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Towards a Portable Human Gait Analysis & Monitoring System
No full textHuman Gait analysis is useful in many cases, such as, detecting the underlying cause of an abnormal gait, rehabilitation of subjects suffering from motor related diseases such as Parkinson's disease or Cerebral Palsy, improving the athletic performance of sports person etc. However, gait analysis has seen limited usage, especially in developing countries, because of the high cost involved in setting up a gait laboratory. We present a portable gait analysis system using Inertial Measurement Unit (IMU) sensors to collect movement data and a Smart-phone to process it. IMU sensors has gained significant popularity in the last few years as viable option for gait analysis because its low cost, small size and ease of use. Using the accelerometer and gyroscope data from 3 EXLS3 IMU sensors (on thigh, shank and foot), we measure kinematic angles in the sagittal plane and detect Heel Strike (HT) and Toe Off (TO) events using methods based on 11] and 4] respectively. To measure the accuracy of our system, we compare it with an Optical Gait Analysis system, which is the current gold standard for gait analysis 1. We measure the gait parameters for 3 healthy individuals belonging to different age group and achieve an RMSE of 4:739 degrees +/- 1:961 degrees, 3:7 degrees +/- 3:02 degrees and 4:12 degrees +/- 1:21 degrees for Knee Flexion Extension, Ankle Dorsi Flexion respectively and Hip Flexion Extension respectively. We measure the Heel Strike and Toe Off using shank and foot mounted sensor independently. 34:5 +/- 28:3 ms and 27:5 +/- 32:8 ms is the RMSE for HT calculated by shank and foot sensor w. r. t. optical system respectively. The RMSE for Toe Off is 36:2 +/- 36:8 ms and 37:5 +/- 35:9 ms for shank and foot sensor w. r. t. optical system respectively
Resonance based Current-fed Isolated DC/DC Converter for High Voltage Applications
No full textThis paper presents a novel resonance based modulation strategy for a full-bridge current-fed isolated DC/DC converter for high voltage applications. Output regulation is obtained using variable frequency modulation on the primary side to compensate for line and load variations. A two-step method is used for current commutation and usage of active clamp based snubbers are avoided. Circuit operation under different operating modes in steady state are described in detail. Closed firm expression for the converter gain and other values of interest are derived using state plane concepts. The presence of a discontinuous conduction mode is discussed and the mode boundary is identified. Design steps for arriving at the component values of the converter based on set of specifications is discussed. Proposed concept, operation and derived closed form expressions are validated through simulation
Pole Changing Wide Speed Range Induction Motor Drive for Electric Vehicles
No full textThe paper presents a two phase variable speed induction motor drive for wide speed application. The drive is designed to meet drive cycle requirements of Worldwide harmonized Light vehicles Test Procedure (WLTP). The required torque speed specifications of the induction machine are obtained from the drive cycle. The wide speed range operation of the drive obtained by pole changing technique. The proposed induction motor drive system consists of an online pole changing two phase induction motor which is driven using a four leg voltage source converter. Using the voltage source converter currents are controlled in certain coil groups of the machine to enable operation as two pole and four pole motor. The paper describes the windings configuration and operation of the two phase induction machine drive
Multicomponent 2-D AM-FM Modeling of Speech Spectrograms
No full textIn contrast to 1-D short-time analysis of speech, 2-D modeling of spectrograms provides a characterization of speech attributes directly in the joint time-frequency plane. Building on existing 2-D models to analyze a spectrogram patch, we propose a multicomponent 2-D AM-FM representation for spectrogram decomposition. The components of the proposed representation comprise a DC, a fundamental frequency carrier and its harmonics, and a spectrotemporal envelope, all in 2-D. The number of harmonics required is patch-dependent. The estimation of the AM and FM is done using the Riesz transform, and the component weights are estimated using a least-squares approach. The proposed representation provides an improvement over existing state-of-the-art approaches, for both male and female speakers. This is quantified using reconstruction SNR and perceptual evaluation of speech quality (PESQ) metric. Further, we perform an overlap-add on the DC component, pooling all the patches and obtain a time-frequency (t-f) a periodicity map for the speech signal. We verify its effectiveness in improving speech synthesis quality by using it in an existing state-of-the art vocoder
An Uni-directional Single-Phase Soft-switched Resonant High Frequency Link Inverter
No full textRenewable and alternate energy grid integration is an area of interest in the recent years due to the advancements made in Solar and Fuel Cells. This paper considers a single stage single phase uni-directional High-Frequency Transformer (HFT) link DC-AC converter for grid integration of Distributed Energy Resources (DER). The HFT helps by providing galvanic isolation to protect DER from single faults at significantly low cost and size in comparison with Low Frequency Transformer (LET). Resonant based power conversion in relatively high voltage DC-DC converters results in higher efficiency and power density. Soft switching due to device capacitances and HFT parasitic leakage inductances enables high frequency of operation. This paper presents a novel Parallel Resonant Converter (PRC) based control strategy that results in high quality adjustable frequency and amplitude AC and soft switching of all devices in the entire range of operation. A well-known single stage isolated inverter topology is slightly modified to incorporate PRC based operation. Simulation results are presented to validate the topology and proposed modulation scheme
Stator Flux Based Model Reference Adaptive Observers for Rotor Position and Speed Estimation in Doubly-Fed Induction Machines
No full textSensorless estimation of speed is preferred for Doubly-Fed Induction Generator (DUG) used in wind energy conversion systems, in view of cost, maintenance, cabling and reliability issues. This paper proposes two stator flux based Model Reference Adaptive Observers (MRAO) for rotor position and speed estimation in doubly-fed induction machines. The cross product of reference and estimated stator flux linkage vectors is fed as controller input in the existing method, thereby making the observer model non-linear. The first proposed method, which is based on notch filtering, offers a performance comparable to that of the existing method, while reducing the number of voltage and current sensors required. The second method linearizes the observer model, leading to superior dynamic performance over the existing methods. This also simplifies the design of the controller. Simulations and experiments are performed on a 10 HP DFIG coupled to a Squirrel Cage Induction Motor (SCIM)
Impact of PLL on Harmonic Stability of Renewable Dominated Power System: Modeling and Analysis
No full textFor reliable operation of power system, the system should be stable not only in the fundamental domain but also in harmonic domain. Power electronic converters of renewable generators inject harmonics into the power systems. So, at higher renewable penetration levels, study of power system stability in harmonic domain i.e. harmonic stability is required. The Phase Locked Loop(PLL) is used for grid synchronization of renewable generators. PLL affects the dynamic behavior of power electronic converters in harmonic domain also. This paper analyzes the impact of PLL on the harmonic stability of renewable dominated power systems. A small signal state space model is developed for PLL in harmonic domain to analyze the behavior of PLL. The obtained state space model is a periodic Linear Time Varying (PLTV) system, making the state space model of the whole power systems also a PLTV system. As the obtained state matrix is periodic in nature, the concept of time varying eigen-values is employed to analyze the harmonic stability. The standard IEEE-39 bus system is modified to enable high renewable penetration level and the modified system is used to carryout the harmonic stability analysis. Impact of PLL parameters on harmonic stability is analyzed using the modified IEEE 39 Bus system. The impact of renewable penetration level on harmonic stability for given PIA, parameters is also analyzed. It is observed that the PLL parameters and renewable penetration level have impact on the harmonic stability of power system
Simplified Input Voltage Sensorless Vector Control for PWM Rectifiers
No full textInput voltage information is essential lift vector control of three-phase active pulse-width modulated (PWM) rectifier. Input voltage sensors impact cost, size and reliability of the PWM rectifier. Existing input voltage sensorless methods either involve extensive mathematical computations to estimate the input voltage or have a control structure significantly different from that of conventional vector control. This work proposes an input voltage sensorless control of PWM rectifier which retains the simplicity of vector control and also reduces the computation requirement. Modelling and analysis of the rectifier system with the proposed phase locked loop (PLL) are presented. The design procedure for the PLL is detailed, and is validated through frequency domain studies. Performance of the proposed method is compared with that of conventional sensor based vector control through simulations and experiments. The responses of both are found to be almost indistinguishable while the proposed method is shown to require reduced computational effort
An Algorithm - Architecture Co-Designed System for Dynamic Execution-Driven Pre-Silicon Verification
No full textIn EDA industry, functional verification of a design-under-test (DUT) has been pre-dominantly performed through software based simulation. However, the never-ending growth of DUT size rapidly degrades their execution speed which, in turn, escalates the verification effort. This manifests the requirement for random dynamic simulation, using which only the typical behaviors, and not all possible behaviors of a chip can be verified in a time-bound simulation run. To overcome this bottleneck, the EDA industry is increasingly adopting ``hardware-accelerated simulation platforms'', which are classified as simulation-accelerators, emulators and FPGA prototypes. These platforms still do not address the state-space problem effectively, as they work in cycle-driven or event-driven mode. They also require huge design porting effort to the native development environment. Hence, the need of the hour is a simulator that needs to be design-aware enough to partition and map huge data-flow-graphs (DFGs) of scientific applications, at each abstraction level of verification and schedule it for simulation. In this paper, we present a novel approach for dynamic pre-silicon verification, called EX-DRIVE (execution-driven functional verification methodology). It addresses the state-space explosion problem in verification by hosting a variety of partitioning and mapping algorithms. We show that the proposed functional-verification flow achieves significant improvement in verification performance over industry standard simulators
Defect-Assisted Safe Operating Area Limits and High Current Failure in Graphene FETs
No full textIn this work, a unique measurement setup, involving integration of transmission line pulse tester with Raman spectrometer, is used to investigate the pulsed safe operating area (SOA) boundary of graphene field effect transistors (GFETs). Physical insight into various SOA boundaries, i.e., near-electrical, electro-thermal and thermal, is given. Unique defect-assisted degradation in channel and its correlation with the carrier transport as well as failure is revealed, with the help of electrical as well as Raman spectroscopy based investigations during well controlled pulse-stressing of GFETs. The SOA and power to fail dependency on carrier concentration and nature of carrier transport is addressed