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).

Electron- Spin-Resonance studies of phase transitions in double propionates

Detailed ESR investigations of Mn2+ substituting for Ca2+ in Ca2Sr(C2H5COO)6, (DSP) and Ca2Pb(C2H5COO)6, (DLP) and Ca2Ba(C2H5COO)6, (DBP), in single crystals and powders, over the temperature range from 300°C to -180°C have been carried out to study the successive phase transitions in these compounds. Spectra have been analyzed in terms of axial spin Hamiltonians and the temperature dependences of the parameters studied. Across the I-II transition, new physically and chemically inequivalent sites appear indicating the disappearance of the diad axes on which the propionate groups are located, bringing out the connection between the motional states of the propionate groups and the occurrence of ferroelectricity. The II-III transition also causes chemically inequivalent sites to develop, indicating that the transitions may not be isomorphous as believed previously. Similarities and dissimilarities of the ESR spectra of DLP, DSP and DBP are discussed in relation to the phase transitions.

ESR studies of phase transitions in double propionates

Detailed ESR investigations of Mn2+ substituting for Ca2+ in Ca2Sr(C2H5COO)6 (DSP), Ca2Pb(C2H5COO)6 (DLP) and Ca2Ba(C2H5COO)6 (DBP), in single crystals and powders, over the temperature range from 200°C to -180°C have been carried out to study the successive phase transitions in these compounds. (DSP: [Tetragonal] ← 8.5°C → [tetragonal, ferroelectric] [tetragonal] ← -169°C → [monoclinic, ferroelectric]; DLP : [tetragonal] ← 60°C → [tetragonal, ferroelectric] ← -71.5°C → [monoclinic, ferroelectric]; [Cubic] ← -6°C → [orthorhombic] ← -75°C → [?]). Spectra have been analysed in terms of axial spin Hamiltonians and the temperature dependences of the parameters studied. In DSP and DLP across the I ↔ II transition, new physically and chemically inequivalent sites appear indicating the disappearance of the diad axes on which the propionate groups are located, bringing out the connection between the motional states of the propionate groups and the occurence of ferroelectricity. The II ↔ III transition also causes chemically inequivalent sites to develop, indicating that the transitions may not be isomorphous as believed previously. In DBP, the -6°C transition leads to (i) a doubling of both physically and chemically inequivalent sites (ii) a small (150 G at -6°C to 170 G at -8°C), but abrupt change in the magnitude of the zero-field splitting tensor D, and (iii) displacements of the orientations of the D tensors. Results are interpreted in terms of alternate rotations of the oxygen octahedra, showing participation of the carboxyl oxygens in the transition. No drastic changes in the parameters occur across the -75°C transition consistent with its second order nature. Similarities and dissimilarities of the ESR spectra of the three compounds in relation to the phase transitions, are discussed.

Harmful algae in the planktonic food web of the Baltic Sea

This study deals with algal species occurring commonly in the Baltic Sea: haptophyte Prymnesium parvum, dinoflagellates Dinophysis acuminata, D. norvegica and D. rotundata, and cyanobacterium Nodularia spumigena. The hypotheses are connected to the toxicity of the species, to the factors determining toxicity, to the consequences of toxicity and to the transfer of toxins in the aquatic food web. Since the Baltic Sea is severely eutrophicated, the fast-growing haptophytes have potential in causing toxic blooms. In our studies, the toxicity (as haemolytic activity) of the haptophyte P. parvum was highest under phosphorus-limited conditions, but the cells were toxic also under nitrogen limitation and under nutrient-balanced growth conditions. The cellular nutrient ratios were tightly related to the toxicity. The stoichiometric flexibility for cellular phosphorus quota was higher than for nitrogen, and nitrogen limitation led to decreased biomass. Negative allelopathic effects on another algae (Rhodomonas salina) could be observed already at low P. parvum cell densities, whereas immediate lysis of R. salina cells occurred at P. parvum cell densities corresponding to natural blooms. Release of dissolved organic carbon from the R. salina cells was measured within 30 minutes, and an increase in bacterial number and biomass was measured within 23 h. Because of the allelopathic effect, formation of a P. parvum bloom may accelerate after a critical cell density is reached and the competing species are eliminated. A P. parvum bloom indirectly stimulates bacterial growth, and alters the functioning of the planktonic food web by increasing the carbon transfer through the microbial loop. Our results were the first reports on DSP toxins in Dinophysis cells in the Gulf of Finland and on PTX-2 in the Baltic Sea. Cellular toxin contents in Dinophysis spp. ranged from 0.2 to 149 pg DTX-1 cell-1 and from 1.6 to 19.9 pg PTX-2 cell-1 in the Gulf of Finland. D. norvegica was found mainly around the thermocline (max. 200 cells L-1), whereas D. acuminata was found in the whole mixed layer (max. 7 280 cells L-1). Toxins in the sediment trap corresponded to 1 % of DTX-1 and 0.01 % PTX-2 of the DSP pool in the suspended matter. This indicates that the majority of the DSP toxins does not enter the benthic community, but is either decomposed in the water column, or transferred to higher trophic levels in the planktonic food chain. We found that nodularin, produced by Nodularia spumigena, was transferred to the copepod Eurytemora affinis through three pathways: by grazing on filaments of small Nodularia, directly from the dissolved pool, and through the microbial food web by copepods grazing on ciliates, dinoflagellates and heterotrophic nanoflagellates. The estimated proportion of the microbial food web in nodularin transfer was 22-45 % and 71-76 % in our two experiments, respectively. This highlights the potential role of the microbial food web in the transfer of toxins in the planktonic food web.

RECONNECT: A NoC for polymorphic ASICs using a low overhead single cycle router

A polymorphic ASIC is a runtime reconfigurable hardware substrate comprising compute and communication elements. It is a ldquofuture proofrdquo custom hardware solution for multiple applications and their derivatives in a domain. Interoperability between application derivatives at runtime is achieved through hardware reconfiguration. In this paper we present the design of a single cycle Network on Chip (NoC) router that is responsible for effecting runtime reconfiguration of the hardware substrate. The router design is optimized to avoid FIFO buffers at the input port and loop back at output crossbar. It provides virtual channels to emulate a non-blocking network and supports a simple X-Y relative addressing scheme to limit the control overhead to 9 bits per packet. The 8times8 honeycomb NoC (RECONNECT) implemented in 130 nm UMC CMOS standard cell library operates at 500 MHz and has a bisection bandwidth of 28.5 GBps. The network is characterized for random, self-similar and application specific traffic patterns that model the execution of multimedia and DSP kernels with varying network loads and virtual channels. Our implementation with 4 virtual channels has an average network latency of 24 clock cycles and throughput of 62.5% of the network capacity for random traffic. For application specific traffic the latency is 6 clock cycles and throughput is 87% of the network capacity.

Robust flight stability and control for micro air vehicles.

This chapter presents the real time validation of fixed order robust 112 controller designed for the lateral stabilisation of a micro air vehicle named Sarika2. Digital signal processor (DSP) based onboard computer named flight instrumentation controller (FIC) is designed to operate under automatic or manual mode. FIC gathers data from multitude of sensors and is capable of closed loop control to enable autonomous flight. Fixed order lateral H-2 controller designed with the features such as incorporation of level I flying qualities, gust alleviation and noise rejection is coded on to the FIC. Challenging real time hardware in loop simulation (HILS) is done with dSPACE1104 RTI/RTW. Responses obtained from the HILS are compared with those obtained from the offline simulation. Finally, flight trials are conducted to demonstrate the satisfactory performance of the closed loop system. The generic design methodology developed is applicable to all classes of Mini and Micro air vehicles.

Minimizing buffer requirements under rate-optimal schedule in regular dataflow networks

Large-grain synchronous dataflow graphs or multi-rate graphs have the distinct feature that the nodes of the dataflow graph fire at different rates. Such multi-rate large-grain dataflow graphs have been widely regarded as a powerful programming model for DSP applications. In this paper we propose a method to minimize buffer storage requirement in constructing rate-optimal compile-time (MBRO) schedules for multi-rate dataflow graphs. We demonstrate that the constraints to minimize buffer storage while executing at the optimal computation rate (i.e. the maximum possible computation rate without storage constraints) can be formulated as a unified linear programming problem in our framework. A novel feature of our method is that in constructing the rate-optimal schedule, it directly minimizes the memory requirement by choosing the schedule time of nodes appropriately. Lastly, a new circular-arc interval graph coloring algorithm has been proposed to further reduce the memory requirement by allowing buffer sharing among the arcs of the multi-rate dataflow graph. We have constructed an experimental testbed which implements our MBRO scheduling algorithm as well as (i) the widely used periodic admissible parallel schedules (also known as block schedules) proposed by Lee and Messerschmitt (IEEE Transactions on Computers, vol. 36, no. 1, 1987, pp. 24-35), (ii) the optimal scheduling buffer allocation (OSBA) algorithm of Ning and Gao (Conference Record of the Twentieth Annual ACM SIGPLAN-SIGACT Symposium on Principles of Programming Languages, Charleston, SC, Jan. 10-13, 1993, pp. 29-42), and (iii) the multi-rate software pipelining (MRSP) algorithm (Govindarajan and Gao, in Proceedings of the 1993 International Conference on Application Specific Array Processors, Venice, Italy, Oct. 25-27, 1993, pp. 77-88). Schedules generated for a number of random dataflow graphs and for a set of DSP application programs using the different scheduling methods are compared. The experimental results have demonstrated a significant improvement (10-20%) in buffer requirements for the MBRO schedules compared to the schedules generated by the other three methods, without sacrificing the computation rate. The MBRO method also gives a 20% average improvement in computation rate compared to Lee's Block scheduling method.

A method of tracking the peak power points for a variable speed wind energy conversion system

In this paper, a method of tracking the peak power in a wind energy conversion system (WECS) is proposed, which is independent of the turbine parameters and air density. The algorithm searches for the peak power by varying the speed in the desired direction. The generator is operated in the speed control mode with the speed reference being dynamically modified in accordance with the magnitude and direction of change of active power. The peak power points in the P-omega curve correspond to dP/domega = 0. This fact is made use of in the optimum point search algorithm. The generator considered is a wound rotor induction machine whose stator is connected directly to the grid and the rotor is fed through back-to-back pulse-width-modulation (PWM) converters. Stator flux-oriented vector control is applied to control the active and reactive current loops independently. The turbine characteristics are generated by a dc motor fed from a commercial dc drive. All of the control loops are executed by a single-chip digital signal processor (DSP) controller TMS320F240. Experimental results show that the performance of the control algorithm compares well with the conventional torque control method.

MODLEX: A Multi Objective Data Layout EXploration Framework for Embedded Systems-on-Chip

The memory subsystem is a major contributor to the performance, power, and area of complex SoCs used in feature rich multimedia products. Hence, memory architecture of the embedded DSP is complex and usually custom designed with multiple banks of single-ported or dual ported on-chip scratch pad memory and multiple banks of off-chip memory. Building software for such large complex memories with many of the software components as individually optimized software IPs is a big challenge. In order to obtain good performance and a reduction in memory stalls, the data buffers of the application need to be placed carefully in different types of memory. In this paper we present a unified framework (MODLEX) that combines different data layout optimizations to address the complex DSP memory architectures. Our method models the data layout problem as multi-objective genetic algorithm (GA) with performance and power being the objectives and presents a set of solution points which is attractive from a platform design viewpoint. While most of the work in the literature assumes that performance and power are non-conflicting objectives, our work demonstrates that there is significant trade-off (up to 70%) that is possible between power and performance.

A PPCA based non-parametric modeling and retrieval of PD signal buried in excessive noise

The problem of on-line recognition and retrieval of relatively weak industrial signals such as partial discharges (PD), buried in excessive noise, has been addressed in this paper. The major bottleneck being the recognition and suppression of stochastic pulsive interference (PI) due to the overlapping broad band frequency spectrum of PI and PD pulses. Therefore, on-line, onsite, PD measurement is hardly possible in conventional frequency based DSP techniques. The observed PD signal is modeled as a linear combination of systematic and random components employing probabilistic principal component analysis (PPCA) and the pdf of the underlying stochastic process is obtained. The PD/PI pulses are assumed as the mean of the process and modeled instituting non-parametric methods, based on smooth FIR filters, and a maximum aposteriori probability (MAP) procedure employed therein, to estimate the filter coefficients. The classification of the pulses is undertaken using a simple PCA classifier. The methods proposed by the authors were found to be effective in automatic retrieval of PD pulses completely rejecting PI.

A Long Memory Process Based Parametric Modeling and Recognition of PD Signal

We address the problem of recognition and retrieval of relatively weak industrial signal such as Partial Discharges (PD) buried in excessive noise. The major bottleneck being the recognition and suppression of stochastic pulsive interference (PI) which has similar time-frequency characteristics as PD pulse. Therefore conventional frequency based DSP techniques are not useful in retrieving PD pulses. We employ statistical signal modeling based on combination of long-memory process and probabilistic principal component analysis (PPCA). An parametric analysis of the signal is exercised for extracting the features of desired pules. We incorporate a wavelet based bootstrap method for obtaining the noise training vectors from observed data. The procedure adopted in this work is completely different from the research work reported in the literature, which is generally based on deserved signal frequency and noise frequency.

Space vector based bus clamped PWM algorithms for three level inverters: implementation, performance analysis and application considerations

This paper describes the different types of space vector based bus clamped PWM algorithms for three level inverters. A novel bus clamp PWM algorithm for low modulation indices region is also presented. The principles and switching sequences of all the types of bus clamped algorithms for high switching frequency are presented. Synchronized version of the PWM sequences for high power applications where switching frequency is low is also presented. The implementation details on DSP based digital controller and experimental results are presented. The THD of the output waveforms is studied for the entire operating region and is compared with the conventional space vector PWM technique. The bus clamped techniques can be used to reduce the switching losses or to improve the output voltage quality or both.. Different issues dominate depending on the type of application and power rating of the inverters. The results presented in this paper can be used for judicious use of the PWM techniques, which result in improved system efficiency and performance.

Multilevel Dodecagonal Voltage Space Vector Generation using Flying Capacitor topology for Induction motor drives

In this paper, a multilevel flying capacitor inverter topology suitable for generating multilevel dodecagonal space vectors for an induction motor drive, is proposed. Because of the dodecagonal space vectors, it has increased modulation range with the absence of all 6n +/- 1, (n=odd) harmonics in the phase voltage and currents. The topology, realized by flying capacitor three level inverters feeding an open-end winding induction motor, does not suffer the neutral point voltage imbalance issues seen in NPC inverters and the capacitors have inherent charge-balancing capability with PWM control using switching state redundancies. Furthermore, the proposed technique uses lesser number of power supplies compared to cascaded H-bridge or NPC based dodecagonal schemes and has better ride-through capability. Finally, the voltage control is obtained through a simple carrier-based space vector PWM scheme implemented on a DSP.

Narrowband signal detection techniques in shallow ocean by acoustic vector sensor array

This paper presents the formulation and performance analysis of four techniques for detection of a narrowband acoustic source in a shallow range-independent ocean using an acoustic vector sensor (AVS) array. The array signal vector is not known due to the unknown location of the source. Hence all detectors are based on a generalized likelihood ratio test (GLRT) which involves estimation of the array signal vector. One non-parametric and three parametric (model-based) signal estimators are presented. It is shown that there is a strong correlation between the detector performance and the mean-square signal estimation error. Theoretical expressions for probability of false alarm and probability of detection are derived for all the detectors, and the theoretical predictions are compared with simulation results. It is shown that the detection performance of an AVS array with a certain number of sensors is equal to or slightly better than that of a conventional acoustic pressure sensor array with thrice as many sensors.

A prototype of a first-responder indoor localization system

In this paper we present an approach to build a prototype. model of a first-responder localization system intended for disaster relief operations. This system is useful to monitor and track the positions of the first-responders in an indoor environment, where GPS is not available. Each member of the first responder team is equipped with two zero-velocity-update-aided inertial navigation systems, one on each foot, a camera mounted on a helmet, and a processing platform strapped around the waist of the first responder, which fuses the data from the different sensors. The fusion algorithm runs real-time on the processing platform. The video is also processed using the DSP core of the computing machine. The processed data consisting of position, velocity, heading information along with video streams is transmitted to the command and control system via a local infrastructure WiFi network. A centralized cooperative localization algorithm, utilizing the information from Ultra Wideband based inter-agent ranging devices combined with the position estimates and uncertainties of each first responder, has also been implemented.