Variable Frequency Drive Power & Control Theory Overview

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 One

The 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 Two

The 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.  There is a quiz/test at the end of the course with a passing score of 70%.