Model Of Unified Power Flow Controller Research Articles

Enhancing small signal power system stability by coordinating unified power flow controller with power system stabilizer

Advancement of power electronic technologies makes ac systems to be more adaptive and flexible as new forms of power controller emerges in recent years. Though not yet well developed, underpinned research suggests that unified power flow controller (UPFC) is a promising power system controller. This paper proposes a method to coordinate UPFC with power system stabilizer (PSS) so as to damp down oscillations caused by small signal disturbance. It starts by deriving a mathematical model of UPFC, with which its linearized differential equations are integrated to design an overall control strategy for enhancing small signal stability of the so connected power systems. The approach is to identify the eigenvalue of the largest real part and then minimize it as a nonlinear optimization problem. In order to ensure the robustness of the control system, different operating conditions are simultaneously considered in the parameter optimization process. Results of a case study on the New England test system show that the model is correct and the method is promising for coordinating the model parameters to enhance the small signal stability of the complex power system.

Versatile model of a unified power flow controller in a simple power system

A versatile mathematical model of a unified power flow controller (UPFC) in a single machine infinite bus system is proposed. The model consists of a simple voltage source whose magnitude and angle depend on the UPFC control parameters. The voltage-source model of UPFC can easily be incorporated into the generator output power equation and that simplifies the dynamic analysis of the system. With some appropriate assumptions, the proposed UPFC model can also be used to represent other FACTS devices, such as, the static synchronous compensators, static synchronous series compensators, etc. The proposed model is then used to determine and compare the dynamic behaviour of a simple system equipped with various FACTS devices.

The Line Flow Control of Multiple UPFCs for Enhancing Power System Security

This article presents a method to determine operating points of Unified Power Flow Controllers (UPFC), the line flow control of which can enhance system security level. The decoupledmodel has been employed as a mathematical model of UPFC for power flow analysis so as to analyze the effect of these devices on the power system. The security index that indicates the congestion level of transmission line has been proposed and minimized by iterative method. The sensitivity of objective function for control variables of an UPFC has been derived, and it represents the change in the security index for a given set of changes in real power outputs of UPFC. The proposedalgorithmwithsensitivity analysis gives the optimalset of operatingpoints of multiple UPFCs that reduces the index or increases the security margin, and Marquart method has been adoptedas an optimization methodbecause of stable convergence. The algorithm is verified by the 10-unit, 39-bus New England system that includes multiple UPFCs. The simulation results show that the power flow congestion can be relieved in the normal state and the security margin can be guaranteed even in a fault condition by the cooperative operation of multiple UPFCs.

Application of unified power flow controller in interconnected power systems-modeling, interface, control strategy, and case study

In this paper, a new power frequency model for unified power flow controller (UPFC) is suggested with its DC link capacitor dynamics included. Four principal control strategies for UPFC series element main control and their impacts on system stability are discussed. The main control of UPFC series element can be realized as a combination of the four control functions. The supplementary control of UPFC is added for damping power oscillation. The integrated UPFC model has then been incorporated into the conventional transient and small signal stability programs with a novel UPFC-network interface. Computer tests on a 4-generator interconnected power system show that the suggested UPFC power frequency model and the UPFC-network interface method work very well. The results also show that the suggested UPFC control strategy can realize power flow control fairly well and improve system dynamic performance significantly.

A comprehensive Newton-Raphson UPFC model for the quadratic power flow solution of practical power networks

A new and comprehensive load flow model for the unified power flow controller (UPFC) is presented in this paper. The model is incorporated into an existing Newton-Raphson load flow algorithm. Unlike existing UPFC models available in open literature, it can be set to control active and reactive powers and voltage magnitude in any combination or to control none of them. A set of analytical equations has been derived to provide good UPFC initial conditions. Hence, the algorithm exhibits quadratic or near-quadratic convergence characteristics. Suitable guidelines are suggested for an effective control coordination of two or more UPFCs operating in series or parallel arrangements. Test results are presented which demonstrate the effectiveness of the new model.

Power injection modeling and optimal multiplier power flow algorithm for steady-state studies of unified power flow controllers

Abstract This paper presents an optimal multiplier based Newton-Raphson power flow algorithm for reliably and efficiently handling power systems with embedded flexible AC transmission systems (FACTS) devices such as unified power flow controllers (UPFCs). A power injection transformation of a two voltage source UPFC model is derived in rectangular form. After detailed analyses of issues in implementation of UPFCs in power flow programmes by various power flow algorithms, the optimal multiplier power flow method for ill-conditioned systems is adopted. The proposed UPFC model and power flow algorithm have been programmed and vigorously tested in a number of systems. The results on the IEEE 30-bus test system and a 306-bus practical system are reported and compared with conventional user defined model type programmes, which clearly illustrate the effectiveness of the proposed algorithm.

UPFC Power Frequency Model for Power System Stability Analysis

In this paper a power frequency model is derived for unified power flow controller (UPFC). The UPFC capacitor charging dynamics is considered. Its shunt part control is to keep constant the UPFC terminal bus voltage magnitude and the UPFC capacitor voltage respectively. Its series part control is to keep constant real and reactive power flow of the UPFC-installed line or to act as a series compensator. The integrated UPFC model has been incorporated into power system transient stability program with a novel interface. Computer tests on a 4-generator power system show that the suggested UPFC model and the UPFC-network interface method work very well in transient stability analysis. The tests also show that the different control strategies might have distinct effects on system stability performance.

Incorporation of a UPFC model in an optimal power flow using Newton's method

The paper addresses the issue of unified power flow controller (UPFC) modelling within the context of optimal power flow (OPF) solutions. The nonlinear optimisation problem is solved by Newton's method leading to highly robust iterative solutions even for cases of large-scale power networks, where hundreds of variables are to be optimised. It is shown in the paper that networks modified to include several UPFCs are solved with equal reliability. The UPFC model itself is very flexible, it allows the control of active and reactive powers and voltage magnitude simultaneously. It can also be set to control one or more of these parameters in any combination or to control none of them. Considerable progress has been achieved in UPFC modelling intended for conventional load flow studies but this is the first time that the more complex issue of UPFC modelling intended for OPF solutions has been addressed.

Unified power flow controller: a critical comparison of Newton–Raphson UPFC algorithms in power flow studies

A new and comprehensive load flow model for the unified power flow controller (UPFC) is presented. The UPFC model is incorporated into an existing FACTS Newton-Raphson load flow algorithm. Critical comparisons are made against existing UPFC models, which show the newly developed model to be far more flexible and efficient. It can be set to control active and reactive powers and voltage magnitude simultaneously. Unlike existing UPFC models, it can be set to control one or more of these parameters in any combination or to control none of them. Limits checking and an effective control coordination between controlling devices are incorporated in the enhanced load flow program. The algorithm exhibits quadratic or near-quadratic convergence characteristics, regardless of the size of the network and the number of FACTS devices.

UPFC application on the AEP system: planning considerations

In 1995, American Electric Power (AEP), an investor owned electric utility company, completed detailed planning studies to resolve voltage and thermal loading concerns in parts of its Kentucky/West Virginia service areas. These studies led to the initiation of a project including a unified power flow controller (UPFC), which is currently being developed through a tailored collaboration by AEP, Electric Power Research Institute (EPRI), and Westinghouse Electric Corporation (Westinghouse). This paper describes the planning concerns, the study objectives, and the UPFC function in resolving these concerns. It also provides information on the UPFC modeling for system studies and its technical parameters that would be of interest to transmission system planners and other prospective users of this new technology.