Cooperative Control And Advanced Management Of Distributed Generators In A Smart Grid

Smart grid is more than just the smart meters. The future smart grids are expected to include a high penetration of distributed generations (DGs), most of which will consist of renewable energy sources, such as solar or wind energy. It is believed that the high penetration of DGs will result in the reduction of power losses, voltage profile improvement, meeting future load demand, and optimizing the use of non-conventional energy sources. However, more serious problems will arise if a decent control mechanism is not exploited. An improperly managed high PV penetration may cause voltage profile disturbance, conflict with conventional network protection devices, interfere with transformer tap changers, and as a result, cause network instability. Indeed, it is feasible to organize DGs in a microgrid structure which will be connected to the main grid through a point of common coupling (PCC). Microgrids are natural innovation zones for the smart grid because of their scalability and flexibility. A proper organization and control of the interaction between the microgrid and the smartgrid is a challenge. Cooperative control makes it possible to organize different agents in a networked system to act as a group and realize the designated objectives. Cooperative control has been already applied to the autonomous vehicles and this work investigates its application in controlling the DGs in a micro grid. The microgrid power objectives are set by a higher level control and the application of the cooperative control makes it possible for the DGs to utilize a low bandwidth communication network and realize the objectives. Initially, the basics of the application of the DGs cooperative control are formulated. This includes organizing all the DGs of a microgrid to satisfy an active and a reactive power objective. Then, the cooperative control is further developed by the introduction of clustering DGs into several groups to satisfy multiple power objectives. Then, the cooperative distribution optimization is introduced iii to optimally dispatch the reactive power of the DGs to realize a unified microgrid voltage profile and minimize the losses. This distributed optimization is a gradient based technique and it is shown that when the communication is down, it reduces to a form of droop. However, this gradient based droop exhibits a superior performance in the transient response, by eliminating the overshoots caused by the conventional droop. Meanwhile, the interaction between each microgrid and the main grid can be formulated as a Stackelberg game. The main grid as the leader, by offering proper energy price to the micro grid, minimizes its cost and secures the power. This not only optimizes the economical interests of both sides, the microgrids and the main grid, but also yields an improved power flow and shaves the peak power. As such, a smartgrid may treat microgrids as individually dispatchable loads or generators

Realizing Unified Microgrid Voltage Profile And Loss Minimization: A Cooperative Distributed Optimization And Control Approach

Cooperative distributed optimization is proposed in this paper to optimally dispatch the reactive power of the distributed generators (DGs). The overall objective is to minimize the cost function that is the sum of all quadratic voltage errors of the DG nodes and other critical nodes in the system. It is assumed that each DG is only aware of its own cost function defined as the quadratic voltage error of its respective node. In the proposed method, every DG performs optimization with respect to its own objective function while considering the information received locally from the neighboring nodes in the microgrid, and the critical nodes without DG also contribute to optimization. The proposed distributed optimization and control scheme enables the microgrid to have a unified voltage profile, and incorporating the subgradient method facilitates its application even when the microgrid information is unknown. Microgrid active power loss is also investigated, and it is shown that the unified voltage profile naturally leads to the overall active power loss minimization as well. Stability analysis and criteria are provided. Simulation results of a typical microgrid illustrate superior performance of the proposed technique. © 2014 IEEE

Optimum design and analysis of the cooperative control, applied to the distributed generators control in smart grids

Recently cooperative control has been proposed as a dynamic and self organizing control mechanism for distributed generators (DGs) control in the smart grids. Cooperative control has the advantage that it can properly manage and coordinate a high penetration of DGs to satisfy multiple power objectives. In a smart grid, the communication topology is restricted by the geographical distribution of the system and the range of the communication devices. This paper provides the process to optimally design the cooperative control, utilizing an available communication network. The effect of the communication frequency and topology on the convergence rate and the dynamic performance of the system is also presented. Finally, the simulation results for a case of study are provided. © 2013 IEEE

Optimum Design And Analysis Of The Cooperative Control, Applied To The Distributed Generators Control In Smart Grids

Recently cooperative control has been proposed as a dynamic and self organizing control mechanism for distributed generators (DGs) control in the smart grids. Cooperative control has the advantage that it can properly manage and coordinate a high penetration of DGs to satisfy multiple power objectives. In a smart grid, the communication topology is restricted by the geographical distribution of the system and the range of the communication devices. This paper provides the process to optimally design the cooperative control, utilizing an available communication network. The effect of the communication frequency and topology on the convergence rate and the dynamic performance of the system is also presented. Finally, the simulation results for a case of study are provided. © 2013 IEEE

Single Phase And Three Phase P+Resonant Based Grid Connected Inverters With Reactive Power And Harmonic Compensation Capabilities

Designing optimized and more efficient controllers for grid connected inverters is a challenge. Conventionally such controllers were established in dq or rotational frame; however, recently stationary or alpha-beta frame has found special interest due to some unique features that it can offer for grid connected inverters. On dq frame variables turn into constants after passing through transform matrixes, so PI controllers that have infinite gain on DC quantities are widely used. But PI controllers are unable to achieve zero steady state error in stationary frame and P+Resonant controllers which have infinite gain on their resonant frequency have been implemented instead. This paper will explain step by step P+Resonant based inverter controllers design for grid connected single and three phase inverters with reactive power compensation and then a novel approach for grid harmonics compensation will be implemented. © 2009 IEEE

Clustering and cooperative control of distributed generators for maintaining microgrid unified voltage profile and complex power control

To meet several power objectives, the idea of organizing DGs into several clusters in a microgrid is proposed in this paper. Power objectives include maintaining active power flow to the main grid at a predetermined level, minimizing the reactive power flow to the main grid and maintaining a unified voltage profile across the microgrid. DGs are organized differently for active and reactive power control. All DGs realize active power objective in one group. As reactive power is used to maintain the unified voltage, DGs are grouped in several clusters to regulate multiple critical point voltages. The closest cluster to the point of common coupling, minimizes the reactive power flow and others manage their reactive power to regulate their critical points. Each cluster has a virtual leader which other DGs follow, utilizing the cooperative control. The cooperative law is also derived, based on the dynamics of the inverters. © 2012 IEEE

A Self-Organizing Strategy For Power Flow Control Of Photovoltaic Generators In A Distribution Network

The focus of this paper is to develop a distributed control algorithm that will regulate the power output of multiple photovoltaic generators (PVs) in a distribution network. To this end, the cooperative control methodology from network control theory is used to make a group of PV generators converge and operate at certain (or the same) ratio of available power, which is determined by the status of the distribution network and the PV generators. The proposed control only requires asynchronous information intermittently from neighboring PV generators, making a communication network among the PV units both simple and necessary. The minimum requirement on communication topologies is also prescribed for the proposed control. It is shown that the proposed analysis and design methodology has the advantages that the corresponding communication networks are local, their topology can be time varying, and their bandwidth may be limited. These features enable PV generators to have both self-organizing and adaptive coordination properties even under adverse conditions. The proposed method is simulated using the IEEE standard 34-bus distribution network. © 2011 IEEE

Optimal, Nonlinear, And Distributed Designs Of Droop Controls For Dc Microgrids

In this paper, the problem of optimal voltage and power regulation is formulated for distributed generators (DGs) in DC microgrids. It is shown that the resulting control is optimal but would require the full information of the microgrid. Relaxation of information requirement reduces the optimal control into several controls including the conventional droop control. The general setting of a DC microgrid equipped with local sensing/communication network calls for the design and implementation of a cooperative droop control that uses the available local information and coordinates voltage control in a distributed manner. The proposed cooperative droop control is shown to include other controls as special cases, its performance is superior to the conventional droop control, and it is robust with respect to uncertain changes in both distribution network and sensing/communication network. These features make the proposed control an effective scheme for operating a DC microgrid with intermittent and distributed generation

Single phase and three phase P+Resonant based grid connected inverters with reactive power and harmonic compensation capabilities

Designing optimized and more efficient controllers for grid connected inverters is a challenge. Conventionally such controllers were established in dq or rotational frame; however, recently stationary or alpha-beta frame has found special interest due to some unique features that it can offer for grid connected inverters. On dq frame variables turn into constants after passing through transform matrixes, so PI controllers that have infinite gain on DC quantities are widely used. But PI controllers are unable to achieve zero steady state error in stationary frame and P+Resonant controllers which have infinite gain on their resonant frequency have been implemented instead. This paper will explain step by step P+Resonant based inverter controllers design for grid connected single and three phase inverters with reactive power compensation and then a novel approach for grid harmonics compensation will be implemented. © 2009 IEEE

Clustering And Cooperative Control Of Distributed Generators For Maintaining Microgrid Unified Voltage Profile And Complex Power Control

To meet several power objectives, the idea of organizing DGs into several clusters in a microgrid is proposed in this paper. Power objectives include maintaining active power flow to the main grid at a predetermined level, minimizing the reactive power flow to the main grid and maintaining a unified voltage profile across the microgrid. DGs are organized differently for active and reactive power control. All DGs realize active power objective in one group. As reactive power is used to maintain the unified voltage, DGs are grouped in several clusters to regulate multiple critical point voltages. The closest cluster to the point of common coupling, minimizes the reactive power flow and others manage their reactive power to regulate their critical points. Each cluster has a virtual leader which other DGs follow, utilizing the cooperative control. The cooperative law is also derived, based on the dynamics of the inverters. © 2012 IEEE