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Challenges in Modelling Active Electric Power Networks

Challenges in Modelling Active Electric Power Networks. Dr. S. K. Chakravarthy Department of Elect. Engg., KFUPM. Aspects to be addressed. The conventional electric power transmission network. Analytical methods used. What is an active electric power transmission network?

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Challenges in Modelling Active Electric Power Networks

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  1. Challenges in Modelling Active Electric Power Networks Dr. S. K. Chakravarthy Department of Elect. Engg., KFUPM

  2. Aspects to be addressed • The conventional electric power transmission network. • Analytical methods used. • What is an active electric power transmission network? • Use of numerical simulations. • Why is a new analytical method required? • Some advantages of the new approach.

  3. Aspect One • The conventional electric power transmission network.

  4. R L C1 C1 Modelling a Conventional Power Transmission Network

  5. Purpose of conventional transmission networks • An electric power transmission network is designed to transfer bulk power between two points. • Performance of an electric power transmission network is obtained from the nominal Pi-equivalent circuit.

  6. Aspect Two • Analytical methods used.

  7. Analytical Methods Used

  8. For initial values of control vector u and load vector p one can find the state variable x. State variable x represents the bus voltages in the network. Analytical Methods Used

  9. Knowing the initial values of ( x, u,p) one obtains the solution at a future instant t. This solution represents the slowly evolving dynamics of the system (due to the moment of inertia of rotating machines. Analytical Methods Used

  10. Aspect Three • What is an active electric power transmission network?

  11. R L Bus-1 V1 Bus-2 V2 C1 C2 Two anti-parallel thyristor-pair for each phase. L-TCR An Active Power Transmission Network

  12. An active electric power network? • The extent of power that can be transferred between two points can be controlled by FACTS or Static VAR Systems. • By the use of these local controllers, the surge impedance and propagation constant change rapidly.

  13. An active electric power network? • The changes in these parameters can be enforced at least once every cycle. • Consequently, the network parameters become time dependent (that is, they need to be represented by differential equations).

  14. The Problem • In modeling: • The resonant frequencies of the network will (dynamically) change. • The switching operation of the controllers makes the transmission network nonlinear. • There is a distinct possibility of the occurrence of switching bifurcations.

  15. Aspect Four • Use of numerical simulations.

  16. Analytical Solution (system involving fast and slow dynamics)

  17. Analytical Solution (system involving fast and slow dynamics)

  18. Aspect 5 • Why is a new analytical method required?

  19. Why a new method? • The odes along with the nonlinear transformation can solved by packages such as EMTP or EMTDC. • However, one cannot rule out the possibility of numerical instability providing erroneous results. • Numerical instability arises from the existence of zero eigenvalues in a nonlinear system.

  20. Why a new method? • The system of ode’s have zero eigenvalues. • The inclusion of nonlinear transformations and the presence of zero eigenvalues will give rise to bifurcation leading to several periodic and aperiodic (numerical) oscillations.

  21. Why a new method? • Problem: The numerical solution of a stable (physical) system may be unstable. The conditions that may initiate any of these numerical instability depend on the initial conditions, which are never completely known.

  22. Aspect Six • Some advantages of the new approach.

  23. Advantages of the new approach. • Provide tractability to a nonlinear system with large dimension such as a power system. • The large dimensional nonlinear system can be modeled as an equivalent reduced order system.

  24. Conclusions • In summary, the challenges involved in modelling active EPTN’s involve: • Determining the number of eigenvalues with zero real parts for a large scale system; • Eliminating the fast transient by determining the invariant manifold while still retaining their influence on the nonlinear behaviour of the system; • Eliminating time dependence by the method of averaging.

  25. Conclusions • Since the solutions are dependent on the choice of initial conditions, numerical methods must be integrated with symbolic processing software; • Methods are required for dimensionally reducing the problem.

  26. Conclusions THANK YOU FOR YOUR ATTENTION

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