Category: Variable Frequency Drives

The Quick Guide to AC Variable Frequency Drives launched

Sep 19, 2010-Abhisam Software is thrilled to launch its latest product, “The Quick Guide to AC Variable Frequency Drives“.

This guide book is meant as an easy guide to any electrical or electronic engineer or technician, who would like to know how modern  ac variable speed drives work. Variable Frequency Drives (VFD for short),  also known by other names such as Adjustable Speed Drives  or Variable Frequency Drives are seeing increasing adoption by a host of industries and establishments. The drive towards saving energy costs is a big factor, but so are also other factors such as ease of use, sophisticated functions that allow precise control of ac motors and the ability to hook up these drives to communication networks.

However, even as VFD technology continues to progress by leaps and bounds every year, the amount of real world information available seems to be lacking. So the user of VFDs has very few choices-either refer to published books that are obsolete or depend on VFD vendors for the information.Or oen can surf the internet to find nuggets of information here and there, but it is a time consuming process, without any end and with no guarantee that the information is genuine.

Hence Abhisam Software has introduced this Quick Guide to AC Variable Frequency Drives in order to be a quick reference to the user of these drives. The ebook covers almost everything that is practically needed to use and install VFDs. It is also being offered at a very low introductory price of $27 US, so that it is affordable to everybody.

The Table of Contents is given below.

BASIC CONCEPTS

• Introduction
• VFDs, VSDs, ASDs, VVVF Converters, Inverters
• AC Motors
• An ac induction motor
• Speed Control of ac induction motors
• Power, Speed and Torque
• Torque
• 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
• 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
• Inverter Duty Motors
• Advantages of using a VFD for control of motors
• Speed Regulation
• Better Power Factor
• Soft Starting
• Flexibility in input power
• Precision Controls for torque and speed
• Energy Saving
• Replacement of control valves in process plants
• Built in PID controls
• Communication
• Possibility of replacing DC drives with AC VFDs
• Disadvantages of VFDs
• Harmonics
• Cannot be used with all motors
• Distance limitations
• Noise
• Industrial applications of VFDs

INSIDE A VFD

• Introduction
• Inside a VFD
• Overall design
• Rectifier Block
• DC Link block
• Inverter block
• Controller block
• VFD parts & VFD components
• VFD Components
• Diode
• Diode Curve
• Switching frequency of diodes
• Rectifier Circuits
• Half wave rectifier
• Full wave rectifier (Bridge rectifier)
• Three phase bridge rectifiers
• Thyristors (Silicon Controlled Rectifiers-SCRs)
• Firing angle
• Three phase rectifier using thyristors
• DC link block
• Soft Charge Circuit
• Inverter Block
• Transistor (BJT)
• Working model of a transistor
• Transistor as an amplifier
• Transistor as a switch
• MOSFET
• IGBT
• Pulse Width Modulation
• How does Pulse Width Modulation work?
• Changing the amplitude of the output sinusoidal waveform
• Changing the frequency of the output sinusoidal waveform
• Noise effects of PWM inverters

VFD FUNCTIONS

• Starting/Stopping of the motor
• Acceleration/Deceleration
• Ramping
• Speed Limits
• Speed Changing
• a) Using the digital inputs
• b) Using a potentiometer
• c) Using the analog input signal
• d) Using Digital Communication
• Forward/Reverse operation
• Motor Thermal Overload Protection
• Slip Compensation
• Control schemes in VFDs
• Open Loop controls in VFDs
• Closed loop control with VFDs
• V/f Control
• Vector Control
• What is the “vector” in vector control?
• Sensorless vector control
• Flux Vector control (Closed loop)
• Shaft encoders
• Absolute encoders
• Incremental encoders
• Difference between absolute encoder and incremental encoder
• Closed Loop Flux Vector Control
• Field Oriented Control (FOC)
• Comparison between V/f drives and Vector Control drives.
• PID Control
• Anti-windmill protection and Flying Start
• Anti-windmill protection
• Flying Start-Catching up with the motor at power on
• Skip Frequencies
• Torque Control
• Direct Torque Control
• How does DTC work?
• Advantages of DTC
• Disadvantages of DTC
• Motoring and regeneration
• Braking Resistor
• Dynamic Braking
• Line regenerative braking
• DC injection braking
• Motor Overflux braking

ENERGY SAVINGS USING VFDS

• Types of Loads
• Pumps, Fans and Blowers
• Traditional flow control
• Control of Centrifugal Pumps
• Affinity Laws of Centrifugal Pumps
• Centrifugal Pump basics
• Pump Characteristic Curve
• System Curve
• Energy savings with fans and blowers
• Other energy savings due to VFDs
• Power Factor improvement
• Reduction in demand charges
• Shorter Duty Cycles

SPECIFYING, SELECTING AND INSTALLING VFDs

• Flowchart
• Load considerations
• Evaluate VFD benefits versus traditional motor controls
• VFD features for maximum benefit
• Derating of VFDs
• Temperature Derating
• Altitude Derating
• Overload Capacity
• Harmonics due to VFD installations
• What are Harmonics?
• 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 voltage
• Number of starts
• Fuse Disconnects
• Bypass circuit
• Installation inside a panel or other enclosure
• Earthing
• Maximum Cable length from VFD to the motor
• IGBT switching
• Standing wave & Reflected wave phenomenon
• Voltage drop
• Long cable length solutions
• Multiple inverters in the same VFD

USING VFDS WITH DCS/PLC SYSTEMS

• VFDs used in a process plant
• Detailed Implementation of the above
• Digital Communications
• Need for digital communications
• Functions of a typical digital network
• Profibus
• Modbus
• Safety Aspects
• Summary & Conclusion

You can see how detailed and comprehensive it is; though it has been designated as a “quick guide”-the reason being that everything is explained in very easy to understand language, so that users of VFDs need not feel that they are reading a PhD thesis. They just want to know how to specify, select and install VFDs and this is what the ebook does. A trial preview is available here.

These drives are also known by various other names such as vfd drives, variable speed drives, frequency drives, ac motor drives, vfd inverter, vsd drives, variable frequency ac drives, variable frequency drives, ac drives, frequency inverter.