1. Introduction

To avoid shoot-though in voltage source inverters (VSI), dead-time, a small interval during which both the upper and lower switches in a phase-leg are off, is introduced into the standard pulse width modulation (PWM) control of VSIs. How­ever, such a blanking time can cause problems such as output waveform distortion and fundamental voltage loss in VSIs, es­pecially when the output voltage is low.

To overcome dead-time effects, most solutions focus on dead-time compensation  by introducing complicated PWM compensators and expensive current detection hardware. In practice, the dead-time varies with the gate drive path propa­gation delay, device characteristics and output current, as well as temperature, which makes the compensation less effective, especially at low output current, low frequency, and zero current crossing. Several switching strategies for PWM power converters have been proposed to minimize the dead-time effect. A dead-time minimization algorithm was also discussed earlier to improve the inverter output performance. A phase-leg configu­ration topology proposed prevented shoot through. However, an additional diode in series in the phase-leg increases complexity and causes more loss in the inverter. Also, this phase-leg configuration is not suitable for high-power inverters because the upper device gate turn-off voltage is reversely clamped by a diode turn on voltage. Such a low voltage, usually less than 2 V, is not enough to ensure that a device is in its off-state during the activation of its complement device.

High-power inverters usually need longer dead-time than those low-power counterparts. Also due to complicated struc­tures and severe parasitic parameter variations, in practice, the dead-time for high-power inverters requires specific adjustment and/or compensation, and usually this process is time-con­suming. For general applications, automatically eliminating dead-time by gate drive technology is a desired and complete solution. Gate drives with intelligent functions are in high demand due to the emerging technology of power electronics building blocks (PEBB) and intelligent power modules (IPM) because smart functions can improve power devices’ modu­larity, flexibility and reliability.

In this work, an effective dead-time elimination method is proposed. This method is based on decomposing of a generic phase-leg into two basic switching cells, which are configured with a controllable switch in series with an uncontrollable diode. Therefore, dead-time is not needed. In this paper, the effect of dead-time in VSIs will be first introduced. The prin­ciple of the proposed method to eliminate dead-time effect is explained in detail. Simulation and experimental results are provided to demonstrate the validity and features of the proposed novel method. Flexible implementation methods are also discussed.

ABSTRACT

Yii is a high-performance component-based PHP framework for developing large-scale Web applications. It enables maximum reusability in Web programming and can significantly accelerate the development process. The name Yii (pronounced as Yee or [ji:]) stands for easy, efficient and extensible.

What is Yii Best for?

Yii is a generic Web programming framework that can be used for developing virtually all sorts of Web applications. Because it is light-weighted and equipped with sophisticated caching solutions, it is especially suitable for developing high-traffic applications, such as portals, forums, content management systems (CMS), e-commerce systems, etc.

How is Yii Compared with Other Frameworks?

Like most PHP frameworks, Yii is an MVC framework. Yii excels over other PHP frameworks in that it is efficient, feature-rich and clearly- documented. Yii is carefully designed from the beginning to fit for serious Web application development. It is neither a byproduct of some pro ject nor a conglomerate of third-party work. It is the result of the authors’ rich experience of Web application development and the investigation and reflection of the most popular Web programming frameworks and applications.

INTRODUCTION

The Yii framework is free software. It is released under the terms of the following BSD License.
1.1 New Features

This page summarizes the main new features introduced in each Yii release.

• Version 1.0.7

• Added support for displaying call stack information in trace messages

– Logging Context Information

• Added index option to AR relations so that related ob jects can be indexed using the values of a specific column

– Relational Query Options

• Version 1.0.6

• Added support for using named scope with update and delete methods:

– Named Scopes

• Added support for using named scope in the with option of relational rules

• Added support for profiling SQL executions

– Profiling SQL Executions

• Added support for logging additional context information

– Logging Context Information

• Added support for customizing a single URL rule by setting its urlFormat and case Sensitive options:

– User-friendly URLs

• Added support for using a controller action to display application errors:

– Handling Errors Using an Action

• Version 1.0.5

• Enhanced active record by supporting named scopes. See:

– Named Scopes

– Default Named Scope

– Relational Query with Named Scopes

• Enhanced active record by supporting lazy loading with dynamic query options. See:

– Dynamic Relational Query Options

• Enhanced CUrlManager to support parameterizing the route part in URL rules. See:

– Parameterizing Routes in URL Rules

1.2 What is Yii

Yii is a high-performance component-based PHP framework for developing large-scale Webapplications. It enables maximum reusability in Web programming and can significantly

accelerate the development process. The name Yii (pronounced as Yee or [ji:]) standsfor easy, efficient and extensible.

Requirements

To run an Yii-powered Web application, you need a Web server supporting PHP 5.1.0 or higher.

For developers who want to use Yii, understanding ob ject-oriented programming (OOP)is very helpful, because Yii is a pure OOP framework.

1.3 What is Yii Best for?

Yii is a generic Web programming framework that can be used for developing virtually all sorts of Web applications. Because it is light-weighted and equipped with sophisticated

caching solutions, it is especially suitable for developing high-traffic applications, such as

portals, forums, content management systems (CMS), e-commerce systems, etc.

1.4 How is Yii Compared with Other Frameworks?

Like most PHP frameworks, Yii is an MVC framework. Yii excels over other PHP frameworks in that it is efficient, feature-rich and clearly-documented. Yii is carefully designed from the beginning to fit for serious Web application development. It is neither a byproduct of some pro ject nor a conglomerate of third-partywork. It is the result of the authors’ rich experience of Web application development and the investigation and reflection of the most popular Web programming frameworks and applications.

1.4 Installation

Installation of Yii mainly involves the following two steps:

• Download Yii Framework from yiiframework.com.
• Unpack the Yii release file to a Web-accessible directory.

Requirements

After installing Yii, you may want to verify that your server satisfies all the requirementsof using Yii. You can do so by accessing the requirement checker script at the followingURL in a Web browser:

http://hostname/path/to/yii/requirements/index.php

The minimum requirement by Yii is that your Web server supports PHP 5.1.0 or above.

Yii has been tested with Apache HTTP server on Windows and Linux operating systems.

It may also run on other Web servers and platforms provided PHP 5 is supported.
Download Full Article Yii Framework.doc

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