Independent Control Of Reactive Power Research Articles

Improved Control Strategy for Bidirectional Single Phase AC-DC Converter in Hybrid AC/DC Microgrid

This paper presents the improved control strategy with optimal switching scheme to improve the bidirectional converter's power flow control capability and to allow for different modes of operation in hybrid AC/DC microgrid. Also, this improved control strategy eliminates the need of PI controller for independent reactive power control. With the improvements in digital controllers, it is possible to implement complex control circuitry easily. The performance of bidirectional converter with improved control strategy is verified first in simulation environment and then on lab scale experimental set-up with the control circuit is implemented using hardware in loop in the real-time digital simulation platform. The simulation and experimental results for all the cases show that the controller is highly capable for power transfer between AC and DC grid with very fast response and also control reactive power without additional PI controller. Also, it maintains the current total harmonic distortion (THD) within standard limits.

Steady-state modelling for the integration of a bi-directional AC–DC–AC flexible power link

In the UK, Western Power Distribution (WPD) will be trialling a ‘flexible power link’ (FPL) as a part of the Ofgem-funded low carbon networks fund project, Network Equilibrium. The FPL is a power electronic AC–DC–AC device that allows for bidirectional transfer of real power and independent control of reactive power at each side. The trial device will be sited in WPD's network in the south west of the UK, allowing the interconnection of two separate areas of the network that could not normally be interconnected with AC only. This will allow for the balancing of power flows and management of voltages in the networks, enabling increased network utilisation and the integration of new loads and generation. This study introduces the FPL concept and provides details of the method and results of a study used to understand the FPL's impact on the network, in particular its operational ranges of real power, reactive power, and voltage control set points.

Tip Speed Ratio Based MPPT Algorithm and Improved Field Oriented Control for Extracting Optimal Real power and Independent Reactive Power Control for Grid Connected Doubly Fed Induction Generator

<p>Doubly Fed Induction Generator (DFIG) needs to get adopted to change in wind speeds with sudden change in reactive power or grid terminal voltage as it is required for maintaining synchronism and stability as per modern grid rules. This paper proposes a controller for DFIG converters and optimal tip speed ratio based maximum power point tracking (MPPT) for turbine to maintain equilibrium in rotor speed, generator torque, and stator and rotor voltages and also to meet desired reference real power during the turbulences like sudden change in reactive power or voltage with concurrently changing wind speed. The performance of DFIG is compared when there is change in wind speed only, changes in reactive power and variation in grid voltage along with variation in wind speed.</p>

Tip Speed Ratio Based MPPT Algorithm and Improved Field Oriented Control for Extracting Optimal Real power and Independent Reactive Power Control for Grid Connected Doubly Fed Induction Generator

<p>Doubly Fed Induction Generator (DFIG) needs to get adopted to change in wind speeds with sudden change in reactive power or grid terminal voltage as it is required for maintaining synchronism and stability as per modern grid rules. This paper proposes a controller for DFIG converters and optimal tip speed ratio based maximum power point tracking (MPPT) for turbine to maintain equilibrium in rotor speed, generator torque, and stator and rotor voltages and also to meet desired reference real power during the turbulences like sudden change in reactive power or voltage with concurrently changing wind speed. The performance of DFIG is compared when there is change in wind speed only, changes in reactive power and variation in grid voltage along with variation in wind speed.</p>

System reliability enhancement in a metropolitan area using HVDC technology

Recently, due to the increase of massed demand areas, in terms of system reliability has been raised several issues such as voltage, frequency problems and fault current. In Korean power systems, more than 40% of the total loads are concentrated in metropolitan areas, however most large plants are located in non-metropolitan areas. In these long-distance transmission systems, the transmission capacity is limited not by thermal capacity constraint, but by stability constraint. To solve these problems, the study of enhancing power system stability and increasing transmission capacity has been progressed. In this paper, we analyse domestic power systems in order to discuss the best solutions for current reduction using PSS/E simulation. Fault current problems can be resolved through gird segmentation which adopts Voltage Sourced Converter Back-to-Back High Voltage Direct Current (VSC BTB HVDC). Furthermore, grid segmentation can enhance the interface flow margin with the independent reactive power control in...

Multi-task control for VSC–HVDC power and frequency control

A robust control strategy for a VSC–HVDC transmission scheme between two ac networks is presented. The VSC converters at both ends of the dc line are equipped with a multi-task controller that facilitates: power management between the two ac systems, provision of independent reactive power control at the point of common couplings (PCCs) and frequency regulation at the sending-end side. The paper investigate the utilization of VSC–HVDC system to provide frequency regulation to an ac network; this is useful for networks with high penetration of renewables (e.g. wind), and nuclear generation. The proposed control strategies for the VSCs are presented in detail, investigating further the tuning method for the proper operation of the inner controllers. The robustness of the control system is tested under large disturbances. The study is conducted in Matlab/Simulink and results that substantiate the dynamic performance of the VSC–HVDC with the proposed control are thoroughly discussed.

Derivation of a Four-Quadrant Control System for MLCR-HVDC Conversion

Although the multilevel current reinjection concept has been presented as a possible self-commutating alternative to line-commutated conversion for large power HVDC transmission, in its present form, the lack of independent reactive power control at the two converter terminals constitutes a severe limitation to its eventual acceptability. For very large power ratings, the use of double-group converter terminals has been shown theoretically to overcome the reactive power interdependence; however, the high nonlinearities involved make it difficult to design a practical control system, which is the main purpose of this paper. Comprehensive PSCAD/EMTDC simulation is used to verify that the dynamic and steady-state response of the proposed control system design are perfectly satisfactory.

Flexible Reactive Power Control in Multigroup Current-Sourced HVDC Interconnections

Self-commutating multilevel current reinjection is a potential alternative to conventional HVDC thyristor technology. An important drawback of the multilevel configurations is the interdependence of the reactive power injections at both ends of the link. This paper describes a new concept applicable to large power converters consisting of two series-connected twelve-pulse groups. It is based on the use of a controllable shift between the firings of the two twelve-pulse groups in opposite directions, a new concept that provides independent reactive power control at the sending and receiving ends. The theory is verified by EMTDC simulation.

Multimodular multilevel rectifier/inverter link with independent reactive power control

The feasibility of a DC link made up of multimodular, diode-clamped multilevel power converters to form the rectifier and the inverter has been studied in this paper. Equalization of the DC capacitor voltages is accomplished by auxiliary DC choppers sized at 10% of the current ratings. Real power control makes use of voltage angles as the control levers. Independent reactive power control on both sides makes use of voltage magnitude control. Digital simulations demonstrate the success of local controls. As the rectifier/inverter link plays a pivotal role in the unified power flow controller (UPFC) and the asynchronous DC link, the study has shown that multimodular multilevel versions of these FACTS controllers are feasible.

Mid-point siting of FACTS devices in transmission lines

Many controllers of flexible AC transmission systems (FACTS), such as the STATCOM, the unified power flow controller (UPFC), the PWM asynchronous DC link, the thyristor-controlled series capacitor (TCSC) and the PWM series static VAr compensator have stabilized AC voltage support. Thus, they can be sited at the mid-point of the transmission line, which has been proven by the late E.W. Kimbark, as the optimum location for shunt capacitor compensation. This paper points out that the ability to double the power transfer of the uncompensated line applies also to the aforementioned FACTS devices. The mid-point siting also facilitates the independent control of reactive power at both ends of the transmission line.