psi pump systems inc. 1(800)900-2220. psi pump systems inc. 1(800)900-2220 variable frequency drives...
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PSI Pump Systems Inc.
1(800)900-2220
PSI Pump Systems Inc.
1(800)900-2220
Variable Frequency DrivesPresented by
PSI Pump Systems Inc.“Your Solutions Experts forPumps & Water Treatment”
PSI Pump Systems Inc.
1(800)900-2220
The Purposeof
VFD’s
PSI Pump Systems Inc.
1(800)900-2220
The Purpose
1. Energy savings on most pump and fan applications.
2. Better process control and regulation. 3. Speeding up or slowing down a machine or
process.4. Inherent power-factor correction5. Emergency bypass capability6. Protection from overload currents7. Safe Acceleration
PSI Pump Systems Inc.
1(800)900-2220
Electric & Power Basics
All VFD’s must:Run a machine or process at a desired
speed.Produce adequate torque to handle the
load. Use power efficiently to produce the
necessary torque at a given speed.Effectively monitor the application or
process.
PSI Pump Systems Inc.
1(800)900-2220
Electric & Power Basics
The typical waveform consists of the frequency portion (time based) of the wave and the amplitude portion (the magnitude). This wave is actually in sine-wave form, commonly referred to as the fundamental.
PSI Pump Systems Inc.
1(800)900-2220
Electric & Power Basics
Sinusoidal Waveform With Frequency & Amplitude Components
PSI Pump Systems Inc.
1(800)900-2220
AC-Induction-Motor Theory
PSI Pump Systems Inc.
1(800)900-2220
AC Induction Motor Theory
AC Induction Motor – Squirrel Cage Design
PSI Pump Systems Inc.
1(800)900-2220
AC Induction Motor Theory
Three-phase motor operation.
PSI Pump Systems Inc.
1(800)900-2220
AC Induction Motor Theory
How a motor shaft rotates Torque is produced as the
induction motor generates flux in its rotating field.
This flux must remain constant to produce full-load torque.
PSI Pump Systems Inc.
1(800)900-2220
AC Induction Motor Theory
As shaft torque load increases, the slip increases and more flux lines cut the rotor windings, which in turn increases rotor current, which increases the rotor magnetic field and consequently the rotor torque.
PSI Pump Systems Inc.
1(800)900-2220
AC Induction Motor Theory
Typical speed versus torque curve for a NEMA design B motor.
% Synchronous Speed
PSI Pump Systems Inc.
1(800)900-2220
AC Induction Motor IssuesStarting Induction Motors
The starting current is very high, between 3 to 8 times the full load current. Depending on the size of the motor, this can result in voltage sags in the power system.
The full torque is applied instantly at starting and the mechanical shock can eventually damage the drive system, particularly with materials handling equipment, such as conveyors.
In spite of the high starting current, for some applications the starting torque may be
relatively low, only 1.0 to 2.5 times full load torque.
PSI Pump Systems Inc.
1(800)900-2220
AC Induction Motor Theory
The speed of the rotating electric field within the induction motor.
Synchronous Speed = 120 x frequency # of motor poles
PSI Pump Systems Inc.
1(800)900-2220
AC Induction Motor Theory
AC motor speed change can be accomplished in three ways:
(1) Change the number of poles in the motor; this means separate windings;
(2) Change the slip characteristics of the motor; this is done with varying resistors, such as is done with a wound-rotor motor or by varying the stator voltage; or
(3) Change the frequency of the power supplied to the motor. This is the method of choice .
PSI Pump Systems Inc.
1(800)900-2220
Components of VFD’s
Power electronics is that field of electronics which covers the
conversion of electrical energy from one form to another for high power applications.
PSI Pump Systems Inc.
1(800)900-2220
Components of VFD’s
Vacuum tubes Thyristors (SCR’s) provided the standard method
for rectifying AC. Also referred to as a diode.
PSI Pump Systems Inc.
1(800)900-2220
Components of VFD’s Transistors provide fast switching
capability for a relatively low cost. The general types of transistors are:
» The bipolar transistor;» The gate turn off transistor (GTO)» The field-effect transistor (FET);» The insulated gate-field-effect transistor
(IGFET); » The insulated gate-bipolar transistor (IGBT).
PSI Pump Systems Inc.
1(800)900-2220
VFD Basics
A VFD in a block diagram.
PSI Pump Systems Inc.
1(800)900-2220
Components of VFD’s
All VFD’s need a power section that converts AC power into DC power.
This is called the converter bridge. Sometimes the front end of the
VFD, the converter is commonly a three- phase, full-wave-diode bridge.
PSI Pump Systems Inc.
1(800)900-2220
Components of VFD’s
Rectifier is that special type of converter that converts AC to DC.
PSI Pump Systems Inc.
1(800)900-2220
VFD Basics
DC Bus The DC bus is the true link
between the converter and inverter sections of the drive. Any ripple must be smoothed out before any transistor switches “on”. If not, this distortion will show up in the output to the motor. The DC bus voltage and current can be viewed through the bus terminals.
PSI Pump Systems Inc.
1(800)900-2220
VFD BasicsSimplified Circuit showing DC bus components:
The DC link is an important section of the drive as it provides much of the monitoring and protection for the drive & motor circuit. It contains the base-drive fusing and pre-charge capacitor network, which assures steady voltage DC voltage levels prior to the inverter bridge and allows a path for over-voltage dissipation.
PSI Pump Systems Inc.
1(800)900-2220
VFD Basics
Input Waveforms The voltage that is not stepped down
is rectified through the diodes, and a DC bus voltage should be present.
The DC + and DC – terminals will typically read approximately 325 volts DC on a 230 volts AC supplied drive and 650 volts DC on a 460 volts AC supplied drive.
This waveform, when viewed, is straight DC, possibly with some rippling effect from the AC input.
PSI Pump Systems Inc.
1(800)900-2220
VFD Basics
Power-Module The inverter section is made up
primarily of modules that are each made up of a transistor and diode in combination with each other which inverts the DC energy back to AC.
PSI Pump Systems Inc.
1(800)900-2220
VFD Basics
Simplified Inverter Section of a VFD
PSI Pump Systems Inc.
1(800)900-2220
VFD Basics
The DC waveform looks more like an AC waveform but the voltage
waveform is much different. The power semi-conductors in
the inverter section act as switches, switches of the DC bus, and therefore, are pulsing the motor with some voltage.
PSI Pump Systems Inc.
1(800)900-2220
VFD Basics
A typical square wave takes its shape on the square-wave look due to this switching function ( which explains the sharp rise to peak) rather than a rotational, changing state of amplitude.
This frequency and amplitude pattern is sometimes called the carrier frequency of a PWM drive.
PSI Pump Systems Inc.
1(800)900-2220
VFD Basics
Pulse-width-modulated voltage and current waveforms.
PSI Pump Systems Inc.
1(800)900-2220
VFD Basics The VFD changes the DC energy
into three channels of AC energy that an AC induction motor can
use to function properly. Inverters are classified as
voltage- source, current-source of variable-voltage types. This has to do with the form of DC that the inverter receives from the DC bus.
PSI Pump Systems Inc.
1(800)900-2220
VFD Basics
Types of VFD’s Solid-state AC VFD’s can be
named for their use, by their DC bus/inverter voltage or current source, by their waveform (PWM or PAM), by the type of power device used in their inverter section, or by their performance characteristics.
PSI Pump Systems Inc.
1(800)900-2220
VFD Basics
The main objective of the VFD is to vary the speed of the motor while providing the closest approximation to a sine wave for current (while pulsing DC voltage to the motor).
PSI Pump Systems Inc.
1(800)900-2220
VFD Basics
Volts-per-Hertz Control
The area within each pulse is the power delivered to the motor in volt-microseconds.
PSI Pump Systems Inc.
1(800)900-2220
VFD Basics
How VFD’s Operate
The PWMs drive ability to maintain the AC levels through all types of load conditions at given speeds is the factor which separates one drive manufacturer from the other.
PSI Pump Systems Inc.
1(800)900-2220
VFD BasicsFunctions & Features
Set-up Parameters The Control Method Acceleration or Accel-Ramp
Rate Automatic Restart Stopping Method Automatic Signals
PSI Pump Systems Inc.
1(800)900-2220
VFD Basics
Functions & Features Jump, Skip or Critical Frequencies Fault Logs and On-Board Diagnostics Power Loss Ride Through Slip Compensation Catch a Rotating Motor, Speed Search or Pick-Up a Spinning Load
PSI Pump Systems Inc.
1(800)900-2220
VFD Basics
Conclusion Significant energy savings Easy setup & programming Retrofits Space Better design Competitive edge