Adaptive Switching Control of Large-Scale Complex Power Systems

This chapter proposes a SC for the impulsively disturbed nonlinear systems with arbitrary relative degree based on the 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 CC according to a state-dependent switching strategy. Moreover, the 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 SMIB power system, through which the control performance of the SC and the BCFC is verified with simulation studies.

Time optimal control is preferable in many industrial scenarios, such as landing control of spacecrafts, emergency braking of high-speed rails, emergency braking of electric vehicles, and emergency control of electric power systems suffering severe grid faults. Tradition bang-bang control is normally used in linear systems, and recent works have proposed a bang-bang funnel control method for nonlinear systems. Nevertheless, the bang-bang funnel control requires to calculate high-order derivatives of the objective variables. This can magnify the measurement noise as well as external disturbances, and result in instability of the control system. In order to solve this problem, this chapter presents a RBC based on the high-gain observer for a nonlinear system suffering intermittent disturbances. The intermittent disturbance represents the system faults and sudden changes of operating conditions. A BCFC is employed, and the largest control capabilities of the control system is explored to stabilize the nonlinear system against the disturbances. The BCFC functions with the estimates of the tracking error of control target and its derivatives estimated with a high-gain state observer. This eliminates the use of the derivative calculations with respect to the tracking error of system output. Convergence of the estimation error of the observer is verified. The closed-loop stability of the RBC is proved in the sense of bounded-input bounded-state.

This chapter firstly proposes a coordinated SPSS to enhance the stability of multi-machine power systems. The SPSS switches between a BPSS and a CPSS according to a state-dependent switching strategy. The BPSS is designed as a BCFC, and it is able to provide fast damping of rotor speed oscillations in a bang-bang manner. The closed-loop stability of the power system controlled by the SPSSs and the CPSSs is analyzed. To test the performance of the SPSS, simulation studies were undertaken in a four-generator eleven-bus power system and the IEEE 16-generator 68-bus power system. SPSS is evaluated in aspects of small-signal oscillation control and transient stability enhancement, respectively. Meanwhile, the coordination between different SPSSs and that between SPSS and CPSS are studied therein. Synchronous generators are the main power sources in power systems, and their resilience significantly impact the reliability and resilience of the entire power system. Hence, it is disable to explore the largest control energy of synchronous generators during severe grid faults, in order to damp the oscillations and achieve energy re-balance in the system. Hence, this chapter also proposes two switching controllers working in a coordinated manner to enhance the transient stability of multi-machine power systems. The first one is SEC and the other is SG. The SEC switches between a BEC and a CEC and the SG switches between a BG and a CG, via a state-dependent switching strategy. The BEC and the BG are designed as BCFCs, which are able to provide fast switching of excitation voltage and valve position between their upper and lower limits. The boiler pressure effect is concerned in the detailed steam turbine model in the controller design. Simulation studies were undertaken in the IEEE 16-generator 68-bus power system to evaluate the performance of the switching controllers. Coordination between the excitation loop and speed governing loop was studied. Two system resilience indexes were introduced, and the short-term resilience is investigated for the power systems with and without switching controllers installed, respectively.

This chapter presents a FRTHC for the MMC-based HVDC transmission system. The FRTHC is made up of four loops of cascading SCUs. Each SCU operates in a switching manner between a BBFC and a PI control loop. The BBFC is responsible for exploring the full control power of each control loop, with three-value control commands with the maximum magnitude. A state-dependent switching law is designed for each SCU to obtain the structural stability of SCUs. Simulation studies were carried out to evaluate the fault ride-through performance of the FRTHC.

This chapter firstly proposes a four-loop switching controller (SC) for the DFIG to improve the transient stability of wind power penetrated power systems (WPPSs). The short-term resilience index is employed to reflect the dynamics of both system frequency and load bus voltage. A four-loop SC is designed to control the four outputs of a DFIG, i.e., the rotor speed deviation, the reactive power output of stator winding, the reactive power transferred through grid-side converter and the DC-link voltage. The SC switches between a LBCFC and a VC based continuous controller (CC) in each control loop. The LBCFC is robust to system nonlinearities, uncertainties and external disturbances. Simulation studies were carried out in a modified IEEE 16-generator 68-bus power system, where four DFIG-based wind farms were connected to provide 9.94% power supply. In the second place, this chapter proposes a switching angle controller (SAC) and an automatic generation controller (AGC) for the DFIG to control the frequency of DFIG-based WPPSs. The virtual rotor angle of the DFIG is defined, which is controlled by the SAC in a bang-bang manner such that the DFIG is controlled to offer frequency support to the external power grid. The SAC is also used to regulate the pitch angle to provide a short-term support of the mechanical power input. The long-term control of the mechanical power is realized by the AGC. Small-signal analysis was carried out to evaluate the modal performance of the SAC and the AGC. Simulation studies were undertaken in a two-machine power system and a modified Kundur four-machine two-area power system, respectively.

This chapter proposes a switching fault ride-through controller (SFRTC) for the GSC of PMSGWTs in the first place. The SFRTC switches between an OBFC and a VC via a state-dependent switching scheme. The fault ride-through (FRT) performance of SFRTC was studied with hardware-in-the-loop experiments. In the second place, this chapter proposes a BBFC for the three-phase full-bridge inverter under dual-buck scheme. By adopting the dual-buck scheme, only two switches on the different phase legs are controlled at high frequency, which eliminates the use of dead-time. Moreover, the full-bridge topology can be decoupled into two parallel-connected buck units, which allows the inverter to be formulated and analyzed by the model of buck chopper. The BBFC works with just two control values, and it is able to restrain the tracking error between the system’s output and the reference within the pre-defined funnel boundaries. BBFC makes it simpler, faster and more robust, for the inverter to work in dual-buck manner. The proposed strategy improves the steady-state operation as well as the dynamic response against rapid variations of the load of the converter. Effectiveness of the proposed strategy was validated by the simulation and experimental results.