A Novel Approach to Control the Frequency and Voltage of Microgrids in Islanding Operation (original) (raw)
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Modeling and Control of a Microgrid in Islanding Mode
Renewable Energy and Power Quality Journal, 2017
Recent researches show the importance of modeling and control the DC/DC and DC/AC power converters in order to obtain proper-islanded microgrids or safe connection of different generation sources to the utility grid. The control needs arise because the high penetration of the low scale generation may produce frequency and voltage deviations from desired levels. In this context, this paper develops a model of distinct power converters and proposes a decentralized control strategy to regulate the frequency and voltage in a microgrid with different generators and loads. Simulations show the application of the control strategy in a simple microgrid model with the evaluation of every control stage in the grid.
A Survey on Microgrid Control Techniques in Islanded Mode
Journal of Electrical and Computer Engineering
Traditional power networks with generation in upstream and consumption in the downstream were controlled with centralized controls like SCADA. However, in order to facilitate the penetration of distributed generation, the concept of microgrid was popularized. A microgrid can operate both in grid-connected and in islanded modes. One of the challenges in the microgrid environment is to provide both voltage control and maintain the system frequency while ensuring the stability of the network. This paper is a literature survey focused on different microgrid control techniques with different levels of communication especially in islanded operation.
Microgrid (MG) is a relatively new concept for the integration of distributed generation (DG) along with the loads in a distribution system. Islanded microgrid can be considered as a weak grid that has less inertia compared with the conventional power system. This reality makes the microgrid vulnerable to contingencies. Towards a flexible, safe and secure operation of an islanded MG, researchers have introduced a hierarchical control structure comprising tertiary, secondary and primary control. The primary control plays an important role in maintaining the voltage and frequency stability by sharing the loads among the DGs. This paper reviews and categorizes various primary control methods that have been introduced to control the voltage and frequency of inverter-based microgrids. Moreover, the reviewed methods in terms of their potential advantages and disadvantages are compared. Finally, the future trends are presented. (J.P.S. Catalão).
An overview of control approaches of inverter-based microgrids in islanding mode of operation
Renewable and Sustainable Energy Reviews, 2017
Increased penetration of distributed generation (DG) into the power systems has created fundamental challenges from the viewpoints of control and reliable operation of systems. Microgrids (an aggregation of DG units, loads, and storage elements) with proper control strategies can be a good solution for removing or facilitating these challenges. The introduction of inverter-based microgrid in a distribution network has facilitated the utilization of renewable energy resources, distributed generations, and storage resources; furthermore, it has improved power quality and reduced losses, thus improving the efficiency and the reliability of the system. As most DG units are connected via a power electronic interface to the grid, special control strategies have been developed for inverter interfaces of DG units in islanded microgrids. This paper presents an overview of advanced control methods for microgrids, especially the islanded and inverter-based. Moreover, various control methods are compared and categorized in terms of their respective features. It also summarizes microgrid control objectives with their most problematic solutions as well as their potential advantages and/or disadvantages. Finally, some suggestions are put forward for the future research.
Voltage-Frequency Control (v-f) of Islanded Microgrid Based on Battery and MPPT Control
American Journal of Electrical and Computer Engineering, 2020
With the development and increasing influence of the use of distributed generation resources, distribution networks have changed from passive networks to active networks. In these new networks, operation on an island will increase both the reliability of the network in the competitive market and the maximum utilization of distributed generation resources. But despite the various benefits, Microgrids with distributed generation resources also have disadvantages. One of the disadvantages is the increasing complexity of control systems, protection systems and operating systems of the global distribution network. In recent research, various methods have been proposed for controlling the Microgrids, especially voltage and frequency control. This paper presents a method for controlling a photovoltaic (PV) system with maximum power point tracking (MPPT) controller and battery storage to provide voltage-frequency (v-f) support in an islanded microgrid. It introduces a new algorithm for MPPT control that offers control strategies, effective coordinated between v-f control in inverter, MPPT control, and battery storage control. Finally, the proposed scheme is implemented on the IEEE 13-bus distribution feeder in islanded mode using MATLAB software, the results of which clearly demonstrate the efficiency of the control methods.
Advanced Islanded-Mode Control of Microgrids
2011
This thesis is focused on modeling, control, stability, and power management of electronically interfaced Distributed Energy Resource (DER) units for microgrids. Voltage amplitude and frequency regulation in an islanded microgrid is one of the main control requirements. To that end, first a mathematical model is developed for an islanded DER system and then, based on the developed model, amplitude and frequency control schemes are proposed for (i) balanced and linear loads and (ii) unbalanced and nonlinear loads. The proposed control strategy for unbalanced and nonlinear loads, utilizes repetitive control scheme to reject the effects of unbalanced and/or distorted load currents. Moreover, a new approach is proposed to maintain the effectiveness of the repetitive control under variable-frequency operational scenarios. The thesis also presents an adaptive feedforward compensation strategy to enhance the stability and robustness of the droop-controlled microgrids to droop coefficients and network uncertainties. The proposed feedforward strategy preserves the steady-state characteristics that the conventional droop control strategy exhibits and, therefore, does not compromise the steadystate power shares of the DER systems or the voltage/frequency regulation of the microgrid. Finally, a unified control strategy is proposed to enable islanded and grid-connected operation of DER systems, with no need to detect the microgrid mode of operation or to switch between different controllers, simplifying the control of the host microgrid. The effectiveness of the proposed control strategies are demonstrated through time-domain simulation studies conducted in the PSCAD/EMTDC software environment.
Control strategies of DC-bus voltage in islanded operation of microgrid
International Conference on Electric Utility Deregulation and Restructuring and Power Technologies, 2011
This paper focuses on the energy management system and stability of DC bus in both grid-connected and islanded operations in microgrid system. The microgrid system consists of wind turbines, photovoltaic panels, batteries and super-capacitors, also includes both AC and DC zones. Voltage of DC bus must be kept stable especially in islanded operation. In grid-connected operation voltage of DC bus is controlled by inverter. Real power from renewable energy generations and storage system can be transferred to AC zone through DC bus. In islanded operation, inverter must be controlled to keep magnitude and frequency of AC bus stable, so storage system is used to regulate voltage of DC bus. Simulation results in the paper show that voltage of DC bus can be kept steady and power can be kept balance with the strategy in microgrid system.
Frequency-based control of islanded microgrid with renewable energy sources and energy storage
Journal of Modern Power Systems and Clean Energy, 2016
When a microgrid is mainly supplied by renewable energy sources (RESs), the frequency deviations may deteriorate significantly the power quality delivered to the loads. This paper proposes a frequency-based control strategy, ensuring the frequency among the strict limits imposed by the Standard EN 50160. The frequency of the microgrid common AC bus is determined by the energy storage converter, implementing a proposed droop curve among the state of charge (SoC) of the battery and the frequency. Therefore, the information of the SoC becomes known to every distributed energy resource (DER) of the microgrid and determines the active power injection of the converter-interfaced DERs. The active power injection of the rotating generators remains unaffected, while any mismatch among the power generation and consumption is absorbed by the energy storage system. Finally, in case of a solid short-circuit within the microgrid, the energy storage system detects the severe voltage decrease and injects a large current in order to clear the fault by activating the protection device closer to the fault. The proposed control methodology is applied in a microgrid with PVs, wind generators and a battery, while its effectiveness is evaluated by detailed simulation tests.
Real-Time Frequency and Voltage Control of an Islanded Mode Microgrid
In this paper, we investigated the necessity and effects of optimal control methods in the stability and performance of a micro-grid that operates in islanded mode. The micro-gird is consisted of a combined heat and power (CHP), a capacitor bank (CB), photovoltaic panel (PV) as power generation sources. In addition, battery and the building electricity and thermal load are placed on the load side. A simple comprehensive model is assumed for each component of the micro-gird and the dynamic behavior of micro-grid voltage and frequency is studied in details. Since the micro-grid operates in islanded mode, the fluctuations in the building load act as disturbances and could cause the instability in the voltage and frequency. So it is necessary to design a controller to regulate the voltage and frequency. Particle swarm optimization (PSO) is used as a method to realize the optimal controller in the micro-grid. Simulation results showed the effects of proposed controller on the reduction of voltage and frequency fluctuations.
A Control Strategy for Islanded Microgrids With DC-Link Voltage Control
IEEE Transactions on Power Delivery, 2011
New opportunities for optimally integrating the increasing number of distributed-generation (DG) units in the power system rise with the introduction of the microgrid. Most DG units are connected to the microgrid via a power-electronic inverter with dc link. Therefore, new control methods for these inverters need to be developed in order to exploit the DG units as effectively as possible in case of an islanded microgrid. In the literature, most control strategies are based on the conventional transmission grid control or depend on a communication infrastructure. In this paper, on the other hand, an alternative control strategy is proposed based on the specific characteristics of islanded low-voltage microgrids. The microgrid power is balanced by using a control strategy that modifies the set value of the rms microgrid voltage at the inverter ac side as a function of the dc-link voltage. In case a certain voltage, which is determined by a constant-power band, is surpassed, this control strategy is combined with-droop control. This droop controller changes the output power of the DG unit and its possible storage devices as a function of the grid voltage. In this way, voltage-limit violation is avoided. The constant-power band depends on the characteristics of the generator to avoid frequent changes of the power of certain DG units. In this paper, it is concluded that the new control method shows good results in power sharing, transient issues, and stability. This is achieved without interunit communication, which is beneficial concerning reliability issues, and an optimized integration of the renewable energy sources in the microgrid is obtained.