Stability Control Of Power Systems Based On Switched Control Systems

This thesis proposes a switching control strategy based on bang-bang constant funnel controller,and the proposed switching control strategy is applied in the excitation control and speed governing of synchronous generators,the coordinated control of doubly-fed induction generatorbased wind power generators(DFIG-WPGs),and the inertia control of DFIG-WPGs.The contributions of this paper are summarized as follows.This paper firstly proposes a switching controller(SC)for the impulsively disturbed nonlinear systems with arbitrary relative degree based on the bang-bang constant funnel controller(BCFC).Weaker feasibility assumptions are proposed for the SC in contrast to the conventional bang-bang funnel controller.The SC is designed to switch between a BCFC and a continuous controller(CC)according to a state-dependent switching strategy.Moreover,the impulsive disturbance recovery ability(IDRA),which refers to the ability of returning to the pre-disturbed operation point following an impulsive disturbance,of the nonlinear system controlled by the SC is analyzed.The boundary values and the recovery time of the system output tracking error and its derivatives of an impulsively disturbed nonlinear system controlled by the BCFC are discussed as well.Furthermore,the BCFC and the SC are applied respectively in the excitation control of a synchronous generator for the frequency supervision of a single-machine-infinitebus(SMIB)power system,through which the control performance of the SC and the BCFC is verified with simulation studies.The switching control strategy is applied in the excitation control and speed governing of synchronous generators.A switching excitation controller is designed to switch between a bangbang excitation controller and a conventional excitation controller according to a state-dependent switching strategy.According to the same switching strategy,a switching governor is designed to switch between a bang-bang governor and a conventional governor.The detailed model of steam turbines and the fast switching characteristics of turbine valves are considered in the controller design process.In order to evaluate the performance of the switching excitation controller and the switching governor,simulation studies were carried out in an IEEE 16-generator 68-bus power system.Moreover,the switching control strategy is applied for the design of a switching PSS.The switching PSS switches between a bang-bang PSS and a conventional PSS.The smallsignal oscillation damping performance of the switching PSS is investigated through simulation studies on a Kundur 4-machine 2-area power systems and an IEEE 16-generator 68-bus power systems,respectively.The switching control strategy is also applied for the coordinated control of DFIG-WPGs.A coordinated four-loop switching controller(SC)is designed for the doubly-fed induction generator(DFIG)to improve the transient stability of wind power penetrated power systems.A short-term resilience index is introduced,and it reflects the dynamics of both system frequency and load bus voltage.A four-loop SC is driven by the four outputs of a DFIG,namely,the rotor speed deviation,the reactive power output of stator winding,the reactive power transferred through grid-side converter and the DC-link voltage,respectively.Referring to a statedependent switching strategy,the four-loop SC switches between a logic-based bang-bang constant funnel controller(LBCFC)and a vector control theory based conventional controller(CC)in each control loop.The LBCFC is robust to system nonlinearities,uncertainties and external disturbances.The control signal of the LBCFC is bang-bang with the upper and lower limits of control variables.Simulation studies are undertaken in a modified IEEE 16-generator 68-bus power system,in which four DFIG-based wind farms are penetrated to provide 9.94% power supply.The performance of the four-loop SC is evaluated in aspects of the integral control of the DFIG and the resilience enhancement of the multi-machine power system,respectively.The switching control strategy is also applied to design a switching angle controller(SAC)and an automatic generation controller(AGC)for the DFIG to control the frequency of DFIGbased wind power penetrated power systems(WPPSs).The concept of virtual rotor angle of the DFIG is defined.The virtual rotor angle is controlled by the SAC in a bang-bang manner such that the active power of the DFIG is regulated to provide frequency support to the external power grids.The output of the SAC is also used for the control of pitch angle to offer a short-term regulation of the mechanical power input to the DFIG,and the long-term control of the mechanical power input is achieved with the AGC.Small-signal analysis is undertaken to verify the effectiveness of the SAC and the AGC.Simulation studies are carried out in a two-machine power system and a modified Kundur four-machine two-area power system,respectively.The frequency support performance of DFIGs having different control configurations is investigated.Modal analysis is undertaken to evaluate the effect of the SAC and the AGC in providing additional damping to the rotor oscillation modes of the modified Kundur four-machine two-area power system.