Islanding detection in grid-connected power converters using harmonics due to the non-ideal behavior of the inverter

This paper analyzes the use of the voltage distortions in PWM voltage-source-inverters (VSIs) caused by the non-ideal behavior of the inverter for islanding detection purposes. The non-ideal characteristic of the inverters, mainly due to the dead-time needed to have safe commutations, produces fundamental frequency dependent harmonics (-5th, 7th...) in the output voltage. Although these harmonics are in principle an unwanted effect, since they reduce the power quality, they can potentially be used for islanding detection purposes. The physical principles of the method would be the same as for high frequency signal injection methods that have already been proposed but without the need of injecting a high frequency signa

Sensorless control of doubly-fed induction generators based on stator high frequency signal injection

High frequency signal injection based methods have been widely investigated for sensorless position/speed control of induction machines (IMs), permanent magnet synchronous machines (PMSMs) and more recently for doubly fed induction generators (DFIGs). When used with IMs and PMSMs, the high frequency signal is injected in the stator windings, an asymmetric (salient) rotor being required for this case. Contrary to this, both stator and rotor terminals are accessible and sensored in DFIGs, being therefore possible to inject the high frequency signal either in the stator or the rotor terminals. As consequence of this, the method can be used even if the machine is non-salient. In the implementation of the method with DFIGs, the high frequency voltage signal is typically injected in the rotor, the high frequency components (voltages of currents) induced in the stator being used for rotor position estimation. A drawback of this alternative is that the method is sensitive to the grid impedance in the stator side, which will be affected by the grid configuration, and is normally unknown. This paper proposes the sensorless control a DFIG injecting the high frequency voltage in the stator side, and using a high frequency current cancellation strategy in the rotor side. The main advantage of the proposed strategy is that the estimated position is independent of the grid characteristic

NanoFS: a hardware-oriented file system

NanoFS is a novel file system for embedded systems and storage-class memories (like flash) and is specially designed to be directly implemented in hardware. NanoFS is based on an original internal layout intended to achieve an optimal hardware implementation of the file system’s file lookup and data fetch operations. File system spe-cification on a sample reader module completely implemented in a pro-grammable device is introduced

Coordinated operation of parallel-connected inverters for active islanding detection using high frequency signal injection

The high frequency impedance measured at the terminals of inverters connected in a microgrid by means of the injection of a small magnitude, high frequency voltage, has been shown to be a reliable metric to detect islanding. While the implementation of this method is simple when only an inverter injects the high frequency signal, this case is of limited applicability. On the other hand, several concerns arise when multiple inverters work in parallel, primarily due to risk interference among inverters. Islanding detection using high frequency signal injection in microgrids with multiple parallel-connected inverters is studied in this paper. A strategy for the coordinated operation of the inverters, without the need of communications or pre-established roles is proposed. Simulation and experimental results will be provided to demonstrate the viability of the concep

Islanding detection in three-phase and single-phase systems using pulsating high frequency signal injection

This paper analyzes the use of pulsating high frequency signal injection for islanding detection purposes. Active islanding detection using high frequency signal injection is an appealing option due to its reduced non-detection zone, reduced cost and ease of implementation. The use of a rotating high frequency signal has been reported and analyzed. However, this method can only be applied to three-phase systems. In this paper, the use of a pulsating high frequency signal injection is proposed. While it uses the same principles as rotating signal injection, it can be applied to both threephase and single-phase system

Minimalistic SDHC-SPI hardware reader module for boot loader applications

This paper introduces a low-footprint full hardware boot loading solution for FPGA-based Programmable Systems on Chip. The proposed module allows loading the system code and data from a standard SD card without having to re-program the whole embedded system. The hardware boot loader is processor independent and removes the need of a software boot loader and the related memory resources. The hardware overhead introduced is manageable, even in low-range FPGA chips, and negligible in mid- and high-range devices. The implementation of the SD card reader module is explained in detail and an example of a multi-boot loader is offered as well. The multi-boot loader is implemented and tested with the Xilinx's Picoblaze microcontroller

Automated performance evaluation of skew-tolerant clocking schemes

In this paper the authors evaluate the timing and power performance of three skew-tolerant clocking schemes. These schemes are the well known master–slave clocking scheme (MS) and two schemes developed by the authors: Parallel alternating latches clocking scheme (PALACS) and four-phase parallel alternating latches clocking scheme (four-phase PALACS). In order to evaluate the timing performance, the authors introduce algorithms to obtain the clock waveforms required by a synchronous sequential circuit. Separated algorithms were developed for every clocking scheme. From these waveforms it is possible to get parameters such as the non-overlapping time and the clock period. They have been implemented in a tool and have been used to compare the timing performance of the clocking schemes applied to a simple circuit. To analyse the power consumption the authors have electrically simulated a simple circuit for several operation frequencies. The most remarkable conclusion is that it is possible to save about 50% of the power consumption of the clock distribution network by using PALACS.Ministerio de Ciencia y Tecnología TEC 2004-00840/MI

Combining H-FABP and GFAP increases the capacity to differentiate between CT-positive and CT-negative patients with mild traumatic brain injury

Mild traumatic brain injury (mTBI) patients may have trauma-induced brain lesions detectable using CT scans. However, most patients will be CT-negative. There is thus a need for an additional tool to detect patients at risk. Single blood biomarkers, such as S100B and GFAP, have been widely studied in mTBI patients, but to date, none seems to perform well enough. In many different diseases, combining several biomarkers into panels has become increasingly interesting for diagnoses and to enhance classification performance. The present study evaluated 13 proteins individually—H-FABP, MMP-1, MMP-3, MMP-9, VCAM, ICAM, SAA, CRP, GSTP, NKDA, PRDX1, DJ-1 and IL-10—for their capacity to differentiate between patients with and without a brain lesion according to CT results. The best performing proteins were then compared and combined with the S100B and GFAP proteins into a CT-scan triage panel. Patients diagnosed with mTBI, with a Glasgow Coma Scale score of 15 and one additional clinical symptom were enrolled at three different European sites. A blood sample was collected at hospital admission, and a CT scan was performed. Patients were divided into two two-centre cohorts and further dichotomised into CT-positive and CT-negative groups for statistical analysis. Single markers and panels were evaluated using Cohort 1. Four proteins—H-FABP, IL-10, S100B and GFAP—showed significantly higher levels in CT-positive patients. The best-performing biomarker was H-FABP, with a specificity of 32% (95% CI 23–40) and sensitivity reaching 100%. The best-performing two-marker panel for Cohort 1, subsequently validated in Cohort 2, was a combination of H-FABP and GFAP, enhancing specificity to 46% (95% CI 36–55). When adding IL-10 to this panel, specificity reached 52% (95% CI 43–61) with 100% sensitivity. These results showed that proteins combined into panels could be used to efficiently classify CT-positive and CT-negative mTBI patients

Dynamic behavior of current controllers for selective harmonic compensation in three-phase active power filters

Current regulators are a critical part of active power filters (APFs). The design of current regulators capable of compensating high-frequency harmonics created by nonlinear loads is a challenging task. Selective harmonic current compensation using harmonic regulators is a viable method to achieve this goal. However, their design and tuning is not an easy task. The performance-and even the stability-of harmonic current regulators strongly depends on implementation issues, with the tuning of the controller gains being critical. Furthermore, the presence of multiple current regulators working in parallel can create unwanted couplings with the fundamental current regulator, which can result in a deterioration of APF current control, i.e., oscillations and settling times larger than expected. This paper addresses the design and tuning of selective harmonic compensators, with a focus on their stability analysis and transient behavio

Operation of modular multilevel converters under voltage constraints

MMCs are normally designed to operate in the linear region of the PWM. This limits the peak-to-peak phase voltage in the AC port to be lower than the DC port voltage. It is possible to increase the AC voltage beyond this limit by the use of overmodulation strategies. However, this is at the price of an increase in the harmonic content (THD) of the voltages and currents, and consequently, of a decrease of the power quality. While this type of operation is not desired in normal conditions, there are exceptional circumstances in which the MMC could be forced to operate in this mode. These would include transient anomalies, e.g. a temporary decrease of the DC port voltage or a temporary increase of the AC port voltage, or quasi-permanent conditions, e.g. the failure (and subsequent disconnection) of one or more cells in one or more arms of the MMC. Under this circumstances, the voltage margin between the DC and the AC port voltages required for the normal operation of the MMC might be lost. Consequently, the MMC should operate in the overmodulation region, or turned-off otherwise. This paper addresses the use of overmodulation techniques in MMC under voltage constraints. Under these circumstances, the MMC control should guarantee stable operation, (i.e. a controlled power transfer between the DC and AC ports with the cell voltages maintained at their target values) and minimize the distortion of the currents, and consequently the adverse effect on the power qualit