1,721,103 research outputs found
Control of Electronic Power Converters for Low-Voltage Microgrids
Full text linkThe dissertation focuses on the management of master/slave microgrid architectures, where distributed energy resources (DERs) are interfaced to the grid by means of conventional current-driven power electronics interfaces and the microgrid is interfaced to the mains via a voltage-driven utility interface converter. The so called power-based control is proposed to regulate the contribution to microgrid needs from the energy resources that are available. The control approach ensures an accurate active and reactive power sharing among DERs that takes into account both local (i.e., DER level) and global (i.e., microgrid level) constraints. The described general approach to microgrid control is underpinned by the conservative power theory, which offers a meaningful, robust, and computationally efficient method to manage power quantities referring to different grid nodes
On Microgrid Evolution to Local Area Energy Network (E-LAN)
No full textOwing to the increasing penetration of information and communication technologies and power electronics, low-voltage microgrids with distributed generation may progressively evolve to Local Area Energy Networks (E-LANs), that is, energy networks with degrees of flexibility, reliability, robustness, and readiness similar to LANs of digital devices. Thanks to grid meshing and synergistic exploitation of the control potential of distributed energy resources, E-LANs can provide an independent control of the currents flowing in each feeder of the grid. On this basis, new and advanced functionalities become possible, like, simultaneous demand response at multiple utility terminals, active and reactive power steering through grid feeders, active clearing of lines for maintenance. This paper presents an optimal control for E-LANs, which applies to low-voltage grids of any structure and complexity and assures independent control of the power fed by prosumers
Microgrids Operation Based on Master–Slave Cooperative Control
No full textLow-voltage microgrids can be seen as the basic tiles of the smart grid patchwork owing to their capability to efficiently manage the distributed energy resources (DERs) in aggregate form. They can support the grid in terms of demand response, power quality, ride through capability, and at the same time, they can ensure electrical continuity to the loads, even in case of grid failure. This paper describes a simple and effective approach to manage microgrids by synergistic control of the power electronic interfaces acting therein, i.e., the utility interface (UI), installed at the point of common coupling with the utility and the energy gateways (EGs), interfacing the DERs with the distribution grid. The proposed master-slave control uses the UI as control master for the EGs. In grid-connected operation, the UI performs as a grid-supporting unit and dispatches active and reactive power references to the EGs so as to improve energy efficiency and power quality; in islanded operation, the UI performs as a grid-forming voltage source and ensures the power balance by exploiting every power source and energy storage unit available in the microgrid. This paper discusses the theoretical background, architecture, and algorithms of the proposed master-slave control and demonstrates the resulting microgrid performance by means of simulation and experimental results
Flexible Control of Interlinking Converters for DC Microgrids Coupled to Smart AC Power Systems
No full textReview and Comparison of Grid-Tied Inverter Controllers in Microgrids
Full text linkGrid-tied inverters are widely used for interfacing renewable energy sources or storage devices to low-voltage electrical power distribution systems. Lately, a number of different control techniques have been proposed to address the emerging requirements of the smart power system scenario, in terms of both functionalities and performance. This article reviews the techniques proposed for the implementation of current-controlled or voltage-controlled inverters in microgrids. By referring to a voltage source inverter with an LCL output filter, different control architectures are classified as single, double, and triple loop. Then, the functionalities that are needed or recommended in the grid-connected, islanded, and autonomous operating modes of the grid-tied inverter are identified and their implementation in the different control structures is discussed. To validate the analysis and to better illustrate the merits and limitations of the most effective solutions, six control strategies are finally implemented and experimentally compared on a single-phase, grid-connected inverter setup
Harmonic Current Compensation by GPS-synchronized Grid Forming Converters
No full textIn the last few years the concept of grid forming converters (GFCs) has aroused a significant of interest in the control of grid-tied electronic power system, especially for stability of large interconnected networks and systems in islanded operation. GFCs act as voltage generator behind an impedance and are able to support the grid or to generate the grid voltage when it is absent. The aim of this paper is to develop a control for the stability of GFCs to achieve harmonic current compensation in the grid. Specifically, the compensation of the harmonics is pursued by performing synchronized measurements of the current distortion at the point of common coupling (PCC) and by generating an appropriate voltage reference for the GFCs. The proposed harmonic solution is validated using a hardware in the loop (HIL) experimental set up
Dead-beat current controller for voltage source converters with improved large-signal response
No full textA digital dead-beat current controller for voltage source converters is presented in this paper. The control structure is specified in a digital hardware description language, synthesized, and deployed on a field-programmable gate array chip. By updating, with negligible computation delay, the duty cycle twice in a switching period, the reference current error is nulled in half a modulation period, so that the controller’s small-signal bandwidth is maximized. In addition, due to a simple transient detection circuit, the large-signal response delay is reduced to a small fraction of the modulation period, which is determined by the chosen current signal oversampling rate. The controller can effectively support different voltage-source inverter applications, such as active filters, uninterruptible power supplies, microgrid distributed energy resource controllers, and dc–dc converter applications, including interface converters for renewable energy sources, laboratory battery chargers, and electronic welding machines
A Per-Phase Power Controller for Smooth Transitions to Islanded Operation
Full text linkThis paper presents a droop-based controller for grid-tied three-phase inverters. The controller allows to regulate the inverter output power while operating grid-tied, to support the local grid voltage while operating islanded, and to seamlessly transition into this latter mode of operation. Remarkably, the use of the traditional droop control scheme for per-phase power control would lead to unequal frequencies among the phase voltages, which is not acceptable. Instead, the proposed controller allows independent power references tracking at each of the phases of a three-phase inverter while grid-tied and a proper transition into the islanded operation. Per-phase power control is crucial for several services in modern smart power networks, like demand-response and distributed unbalance compensation. The paper also reports the stability analysis of the whole control system and outlines a procedure for the design of the involved regulators. Simulation and experimental results considering a laboratory-scale prototype are reported and discussed to validate the proposed controller
Integration and control of heterogeneous power sources in meshed distribution grids
No full textWith the advent of low-voltage microgrids, wind farms and photovoltaic power stations, the management of medium-voltage distribution grids must face new challenges, since uncoordinated operation of the various power sources may cause excess power flows, under- and over-voltages, unwanted tripping of protections, and unexpected distribution losses. This paper proposes a general and scalable approach to the integrated control of distributed power sources in meshed distribution grids. The main goal is to minimize the power losses and the voltage deviations at grid nodes, by taking advantage of all the controllable entities
A Non-linear Wide Bandwidth Digital Current Controller for DC-DC and DC-AC Converters
No full textA fully digital, non-linear, wide bandwidth, current controller for DC-AC and DC-DC voltage source converters is presented in this paper. Exploiting oversampling, the controller mimics an analog hysteresis current controller, but does not employ analog comparators and digital to analog converters. Indeed, it fully virtualizes the hysteresis controller’s operation and, based only on a non linear, efficient, current error filter algorithm, determines the optimum switching instants for the power converter that guarantee reference tracking with minimum delay. In addition, it overcomes the typical limitations of conventional hysteretic controllers, i.e. variable switching frequency or, when frequency stabilization is implemented, sensitiveness to switch dead times and sampling delays. Overall, it offers the same dynamic performance of the analog hysteresis controller, but eliminates all the related issues. Because the current error sample processing algorithm is inherently parallel in structure, the controller is suited for VHDL synthesis and FPGA implementation, which guarantees flexibility and low cost. Its intended application areas include active filters, uninterruptible power supplies, microgrid distributed energy resource (DER) controllers, laboratory battery testers, welding machines
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