Variable Frequency Drives

The easiest way to learn all about AC Variable Frequency Drives and get Certified

Are you interested in knowing more about AC Variable Frequency Drives (known as VFDs for short)  These are also called by other names like  Variable Speed Drives, AC Drives, Inverter Drives, Frequency Drives, Adjustable Speed Drives and other similar terms.

A Variable Frequency Drive is an important part of any manufacturing plant or facility today. Nowadays you see them being increasingly used in all kinds of places, not just manufacturing plants and industries, but also in office buildings, warehouses and other commercial places. The reason is easy. They are the best thing that ever happened to the ac induction motor, as you can now control these motors in a variety of ways, which were not at all possible earlier. For years together, the ac motor, the workhorse of all manufacturing as well as all kinds of activity of any kind, was labeled as a "constant speed machine". But with the advent of this new technology, we could easily adjust speed as well as other parameters of these motors easily.

Where can you get more information about Variable Frequency Drives?

The information that is available on how to use these drives is not very easily available. Of course there ARE several sources of information, but are problematic. Why? Read on below:

Source 1: The internet

Of course, there is a lot of "free information" out there that is on the internet, but it is difficult to verify, collate and understand. To do this would also require literally spending endless hours surfing, and trying to find something that can actually be used in your work. What is your time worth? Multiply that by the hours that you would have to spend collecting all this information. Also some of this information may be incorrect as well as outdated. You also don't get a Certificate for your labors.

Source 2: Textbooks

You could buy a textbook on the subject from any of the bookstores; the only problems being that the information is very likely outdated and secondly many of these are written in a way that is difficult to understand for the practising engineer or technician like you. Seriously, do you have the time to solve some complex vector mathematics, differential equations and the like? Or would you want to find out quickly how to select and use a commercially available VFD for your application? Also no Certificate gets issued if you read the book.

Source 3: Vendor literature & training courses

Would you ask a barber whether you need a haircut? What would be the answer? No prizes for guessing! If you ask a vendor (nothing against them, they are the ones who develop the technology behind these wonderful devices), the chances are that you will not get UNBIASED answers. Suppose a standard V/f drive is good enough for your application. Would a typical vendor tell you that? Or would he/she try to "upsell" you to a more advanced one? I think you get the point....
Vendor specific training programs will cover only the models and types of VFDs that the vendor sells.

So, we at Abhisam Software (who develop a lot of e-learning courses for engineers and technicians), thought about it and decided that we should have an UNBIASED, VENDOR NEUTRAL, COMPLETE  TRAINING COURSE WITH CERTIFICATION about this wonderful technology which is also

a) Easy to understand with graphics and animations to explain key concepts

b) Having a complete, unbiased and current vendor neutral information

c) Not too long winded and boring, without skipping anything important

d) Easily accessible- Either download it to your PC/laptop or access it online based on the version that you select

d) Having an associated exam and Certification with an electronic badge- display your competence to the world!

So we decided to make this software based training program for it,  which we call an XPRTU. (It makes an expert out of you). 


Read on below to see the Table of Contents

Module 1 – Basic Concepts

  • Introduction to the Course
  • Introduction to AC Motor Drives
  • Better Load Matching
  • Focus on AC Motors
  • What you will learn
  • VFDs, VSDs, ASDs, VVVF Converters, Inverters
  • AC Motors-1
  • An ac induction motor
  • An AC Induction Motor working
  • Speed Control of ac induction motors
  • Speed of an AC Induction Motor
  • Power, Speed and Torque
  • Torque
  • Lifting Torque
  • Torque for different types of loads
  • Locked Rotor Torque
  • Motor characteristics and types
  • Design A Motor
  • Design B Motor
  • Design C Motor
  • Design D motor
  • Design E Motor
  • Which type is best for my application?
  • Load torque characteristics for different kind of loads
  • Load torque characteristics Animation
  • Classification of loads
  • Constant Torque loads
  • Variable Torque loads
  • Constant Power loads
  • Four Quadrant Operation
  • Overview of AC motor controls
  • DOL starter (Direct On Line starter)/Across the line starter
  • Star (Wye) and Delta connections
  • Control with a VFD
  • Why use VFDs?
  • Advantages of using a VFDs
  • Disadvantages of VFDs
  • Industrial applications of VFDs
  • Self Assessment Test

Module 2 - Inside a VFD

  • Introduction to the module
  • Overall Design
  • Rectifier Block
  • DC Link Block
  • Inverter Block
  • Controller Block
  • How it all works together
  • VFD parts & VFD components
  • Diode
  • Diode Curve
  • Switching frequency of diodes
  • Rectifier Circuits
  • Freewheeling Diode
  • Full Wave Rectifier
  • Three Phase Rectifiers
  • Rectifier Circuits-Representation
  • Thyristors (Silicon Controlled Rectifiers-SCRs)
  • Thyristor Firing Angle
  • Three Phase Thyristor Rectifiers
  • DC link block
  • Soft Charge Circuit
  • Inverter Block
  • Transistor (BJT)
  • Working model of a transistor
  • Transistor as an amplifier
  • Transistor as a switch
  • IGBT
  • Pulse Width Modulation
  • How does PWM work
  • PWM Waveform Generation
  • Changing the PWM amplitude
  • Changing the PWM frequency
  • Noise effects of PWM inverters
  • Self Assessment

Module 3 - VFD Functions

  • Introduction to the module
  • Introduction
  • Schematic of a typical VFD
  • Starting/Stopping of the motor
  • Acceleration/Deceleration
  • Ramping
  • Speed Limits
  • Speed Changing
  • Forward/Reverse operation
  • Motor Thermal Overload Protection
  • Braking
  • Braking- Electrical or Mechanical?
  • Electrical Braking using VFDs
  • Motoring and regeneration
  • Braking Resistor
  • Dynamic Braking
  • Regenerative Braking
  • Slip Compensation
  • Application Example
  • Open Loop Control
  • Closed Loop Control
  • Control schemes in VFDs
  • V/f Control
  • Vector Control
  • Sensorless vector control
  • Flux Vector control (Closed loop)
  • Shaft encoders
  • PID Control
  • Anti-windmill protection and Flying Start
  • Skip Frequencies
  • Torque Control
  • How does DTC work?
  • Advantages and Disadvantages of DTC
  • Self Assessment

Module 4 - Energy Saving using VFDs

  • Types of Loads
  • Pumps, Fans and Blowers
  • Traditional flow control
  • Control of Centrifugal Pumps
  • Centrifugal Pump basics
  • Pump Characteristic Curve
  • System Curve
  • Operating Point
  • Throttling the flow
  • Control Valve
  • Effect of discharge throttling
  • Throttled Flow Curve
  • Energy Savings
  • Other energy savings due to VFDs
  • Shorter Duty Cycles
  • Self Assessment

Module 5 - Specifying, Selecting and Installing VFDs

  • Introduction
  • Selection Process Flowchart
  • Load considerations
  • Evaluate VFD benefits versus traditional motor controls
  • VFD features for maximum benefit
  • Derating of VFDs
  • Temperature Derating
  • Altitude Derating
  • Protection
  • Harmonics due to VFD installations
  • Total Harmonic Distortion
  • Problems due to harmonics
  • What could be the PCC? Says who?
  • Measurement of harmonics
  • Harmonics in PWM type drives
  • Mitigation of harmonics
  • Supply Voltages
  • Number of Starts
  • Fuse Disconnects & Bypasses
  • Bypass Circuit
  • Panels and Enclosures
  • Installation in Panels & Enclosures
  • Earthing
  • Maximum Cable lengths
  • Self Assessment

Module 6 - Using VFDs with DCS/PLC systems

  • Introduction
  • Communication Networks
  • VFDs used in process plants
  • Digital Communication
  • Agitator Control via DCS Example
  • Implementation-1
  • DCS Configuration
  • Implementation-Option
  • Digital Communications
  • Profibus
  • Modbus
  • Functional Safety

Self Assessment Test


Choose from any of the Versions Below

For Individuals

Online $ 199 US
For Individuals
Course Duration: 10 hours (Approx 1 & 1/2 days of self paced learning)
Get 10 PDH (Professional Development Hours)
Includes Online Exam and Certification for 1 learner
Certificate Validity: Lifelong
Unlimited Online Access to the course for 1 Year
Course access renewal (if required) at discount
All modules
View with any device with a standard browser (PC/Laptop/Tablet/Mobile)
Standard $ 299 US
For Individuals
Course Duration: 10 hours (Approx 1 & 1/2 days of self paced learning)
Get 10 PDH (Professional Development Hours)
Includes Online Exam and Certification for 1 learner
Certificate Validity: Lifelong
Download the Course to your own PC. Unlimited access to the course for 3 years
Course access renewal (if required) at discount
All modules
View with any PC/laptop with Windows OS (7,8,10). Single PC license
Included in Gold Membership
For Individuals
Gold Membership : First Month $399 US and then $149 US Per Month only
Access to All Abhisam Courses (Online Versions) 24/7 for Gold Members
More Courses are being added every month
Cancel Subscription Anytime
Get One Free Certification Exam Per Month ( Certificate Validity : Lifelong)
Additional Certification Exams can be purchased at discounted price
All modules
View with any device with a standard browser (PC/Laptop/Tablet/Mobile)

By clicking 'BUY NOW', you will continue to the FastSpringLogo FastSpring checkout page where payment will be taken, and your order fulfilled by FastSpring, our trusted reseller, and Merchant of Record.

Earn Certificates and Badges

When you complete this e-learning course, you can take the associated exam and earn a Certificate of Competency, as well as an electronic badge, that you can display online on places such as LinkedIn and Facebook.

abhisam_vfd_samplecertificate            Abhisam Badge



Still Have Questions? No Problem, Here's A List Of Our Most Frequently Asked Questions (FAQ).

What is this? Is it just a power point presentation?

No, it is NOT a power point presentation at all! It is a full fledged, comprehensive e-learning course that we call as an XPRTU. It has text, graphics, animations, exercises that form a complete learning course. You can view a demo version here.

How will I get access to the course?

The course is available in three versions. The Online Version gives you a one year access to the course via the internet via any browser. The Download version is a Windows program that you can download and install on your own Windows OS (Windows XP, Vista, 7, 8/8.1/10). The Enterprise version is ideal for organizations that need to train larger numbers . You can buy any of these versions immediately via our e-commerce partner,Fastspring. Credit Cards, Bank payments are accepted.

What Operating Systems will it work on?

The Standard Download version will work on any Windows systems (Windows 7, 8, 8.1 or 10). The Online and Enterprise versions are accessible from any device (including Macs) that have a browser.

How do I get  Certified?

Simply take the Abhisam online exam within the validity of the license period. On passing you get an Electronic Certificate (pdf) as well as a Badge (issued via Credly), that you can display online on places such as LinkedIn or Facebook. This shows the world, including your prospective employers, customers or clients that you are competent in the subject. Our Badges conform to the Mozilla Open Badges standard and can be added to your backpack.

What is the ordering process?

When you click on the Buy Now button, you will be taken to the Fast Spring  secured payment site. Ordering is completely secure. You can pay online by either Credit Card or wire transfer/manual order. Note that you will get the license key to activate only after payment is approved.

Still Have Questions? No Problem. Contact Us by filling the form below and we will get back to you.