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Chaotic nature of renewable energy sources connected with nonlinear loads may cause serious problems to the utility grid, e.g. voltage and frequency disturbances, harmonic pollution. Due to that, many European governments have set strict regulations to the grid energy injection. As a result, the power quality has become one of the major obstacles for nearly zero energy buildings to be connected with...
Fault current limiters (FCLs) are one class of solutions to cope with the upcoming challenges in microgrid protection. Considering high penetration of distributed generations (DGs) in microgrids, the necessity of designing cheap and effective FCL is getting higher. This paper attempts to fill this gap by proposing an embedded FCL operating based on modifying the secondary control of DGs. As this method...
This paper proposes a novel universal control for multi-bus AC microgrid with the capability to operate in both grid-connected (GC) and islanded (IS) modes. The control scheme is based on distributed manner, and the leader-follower consensus protocol is designed. Only few leader distributed generators (DGs) receive the correction signals from the unified mode controller, which is installed at the...
A robust grid structure, which makes use of distributed renewable energy generation, should consist of grid sections, which are able to seamlessly switch between grid-connected and islanding mode of operation. This way, failures in the upper level part of the grid can be mitigated. This contribution discusses local and supervisory control strategies, and requirements for microgrids. A robust hierarchical...
This paper presents a case study of different control approaches for a single phase Dual Active Bridge (DAB) based MVDC Shipboard power system (SPS). The Line Regulating Converters (LRCs) are based on DAB topology and the load side converters or Point of Load Converters (POLs) are based on buck topology. The tightly controlled POLs exhibit a constant power load (CPL) behaviour, which has a destabilising...
In this paper, the relationship between real and reactive power sharing in islanded microgrid considering the complex impedance effect is analyzed. It is determined that traditional droop control has drawbacks in achieving accurate power sharing caused by the mismatched feeder line effect. In order to enhance the power sharing accuracy, an adaptive droop control using virtual impedance for islanded...
In this paper, a new distributed cooperative control for voltage unbalance compensation in an islanded microgrid is proposed. In order to decrease the negative impacts of impedance of distributed lines upon conventional negative-sequence reactive power-conductance droop control, a cooperative control component is added to accomplish the trade-off between the accuracy of negative-sequence reactive...
The paper presents an overview about operation and control of the inverter-interface generation units (IGUs) when connected to a microgrid either alone or together with other generation units. The following key connection paradigms are considered: i) one IGU and a grid, ii) one IGU and one machine-interface generation unit, iii) a single IGU, and iv) two IGUs. After illustrating how the IGUs operate...
Generally, operating voltage of photovoltaic (PV) arrays are low. To interface such systems with high voltage DC bus, a high gain converter is needed. Moreover, power generated by the PV systems is non-uniform most of the time. Therefore, for this purpose, a battery port is mandatory. Hence, for this application a high gain multi port converter is suitable candidate that increases conversion efficiency...
The microgrid with distributed PV and air source heat pump is studied, aim at the problem of controller saturation caused by the lag of the static switch and the mismatch between the operation mode and the control method, droop control is used in island mode and grid-connected mode, an improved pre-synchronization control algorithm is proposed to ensure the smooth transition of the microgrid transient...
In this paper, a bidirectional buck-boost converter for connecting energy storages to a DC microgrid is presented. The integration of energy storages into the microgrid allows an enhanced utilization of renewable energy sources. Therefore, an efficient control of energy storages and corresponding power converters is required. Two operating modes of the converter are considered: current control mode...
In this work is present the comparison of two methods of controllers design and the model of a single phase inverter for island mode operation in a microgrid. These methods are: direct current conventional method based on frequency analysis that allows the design of a proportional-integral controller and a second method based on dc-ac coordinate transformation, that allows the design of a proportional...
Cascaded H-bridge converters based islanded microgrids are applied to integrate the distributed generators (DGs). The accurate load sharing is an important task for the research of microgrids. Due to the characteristics of series connection, all DGs share a single common current. In this paper, the power factor of each DG is assigned to be consistent via regulating both the frequency and voltage....
Nonlinear loads connected to the microgrid distort the voltage of the Point of Common Coupling (PCC) and the grid current. Therefore, A droop control based harmonic voltage compensation strategy of voltage controlled inverter in islanded/grid-connected mode is proposed in this paper. To compensate the PCC voltage distortion, fundamental and harmonic voltage components are controlled separately in...
Recently, more and more small-scale renewable generation sources based distributed generators are integrated to the existing power network through power electronic-based converters. Microgrid has been proposed as a solution to meet the challenges posed by highly intermittent renewable generations. To address the fast response and complex operating conditions of various inverters in an autonomous microgrid,...
This paper extensively analyzes the operation limits, system stability and disturbance rejection capability of the voltage control loops used in master-slave AC and DC Microgrids (MGs). Two different control schemes are studied analytically, simulated and experimentally tested, focusing on Constant Power Loads (CPL). Additionally, the use of the virtual capacitance (VC) as a tool for response enhancement...
Customers may have different power quality requirements, thus, the economic operational strategy can try to provide them with distinctive quality levels as customized service. An optimization based method is proposed in this paper to realize this functionality, offering the possibility that the customers can flexibly set and adjust their requirements. Converter interfaced distributed generators are...
A 15 kVA power electronic system with a battery energy storage system is presented in the paper. The system is designed for areas where a problem with the quality of the electrical power arises. The system is intended for households and small industrial facilities and provides a variety of functionalities such as: ability of providing high quality voltage for the customers load, uninterruptible power...
A linear controller is proposed for dc microgrids with SEPIC, Cuk and Zeta power electronic converters supplying constant power loads. The controller is implemented in two stages. During the first stage, also known as active damping stage, limit cycle oscillations are damped by inserting a virtual resistance in series with the input inductor of each of the converters. In the second stage, an integral...
A control concept is presented to include grid supporting schemes into the droop control of grid-supporting and grid-forming power electronic converters. This control scheme adopts advanced power reference strategies used for grid-feeding converters to voltage controlling converters during unbalanced faults. The strategies are evaluated first with respect to the maximum power injection in case of...
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