PSI Pump Systems Inc. 1(800)900-2220

gilamonsterbirdsElectronics - Devices

Nov 24, 2013 (3 years and 8 months ago)

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PSI Pump Systems Inc.

1(800)900
-
2220

PSI Pump Systems Inc.

1(800)900
-
2220

Variable Frequency Drives


Presented by

PSI Pump Systems Inc.


Your Solutions Experts for

Pumps & Water Treatment”

PSI Pump Systems Inc.

1(800)900
-
2220

The Purpose

of

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 correction

5.
Emergency bypass capability

6.
Protection from overload currents

7.
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 Issues

Starting 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 Basics

Simplified 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 Basics

Functions & 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