An Advanced Control and Extensible Configuration for Static Var Generator

An extensible configuration is proposed for static var generator (SVG) with advanced controller included for reactive power compensation of grid. Compared with the traditional configurations, the major advantage of such system configuration is that the power modules are very flexible and easy to extend or reduce without changing the main equipment of SVG under the different voltage levels. Furthermore, in order to solve the problems of modeling uncertainty, nonlinearities, and outside disturbance by using proportion integration (PI) controller, an advanced controller is proposed based on auto disturbance rejection control (ADRC). By controlling the amount and direction of reactive current, the reactive power is generated or absorbed from SVG into power grid with fast response, which can realize the excellent dynamic compensation for both the internal and external interferences. Simulations results show that the proposed controller has better performance of the transient and steady state than PI controller. Moreover, the verification tests are executed in 380 V, 6.5 kVA experiment systems, suggesting that the excellent dynamic performance and strong robustness are achieved

Simuliranje i upravljačka strategija 5.6 kV 17-razniskog STATCOM sustava uz SVG uvjet

To achieve high-voltage reactive power compensation, a 5.6kV 17-level STATCOM under SVG Condition is presented. In this paper, we use a cascaded H-bridge multilevel star-connection converter whose system structure and circuit schematic are described. Then by using the phase-shifted carrier modulation strategy and the active-reactive current decoupling method, the STATCOM performs quite well. Moreover modulation strategy of the 17-level STATCOM based on the active disturbance rejection control (ADRC) is presented and the analytical formulas are described. For implementation, control strategy for DC bus voltage balance in cascaded H-bridge multilevel converters, time average distribution method and extreme value offset method are applied in our design. Finally, simulation results demonstrate that the proposed 17-level STATCOM is capable of reactive power compensation, simultaneous controlling and balancing the DC side voltages during the work and verify that high-voltage reactive power can be accurately and effectively compensated.Za postizanje kompenzacije jalove snage uz visoki napon, predstavljen je STATCOM s 5.6 kV i 17-razina uz SVG uvjet. U ovom radu koristimo kaskadni višerazinski H-mosni pretvarač u zvijezda spoju uz opisane strukturu i shemu spoja. Zatim korištenjem strategije modulacije s fazno-pomaknutim signalom nosioca i metode rasprezanja radno-jalove struje, STATCOM pokazuje prilično dobro vladanje. Uz to, prikazana je strategija modulacije 17-razinskog STATCOM-a zasnovana na upravljanju s aktivnim odbacivanjem smetnji (ADRC) te su opisane analitičke formule. Za implementaciju, u naš dizajn primjenjene su upravljačka strategija balansiranja napona DC sabirnice u kaskadnom višerazinskom H-mosnom pretvaraču te metoda vremenskog uprosječavanja razdiobe i metoda ekstremne vrijednosti pomaka. Konačno, simulacijski rezultati pokazuju da je predloženi 17-razinski STATCOM sposoban za kompenzaciju jalove snage, istovremeno upravljanje i balansiranje napona DC strane u radu te potvrđuju da je jalovu snagu uz visoki napon moguće točno i djelotvorno kompenzirati

Integration of energy storage components with cascaded H-bridge multilevel converters

In recent years, multilevel converters have gained considerable attention in medium-voltage motor drive and grid applications. This popularity is owed to their reduced voltage stress on the semiconductor devices used in their structure. In addition, multilevel converters generate near sinusoidal outputs with low harmonic distortions. Other advantages of such converters include inherent modularity and low dv/dt stresses. In general, multilevel power electronic converters are classified into three main topologies: diode-clamped, flying-capacitor, and cascaded H-bridge. A cascaded H-bridge multilevel converter is created when several H-bridge cells are placed in series. Each H-bridge cell must be fed by a stiff voltage source. In earlier implementations, every one of these voltage sources had to contribute to the overall power supplied to the load. Later, it was demonstrated that under certain operating conditions, one can replace all but one of these sources with energy storage devices, e.g., capacitors. In other words, the entire power can be supplied by only one source. The replacing capacitors must only maintain a constant dc voltage supplying zero net power. Although this approach benefits from cost reductions, balancing the voltages across the replacing capacitors turns out to be a challenge. In this thesis, the operating conditions under which the capacitor voltage regulation is feasible are first analytically investigated. The results show that the amplitude of the output voltage as well as the power factor of the load current determines the regulation range when the staircase modulation method is employed. In order to extend the regulation range for the replacing capacitors, a new control scheme - phase shift modulation - is proposed. This method is more robust when compared to existing methods. In this method, the main H-bridge cell of the multilevel converter operates at the fundamental frequency and the auxiliary cells run at the PWM frequency. Finally, the sigma-delta modulation method has been utilized to extend the capacitor voltage regulation range. This method benefits from simplicity in implementation in comparison to PWM techniques. The analytical and simulation results prove the effectiveness of the proposed approaches. They are also consistent with the results of the experiment --Abstract, page iv

Modelling of active flow control devices using hybrid RANS/LES techniques

The focus of the present thesis is on the effects of two active flow control devices on the periodic components of the turbulent shear layers and the Reynolds stresses. One of the main aims is to demonstrate the capability to control individual structures that are larger in scale and lower in frequency against the richness of the time and spatial scales in a turbulent boundary layer. In order to carry out this investigation, computational fluid dynamics CFD simulations are performed. The turbulence modelling approach for the two dimensional initial cases is RANS and URANS and with regards to 3D simulations IDDES, a hybrid RANS/LES technique, is applied. The geometry for the studies is taken from experimental configurations for each case; both cases comprise a turbulent flow over a backward facing step (BFS), where separation is induced after the step edge. The results from the simulations are compared to the experimental data for both cases with and without control. The first active flow control device is a single DBD plasma actuator located upstream of the step. The effects of quasi-steady and unsteady – or pulsated- plasma actuation using two different phenomenological models are studied. The resulting turbulent structures, Reynolds stresses, skin friction and velocity profiles are analysed applying the aforementioned models to simulate the plasma actuation. The results for quasi-steady plasma mode show very good agreement with the available experimental data and a reduction of the reattachment length which matches the experimental data is observed. Regarding modulated actuation of the DBD plasma device, three dimensional simulations were carried out and the results also showed excellent agreement of the overall behaviour flow when compared to the experimental data. The second flow control device is a novel device known as spanwise vortex generators. It consists of a strip of magnets placed along the span of the BFS upstream of step and the device oscillates at a given frequency and amplitude. Like for the first control device, turbulent structures, Reynolds stresses, skin friction distributions and velocities are analysed and compared to the experimental measurements. A remarkable effect of the device is observed especially in the reattachment length which is considerably reduced. Experimental measurements for the baseline case were available and a comparison with such data is performed

Power Quality in Electrified Transportation Systems

"Power Quality in Electrified Transportation Systems" has covered interesting horizontal topics over diversified transportation technologies, ranging from railways to electric vehicles and ships. Although the attention is chiefly focused on typical railway issues such as harmonics, resonances and reactive power flow compensation, the integration of electric vehicles plays a significant role. The book is completed by some additional significant contributions, focusing on the interpretation of Power Quality phenomena propagation in railways using the fundamentals of electromagnetic theory and on electric ships in the light of the latest standardization efforts

Phase tracking electronically variable attenuators with receiver protection

Thesis (PhD)--Stellenbosch University, 2018.ENGLISH ABSTRACT: This dissertation presents the development of a set of optimal phase tracking electronically variable attenuators. Secondly, a compact high power PIN diode limiter is developed and its minimum attainable resistance is extracted through high power measurements. Close range reflections cause the receiver of a multi-channel digital beamforming radar to saturate. Controlled attenuation over time, implemented with electronically variable attenuators, is used to prevent receiver saturation (sensitivity time control). An electronically variable attenuator is placed in front of the first low noise amplifier in each channel; its insertion loss directly adds to the receiver’s noise figure. A multi-channel digital beamforming radar receiver requires good phase tracking between its receiver channels to minimise direction of arrival estimation errors. The set of electronically variable attenuators used for sensitivity time control need to track in phase over the control range. In this dissertation, sensitivity analysis is used to identify a set of optimal phase tracking electronically variable attenuators. A root sum square error measure is derived from the multiple output sensitivities of an electronic network. The error measure gives the expected RMS phase error within a set of networks. Applying the error measure to several electronically variable attenuators over the control range, the cascaded parallel quarter-wave attenuator is identified as having optimal phase tracking within a set of attenuators over control range. The cascade parallel quarter-wave attenuator is developed further and optimised through the application of sensitivity analysis. The final attenuator has excellent attenuation flatness, attenuation range, phase tracking and a simple biasing scheme. A multi-channel digital beamforming radar receiver also has to be protected against large signals. These large potentially damaging signals are either due to the radar’s own transmitted signal, or from other radars transmitting large amounts of power in the same frequency band. A receiver protector (e.g. a limiter) typically supplies this function. In a multi-channel digital beamforming radar, a compact circuit based high power limiter has many advantages in terms of space and cost when it is compared to a waveguide limiter. The compact high power limiter developed in this dissertation consists of PIN diodes implemented on a multi-layer printed circuit board. The circuit is referred to as an active PIN-Schottky limiter. The maximum power handling capability of the active PIN-Schottky limiter is determined by the PIN diode at the limiter’s input. The minimum attainable resistance is not given by the manufacturers, so that the diode’s minimum attainable resistance can not be found from the datasheet information. It is difficult to estimate how much power is dissipated in the diode when a large signal is incident. Through a temperature controlled measurement, the PIN diode’s voltage decrease as a function of junction temperature increase is measured. By fitting the PIN diode’s measured and simulated junction temperature increase, it is possible to extract the resistance of the diode when large forward bias is applied. Once the resistance is known, the power dissipated in the PIN diode can be calculated for different operating conditions.AFRIKAANSE OPSOMMING: In hierdie proefskrif word ’n stel van optimale fasesporende elektronies verstelbare verswakkers ontwikkel. Tweedens word ’n kompakte hoëdrywing PIN diode beperker ontwikkel. Die beperker se maksimum drywing hanteringsvermoë word bepaal deur die PIN diode se minimum haalbare weerstand te onttrek met hoëdrywing metings. Naby teikens veroorsaak onvanger versadiging in ’n multi-kanaal digitale bundelvormende radar. Beheerde verswakking oor tyd, geïmplementeer deur elektronies verstelbare verswakkers, voorkom ontvanger versadiging (sensitiwiteits tyd beheer). ’n Elektronies verstelbare verswakker word voor die eerste lae ruis versterker in elke ontvanger kanaal geplaas; die inset verlies word direk by die ontvanger se ruissyfer getel. Multi-kanaal digitale bundelvormende radar ontvangers benodig goeie fasesporing tussen die verskillende kanale om foute in die teiken rigting skatting te voorkom. As ’n stel van elektronies verstelbare verswakkers gebruik word om sensitiwiteits tyd beheer toe te pas, moet die stel van verswakkers ook spoor in fase oor die verswakking bereik. In hierdie proefskrif word sensitiwiteitsanalise gebruik om ’n stel van fasesporende elektronies verstelbare verswakkers te identifiseer. ’n Wortel kwadraat som foutmaatstaf word afgelei van ’n elektroniese netwerk se veelvuldige uittree sensitiwiteite. Die foutmaatstaf gee die verwagte wortel gemiddelde kwadraat (WGK) fasefout binne ’n stel van elektoniese netwerke. Die fasefout van verskeie aangepaste elektronies verstelbare verswakkers word bereken en die kaskade parallel kwartgolf-lengte verswakker word geïdentifiseer as die topologie met optimale fasesporing binne ’n stel van verswakkers oor die verswakkingsbereik. Deur die toepassing van sensitiwiteitsanalise word die kaskade parallel kwartgolf-lengte verswakker se werksverrigting verder ontwikkel en geoptimiseer. Die kaskade kwartgolf-lengte verswakker het uitstekende verswakking platheid, verswakking bereik, fasesporing en ’n eenvoudige voorspanningskema. ’n Multi-kanaal digitale bundelvormende radar benodig ook beskerming teen skadelike seine afkomstig van die radar se eie sender, sowel as drywing wat uitgesaai word deur ander radars in dieselfde frekwensieband. ’n Ontvanger beskermer (bv. ’n beperker) word tipies vir hierdie toepassing gebruik. Dit is baie meer voordelig om ’n kompakte beperker te gebruik in plaas van ’n golfleier beperker in ’n multi-kanaal digitale bundelvormende radar in terme van prys en spasie in die ontvanger. Die kompakte hoëdrywing beperker wat hier bespreek word bestaan uit PIN diodes wat geïmplementeer is op ’n multi-laag gedrukte stroombaanbord. Die PIN diode beperker beskerm die ontvanger teen beide sy eie sender drywing (aktief) en ander radars se seine (passief). Die maksimum drywing hanteringsvermoë van die beperker word bepaal deur die minimum haalbare weerstand van die eerste PIN diode. Verskaffers gee nie die PIN diode se minimum weerstand nie, sodat die minimum haalbare diode weerstand nie gevind kan word uit datablad inligting nie. Dit maak dit moeilik om die maksimum intreedrywing van ’n spesifieke beperker opstelling te bepaal. ’n Temperatuur beheerde toetsopstelling word gebruik om die afname in PIN diode spanning te meet vir toenemende vlaktemperatuur. Die gemete vlaktemperatuur word vergelyk met ’n termiese model van die PIN diode. Die PIN diode se minimum haalbare weerstand word onttrek deur die gemete en gesimuleerde vlaktemperatuur te pas. As die PIN diode se minimum haalbare weerstand bekend is, kan die drywing wat die diode verkwis bereken word vir verskillende werkstoestande