DC CIRCUITS

Part I of III Parts

Part II installation

Part III troubleshooting

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What is a Variable Frequency Drive?

A Variable Frequency Drive is an electronic device

designed to vary the speed of a motor while maintaining

power factors that are comparable to that of the motor at

it’s synchronous speed

VFD Cooling Tower

Fan Control

Adjustable Speed Drives

ALTIVAR 58

ALTIVAR

66

VLT 6000 Dan Foss

IntelliPak Rooftops

Voyager III Rooftops

HVAC Applications - Trane Equipment

M Series Air Handlers

Commercial Self-Contained

Have VFDs installed and commissioned right at the Trane factory

CenTraVac Chillers

T Series Air Handlers

Orderable with

Factory Mounted &

Commissioned VFDs

HVAC Applications - Field Applied

Special Purpose such as Parking Garage Fans

Cooling Towers

Primary & Secondary Pumping Applications

General Purpose HVAC Fans

Buildings are rich with Field Applied VFD opportunities

Simplified Operation

• Larger, easier-to-read display graphs

– Plain text

– Icons

– Up to 5 data items displayed

– Real Time Clock

– Free text displays

• Redesigned intuitive keypad

• LEDs indicate Hand/Off/Auto Mode

• One-touch alarm log key

TR1 TR200

Usability enhanced with the TR200 local control panel

Read The Tag!

The VFD

Benefits of VFD

• Efficient means of modulating the output of conventional induction motors

and synchronous motors.

• Make it practical to use precise motor speed in a wide variety of applications.

• VFDs offer the best turndown ratio.

• Some of the new models approach the near-zero-speed capability of DC

drives.

• Low maintenance—no moving parts other than push-buttons.

• Ease of installation and retrofit.

• Improved power factor

• Better control of variables

Limitations • VFDs waste more energy as heat, particularly when there is significant speed reduction.

• The VFD does not deliver a true sine wave voltage to the motor. Harmonics may be an

issue.

• VFDs increase losses in the transformers that feed them because of distortion of the

input waveform.

• Some VFDs may cause existing motors to run substantially hotter.

• Not usable with conventional ac motors in applications where the motor must maintain

high torque as the speed is reduced.

• Conventional motors lose their ability to get rid of heat as speed is reduced (limitation of

the motor rather than a limitation of the drive.)

• Motors need to have cooling independent of motor speed, which is typically a special

requirement.

• Overall system efficiency of modern dc drive systems and variable-pulley drives can be

higher than the system efficiency of VFDs on induction or synchronous motors.

• Can lead to system power problems

• Can lead to system component or equipment failures

• Will not fix system problems

• More complexity more problems

• Need for qualified people to install, maintain and service

Types of VFD’s

• Variable Voltage Input (VVI)—This is the simplest type of VFD. The output

switching devices approximate a sine wave voltage for the motor by a series of

square waves at different voltages. VVI drives use a large capacitor in the DC

link to provide a relatively constant DC voltage to the inverter.

• Current Source Input (CSI)—Similar to a VVI, the main difference with

CSI is that the CSI drive is able to force a square wave of current, rather than

voltage, through the motor. CSI drives use a large inductor to keep the DC

current relatively constant.

• Pulse Width Modulated (PWM)—This is the most complex VFD design, but

also offers the most potential for increasing motor efficiency. The PWM

inverter uses transistors to switch the direct current at high frequency to

deliver a series of voltage pulses to the motor. The width of each pulse is

tailored so that the voltage pulses interact with the reactance of the motor

windings to produce current flow in the motor that approximates a sine wave.

• Vector Drives-(VVFD)-- Vector drive is like an inverter drive except the

Vector drive has feedback on rotor position. Feedback includes motor speed,

current and back EMF. This takes place with open or closed loop control.

Part II installation

Control

• Analog Inputs

• Analog Outputs

• Binary Inputs

• Binary Outputs

• Communicating system interfaces

Control Testing

TR-1 Control

TR-200 Control

Safety Stop

MCB 101 General Purpose

MCB 105 Relay

MCB 115 Analog I/O

• BACnet will be offered on-board as standard

• Easy-to-install, plug-in optional I/O

On-Board: Modbus RTU

Johnso N2

Siemens FLN

BACnet MS/TP (2Q 2009)

Optional Modules: LonWorks FTP

BACnet MS/TP

DeviceNet (future)

PROFIBUS DP (future)

Control

Magic Component's • Regulator

– Electronic controls

– Filters

– Lots of Magic in the boxes which in realty is

just electronics switching between 0 and 1.

VFD sections

• Regulator—Controls the rectifier and

inverter to produce the desired ac frequency

and voltage.

• Rectifier—Converts the fixed 60 Hz ac

voltage input to dc.

• Inverter—Switches the rectified dc voltage

to ac, creating variable ac frequency (and

controlling current flow, if desired).

Components

• Rectifier

• Inverter

• Power Quality

Drive Layout Input PWR

Quality

Output

TR200 Layout

TR-1

The Value of a Drive

• Return on investment

1. Drive Horsepower

• 746 watts equals 1 horsepower

• Horsepower

– Srpm = synchronous revolutions per minute.

– 120 = constant

– F = supply frequency (in cycles/sec)

– P = number of motor winding poles

» Srpm = 120 x F

P

» HP = Torque x rpm

5250

2. Power Factor

3. Performance

–

TR-200

Safety Stop

An adjustable frequency

drive converts AC to DC

and then back to AC.

AC DC AC

Rectifier Inverter

PWM Drive:

Diode Bridge

Rectifier

DCAC Rectifier

Rectifier

Half-Wave Rectifier

The Full Wave Rectifier

The Full Wave Rectifier

Period, range of q Diode Pair in conduction

30o to 90o D1 and D6

90o to 150o D1 and D2

150o to 210o D2 and D3

210o to 270o D3 and D4

270o to 330o D4 and D5

330o to 360o and 0o to 30o D5 and D6

CAPACITOR

A capacitor is an electronic device which consists of two plates

separated by some type of insulator. A capacitor's value is

commonly referred to in microfarads, one millionth of a farad. It

is expressed in micro farads because the farad is such a large

value of capacitance.

When a DC voltage source is applied to the capacitor there is an initial

surge of current, then the current stops. When the current stops flowing,

the capacitor is in a charged state. If the DC source is removed from the

capacitor, the capacitor will retain a voltage across its terminals. This

charge can be discharged by connecting the plates together. Generally, if

an AC voltage source is connected across the capacitor, the current will

flow through the capacitor until the source is removed. The exceptions

to the situation, where an AC voltage is applied to a capacitor, are going

to be explained later.

• DC BUSS CAPACITORS:

THE GOOD, THE BAD, AND THE UGLY!

Inductors (Chokes)

• Inductors are simple coils of wire

• Stores energy in the form of magnetic fields

• Unit of measure is Henries

• Used to delay and reshape alternating

currents

• An inductor stores energy in the magnetic

field created by the current.

• When the current through a coil changes

and an induced voltage is created as a result

of the changing magnetic field, the direction

of the induced voltage is such that it always

opposes the change in current.

• What reactions do you see in AC or DC .

• DC current

• Back EMF present during DC turn-on until

stabilized, Back EMF present with polarity

reversed during DC turn-off until decay is

complete.

• AC current

• Back EMF present alternating in each

direction due to on off action of AC

Inductor Applications

• Coils resist rapid changes in the current

flowing through them.

• Inductors freely pass steady dc current.

The Inverter

Section

• Controls the frequency applied to the motor.

• Controls the speed of the motor.

A/C Power

//upload.wikimedia.org/wikipedia/commons/d/d0/PWM_VFD_Waveform.png

Position A B C

T0 ++ - -

T1 + + - -

T2 - ++ -

T3 - - + +

T4 - - ++

T5 + - - +

T6 ++ - -

• How they do it:

• Change the frequency of the electricity to the AC motor to change its speed

• Change the voltage to the AC motor as appropriate for the frequency and load

Low Speed

High Speed

Frequency

Voltage

Voltage

Frequency

VFD Introduction

Half the Frequency, Half the Synchronous Motor Speed

Input Harmonics

VFD meets IEEE-519 1992 harmonic distortion

voltage and current limits.

VFD is supplied with a minimum 18 pulse

input.

VFD manufacturer guarantees compliance to

IEEE-519 1992 by offering on-site testing.

Institute of Electrical Engineers L'institut des ingénieurs électroniciens et électriques, inc..

If a drive must be supplied with an input

harmonic filter to meet IEEE-519 1992, the

drive manufacturer must address if filter must

be modified if the user:

a. moves the VFD to a different power system,

b. changes the present power system (e.g.

changes upstream transformers, cables, etc.)

or

c. operates the VFD on two different power

sources (e.g. normal operation and generator

operation).

VFD system efficiency shall be a

minimum of 96%. VFD system

efficiency includes losses in:

power conversion equipment

input transformers

output transformers (if needed)

power factor correction (if needed)

harmonic filters (if needed).

VFD system efficiency value is guaranteed by vendor.

A drive should have an efficiency rating of 95% or better at full load.

Variable frequency drives should also offer a true system power factor

of 95% or better across the operational speed range, to avoid penalties

from the power utility, save on energy bills, and to protect you equipment

(especially motors).

Motor Issues

Standard AC induction motors can be operated by the VFD system

without motor de-rating.

VFD system is supplied with input transformer to protect motor from

common mode voltages. VFD systems using an input line reactor in

lieu of an input transformer are unacceptable.

All output voltage harmonics in the motor waveform up to the 200th

harmonic are less than 10% of the fundamental.

The motor voltage maximum step size is less than 1200V in order to

reduce reflected wave insulation stress associated with long motor

cables.

All current harmonics in the motor waveform up to the 200th

harmonic are less than 3% of the fundamental at full load.

VFD system can produce at least 100% full load torque at locked

rotor conditions

Input Power Ridethrough

Capabilities

VFD can ride through a 5 cycle

loss of input power without

tripping.

VFD can ride through a 30%

voltage dip indefinitely without

tripping. A decrease in output

speed and power is allowable.

Power Component Replacement/Repair

Since minimizing drive down-time is essential to

maximizing the user’s profits, the time required to

replace a failed power component or cell is

critical. The drive vendor shall provide a timed

demonstration of the replacement of a failed

power module.

Power module replacement time shall be less

than fifteen (15) minutes.

Rear or side access to the equipment is NOT

required for troubleshooting or periodic

maintenance

Operating Experience

The VFD vendor shall provide a

users list of operating units in the

field. This list shall only include

those units that are similar in power

circuit topology to those being

proposed for the present project.

VFD vendor shall have units of

similar power circuit technology

operating in the field for at least two

(2) years