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This study proposes an inverter circuit topology capable of generating multilevel dodecagonal (12-sided polygon) voltage space vectors by the cascaded connection of two-level and three-level inverters. By the proper selection of DC-link voltages and resultant switching states for the inverters, voltage space vectors whose tips lie on three concentric dodecagons, are obtained. A rectifier circuit for the inverter is also proposed, which significantly improves the power factor. The topology offers advantages such as the complete elimination of the fifth and seventh harmonics in phase voltages and an extension of the linear modulation range. In this study, a simple method for the calculation of pulse width modulation timing was presented along with extensive simulation and experimental results in order to validate the proposed concept. [ABSTRACT FROM AUTHOR]

A new type of multi-port isolated bidirectional DC-DC converter is proposed in this study. In the proposed converter, transfer of power takes place through addition of magnetomotive forces generated by multiple windings on a common transformer core. This eliminates the need for a centralised storage capacitor to interface all the ports. Hence, the requirement of an additional power transfer stage from the centralised capacitor can also be eliminated. The converter can be used for a multi-input, multi-output (MIMO) system. A pulse width modulation (PWM) strategy for controlling simultaneous power flow in the MIMO converter is also proposed. The proposed PWM scheme works in the discontinuous conduction mode. The leakage inductance can be chosen to aid power transfer. By using the proposed converter topology and PWM scheme, the need to compute power flow equations to determine the magnitude and direction of power flow between ports is alleviated. Instead, a simple controller structure based on average current control can be used to control the power flow. This study discusses the operating phases of the proposed multi-port converter along with its PWM scheme, the design process for each of the ports and finally experimental waveforms that validate the multi-port scheme. [ABSTRACT FROM AUTHOR]

This study presents a novel magnetic arm-switch-based integrated magnetic circuit for a three-phase series-shunt compensated uninterruptible power supply (UPS). The magnetic circuit acts as a common interacting field for a number of energy ports, viz., series inverter, shunt inverter, grid and load. The magnetic arm-switching technique ensures equivalent series or shunt connection between the inverters. In normal grid mode (stabiliser mode), the series inverter is used for series voltage correction and the shunt one for current correction. The inverters and the load are effectively connected in parallel when the grid power is not available. These inverters are then used to share the load power. The operation of the inverters in parallel is ensured by the magnetic arm-switching technique. This study also includes modelling of the magnetic circuit. A graphical technique called bond graph is used to model the system. In this model, the magnetic circuit is represented in terms of gyrator-capacitors. Therefore the model is also termed as gyrator-capacitor model. The model is used to extract the dynamic equations that are used to simulate the system using MATLAB/SIMULINK. This study also discusses a synchronously rotating reference frame-based control technique that is used for the control of the series and shunt inverters in different operating modes. Finally, the gyrator-capacitor model is validated by comparing the simulated and experimental results. [ABSTRACT FROM AUTHOR]

Handling unbalanced and non-linear loads in a three-phase AC power supply has always been a difficult issue. This has been addressed in the literature by either using fast controllers in the fundamental rotating reference frame or using separate controllers in reference frames specific to the harmonics. In the former case, the controller needs to be fast and in the latter case, besides the need for many controllers, negative-sequence components need to be extracted from the measured signal. This study proposes a control scheme for harmonic and unbalance compensation of a three-phase uninterruptible power supply wherein the problems mentioned above are addressed. The control takes place in the fundamental positive-sequence reference frame using only a set of feedback and feed-forward compensators. The harmonic components are extracted by a process of frame transformations and used as feed-forward compensation terms in the positive-sequence fundamental reference frame. This study uses a method wherein the measured signal itself is used for fundamental negative-sequence compensation. As the feed-forward compensator handles the high-bandwidth components, the feedback compensator can be a simple low-bandwidth one. This control algorithm is explained and validated experimentally. [ABSTRACT FROM AUTHOR]

An isolated wind power generation scheme using slip ring induction machine (SRIM) is proposed. The proposed scheme maintains constant load voltage and frequency irrespective of the wind speed or load variation. The power circuit consists of two back-to-back connected inverters with a common dc link, where one inverter is directly connected to the rotor side of SRIM and the other inverter is connected to the stator side of the SRIM through LC filter. Developing a negative sequence compensation method to ensure that, even under the presence of unbalanced load, the generator experiences almost balanced three-phase current and most of the unbalanced current is directed through the stator side converter is the focus here. The SRIM controller varies the speed of the generator with variation in the wind speed to extract maximum power. The difference of the generated power and the load power is either stored in or extracted from a battery bank, which is interfaced to the common dc link through a multiphase bidirectional fly-back dc–dc converter. The SRIM control scheme, maximum power point extraction algorithm and the fly-back converter topology are incorporated from available literature. The proposed scheme is both simulated and experimentally verified. [ABSTRACT FROM AUTHOR]

Bond graph is an apt modelling tool for any system working across multiple energy domains. Power electronics system modelling is usually the study of the interplay of energy in the domains of electrical, mechanical, magnetic and thermal. The usefulness of bond graph modelling in power electronic field has been realised by researchers. Consequently in the last couple of decades, there has been a steadily increasing effort in developing simulation tools for bond graph modelling that are specially suited for power electronic study. For modelling rotating magnetic fields in electromagnetic machine models, a support for vector variables is essential. Unfortunately, all bond graph simulation tools presently provide support only for scalar variables. We propose an approach to provide complex variable and vector support to bond graph such that it will enable modelling of polyphase electromagnetic and spatial vector systems. We also introduced a rotary gyrator element and use it along with the switched junction for developing the complex/vector variable's toolbox. This approach is implemented by developing a complex S-function tool box in Simulink inside a MATLAB environment This choice has been made so as to synthesise the speed of S-function, the user friendliness of Simulink and the popularity of MATLAB. [ABSTRACT FROM AUTHOR]

A rotor position estimation scheme for stator flux-oriented speed sensorless control of slip ring induction machine (SRIM) is presented in this paper. Position of the rotor is estimated by integrating the rotor back-electromotive force. The problem of DC drift during integration is eliminated using an error-decaying mechanism in the estimator. This estimation scheme reduces the propagation of noise in the sensed current to the estimated rotor side unit vectors. This scheme also eliminates the need for differentiating the unit vectors for estimating slip frequency. The proposed scheme is simulated and experimentally verified. [ABSTRACT FROM AUTHOR]

The speed-sensorless vector-controlled induction-motor drive is superior to the conventional vector-controlled induction-motor drive in terms of drive cost and reliability. In speed-sensorless control, one common practice is to estimate the flux position from the terminal voltage and current using a stator-voltage model. The accuracy of estimated flux position decides the performance of the vector-controlled drive. However, the performance is limited by the DC-drift problems that prohibit the use of open integration of the flux-producing voltage component for flux estimation. The paper proposes a flux-estimation method that gives the effect of open integration along with an inherent error-decaying mechanism to resolve the DC-drift problem. A stator-resistance-adaptation method is also incorporated in the flux estimator, which makes the flux-position estimation independent of resistive parameters of the motor. Using this flux-estimation algorithm, a rotor-flux-oriented speed-sensorless speed-control scheme of induction motor is proposed. The scheme is both simulated and experimentally verified. [ABSTRACT FROM AUTHOR]

Modelling of the switched mode power converter (SMPC) involves obtaining the large signal, steady-state and small signal representations. Transfer functions and state equations are used for mathematical representation of the SMPC. Obtaining these dynamic models using a mathematical or graphical approach sometimes lead to loss of an intuitive understanding of the system dynamics. A unified graphical method of modelling SMPC using bond graphs is presented. Only the PWM DC-DC converters are considered. The concept of switched power junctions is used for modelling of switching phenomenon in the SMPC. This approach uses a logical process of graphical reduction, which ultimately results in the state equations of the large signal and small signal AC models of the SMPC including the steady-state equations of the SMPC. This method is applicable to SMPC, in both continuous conduction mode and discontinuous conduction mode The proposed modelling approach is illustrated by a few examples. [ABSTRACT FROM AUTHOR]

Presents a topology for a voltage-space phasor generation equivalent to a five-level inverter for an open-end winding induction motor. Structure of the proposed inverter; Use of open-end winding induction motor; Absence of neutral point fluctuations.