Mahinda Vilathgamuwa

Control of energy optimized dynamic voltage restorer

The dynamic voltage restorer (DVR) is a custom power device used for voltage compensation of sensitive loads against voltage disturbances in power distribution lines. This paper illustrates a correction technique, which draws a minimum amount of energy from the DVR during the process of compensation of a voltage sag or swell. Using the proposed method it can be shown that a particular disturbance can be corrected with less amount of storage energy compared to that of existing in-phase boosting method. The paper also discusses a multiloop feedback control method applicable for the DVR to obtain good dynamic performance.

Modeling and robust adaptive control of a 3-axis motion simulator

In this paper, the development of a 3-axis motion simulator is described. The simulator is used to test and calibrate certain spacecraft instruments within a hardware-in-the-loop environment. A mathematical electromechanical model of the simulator is developed. Moreover, a novel robust adaptive nonlinear control law for the simulator is developed based on Lyapunov stability theory. The controller can be made adaptable to constant unknown parameters as well as robust to unknown but bounded fast varying disturbances. The motion simulator actuators are permanent magnet synchronous motor (PMSM) drives. The simulation and experimental results are presented to verify the efficacy of the proposed control system and the validity of the mathematical model of the simulator.

A Bit-Stream based space vector modulator

Bit-Stream based control, which uses one bit wide signals to control power electronics applications, is a new approach for controller design in power electronic systems. Bit-Stream signals are inherently high frequency in nature, and as such some form of down sampling or modulating is essential to avoid excessive switching losses. This paper presents a novel three-phase space vector modulator, which is based on the Bit-Stream technique and suitable for standard three-phase inverter systems. The proposed modulator simultaneously converts a two phase reference to the three-phase domain and reduces switching frequencies to reasonable levels. The modulator consumes relatively few logic elements and does not require sector detectors, carrier oscillators or trigonometric functions. The performance of the modulator was evaluated using ModelSim. Results indicate that, subject to limits on the modulation index, the proposed modulator delivers a spread-spectrum output with total harmonic distortion comparable to standard space vector pulse width modulation techniques.

Dissimilar trend of nonlinearity in ultrasound transducers and systems at resonance and non-resonance frequencies

HighlightsAt high voltage range (>100 V), the ultrasound transducer could be saturated.The impedance of the transducer is changed when the excitation signal is increased.Nonlinearity of the ultrasound transducer is concluded from experimental results.The ultrasound system is nonlinear because it does not obey the superposition rule. &NA; Several factors can affect performance of an ultrasound system such as quality of excitation signal and ultrasound transducer behaviour. Nonlinearity of piezoelectric ultrasound transducers is a key determinant in designing a proper driving power supply. Although, the nonlinearity of piezoelectric transducer impedance has been discussed in different literatures, the trend of the nonlinearity at different frequencies with respect to excitation voltage variations has not been clearly investigated in practice. In this paper, to demonstrate how the nonlinearity behaves, a sandwich piezoceramic transducer was excited at different frequencies. Different excitation signals were generated using a linear power amplifier and a multilevel converter within a range of 30–200 V. Empirical relation was developed to express the resistance of the piezoelectric transducer as a nonlinear function of both excitation voltage and resonance frequency. The impedance measurements revealed that at higher voltage ranges, the piezoelectric transducer can be easily saturated. Also, it was shown that for the developed ultrasound system composed of two transducers (one transmitter and one receiver), the output voltage measured across receiver is a function of a voltage across the resistor in the RLC branches and is related to the resonance frequencies of the ultrasound transducer.

Power Electronics for Photovoltaic Power Systems

Abstract The world energy demand has been increasing in a rapid manner with the increase of population and rising standard of living. The world population has nearly doubled in the last 40 years from 3.7 billion people to the present 7 billion people. It is anticipated that world population will grow towards 8 billion around 2030. Furthermore, the conventional fossil fuel supplies become unsustainable as the energy demand in emerging big economies such as China and India would rise tremendously where the China will increase its energy demand by 75% and India by 100% in the next 25 years. With dwindling natural resources, many countries throughout the world have increasingly invested in renewable resources such as photovoltaics (PV) and wind. The world has seen immense growth in global photovoltaic power generation over the last few decades. For example, in Australia, renewable resources represented nearly 15% of total power generation in 2013. Among renewable resources, solar and wind account for 38% of g...

Volterra series analysis of spectral components in quasi‐resonant d.c.–d.c. converters

The Volterra series method is used to predict the spectral components of a d.c.–d.c. quasi-resonant converter output wave-form. The Volterra kernels computed for quasi-resonant converters are based on their small-signal non-linear model. Illustrative analytic and simulation results are presented for several quasi-resonant converter topologies and are shown to match very closely.

Percutaneous and transcutaneous connections

Device-related infection is one of the major complications of mechanical circulatory support (MCS) and hinders long-term MCS success. Biofilm formation and migration are important strategies of microorganisms in the pathogenesis and persistence of MCS device infections. Biofilm formation provides a shield against antimicrobials and human immune responses, and biofilm migration further extends the infections to deeper tissues. Replacement of infected MCS devices, such as ventricular assist devices or extracorporeal membrane oxygenation, is associated with significant morbidity and mortality, underscoring the importance of developing preventative strategies for MCS device infections. Such strategies include optimizing the design of MCS devices to increase its tissue integration and developing antiinfective coatings for the device surfaces. Replacing the percutaneous device cable with wireless energy transfer systems is considered an ultimate solution for these infections. Thus, transcutaneous energy supply systems, an “infection-free” power supply for MCS, are now under development.

A Padé Approximate Model of Lithium Ion Batteries

We present a reduced order model for a lithium ion battery in which Pade approximants are used to simplify complex, transcendental, transfer functions associated with the linearized, pseudo 2-dimensional (P2D) electrochemical model of the battery. The resulting transfer functions take the form of simple, rational polynomial functions, which can be used to compute any variable at any location within a one-dimensional representation of the battery domain. Corrections for nonlinear behavior are also incorporated into the reduced model. The results obtained using the reduced model compare favorably to those from the full (nonlinear) P2D model and the computational time required to produce these results is significantly reduced. Importantly, the form of the reduced model means that variables can be evaluated at specific discrete locations within the cell domain, without the need to compute all values of the variable at all discrete locations, as is the case with the spatial discretization methods most commonly used to implement the P2D model. We show that this results in further significant time savings and enhances the suitability of the model for variety of applications.

Morphological Fault Detector for Adaptive Overcurrent Protection in Distribution Networks With Increasing Photovoltaic Penetration

In this paper, a versatile and robust algorithm for overcurrent protection that is adaptive to the feeder PV penetration level as well as changing load condition in the distribution feeder is proposed. The algorithm has built-in dc-offset suppression capability as well as recursive least square error filter for current phasor estimation to provide input to the overcurrent fault detector. The proposed multistage morphological fault detector analyzes sudden change in fault current magnitude and its structure makes it convenient to update the fault threshold dynamically by measuring the current magnitude at regular interval, thus making the algorithm versatile and adaptive. The performance of the proposed algorithm is investigated by simulating different fault distances and fault types for increasing penetration levels of PVs on a simple radial distribution feeder .

Modelling of DC arcs for photovoltaic system faults

Arc faults in a PV system are difficult to study using models developed for conventional power sources mainly due to non-linear behavior of PV current and its dependence on external factors such as irradiance, shading and maximum power tracking controls. This paper presents a unique model derived from fundamentals of Mayr and Cassie arc models and introducing a hyperbolic tangent function to approximate arc current at near zero gap. Arc impedance widely changes with heat dissipated through arcs periphery. Unique feature of the proposed model is that it takes into account this change of impedance with time which could be used to analyze arcs with changing lengths due to movements of current carrying elements. A test bench has been built with adjustable gap between two electrodes to conduct experiments. Both experimental results and simulation outcomes are presented to verify the proposed model.