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This work presents a back to back converter topology with the ability to connect two power systems of different voltages and frequencies for the exchange of power. By utilizing indirect AC to AC conversion decoupling is achieved between the power systems with one of three phase, two level voltage source converters performing the AC to DC conversion that maintains the required DC bus voltage level...
By intensifying renewable energy sources integration to the power grid and forming the microgrids (MGs) concept, many studies have been done to investigate MGs operation, control, protection, and etc. The performance of loads can play a major role in the MG behavior. Different load models can be implemented in MGs. The voltage and frequency (VF) dependent load is a substantial load model which few...
Small signal stability of inverter based droop controlled microgrid is a major problem from past decade. In this work, an optimal state feedback controller is designed to improve the stability of the two inverter based test microgrid. The detailed full order small signal model of the test microgrid is developed in state space considering network and load dynamics. Eigen value and sensitivity analysis...
Hybrid AC/DC microgrid (MG) has attracted more and more attention due to its advantages such as better power sharing, improved system dynamics, and optimal management. But the complicated structure brings a great challenge to the modeling and stability analysis. In recent years, dynamic phasor model has been well applied in the modeling of AC MGs. Dynamic phasor tranforms sinusoidal quantities to...
The voltage source inverters operating in islanded microgrid are used as sources of power similar to synchronous generators (SG) in conventional power system. Unlike synchronous generators, these inverters neither have a natural droop (P-f and Q-V) characteristics nor rotational inertia. The electrical time constant is much lesser than mechanical time constant and hence the load changes will show...
Solid state transformers (SSTs) can be interconnected with each other through a distribution feeder to form a smart grid. When the main grid is disconnected, SSTs form an islanded microgrid. With available communications, master-slave microgrid control structure can be adopted. The system-level stability analysis can be simplified by considering only the grid interface stage of the SST. The loop feeder...
The challenge of failure management emerges in decentralized architectures due to the distributed nature of the layered control process. Failures in microgrid system may occur at the microgrid level or any of the control layers. A failure detection and response mechanism is required to attain a reliable, fault-tolerant microgrid operation. This paper introduces a Failure Management Unit as an essential...
The droop control technology, which can achieve an autonomous power sharing among distributed resources interface converters, provides the advantages of enhanced system reliability and reduced complexity. However, the reactive power sharing accuracy of the conventional Q — V droop method can be degraded due to its dependence on the line impedances. The Q — V droop control method was proposed to reduce...
A highly flexible and reliable control strategy is proposed to achieve bounded voltage and precise current sharing, which is implemented in a reverse-droop-based dc Micro-Grid. To acquire the fast-dynamic response, the reverse droop control is used to replace the V-I droop control in the primary level. In the secondary level, the containment-based controller is proposed to bound the bus voltages within...
This work proposes and investigates a renewable energy distributed generation system involving a matrix converter with an output filter working as a stable voltage supply. This is especially relevant for the stand-alone operation of a renewable energy microgrid where a stable sinusoidal voltage with prescribed amplitude and frequency under various load conditions is the main control objective. A controllable...
The well-known droop control and master-slave control methods are two dominant coordinative control schemes for inverter interfacing parallel distributed energy resources (DERs) in islanded AC microgrids. However, both these two control methods have some drawbacks and inherent limitations in practical application. After analyzing their complementary strengths and weaknesses, this paper proposed a...
This paper presents a novel hybrid adaptive droop controller to simultaneously regulate both the AC-side and DC-side parameters for power electronic converters in single-phase Microgrids. The main contribution of this paper is to integrate the AC-side and DC-side controllers. Unlike previously presented control schemes, where the DC-bus is considered as an infinite bus or constant voltage bus, the...
Parallel three-level T-type inverters (3LT2Is) can increase power rating and reliability, but the circulating current problem will arise. Unbalanced conditions including unbalanced filter inductances and unbalanced grid voltage have negative effects on the operation of parallel 3LT2Is. This paper presents an improved repetitive control scheme for circulating current suppression in parallel 3LT2Is...
This paper highlights the power limited nature of the Distributed Generation inverter and demonstrates the practical way to integrate them into the microgrid. Since the energy source of Distributed Generation inverters is power limited in nature, they constrain the operation of inverters to which they are coupled. If the power demanded from these inverters is beyond their capability, their DC-link...
This paper presents a power-based droop controller for distributed energy resources converters in dc microgrids that are connected to the utility ac grid by a grid-interface converter. Typically, when dc microgrids are interfaced to ac power systems, the microgrid dc bus voltage can be affected by fluctuations caused, for example, by background harmonics present in the ac systems or by fluctuating...
One of the major feature of DC microgrids is its high penetration of power electronic converters, as a result, the system inertia becomes a problem. In this paper, an admittance-type droop control with additional capability of introducing virtual inertia to the system. With the proposed method, each energy source will also contribute virtual inertia to the system, thus improving transient response...
This paper presents a proportional harmonic power sharing (PHPS) control scheme to improve the voltage quality at point of common coupling (PCC) and share harmonic power simultaneously for an islanded microgrid. The proposed control strategy employs P+ multiple resonant controller, and P+ plus Q+-based improved droop control scheme to improve the voltage quality at the load bus. Additionally, the...
A novel control strategy which enables proportional linear and nonlinear loads sharing among paralleled inverters and voltage harmonic suppression is proposed in this paper. The proposed method is based on the autonomous currents sharing controller (ACSC) instead of conventional power droop control to provide fast transient response, decoupling control and large stability margin. The current components...
In a microgrid with distributed generation (DG) units, proper control of the grid interfacing inverter is critical to facilitate safe and stable operation of the system. The droop control mechanism is a widely accepted control method in a microgrid operation. However, a droop controller is unable to provide inertia support in such systems, and thus, cannot contribute in primary frequency control during...
A transformerless two-stage bidirectional single-phase ac-dc converter is designed to connect 380 V bipolar dc microgrids with 240 V split-phase single-phase ac systems. The converter consists of a full-bridge ac-dc stage and a full-bridge dc-dc stage. This decouples the common-mode (CM) voltage between the connected ac and dc systems. To achieve high efficiency, interleaving and state-of-the-art...
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