MATLAB/Simulink Model Of Wind Farm To Weak Grid Connection

Abstract

Wind Farms (WF) employing squirrel cage induction generator (SCIG) directly connected to the grid; represent a large percentage of the wind energy conversion systems around the world. In facilities with moderated power generation, the WF is connected through medium voltage (MV) distribution headlines. In this scheme, the power generated is comparable to the transport capacity of the grid. This case is known as Wind Farm to Weak Grid Connection, and its main problem is the poor voltage regulation at the point of common coupling (PCC). Thus, the combination of weak grids, wind power fluctuation and system load changes produce disturbances in the PCC voltage, worsening the Power Quality and WF stability. This situation can be improved using control methods at generator level, or compensation techniques at PCC. In case of wind farms based on SCIG directly connected to the grid, is necessary to employ the last alternative. Custom power devices technology (CUPS) results are very useful for this kind of application. In this paper is proposed a compensation strategy based on a particular CUPS device, the Unified Power Quality Compensator (UPQC). A customized internal control scheme of the UPQC device was developed to regulate the voltage in the WF terminals, and to mitigate voltage fluctuations at grid side. The internal control strategy is based on the management of active and reactive power in the series and shunt converters of the UPQC, and the exchange of power between converters through UPQC DC– Link. This approach increases the compensation capability of the UPQC with respect to other custom strategies that use reactive power only. MATLAB/Simulink ® Simulations results show the effectiveness of the proposed compensation strategy for the enhancement of Power Quality and Wind Farm stability.

Control of Wind Energy Conversion System with SOFC Based Fuel Cell at Variable Speed

Abstract -- 

In recent years the statistical data conveys that Doubly-fed Induction Generator (DFIG) based wind turbine with variable speed and variable pitch control is the most common wind turbine in the growing wind market. Due to the fluctuating nature of wind power, a dynamic model of Solid Oxide Fuel Cell energy source is integrated with the wind turbine for sudden load changes to ensure reliable and efficient operation of the power system. This paper deals with simulation of a wind turbine based on a doubly-fed induction machine hybrid with fuel cell energy system used in generating mode to produce electrical energy on a power network. Among the various renewable energy sources, fuel cell is gaining more popularity due to their higher efficiency, cleanliness and cost-effective supply of power demanded by the consumers. Wind Energy is gaining interest now-a-days as one of the most important renewable sources of energy due to its eco-friendly nature. But the major disadvantage lies in variable speed wind generation, so a vector control technique of Wind driven doubly fed Induction Generators is required. The speeds above and below Synchronous speeds are obtained using a bidirectional power flow converter. The wind energy conversion system (WECS) is equipped with a DFIG and two back-to-back Pulse Width Modulated (PWM) Insulated Gate Bipolar Transistors (IGBTs) based voltage source converters (VSCs) in the rotor circuit. A dynamic model of SOFC based fuel cell using Nernst equation and the response of the fuel cell for sudden load changes is analysed and simulated. Simulation results for different operating conditions are demonstrated to reveal the performance of the proposed technique.

A Robust DC-Link Voltage Control Strategy to Enhance the Performance of Shunt Active Power Filters Without Harmonic Detection Schemes

Abstract—

Shunt active power filters (SAP F s) implemented without harmonic detection schemes are susceptible to sudden load variations. This paper proposes a robust control strategy to reduce this drawback. In this strategy, the dc-link voltage is regulated by a hybrid control technique combining a standard proportional–integral PI and a sliding-mode (SM) controllers. The SM scheme continuously determines the gains of the PI controller based on the control loop error and its derivative. The chattering due to the SM scheme is reduced by a transition rule that fixes the controller gains when steady-state condition is reached. This controller is termed as dual-sliding-mode-proportional–integral. The phase currents of the power grid are indirectly regulated by double-sequence controllers with two degrees of freedom, where the internal model principle is employed to avoid reference frame transformation. The proposed control strategy ensures zero steady-state error and improves the performance under hard transients such as load variation. Additionally, it presents robustness when the SAP F is operating under unbalanced conditions. Experimental results demonstrate the performance of the proposed control scheme.

A Series-Parallel Current-Driven Full-Bridge DC/DC Converter

Abstract—

This paper presents a novel Series-Parallel Current-Driven (SPCD) full-bridge DC/DC converter, which is able to process and deliver power efficiently over a wide range of load variations. In order to guarantee reliable operation of high frequency DC/DC converters, the converter should be able to sustain soft-switching for a wide range of operating conditions. The SPCD full-bridge converter, proposed in this paper, is able to offer soft-switching for the input power semiconductors and smooth commutations for the output diodes. Also, the particular structure of the proposed converter eliminates the need for extra auxiliary circuits to provide reactive current for soft-switching at light loads. The proposed topology can fully eliminate voltage spikes across the output diodes by providing smooth and lossless commutations for the output diodes. Thus, the proposed converter can be a efficient and reliable solution for variety of applications with a high switching frequency and a high output voltage. The SPCD full-bridge converter has the ability to integrate all magnetic components into an integrated transformer in order to achieve a high power density. The integrated transformer is thoroughly analysed using ANSYS HFSS. Simulation and experimental results confirm the superior performance of the proposed SPCD full-bridge DC/DC converter.

Energy storage system for self-consumption of photovoltaic energy in residential zero energy buildings

limate and energy targets, as well as decreasing costs have been leading to a growing utilization of solar photovoltaic generation in residential buildings. However, even in buildings with the same level of yearly generation and consumption the mismatch between the demand and photovoltaic generation profiles leads to large power flows between the household and the grid. Such situation creates problems to the electrical grid management and can be a source of economic losses to the end-user.

This paper presents an energy storage system designed in the context of residential buildings with photovoltaic generation. The objective of such system is to increase the matching between the local generation and consumption, as well as to decease the energy bill, using lithium-ion batteries as a storage device. Such system was modelled and simulated using real data of solar radiation and energy consumption from a typical residential household in Coimbra (Portugal). The results show that the designed system was able to reduce the energy sent to and consumed from the grid in 76% and in 78.3%, respectively, as well as the energy bill in 87.2%.

Interleaved Boost DC-DC Converter Using Delta-Sigma Modulation Suitable for Renewable Energy Applications

Abstract—

It is generally accepted that interleaving techniques are efficient at reducing the input/output ripples and increasing the power output of boost converters operating in critical conduction mode.Pulse width modulation (PWM) is used to produce the switching pattern. But this technique causes large switching noise peaks at a multiple number of the carrierfrequency. This paper proposes Interleaved Boost DC-DC suitablefor renewable energy applications. The proposed converterutilizes delta-sigma modulation to control pulse generator. A thorough and effective analysis of the converter is carried out in order to achieve the system stability and to improve the dynamic performance. The output response obtained by this method is very much improved compared to the conventional PWM method of control. Simulation results are provided to illustrate the advantages of the proposed converter and controller scheme. All the advantages of interleaving, such as higher efficiency and reduced ripple for voltage/current, are also achieved in the proposed converter.