Variable Frequency Drive Basic Theory & Power Flow Explained

An introduction to variable frequency drive motor control technology and VFD power flow theory explained.

What you'll learn

The purpose of variable frequency drive (VFD) motor control.

List the two main sections of a VFD and list the subsections within these sections.

Describe the various control functions of a modern VFD.

List VFD input and output (I/O) signal types, analog and digital.

Describe how a VFD multifunction input and output works and how these functions are assigned.

Describe the power flow from the AC line supply to the motor in a modern VFD.

Name each electronic power component in a modern VFD.

Explain how energy is returned from the motor and how the DC link section or bus deals with this energy.

Understand important terms such as carrier frequency, switching frequency, pulse width modulation (PWM), volts per hertz or scalar control and dc injection.

Requirements

This course is designed for the beginner to advanced electrical student, technician, technologist or electrician that wants to learn about variable frequency drives (VFDs) or wants to improve existing skills when working with VFDs.

Description

This short course is designed to help an electrical technologist, technician, student, or experienced tradesperson to quickly get up to speed when learning about variable frequency drives (VFDs). The course is also useful for engineering students when understanding important VFD power and control concepts.A theoretical understanding of power flow and components is crucial when installing, commissioning, and troubleshooting variable frequency drive motor control systems.Part OneThe first portion of the course uses simple graphics to explain the functionality of the power and control sections of a VFD. Important drive power sections are discussed such as the converter, dc bus or link and the inverter section. The VFD control section is broken down into subsections with each part being explained.Part TwoThe second part of the course uses a VFD power schematic diagram to explain the power flow through each electronic power component in the drive. This video lesson describes the power flow through all sections of the VFD. The PWM inverter output waveform is shown and changing the carrier, or switching frequency is explained and demonstrated. The PWM waveform is shown at different carrier frequencies and output frequencies. The lesson also focuses on the DC link or "bus" and how energy is returned from the motor and is sent to a braking resistor. The front-end active drive is shown and briefly discussed.An assignment is attached to each video lesson along with an answer key. Also, to review information covered, there is a quiz at the end of each section.

Overview

Section 1: Introduction

Lecture 1 Introduction to Variable Frequency Drives Assignment

Section 2: Introduction to VFDs, the Block Diagram and Basics Overview

Lecture 2 Section 2 Assignment for Lecture 3 Video Lesson

Lecture 3 Introduction to VFDs, the Block Diagram and Basics Overview

Section 3: The VFD Power Schematic & Power Flow Explained

Lecture 4 Section 3 Assignment for Lecture 5 Video Lesson

Lecture 5 The VFD Power Schematic & Power Flow Explained

This short course is designed to help an electrical technologist, technician, student, or experienced tradesperson to quickly get up to speed when learning about variable frequency drives (VFDs). The course is also useful for engineering students when understanding important VFD power and control concepts. A theoretical understanding of power flow and components is crucial when installing, commissioning, and troubleshooting variable frequency drive motor control systems.