In electrical power distribution and power electronic applications, a transformer is an indispensable component which performs many functions. At its operating frequency (60/50 Hz), it is one of the most bulky and expensive components. The concept of the electronic transformer introduced previously has shown considerable reduction in size, weight, and volume by operating at a higher frequency. In this dissertation, the concept of the electronic transformer is further extended to the auto-connected phase-shifting type to reduce harmonics generated by nonlinear loads. It is shown that with the addition of primary side and secondary side AC/AC converters achieves phase-shifting. With the addition of converters, magnetic components are operated at a higher frequency to yield a smaller size and weight. Two types of auto-connected electronic transformer configurations are explored. In the first configuration, the secondary converter is eliminated and the output is suitable for rectifier type loads such as adjustable speed drives. In the second configuration, the secondary converter is added to obtain a sinusoidal phase-shifted AC output voltage. This approach is applicable in general applications. With the proposed approaches, the th and 7th harmonic in utility line currents, generated by two sets of nonlinear loads, are subtracted within the electronic transformer, thereby reducing the total harmonic distortion (THD) of the line current. The analysis and simulation results are presented. In the second part of the dissertation, the electronic transformer concept is applied to a telecommunication power supply (-48 VDC) system. The proposed approach consists of a matrix converter to convert the low frequency three-phase input AC utility to a high frequency AC output without a DC-link. The output of the matrix converter is then processed via a high frequency isolation transformer to produce -48 VDC. Digital control of the system ensures that the output voltage is regulated and the input currents are of high quality, devoid of low frequency harmonics and at near unity input power factor under varying load conditions. Due to the absence of DC-link electrolytic capacitors, the power density of the proposed rectifier is shown to be higher. Analysis, design example and experimental results are presented from a three-phase 208 V, 1.5 kW laboratory prototype converter.

This work deals with problems where multiple actors simultaneously take control decisions and implement the corresponding actions in large multi-area power systems. The fact that those actions take place in the same transmission grid introduces a coupling between the various decision-making problems. First, transmission constraints involving all actors' controls must be satisfied, while, second, the satisfaction of an actor's operational objective depends, in general, not only on its own actions but on the others' too. Algorithms and/or operational procedures are, thus, developed seeking to reconcile the multiple actors' simultaneous decisions. The confidentiality and operational autonomy of the actors' decision-making procedures are preserved. In particular, two specific problems leading to such a multi-actor situation have been treated. The first is drawn from a recently emerging situation, at least in Europe, where several Transmission System Operators (TSOs) have installed and/or are planning to install Phase Shifting Transformers (PSTs) in such locations in their areas that, by properly adjusting the PST phase angle settings, they can significantly control the power flows entering and exiting their systems. A general framework is proposed for the control of PSTs owned by several TSOs, taking into account their interactions. The proposed solution is the Nash equilibrium of a sequence of optimizations performed by the various TSOs, each of them taking into account the other TSOs' control settings as well as operating constraints relative to the whole system. The method is applied to a linearized network model and illustrated on the IEEE 118-bus system. The second multi-actor situation dealt with in this work stems from the recently increasing amount of discussions and efforts made towards creating the right market structures and operational practices that would facilitate a seamless inter-area trade of electricity throughout large interconnections. In this respect, in accordance with European Union's goal of a fully functional Internal Electricity Market where ideally every consumer will be able to buy electric energy from every producer all across the interconnection, the possibility of every market participant to place its bid in whatever electricity market of an interconnection has been considered. This results in overlapping markets, each with its own schedule of power injections and withdraws, comprising buses all around the interconnection, that are cleared simultaneously by Transaction Schedulers (TSs). An iterative procedure is proposed to reconcile the various TS schedules such that congestion is managed in a fair and efficient way. The procedure converges to such schedules that the various TS market clearings are in a Nash equilibrium. The method is then extended towards several directions: enabling market participants to place their bids simultaneously in more than one TS's market, incorporating $N-1$ security constraints, allowing for joint energy-reserve dispatch, and, accounting for transmission losses. The corresponding iterative algorithms are thoroughly illustrated in detail on a 15-bus as well as the IEEE RTS-96 system.

<p>In this thesis, controllers for power oscillation damping, transient stability improvement and power flow control by means of a Controlled Series Compensator (CSC) and and a Dynamic Power Flow Controller (DPFC) are proposed. These devices belong to the group of power system components referred to as Flexible AC Transmission System (FACTS) devices. The developed controllers use only quantities measured locally at the FACTS device as inputs, thereby avoiding the risk of interrupted communications associated with the use of remote signals for control.</p><p>For power systems with one dominating, poorly damped inter-area power oscillation mode, it is shown that a simple generic system model can be used as a basis for damping- and power flow control design. The model for control of CSC includes two synchronous machine models representing the two grid areas participating in the oscillation and three reactance variables, representing the interconnecting transmission lines and the FACTS device. The model for control of DPFC is of the same type but it also includes the phase shift of the internal phase-shifting transformer of the DPFC.</p><p>The key parameters of the generic grid models are adaptively set during the controller operation by estimation from the step responses in the FACTS line power to the changes in the line series reactance inserted by the FACTS device. The power oscillation damping controller is based on a time-discrete, non-linear approach which aims to damp the power oscillations and set the desired power flow on the FACTS line by means of two step changes in the line reactance separated in time by half an oscillation cycle.</p><p>A verification of the proposed controllers was done by means of digital simulations using power system models of different complexities. The CSC and DPFC controllers were shown to significantly improve the small-signal- and transient stability in one four-machine system of a type commonly used to study inter-area oscillations. The CSC controller was also tested for 18 different contingencies in a 23-machine system, resulting in an improvement in both the system transient stability and the damping of the critical oscillation mode. </p>

This thesis studies different aspects of Flexible AC Transmission System (FACTS) devices which are used to improve the power transfer capability and increase the controllability in electric power systems. In the thesis, different aspects on the usage and control of Dynamic Power Flow Controllers (DPFC) and related FACTS devices are studied. The DPFC is a combination of a Phase Shifting Transformer (PST) and a Thyristor Switched Series Capacitor (TSSC)/Thyristor Switched Series Reactor (TSSR). The thesis proposes and studies a new method, the Ideal Phase-Shifter (IPS) method, for selection and rating of Power Flow Controllers (PFC) in a power grid. The IPS method, which is based on steady-state calculations, is proposed as a first step in the design process for a PFC. The method uses the Power controller plane, introduced by Brochu et al in 1999. The IPS method extends the usage of decoupling methods in the Power controller plane to a power system of arbitrary size. The IPS method was in the thesis used to compare the ratings of different PFC:s required to improve the power transfer capability in two test systems. The studied devices were here the PST, the TSSC/TSSR and the DPFC. The thesis treats control of ideal Controlled Series Capacitors (CSC), TCSC, TSSC/TSSR, and DPFC. The goals of the FACTS controllers which are developed are Power Oscillation Damping (POD), fast power flow control, and transient stability improvement in the power system. New adaptive control strategies for POD and power flow control are proposed and studied in different models of power systems by time-domain simulations. A strategy for transient stability improvement is also proposed and studied. Additionally, different methods for study of Subsynchronous Resonance (SSR), which is associated with series compensation in power systems, are investigated. Here, four of the most common methods for frequency scanning to determine the electrical damping of subsynchronous oscillations in a power grid are studied. The study reveals significant differences of the electrical damping estimates of the studied standard methods when applied to a four-machine test system. / QC 20110819

In this thesis, controllers for power oscillation damping, transient stability improvement and power flow control by means of a Controlled Series Compensator (CSC) and and a Dynamic Power Flow Controller (DPFC) are proposed. These devices belong to the group of power system components referred to as Flexible AC Transmission System (FACTS) devices. The developed controllers use only quantities measured locally at the FACTS device as inputs, thereby avoiding the risk of interrupted communications associated with the use of remote signals for control. For power systems with one dominating, poorly damped inter-area power oscillation mode, it is shown that a simple generic system model can be used as a basis for damping- and power flow control design. The model for control of CSC includes two synchronous machine models representing the two grid areas participating in the oscillation and three reactance variables, representing the interconnecting transmission lines and the FACTS device. The model for control of DPFC is of the same type but it also includes the phase shift of the internal phase-shifting transformer of the DPFC. The key parameters of the generic grid models are adaptively set during the controller operation by estimation from the step responses in the FACTS line power to the changes in the line series reactance inserted by the FACTS device. The power oscillation damping controller is based on a time-discrete, non-linear approach which aims to damp the power oscillations and set the desired power flow on the FACTS line by means of two step changes in the line reactance separated in time by half an oscillation cycle. A verification of the proposed controllers was done by means of digital simulations using power system models of different complexities. The CSC and DPFC controllers were shown to significantly improve the small-signal- and transient stability in one four-machine system of a type commonly used to study inter-area oscillations. The CSC controller was also tested for 18 different contingencies in a 23-machine system, resulting in an improvement in both the system transient stability and the damping of the critical oscillation mode. / QC 20101112

This thesis deals with a power flow control in the electric power system. An overview of FACTS devices is introduced; their basic characteristics as well as examples of their application are discussed. A significant part of this thesis investigates phase shifting transformers (PST´s), which seem to be suitable for implementation in the transmission system of the Czech Republic. The PST´s are useful devices that control active power flows on cross-border lines and regulate unwanted and unexpected power flows. Basic types and characteristics of the PST´s are discussed. In chapter 7 is designed laboratory task that should validate the regulatory capabilities of the transformer PST. Designs of models of individual parts of this laboratory task are presented. In the last part of this thesis the regulation effect of the PST is validated in the GLF/AES program.

Power flow (PF) control can increase the utilization of the transmission system and connect lower cost generation with load. While PF controllers have demonstrated the ability to realize dynamic PF control for more than 25 years, PF control has been sparsely implemented. This research re-examines PF control in light of the recent development of fractionally-rated PF controllers and the incremental power flow (IPF) control concept. IPF control is the transfer of an incremental quantity of power from a specified source bus to specified destination bus along a specified path without influencing power flows on circuits outside of the path. The objectives of the research are to develop power system operation and planning methods compatible with IPF control, test the technical viability of IPF control, develop transmission planning frameworks leveraging PF and IPF control, develop power system operation and planning tools compatible with PF control, and quantify the impacts of PF and IPF control on multi-decade transmission planning. The results suggest that planning and operation of the power system are feasible with PF controllers and may lead to cost savings. The proposed planning frameworks may incent transmission investment and be compatible with the existing transmission planning process. If the results of the planning tool demonstration scale to the national level, the annual savings in electricity expenditures would be $13 billion per year (2010$). The proposed incremental packetized energy concept may facilitate a reduction in the environmental impact of energy consumption and lead to additional cost savings.