Grid-side cascade inverter system as an interface for wind energy storage

Additional converters that are used to interface energy storage devices incur power losses as well as increased system cost and complexity. The need for additional converters can be eliminated if the grid side inverter can itself be effectively used as the interface for energy storage. This paper therefore proposes a technique whereby the grid side inverter can also be used as an interface to connect a supercapacitor energy storage for wind energy conversion systems. The proposed grid side inverter is formed by cascading a 3-level inverter and a 2-level inverter through a coupling transformer. The three-level inverter is the main inverter and it is powered by the rectified output of the wind turbine coupled AC generator while the 2-level auxiliary inverter is connected to the super capacitor bank that is used to compensate short term power fluctuations. Novel modulation and control techniques are proposed to address the problems associated with non-integer and dynamically-changing dc-link voltage ratio, which is caused by the random nature of wind. Simulation results are presented to verify the efficacy of the proposed system in suppressing short term wind power fluctuations.

HFL micro inverter with front-end diode clamped multi-level inverter and half-wave cycloconverter

A high-frequency-link (HFL) micro inverter with a front-end diode clamped multi-level inverter and a grid-connected half-wave cycloconverter is proposed. The diode clamped multi-level inverter with an auxiliary capacitor is used to generate high-frequency (HF) three level quasi square-wave output and it is fed into a series resonant tank to obtain high frequency continuous sinusoidal current. The obtained continuous sinusoidal current is modulated by using the grid-connected half-wave cycloconverter to obtain grid synchronized output current in phase with the grid voltage. The phase shift power modulation is used with auxiliary capacitor at the front-end multi-level inverter to have soft-switching. The phase shift between the HFL resonant current and half-wave cycloconverter input voltage is modulated to obtain grid synchronized output current.

A Battery Energy Storage interface for wind power systems with the use of grid side inverter

This paper presents a novel concept of Energy Storage System (ESS) interfacing with the grid side inverter in wind energy conversion systems. The inverter system used here is formed by cascading a 2-level inverter and a three level inverter through a coupling transformer. The constituent inverters are named as the “main inverter” and the “auxiliary inverter” respectively. The main inverter is connected with the rectified output of the wind generator while the auxiliary inverter is attached to a Battery Energy Storage System (BESS). The BESS ensures constant power dispatch to the grid irrespective of change in wind condition. Furthermore, this unique combination of BESS and inverter eliminates the need of additional dc-dc converters. Novel modulation and control techniques are proposed to address the problem of non-integer, dynamically-changing dc-link voltage ratio, which is due to random wind changes. Strategies used to handle auxiliary inverter dc-link voltage imbalances and controllers used to charge batteries at different rates are explained in detail. Simulation results are presented to verify the efficacy of the proposed modulation and control techniques in suppressing random wind power fluctuations.

A dual inverter with integrated energy storage for wind power systems

This paper explores the possibility of using grid side inverter as an interface to connect energy storage systems. A dual inverter system, formed by cascading two 2-level inverters through a coupling transformer, is used as the testing model. The inverters are named as “main inverter” and “auxiliary inverter”. The main inverter is powered by the rectified output of the wind generator while the auxiliary inverter is attached to a Battery Energy Storage System (BESS). If there is a surplus of wind power compared to the demand, then that would be stored in BESS while if there is a deficit in wind power then the demand will be satisfied by supplying power from the BESS. This enables constant power dispatch to the grid irrespective of wind changes. Novel modulation and control techniques are proposed to address the problem of non-integer, dynamically-varying dc-link voltage ratio, which is due to random wind changes. Furthermore, a maximum power tracking controller for this unique system is explained in detail. Simulation results verify the efficacy of proposed modulation and control techniques in suppressing random power fluctuations.

Connecting two wind turbine generators to the grid using only one three level NPC inverter

This paper explores the possibility of connecting two Wind Turbine Generators (WTG) to the grid using a single three level inverter. In the proposed system the rectified output of one WTG is connected across the upper dc-link capacitor of a standard diode clamped three level inverter. Similarly the rectified output of the other WTG is connected across the lower capacitor. This particular combination has several advantages such as, direct connection to the grid, reduced parts count, improved reliability and high power capacity. However, the major problem in the proposed system is the imminent imbalance of dc-link voltages. Under such conditions conventional modulation methods fail to produce desired voltage and current waveforms. A detailed analysis on this issue and a novel space vector modulation method, as the solution, are proposed in this paper. To track the Maximum power point of each WTG a power sharing algorithm is proposed. Simulation results are presented to attest the efficacy of the proposed system.

Dual inverter based battery energy storage system for grid connected photovoltaic systems

This paper explores a new breed of energy storage system interfacing for grid connected photovoltaic (PV) systems. The proposed system uses the popular dual inverter topology in which one inverter is supplied by a PV cell array and the other by a Battery Energy Storage System (BESS). The resulting conversion structure is controlled in a way that both demand matching and maximum power point tracking of the PV cell array are performed simultaneously. This dual inverter topology can produces 2, 3, 4 and 5 level inverter voltage waveforms at the dc-link voltage ratios of 0:1, 1:1, 2:1 and 3:2 respectively. Since the output voltage of the PV cell array and the battery are uncorrelated and dynamically change, the resulting dc-link voltage ratio can take non-integer values as well. These noninteger dc-link voltage ratios produce unevenly distributed space vectors. Therefore, the main issue with the proposed system is the generation of undistorted current even in the presence of unevenly distributed and dynamically changing space vectors. A modified space vector modulation method is proposed in this paper to address this issue and its efficacy is proved by simulation results. The ability of the proposed system to act as an active power source is also verified.

Space vector modulated cascade multi-level inverter for PMSG wind generation systems

Modulation and control of a cascade multilevel inverter, which has a high potential in future wind generation applications, are presented. The inverter is a combination of a high power, three level “bulk inverter” and a low power “conditioning inverter”. To minimize switching losses, the bulk inverter operates at a low frequency producing square wave outputs while high frequency conditioning inverter is used to suppress harmonic content produced by the bulk inverter output. This paper proposes an improved Space Vector Modulation (SVM) algorithm and a neutral point potential balancing technique for the inverter. Furthermore, a maximum power tracking controller for the Permanent Magnet Synchronous Generator (PMSG) is described in detail. The proposed SVM technique eliminates most of the computational burdens on the digital controller and renders a greater controllability under varying DC-link voltage conditions. The DC-link capacitor voltage balancing of both bulk and conditioning inverters is carried out using Redundant State Selection (RSS) method and is explained in detail. Experimental results are presented to verify the proposed modulation and control techniques.

Emotion as a boost to metacognition : how worry enhances the quality of confidence

Emotion and cognition are known to interact during human decision processes. In this study we focus on a specific kind of cognition, namely metacognition. Our experiment induces a negative emotion, worry, during a perceptual task. In a numerosity task subjects have to make a two alternative forced choice and then reveal their confidence in this decision. We measure metacognition in terms of discrimination and calibration abilities. Our results show that metacognition, but not choice, is affected by the level of worry anticipatedbefore the decision. Under worry individuals tend to have better metacognition in terms of the two measures. Furthermore understanding the formation of confidence is better explained with taking into account the level of worry in the model. This study shows the importance of an emotional component in the formation and the quality of the subjective probabilities.

Synthesis of biodegradable polymer-mesoporous silica composite microspheres for DNA prime-protein boost vaccination

DNA vaccines or proteins are capable of inducing specific immunity; however, the translation to the clinic has generally been problematic, primarily due to the reduced magnitude of immune response and poor pharmacokinetics. Herein we demonstrate a composite microsphere formulation, composed of mesoporous silica spheres (MPS) and poly(d,l-lactide-co-glycolide) (PLGA), enables the controlled delivery of a prime-boost vaccine via the encapsulation of plasmid DNA (pDNA) and protein in different compartments. Method with modified dual-concentric-feeding needles attached to a 40 kHz ultrasonic atomizer was studied. These needles focus the flow of two different solutions, which passed through the ultrasonic atomizer. The process synthesis parameters, which are important to the scale-up of composite microspheres, were also studied. These parameters include polymer concentration, feed flowrate, and volumetric ratio of polymer and pDNA-PEI/MPS-BSA. This fabrication technique produced composite microspheres with mean D[4,3] ranging from 6 to 34 μm, depending upon the microsphere preparation. The resultant physical morphology of composite microspheres was largely influenced by the volumetric ratio of pDNA-PEI/MPS-BSA to polymer, and this was due to the precipitation of MPS at the surface of the microspheres. The encapsulation efficiencies were predominantly in the range of 93-98% for pDNA and 46-68% for MPS. In the in vitro studies, the pDNA and protein showed different release kinetics in a 40 day time frame. The dual-concentric-feeding in ultrasonic atomization was shown to have excellent reproducibility. It was concluded that this fabrication technique is an effective method to prepare formulations containing a heterologous prime-boost vaccine in a single delivery system.

HFL PV micro-inverter with front-end current-fed converter and half-wave cycloconverter

A high-frequency-link micro inverter is proposed with a front-end dual inductor push-pull converter and a grid-connected half-wave cycloconverter. Pulse width modulation is used to control the front-end converter and phase shift modulation is used at the back-end converter to obtain grid synchronized output current. A series resonant circuit and high-frequency transformer are used to interface the front-end and the back-end converters. The operation of the proposed micro-inverter in grid-connected mode is validated using MATLAB/Simpower simulation. Experimental results are provided to further validate the operation.

How everyday language can and will boost effective information retrieval

Typing 2 or 3 keywords into a browser has become an easy and efficient way to find information. Yet, typing even short queries becomes tedious on ever shrinking (virtual) keyboards. Meanwhile, speech processing is maturing rapidly, facilitating everyday language input. Also, wearable technology can inform users proactively by listening in on their conversations or processing their social media interactions. Given these developments, everyday language may soon become the new input of choice. We present an information retrieval (IR) algorithm specifically designed to accept everyday language. It integrates two paradigms of information retrieval, previously studied in isolation; one directed mainly at the surface structure of language, the other primarily at the underlying meaning. The integration was achieved by a Markov machine that encodes meaning by its transition graph, and surface structure by the language it generates. A rigorous evaluation of the approach showed, first, that it can compete with the quality of existing language models, second, that it is more effective the more verbose the input, and third, as a consequence, that it is promising for an imminent transition from keyword input, where the onus is on the user to formulate concise queries, to a modality where users can express more freely, more informal, and more natural their need for information in everyday language.

MATLAB/Simulink simulation and C2000 code generation model for a grid-interactive 3-phase 4-wire inverter

This work is a MATLAB/Simulink model of a controller for a three-phase, four-wire, grid-interactive inverter. The model provides capacity for simulating the performance of power electroinic hardware, as well as code generation for an embedded controller. The implemented hardware topology is a three-leg bridge with a neutral connection to the centre-tap of the DC bus. An LQR-based current controller and MAF-based phase detector are implemented. The model is configured for code generation for a Texas Instruments TMS320F28335 Digital Signal Processor (DSP).

De-risking development of medium density housing to improve housing affordability and boost supply

Housing price inflation is a national concern given the serious decline in the number of low and middle income households able to purchase housing. In addition housing supply lags well behind demand. In Melbourne, urban consolidation policies explicitly seek intensification to promote housing supply but planning regulation is often criticised for being a significant cost driver for medium density housing. It is assumed that easing supply constraints will improve affordability. We suggest that laissez-faire planning exacerbates affordability issues because this approach fails to address the basic economic problem: the current inability of the market to efficiently match supply and demand in order to progress an orderly and de-risked development process. The role of “exchange” one of the four housing market sub-systems identified by Burke (2012) has until recently generally been ignored but our examination reveals significant economic transaction costs that manifest as development risks that impact on affordability. Fortunately these can be mitigated, but only if there is a more consumer driven supply response.

ACE Research Vignette 048: Can Policy Initiatives Boost High-Growth Entrepreneurs

This series of research vignettes is aimed at sharing current and interesting research findings from our team of international Entrepreneurship researchers. This vignette is written by Professor Erkko Autio at Imperial College (UK) with some editing by the Director of ACE, Professor Per Davidsson.

Micro inverter with a front-end current-fed converter

The reliability of micro inverters is an important factor as it would be necessary to reduce cost and maintenance of the small and medium scale distributed PV power conversion systems. Electrolytic capacitors and active power decouple circuits can be avoided in micro inverters with the use of medium voltage DC-link. Such a DC-link based micro inverter is proposed with a front-end dual inductor current-fed push-pull converter. The primary side power switches of the front-end converter have reduced switching losses due to multi-resonant operation. In addition, the voltage and current stresses on the diodes of the secondary diode voltage doubler rectifier are reduced due to the presence of a series resonant circuit in the front-end converter. The operation of the proposed micro inverter is explained using an in-depth analysis of the switching characteristics of the power semiconductor devices. The theoretical analysis of the proposed micro inverter is validated using simulation result.