HIGH PERFORMANCE DIGITAL CURRENT CONTROL IN THREE PHASE ELECTRICAL DRIVES

Majority of contemporary static power converters makes use of three-phase, PWM controlled IGBT inverters. Typical applications include the electrical drives and grid connected converters. In both cases, it is of uttermost importance to obtain a high bandwidth control of the output current. The bandwidth is constrained by the problems of the feedback acquisition. The current ripple at the PWM frequency requires anti-aliasing measures that introduce delays, reduce the stability margin and restrain the bandwidth. We propose the feedback acquisition method which is robust against the ripple and noise, and minimizes delays. We also devise the current controller with control actions which suppress the effects of the delays. Proposed parameter setting procedures meet both the bandwidth requirements and the robustness against the noise and the parameter changes. Experimental verification proves that the proposed current controller achieves the response speed and the robustness against the noise which outperforms the competitive solutions.

NetDiff – Bayesian model selection for differential gene regulatory network inference

Differential networks allow us to better understand the changes in cellular processes that are exhibited in conditions of interest, identifying variations in gene regulation or protein interaction between, for example, cases and controls, or in response to external stimuli. Here we present a novel methodology for the inference of differential gene regulatory networks from gene expression microarray data. Specifically we apply a Bayesian model selection approach to compare models of conserved and varying network structure, and use Gaussian graphical models to represent the network structures. We apply a variational inference approach to the learning of Gaussian graphical models of gene regulatory networks, that enables us to perform Bayesian model selection that is significantly more computationally efficient than Markov Chain Monte Carlo approaches. Our method is demonstrated to be more robust than independent analysis of data from multiple conditions when applied to synthetic network data, generating fewer false positive predictions of differential edges. We demonstrate the utility of our approach on real world gene expression microarray data by applying it to existing data from amyotrophic lateral sclerosis cases with and without mutations in C9orf72, and controls, where we are able to identify differential network interactions for further investigation

Bezsenzorski pogon za vuču s estimatorima u kliznom režimu i MRASCC-u koristeći izravno upravljanje momentom

In the paper two types of speed, torque and flux estimators are described. The Sliding Mode Observer (SMO) and the Model Reference Adaptive System (MRAS) type estimators are applied in the sensorless Direct Torque Control with Space Vector Modulation algorithm (DTC-SVM) of Induction Motor (IM) drive. Dynamical performance of the drive and the estimator properties in field weakening and low speed regions for traction drive system are presented.U članku su opisana dva tipa estimatora brzine, momenta i toka – observer u kliznom režimu (SMO) i adaptivni sustav reference modela (MRAS). Oba tipa estimatora su primijenjena u bezsenzorskom izravnom upravljanju momentom s modulacijom prostornih vektora (DTC-SVM) na pogonu s asinkronim motorom (IM). Prikazane su dinamičke karakteristike pogona i estimatora u režimima slabog polja i male brzine za slijedni sustav

Stator Design and Air Gap Optimization of High Speed Drag-Cup Induction Motor using FEM

A huge number of modern applications nowadays require the use of high speed electrical machines which need to be highly optimized in order to achieve the best efficiency and the lowest mass and price. The low rotor inertia is also an important requirement in order to reduce rotor kinetic energy. The subject of this paper is high speed drag-cup induction motor (IM) with low inertia which is designed for use as an auxiliary motor in automotive systems such as Kinetic Energy Recovery System (KERS) in Formula 1. This work presents the procedure for stator design and optimization of the air gap length and rotor thickness of this kind of motor in order to achieve the highest efficiency in the speed range of interest. Simple procedure for stator dimensioning was developed and it was shown how the optimal number of stator conductors could be calculated. The effect of change in rotor thickness and air gap lengths on motor performance is demonstrated through some analytical considerations. The machine is then modeled in FEM software by means of which the optimization of the air gap and rotor thickness was performed. At the end, the simulation results were presented and analyzed and conclusions were drawn

Dead-Time Effects in Voltage Source Inverter Fed Multi-Phase AC Motor Drives and Their Compensation

Inverter dead-time effects have been investigated in detail in the past for three-phase drives supplied from a three-phase voltage source inverter (VSI). A similar study has never been conducted in conjunction with multi-phase (more than three phases) drives, supplied from multi-phase VSIs. Regardless of the type of ac machine and its number of phases, the power supply of the drive is typically a two-level VSI, which requires a method of PWM for its operation. If a multi-phase machine is with sinusoidal field distribution, the PWM technique must generate sinusoidal harmonic-free output voltages in order to avoid appearance of low-order stator current harmonics. Recently a great deal of research has concentrated on PWM methods suitable for multi-phase VSIs. All of these PWM methods theoretically produce sinusoidal output voltages with no low order harmonics. As a consequence, rotor flux oriented control of multi-phase ac machines with sinusoidal MMF distribution can be theoretically realised by using only two current controllers in the synchronous reference frame. The paper shows that despite using a PWM method that does not produce low-order harmonics, in practice they do appear in the output voltage, and consequently currents, of the multi-phase VSI. Simulation studies show that low-order harmonics are generated as a result of inverter dead-time and that the effect of such harmonics on a five-phase ac machine can be significant due to the low machine impedance presented to these harmonics. Experimental results collected from a five-phase induction motor drive laboratory prototype are presented which reinforce this hypothesis. The paper further suggests a modified current control scheme that is able to fully compensate inverter dead-time effect and thus provide practically perfect sinusoidal currents. The proposed current control scheme is validated via simulation and experimentally

A two-motor centre-driven winder drive with a reduced switch count

Industrial applications often require two (or more) variable speed electric drives, which have to be controlled independently. An example is a centre-driven two-motor winder, where ac machines are traditionally supplied from their individual three-phase voltage source inverters (VSIs). Over the past decade research efforts have been made to reduce the number of power electronic devices required in multi-motor drive systems in order to reduce the complexity and hence cost of the drive. One such configuration consists of two three-phase induction machines, supplied using a five-leg VSI, with one inverter leg being common to both machines. A PWM method for the five-leg VSI control, which enables an arbitrary distribution of the available dc link voltage between the two machines, has been recently developed and its suitability for application in a two-motor centre-driven winder has been demonstrated by simulation. This paper reports results of the practical realization of this drive system. In the first stage the two-motor drive supplied from a five-leg VSI is built and tested by performing the winder emulation experiments under no-load conditions. Suitability of the configuration for real winder system is thus demonstrated. In the second stage the complete two-motor centre-driven paper winder is built and results of the experimental testing are provided. The advantages of the analyzed solution over the standard one are also addressed

Experimental performance evaluation of a five-phase parallel-connected two-motor drive

The paper reports the results of an experimental investigation of a five-phase two-motor drive system, consisting of a parallel connection of two induction machines (IM). Thanks to an appropriate connection of the motors, two machines are controlled independently although a single five-phase voltage source inverter (VSI) is used as the supply. An overview of the operating principles is provided first together with the vector control algorithm. The experimental set-up is described next. Decoupling of control within the two-motor drive is illustrated using experimental results, which show performance of the drive system during acceleration, deceleration and speed reversal of one of the motors. Finally, shortcomings of this multi-motor drive solution are addressed