Summa rerum genera esse tantum duo: substantiam nimirum & accidens, ex suffragio ampliss. facult. philos. in florentissimo ad Auram Athenaeo, sub umbone ... dn. mag. Simonis T��lpo, met & log. professoris famigeratissimi, consistorii Acad. assessoris gravissimi nec non annexae Pijkensis pastoris longe fidelissimi. Summos in philosophia honores aditurus dissertatione philosophica ad sobrie philosophantium examen modeste delata statuere conabitur Jeremias Wallenius J. f. Tavastensis. Ad diem 21. Nov. anni redempti orbis M. DC. XC. IV. Horis pomeridianis in auditorio maximo

Invokaatio: A.J.

Electrical Safety of Island Operated Low Voltage DC Network

Today, renewable energy technologies and modern power electronics have made it feasible to implement low voltage direct current (LVDC) microgrids (MGs) ca-pable to island operation. Such LVDC networks are particularly useful in remote areas. However, there are still pending issues in island operated LVDC MGs like electrical safety and controlled operation, which should be addressed before wide-scale implementation. This thesis is focused on the overall protection of an island operated LVDC network concept, including protection against electrical shocks, mains equipment protection and protection of photovoltaic (PV) power sources and battery energy storage systems (BESSs). The topic is approached through ex-amination of the safety hazards and the appropriate methods to protect against them, comprising considerations for earthing system selection and realisation of the protection system.

Piirilevyn suunnittelu suurelle virralle DC/DC-muuntimeen

Ajoneuvoissa, kuten busseissa, k��ytet����n yleens�� 24 VDC j��rjestelmi�� ja t��m�� ei muutu my��sk����n s��hk��ajoneuvojen kohdalla. S��hk��ajoneuvoissakin tarvitaan siis 24 VDC matalaj��nniteakustoja valoille, pyyhkij��ille ja muille matalan j��nnitteen j��rjestelmille. Lis��ksi s��hk��ajoneuvoissa on esimerkiksi ilmastointi ja paineilmankompressori, jotka tarvitsevat taajuusmuuttajan py��ritt��m����n niit��. T��ss�� ty��ss�� suunnitellaan suuren virran piilevy DC/DC-muuntimeen, joka on osa ajoneuvok��ytt����n suunnitellun invertterin ja DC/DC-muuntimen yhdistelm��laitetta. Ty��n p����paino on piirilevyn suunnittelussa, mutta ty��ss�� kerrotaan lyhyesti koko laitteen kytkent�� ja k��ytt��tarkoitus. Ty��ss�� kerrotaan my��s tehopiirilevylle tulevien komponenttien valinta, mitoitus ja j����hdytys. K��yd����n l��pi suuren virran piirilevysuunnittelun mitoitusperiaatteet ja mit�� seikkoja siin�� erityisesti tulee ottaa huomioon. Lis��ksi k��sitell����n piirilevyn liitynt��j�� ja virtakiskojen l��mpenem���� virranahtautumisen takia. Suunniteltua piirilevy�� mitataan ja sen toimintaa kokeillaan prototyyppilaitteessa. Protoyyppilaitteella havaitaan virtakiskojen l��mpenev��n liikaa ja huomataan ongelma kytkenss��. Kytkent���� korjattiin ja toimintaa analysoitiin uudestaan, jonka j��lkeen havaittiin piirilevyn l��mpenem��n tippuneen 20 ��C. Lopputuloksena piirilevyn l��mpenem��, korjatulla kytkenn��ll��, on suunnitellun mukainen. Lopussa esitet����n piirilevyn korvaamista moduuliratkaisulla laitteen parantamiseksi sarjatuotantoon.

Power Electronic Converters in Low-Voltage Direct Current Distribution ��� Analysis and Implementation

Over the recent years, smart grids have received great public attention. Many proposed functionalities rely on power electronics, which play a key role in the smart grid, together with the communication network. However, ���smartness��� is not the driver that alone motivates the research towards distribution networks based on power electronics; the network vulnerability to natural hazards has resulted in tightening requirements for the supply security, set both by electricity end-users and authorities. Because of the favorable price development and advancements in the field, direct current (DC) distribution has become an attractive alternative for distribution networks. In this doctoral dissertation, power electronic converters for a low-voltage DC (LVDC) distribution system are investigated. These include the rectifier located at the beginning of the LVDC network and the customer-end inverter (CEI) on the customer premises. Rectifier topologies are introduced, and according to the LVDC system requirements, topologies are chosen for the analysis. Similarly, suitable CEI topologies are addressed and selected for study. Application of power electronics into electricity distribution poses some new challenges. Because the electricity end-user is supplied with the CEI, it is responsible for the end-user voltage quality, but it also has to be able to supply adequate current in all operating conditions, including a short-circuit, to ensure the electrical safety. Supplying short-circuit current with power electronics requires additional measures, and therefore, the short-circuit behavior is described and methods to overcome the high-current supply to the fault are proposed. Power electronic converters also produce common-mode (CM) and radio-frequency (RF) electromagnetic interferences (EMI), which are not present in AC distribution. Hence, their magnitudes are investigated. To enable comprehensive research on the LVDC distribution field, a research site was built into a public low-voltage distribution network. The implementation was a joint task by the LVDC research team of Lappeenranta University of Technology and a power company Suur-Savon S��ahk��o Oy. Now, the measurements could be conducted in an actual environment. This is important especially for the EMI studies. The main results of the work concern the short-circuit operation of the CEI and the EMI issues. The applicability of the power electronic converters to electricity distribution is demonstrated, and suggestions for future research are proposed.

Oratio introductoria ad gymnasii Wiiburgensis rectoratum de ejusdem gymnasii anno qvinqvagesimo sive jubilaeo. Habita & dicta in gratissimorum hospitum praesentia die 21 augusti anni M. DC. LXXXX. ore ac stylo Petri Carstenii s. theol. lectoris primarii & archipraep. Wiiburgensis

Arkit: A-D4 E1. - S. 34 tyhj��.

Power quality improving with virtual flux-based voltage source line converter

Line converters have become an attractive AC/DC power conversion solution in industrial applications. Line converters are based on controllable semiconductor switches, typically insulated gate bipolar transistors. Compared to the traditional diode bridge-based power converters line converters have many advantageous characteristics, including bidirectional power flow, controllable de-link voltage and power factor and sinusoidal line current. This thesis considers the control of the lineconverter and its application to power quality improving. The line converter control system studied is based on the virtual flux linkage orientation and the direct torque control (DTC) principle. A new DTC-based current control scheme is introduced and analyzed. The overmodulation characteristics of the DTC converter are considered and an analytical equation for the maximum modulation index is derived. The integration of the active filtering features to the line converter isconsidered. Three different active filtering methods are implemented. A frequency-domain method, which is based on selective harmonic sequence elimination, anda time-domain method, which is effective in a wider frequency band, are used inharmonic current compensation. Also, a voltage feedback active filtering method, which mitigates harmonic sequences of the grid voltage, is implemented. The frequency-domain and the voltage feedback active filtering control systems are analyzed and controllers are designed. The designs are verified with practical measurements. The performance and the characteristics of the implemented active filtering methods are compared and the effect of the L- and the LCL-type line filteris discussed. The importance of the correct grid impedance estimate in the voltage feedback active filter control system is discussed and a new measurement-based method to obtain it is proposed. Also, a power conditioning system (PCS) application of the line converter is considered. A new method for correcting the voltage unbalance of the PCS-fed island network is proposed and experimentally validated.

Sliding Mode Control for Switched Mode Power Supplies

Control applications of switched mode power supplies have been widely investigated. The main objective ofresearch and development (R&D) in this field is always to find the most suitable control method to be implemented in various DC/DC converter topologies. Inother words, the goal is to select a control method capable of improving the efficiency of the converter, reducing the effect of disturbances (line and load variation), lessening the effect of EMI (electro magnetic interference), and beingless effected by component variation. The main objective of this research work is to study different control methods implemented in switched mode power supplies namely (PID control, hysteresis control, adaptive control, current programmed control, variable structure control (VSC), and sliding mode control (SMC). The advantages and drawbacks of each control method are given. Two control methods, the PID and the SMC are selected and their effects on DC/DC (Buck, Boost, and Buck-Boost) converters are examined. Matlab/SimulinkTM is used to implement PID control method in DC/DC Buck converter and SMC in DC/DC (Buck, and Buck Boost) converters. For the prototype, operational amplifiers (op-amps) are used to implement PID control in DC/DC Buck converter. For SMC op-amps are implemented in DC/DC Buck converter and dSPACETM is used to control the DC/DC Buck-Boost converter. The SMC can be applied to the DC/DC (Buck, Boost, and Buck-Boost) converters. A comparison of the effects of the PID control and the SMC on the DC/DC Buck converter response in steady state, under line variations, load variations, and different component variations is performed. Also the Conducted RF-Emissions between the PID and SMC DC/DC Buck Converter are compared. The thesis shows that, in comparison with the PID control, the SMC provides better steady-state response, better dynamic response, less EMI, inherent order reduction, robustness against system uncertainty disturbances, and an implicit stability proof. Giving a better steady-state and dynamic response, the SMC is implemented in a DC/DC resonant converter. The half-wave zero current switching (HWZCS) DC/DC Buck converter is selected as a converter topology. A general guideline to select the tank component values, needed for the designing of a HWZCS DC/DC Buck, is obtained. The implementation of the SMC to a HWZCS DC/DC Buck converter is analysed. The converter response is investigated in the steady-state region and in the dynamic region.

Moottorimalliton skalaaris����t��

Ty��ss�� tutkitaan nopeusanturittoman vaihtovirtak��yt��n skalaarisia ohjaus- ja s����t��menetelmi��. Ty��n alussa esitet����n perusteoriat taajuusmuuttajista ja oikosulkumoottoreista. T��m��n j��lkeen esitell����n yleisimmin kirjallisuudessa esiintyneet skalaariohjaukset ja ���s����d��t. Vektoris����t���� ja erityisesti moottoriparametrien vaikutusta s����d��n toimivuuteen esitell����n lyhyesti. Ty��n tavoitteena on ACS800 taajuusmuuttajan skalaaris����d��n tutkiminen. ACS800:n nykyinen skalaaris����t�� on liian sidoksissa vektoris����t����n, joten simulointien ja kirjallisuustutkimuksen tarkoituksena on t��ysin vektoris����d��st�� eriytetyn skalaaris����d��n kehitysmahdollisuuksien tutkiminen. Kirjallisuudessa esiintyneiden s����t��jen avulla muodostetaan diskreettiaikainen toteutus skalaaris����d��lle vaihtovirtak��yt��ss��, jossa on k��yt��ss�� virran ja v��lipiirij��nnitteen takaisinkytkent��. S����dett��v���� moottoria mallinnetaan jatkuvaaikaisella L-sijaiskytkenn��ll��. V��lipiirin mallinnus toimii my��s jatkuva-aikaisena lukuun ottamatta v��lipiirin tasavirtakomponenttia, joka muodostetaan virran takaisinkytkenn��n ja PWM-modulaattorin kytkinasentojen avulla. Simuloinnin tarkoituksena on mallintaa skalaaris����d��n suurimpia ongelmia, kuten virta- ja v��lij��nnites����t����. Tuloksista voidaan p����tell��, ett�� peruss����d��t toimivat moitteettomasti, mutta erityisesti virtas����t���� tulisi kehitt����.