Variable Frequency Drives (also known by other names such as Variable Speed Drives, Inverter Drives, Frequency Drives, Adjustable speed drives) are growing in importance every day as 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. Variable Frequency Drives 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.
However, 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:
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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
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Originally Posted by mdtrivedi
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