SimPowerSystems

Simulation Results

The performance of the nonlinear controller is tested on the nonlinear turbine-generator system. The controller and turbine are simulated using Simulink blocks, while the generator is represented by the Synchronous Machine block from the powerlib library. A three-phase short-circuit is simulated on the load bus bar and the fault is cleared after 100 ms. The performance of the nonlinear controller is analyzed.

Open the psbregulator model. Before running the simulation, make sure that the simulation parameters are set as follows.

• Solver: ode23tb; Maximum order: 5
  Stop time: 1.0
  Max step size: auto; Initial step size: auto
  Relative tolerance: 1e-3; Absolute tolerance: auto
  Workspace I/O: Load initial states: init_regulator.mat
  
  
  

Figure 2-17: Simulink Diagram of Case Study (psbregulator.mdl)

Because of nonlinearities present in this system, computation of initial conditions is not carried out. Instead, a long simulation (10 s) is executed and the final states are saved in file data_regulator.mat.

These final states are used as initial states in this case study. The simulation consequently starts in steady state. At t = 0.1 s, the fault is suddenly applied, and it is removed after 100 ms (6 cycles). The postfault transient is then observed.

The nonlinear controller calls a MATLAB initialization function to compute the gains before the simulation. Although this process has been automated to take into account the parameters in the dialog boxes of the various blocks, it is not recommended that you change any value in any block.

If you decide to change some values, a long simulation must be run and the final states must be in a file called init_regulator.mat. The next figure shows the response of the generator's terminal voltage, load angle, and the control effort of the regulator. You can observe how the stabilization of V_t is obtained in less than 0.25 seconds with this controller. The load angle takes longer to stabilize, because the time constant of the mechanical part of the system is much larger than the electrical time constants. If you want to compare results with classical regulators, replace the nonlinear controller with the same excitation system and Hydraulic Turbine and Governor block used in the psbturbine model. You can see that the system takes longer to stabilize than in this case study.

Figure 2-18: Simulation Results Obtained with Case Study

References

[1] Akhrif, O., F.A. Okou, L.A. Dessaint, and R. Champagne, "Application of a Multivariable Feedback Linearization Scheme for Rotor Angle Stability and Voltage Regulation of Power Systems," IEEE Transactions on Power Systems, Vol. 14, No. 2, May 1999, pp. 620-628.

Feedback Linearization Design

Variable-Frequency Induction Motor Drive