Design Of Load Frequency Controller For Power System Under Full-state Constraints

Load frequency control plays a crucial role in the stable operation of the power systems.With the development of science and technology,more and more advanced equipment is put into use at the load side,and some precision instruments have higher requirements for transient and steady-state performance specifications for load frequency fluctuations.At the same time,during the load frequency control process,the fluctuation of system state varibles may exceed the rated operating range of the electrical equipment.However,the existing controller do not solve the above problems.Aiming at the above performance specifications and state constraint,new types of load frequency controllers are designed and their stability are analyzed based on the prescribed performance control theory and full-state constrainted theory of nonlinear systems.The main research contents are as follows:Firstly,the model and control method of load frequency control system with single-zone single-turbine and multi-zone multi-turbine are respectively improved.A nonlinear system model with unknown parameters is established by considering the dead-zone problem and the multi-time scale problem in the frequency control system of the thermal steam turbine.The necessity of model improvement is illustrated by simulations in the end.Secondly,for the single-zone single-turbine load frequency control system with the transient and steady state performance specifications,the behavior-shaping function and coordinate transformation are constructed,the load frequency controller is designed based on the Backstepping strategy combined with the symmetric barrier Lyapunov function.This control algorithm not only limits the overshoot of all state variables within prescribed ranges,but also make the frequency deviation converge to a specified interval within a prescribed limit time and finally reduce to a smaller residual set.The prescribed transient performance specifications are achieved.The simulations are carried out to verify the control effect of the controller and the stability of the system.Thirdly,for the single-zone single-turbine load frequency control system,a full-state constrained load frequency controller is designed based on the adaptive technology and the dynamic surface control strategy using the backstepping method.By constructing a state-constrained transformation function,the state-constrained problem is transformed into a function boundedness problem.Then combined with the dynamic surface control strategy,coordinate transformation is performed to reduce the complexity of the traditional Backstepping method.Based on the adaptive method to deal with the unknown parameters,an adaptive load frequency controller under full-state asymmetric constraints is designed.The target of load frequency control is achieved.In the end,simulations with several cases are designed to verify the effectiveness of the controller.Finally,for the improved multi-zone multi-turbine load frequency control system,combined with dynamic surface control method and disturbance observer,an adaptive load frequency controller under the condition of full-state asymmetric constraints is designed for the governor of each prime mover based on the Backstepping method.The multi-turbine system is divided into mutually coupled single-turbine subsystems for controller design,and only the signals of the subsystem state varibles are sampled.While realizing the frequency control,the full-state constraints and the reliability of operation of the system are guaranteed.In the end,the control performance of the controller is verified by simulations.