Faculty of Electrical Engineering

Czech Technical University in Prague

CTU in Prague

State doctoral exam topics

Electric Machines, Apparatus and Drives

  1. Mathematical simulation of electric machines.
    Overview of mathematical models of electrical machines, their validity conditions. General commutator machine and system of its equations. Real and complex linear transformation of electrical machine quantities, their meaning, definition, relation, advantages and disadvantages. Using mathematical models to solve transient and steady states of electric machines.
  2. The impact of higher time harmonics of voltages and currents on the AC electric machine behaviour. The causes of higher time harmonics of voltages and currents. Calculating currents and torques at periodic non harmonic feeding. Increase in losses and warming of electric machines due to higher time harmonics.
  3. Effects of short-circuit currents on the electrical machine operation and dimensioning. Waveforms of short-circuit currents, influence of machine parameters on its size and time constants. Types of short-circuits in three phase systems and their dynamic and thermal effects on the winding. Structural measures to reduce the effects of short-circuit currents in electrical machines.
  4. Use of permanent magnets in electric machines.
    Material properties of permanent magnets and their use in electric machines. Methods of solution of the magnetic circuit with a permanent magnet. Engineering design of machines with permanent magnets. Evaluation of such machine properties.
  5. Electric discharges in electrical apparatuses.
    Theory of electric arc. Properties of arc in electric apparatuses in various environments (vacuum, SF6, air, oil, etc.). Methods of influencing electric arc characteristics. Influence of the electric arc properties on the cut-out process, the emergence of switching surges. Interrupters and quenching systems.
  6. Systems and instruments for electric equipment protection.
    Basic types of electric equipment protection. Renewable and non-renewable protective components and devices. Physical principles of protective devices. Choice of the protective device type and parameters with regard to the protected facility. Typical characteristics of protective devices. Economic aspects of protection.
  7. Switching problems in electric networks.
    Switching problems in DC and AC networks. Switching off the AC electric circuit at zero and non-zero instantaneous value of the breaking current. Turning off various types of loads. Switching surges and their reduction.
  8. Testing of electrical devices and its automation.
    Sorting of electric device tests, basic configuration of test beds and test circuits. Quantities monitored during the test. Options in automated test control and data collection. Computer processing of the measurement results. Ways of ensuring long-term unattended operation (durability) tests. Using simulation methods for testing electrical appliances with high performance characteristics.
  9. Compatibility and backward effects of semiconductor converters on the power network. Fundamental and higher harmonics of currents and voltages in the power grid and converters. Technical measures of reducing the higher harmonic content in network. Active power, reactive power and deformation power of semiconductor converters, the converter as a source of high frequency interference. High frequency filters. Methods of experimental detection of converter backward effects on the power grid, active means with high compatibility.
  10. Inverters and frequency converters.
    Operation principles of single-phase and multi-phase inverters of the voltage and current types. Typical schemes of the power part connection of transistor and thyristor inverters. Methods of commutation ensuring in thyristor inverters. Ways of the output voltage, current, and frequency control. The operation principle of direct single-phase and multi-phase frequency converter. Principles of dimensioning and control methods. Indirect frequency converters, typical connection diagrams.
  11. AC variable speed drives.
    Synchronous and asynchronous motor drives fed from inverters, synchronous and asynchronous motor with direct frequency converter, sub synchronous and over synchronous cascade drives, drives with stepper motors. In all mentioned drives power scheme, principles of dimensioning, mechanical characteristics. Typical block diagrams of used control methods, control characteristics.
  12. Adjustment and control of drives.
    Linear continuous systems: Methods for characterization, stability criteria, optimization criteria, used types of controllers and methods of their synthesis. Linearization of discrete systems, algorithms used in digital controllers, implementation by means of microprocessors. Logic control: description methods, methods of implementation. Simulation methods.
  13. Electric traction drives.
    Specific requirements of traction operation. Drive types used on dependent and independent traction vehicles. Typical connection schemes of power circuits. Control methods. Energy balance of various operation modes.
  14. Electrical equipment of traction vehicles.
    Apparatus equipment of HV and LV circuits of dependent and independent traction vehicles. Principles of structural design of main and auxiliary drives. Electro-pneumatic devices of traction vehicles. Protection.
  15. Control electronic systems for traction vehicles.
    Architecture of control systems used on vehicles and measures of their implementation (analogue and digital). Structural design of control modules and methods of their interconnection with regard to the traction operation conditions.
Responsible person: RNDr. Patrik Mottl, Ph.D.