Control Method For Microgrid Research Articles

Robust adaptive H‐infinity based controller for islanded microgrid supplying non‐linear and unbalanced loads

This study introduces a proposed control method for microgrids (MGs) in islanded (off-grid) mode. The proposed control method is developed by modifying the droop control method using H-infinity controller. In this control method, the droop control loop, current and voltage control loops are adjusted to respond to system load variation. The proposed method is an adaptive control one as it regulates the system voltage and frequency to their nominal values after system load variations. Also, it is a repetitive control method as it depends on the internal model principle that provides good performance for voltage and current error tracking. To prove the applicability and effectiveness of the proposed method, it is applied to a test system using MATLAB/Simulink under three different loading conditions. The results are compared with those of droop control and they prove the effectiveness of the proposed method in adjusting MGs under the off-grid mode of operation. Also, a system stability analysis is performed based on root locus and system step response. Robustness analysis is performed to prove the ability of the proposed controller to restore the system performance after the fault clearance.

A Practical Structure and Control for Reactive Power Sharing in Microgrid

Due to the uncertainty of feeder impedance, conventional droop control-based power sharing scheme presents poor reactive power sharing accuracy in microgrid. As microgrid configuration becomes more and more complicated, reactive power sharing between various distributed generation (DG) equipment is very challenging. To achieve proper power sharing with a simple control method in microgrid, a new structure and power sharing method is proposed in this paper. Instead of using complicated reactive power sharing scheme, this paper proposes separated energy server (ES) units to provide reactive power. Then, active power supplying and reactive power supplying can be achieved separately by energy routers (ERs) and ESs, respectively. With the introduction of ES, the power sharing between DG units can be easily achieved without any supplementary communications or control algorithms. In addition, to reduce costs,a hybrid reactive power compensation configuration with capacitor banks and ESs is provided. Operation principle and power control strategy for DG units and ESs are explained and analyzed in this paper. In order to properly select the coefficients of the power controllers, sensitivity and stability of the system are investigated. Simulation and experimental results are presented to prove the validity of the proposed power sharing method, showing that ERs can effectively share the active power and ESs can effectively share the reactive power according to their capacity.

A review of microgrid development in the United States – A decade of progress on policies, demonstrations, controls, and software tools

Microgrids have become increasingly popular in the United States. Supported by favorable federal and local policies, microgrid projects can provide greater energy stability and resilience within a project site or community. This paper reviews major federal, state, and utility-level policies driving microgrid development in the United States. Representative U.S. demonstration projects are selected and their technical characteristics and non-technical features are introduced. The paper discusses trends in the technology development of microgrid systems as well as microgrid control methods and interactions within the electricity market. Software tools for microgrid design, planning, and performance analysis are illustrated with each tool’s core capability. Finally, the paper summarizes the successes and lessons learned during the recent expansion of the U.S. microgrid industry that may serve as a reference for other countries developing their own microgrid industries.

Energy Management of PV-diesel-battery Hybrid Power System for Island Stand-alone Micro-grid

Abstract The emergence of micro-grid provides new approach to integrate and utilize large scale distributed generation, and suitable for supply electricity to these areas especially island and remote village. In this paper, on the basis of analyzing hybrid power system and control strategies, a kind of utility engineering micro-grid structure is proposed to realize rapid response and efficient operation. Based on the topology structure, for the goal of coordinate power allocation among variety renewable energy effectively, the dispatch control and energy management are analyzed and designed. The operation results of PV-diesel-battery hybrid power system verify the effectiveness of the micro-grid architecture, and the optimal operation of energy system and improved control method of micro-grid should be paid more attention.

Hybrid cooperative control method for microgrid with large generation or load fluctuations

Hybrid cooperative control method for microgrid with large generation or load fluctuations

High stability adaptive microgrid control method using fuzzy logic

Appropriate control strategies for power sharing between multiple generation units operating in parallel are required to create a stable AC microgrid bus. In this paper, we explore the droop control strategy, implemented by power electronics units, to maintain a stable AC bus voltage without the need for a separate (central) communication layer. In particular, our suggested control method is based on adaptive fuzzy logic control (FLC). Fundamentally in low voltage microgrids, due to the effects of feeder and line impedance, the droop control method is subject to real and reactive power coupling and steady-state reactive power sharing errors, and in particular for complex microgrid configurations, the reactive power sharing poses certain challenges. To improve the reactive power sharing equalization, an enhanced FLC strategy has been utilized to calculate a droop coefficient for reactive power control. A second FLC is implemented in an integrator controller, where the reactive power error has been compensated through the injection of small real power disturbances. Root locus analysis of a representative microgrid with three inverters has been undertaken to confirm that stable solutions are feasible. Implementation of a set of gain values into time domain analysis demonstrates excellent voltage and frequency stability on the main bus, as well as equalized real and reactive power sharing between inverters to within ±5W and ±10 VAR, respectively.

Pattern Discovery Based Preventive Control Strategy for Voltage Source Inverter Based Microgrids Against Islanding

—This article presents a statistical learning-based method for preventive control of microgrids against isolating from the main grid. Based on the stability criteria, the microgrid pre-islanding conditions are divided into secure and insecure classes. Critical variables regarding microgrid dynamic security are first selected via a feature selection procedure known as RELIEF. An unsupervised learning method, the pattern discovery method, is then applied to the space of the critical variables to extract the detailed structure knowledge called patterns. The patterns are in hyperspace and can effectively encode the microgrid security boundaries. The extracted patterns are used as preventive control laws to change the pre-islanding microgrid operating point if it is in the insecure region. Applying the proposed preventive control strategy guarantees that the microgrid can be isolated from the main grid without any instability problem. The studies are conducted in the time domain using the developed program in a MATLAB environment (The MathWorks, Natick, Massachusetts, USA). The results demonstrate the effectiveness and accuracy of the proposed preventive control method of microgrid against islanding in comparison with the decision tree based method.

Some Aspects of Stability in Microgrids

This paper investigates some aspects of stability in microgrids. There are different types of microgrid applications. The system structure and the control topology vary depending on the application and so does the aspect of stability in a microgrid. This paper briefly encompasses the stability aspects of remote, utility connected and facility microgrids depending on the modes of operation, control topology, types of micro sources and network parameters. The small signal, transient and the voltage stability aspects in each type of the microgrid are discussed along with scope of improvements. With a brief review of the existing microgrid control methods in the literature and different industry solutions, this paper sets up an initial platform for different types of microgrids stability assessment. Various generalized stability improvement methods are demonstrated for different types of microgrids. The conventional stability study of microgrids presented in this paper facilitates an organized way to plan the micro source operation, microgrid controller design, islanding procedure, frequency control and the load shedding criteria. The stability investigations are presented with different control methods, eigen value analysis and time domain simulations to justify different claims.

E201 Islanding Operation Control Method of Micro-grid Including Seamless Transition from Grid-connecting Operation(Distributed Energy System-3)

E201 Islanding Operation Control Method of Micro-grid Including Seamless Transition from Grid-connecting Operation(Distributed Energy System-3)