Experimental study on the Unified Power Flow Controller

Flexible AC Transmission System (FACTS) controllers are advanced power electronic devices employed in electrical power systems to enhance system stability, reliability, and power transfer capabilities. These controllers enable dynamic and flexible control of various transmission parameters such as voltage, current, impedance, and phase angle, thereby improving the overall power system performance. FACTS devices are broadly classified into series, shunt, series- series, and series-shunt configurations, each designed to manage reactive power and regulate voltage either by injecting voltage in series or current in shunt with the transmission line. Well-known FACTS devices include Static Var Compensators (SVC), Static Synchronous Compensators (STATCOM), Thyristor Controlled Series Capacitors (TCSC), Static Synchronous Series Compensators (SSSC), and Unified Power Flow Controllers (UPFC), each serving specific roles in power flow control, voltage regulation, and transient stability enhancement. The integration of these controllers provides significant benefits such as increased transmission line capacity, improved voltage stability, minimized transmission losses, and damping of power system oscillations. They are capable of rapid response during transient disturbances, effectively mitigating voltage collapses and enhancing system resilience against faults and contingencies. FACTS controllers not only improve steady-state operational parameters but also address dynamic stability and transient conditions, enabling power systems to operate closer to their stability limits while maintaining security. Their deployment helps avoid costly infrastructural expansions by optimizing existing transmission assets, which is critical given environmental and economic constraints. Recent advances in semiconductor technologies and control algorithms have made FACTS devices more reliable, efficient, and adaptable to modern grids, including renewable integration and deregulated power markets. In summary, FACTS controllers play a vital role in modern power systems by providing flexible, efficient, and reliable solutions for power flow management, voltage control, and system stability enhancement, thereby supporting the evolving demands of today's complex electrical networks.

– The unified power flow controller (UPFC) is the most versatile and complex power electronic equipment that has emerged as the indispensable equipment for the control and optimization of power flow in electrical power transmission system. In this manuscript is investigated the control of real and reactive power flow through a transmission line with the use of UPFC at the sending end. Computer simulation using MATLAB Simulink is done and the behavior of the UPFC is studied. In the UPFC based control of transmission line parameter control systems, it is observed that whenever the SSSC sources some real power into the transmission line it is manifested as a voltage drop across the DC link. Reactive power demand is indicated as fall in the bus bar AC voltage. The fall of the DC link voltage is an indication of real power demand from the receiving end. Similarly a fall of the bus bar AC voltage is an indication of reactive power demand from the receiving end. Fuzzy Logic and PI controllers are used in this works, the control of DC voltage, AC voltage and power transfer.

Voltage instability and voltage collapse have been considered as a major threat to present power system networks due to their stressed operation. It is very important to do the power system analysis with respect to voltage stability. Flexible AC Transmission System (FACTS) is an alternating current transmission system incorporating power electronic-based and other static controllers to enhance controllability and increase power transfer capability. A FACTS device in a power system improves the voltage stability, reduces the power loss and also improves the load ability of the system. FACTS have made the power systems operation more flexible and secure. Amongst the several FACTS controllers, the Unified Power Flow Controller (UPFC) is most effective to improve the enhancement of voltage stability and reduces the power loss. This study investigates the application of Particle Swarm Optimization (PSO) to find sizing of Unified Power Flow Controller (UPFC) device to minimize the voltage stability index, total power loss, load voltage deviation, and cost of FACTS devices to improve voltage stability in the power system. A new model is proposed in this thesis to improve existing power-based model by using the Norton Equivalent Theorem. The proposed model can be integrated with the Equivalent Current Injection (ECI) power flow model easily. By ECI algorithm, it is much quickly and precisely to implement power flow calculations. Finally It is observed from the results that the voltage stability margin is improved, the voltage profile of the power system is increased and real power losses also reduced by optimally sizing UPFC device in the power system. Index Terms: Voltage stability, Unified Power Flow Controller (UPFC), Equivalent -Current Injection (ECI), Modified particle swarm optimization (MPSO)

The interline power flow controller (IPFC & UPFC) is one of the latest generation flexible AC transmission systems (FACTS) controller used to control power flows of multiple transmission lines. The main objective of this paper is detailed study about a new real and reactive power coordination controller for a interline power flow controller (IPFC & UPFC). The basic control for the IPFC is such that the series converter of the UPFC controls the transmission line real/reactive power flow and the shunt converter of the (IPFC & UPFC) controls the bus voltage/shunt reactive power and the DC link capacitor voltage. Because of the common link, any inverter within the (IPFC & UPFC) is able to transfer real power to any other and thereby facilitate real power transfer among the lines of the transmission system. Since each inverter is able to provide reactive compensation, the (IPFC & UPFC) is able to carry out an overall real and reactive power compensation of the total transmission system. This capability makes it possible to equalize both real and reactive power flow between the lines, transfer power from overloaded to under loaded lines, compensate against reactive voltage drops and corresponding reactive line power and to increase the effectiveness of the compensating system against dynamic disturbances. A simulation in MATLAB has been done in order to extend conventional algorithm based on this model.

Adaptive algorithm for transmission line protection in the presence of UPFC

Optimization of system capacity electric power transmission systems requires a reliable power flow controller. The power flow controllers must be able to control the level of electrical voltage and active and reactive power flow without reducing the level of stability and security of the transmission system. Latest technology in the control of power flow is a Unified Power Flow Controller (UPFC). The entire transmission line parameters are impedance, voltage, and phase angle can be controlled simultaneously by the UPFC. The method used in the conventional algorithms based UPFC is still firmly with logic. These algorithms have difficulties to electric power transmission systems multimachine very dynamic, i.e. systems that are experiencing rapid changes in the electrical load from time to time. Therefore, in this study was developed based on neuro-fuzzy method is applied to the adaptive UPFC for adaptively controlling the power flow in electric power transmission systems multimachine very dynamic. In this study, three phase fault is applied to the multimachine system. The results are taken to be consideration of PI and neuro-fuzzy controllers. The PI and neuro-fuzzy controllers show nearly same results but there is a low overshoot occurred during the fault in the neuro-fuzzy controllers results. According to results that UPFC improves the system performance under the transient and the normal conditions. However, it can control the power flow in the transmission line, effectively.

UPFC (Unified power flow controller) is one of the most powerful and complex FACTS (Flexible AC transmission system) devices in a power system today. It is primarily used for simultaneous or independent control of real and reactive power in transmission lines for flexible, reliable and economic operation and loading of power systems. In this paper, the effectiveness of UPFC has been explored in transmission system network when subjected to three phase to ground fault condition. The comparison has been made between VSI (Voltage Source Inverter) based UPFC and ZSI (Z-Source Inverter) based UPFC. From the results so obtained, it has been established that the performance of ZSI based UPFC is superior as compared to that of VSI based UPFC.

The flexible ac-transmission system (FACTS) family called distributed power flow controller (DPFC). The DPFC is derived from the unified power flow controller (UPFC) with eliminated common dc link. The active power exchange between the shunt and series converters, which is through the common dc link in the UPFC, is now through the transmission lines at the third-harmonic frequency. The DPFC is to use multiple small size single phase converters instead of large size three phase series converter in the UPFC. The large number of series converters provides redundancy, thereby increasing the system reliability. As the D-FACTS converters are single phase and floating with respect to the ground, there is no high voltage isolation required between the phases. The cost of the DPFC system is lower than the UPFC. The DPFC has the same control capability as the UPFC, which comprises the adjustment of the line impedance, the transmission angle, and the bus voltage. Due to the high control capability DPFC can also be used to improve the power quality and system stability, such as low frequency power oscillation damping, voltage sag restoration or balancing asymmetry.

Due to ever-increasing power demand, the power system is facing issues such as congestion, line outages, system reliability, and stability challenges. The impetus to revise the traditional power transmission theory and practice, and to introduce new concepts for improving the performance of the existing AC transmission system caused the development of flexible AC transmission system controllers (FACTs). Due to their capability of controlling transmission system parameters, the utilization of FACTs controllers has become essential to enhance the power system capability. To investigate the performance of FACTs controllers, this study incorporates the Unified Power Flow Controller (UPFC) in the power system. UPFC is used to mitigate transmission line congestion by controlling the transmission line power flow. In this paper, a modified control circuit for UPFC is implemented. Moreover, the selection of a suitable location for UPFC is necessary because of its techno-economic impacts. Therefore, this work uses a sensitivity-based approach for the selection of a suitable place of UPFC. To decide the suitable location, control parameters of UPFC along with system loss sensitivity indices are used. The model of UPFC along with the control circuit is simulated in PSCAD/EMTDC. To investigate the performance of UPFC, a five bus seven-line transmission system is used. After installing the UPFC at an appropriate location, the power flow results of transmission lines are compared with and without the usage of UPFC.

The independent control of active and reactive power flow in a transmission line is necessary for the transfer of bulk power along a desired path in the most economical way. A 'Sen' transformer (ST) uses transformer and tap changers that are traditionally used to build a voltage-regulating transformer (VRT) and a phase angle regulator (PAR). The ST regulates the voltage at a point in the transmission line as a VRT does. Additionally, the ST provides an independent and bidirectional active and reactive power (P and Q) flow control in the transmission line as a voltage-sourced converter (VSC)-based unified power flow controller (UPFC) does. Although both the ST and the PAR use a comparable number of components, the ST provides an area of controllability in the P-Q plane similar to a UPFC, while the PAR provides a linear P-Q characteristic. The technology of transformer and tap changer is proven to be reliable and cost-effective when compared with the emerging technology of VSC. The new ST is adequate to provide independent control of active and reactive power flow in most utility applications.

This paper presents a new methodology of incorporating power flow controllers, specifically flexible AC transmission systems (FACTS), into distributed DC optimal power flow (DCOPF). The distributed DCOPF problems are then solved by the alternating direction method of multipliers (ADMM). Efficient modeling of the power flow control capabilities of prominent FACTS devices, such as the unified power flow controller (UPFC) and the static synchronous series compensator (SSSC), enables the seamless integration of FACTS into the ADMM-based distributed DCOPF, thus allowing FACTS operation to be co-optimized with generator dispatch under a distributed control paradigm for the power system. The proposed ADMM-based distributed DCOPF problem with FACTS devices are studied through simulations on a 6-bus system and a modified IEEE 118-bus system to verify its convergence to the optimal generator dispatch.

The FACTS (Flexible ac transmission systems) devices have all the capabilities to provide fast control of active and reactive power through a transmission line. The UPFC (unified powerflow controller) is a member of the FACTS family with very unique features. UPFC can control active and/or reactive power simultaneously or independently. This paper establishes the improved performance of ZSI (Z-Source inverter) based UPFC over VSI (Voltage source inverter) based UPFC for power flow improvement. The simulation models developed in MATLAB/SIMULINKhave been used to show the improvement in active and reactive power flows in an interconnected network.

The introduction of the flexible AC transmission system (FACTS) in the power system reduces the losses, reduces the cost of the generation, improves the stability and also improves the load capability of the system. Some application of the Flexible AC transmission system (FACTS) technologies to existing high voltage power system has proves the use of FACTS technology may be a cost effective option for power delivery system enhancement. Amongst various power electronic devices unified power flow controller (UPFC) may be considered to be a capable of regulating the power flow and minimizing the power loss simultaneously. Since for the cost effective application of the FACTS technology a proper selection of the number and the placement of these devices is required. The main aim of this paper is to propose the methodology based on the genetic algorithm, able to identify the optimal number and the location of the UPFC devices in an assigned power system network for maximizing system capabilities. In order to validate the usefulness of the approach suggested here is , a case study using a IEEE 30-bus power system is presented and discussed.

In order to utilize the existing transmission line to its full capacity Flexible AC Transmission system (FACTS) are used. The power flow control is effective if all the elements of the transmission line must be varied simultaneously or individually. To achieve this, the key appropriate FACTS device is Unified Power Flow controller (UPFC). The use of conventional controllers delays the decision making process to take suitable control action during dynamic conditions. In this paper a fuzzy logic based controller is used to generate supplementary damping signals and to control the shunt converter of IPFC. Two separate neuro-controllers are used for series converter control. Hence coordination between shunt and series converters of UPFC is achieved. The results in MATLAB environment will explain the performance of UPFC during step change of real and reactive powers.

High‐power electronic converter topologies, in such forms as Unified Power Flow Controllers (UPFC), Static Compensators (STATCOM) and Interline Power Flow Controllers (IPFC), have been used to enhance and optimize the use of transmission facilities, under the concept of a flexible ac transmission system (FACTS). In Europe, the anticipated proliferation of distributed‐generation (DG) in the near future, driven by governmental initiatives and the European Commission's Framework Programs, has prompted new interests in the reliability and economy of power delivery and interconnection at the lower sub‐station level of 15kV. This paper investigates the use of IPFC, which are dc/ac converters linked by common DC terminals, in a DG‐power system from an economy perspective. By using a probabilistic approach, it can be shown that the power ratings of parallel active power filters used in the IPFC are considerably reduced from those of the deterministic approach, when reliability is not compromised. Analytical predications, and experimental measurements at a 15kV substation fed by a number of wind generators, confirm the validity of the proposed approach.