Bidirectional partial power converter interface for energy storage systems to provide peak shaving in grid-tied PV plants

The ever growing participation of modern renewable resources in electric markets has shaken the paradigm of generation-demand constant match. Most modern renewables add intermittent behaviour and high variability to electric markets, forcing other renewables and themselves to perform power curtailment and/or having extra generating units connected to the network to compensate power, voltage and frequency variations. In order to handle this scenario, Energy Storage Systems (ESSs) have risen as enabling technologies capable to provide backup energy to compensate power, voltage and frequency fluctuations and, at the same time, offer additional benefits as ancillary services, peak shaving, load shifting, base load generation, etc. This paper presents a novel bidirectional Partial Power Converter (PPC), as an interface between a Battery ESS (BESS) and a grid-tied Photovoltaic (PV) plant. To obtain a better understanding of the converter, its mathematical model is presented and its operation modes are explained. The main purpose of this configuration is to provide peak shaving capability to a grid-tied PV plant, while providing a high efficiency BESS. Simulation results show the operation of the full system (grid-tied PV plant and BESS), performing peak shaving under a step-down and up in solar irradiation

The Essential Role and the Continuous Evolution of Modulation Techniques for Voltage-Source Inverters in the Past, Present, and Future Power Electronics

The cost reduction of power-electronic devices, the increase in their reliability, efficiency, and power capability, and lower development times, together with more demanding application requirements, has driven the development of several new inverter topologies recently introduced in the industry, particularly medium-voltage converters. New more complex inverter topologies and new application fields come along with additional control challenges, such as voltage imbalances, power-quality issues, higher efficiency needs, and fault-tolerant operation, which necessarily requires the parallel development of modulation schemes. Therefore, recently, there have been significant advances in the field of modulation of dc/ac converters, which conceptually has been dominated during the last several decades almost exclusively by classic pulse-width modulation (PWM) methods. This paper aims to concentrate and discuss the latest developments on this exciting technology, to provide insight on where the state-of-the-art stands today, and analyze the trends and challenges driving its future

Ultracapacitor storage enabled global MPPT for photovoltaic central inverters

In most large scale grid-tied photovoltaic (PV) plants, central inverter configurations are used, mainly due to higher efficiency and lower cost per kW. However, compared to other configurations its Maximum Power Point Tracking (MPPT) efficiency is the lowest since it is the less distributed configuration. Under non-uniform conditions, as partial shading, several local maxima may arise in the PV curve, hence requiring additional actions to maximize the output power of the PV plant. Moreover the growth of renewable sources in electric markets has tightened grid codes; requiring for PV systems to limit power fluctuations to a certain maximum. This paper presents an alternative to perform Global MPPT (GMPPT) while complying with new grid code limitations for electric markets with high penetration of renewables. The proposed alternative consists on adding an Energy Storage System (ESS) at inverter level. The proposed system consists in an ultracapacitor (UC) bank connected to the DC-link of the central inverter through interleaved DC-DC power converters. The proposed configuration is validated through simulations and tested through extreme conditions. The performance of the system is analyzed and compared to other existing solutions

Charging Architectures Integrated with Distributed Energy Resources for Sustainable Mobility

Abstract This paper introduces a study on the charging infrastructures, integrated with distributed energy sources, showing their ability to support the electric and hybrid mobility in a smart grid scenario. This analysis starts from a description of the main AC and DC architecture and then goes through the advantages derived by the integration of renewable energy sources within the existing electric power network. A section of this paper is then dedicated to the main technologies of energy storage systems, which allow and support the integration of unpredictable energy sources into the grid. Finally, the power on-board and off-board vehicle charging devices are analyzed with specific focus on PWM control schemes, for the regulation of AC/DC and DC/DC power converters, and on grid operations (V2G) related to different aggregation schemes

Control methods for low voltage ride-through compliance in grid-connected NPC converter based wind power systems using predictive control

This material is presented to ensure timely dissemination of scholarly and technical work. Copyright and all rights therein are retained by authors or by other copyright holders. All persons copying this information are expected to adhere to the terms and constraints invoked by each author's copyright. In most cases, these works may not be reposted without the explicit permission of the copyright holder.In presence of grid voltage dips, Low Voltage Ride-Through (LVRT) requirements demand the wind power plant to remain connected to the grid, helping the network to keep voltage and frequency stable. Neutral-Point-Clamped (NPC) converters are appropriate for wind power systems, because the current trend of increasing voltage levels. Predictive current control presents as fast dynamic response and accurate reference tracking as other well established control methods, while providing more flexibility. In this work, three different control strategies are applied to the grid-side NPC converter, in order to fulfil LVRT requirements, which are implemented with the predictive current control technique. Dc-link neutral point voltage is kept balanced by the predictive control algorithm, using the redundant switching states of the NPC converter. Simulation results confirm the validity of the proposed control approach.Peer ReviewedPostprint (published version

Novel modulator for the hybrid two-cell flying-capacitor based ANPC converter

Among the multilevel converters present in the industry, the hybrid flying-capacitor based active-neutral-point-clamped converter is very recent. It presents good features such as high quality output voltage, high modularity and easy extension to achieve a high number of levels with reduced number of power devices. This paper introduces a simple modulator for the single-phase two-cell hybrid flying-capacitor based active-neutral-point-clamped converter. The modulation technique is based on the determination of a switching sequence formed by two switching states which generate the two nearest voltage levels to the reference phase voltage. Some extra calculations are added to the modulation method to control the dc-link capacitors and the floating capacitor voltages. The computational cost of the modulation technique is low only including simple comparisons and mathematical expressions. Simulation results show the high quality output voltages and currents including the dc voltage control

Guidelines for Weighting Factors Adjustment in Finite State Model Predictive Control of Power Converters and Drives

INTERNATIONAL CONFERENCE ON INDUSTRIAL TECHNOLOGY () (.2009.VICTORIA, AUSTRALIA)Model Predictive Control with a finite control set has emerged as a promising control tool for power converters and drives. One of the major advantages is the possibility to control several system variables with a single control law, by including them with appropriate weighting factors. However, at the present state of the art, these coefficients are determined empirically. There is no analytical or numerical method proposed yet to obtain an optimal solution. In addition, the empirical method is not always straightforward, and no procedures have been reported. This paper presents a first approach to a set of guidelines that reduce the uncertainty of this process. First a classification of different types of cost functions and weighting factors is presented. Then the different steps of the empirical process are explained. Finally, results for several power converters and drives applications are analyzed, which show the effectiveness of the proposed guidelines to reach appropriate weighting factors and control performance

Multilevel Converters: An Enabling Technology for High-Power Applications

| Multilevel converters are considered today as the state-of-the-art power-conversion systems for high-power and power-quality demanding applications. This paper presents a tutorial on this technology, covering the operating principle and the different power circuit topologies, modulation methods, technical issues and industry applications. Special attention is given to established technology already found in industry with more in-depth and self-contained information, while recent advances and state-of-the-art contributions are addressed with useful references. This paper serves as an introduction to the subject for the not-familiarized reader, as well as an update or reference for academics and practicing engineers working in the field of industrial and power electronics.Ministerio de Ciencia y Tecnología DPI2001-3089Ministerio de Eduación y Ciencia d TEC2006-0386

Variable-Angle Phase-Shifted PWM for Multilevel Three-Cell Cascaded H-bridge Converters

Multilevel cascaded H-bridge converters have become a mature technology for applications where high-power medium ac voltages are required. Normal operation of multilevel cascaded H-bridge converters assumes that all power cells have the same dc voltage, and each power cell generates the same voltage averaged over a sampling period using a conventional phase-shifted pulse width modulation (PWM) technique. However, this modulation method does not achieve good results under unbalanced operation per H-bridge in the power converter, which may happen in grid-connected applications such as photovoltaic or battery energy storage systems. In the paper, a simplified mathematical analysis of the phase-shifted PWM technique is presented. In addition, a modification of this conventional modulation method using variable shift angles between the power cells is introduced. This modification leads to the elimination of harmonic distortion of low-order harmonics due to the switching (triangular carrier frequency and its multiples) even under unbalanced operational conditions. The analysis is particularized for a three-cell cascaded H-bridge converter, and experimental results are presented to demonstrate the good performance of the proposed modulation method

Modulador simple con control del equilibrio de tensiones para un convertidor hibrido ANPC+ Flying-capacitor de cinco niveles

El convertidor híbrido basado en una celda active neutral-point-clamped conectada en serie con celdas con condensadores flotantes es una topología multinivel reciente con propiedades interesantes como una tensión de salida de alta calidad y una fácil extensión para lograr un elevado número de niveles con un reducido número de dispositivos de potencia. Este trabajo se centra en la introducción de un modulador monofásico simple para el convertidor hibrido de cinco niveles. El control de la tensión de los condensadores flotantes del convertidor se realiza mediante una técnica de control que aprovecha el gran número de estados de conmutación redundantes presentes en la topología. Utilizando esta técnica de modulación, la tensión de los condensadores del dc-link y las tensiones de los condensadores flotantes se controlan a sus valores deseados. Los resultados de la simulación muestran el buen desempeño del control de las tensiones obteniendo simultáneamente buenos resultados en cuanto a la calidad de las tensiones y corrientes de salida