Design Of Nonlinear Robust Control And Study On Transient Performances For Power Systems

Power systems are a kind of complex strongly nonlinear systems. Power system stability has a direct bearing on people's daily production and life. With the development of electric power science and technology, the composition and structure of modern power systems are becoming more and more diversified and complicated, and the requirements of people for power system stability are increasingly higher than ever before, so the traditional power system control method often can not satisfy this demand. Recently, there has been great progress in the science and technology of automatic control, which has provided the advanced control technology for the power system area and, particularly, has provided theoretical and technical support for improving stability, robustness and transient performances of power systems. Under this circumstance, we concentrate our attention on the study of power system nonlinear robust control in this thesis, and propose some new control design schemes, thus the transient performance of power systems is improved to a great extent. The main contributions are as follows:Chapter 2 studies the stability of single machine infinite bus power systems with superconducting magnetic energy storage (SMES) via simultaneous design of generator excitation control and SMES control. Since the object model is of non-strict-feedback form and thus the traditional backstepping method is not applicable, we propose an extended backstepping method for a class of general n-order nonlinear systems in non-strict-feedback form. Then, we apply the proposed method to the object model and design the generator excitation controller and SMES controller simultaneously, which stabilize the power angle, the generator terminal voltage and the power oscillation. In addition, we improve the transient and steady-state performances of power systems by introducing class K functions in the design process. Simulation results also show the effectiveness and advantage of the proposed method.Chapter 3 studies the H? control problem for single machine infinite bus power systems with SMES via simultaneous design of generator excitation control and SMES control. In the control system design, we use a novel equivalent generator model to avoid using unmeasurable infinite bus voltage, also the exciter dynamics, unknown external disturbances and the transient performances improvement are considered for practical implementation in power systems. Obviously, it is challenging and difficult to design the controller for power systems considering the above mentioned practical considerations, so a new synthesis framework is proposed to address the robust control problem of power systems with SMES. First, from the energy perspective, the interconnection and damping assignment (IDA) approach is applied to improve the transient performance of power systems. Second, by introducing the idea of virtual control in the design process, we get the solution of a partial differential equation (PDE) which is a crucial point and can not be obtained by using the traditional IDA method. Third, in order to enhance the robustness of the closed-loop system, we study the H? control design for the power systems. Simulation results also show the effectiveness and advantage of the proposed controller.In Chapter 4, a new control synthesis framework is developed to solve a robust stabilization problem for a single-machine infinite-bus power system with a static var compensator (SVC). The uncertainties in the infinite bus voltage and the internal and external reactances to the generating station are considered. First, control inputs for the excitation and the SVC are obtained via immersion and invariance (I&I) method. Then, the controller is redesigned using a parameter update law and a filter using indirect I&I adaptive control and a two-time-scale technique. The transient and steady-state performances are enhanced by introducing class K functions. The simulation results show that the developed controller improves the system performance.Chapter 5 studies the stability of multi-machine power systems via simultaneous design of boiler fuel flow control, turbine main steam valve control and generator excitation control for the boiler-turbine-generator unit. Since the whole system is coupled among generators and has multi-parametric uncertainties, the decentralized adaptive coordinated controller design is considered and is based on the adaptive backstepping method. Moreover, in addition to the transient stability of the power angle and power oscillation, the voltage regulation is also an important property in power systems. Thus, the global control technique is used to simultaneously ensure both the transient stability and the voltage regulation. Furthermore, we improve the transient performance of power systems greatly by introducing the state-constrained control. Simulation results show the effectiveness and advantage of the proposed controller.The conclusions and perspectives are presented in the end of the thesis.