PE in CS and included the Session 01.pptx

Power Electronics

1. Unit – 01 Modelling of Power Electronic Converters

2. Session – 01 Introduction to Power Electronic Converter Modelling Lecture delivered by Mr. T. Naveen Kumar

3. Objectives At the end of this lecture, student will be able to : Explain overview of power electronic converter roles and objectives in the context of their use .

4. Topics Introduction Requirements of Modelling, Simulation and Control of Power Electronic C onverters What Is a Model? Modelling approaches Scope of Modelling Modelling Assumptions Summary

5. Introduction Power electronics concerns electrical power processing by electronic devices. Use of power electronic converters for controlling the electric energy flows within power structures. Output power conditioning with respect to a certain application . Raw input power processing. Control structure corresponding control input acting on the converter. Power structures with converters have become More diversified More flexible More efficient .

6. Introduction Combination of microprocessor-based control devices and high-quality switching devices power handling capabilities and output power quality is improved. Various basic functions performed by power electronic converters: DC-DC converters (Choppers) DC-AC converters (Inverters) AC-DC converters (Rectifiers) AC-AC converters (ACVC or Cyclo-converters) The power flow through all these systems may be reversible – that is, the converters may be bidirectional

7. Introduction Applications of Power electronic converters: Electrical machine motion control Switched - Mode Power Supplies ( SMPS ) Lighting drives Energy storage Distributed power generation Active power filters Flexible AC Transmission Systems (FACTS) Renewable energy conversion Vehicular and embedded technology.

8. Introduction Control of power converters is ubiquitous and it is responsible for the overall application’s proper operation. Control goals that issue from the converter role may include a multitude of functional objectives that are complex and must ensure power quality and efficiency are not affected. Converter control structures should work in a most polluted (noisy) environment due to the hard switching and high-frequency modulation. The intrinsic nonlinearities , limitations, parameter and load variations do not render easy the operation of the control structures

9. Introduction Control of power converters is ubiquitous and it is responsible for the overall application’s proper operation. Control goals that issue from the converter role may include a multitude of functional objectives that are complex and must ensure power quality and efficiency are not affected. Converter control structures should work in a most polluted (noisy) environment due to the hard switching and high-frequency modulation. The intrinsic nonlinearities , limitations, parameter and load variations do not render easy the operation of the control structures

10. Requirements of Modelling, Simulation and Control of Power Electronic Converters Design of a switching converter is a nontrivial task due to multiple objectives In design process Cost , gauge, power efficiency, power quality and reliability of the overall structure must be considered. Good operation and energy efficiency depends on: Choosing the appropriate topology and component types Sizing in terms of voltage and current handling capacities Choosing the switching frequency Voltage and current filters are crucial for the power quality and converter time response.

11. Requirements of Modelling, Simulation and Control of Power Electronic Converters Choice and design of gate drivers, including modulation stage , galvanic insulation, etc., affect the accuracy of control input delivery . Insertion of sensors adds complexity to the power conversion structure and negatively affects its reliability . The analysis and design of power electronic converters presents significant challenges

12. What Is a Model? Modeling of a phenomenon or process is based on its observation. In application point of view modeling relies on: Capturing into an approximate Sufficiently comprehensive Representation Significant features Modelling requires generalization.

13. Modelling approaches There are two main modeling approaches: Based on the process behavior observation of its response to some known input signals (black-box models) Based on the known information about the system to be modeled (employed not only to model physical processes, but also biological, economics or even social systems) Mixing between the two approaches is also encountered, leading to the so-called gray-box models.

14. Scope of Modelling To obtain quasi-general power electronic converter dynamical models to simulate converter dynamic behavior and to construct various control laws. Steady-state converter behavior (static models) can also be obtained by: Zeroing the time derivatives in the dynamical models in case of DC variables Zeroing the derivative of both magnitude and phase in the case of AC variables Concerning simulation, a set of software renders power converter time domain behavior in a very precise and reliable way like SPICE®, SABER®, MATLAB® etc.

15. Scope of Modelling Simulation results are not general even if they provide various time waveforms of the internal variables and they do not give direct information about the converter modes. Obtaining a model necessary for control purposes cannot be done by using these software packages directly. It is possible to identify a power electronic converter based on the input-output variables evolution file obtained by simulation and to elaborate a frequency-domain model.

16. Scope of Modelling The resemblance of power electronic converters is naturally a nonlinear or linear time-varying system, and any linear input-output model depends on the operating point, the information acquired has limited validity. Drawback of the linear identification approach is that system identification in the frequency domain will be limited at half the switching frequency

17. Scope of Modelling An analytical model based on knowledge of the circuit’s physical behavior is needed for control purposes. According to the intended use, various levels of modeling can be considered. Model choice also relies on the following criteria: Dynamic or steady-state accuracy requirement Whether internal, input or output variables should explicitly appear in the model An acceptable level of complexity The domain of definition

18. Modelling Assumptions Some simplifying assumptions, sufficiently accurate so as not to affect the validity of the models to be implemented: Switches are considered ‘perfect’: Zero ON-state resistance Infinite OFF-state resistance Infinitely short switching time Generators are considered ‘perfect’: they provide infinite short circuit power in the case of voltage sources Passive elements are considered linear and invariant.

19. Modelling Assumptions Understanding the assumption “Passive elements are considered linear and invariant”. Example: a nonlinear inductance whose value depends both on time and on the current i(t) passing through it . Inductance voltage is given by: Developing this equation gives a nontrivial expression :  

20. Modelling Assumptions To increase modelling accuracy, one can successively add detail to an initial, simplified model. For example, models of circuit elements can be enriched by taking into account the dissipative elements (internal resistance of a power source, winding resistance of a coil, etc .) Diode schematic and ideal model possible enriched model

21. Modelling Assumptions Single-pole–single-throw (SPST) switches can be implemented in various power electronic devices. Diode Transistor Two-quadrant voltage-bidirectional SPST two-quadrant current-bidirectional SPST

22. Summary Power electronic converters play a major role in power conversion. Modelling of a phenomenon or process is based on its observation. Various considerations like cost, compatibility, size, efficiency etc. have to be accounted in modelling a power converter.