, yet often misunderstood concept of yield in solar power systems and sets out to dispel potentially harmful (to customers and the industry) misconceptions about yield. Also in this issue, power devices with new twists on SiC, an evaluation tool for bus converters, high-performance energy metering and gate driver ICs, and more.

HOW2POWER EXCLUSIVE DESIGN ARTICLES

Predictive Energy Balancing Enhances Control of Power Converters

by Tom Lawson, CogniPower, Malvern, Penn.

Conventional pulse width modulation (PWM) control for switched-mode power supplies (SMPSs) must compromise two conflicting goals; stability versus agility. Various schemes for improving the outcome of the stability/agility compromise fill the literature, but do not dispatch the issue. However, a novel control technique known as Predictive Energy Balancing sidesteps the PWM control problem entirely. Through energy prediction, the phase lag of the output filter is removed from the feedback path. The underlying principle is that the voltage on the filter capacitor after the inductive energy from the switched inductor has been transferred can be calculated in advance. Given that information, the decision to switch from energizing the inductor to transferring inductive energy to the output can be made on the basis of the energy outcome at the end of the control cycle. That simple concept removes constraints that have long limited the performance of power converters. In this article, the underlying math and practical techniques for implementing Predictive Energy Balancing are explained, and experimental results are presented. Read the full story…

The extra circuitry required to implement a predictive converter with
near-ideal behavior is entirely manageable. This flyback converter
block diagram shows inputs required for the control circuitry.

At a 1.5-MHz frequency and 50-ns pulse width, the
IR’s new modulator scheme achieves very low jitter.

Voltage-Mode Control Scheme Improves Buck Converter Performance At High Frequencies

by Suresh Kariyadan and Parviz Parto, International Rectifier, El Segundo, Calif.

Higher operating frequency combined with jitter-free operation allows synchronous buck converter designs to run at higher closed-loop bandwidth, which results in the use of fewer output capacitors, saving board space and system cost. This article will explain the theoretical details of a new pulse-width modulator scheme for achieving jitter-free operation at high frequency and narrow duty cycle using a voltage-mode controller.

This modulator scheme has been implemented in International Rectifier’s IR3899 synchronous buck regulator, which also contains built-in features that provide enhanced flexibility in implementing point-of-load regulator designs. Test results will be presented to demonstrate the performance advantages of the new modulator scheme versus a traditional voltage-mode controller. In addition, the special features of the IR3899 will described. Read the full story…

System-On-Chip Architecture Raises Performance Of Microstepping Motor Driver Designs

by Enrico Poli, Vincenzo Marano, and Giovanni Frezza, STMicroelectronics, Agrate, Italy and Schaumburg, Ill.

In this article, a unique motor-drive architecture for microstepping will be presented. This architecture includes a novel approach to driving stepper motors based on voltage-mode control and an advanced motion engine controlled through an SPI interface.

The novel voltage-mode approach removes the need for sensing the motor’s phase currents and eliminates the special efforts normally required in phase-current control systems to reach acceptable performance. In the end, this control method allows high microstepping resolution with an extremely reduced torque ripple. This control system has been integrated in a single-chip device, called dSPIN (the L6470), which also includes an advanced logic core that implements a set of positioning and speed commands, stall detection, as well as protection features. In this article, the key features and operation of dSPIN including its voltage-mode control technique are described and experimental results are presented. Read the full story…

The L6470 dSPIN, a fully integrated microstepping
motor driver with motion engine and SPI, reduces the
MCU resources needed in typical motor control applications.

Current-Loop Control In Switching Converters
Part 5: Refined Model

by Dennis Feucht, Innovatia Laboratories, Cayo, Belize

In the previous sections of this article, we have discussed the historical development of the various models of current-mode control, compared and contrasted those models, and derived various expressions that lay the groundwork for developing a refined version of the unified model originated by Tan and Middlebrook. Here in part 5, we now present a refined model of current-mode control that overcomes some of the limitations of the existing models that have been previously discussed. Read the full story…

Have comments or questions about Dennis Feucht's series on Current-Loop Control or any of the other design articles? Send them to david@how2power.com and we'll publish the author's response in an upcoming issue.

POWERING THE DIGITAL MEDIA WORLD        
A monthly column sponsored by Integrated Device Technology

CES 2012 Signals Emergence Of Solar Inverters For Consumer Products

by Ashok Bindra, Technology Writer, Technika

The International Consumer Electronics Show (CES) in Las Vegas is a harbinger of new trends in consumer products and technologies. While there were many innovative gadgets unwrapped this year at CES 2012, the one that is of interest to power designers is the solar power inverter. The growth potential for this product category is strong and, therefore, more suppliers are entering this space. In this column, Bindra discusses the power products introduced by three startups—Wagan Tech, Goal Zero, and SolarFocus. Read the full story…

Special Guest Commentary       

Debunking Solar Power Myths: Misconceptions About Solar System Metrics Could Hamper Solar Success

by Richard Leverton, Hybridyne Power Electronics, Newmarket, Ontario, Canada

In response to Ontario’s very favorable feed-in tariff, there’s been a “gold rush” of companies hopping onto the solar bandwagon. For a company such as Hybridyne, which supplies hardware to this industry, there is a concern that the investors paying for these new solar installations might find themselves disappointed with the low yield they could experience. Such disappointment is a potential threat to the solar industry as it may lead to unfavorable publicity or possible lawsuits, which could discourage future adoption of solar technology.

At the core of this problem are several widely held misconceptions about the yield of photovoltaic (PV) systems. In this commentary, the author aims to debunk five myths concerning yield in a discussion that will be relevant to all those involved with the development, installation, and purchase of PV systems. On the development end, this includes power electronics engineers since the performance of the solar power inverter is central to this discussion. For more details…

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