Electronics. Modelling, Analysis and Design.
Physical Process Modeling Team:
SOLID STATE DC DRIVES
DC MOTORS FUNDAMENTALS AND MECHANICAL SYSTEMS
DC motor- Types, induced emf, speed-torque relations; Speed control - Armature and field speed control;
Ward Leonard control - Constant torque and constant horse power operation - Introduction to high speed drives and modern drives.
Characteristics of mechanical system - dynamic equations, components of torque, types of load;
Requirements of drives characteristics - multi-quadrant operation; Drive elements, types of motor duty and selection of motor rating.
Principle of phase control - Fundamental relations; Analysis of series and separately excited DC motor with single-phase and three-phase
converters - waveforms, performance parameters, performance characteristics.
Continuous and discontinuous armature current operations; Current ripple and its effect on performance;
Operation with free wheeling diode; Implementation of braking schemes; Drive employing dual converter.
Introduction to time ratio control and frequency modulation; Class A, B, C, D and E chopper controlled DC motor - performance analysis,
multi-quadrant control - Chopper based implementation of braking schemes; Multi-phase chopper; Related problems.
CLOSED LOOP CONTROL
Modeling of drive elements - Equivalent circuit, transfer function of self, separately excited DC motors; Linear Transfer function model
of power converters; Sensing and feeds back elements - Closed loop speed control - current and speed loops, P, PI and PID controllers -
response comparison. Simulation of converter and chopper fed d.c drive.
DIGITAL CONTROL OF D.C DRIVE
Phase Locked Loop and micro-computer control of DC drives - Program flow chart for constant horse power and load disturbed operations; Speed detection and gate firing.
SOLID STATE AC DRIVES
INTRODUCTION TO INDUCTION MOTORS
Steady state performance equations - Rotating magnetic field - torque production, Equivalent circuit- Variable voltage,
constant frequency operation - Variable frequency operation, constant Volt/Hz operation. Drive operating regions, variable stator
current operation, different braking methods.
VSI AND CSI FED INDUCTION MOTOR CONTROL
AC voltage controller circuit - six step inverter voltage control-closed loop variable frequency PWM inverter with dynamic braking-CSI fed
IM variable frequency drives comparison.
ROTOR CONTROLLED INDUCTION MOTOR DRIVES
Static rotor resistance control - injection of voltage in the rotor circuit - static scherbius drives - power factor considerations - modified Kramer drives.
FIELD ORIENTED CONTROL
Field oriented control of induction machines - Theory - DC drive analogy - Direct and Indirect methods -
Flux vector estimation - Direct torque control of Induction Machines - Torque expression with stator and rotor fluxes, DTC control strategy.
SYNCHRONOUS MOTOR DRIVES
Wound field cylindrical rotor motor - Equivalent circuits - performance equations of operation from a voltage source -
Power factor control and V curves - starting and braking, self control - Load commutated Synchronous motor drives - Brush and Brushless excitation.
In discussion of the other basic materials, iron and copper, mention has already
been made of the energy losses which their use entails. These, of course,
manifest themselves in the form of heat. This results in a rise in temperature
of the system, be it core and windings, core frames, tank, or other ancillary
parts. These will reach an equilibrium when the heat is being taken away
as fast as it is being produced. For the great majority of transformers, this
limiting temperature is set by the use of paper insulation, which, if it is to
have an acceptable working life, must be limited to somewhere in the region
of 100°C. Efficient cooling is therefore essential, and for all but the smallest
transformers, this is best provided by a liquid.
For most transformers mineral oil is the most efficient medium for absorbing
heat from the core and the windings and transmitting it, sometimes aided by
forced circulation, to the naturally or artificially cooled outer surfaces of the
transformer. The heat capacity, or specific heat, and the thermal conductivity
of the oil have an important influence on the rate of heat transfer.
When the resistive and other losses are generated in transformer windings
heat is produced. This heat must be transferred into and taken away by the
transformer oil. The winding copper retains its mechanical strength up to
several hundred degrees Celsius. Transformer oil does not significantly degrade
below about 140oC, but paper insulation deteriorates with greatly increasing
severity if its temperature rises above about 90oC. The cooling oil flow must,
therefore, ensure that the insulation temperature is kept below this figure as far as possible.
The maximum temperature at which no degradation of paper insulation
occurs is about 80oC. It is usually neither economic nor practical, however,
to limit the insulation temperature to this level at all times. Insulation life
would greatly exceed transformer design life and, since ambient temperatures
and applied loads vary, a maximum temperature of 80oC would mean that on
many occasions the insulation would be much cooler than this. Thus, apart
from premature failure due to a fault, the critical factor in determining the
life expectancy of a transformer is the working temperature of the insulation
or, more precisely, the temperature of the hottest part of the insulation or hot
spot. The designer’s problem is to decide the temperature that the hot spot
should be allowed to reach. Various researchers have considered this problem
and all of them tend to agree that the rate of deterioration or ageing of paper
insulation rapidly increases with increasing temperature.
Figure 1   Figure 1
In situ measurements of conditions such as temperature can be used to infer
the quality of the wafers being produced in thermal processes. In many types
of thermal processing equipment, temperature is measured using a thermocouple
embedded in the wafer holder (or susceptor). A thermocouple is a circuit consisting
of a pair of wires made of different metals joined at one end (the “sensing
junction”) and terminated at the other end (the “reference junction”) in such a
way that the terminals are both at a known reference temperature. Leads from
the reference junction to a load resistance (i.e., an indicating meter) complete
the thermocouple circuit. Due to the thermoelectric effect (or Seebeck effect), a
current is induced in the circuit whenever the sensing and reference junctions are
different temperatures. This current varies linearly with the temperature difference
between the junctions.
In some cases (such as in rapid thermal processes), the use of a thermocouple
is not possible because there is no susceptor. Alternative temperature sensors
used in such situations include thermopiles and optical pyrometers. A thermopile,
which also operates via the Seebeck effect, consists of several sensing junctions
made of the same material pairs located in close proximity and connected in
series in order to multiply their output.
The second alternative method to the thermocouple is pyrometry. Pyrometers
operate by measuring the radiant energy received in a certain band of energies,
assuming that the source is a graybody of known emissivity. The input energy can
then be converted to a source temperature using the Stefan–Boltzmann relationship.
Most commercial systems monitor the mid-infrared band (3–6 m).
One major issue in using pyrometry is that the effective emissivity of the source
must be accurately known. The effective emissivity includes both intrinsic and
extrinsic contributions. Intrinsic emissivity is a function of the material, surface
finish, temperature, and wavelength. Extrinsic emissivity is affected by the amount
of radiant energy from other sources reflected back to the spot being measured
(which can increase the apparent temperature). In addition, the presence of multiple
layers of different thin-film materials can also alter the apparent emissivity
due to interference effects.
Measurement, or measuring, is also the most important part of an experiment.
Measuring is not absolute, as it does not define a quantity (standard) to be measured.
Measuring is a relative effort and is made to compare and to evaluate. To be independent,
a comparison requires a measure, a standard unit.
The art of measuring is at least as old as humanity itself. The human body performs
measurements all the time. One of the most basic quantities continuously measured by
the human body is the environment temperature. Feeling hot or cold is a consequence
of this measuring. Although not descriptive (not quantified with a parameter such as
temperature), the natural measuring of the environmental temperature by the human
body is nevertheless a relative process. This process is based on a comparison of the
environmental temperature with a certain standard, in this case the temperature at
which the body feels neitherhot norcold—the null point of human thermal control.
In heat transfer, temperature and heat flow are unquestionably the most important
quantities to be measured. Other quantities of interest to heat transfer include fluid
speed, pressure (force), mechanical stress, electric current, voltage, length, surface
area, volume, and displacement. In this chapter the focus is on temperature and heat
General measuring concepts such as sensitivity, hysteresis, calibration, accuracy,
and readability are presented first. Then the discussion turns to statistical concepts
such as mean, deviation, standard deviation, normal distribution, Chauvenet’s criterion,
and the chi-square test, related to the determination of precision, bias error, and
measuring uncertainty. The final section of this chapter is devoted to a brief discussion
of some common instruments for measuring temperature or heat flow.
Among the two possible alternatives for sensing devices, the most common are the
contact sensing devices such as thermocouples that measure by physical contact. In
general, contact sensing devices are rugged, economical, relatively accurate, and easy
to use. Disadvantages commonly associated with contact sensing devices include
susceptibility to wear (e.g., breaking of thermocouple junction). They also require
accessibility forphysical contact. Because of the contact nature of these devices,
they tend to interfere with the medium where measurement is to be taken, frequently
affecting the state and the value of the quantity to be measured. The last disadvantage
can be a serious problem. For instance, the conductive wires of a thermocouple
will always provide a heat path when in contact with the medium where temperature
is to be measured. This heat path can modify the state of the medium where
temperature is to be measured by adding energy to, or extracting energy from, the medium.
Natural convection is generated by the density difference induced by the temperature differences
within a fluid system. Because of the small density variations present in these types
of flows, a general incompressible flow approximation is adopted. In most buoyancy-driven
convection problems, flow is generated by either a temperature variation or a concentration
variation in the fluid system, which leads to local density differences. Therefore, in such
flows, a body force term needs to be added to the momentum equations to include the effect
of local density differences.
Mixed convection involves features from both forced and natural flow conditions. The
buoyancy effects become comparable to the forced flow effects at small and moderate
Reynolds numbers. Since the flow is partly forced, a reference velocity value is normally
known (Example: velocity at the inlet of a channel). Therefore, non-dimensional scales
of forced convection can be adopted here. However, in mixed convection problems, the
buoyancy term needs to be added to the appropriate component of the momentum equation.
If we replace 1/P r with Re in the non-dimensional natural convection equations of the
previous subsection, we obtain the non-dimensional equations for mixed convection flows.
These equations are the same as for the forced convection flow problem except for the
body force term, which will be added to the momentum equation in the gravity direction.
Forced convection heat transfer is induced by forcing a liquid, or gas, over a hot body or
surface. Two forced convection problems will be studied in this section. The first problem
is the extension of flow through a two-dimensional channel as discussed in the previous
section and the second one is of forced convection over a sphere. The difference between
the first problem and the one in the previous section is that the top and bottom walls are
at a higher temperature than that of the air flowing into the channel.
Movie - force convection heat flux
Many physical situations involve the transfer of heat in a material by conduction and its
subsequent dissipation by exchange with a fluid or the environment by convection. The
heat sinks used in the electronic industry to dissipate heat from electronic components to
the ambient are an example of a conduction–convection system. Other examples include
the dissipation of heat in electrical windings to the coolant, the heat exchange process in
heat exchangers and the cooling of gas turbine blades in which the temperature of the
hot gases is greater than the melting point of the blade material. In Section 3.6, we have
already demonstrated the applications of the finite element method for extended surfaces
with different cross sections. Also, the problems discussed in the previous section of this
chapter include the influence of convective boundary conditions. However, all the problems
studied previously in this chapter assumed that the domains were of infinite length.
Figure 1 shows various types of fins used in practice. Let us now consider the case
of a tapered fin (extended surfaces) with plane surfaces on the top and bottom. The fin
also loses heat to the ambient via the tip. The thickness of the fin varies linearly from t2 at
the base to t1 at the tip as shown in Figure 2 The width, b, of the fin remains constant
along the whole length.
In Figure 1 and Figure 2, we have discussed steady state heat conduction in which the
temperature in a solid body was assumed to be invariant with respect to time. However,
many practical heat transfer applications are unsteady (transient) in nature and in such
problems the temperature varies with respect to time. For instance, in many components
of industrial plants such as boilers, refrigeration and air-conditioning equipment, the heat
transfer process is transient during the initial stages of operation. Other transient processes
include crystal growth, casting processes, drying, heat transfer associated with the earth’s
atmosphere, and many more. It is therefore obvious that the analysis of transient heat
conduction is very important.
Analytical techniques such as variable separation, which are employed to solve transient
heat conduction problems, are of limited use (Ozisik 1968), and a solution for practical heat
transfer problems by these methods is difficult. Thus, it is essential to develop numerical
solution procedures to solve transient heat conduction problems.
Heat conduction solutions for many geometric shapes of practical interest cannot be found
using the charts available for regular geometries (Holman 1989). Because of the timedependent
boundary, or interface conditions, prevalent in many transient heat conduction
problems, analytical or lumped solutions are also difficult to obtain. In such complex
situations, it is essential to develop approximate time-stepping procedures to determine the
transient temperature distribution.
Over the past few decades, major advances in the applications & control of electric machinery have occurred as a result of advances in power electronics & microprocessor based control systems. Consequently a much broader spectrum of Electric Machine types can be found in modern applications. This course provides an introduction to the theory of Electro-Mechanical devices & gives emphasis on a physical understanding of fundamental principles behind the operation of Electric Machines.
Polyphase Circuits: Review of Polyphase Circuits, Balanced & Unbalanced Loads, Unbalanced Delta Connected Load, Three Phase Three Wire & Three Phase Four Wire Star Connected Unbalanced Load, Millman's Theorem, Delta/Star & Star/Delta Conversion
Transformers: EMF Equation, Phasor Diagram & Equivalent Circuit, Determination of Losses by Open Circuit Test and Short Circuit Test, Sumpner's Test, Regulation & Efficiency, Special Constructional Features of Three Phase Transformers, Connections, Labeling of Terminals, Specifications, , Phase Groups, Harmonics & Transients , Parallel Operation, Three Winding Transformers, Phase Conversion, On Load Tap Changers, Ratio And Polarity Tests, Phasing Out Test, Instrument Transformers: Theory, expression for ratio and phase angle errors, design consideration and testing
Auto Transformer, Pulse Transformer, Isolation Transformer
DC Generators: Constructional Features, Basic Principle of Working, EMF Equation, Armature Windings, Types, Characteristics and Applications, Armature Reaction, Commutation
DC Motors: Principles of Working, Significance of Back Emf, Torque Equation, Separately & Self Excited Motors, Characteristics and Selection of DC Motors for Various Applications, Starting, Speed Control, Various Tests to find Losses and Efficiency
(1) M.G. Say,Performance & design of AC machines, CBS publishers & distributors, Delhi, 3rd edition
(2) A.E. Clayton & N.N. Nancock, The Performance & design of DC machines CBS publications & distributors, Delhi, 3rd edition
(3) Nagrath I.J.& Kothari D. P., Electric Machines, Tata McGraw Hill , New Delhi, 2nd edition
(4) Bharat Heavy Electricals Ltd, Transformers, Tata McGraw Hill
(5) Syed A. Nasar,Electric Machines & Power Systems, Volume I , Tata McGraw Hill, New Delhi
(6) A. E. Fitzerald & C. Kingsley & S.D. Umans , Electric Machinery Tata McGraw Hill ,New Delhi ,5th edition
(7)Dr. P.S. Bhimbra, Generalized theory of Electrical Machines, Khanna publishers, Delhi, 5th edition