Reactive Power Coordination Research Articles

Study on the reactive power coordinated control in hybrid parallel HVDC system

Hybrid parallel HVDC system adopts line commutated converter high voltage direct current(LCC-HVDC) and voltage source converter high voltage direct current(MMC-HVDC) parallel structure, which combines the advantages of LCC-HVDC and MMC-HVDC. Based on the existing reactive power control of HVDC system, the reactive power coordination control strategy of hybrid parallel HVDC system is innovatively proposed in this paper. Firstly, the reactive power control of LCC-HVDC and MMC-HVDC are studied respectively. And then the voltage stability of LCC-HVDC fed weak AC system is analyzed. Furthermore, a reactive power coordination control strategy between reactive power compensation device of the converter station and MMC-HVDC is proposed. Finally, based on PSCAD/EMTDC simulation platform, a hybrid parallel HVDC simulation system is built. The reactive power coordination control strategy under steady and transient conditions is simulated and analyzed respectively. The analysis results show that the reactive power coordinated control strategy can suppress the voltage fluctuation of converter bus in steady state. At the same time, the reactive power coordinated control strategy can restrain the commutation failure of LCC-HVDC in the fault of receiving power grid and improve its fault recovery ability.

Leader-Following Diffusion-Based Reactive Power Coordination and Voltage Control of Offshore Wind Farm

This paper proposed a distributed reactive power coordination and voltage control of offshore wind farm based on the leader-following diffusion algorithm. Designating several wind turbine generators (WTGs) as the leaders to receive the information of voltage at point of common coupling (PCC), the reactive power generations required to minimize the voltage deviation could be computed by these leaders. The required reactive power generations are diffused throughout all WTGs by the diffusion algorithm, resulting in the coordinated operation of WTGs to regulate the PCC voltage. The proposed offshore wind farm controller is based on the hierarchical control strategy, which consists of primary and secondary layers. The primary layer is responsible for the inner current, voltage or power regulations whereas the secondary layer is based on the proposed diffusion algorithm to achieve the coordinated operation among WTGs. The proposed strategy could maintain accurate reactive power sharing among WTGs and regulate the PCC voltage. A comparison study with the conventional consensus-based control is presented to show the effectiveness of the proposed diffusion controller. The comparison results show the better performance of the proposed method in terms of dynamic responses of PCC voltage and reactive power coordination. Simulation scenarios of constant wind speed, variable wind speed, and voltage sag in the utility grid are carried out to evaluate the performance of proposed method. The proposed diffusion control is tested either in a small or large offshore wind farm systems. Effect of communication delay on the performance of proposed diffusion control is also described. An experiment of the small-scale wind farm system is conducted to show the feasibility of proposed diffusion strategy.

Dynamic Reactive Power Coordination Control Method for UHVDC Converter Station

In recent years, UHVDC transmission has developed rapidly. However, large-capacity DC converters generally use semi-controlled devices. The receiving converter station consumes a large amount of reactive power, which is easy to change when the AC bus voltage drops. The commutation failure happened, and more reactive power is absorbed from the AC system, which threatens the stability of the bus voltage. In order to study the dynamic reactive power coordination control strategy of UHVDC converter station, this paper compares the commonly used reactive power compensation equipment, and points out that synchronous condenser (SC) has significant advantages in reactive power regulation. This paper proposes a DC control system and SC coordination control scheme, and simulates the strategy through the electromagnetic transient simulation software PSCAD. The simulation shows that the synchronous condenser can provide continuously adjustable dynamic reactive power support during the change of the system switching filter, avoiding the risk of grid voltage drop exceeding the limit and improving the stability of the AC bus voltage.

PSO Based Reactive Power Coordination of Multiple Dispatchable Distributed Generations & Voltage Controlled Devices

The presence of multiple distributed generations on radial distribution system increases switching operations of voltage controlled devices (VCDs). Reduction of switching operations (SOs) of VCDs in the presence of multiple dispatchable distributed generations (MDDGs) is a demanding research area now a days. This paper proposes a novel method for the reduction of SOs of VCDs together with system power loss, in which we estimated the load one day in advance which makes MDDGs to dispatch the reactive power cooperatively with VCDs and particle swarm optimization (PSO) method used for solving multiple objective function. Multiple objective function (MOF) is formulated with cost of power loss and cost of SOs. The proposed method is tested on 16 nodes practical system under different operating output patterns and locations considering under load tap changers (ULTCs) and shunt capacitors (SCs) as VCDs. Simulation results clearly depicts that this method is effectively achieved the goals compared with existing conventional optimization techniques..

Reactive power dynamic multi-objective optimization for multi-terminal AC/DC interconnected power systems under wind power fluctuation

In view of the reactive power coordination difficulties caused by reactive power strong coupling, the provincial power grids in the interconnected system are formed by the multi-AC/DC transmission. Wind power channels are under the conditions of large-scale long-distance transmission of wind power and other forms of renewable power generation. The AC-DC hybrid power flow equation of the interconnected system, including the AC-DC tie lines, is presented in this paper, along with the robust dynamic evolutionary optimization of the reactive power system in interconnected systems under fluctuating and uncertain wind power conditions. Therefore, the rapid collaborative optimization of reactive power flow and the exchange of reactive power between tie lines between provincial power grids are realized. The analysis was made by taking four interconnected large-scale provincial power grids of Eastern Mongolia, Jilin, Liaoning and Shandong as an example. The simulation results demonstrate the effectiveness and superiority of the proposed reactive power dynamic multi-objective optimization method for interconnected power grids.

Multi-objective Optimization of Distribution Network Based on Model Predictive Control

With the increasing penetration of distributed generation(DG) in distribution network and the rising demand of electricity users, the uncertainty of distributed generation output and randomness of load will lead to over-voltage and power backward in distribution network. This paper proposes a multiobjective active and reactive power coordination optimal control strategy, which based on multi-time scale model predictive control (MPC). The objectives of proposed strategy consists of increasing distributed energy consumption, decreasing grid voltage deviation and decreasing system network loss, which are implemented in long time scale. And in short time scale, the energy storage active power is adjusted according to the prediction errors of load and new energy power generation. The effectiveness of the proposed optimization scheme is verified in simulation analysis.

Active and reactive power coordination control strategy of overvoltage for distributed PV integrated grid

Aiming at the voltage rise due to the photovoltaic generation system (PVGS) at the point of common coupling (PCC), the cause is analysed with power transmission theory. Here, the principle and strategies of voltage regulation based on active and reactive power in PVGS are proposed. In this control strategy, the voltage of PCC is tracked by PV system in real time. When the voltage of PCC is normal, inverter will output in the way of maximum power point tracking (MPPT).When the voltage of PCC exceeds the upper limit, the inverter will regulate the voltage using the remaining capacity preferentially. If the remaining capacity is insufficient, the inverter will adjust active output and dynamically calculate the active and reactive best out values. In this way, the voltage of PCC is adjusted in an appropriate range to achieve the active output minimisation and reactive output optimisation of inverter. The experimental results validate the effectiveness of the proposed control scheme for voltage regulation.

Reactive Power Compensation Game Under Prospect-Theoretic Framing Effects

Reactive power compensation is an important challenge in current and future smart power systems. However, in the context of reactive power compensation, most existing studies assume that customers can assess their compensation value, i.e., Var unit, objectively. In this paper, customers are assumed to make decisions that pertain to reactive power coordination. In consequence, the way in which those customers evaluate the compensation value resulting from their individual decisions will impact the overall grid performance. In particular, a behavioral framework, based on the framing effect of prospect theory (PT), is developed to study the effect of both objective value and subjective evaluation in a reactive power compensation game. For example, such effect allows customers to optimize a subjective value of their utility which essentially frames the objective utility with respect to a reference point. This game enables customers to coordinate the use of their electrical devices to compensate reactive power. For the proposed game, both the objective case using expected utility theory (EUT) and the PT consideration are solved via a learning algorithm that converges to a mixed-strategy Nash equilibrium. In addition, several key properties of this game are derived analytically. Simulation results show that, under PT, customers are likely to make decisions that differ from those predicted by classical models. For instance, using an illustrative two-customer case, we show that a PT customer will increase the conservative strategy (achieving a high power factor) by 29% compared to a conventional customer. Similar insights are also observed for a case with three customers.

GWO Based Optimal Reactive Power Coordination of DFIG, ULTC and Capacitors

<p>Wind is available with free of cost anywhere in the world, this wind can be used for power generation due to many advantages. This attracts the researchers to work on wind power plants. The presence of wind power plants on distribution system causes major influence on voltage controlled devices (VCDs) in terms of life of the devices. Therefore, this paper proposes grey wolf optimization method (GWO) together with forecasted load one day in advance. VCDs are on load tap changer (ULTC) and capacitors (CS), there are two main objectives first one is curtail of distribution network (DN) loss and second one is curtailing of ULTC and CS switching’s. Objectives are achieved by controlling the reactive power of DFIG in coordination with VCDs. The proposed method is planned and applied in Matlab/Simulink on 10KV practical system with DFIG located at different locations. To validate the efficacy of GWO, results are compared with conventional and dynamic programming methods without profane grid circumstances.</p>

Multi-time scale optimal dispatch in ADN based on MILP

With the development of active distribution network (ADN) and the increase of penetration rate of new energy such as wind power and photovoltaic, the optimal operation problem of ADN is facing challenges. So, this paper proposes a multi-time scale optimal dispatch method based on mixed-integer linear programming to improve the calculation speed of the traditional dispatching model. First, the linear branch power flow of distribution network is introduced, and the main elements in ADN are modeled, meanwhile, the linearization method is used to simplify the non-linear components. Then, the day-ahead dispatch model is established by considering the active and reactive power coordination. In addition, in order to reduce the influence of the stochastic power from DG and FL on dispatch results, taking the results of day-ahead dispatch as reference, an auxiliary short-term dispatch model is also constructed to maximize the consumption of wind and photovoltaic (PV) power. Finally, the validity and reliability of the proposed method are verified by a modified IEEE 33-node distribution system.

Multi-Objective Coordinated Control of Reactive Compensation Devices Among Multiple Substations

The multi-objective reactive power coordination control model was presented in this paper to overcome the drawback that reactive power compensation devices lack in coordination and have high active power loss. In this model, the minimum bus voltage deviation and total power loss of reactive power compensation devices are taken as objective functions, by bringing the lower voltage reactors and capacitors into the static var compensator control system and considering the reactive power compensation devices interaction between different transformer substations. Due to the different sensitivity of control variables in control model and lack of the local search ability, control variables are divided into sensitive variables and non-sensitive variables. Then, the improved non-dominated sorting genetic algorithm II (NSGA-II) with secondary search ability is used to search the Pareto optimal solution set. Two substations in large power grid with strong voltage coupling are coordinated in different load level. The results obtained by proposed NSGA-II algorithm can provide a variety of optimal control strategies. Compared to the conventional NSGA-II algorithm and normal boundary intersection method, the improved NSGA-II algorithm has better convergence curve and distribution of the Pareto solution sets.

Reactive Power Management in Renewable Rich Power Grids: A Review of Grid-Codes, Renewable Generators, Support Devices, Control Strategies and Optimization Algorithms

Power electronic converter (PEC)-interfaced renewable energy generators (REGs) are increasingly being integrated to the power grid. With the high renewable power penetration levels, one of the key power system parameters, namely reactive power, is affected, provoking steady-state voltage and dynamic/transient stability issues. Therefore, it is imperative to maintain and manage adequate reactive power reserve to ensure a stable and reliable power grid. This paper presents a comprehensive literature review on the reactive power management in renewable rich power grids. Reactive power requirements stipulated in different grid codes for REGs are summarized to assess their adequacy for future network requirements. The PEC-interfaced REGs are discussed with a special emphasis on their reactive power compensation capability and control schemes. Along with REGs, conventional reactive power support devices (e.g., capacitor banks) and PEC-interfaced reactive power support devices (e.g., static synchronous compensators) play an indispensable role in the reactive power management of renewable rich power grids, and thus their reactive power control capabilities and limitations are thoroughly reviewed in this paper. Then, various reactive power control strategies are reviewed with a special emphasis on their advantages/disadvantages. Reactive power coordination between support devices and their optimal capacity are vital for an efficient and stable management of the power grid. Accordingly, the prominent reactive power coordination and optimization algorithms are critically examined and discussed in this paper. Finally, the key issues pertinent to the reactive power management in renewable rich power grids are enlisted with some important technical recommendations for the power industry, policymakers, and academic researchers.

Business case in support for reactive power services from distributed energy storage

The integration of energy storage (ES) in future low-carbon networks can offer significant opportunities to distribution network operators and other players in the electricity industry. The potential of ES to support distribution network by reducing peak demand, provide security of supply and resilience, manage voltage levels and ultimately defer (and avoid) investment in network reinforcements has been widely reported in the literature. This paper, however, sets out to investigate not only the value of coordinating ES active and reactive power outputs to support network operator activities but also to other stakeholders in future low-carbon networks. The proposed model coordinates active and reactive power outputs from an ES plant at the distribution level. Fundamentally, ES plant operation is optimised to deliver maximum benefits by considering its capability to provide active and reactive power in a coordinated fashion. It is demonstrated that the proposed methodology to determine ES power outputs is fundamental to ensure effective (and robust) delivery of network services at critical ES energy levels. The results have also shown that in a multiple service business model, the coordination of active and reactive power may increase total revenue by ca. 2400 £/month, when compared to an active power only operation mode.

Fuzzy logic approach for reactive power coordination in grid connected wind farms to improve steady state voltage stability

This study presents a fuzzy logic approach for reactive power coordination in grid connected wind farms with different types of wind generator units to improve steady state voltage stability of power systems. The load bus voltage deviation is minimised by changing the reactive power controllers according to their sensitivity using fuzzy set theory. The proposed approach uses only few controllers of high sensitivity to achieve the desired objectives. The 297-bus and 417-bus equivalent grid connected wind systems are considered to present the simulation results. To prove the effectiveness of the proposed approach, a comparative analysis is carried out with the conventional linear programming based reactive power optimisation technique. Results demonstrated that the proposed approach is more effective in improving the system performance as compared with the conventional existing technique.

Research on technical requirements of line‐commutated converter‐based high‐voltage direct current participating in receiving end AC system's black start

This study discusses the technical requirements of line-commutated converter-based high-voltage direct current (LCC-HVDC) power transmission participating in a receiving end AC system's black start. The control and start-up modes of LCC-HVDC suitable for black start are discussed. Through short-circuit capacity analysis and frequency estimation, the appropriate strength of the receiving end AC system to start the LCC-HVDC is studied. A reactive power coordination strategy is proposed to reduce overvoltage caused by the HVDC filter. An innovative additional frequency control at the inverter side is proposed to suppress the frequency oscillation in the black-start procedure. This control is realised through the constant voltage at rectifier and constant current at inverter control mode. Compared with the conventional rectifier-side additional frequency control method, the inverter-side additional frequency control method requires no remote communication and is thus more practical and effective when the receiving end is in a blackout. On the basis of the analysis, the conventional LCC-HVDC is started successfully under the proposed requirements of black start and the overvoltage and frequency oscillation are also reduced effectively by the proposed control strategies, both of which are validated through electromagnetic transient simulation based on PSCAD/EMTDC software.

MODELING AND CONTROL OF FACTS DEVICES FOR REAL & REACTIVE POWER ENHANCEMENT

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). The reactive power transfer is occurring at reactive power coordination of IPFC The basic control for the IPFC is such that the series converter of the IPFC controls the transmission line real/reactive power flow and the shunt converter of the IPFC controls the IPFC bus voltage/shunt reactive power and the DC link capacitor voltage. In steady state, the shunt converter of the IPFC supplies the real power demand of the series converter. The interline power flow controller (IPFC) is one of the latest generation flexible AC transmission systems (FACTS) controller used to control power flows of multiple transmission lines To avoid instability/loss of DC link capacitor voltage during transient conditions, a new real power coordination controller has been designed.

Coordination of Reactive Power in Grid-Connected Wind Farms for Voltage Stability Enhancement

This paper studies the feasibility of utilizing the reactive power of grid-connected variable-speed wind generators to enhance the steady-state voltage stability margin of the system. Allowing wind generators to work at maximum reactive power limit may cause the system to operate near the steady-state stability limit, which is undesirable. This necessitates proper coordination of reactive power output of wind generators with other reactive power controllers in the grid. This paper presents a trust region framework for coordinating reactive output of wind generators with other reactive sources for voltage stability enhancement. Case studies on 418-bus equivalent system of Indian southern grid indicates the effectiveness of proposed methodology in enhancing the steady-state voltage stability margin.

Distribution Voltage Control Considering the Impact of PV Generation on Tap Changers and Autonomous Regulators

The uptake of variable megawatts from photovoltaics (PV) challenges distribution system operation. The primary problem is significant voltage rise in the feeder that forces existing voltage control devices such as on-load tap-changers and line voltage regulators to operate continuously. The consequence is the deterioration of the operating life of the voltage control mechanism. Also, conventional non-coordinated reactive power control can result in the operation of the line regulator at its control limit (runaway condition). This paper proposes an optimal reactive power coordination strategy based on the load and irradiance forecast. The objective is to minimize the number of tap operations so as not to reduce the operating life of the tap control mechanism and avoid runaway. The proposed objective is achieved by coordinating various reactive power control options in the distribution network while satisfying constraints such as maximum power point tracking of PV and voltage limits of the feeder. The option of voltage support from PV plant is also considered. The problem is formulated as constrained optimization and solved through the interior point technique. The effectiveness of the approach is demonstrated in a realistic distribution network model.

Reactive Power Coordination of Shipboard Power Systems in Presence of Pulsed Loads

Voltage and reactive power control is a fundamental issue in all-electric shipboard power systems (SPS). However, coordination between generation and propulsion management to match reactive power is poor in current SPS designs. This paper presents a new model predictive control based dynamic Volt/Var control scheme to control the voltage in the system. This method uses a dynamic model of the sources and loads and finds the optimal reactive control inputs to the system to minimize the voltage deviations in the future. Since this method uses prediction of the reactive demand of pulsed loads, it is able to achieve a smooth voltage profile in the SPS in presence of pulsed power loads. This method is also able to control voltage of the system during propulsion motor startup. The controller is tested in presence of high power pulsed loads in the system. The results demonstrate that the dynamic reactive controller is able to keep the voltage profile of the system smooth and within system limits.

On the inter-area optimal voltage and reactive power control

Scheduling voltage and reactive power is one of the major problems and concerns of the Transmission System Operators (TSOs) especially after deregulation of power market. Due to locally provision of the reactive power resources, each TSO has developed its own specific method. Hence, the voltage and reactive power coordination in the interconnected system has got less attention. In this respect, current practices of different TSOs in Europe and North America, as examples of interconnected power systems, are investigated in this paper. Afterwards, it focuses on the inter-area optimization of the voltage and reactive power. Instead of performing the studies around one particular optimization, different aspects of the mathematical formulation of the optimization problem in the interconnected power system, including objective function, constraints and appropriate modeling of neighboring areas, are revisited more in depth. Various possible implementations of coordinated approaches, including centralized and decentralized structures, as well as non-coordinated approach in collaborative and non-collaborative environments are studied. In this respect, new contributions are proposed in this paper by using the distributed slack bus model and the limitation of the voltage and reactive power in the interconnections links. The comparative analysis between the available and proposed methods are discussed in terms of sub-optimality and time to convergence. The discussions are based on New England 39 bus system and the presented results in the literatures.