Recently NAFU SA and other role players expressed some criticism about government programmes. The criticism was not so much about the objectives and content of these programmes, but rather about their accessibility, or lack thereof, to emerging farmers.

What about the messenger

I introduce batman, a Python package for modeling exoplanet transit light curves. The batman package supports calculation of light curves for any radially symmetric stellar limb darkening law, using a new integration algorithm for models that cannot be quickly calculated analytically. The code uses C extension modules to speed up model calculation and is parallelized with OpenMP. For a typical light curve with 100 data points in transit, batman can calculate one million quadratic limb-darkened models in 30 seconds with a single 1.7 GHz Intel Core i5 processor. The same calculation takes seven minutes using the four-parameter nonlinear limb darkening model (computed to 1 ppm accuracy). Maximum truncation error for integrated models is an input parameter that can be set as low as 0.001 ppm, ensuring that the community is prepared for the precise transit light curves we anticipate measuring with upcoming facilities. The batman package is open source and publicly available at https://github.com/lkreidberg/batman. Subject headings: methods: data analysis – methods: numerical

batman: BAsic Transit Model cAlculatioN in Python

Multilevel inverters (MLIs) are being used in wide range of power electronic applications. These converters have attracted a lot of attention during recent years and exist in different topologies with similar basic concepts. This paper presents five main submodules (SMs) to be used as the basic structures of MLIs. The paper reviews the common MLI topologies from the structural point of view. The topologies are divided into the different SMs to show conventional MLI configurations and future topologies that can be created from the main SMs. A comparative study between different topologies is performed in detail. The MLIs are categorized and investigated with from different perspectives such as the number of components, the ability to create inherent negative voltage, working in regeneration mode and using single dc source.

A General Review of Multilevel Inverters Based on Main Submodules: Structural Point of View

Doppler spectroscopy has uncovered or confirmed all the known planets orbiting nearby stars. Two main techniques are used to obtain precision Doppler measurements at optical wavelengths. The first approach is the gas cell method, which consists on the least-squares matching of the spectrum of Iodine imprinted on the spectrum of the star. The second method relies on the construction of a stabilized spectrograph externally calibrated in wavelength. The most precise stabilized spectrometer in operation is HARPS, operated by ESO in La Silla Observatory/Chile. The Doppler measurements obtained with HARPS are typically obtained using the Cross-Correlation Function technique (CCF). It consists of multiplying the stellar spectrum with a weighted binary mask and finding the minimum of such product as a function of the Doppler shift. It is known that CCF is suboptimal in exploiting the Doppler information in the stellar spectrum. Here, we describe an algorithm to obtain precision RV measurements using least-squares matching of each observed spectrum to a high signal-to-noise ratio template derived from the same observations. Such algorithm is implemented in our software called HARPS-TERRA (Template Enhanced Radial velocity Re-analysis Application). New radial velocity measurements on a representative sample of stars observed by HARPS is used to illustrate the benefits of the proposed method. We show that, compared to CCF, template matching provides a significant improvement in accuracy, specially when applied to M dwarfs.

The HARPS-TERRA project I. Description of the algorithms, performance and new measurements on a few remarkable stars observed by HARPS

In this paper, finite-set model-predictive control (FS-MPC) methodologies for a grid-connected three-level neutral-point-clamped converter are investigated. The proposed control strategies produce fixed switching frequency, maintaining all the advantages of predictive control such as fast dynamic response, inclusion of nonlinearities and restrictions, and multivariable control using a single control loop. The first of the proposed FS-MPC strategies is based on a multiobjective cost function, designed to regulate both the inverter currents and the balancing of the dc-link capacitor voltages. The second FS-MPC strategy is derived from the first one, and it is based on a cost function that regulates only the grid current, with the balancing of the capacitor voltages being realized by controlling the duty cycles of the redundant vectors. The proposed control systems are experimentally validated using a 5-kW prototype. The experimental results show a good performance for both strategies, in steady-state and transient response, with a total harmonic distortion lower than $\text{2}\%$ for the currents supplied to the grid.

Finite-Set Model-Predictive Control Strategies for a 3L-NPC Inverter Operating With Fixed Switching Frequency

This paper presents a new enhanced single-stage two-step Continuous Control Set Model Predictive Control (CCS-MPC) algorithm, for Modular Multilevel Converters (MMCs) operating with variable output frequency at the AC port. The proposed two-step CCS-MPC allows the implementation of feed-forward compensation of the one-step ahead perturbations at the AC side, using an algorithm based on the Moore-Penrose pseudoinverse matrix. Limitations of the current and voltages in the MMC clusters are implemented to avoid overmodulation and overcurrents, being the solution of the constrained CCS-MPC online solved using the active-set method. Without losing generality, the experimental validation of the single-stage CCS-MPC is performed using an 18-cell MMC prototype, driving a 7.5 kW cage induction machine operating in a wide speed range. A dSPACE MicroLabBox platform is used to control the MMC-based drive by implementing the CCS-MPC algorithm, the modulation stage and the active-set method. It is experimentally demonstrated that the compensation of the low-frequency perturbations allows a considerable reduction in the required circulating currents at the low-frequency operation of the drive. Reduction in the capacitor voltage ripple, improved efficiency, and a smaller Total Harmonic Distortion (THD) in the output currents are also achieved with the proposed single-stage two-step CCS-MPC. 

A Two-Step Continuous-Control-Set MPC for Modular Multilevel Converters Operating with Variable Output Voltage and Frequency

Modular Multilevel Converters (MMC) are becoming increasingly popular for HVDC applications and in medium voltage grids and drives. On the contrary, in high-speed low-voltage drives MMCs are typically not considered a good option due to their relatively low power density. In this paper, a new topology is proposed, enhancing the MMC by coupling upper and lower arm sub-modules via Dual Active Bridge (DAB) converters, leading to a sensible reduction of the sub-module capacitance whilst keeping low control complexity. The resulting topology is applied to a high-speed low voltage permanent magnet drive, analyzing the drive startup and its practical operation. Finally, the theoretical claims are validated with simulation results.

Improved Modular Multilevel Converter topology for low voltage variable speed drives

Low-frequency AC transmission systems have been suggested as a suitable option for high-power transmission as they offer advantages compared to conventional high-voltage AC or high-voltage DC transmission systems. However, this application requires direct AC-AC conversion at high power-voltage ratios. In the context of high-power converters, several publications have been made on the Modular Multilevel Cascaded Converters, characterised as topologies with high voltage levels, full scalability, increased flexibility of control, and both high power and energy quality. Therefore, this paper studies a new topology for a Low-Frequency AC transmission system referred to as Shunt-Series Modular Multilevel Converter, a decoupled control strategy is proposed and simulation results are presented and analysed.

Control of a Shunt-Series Modular Multilevel Converter for Low-Frequency AC Transmission Systems

This article presents the implementation of a Dual Active Bridge converter with Single Phase Shift modulation, capable of controlling current and voltage at the converter output independently, through the design of simple PI controllers based on the model's transfer functions small phasor signal. It is validated in a 1 kW converter prototype, whose main passive components are designed and the graphs of the current and voltage controls at the output of the converter are obtained as an experimental result.

Design and implementation of dual active bridge converter with single phase shift modulation for electric vehicle charging system

Hybrid Alternating Current (AC) and Direct Current (DC) microgrids have been in the spotlight in the last years because they allow connection of AC and DC resources and reduces multiple power conversion in single AC or DC microgrids. The AC and DC stages are connected through interlinking converters, which manage the power transference among both sub-microgrids using droop control strategies for each single AC or DC microgrid. This paper proposes a threestage droop control strategy to regulate the power inside the sub-microgrids at the same time that bidirectional AC-DC power transference is enabled. Simulation results obtained with a hybrid microgrid model composed of five generation units are presented to validate the effectiveness of this proposal..

Matias Diaz

Papers

A Two-Step Continuous-Control-Set MPC for Modular Multilevel Converters Operating with Variable Output Voltage and Frequency

Improved Modular Multilevel Converter topology for low voltage variable speed drives

Control of a Shunt-Series Modular Multilevel Converter for Low-Frequency AC Transmission Systems

Design and implementation of dual active bridge converter with single phase shift modulation for electric vehicle charging system

A Droop Based Control Strategy for Bidirectional Power Regulation in Hybrid ACmC Microgrids