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VARIABLE FREQUENCY
DRIVES
Need for variable frequency drives
•
Match the Torque of a drive to the process requirements
•
Match the Speed of a drive to the process requirements
•
Save Energy and improve efficiency
Need for variable frequency drives

Smooth acceleration/deceleration to .....



Energy savings are possible .....



Reduce mechanical wear and water hammer
Reduce current surges in the power supply system
Most significant with centrifugal pumps and fans because
Power/energy consumption changes with Speed3
Speed controlled to match the process requirements
....
e.g. ... flow or pressure controlled to match demand

Automatic Control of the Process Variable is
possible

Closed loop control from a Process Controller
Variable speed – Energy
consumption

Principles applied to centrifugal Pumps and Fans
Variable speed – Energy
consumption

Compare two methods of speed control in a Motor Car ....
 Speed controlled using Drive Control (AB)
 Speed controlled by using Load Control (AC)
Common example of VS control

The Motor Car is a common example of VS control
 Control Torque to provide Acceleration and
Braking
 Controls Speed to match the traffic conditions
 Controls the use of Fuel

Main controls in a Motor Car are :
 Accelerator, which controls the Driving torque
 Brake, which adjusts the Load torque
 Control System .... the driver
4 – Quadrant drive
4 – Quadrant drive




1st QUADRANT ..... Torque is +ve and Speed is +ve
 Therefore ..... Power is +ve
 Energy transferred from Drive to Load
2nd QUADRANT ..... Torque is -ve and Speed is +ve
 Therefore ..... Power is -ve
 Energy transferred from Load to Drive .... Braking
3rd QUADRANT ..... Torque is -ve and Speed is -ve
 Therefore ..... Power is +ve
 Energy transferred from Drive to Load
4th QUADRANT ..... Torque is +ve and Speed is -ve.
 Therefore ..... Power is -ve
 Energy transferred from Load to Drive .... Braking
Fundamental principles

Power is Rate at which Work is being done by a machine
 Power is measured in Watts, or usually kW or MW
 Power is product of Torque x Speed
 At standstill .... Output Power = Zero
Power (kW) =
Torque (Nm) x Speed (rev/ min )
9550
Torque (Nm) =

9550 x Power (kW)
Speed (rev/ min )
Energy represents the work done over a period of time
 Energy is the product of Power x Time
 Energy is measured as kiloWatt-hours .... kWh
Load Torque
Machine Load
Characteristic Curve
Formulae
Conveyors
Screw Conveyors
Pos. Displ. Pumps
Compressors
T = k (Constant)
Centrifugal Pumps
Centrifugal Fans
T = k x n2
Extruders
Slurry Pumps
T B = Breakaway
Winders
Lathes
P= k
P = k . n .T
k = Constant
P = k x n3
T=
k .P
n
Load Torque
Machine Load
Reciprocating
Machines
Presses
Crushers
Mills
Wood Chippers
Cranes
Sawmills
Presses
Characteristic Curve
Formulae
Torque – Speed curves

Torque, Power & Speed are the most important
parameters

Torque-Speed curves illustrate the performance of the
VSD


Power-Speed curves illustrate the performance of the VSD


shows the rotational force at various speeds
shows the rate of energy consumption at various speeds
These parameters are all related ... for example the Motor
Car

Pressing the accelerator produces more torque
.... which provides acceleration and gives more speed
.... which requires more power (torque x speed)
.... which requires more energy (fuel) (power x time)
Types of variable speed drives



Mechanical Variable Speed Drives
 Belt and chain drives with adjustable diameter sheaves
 Metallic friction drives
Hydraulic Variable Speed Drives
 Hydrodynamic types
 Hydrostatic types
Electrical Variable Speed Drives
 DC Drive with DC motor
 VVVF Converter with AC motor
 Slip Control with Slip ring Induction Motor
 Cyclo-converter with AC motor
 Electromagnetic Coupling or "Eddy Current" Coupling
 Servo Drives and Stepper Drives
Common types of variable frequency drives
Migration from DC to AC drives
Principles of AC variable drives

Speed controlled by adjusting the Power Frequency (f)
120 f
 Synchronous Speed
=
rev/ min
n
s


Actual speed is slower due to the Slip
 Actual Speed
n = ( ns - slip)
rev/ min
Stator field flux () is derived from the supply voltage
 Air-gap Flux
V
 

p
f
Output Torque is product of flux density and rotor current IR
 Output Torque
T   I R Nm
AC Variable speed drive
From these equations, the following deductions can be made
 Speed is controlled by Frequency AND Stator Voltage




Speed reaches Base Speed when VS = maximum,
 Further speed increase reduces the Field Flux 
 This is known as the Field Weakening range
Torque is dependent on VS
 Full torque possible at ALL speeds in normal speed range
 But Torque falls to zero at standstill
In the Normal Speed range
 Output power increases in proportion to the speed
In the Field Weakening range,
 Torque falls in proportion to the speed
 Output power of the AC Motor remains constant
AC Variable speed drive
AC Variable speed drive

Main Features of the AC Variable Speed Drive
 Good control and performance characteristics
 AC converter relatively complex and expensive
 AC Motor needs no maintenance ... high reliability
 Efficiency : Converter ± 97% ... overall AC drive >90%
Basic definitions

Rectifier ... AC to DC converter

Inverter … DC to AC converter
Basic definitions

AC Converter converts one AC voltage and frequency to
another AC voltage and frequency .... often variable

Usually requires an intermediary DC link with smoothing
Basic definitions

DC Converter ... Converts one DC voltage to another DC voltage

Usually requires an intermediary AC link, such as a transformer
Basic definitions

Electronic Switch .......
 Electronically connects or disconnects an AC or DC circuit
 Can often be switched ON or OFF from a gate terminal
Bistable switching

Electronic Switch usually operated in the bistable mode
 Blocking Mode :
fully switched OFF
• Voltage across switch is High
• Current through switch is Low (only leakage current)
 Conducting Mode :
fully switched ON
• Voltage across the component is Low
• Current through the component is High

Diodes, Thyristors & GTOs are inherently bistable

Transistors are NOT inherently bistable
 Must be biased fully ON or OFF to behave like a bistable
device
Power diodes
IDEAL : Forward Conduction



: Resistanceless
Reverse Blocking
: Lossless
Switch on/off Time
: Instantaneous
Main terminals are the Anode (A) and the Cathode (K)
 Names come from the days when Valves were common
When the anode is positive relative to the cathode
 it is said to be forward biased and the diode conducts
When the anode is negative relative to the cathode
 is said to be reverse biased and current is blocked
Power diodes

Many different mechanical designs are used

Rated from a few amps … to thousands of amps

Most common is for several diodes to be encapsulated into an
Insulated Module ... 6-pulse bridge, half bridge, etc

The base of the module electrically isolated ... Can be mounted
directly onto heatsink
Bipolar junction transistor


Main advantage of Bipolar Junction Transistors (BJT) ....
 Turned on and off from the base terminal
 Suitable for Self commutated inverter circuits
Disadvantage is low base amplification factor .... 5 to 10
 base circuit must be driven by an auxiliary transistor
 called the Darlington connection
Field effect transistor


FET is a special type of transistor ...
 particularly suitable for high speed switching applications
 Gate is voltage controlled .... not current controlled
 behaves like a HF voltage controlled resistance
MOSFET is a three terminal device
 Source (S), Drain (D) and the Gate (G)
 correspond to Emitter (E), Collector (C) and Gate (G) of BJT
Field effect transistor

MOSFET is a majority carrier device .... short switching time
 so ... switching losses are low
 best suited to high frequency switching applications

With development of Pulse Width Modulated (PWM) inverter
 high frequency switching has become a desirable feature
 to provide a smooth output current waveform

MOSFETs are used for Small PWM frequency converters
 MOS stands for Metal Oxide Silicon.
 Ratings from 100Amp @ 50Volt to 5Amp @ 1000Volt
Insulated gate bipolar transistor


Insulated Gate Bipolar Transistor (IGBT) .....
 unites best features of BJT and MOSFET technologies
 Construction similar to a MOSFET with additional layer to
 provide conductivity modulation, similar to BJT
 low conduction voltage drop
IGBT is a three terminal device ....
 Power terminals are called Emitter (E) and Collector (C)
 Control terminal is called the Gate (G)
Insulated gate bipolar transistor


IGBT has ...... good forward blocking ability
 very limited reverse blocking ability
 Operates at higher current densities than BJT or MOSFET
Electrical equivalent circuit of the IGBT .... hybrid device
 MOSFET driver integrated with a Bipolar PNP transistor
Insulated gate bipolar transistor



Gate driver requirements similar to those of power MOSFET
 Turn-on : 10V - 15V takes 1s .... Threshold typically 4V
 Turn-off : zero volts takes 2s ... accelerated by -ve volts
IGBT devices can be produced with faster switching times at the
expense of increased forward voltage drop
Main advantages of IGBT are :
 Good power handling capabilities .... 500A at 1,500V
 Low forward conduction voltage drop of 2V to 3V … higher
than BJT but lower than MOSFET of similar size
 Gate is voltage controlled with low gate current
 Relatively simple voltage controlled gate driver
 High speed switching capability .... up to about 20kHz
 VF increases with temperature .... making device suitable
for parallel operation ... without thermal instability
Comparison of PE switches
Overall control system

Overall Control System divided into 4 main areas :
 Inverter Control System
 Speed Control System and Speed feedback
 Current (Torque) Control System and Current feedback
 External System Control Interface
Overall control system



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Inverter Control System
 Controls the Switching Sequence of Inverter Switches
 Provides Component Protection
Speed feedback and Speed Control System
 Controls the Speed output relative to Setpoint
Current Control System and Current feedback
 Controls the Current output relative to Limits
 Provides Short-circuit and Earth-Fault Protection
 Motor Modelling and Thermal Overload Protection
External System Control Interface
 User Settings and Programming
 Digital and Analog interface to Control System (PLCs)
 Fault Diagnostics
Power supply requirements



Simplest Method for Power Supply ... Mains Transformer
 Major problem ... interruption of the Mains Power
 VSD Stops ... even for short dips in the supply
Commonly use Switched Mode Power Supplies (SMPS)
 Control power maintained until motor stops
 Mains failure ... power initially from large DC Capacitors
 Thereafter ... motor behaves as AC induction generator
Usually have several Power Supplies to modules such as ...
 Device Driver Power Supplies need to be isolated
 Cooling fans for the converter heatsinks
 DC Link Bus Charging Circuits
 Control Cards .... Microprocessor circuits
DC Bus charging

Two main approaches to DC Bus Charging ....
 Charging resistors with Contactor Bypass (most common)
 Phase-controlled bridge rectifier instead of diode bridge
DC Bus charging - Resistors

Many variations on Charging Resistor theme ...
 Resistors can be in DC link or on 3-phase supply lines
 Single large resistor or multiple sets of smaller resistors
 Electronic Switch instead of Relay ... smaller VSDs

Main Advantages of Charging Resistors are ....
 Simplicity of the control circuit
 Cheap and easy to implement
Main Disadvantages are .....
 Losses due to relay contacts and coils
 Physical size of these components
 Reliability of electromechanical devices ...
 Can be a problem with numerous starts and stops

Controlled thyristor bridge

Phase-controlled rectifier bridge ...
 Used mainly on larger sizes ... above 22kW
Controlled thyristor bridge

Phase-controlled rectifier bridge ....
 Capacitor voltage increased gradually


Main Advantages of Controlled Thyristor Bridge are ....
 Conduction losses are lower
 Physical size reduced by not having the relay
Main Disadvantages are .....
 Thyristors more expensive than Diodes
 More complex control circuit
 Reactive power requirements are slightly higher

Some VSDs with PWM Rectifier ... other advantages
PWM Rectifier bridge

Controlled PWM Rectifier Bridge ... also called Active Front End
 Capacitor DC Voltage increased gradually
 Also has other advantages …
 Also called ... Active Front End Drive
PWM Rectifier bridge

Main Advantages of PWM Rectifier Bridge are :
 Reduces the level of harmonic currents in mains … AC Line
current waveform is much smoother
 Makes full 4-quadrant operation possible
 Can control power factor angle ... power factor correction

Main Disadvantages of PWM Rectifier are .....
 IGBT Bridge is more expensive than Diode Bridge
 Control Circuit is more complex and expensive
 Require line chokes to limit rate of current rise
AC Waveform-Ideal
Synthesized AC Waveform-Square
Synthesized AC Waveform-Part
Square
Synthesized AC WaveformTrapezoidal
PWM Inverter

Output Frequency controlled ... by changing switching speed

Output Voltage controlled ... by changing the Pulse Width

Output Current waveform … depends on load impedance
Synthesized AC Waveform-PWM
PWM Inverter
PWM Inverter

Modulation Technique for sine-coded PWM using the SineTriangle intersection method - digital implementation
3-Phase PWM Inverter
3-Phase PWM Inverter
AC Variable speed drives

In general, AC Variable Speed Drives are designed to ...
 Transform Electrical Energy into rotational Mechanical
Energy

In most applications ...
 Control Speed with reasonable accuracy

In special Applications ...
 Need accurate and fast dynamic control of speed and
torque
AC Variable speed drives
There are 3 basic types of AC Variable Speed Drive available
today



“Standard” Fixed V/f Drive (also known as a VVVF Drive) …
 OK for Pumps & Fans
 Less expensive than the devices below
Sensorless Vector Control Drive …
 Better Speed Regulation
 Better Starting Torque & Acceleration
Field Oriented Flux Vector Control Drive ...
 Full implementation of Vector Control Strategy
 Excellent Speed and Torque control characteristics
Variable speed drive control loops
The Level of Control can be ...



Simple Open-Loop Control ...
 This is the strategy used for Fixed V/f drives
 No internal feedback from the motor (except for protection)
Closed-Loop Control ...
 This is the strategy used for Vector Control drives
 Feedback from the motor used to adjust PWM output
 Achieves enhanced performance
Cascade Closed-Loop Control ...
 Strategy used for Field Oriented Flux Vector Control drives
 Feedback of Torque and Speed used to improve dynamic
performance
 Achieves better than DC Drive performance
Open loop control


Open loop speed control is suitable for ....
 Applications where Speed Accuracy not important
 Consequences of changes in the process not severe
Standard fixed V/f drives ... are essentially Open Loop type
Open loop control

Speed Reference fed to Ramp Circuit to convert step change in
the speed request to a slowly changing signal

V/f Regulator sets magnitude of Voltage and Frequency

Finally, PWM Switching logic section controls the switches
according to a PWM algorithm (sine-coded, etc)

No speed feedback from the motor .... open-loop control

Current feedback is for protection, indication & current limit
Closed loop control

Closed Loop Control used for more difficult drive applications ...
 Torque, Speed or Position accurately controlled
 Accuracy of control ..... very important
 Errors .... have a large influence on the process

For these applications, Closed Loop Control is necessary
 Generally applies to high performance VSDs .... such as DC
Drives and Vector controlled AC VSDs
 Standard fixed V/f AC Drives can be used in closed loop
systems ... but they are not capable of high performance
Closed loop control

Accurate Feedback from motor transducer.....
 Speed transducer …
tacho or encoder
 Position transducer …
position encoder
 Torque transducer …
current transducer
Power Converter .... controls the Motor response

Controller .... which controls the Converter

Closed loop control

Closed Loop Control System operates as follows ....
 Measurement of Process Variable (PV) .... eg an encoder
 Comparison of PV with Set Point (SP) gives an error value
....
error value = SP - PV
Error value processed by Controller to adjust the Output,
which in turn Controls the AC converter and motor
In industrial applications, the controller is a Microprocessor


Closed loop control

Motor Car ..... example of a closed-loop feedback control
 Speed assessed by the driver looking at speedometer
 Measured speed (PV) is compared to desired speed (SP)
 Depending on the error, the driver may decide to
• increase speed by pressing the accelerator
• decrease speed by pressing the brake
 Driver continually measures PV, calculates the error and
gives the appropriate Output

At the same time, Driver might be simultaneously engaged in
several other tasks of closed-loop feedback control, such as
steering, controlling cabin temperature, etc.
Cascaded loop control



If each variable was proportional to the variable before it
 Simple Open-loop control, without feedback would be OK
 In a VSD .... some time delays not simply proportional ...
motor current responds to new frequency with a rise
 The time is dependent on its leakage inductance
 Motor speed follows the torque with a rise time ... dependent
on its inertia
Inaccuracies acceptable in simple applications ....
 Speed control for pumps, conveyors, etc
Some applications require Close Speed and Torque control
 Speed and Torque control of paper machine VSDs
Cascaded loop control

Design techniques have evolved from DC Drives ... and deals
with control problem in two smaller stages
 Speed Loop compares speed ... calculates current setpoint
 Current Loop compares current ... calculates frequency
setpoint
Cascaded loop control

Speed Loop allows for one of time delays in system
 delay between the torque and the measured speed

Current Loop allows for other time delay ....
 delay between the output frequency and the current
 rate of change of current is faster than change of speed

The two control loops required for accurate speed control are
 An outer Speed Control Loop, which compensates for the
mechanical transients, mainly load inertia
 An inner Torque Control Loop, which compensates for the
electrical transients, mainly winding X and R
Vector control

Vector Control ...
 Been available since the mid-1980s
 Promoted as an AC equivalent to DC Drives
 Only become possible as a result of the large strides in the
fields of power electronics and digital control

Gets its name from the fact that ....
 System can separately measure and control the two Vector
components of the stator current
 Vectors represent magnitude and direction of the current
 Specifically ....Flux current and Torque-producing current
Vector control

Vector Control is a “generic” name applied to all AC Drives that
provide performance that is higher than “standard” AC Drives

Vector Control is one of the more abused terms used to
promote the use of modern AC Variable Speed Drives ...
 performance said to be equivalent to high performance DC
Drives
Dynamic Performance that is equivalent to a DC Drive is only
possible if Vector Control is fully implemented
 There are many Vector Control Drives on the market that
only partially implement the strategy

Vector control

Simplified equivalent circuit of an AC Induction Motor

Using a Hall-effect current transducer, the drive can measure
the Stator Current IS flowing to the motor ... but NOT IR and IM
Vector control

IR and IM are the Vector components of Current IS

Vector components can be calculated from measured values
Vector control


Therefore, the main purpose of Vector controller is to ...
 Continuously calculate value of Flux Current IM
 Continuously calculate value of Torque Producing Current IR
 Continuously calculate other variables such as Slip, Shaft
Speed, etc
Central part of Vector control is the Active Motor Model ...
 Uses motor constants stored in memory as part of calculation to
continuously model the connected motor
 Measures stator current in each phase and uses this to
calculate the torque current (IR) and flux current (IM)
 Measures actual speed and calculates slip
 For adequate dynamic response of the drive, these calculations
need to be done at a rate of more than 2,000 times per sec
 This only became commercially viable within last 10 years with
development of 16-bit microprocessors
Sensorless vector control

These are essentially Fixed V/f “open loop” drives with some
performance enhancements due to a digital “Motor Model”

The Motor Model is used to calculate 2 main variables
 Flux Current (IM) ... to automatically regulate output V/f
ratio. This results in improved Torque performance,
particularly at low speeds
 Percentage Slip ... to automatically regulate output
frequency. This results in improved Speed holding
performance ... without the need for a shaft mounted
encoder (hence the name Sensorless Vector Control)
For Sensorless Vector Control to be effective, the drive needs
to be “tuned” to the connected motor
 Auto-tuning feature normally available ... used to measure
the required motor parameters and store them in memory

Field oriented flux vector drives

These are ”Closed loop” drives with an Active Motor Model
and cascaded Speed and Torque control loops

The high performance microprocessor runs a Motor Model that
can calculate numerous drive variables

For the Vector Control to be effective, the drive needs to be
“tuned” to the connected motor
 Auto-tuning feature normally available ... used to measure
the required motor parameters and store them in memory
Field Oriented Flux-Vector Control necessary on drives where ...
 Accurate speed and/or torque control is necessary
 High dynamic performance is required ... speeds and/or load
torque change rapidly
 Full torque is required at zero speed ... for example on hoists

Field oriented flux vector drives

In a Flux Vector drive ...
 The Power circuit is identical to fixed V/f drive
 Main difference ...... is in the control system
Field oriented flux vector drives

Flux-Vector control of a PWM Converter ....
 Control is essentially Cascaded Closed-loop type
Vector control performance
Some interesting Figures …
Speed
Accuracy
Torque
Response
DC Drive
with
encoder
V/f Vector
Sensorless
V/f Vector
with
encoder
Field
Oriented
Sensorless
Field
Oriented
with
encoder
0.01%
1.0%
0.1%
0.5%
0.001%
10-20msec
100msec
10-20msec
1-10msec
1-10msec
Basic setting parameters
Remaining Parameters settings can be selected as follows :
 Maximum speed ... usually set to 50Hz or higher
 Minimum speed ... usually 0Hz for a pump or fan drive and
higher for constant torque applications
 Rated Motor Current ... size of motor may be small
 Current Limit ... determines Starting Torque
 Acceleration Time ... determines the Ramp-up Time
 Deceleration Time ... determines the Ramp-down Time
 Braking Method ... 3 Options usually available
 Starting Torque Boost ... cover Breakaway Torque
Note : Avoid over-fluxing the motor !!!


Other Settings ... possibly adjust "default" settings
Synthesizing an AC WaveExamples




Simple square wave
Square wave with smaller conduction width
Trapezoidal waveform
A series of pulses of fixed amplitude but varying width within a
cycle (known as pulse width modulation or PWM)
Protection of AC variable speed
drives

The protection of AC Variable Speed Drives includes ...
 Protection of the AC Converter
 Protection of the Electric Motor
AC Converter protection

Protection for front-end rectifier usually NOT provided …
 Usually require external upstream short-circuit protection
 HRC fuses or fast Circuit Breaker

Following protection usually included ...
 Protection systems for the PWM Inverter
 Protection for DC Busbar
 Protection for Output … Motor and Motor Cable
• Motor thermal overload protection
• Motor short circuit protection
• Motor earth fault protection
Summary of overall protection
Input phase imbalance

One input phase voltage low ....
 Other 2 phases will conduct majority of supply current
 Possible failure of rectifier diodes

DC Current ... miss every 3rd pulse, other 2 pulses higher
 can lead to failure of the rectifier diodes or capacitors

Input Phase Imbalance Protection implemented by .....
 Measuring the Input Currents .... Costly
 Monitoring the DC bus .... analyse waveform distortion
DC bus under voltage

Power Circuit can operate at any voltage 0 - VMax

Under-voltage protection required for Power Supplies
 Typically set to 15% below lowest rated voltage

When Power Supply output voltage regulation is lost ...
 Microprocessor could switch to an indeterminate state
 Driver circuits lose control of the Power Switches
 Power Switch may attempt to operate in the linear region
 Power Switch may be slow to switch off
 Power Electronic Switches will fail
DC bus over voltage

All electrical components fail if exposed to high Over-voltage

In AC drives, high DC over-voltages can occur due to ...
 High voltages in the mains power supply ... Very Rare
 Motor behaving as Induction Generator .... dynamic
braking of a high inertia load

The following components have the lowest tolerances to High
Voltages ....
 DC bus Capacitor Bank
 DC bus connected Power Supply Modules
 Power Electronic Switching Devices
DC bus over voltage

DC capacitor bank ... series and parallel capacitors
 Sharing will not be perfect

Peak voltage on DC bus is approx 1.4 x supply voltage
 With a maximum capacitor voltage of VMax = 750VDC ... the
practical limit for input voltage is 480VAC + 10%
 For AC drives with >500Volt input, special capacitors are
required

Maximum voltage of Semiconductor switches is 1,400 VDC
 Seems well above Capacitor rating
 But, voltage across a device during turn-off can be
 400V higher, due to stray circuit inductances
 Bus voltage must be limited to 800 VDC Maximum
DC bus over voltage

In Modern Digital AC drives ...
 Over-voltage Protection provided by microprocessor
because DC bus voltage changes relatively slowly

Digital controller can also provide over-voltage control
 During deceleration of load ... override ramp-down setting to
prevent the over-voltage trip
 DC bus voltage allowed to rise to safe 750 VDC
 Trip level typically at 800 VDC
Operation interface & diagnostics

Human Interface Module (HIM) .... LCD or LED Display

3 Main levels of operator information and fault diagnostics :
1. Parameters ... Settings, Status and Metering
2. Diagnostic information ... Status of Protection Circuits
3. Diagnostic information ... Status of Internal Circuits
... internal diagnostics only found in special VSDs
Internal parameters

Typical Internal Parameters and Fault Diagnostics ...
Module
Parameters and Fault Diagnostics
Power Supply
Power Supply Voltage, Current and Frequency
DC Bus
DC Link Voltage and Current
Motor
Output Voltage, Current, Frequency, Speed, Torque, Temperature
Control Signals
Setpoint, Process Variable, Error, Ramp times
Status
Protection circuits, module failures, internal temps, fans running,
switching frequency, current limit, motor protection, etc
Fault Conditions
Power device fault, power supply failed, driver circuit failed, current
feedback failed, voltage feedback failed, main controller failed
Fault diagnostics - parameters

Common Faults ... possible Internal/External Problems
Protection
Internal Fault
External Fault
Over-voltage
Deceleration rate set too fast
Mains voltage too high
Transient over-voltage spike
Under-voltage
Internal power supply failed
Mains voltage too low
Voltage sag present
Over-current
Power electronic switch failed
Driver circuit failed
Short circuit in motor or cable
Thermal Overload
Control circuit failed
Motor over-loaded or stalled
Earth Fault
Internal Earth fault
Earth fault in motor or cable
Phase Imbalance
Power diode in rectifier failed
Mains phase voltage imbalance
Phase connection loose
Over-temperature
Cooling fan failed
Heatsink blocked
Ambient too high
Enclosure cooling blocked
Thermistor Trip
Motor thermistor protection
Motor side filter

Connection Example of Line Filter and Motor Filter
Natural ventilation


Enclosure can be Smaller ... additional Ventilation required
 Exchange air between Inside and Outside of enclosure
Natural Ventilation
 Convectional cooling airflow through air vents
 Vents at Bottom and Top ..... the "chimney" effect
Forced ventilation

Cooling airflow assisted by fan at Top or Bottom of cubicle
General safety requirements

Requirements for Safety .... should be carefully followed
 Australian Standard AS 3000 : SAA Wiring Rules apply
 Safety earths must be installed before power connected

AC Converters have Large Capacitors on the DC link
 After VSD switched off ..... wait several minutes
 Allow internal capacitors to fully discharge
 Visual Indication ... shows when capacitors are charged
Hazardous areas

AC Converters should NOT be mounted in Hazardous Areas .....
even when connected to an Ex rated motor

When necessary .....
 AC converters may be mounted in Approved Enclosure
 Certification should be obtained for entire VSD System ....
including both Converter and Motor
Any questions ?