Nonlinear control of STATCOM for stabilization of synchronous generator

A Static Synchronous Compensator (STATCOM) is a typical Flexible AC Transmission System (FACTS) device playing a vital role as a stability aid for small and large transient disturbances in an interconnected power system. This paper deals with design and evaluation of a feedback linearizing nonlinear controller for STATCOM installed in a single-machine infinite-bus power system. In addition to the co-ordinated control of AC and DC bus voltages, the proposed controller also provides good damping to the electromechanical oscillation of the synchronous generator under transient disturbances. The efficiency of the control strategy is evaluated by computer simulation studies. The comparative study of these results with the conventional cascade control structure establishes the elegance of the proposed control scheme

Decentralized Synergetic Control of Power Systems

The objective of this dissertation is to design decentralized controllers to enhance the transient stability of power systems. Due to the nonlinearities and complexities of the system, nonlinear control design techniques are required to improve its dynamic performance. In this dissertation a synergetic control technique is being proposed to design supplementary controller that is added to the exciter of the generation unit of the system. Although this method has been previously applied to a Single Infinite Machine Bus (SMIB) system with high degree of success, it has not been employed to systems with multi machine. Also, the method has good robust characteristic like that of the popular Sliding Mode Control (SMC) technique. But the latter technique introduces steady state chattering effect which can cause wear and tear in actuating system. This gives the proposed technique a major advantage over the SMC. In this work, the method is employed for systems with multi machine. Each of the machines is considered to be a subsystem and decentralized controller is designed for each subsystem. The interconnection term of each subsystem with the rest of the system is estimated by a polynomial function of the active power generated by the subsystem. Particle Swarm Optimization (PSO) technique is employed for optimum tuning of the controller\u27s parameters. To further enhance the performance of the system by widening its range of operation, Reinforcement Learning (RL) technique is used to vary the gains of the decentralized synergetic supplementary controller in real time. The approach is illustrated with several case studies including a SMIB system with or without a Static Var Compensator (SVC), a Two Area System (TAS) with or without an SVC, a three --machines-nine-bus system and a fifty machine system. Results show that the proposed control technique provides better damping than the conventional power system stabilizers and synergetic controllers with fixed gains

Power system damping controllers design using a backstepping control technique

The objective of this dissertation is to design and coordinate controllers that will enhance transient stability of power systems subject to large disturbances. Two specific classes of controllers have been investigated, the first one is a type of supplementary signals added to the excitation systems of the generating units, and the second is a type of damping signal added to a device called a Static Var Compensator that can be placed at any node in the system. To address a wide range of operating conditions, a nonlinear control design technique, called backstepping control, is used. While these two types of controllers improve the dynamic performance significantly, a coordination of these controllers is even more promising. Control coordination is presented in two parts. First part concerns simultaneous optimization of selected control gains of exciter and SVC in coping with the complex nature of power systems. Second part proposes a combination of reinforcement learning and a backstepping control technique for excitation control system. The reinforcement learning progressively learns and adapts the backstepping control gains to handle a wide range of operating conditions. Results show that the proposed control technique provides better damping than conventional power system stabilizers and backstepping fixed gain controllers

Decentralized and Fault-Tolerant Control of Power Systems with High Levels of Renewables

Inter-area oscillations have been identified as a major problem faced by most power systems and stability of these oscillations are of vital concern due to the potential for equipment damage and resulting restrictions on available transmission capacity. In recent years, wide-area measurement systems (WAMSs) have been deployed that allow inter-area modes to be observed and identified.Power grids consist of interconnections of many subsystems which may interact with their neighbors and include several sensors and actuator arrays. Modern grids are spatially distributed and centralized strategies are computationally expensive and might be impractical in terms of hardware limitations such as communication speed. Hence, decentralized control strategies are more desirable.Recently, the use of HVDC links, FACTS devices and renewable sources for damping of inter-area oscillations have been discussed in the literature. However, very few such systems have been deployed in practice partly due to the high level of robustness and reliability requirements for any closed loop power system controls. For instance, weather dependent sources such as distributed winds have the ability to provide services only within a narrow range and might not always be available due to weather, maintenance or communication failures.Given this background, the motivation of this work is to ensure power grid resiliency and improve overall grid reliability. The first consideration is the design of optimal decentralized controllers where decisions are based on a subset of total information. The second consideration is to design controllers that incorporate actuator limitations to guarantee the stability and performance of the system. The third consideration is to build robust controllers to ensure resiliency to different actuator failures and availabilities. The fourth consideration is to design distributed, fault-tolerant and cooperative controllers to address above issues at the same time. Finally, stability problem of these controllers with intermittent information transmission is investigated.To validate the feasibility and demonstrate the design principles, a set of comprehensive case studies are conducted based on different power system models including 39-bus New England system and modified Western Electricity Coordinating Council (WECC) system with different operating points, renewable penetration and failures

Novel Night and Day Control of a PV Solar System as a STATCOM (PV-STATCOM) for Damping of Power Oscillations

Installations of large scale PV solar farms are rapidly increasing, worldwide. This is causing a growing apprehension that inertialess power injections from these inverter based generators will result in a decline in power system stability. Instead, this thesis presents novel applications of a patent pending technology whereby the PV solar farms actually help significantly increase system stability. A novel 24/7 (night and day) control of a large-scale PV solar farm as a dynamic reactive power compensator STATCOM, termed PV-STATCOM, is presented for damping low-frequency electromechanical power oscillations resulting in a significant improvement in power transfer capability of existing power transmission systems. A new real and reactive power modulation based control of PV-STATCOM is demonstrated during daytime that combines the functionalities of both a STATCOM and a Battery Energy Storage System (BESS) to provide significantly enhanced levels of power oscillation damping than that achieved by either a STATCOM or a BESS. The effectiveness of the proposed PV-STATCOM Power Oscillation Damping (POD) control techniques based on modulation of reactive power, real power or a combination of both is evaluated through both small signal and Electromagnetic Transients simulations studies. Participation factor analysis is utilized for selection of appropriate control signals and damping controllers. The POD controllers are designed through small signal Residue analysis and validated through Simplex Optimization technique in electromagnetic transient simulations. The efficacy of the proposed PV-STATCOM controls is demonstrated on three power systems: Single Machine Infinite Bus SMIB system, Two-Area system, and the 12 bus FACTS power system, which exhibit different power oscillation modes. New ramp up techniques for power restoration from solar farms are also presented, which are substantially faster than those specified by grid codes. A methodology for coordination of proposed PV-STATCOM controls with existing Power System Stabilizers (PSSs) on synchronous generators is further described for further damping enhancement. This thesis thus presents a novel technology that can not only help increase the penetration of large scale PV solar farms but utilize them for reducing the need for construction of expensive new lines or use of costly Flexible AC Transmission systems for stability improvement

Nonlinear Analysis of an Improved Swing Equation

In this paper, we investigate the properties of an improved swing equation model for synchronous generators. This model is derived by omitting the main simplifying assumption of the conventional swing equation, and requires a novel analysis for the stability and frequency regulation. We consider two scenarios. First we study the case that a synchronous generator is connected to a constant load. Second, we inspect the case of the single machine connected to an infinite bus. Simulations verify the results

MODELING AND CONTROL OF INTERLINE POWER FLOW CONTROLLER FOR POWER SYSTEM STABILITY ENHANCEMENT

Mitigation of power system oscillations is the problem of concern in the power industry as these oscillations, when exhibiting poor damping; affect the transmission line power transfer capability and power system stability. These oscillations greatly restrict power system operations and, in some cases, can also lead to widespread system disturbances. In this context, the Flexible AC Transmission System (FACTS) device, Interline Power Flow Controller (IPFC) employed to improve the transmission capability can be additionally utilized for damping control of power system oscillations. IPFC based damping controller design for power system stability requires proper and adequate mathematical representation of power system incorporating the FACTS device. This thesis reports the investigation on the development of steady state model, the dynamic nonlinear mathematical model of the power system installed with the IPFC for stability studies and the linearized extended Phillips Heffron model for the design of control techniques to enhance the damping of the lightly damped oscillations modes. In this context, the mathematical models of the single machine infinite bus (SMIB) power system and multi-machine power system incorporated with IPFC are established. The controllers for the IPFC are designed for enhancing the power system stability. The eigenvalue analysis and nonlinear simulation studies of the investigations conducted on the SMIB and Multi-machine power systems installed with IPFC demonstrate that the control designs are effective in damping the power system oscillations. The results presented in this thesis would provide useful information to electric power utilities engaged in scheduling and operating with the FACTS device, IPFC

A Review On SVC Control For Power System Stability With And Without Auxiliary Controller

Since the beginning of the last century, power system stability has been recognized as a vital problem in securing system operation. Power system instability has caused many major blackouts. This paper reviewed the previous technical works consisting of various methods of optimization in controlling power system stability. The techniques presented were compared to optimize the control variables for optimization of power system stability. Power system stability enhancement has been investigated widely in literature using different ways. This paper is focusing on SVC performance for enhancing power system stability either through SVC controlled itself or SVC controlled externally by other controllers. Static VAR compensators (SVCs) are used primarily in power system for voltage control as either an end in itself or a means of achieving other objectives, such as system stabilization. The analysis on performance of the previous work such as advantages and findings of a robust method approach in each technique was included in this paper