12-10-2012, 03:01 PM
Advanced Power Systems
Advanced Power.ppt (Size: 2.7 MB / Downloads: 85)
Course Content
Working principles, construction, mathematical modeling, operating characteristics and control techniques for synchronous machines
Working principles, construction, mathematical modeling, operating characteristics and control techniques for induction motors
Introduction to power switching devices
Rectifiers and inverters
Variable frequency PWM-VSI drives for induction motors
Control of High Voltage Direct Current (HVDC) systems
Operation Principle
The rotor of the generator is driven by a prime-mover
A dc current is flowing in the rotor winding which produces a rotating magnetic field within the machine
The rotating magnetic field induces a three-phase voltage in the stator winding of the generator
PU System
Per unit system, a system of dimensionless parameters, is used for computational convenience and for readily comparing the performance of a set of transformers or a set of electrical machines.
Classical Model of Synchronous Generator
The leakage reactance of the armature coils, Xl
Armature reaction or synchronous reactance, Xs
The resistance of the armature coils, Ra
If saliency is neglected, Xd = Xq = Xs
Direct and Quadrature Axes
The direct (d) axis is centered magnetically in the center of the north pole
The quadrature axis (q) axis is 90o ahead of the d-axis
q: angle between the d-axis and the axis of phase a
Machine parameters in abc can then be converted into d/q frame using q
Mathematical equations for synchronous machines can be obtained from the d- and q-axis equivalent circuits
Advantage: machine parameters vary with rotor position w.r.t. stator, q, thus making analysis harder in the abc axis frame. Whereas, in the d/q reference frame, parameters are constant with time or q.
Disadvantage: only balanced systems can be analyzed using d/q-axis system
Related Terms
Generator Modeling using the d- and q-axis equivalent circuits
Transmission System Modeling with a RL circuit
A Small Disturbance is a disturbance for which the set of equations describing the power system may be linearized for the purpose of analysis
Steady-State Stability is the ability to maintain synchronism when the system is subjected to small disturbances
Loss of synchronism is the usual symptom of loss of stability
Infinite Bus is a system with constant voltage and constant frequency, which is the rest of the power system
Eigen values and eigen vectors are used to identify system steady-state stability condition
Analyzing the Eigen Values of the System State Matrix
Compute the eigen values of the system state matrix, A
The eigen values will give necessary information about the steady-state stability of the system