Power Sharing Method for a Grid connected Microgrid with Multiple Distributed Generators (original) (raw)
Related papers
IEEE Transactions on Power Delivery, 2010
This paper describes the active power and frequencycontrol principles of multiple distributed generators (DGs) in a microgrid. Microgrids have two operating modes: 1) a grid-connected mode and 2) an islanded mode. During islanded operation, one DG unit should share output generation power with other units in exact accordance with the load. Two different options for controlling the active power of DGs are introduced and analyzed: 1) unit outputpower control (UPC) and 2) feeder flow control (FFC). Taking into account the control mode and the configuration of the DGs, we investigate power-sharing principles among multiple DGs under various system conditions: 1) load variation during grid-connected operation, 2) load variation during islanded operation, and 3) loss of mains (disconnected from the main grid). Based on the analysis, the FFC mode is advantageous to the main grid and the microgrid itself under load variation conditions. However, when the microgrid is islanded, the FFC control mode is limited by the existing droop controller. Therefore, we propose an algorithm to modify the droop constant of the FFC-mode DGs to ensure proper power sharing among DGs. The principles and the proposed algorithm are verified by PSCAD simulation. Index Terms-Active power control, distributed generator, droop characteristics, feeder flow control, microgrid. I. INTRODUCTION D ISTRIBUTED energy resources (DERs), such as fuel cells, microturbines, and photovoltaic systems offer many advantages for power systems [1], [2]. For example, they can effectively mitigate peak demand, increase reliability against power system faults, and improve power quality (PQ) via sophisticated control schemes. Accordingly, distributed generators (DGs) have been installed in power systems and tested for better configurations and control schemes. The concept of
A load-sharing control scheme for a microgrid with a fixed frequency inverter
Electric Power Systems Research, 2010
In this paper, a load-sharing control strategy is developed for a microgrid consisting of a fuel cell power module and two synchronous generators in a stand-alone environment. The fuel cell is interfaced with the synchronous generators through a DC/AC inverter to convert unregulated DC to a three-phase AC. Since the frequency of the DC/AC inverter is fixed, the conventional load-frequency control scheme cannot be used for load-sharing control. To alleviate this problem, a load-voltage control scheme is developed. The theoretical analysis and experimental validation of the proposed scheme are presented. It is shown, by theoretical analysis and experiments, that this control strategy can effectively distribute the load among the different energy sources based on their individual pre-defined load-voltage droop characteristics.
Control Methods of Inverter-Interfaced Distributed Generators in a Microgrid System
IEEE Transactions on Industry Applications, 2000
Microgrids are a new concept for future energy distribution systems that enable renewable energy integration and improved energy management capability. Microgrids consist of multiple distributed generators (DGs) that are usually integrated via power-electronic inverters. In order to enhance power quality and power distribution reliability, microgrids need to operate in both grid-connected and island modes. Consequently, microgrids can suffer performance degradation as the operating conditions vary due to abrupt mode changes and variations in bus voltages and system frequency. This paper presents controller design and optimization methods to stably coordinate multiple inverter-
Energies
Microgrids (MG) are small-scale electric grids with local voltage control and power management systems to facilitate the high penetration and grid integration of renewable energy resources (RES). The distributed generation units (DGs), including RESs, are connected to (micro) grids through power electronics-based inverters. Therefore, new paradigms are required for voltage and frequency regulation by inverter-interfaced DGs (IIDGs). Notably, employing effective voltage and frequency regulation methods for establishing power-sharing among parallel inverters in MGs is the most critical issue. This paper provides a comprehensive study, comparison, and classification of control methods including communication-based, decentralized, and construction and compensation control techniques. The development of inverter-dominated MGs has caused limitations in employing classical control techniques due to their defective performance in handling non-linear models of IIDGs. To this end, this articl...
A Control Strategy for a Distributed PowerGeneration Microgrid Application
International Journal of Advanced Research in Electrical, Electronics and Instrumentation Energy, 2013
In this paper, a high performance inverter, including the functions of stand-alone and grid connected power supplies, is developed so that distributed generation units can operate individually or in a microgrid mode. Off-grid islanding describes the condition in which a microgrid or a portion of the power grid, which consists of a load and a distributed generation (DG) system, is isolated from the remainder of the utility system. In this situation, it is important for the microgrid to continue to provide adequate power to the load. Under normal operation, each DG inverter system in the microgrid usually works in constant current control mode in order to provide a preset power to the main grid. When the microgrid is cut off from the main grid, each DG inverter system must detect this islanding situation and must switch to a voltage control mode. In this mode, the microgrid will provide a constant voltage to the local load. This paper describes an Adaptive Total Sliding Mode Control (...
Coordinated Control and Energy Management of Distributed Generation Inverters in a Microgrid
This paper presents a microgrid consisting of different distributed generation (DG) units that are connected to the distribution grid. An energy-management algorithm is implemented to coordinate the operations of the different DG units in the microgrid for grid-connected and islanded operations. The proposed microgrid consists of a photovoltaic (PV) array which functions as the primary generation unit of the microgrid and a proton-exchange membrane fuel cell to supplement the variability in the power generated by the PV array. A lithium-ion storage battery is incorporated into the microgrid to mitigate peak demands during grid-connected operation and to compensate for any shortage in the generated power during islanded operation. The control design for the DG inverters employs a new model predictive control algorithm which enables faster computational time for large power systems by optimizing the steady-state and the transient control problems separately. The design concept is verified through various test scenarios to demonstrate the operational capability of the proposed microgrid, and the obtained results are discussed.
Energy Conversion and Management, 2015
This paper describes a control technique for enhancing the stable operation of distributed generation (DG) units based on renewable energy sources, during islanding and grid-connected modes. The Passivity-based control technique is considered to analyse the dynamic and steady-state behaviours of DG units during integration and power sharing with loads and/or power grid, which is an appropriate tool to analyse and define a stable operating condition for DG units in microgrid technology. The compensation of instantaneous variations in the reference current components of DG units in ac-side, and dc-link voltage variations in dc-side of interfaced converters, are considered properly in the control loop of DG units, which is the main contribution and novelty of this control technique over other control strategies. By using the proposed control technique, DG units can provide the continuous injection of active power from DG sources to the local loads and/or utility grid. Moreover, by setting appropriate reference current components in the control loop of DG units, reactive power and harmonic current components of loads can be supplied during the islanding and grid-connected modes with a fast dynamic response. Simulation results confirm the performance of the control scheme within the microgrid during dynamic and steadystate operating conditions.
A dual control strategy for power sharing improvement in islanded mode of AC microgrid
springer open, 2018
Parallel operation of inverter modules is the solution to increase the reliability, efficiency, and redundancy of inverters in microgrids. Load sharing among inverters in distributed generators (DGs) is a key issue. This study investigates the feasibility of power-sharing among parallel DGs using a dual control strategy in islanded mode of a microgrid. PQ control and droop control techniques are established to control the microgrid operation. P-f and Q-E droop control is used to attain real and reactive power sharing. The frequency variation caused by load change is an issue in droop control strategy whereas the tracking error of inverter power in PQ control is also a challenge. To address these issues, two DGs are interfaced with two parallel inverters in an islanded AC microgrid. PQ control is investigated for controlling the output real and reactive power of the DGs by assigning their references. The inverter under enhanced droop control implements power reallocation to restore the frequency among the distributed generators with predefined droop characteristics. A dual control strategy is proposed for the AC microgrid under islanded operation without communication link. Simulation studies are carried out using MATLAB/SIMULINK and the results show the validity and effective power-sharing performance of the system while maintaining a stable operation when the microgrid is in islanding mode.
Microgrids have been defined as an efficient and practical concept to cover flaws in traditional power system related to system expansion and renewable energy utilization. By increasing demand energy, the need to generate more electric power is raised. However, the distance between generation centers and consumption centers causes more energy loss in power system and power system expansion is considered costly and to some extent infeasible. In addition, nowadays using renewable energies such as wind energy is inevitable, as a result using power electronic mediums is necessary. Microgrids are mostly preferable because of the ability to perform in islanded mode. In order to have stable-islanded Microgrid, electric loads inside the network should be shared on Voltage Source Converters respect to their nominal capacity. Droop control has been known as a method to share loads in decentralized way, although it has shortcomings. In this paper by introducing novel method named Frequency Tracking and applying that on droop control system, electric loads inside an islanded Microgrid are shared on generation units properly with fast and acceptable dynamics and droop control system is modified. Simulation results in PSCAD are confirmation of proposed system to have stable islanded Microgrid.
This paper presents a centralized control system that coordinates parallel operations of different distributed generation (DG) inverters within a microgrid. The control design for the DG inverters employs a new Model Predictive Control algorithm that allows faster computational time for large power systems by optimizing the steady-state and the transient control problems separately. An overall energy management system is also implemented for the microgrid to coordinate load sharing among different DG units during both grid-connected and islanded operations. The design concept of the proposed control system is evaluated through simulation studies under different test scenarios. The impact of the increased penetration of DG units on the distribution grid is also investigated using the proposed microgrid. The simulation results show that the operations of the DG units within the microgrid can be coordinated effectively under the proposed control system to ensure stable operation of the overall microgrid.