Juan Ramon Hermoso

Multiple second order generalized integrators for harmonic synchronization of power converters

This paper presents a new frequency-adaptive synchronization method for grid-connected power converters which allows estimating not only the positive- and negativesequence components of the power signal at the fundamental frequency, but also other sequence components at multiple frequencies. The proposed system is called the MSOGI-FLL since it is based on a decoupled network consisting of multiple second order generalized integrators (MSOGI) which are frequency-adaptive by using a frequency-locked loop (FLL). In this paper, the MSOGI-FLL is analyzed and its performance is evaluated by both simulations and experiments.

Grid Voltage Synchronization for Distributed Generation Systems Under Grid Fault Conditions

The actual grid code requirements for the grid connection of distributed generation systems, mainly wind and photovoltaic (PV) systems, are becoming very demanding. The transmission system operators (TSOs) are especially concerned about the low-voltage-ride-through requirements. Solutions based on the installation of STATCOMs and dynamic voltage regulators (DVRs), as well as on advanced control functionalities for the existing power converters of distributed generation plants, have contributed to enhance their response under faulty and distorted scenarios and, hence, to fulfill these requirements. In order to achieve satisfactory results with such systems, it is necessary to count on accurate and fast grid voltage synchronization algorithms, which are able to work under unbalanced and distorted conditions. This paper analyzes the synchronization capability of three advanced synchronization systems: the decoupled double synchronous reference frame phase-locked loop (PLL), the dual second order generalized integrator PLL, and the three-phase enhanced PLL, designed to work under such conditions. Although other systems based on frequency-locked loops have also been developed, PLLs have been chosen due to their link with dq0 controllers. In the following, the different algorithms will be presented and discretized, and their performance will be tested in an experimental setup controlled in order to evaluate their accuracy and implementation features.

Current control method for distributed generation power generation plants under grid fault conditions

The operation of distributed power generation systems under grid fault conditions is a key issue for the massive integration of renewable energy systems. Several studies have been conducted to improve the response of such distributed generation systems under voltage dips. In spite of being less severe, unbalanced fault cause a great number of disconnections, as it may produce the injection of unbalanced currents that can easily conduct to the tripping of the converter. In this paper a current control strategy for power converters able to deal with these grid conditions, without exceeding the current ratings of the converter is introduced. Moreover, a novel flexible algorithm has been proposed in order to regulate easily the injection of positive and negative currents for general purpose applications.

Registration of X-rays at 2500 m altitude in association with lightning flashes and thunderstorms

Electric fields and high-energy radiation of natural lightning measured at close range from a mountaintop tower are discussed. In none of the 12 negative cloud-to-ground upward flashes were X-rays observed. Also no energetic radiation was found in one negative upward leader at close range (20?m). In the first of two consecutive negative cloud-to-ground flashes, X-rays were detected during the last ~1.75?ms of the leader. During the time of energetic radiation in the flash an intense burst of intracloud VHF sources was located by the interferometers. The X-ray production is attributed to the high electric field runaway electron mechanism during leader stepping. Even though the second flash struck closer than the previous one, no X-rays were detected. The absence of energetic radiation is attributed to being outside of the beam of X-ray photons from the leader tip or to the stepping process not allowing sufficiently intense electric fields ahead of the leader tip. High-speed video of downward negative leaders at the time when X-rays are commonly detected on the ground revealed the increase of speed and luminosity of the leader. Both phenomena allow higher electric fields at the leader front favoring energetic radiation. Background radiation was also measured during thunderstorms. The count rate of a particular day is presented and discussed. The increases in the radiation count rate are more coincident with radar reflectivity levels above ~30 dBZ than with the total lightning activity close to the site. The increases of dose are attributed to radon daughter-ion precipitation

Improving long line stability by integrating renewables using static synchronous generators

Daily increasing in renewable energy sources installed in dispersed location, has led to greater need for long transmission lines to use these green sources. Voltage and phase stability are major challenges for transmission system operators in the operation of these lines. In this paper, a Static Synchronous Generators based in Synchronous Power Controller (SSG-SPC) is presented and implemented in a long AC transmission system in order to reducing stability problems. Power control strategies, compatibility with the grid codes and improvement in voltage and phase stability by SSG-SPC are investigated. Simulations and Experimental test results confirms SSG-SPC capability for participation in reactive compensation, damping active power oscillations and modify stability margins.

Phase stability enhancement in big power networks using renewable generation units controlled by SPC

High penetration of Renewable Generation Units (RGU), has led to that the interaction of this newfound participators in power network with conventional units be more critical challenges for network operators. Effect on the phase stability in emplacement as well as on neighbor generation units is one of this essential challenges. In this paper, a RGU controlled by Synchronous Power Controller (SPC) which behaves as a big Static Synchronous Generation (SSG-SPC) units, are presented as solution to cope with this challenge. Small signal modelling of a power network in presence of SSG-SPC unit is used to analysis this solution. After illustrating SPC dynamic capabilities, study on IEEE-14B test system based on modal analysis, time domain investigation and real time test confirms that a SSG-SPC not only has not damaging impact on phase stability and dynamic of network, but on the contrary can improve it. Moreover, by having at least two dynamic freedom degrees in SPC, the SSG-SPC can adapt itself for keeping this improvement effect.

Synchronous power controller merits for dynamic stability improvement in long line by renewables

Growing universal demand for greater use of renewable energy resources (RES) installed in dispersed location, has caused to more urgent need for long transmission systems to use these green sources. Small signal stability is one of vital challenges for transmission system operators in presence of big RES. In this paper, a Static Synchronous Generators based in Synchronous Power Controller (SSG-SPC) is presented and its capabilities for dynamic stability enhancement in a long AC transmission system is investigated. Dynamic modelling of a long line and then study in Uncompensated and Compensated cases by using time domain simulation and modal analysis, and then experimental test confirms that SSG-SPC can be effective in active damping of power oscillations and reducing small signal stability challenges.

High-speed videos of laboratory leaders emerging from wind turbine blade tips

This paper presents some observation results of the attachment test of a wind turbine blade as described in the upgrade of the IEC-61400-24. The optical observations were performed by means of high-speed video and UV-sensitive photo camera. This study investigates the effects on the leaders emerging from the blade comparing three different air-terminals: discrete receptors, discrete receptors with diverter strips and metallic tip. In the first two types, salt mist pollution was applied to the blade. For non polluted tips positive leaders appeared from receptors towards the ground avoiding the blade surface. When the blade was polluted additional leaders emerged moving horizontally. Moreover, in this situation the leader progressed on the blade surface. Pollution also produced the inception of more leaders when the blade was equipped with discrete receptors and diverter strips.

A propagative model for simulations of electric fields produced by downward leaders

This paper presents simulations of a downward negative leaders performed by means of 3D finite element method (FEM). The leaders are considered do progress vertically leaders in which different charge distributions and leader speeds can be adjusted. The output of the model is the electric field at ground level for different leader heights and time. By comparison with experimental measurements of natural cloud-to-ground stepped leaders we find consistent results by adjusting the speed of the leader.