07-11-2012, 01:37 PM
Voltage Regulator for Reactive Power Control on Synchronous Generators in Wind Energy Power Plants
1Voltage Regulator.ppt (Size: 2.05 MB / Downloads: 30)
Motivation
In a project with the Voith Co. the AEM Co. and the TU Dresden preliminary
studies of a windmill using a hydrodynamic torque converter (VORECON)
were carried out.
The TU Chemnitz accomplished the following tasks:
Modelling and simulation of a synchronous generator
Emulation of the E-On cases for power plant connection to the electrical grid
1. Synchronisation and connection with the mains supply
2. Reactive power exchange with the net
3. Load drop
4. Active power limiting with frequency variation
5. Short-circuit behaviour
Controller Tasks and Structure
The field controller has to accomplish the following tasks:
regulate the induced voltage at the machine terminals during synchronisation
control the power factor or the reactive power flow during normal operation
guarantee the dynamical stability during undesired transient conditions
An outer power factor control loop influences the induced voltage in normal operating conditions, as well as compensates the voltage drop over the stator windings during loading
Synchronisation Starting Currents
Connecting the machine to the mains with an angle error from less than 10 degrees gives transient currents which peak values lie under 40 % of rated value vanishing in less than one second, as shown in the left figure.
With a neglectiable angle error the start-up currents are much smaller, as can be observed in the right figure.
Coupling with the Reactive Power Control
After a negative mechanical torque step over-shoots on the electromechanical torque occur during the transient period.
The well-damped power factor controller reduced the over-shoots due to the coupling with the active power canal and let the actual value reach the reference smoothly after some seconds.
Power Factor Step
The power factor step presents a retarded response due to the coupling with the active power channel.
The increase on the torque caused by the reference power factor step is less damped than the reaction caused again on the power factor.
Such extremes reactive power steps must be avoided in the normal operation of the generator in order to avoid the observed torque steps.
Summary and Future Works
A synchronous machine classical model was used to simulate different situations before and after synchronisation with the electrical grid.
A voltage regulator for the field excitation of the synchronous generator was designed. This controller has to guarantee stable operation of the generator under various conditions including faults.
Simulation results show the good performance of the controller. With the already existing controller the machine is kept stable during extreme conditions like torque steps and reactive power variations. Faulty conditions were also simulated.
Further studies will investigate the effects of faulty conditions on the mechanical drive train caused by high electromechanical torque and its harmonics and of the distribution line and the transformer on the performance of the machine under voltage drops.