| Popis: |
Automatic control of modern power stations is generally not achieved with single control loops, but requires strongly interacting, hierarchical multi-loop control schemes. In these complex control systems, sustained oscillations may arise due to nonlinearities in the low-level control loops, if the control is designed improperly. It is shown by means of the method of harmonic balance, why continuous oscillations arise and how they may be avoided by implementing adaptive nonlinear compensators. A power station unit serves as an example that demonstrates the use of adaptive nonlinear compensators to prevent continuous oscillations without a degradation in control performance of the unit. As an additional benefit, the control is very steady during regular operation (small disturbances) resulting in a low switching rate of the actuators and thus reduced wear on the equipment. After large disturbances, however, hard control action is still ensured. Practical experience with these nonlinear compensators during several years in various units of different size and make are very satisfactory. |
