Voltage Control Of Microgrids Research Articles

Frequency and voltage control of microgrid with high WECS penetration during wind gusts using superconducting magnetic energy storage

The intermittent behavior of wind power generation results in a fast variation of both frequency and voltage magnitudes of isolated microgrids with high wind power penetration. In this paper, a hybrid energy microgrid with wind energy conversion system (WECS) and diesel synchronous generators are analyzed during wind gust conditions. Superconducting magnetic energy storage (SMES) is connected at the same node of the WECS to mitigate the intermittent wind power generation. A developed fuzzy logic controller has been applied to achieve active power sharing. The damping of voltage fluctuation depends on SMES reactive power, which is controlled by a voltage source converter. The studied microgrid comprises 33 nodes, two diesel SGs, and two WECSs of squirrel cage induction generator type at 30% penetration level. The results demonstrate the effectiveness of the proposed control strategy to mitigate the frequency fluctuations during the wind speed gusts by smoothing power output from WECSs/SMES system. Moreover, voltage control is achieved by injecting reactive power from the SMES system. All simulations are performed by MATLAB/Simulink package.

Distributed Event-Triggered Secondary Voltage Control for Microgrids With Time Delay

We consider the distributed secondary voltage control problem for microgrids subject to delays in a connected communication topology. For each distributed generator (DG), a distributed event-triggered control law, which uses its own voltage and those of its neighbors, along with a strategy for its triggering, are designed. Under these distributed event-triggered control laws, the magnitudes of the output voltages of all DGs can be synchronized to their reference value subject to a bounded time-varying delay that can be arbitrarily large, and no Zeno behavior will occur. The simulation results illustrate the theoretical conclusions.

Micro-grid voltage control strategies considering uncertain PV generation with analysis method

PV is one of intermittent renewable sources, which are complicated to forecast its influence on the voltage of micro-grid system. The strategies of maintaining voltage stability of micro-grid with uncertain PV are studied in this paper. Randomize values based on real PV output and loads are used. The effects of both quantity and content of traditional or new micro-grid device on voltage stability are analysed. Other factors which can improve the performance like various algorithms and parameters are discussed in this paper. Energy saving issue is also included in the paper.

Stability Robustness for Secondary Voltage Control in Autonomous Microgrids With Consideration of Communication Delays

The future extensive usage of open communication networks for secondary voltage control in autonomous microgrids (MGs) inherently introduce time delays, which would degrade the system performance or even cause instability in the worst case. However, existing literatures have largely ignored these communication delays between the microgrid central controller and primary local controllers. To fill the knowledge gap, this paper proposes an analytical method to determine the stability robustness of secondary voltage control in MGs by taking into account the communication latency effect. Based on static output feedback, a closed loop small-signal model of an MG installed with proportional-integral secondary voltage controllers is first derived. Delay-dependent criteria are then formulated to detect the stability posture of MG system by tracing critical eigenvalues and cluster treatment of characteristic roots, in the forms of delay margin for a single delay and stability tableau over the delay domain for multiple delays, respectively. By a series of trial declarations, the qualitative impact of secondary controller gains on system stability regions against uncertain delays is investigated, from which it can be observed that generally the increase of integral gains would yield to a less delay-dependent stability of control system and the results can be utilized to guide the controller design for a compromise between the dynamic performance and stability robustness. The effectiveness of the proposed methodology is verified by a simulation study.

A Distributed, Cooperative Frequency and Voltage Control for Microgrids

This paper presents a novel secondary frequency and voltage control method for islanded microgrids based on distributed cooperative control. The proposed method utilizes a sparse communication network where each DG unit only requires local and its neighbors’ information to perform control actions. The frequency controller restores the system frequency to the nominal value while maintaining the equal generation cost increment value among DG units. The voltage controller simultaneously achieves the critical bus voltage restoration and accurate reactive power sharing. Subsequently, the case when the DG unit ac-side voltage reaches its limit value is discussed and a controller output limitation method is correspondingly provided to selectively realize the desired control objective. This paper also provides a small-signal dynamic model of the microgrid with the proposed controller to evaluate the system dynamic performance. Finally, simulation results on a microgrid test system are presented to validate the effectiveness of the proposed method.

Performance optimization of a hybrid micro-grid based on double-loop MPPT and SVC-MERS

With ever-increasing concerns on environmental pollution and energy shortage, the development of renewable resource has attracted a lot of attention. This paper first reviews both the wind and photovoltaic (PV) generation techniques and approaches of micro-grid voltage control. Then, a novel islanded micro-grid, which consists of wind & PV generation and hybrid-energy storage device, is built for application to remote and isolated areas. For the PV power generation branch, a double- maximum power point tracking (MPPT) technique is developed to trace the sunlight and regulate the tilt angle of PV panels. For wind-power generation branch, squirrel cage induction generator (SCIG) is used as its simple structure, robustness and less cost. In order to stabilize the output voltage of SCIGs, a new Static Var Compensator named magnetic energy recovery switch (SVC-MERS) is applied. Finally, experimental results confirm that both of the proposed methods can improve the efficiency of PV power generation and voltage stability of the micro-grid, respectively.

Distributed Control of Multiple Electric Springs for Voltage Control in Microgrid

Dispersed distribution of many inverter-based electric springs (ESs) over the power grid as a means to provide stability support for smart grid against high penetration of intermittent renewable power has been suggested recently. While single ES has its own local controller, their wide dispersion makes it difficult to coordinate multiple ESs operation. In this paper, a complete design and implementation procedure of the consensus control methodology for the distributed voltage control of multiple ES is presented. First, the specific control scheme for the single ES is designed by introducing the proportional resonant controller. Then, incorporating with the consensus algorithm by neighboring information exchange instead of global communication, the control strategy for multiple ESs is implemented to discover the voltage reference which will be assigned to ESs for tracking the reference voltage. Compared with the conventional droop control, the scheme can maintain the voltage level of the critical load without sacrificing the voltage control accuracy. Simulation results show that the distributed voltage control can guarantee the overall coordination of parallel ESs under various operation conditions.

Dispersed Voltage Control in Microgrids

The deeper penetration of distributed energy resources (DERs) in microgrids ( μgs) has led to their wider deployment in specific applications. The inherent variability in loads and in renewable energy resource outputs necessitates the development and implementation of effective voltage control strategies so as to reliably serve the loads, particularly under islanded operations mode. We propose a dispersed control strategy to maintain voltage levels within the operational limits by means of the DERs reactive and active power outputs. We implement an optimization approach and demonstrate the effectiveness and the robustness of the proposed voltage control scheme using a set of representative studies from the extensive testing of the simulation approach performed with the methodology. Simulation results demonstrate the absence of any opportunity cost to implement the control action and the maximization of active power production by renewable energy resources.

Sampling Effects on Secondary Voltage Control of Microgrids Based on Network of Multiagent

Sampling Effects on Secondary Voltage Control of Microgrids Based on Network of Multiagent

Distributed Data Traffic Scheduling With Awareness of Dynamics State in Cyber Physical Systems With Application in Smart Grid

The design of communication infrastructure in cyber physical system (CPS) is of vital importance for proper operations of physical dynamics. In this paper, the scheduling of packet transmission over wireless communication networks in CPS is studied for the purpose of system state stabilization. To measure the effective information amount of different packets, the concept of virtual queue (VQ) is defined based on the delay-tolerant Kalman filtering. VQ-based back pressure algorithm is proposed for the distributed data traffic scheduling. The impact of transmission delays on VQ lengths is also studied for the formulation of distributed scheduling strategy. The scheduling method is then applied in the context of voltage control in microgrid and is demonstrated to achieve better performance than general scheduling algorithm without the awareness of dynamics state. Further numerical simulations of data traffic scheduling considering transmission delay are carried out to demonstrate the validity of the scheduling algorithm, which is established according to VQ lengths affected by transmission time delays.

Distributed Adaptive Voltage Control of Inverter-Based Microgrids

This paper proposes an adaptive and distributed secondary voltage control for microgrids with inverter-based distributed generators (DG). The proposed control is fully adaptive and does not require the information of DG parameters. Neural networks are used to compensate for the uncertainties caused by the unknown dynamics of DGs. The controller structure is fully distributed such that each DG only requires its own information and the information of its neighbors on the communication network. Therefore, this secondary control is associated with a sparse communication network. The effectiveness of the proposed methodology is verified for different loading, outage, and islanding scenarios, as well as variable communication structures in a microgrid setup.

A new method of voltage and frequency control in isolated microgrids using enhanced droop controller optimized by frog algorithm

This paper presents a new method for optimal frequency and voltage control in microgrids (MG) considering the mutual effect of line parameters on power transfer. In MGs each distributed generation (DG) has its special droop characteristics. When a load consumption change occurs in the MG, an imbalance between generation and consumption rises, thus a change occurs in the voltage and frequency of DGs according to their droop characteristics. In order to minimize oscillations of voltage and frequency, we have used optimal droop controller which is based on considering the mutual effects of transfer parameters on active and reactive powers. Since line parameters heavily affect the droop characteristics, these parameters are obtained optimally by the frog algorithm such that oscillations in voltage and frequency are minimized. In order to enhance the controlling scheme, effects of line resistance on reactive power changes and effects of line reactance on active power changes are also considered. Since enhanced droop control depends on line parameters, it cannot be implemented in large MGs; therefore, it is modeled by multi-layer perceptron neural networks. We have used the frog algorithm in order to train the perceptron network. The obtained results show satisfactory voltage and frequency control in various load level. In this paper, MGs are studied and simulated in an isolated state.

Distributed Cooperative Secondary Control of Microgrids Using Feedback Linearization

This paper proposes a secondary voltage control of microgrids based on the distributed cooperative control of multi-agent systems. The proposed secondary control is fully distributed; each distributed generator only requires its own information and the information of some neighbors. The distributed structure obviates the requirements for a central controller and complex communication network which, in turn, improves the system reliability. Input-output feedback linearization is used to convert the secondary voltage control to a linear second-order tracker synchronization problem. The control parameters can be tuned to obtain a desired response speed. The effectiveness of the proposed control methodology is verified by the simulation of a microgrid test system.