ADMM-based Distributed Active and Reactive Power Control for Regional AC Power Grid with Wind Farms

A distributed active and reactive power control(DARPC)strategy based on the alternating direction method of multipliers(ADMM)is proposed for regional AC transmission system(TS)with wind farms(WFs).The proposed DARPC strategy optimizes the power distribution among the WFs to minimize the power losses of the AC TS while tracking the active power reference from the transmission system operator(TSO),and minimizes the voltage deviation of the buses inside the WF from the rated voltage as well as the power losses of the WF collection system.The optimal power flow(OPF)of the TS is relaxed by using the semidefinite programming(SDP)relaxation while the branch flow model is used to model the WF collection system.In the DARPC strategy,the large-scale strongly-coupled optimization problem is decomposed by using the ADMM,which is solved in the regional TS controller and WF controllers in parallel without loss of the global optimality.The boundary information is exchanged between the regional TS controller and WF controllers.Compared with the conventional OPF method of the TS with WFs,the optimality and accuracy of the system operation can be improved.Moreover,the proposed strategy efficiently reduces the computation burden of the TS controller and eliminates the need of a central controller.The protection of the information privacy can be enhanced.A modified IEEE 9-bus system with two WFs consisting of 64 wind turbines(WTs)is used to validate the proposed DARPC strategy.

Coupling Characteristics of DFIG-based WT Considering Reactive Power Control and Its Impact on Phase/Amplitude Transient Stability in a Rotor Speed Control Timescale

The transient stability issues caused by doubly fed induction generator(DFIG)-based wind turbines(WTs)are receiving increasing attention.The q-axis reactive power control(QCtrl),as an essential part of DFIG-based WTs,has a significant impact on its transient response.In this paper,the impact of QCtrl on the phase/amplitude transient stability of a DFIGbased WT-dominated system is analyzed from the perspective of internal voltage amplitude-phase coupling characteristics.First,an amplitude/phase dynamic model of a DFIG-based WT in rotor speed control timescale(in seconds,corresponding to traditional electromechanical timescale)is developed.Then,in comparison with familiar synchronous generators(SGs),an inherently amplitude-phase characteristic of internal voltage for a DFIG-based WT is identified.Next,taking the DFIG-based WTdominated system as an example,the impact of QCtrl on system transient stability via the internal coupling paths is analyzed.A novel phase-amplitude coupling instability mechanism is found,which is different from that in a traditional SG-dominated system.Finally,the effects of different QCtrl strategies on transient stability are discussed.

Complete active-reactive power resource scheduling of smart distribution system with high penetration of distributed energy resources

In traditional power systems,besides the conventional power plants that provide the necessary reactive power in transmission system,the shunt capacitors along with the tap changers of transformers are also employed in distribution networks.In future years,because of the high number of distributed resources integrated into the distribution networks,it will be essential to schedule complete active-reactive power at distribution level.In this research work,an economic framework based on the active-reactive power bids has been developed for complete active-reactive power dispatch scheduling of smart distribution networks.The economical complete active-reactive power scheduling approach suggested in this study motivates distributed energy resources(DERs)to cooperate in both active power markets and the Volt/Var control scheme.To this end,using DER’s reactive power capability,a generic framework of reactive power offers for DERs is extracted.A 22-bus distribution test system is implemented to verify the impressiveness of the suggested active-reactive power scheduling approach.

Fixed-time Distributed Voltage and Reactive Power Compensation of Islanded Microgrids Using Sliding-mode and Multi-agent Consensus Design

This paper investigates a fixed-time distributed voltage and reactive power compensation of islanded microgrids using sliding-mode and multi-agent consensus design.A distributed sliding-mode control protocol is proposed to ensure voltage regulation and reference tracking before the desired preset fixed-time despite the unknown disturbances.Accurate reactive power sharings among distributed generators are maintained.The secondary controller is synthesized without the knowledge of any parameter of the microgrid.It is implemented using a sparse one-way communication network modeled as a directed graph.A comparative simulation study is conducted to highlight the performance of the proposed control strategy in comparison with finite-time and asymptotic control systems with load power variations.

Real-Time Operation of Microgrids

Microgrid (MG) systems effectively integrate a generation mix of solar, wind, and other renewable energy resources. The intermittent nature of renewable resources and the unpredictable weather conditions contribute largely to the unreliability of microgrid real-time operation. This paper investigates the behavior of microgrid for different intermittent scenarios of photovoltaic generation in real-time. Reactive power coordination control and load shedding mechanisms are used for reliable operation and are implemented using OPAL-RT simulator integrated with Matlab. In an islanded MG, load shedding can be an effective mechanism to maintain generation-load balance. The microgrid of the German Jordanian University (GJU) is used for illustration. The results show that reactive power coordination control not only stabilizes the MG operation in real-time but also reduces power losses on transmission lines. The results also show that the power losses at some substations are reduced by a range of 6% - 9.8%.

Power Flow Based Volt/var Optimization Under Uncertainty

Volt/var optimization(VVO)is a control function that is employed in distribution systems to keep the load voltages within the standard limits,and it includes secondary objectives such as loss minimization.The power flow based VVO is the way of choice in practical applications because it can handle a variety of objective functions and provides a solution even for large-scale network instances.This paper extends the power flow based VVO to account for uncertainty in both the load values and the power generation from photovoltaic sources.The proposed method employs circular arithmetic in complex variables to compute VVO settings that guard against load uncertainty and an optimized linear decision rule that modulates the reactive power of photovoltaic inverter in function of its active power.Finally,the proposed method is tested on distribution networks with up to 3146 nodes and is shown to produce optimal solutions that are robust against power variations.