Combined voltage-frequency control with power electronics-based devices

<span>The rise in demand for electricity and the high cost of constructing new power networks reckons optimal utilization of electric power overloading and excessive power transfer along transmission lines, high losses, voltage instability, poor power quality, reliability issues. Flexible AC transmission system (FACTS) boosts the static and dynamic performance of power systems. Although efficient power transmission by improving power quality and voltage profile enhancement is controlled using the FACTS devices the placement, types, and sizing are important parameters to be optimized for the power system. This paper develops the economic multiple FACT placements and sizing solution during N-1 contingency conditions. Placement and sizing being the stochastic problem meta-heuristic algorithm genetic algorithm (GA) is used and applied on the standard IEEE 9 bus system. MATLAB-based simulation is developed for economic placement of multiple FACTS and single FACTS devices in different scenarios (without FACTS devices, with single FACTS devices, and with multiple FACTS devices). Both static VAR compensators (SVC) and thyristor-controlled series capacitors (TCSC) are used (either single or multiple) to optimize the transmission loss and total cost. The results show that transmission loss and cost reduction with 70% compensation is working better with about 0.1 MW lesser loss in many cases.</span>

Optimal placement and sizing of multi-type FACTS devices in power systems using metaheuristic optimisation techniques: An updated review

Growing number of wind turbines is changing electricity generation profile all over the world. This brings challenges for power system operation, which was designed and developed around conventional power plants with directly coupled synchronous generators. In result, safety and stability of the electrical network with high wind energy penetration might be compromised. For this reason transmission system operators (TSO) impose more stringent connection requirements on the wind power plant (WPP) owners. On the other hand flexible AC transmission systems (FACTS) devices offer enhancement of grid stability and can facilitate grid code compliance for WPP. In this paper state-of-the-art in FACTS for WPPs with AC connection is given. FACTS devices with their properties are described. HVDC, which in literature is also often recognized as FACTS device, is out of this paper scope. Academic and industrial research in FACTS applicability for WPPs is summarized. Examples of few existing FACTS applications for wind farms are given.

Transmission systems are under stress and need to be upgraded. Better utilization of the existing grid provides a fast and cheap alternative to building new transmission. One way to improve the utilization of the transmission network is power flow control via flexible ac transmission system (FACTS) devices. While FACTS devices are used today, the utilization of these devices is limited; traditional dispatch models (e.g., security constrained economic dispatch) assume a fixed, static transmission grid even though it is rather flexible. The primary barrier is the complexity that is added to the power flow problem. The mathematical representation of the DC optimal power flow, with the added modeling of FACTS devices, is a nonlinear program (NLP). This paper presents a method to convert this NLP into a mixed-integer linear program (MILP). The MILP is reformulated as a two-stage linear program, which enforces the same sign for the voltage angle differences for the lines equipped with FACTS. While this approximation does not guarantee optimality, more than 98% of the presented empirical results, based on the IEEE 118-bus and Polish systems, achieved global optimality. In the case of suboptimal solutions, the savings were still significant and the solution time was dramatically reduced.

Growing environmental concerns as well as the decline in renewable energy project costs have led to drastic changes in the generation mix, and increasing penetration from renewable energy resources. However, the intermittency of renewable energy resources in contrast to legacy design of transmission system remains as one main obstacle against renewable energy integration. Several solutions, including energy storage, demand response and transmission system expansion have been proposed in response to this problem. Flexible ac transmission system (FACTS) devices are also shown as to offer a cost-effective solution for congestion problem in transmission system. This paper studies the environmental impacts of power flow control through FACTS devices as well as the economic benefits. Results show that implementing power flow control can effectively reduce dispatch cost and carbon emissions. However, the location of FACTS devices and renewable energy sites can critically affect carbon emission and renewable energy curtailment.

In this paper, multi – type Flexible AC Transmission System (FACTS) devices are optimally located for enhancing the loadability of an existing power network within the security margins. Line Stability Index is used to determine the critical lines of the system in increased loading of transmission lines and is used to determine the optimal location of FACTS devices. Differential Evolution Algorithm (DE) is used to determine the optimal location and control parameter settings of the FACTS devices. Among the various FACTS devices, Unified Power Flow Controller (UPFC) and Thyristor Controlled Series Capacitor (TCSC) are chosen and modeled for steady state studies. IEEE- 30 bus test system is used for simulation studies and the results are compared with Genetic Algorithm (GA) to show the advantage and feasibility of the DE approach. Further the results demonstrate that the system loadability can be increased by optimal location and control parameter settings of the multi – type FACTS devices.

ABSTRACTIn the present work, symbiotic organism search (SOS) algorithm is applied for the solution of optimal reactive power dispatch (ORPD) problem of power system considering flexible AC transmission system (FACTS) devices. The proposed method is tested and examined on modified IEEE 30 bus test system with two types of FACTS devices namely thyristor-controlled series capacitor (TCSC) and thyristor-controlled phase shifter (TCPS), placed at some strategic locations. In this study, ORPD problem has been formulated as single objective, constrained optimization problem that aims to reduce active power loss or total absolute voltage deviation individually. The formulation for conventional OPRD problem is evaluated by considering the settings of control parameters and maintaining the constraints of the FACTS devices as an additional entity. The effectiveness of the proposed method is analysed and compared to the results offered by some other optimization methods. The outcomes of the present work prove the potential of the SOS algorithm in solving ORPD problems of the power system incorporating FACTS devices.

This paper deals with a new operation strategy of FACTS (flexible AC transmission system) device, especially the series compensating device like TCSC (thyristor controlled series compensator) using the linearized sensitivity derived in this paper. In case of a line overflow under contingency state or line congestion at normal state, the FACTS device must change its operating point to relieve the flow congestion and eventually to increase the system security level. In this paper, line flow sensitivity to FACTS device is derived analytically. The sensitivity derivation is based on the DC flow model under the assumption that the generator dispatch is maintained. The power flow control algorithm based on the sensitivity analysis proposed in this paper has several advantages; it is easy to compute, its computation time is short, and its form is very simple etc. Each FACTS device installed in the power system changes its reactance according to the dynamic algorithm proposed in this paper. Its direction and the amount of reactance change depend on the sensitivity of each device. The proposed algorithm in this paper is tested and verified on the IEEE 39 system.

In this paper, a fully fledged optimal power flow (OPF) algorithm with flexible AC transmission systems (FACTS) devices has been developed and presented aiming at the advancement of how FACTS equipment impacts on the security and economy of the wider power network. The proposed modelling uses Newton’s method along with Lagrangian multipliers, leading to an ecient algorithm that can handle practical power networks independence of initial settings of FACT controllers parameters. Newton’s method provides a suitable vehicle for incorporating the newly developed nonlinear, linearized FACTS models. In this paper, mainly a firing angle-based thyristor controlled series compensators (TCSC) model, a coordinated two-voltage source unified power flow controller (UPFC) model have been developed and presented in details and can easily be extended to other modern FACTS devices such as interline power flow controller (IPFC) and generalized unified power flow controller (GUPFC). The proposed model has capability of converting multi-objective functions into single objective and also can be extended to multiple multi-type FACTS devices. The performance of the proposed model has been validated for IEEE 30 bus system and the solutions so obtained are presented in detail.

This paper proposes a reactive power planning model, which incorporates flexible AC transmission system (FACTS) devices. The optimal location of multi-type FACTS devices and their control parameters are optimized by a novel bacterial swarming algorithm (BSA) to minimize the real power losses and also to improve voltage profile. The simulation studies have been undertaken on both IEEE 30-bus and 118-bus test systems. Simulation results show that the performance of the power system is improved with multi-type FACTS placed optimally in the reactive power planning model. The advantage of using BSA to determine the location of FACTS devices is demonstrated, in comparison with two other evolutionary algorithms (EAs), i.e., genetic algorithm (GA) and particle swarm optimizer (PSO).

Chapter 31 - Flexible AC transmission systems

Comparison of BBO, WIPSO & PSO Techniques for the Optimal Placement of FACTS Devices to Enhance System Security

High electricity growth in Nigeria coupled with an obsolete transmission network has necessitated novel approaches to power grid optimization. This paper compares the two technologies- Solar Photovoltaic (PV) system and Flexible AC Transmission System (FACTS) devices, in particular Static Synchronous Compensator (STATCOM), individually embedded to the 330 kV Nigeria 48-bus transmission grid in a simulation-based study. With the assistance of Power System Analysis Toolbox (PSAT) in MATLAB, this paper summarizes how these are the technologies that developed to increase Available Transfer Capability(ATC), gain better voltage stability and change power flow under normal as well as under Single Line Contingency. Five weak buses were used for the simulation featuring poor voltage performance and three deployment confirmations were studied (FACTS, PV, and the the base case without any enhancement). The results prove that solar PV and FACTS devices can independently be used to enhance the performance. ATC enhancement of FACTS deployment are almost 35.7% in ATC whereas solar PV gave an ATC enhancement of 29.6%. Voltage variation was decreased by 24.6% and 29.4% in the FACTS-only and PV-only case respectively, over the base case. These findings imply that FACTS has more transfer capacity, while PV systems have more voltage support. The results of this study offer valuable knowledge for power system planners and decision makers in developing countries where additional infrastructure development may not be feasible or immediate, but a need to reinforce the transmission network using flexible and low-cost solutions exists.

Managing transmission congestion in an unbundled electric power system poses a challenge to ISO. Flexible AC transmission system (FACTS) can provide ancillary services to solve congestion problem. However, how to assess the ancillary service provided by FACTS devices and allocate the charge is a key issue need to be solved. This paper proposes a new method for assessing ancillary service of phase-shifter used in congestion management, which is based on a new electrical dissecting method. Considering of that the FACTS devices are used to relieve congestion and reduce energy price for consumers, it is reasonable to allocate the utilization charge among consumers or suppliers who caused the congestion. And the electrical dissecting method is used to obtain responsible factors of consumers or suppliers causing congestion. Example shows the method is effective and correct, which can not only provide accurate electrical information to assess ancillary services of phase-shifters, but also provide useful reference to the assessment of ancillary services with other FACTS devices.

This paper presents the solution of optimal power flow (OPF) of power system with flexible AC transmission systems (FACTS) devices by using opposition-based gravitational search algorithm (OGSA). OPF problem with FACTS is solved by the way of minimizing an objective function which reflects cost of generation, emission and active power transmission loss. FACTS devices considered include thyristor controlled series capacitor and thyristor controlled phase shifter. The proposed approach has been examined and tested on the IEEE 57-bus test power system. The obtained results are compared with those reported in the literature. Simulation results demonstrate the superiority and accuracy of the proposed algorithm. Considering the quality of the solution obtained, the proposed algorithm seems to be effective and robust to solve the studied problem.