For medium and high-voltage drive applications, multilevel inverters are very popular. It is due to their superior performance compared to 2-level inverters such as reduced harmonic content in the output voltage and current, lower common mode voltage and dv=dt, and lesser voltage stress on power switches. The popular circuit topologies for multilevel inverters are neutral point clamped, cascaded H-bridge and flying capacitor based circuits. There exist different combinations of these basic topologies to realize multilevel inverters with modularity, better fault tolerance, and reliability. Due to these advantages, multilevel converters are getting good acceptance from the industry, and researchers all over the world are continuously trying to improve the performance of these converters. To meet such demands, three multilevel inverter topologies are proposed in this thesis. These topologies can be used for high-power induction motor drives, and the concepts presented are also applicable for synchronous motor drives, grid-connected inverters, etc. To get nearly sinusoidal phase current waveforms, the switching frequency of the conventional inverter has to be increased. It will lead to higher switching losses and electromagnetic interference. The problem with lower switching frequency is the intro- duction of low order harmonics in phase currents and undesirable torque ripple in the motor. The 5th and 7th harmonics are dominant for hexagonal voltage space-vector based low frequency switching, and it is possible to eliminate these harmonics by dodecagonal switching. Further improvement in the waveform quality is possible by octadecagonal voltage space-vectors. In this case, the complete elimination of 11th and 13th harmonic is possible for the entire modulation range. The concepts of dodecagonal and octadecagonal voltage space-vectors are used in the proposed inverter topologies. The first topology proposed in this thesis consists of cascaded connection of two H-bridge cells. The two cells are fed from unequal DC voltage sources having a ratio of 1 : 0:366, and this inverter can produce six concentric dodecagonal voltage space- vectors. This ratio of voltages can be obtained easily from a combination of star-delta transformers, since 1 : 0:366 = ( p 3 + 1) : 1. The cascaded connection of two H-bridge cells can generate nine asymmetric pole voltage levels, and the combined three-phase inverter can produce 729 voltage space-vectors (9 9 9). From this large number of combinations, only certain voltage space-vectors are selected, which forms dodecagonal pattern. In the case of conventional multilevel inverters, the voltage space-vector diagram consists of equilateral triangles of equal size, but for the proposed inverter, the triangular regions are isosceles and are having different sizes. By properly placing the voltage space-vectors in a sampling period, it is possible to achieve lower switching frequency for the individual cells, with substantial improvement in the harmonic spectrum of the output voltage. During the experimental veri cation, the motor is operated at di erent speeds using open loop v=f control method. The samples taken are always synchronised with the start of the sector to get synchronised PWM. The number of samples per sector is decreased with increase in the fundamental frequency to limit the switching frequency. Even though many topologies are available in literature, the most preferred topology for drives application such as traction drives is the 3-level NPC structure. This implies that the industry is still looking for viable alternatives to construct multilevel inverter topologies based on available power circuits. The second work focuses on the development of a multilevel inverter for variable speed medium-voltage drive application with dodecagonal voltage space-vectors, using lesser number of switches and power sources compared to earlier implementations. It can generate three concentric 12-sided polygonal voltage space-vectors and it is based on commonly available 2-level and 3-level inverters. A simple PWM timing computation method based on the hexagonal space-vector PWM is developed. The sampled values of the three-phase reference voltages are initially converted to the timings of a two-level inverter. These timings are mapped to the dodecagonal timings using a change of basis transformation. The voltage space- vector diagram of the proposed drive consists of sixty isosceles triangular regions, and the dodecagonal timings calculated are converted to the timings of the inner triangles. A searching algorithm is used to identify the triangular region in which the reference vector is located. A front-end recti er that may be easily implemented using standard star-delta transformers is also developed, to provide near-unity power factor. To test the performance of the inverter drive, an open-loop v=f control is used on a three-phase induction motor under no-load condition. The harmonic spectra of the phase voltages were computed in order to analyse the harmonic distortion of the waveforms. The carrier frequency was kept around 1.2 KHz for the entire range of operation. If the switching frequency is decreased, the conventional hexagonal space-vector based switching introduce signifi cant 5th, 7th, 11th and 13th harmonics in the phase currents. Out of these dominant harmonics, the 5th and 7th harmonics can be completely suppressed using dodecagonal voltage space-vector based switching as observed in the first and second work. It is also possible to remove the 11th and the 13th harmonics by using voltage space-vectors with 18 sides. The last topology is based on multilevel octadecagonal (18-sided polygon) voltage space-vectors, and it has better harmonic performance than the previously mentioned topologies. Here, a multilevel inverter system capable of producing three octadecagonal voltage space-vectors is proposed for the fi rst time, along with a simple timing calculation method. The conventional three-level inverters are only required to construct the proposed drive. Four asymmetric power supply voltages with 0:3054Vdc, 0:3473Vdc, 0:2266Vdc and 0:1207Vdc are required for the operation of the drive, and it is the main drawback of the circuit. Generally front-end isolation transformer is essential for high-power drives and these asymmetric voltages can be easily obtained from the multiple windings of the isolation transformer. The total harmonic distortion of the phase current is improved due to the 18-sided voltage space-vector switching. The ratio of the radius of the largest polygon and its inscribing circle is cos10 = 0:985. This ratio in the case of hexagonal voltage space-vector modulation is cos30 = 0:866, which means that the range of the linear modulation for the proposed scheme is signifi cantly higher. The drive is designed for open-end winding induction motors and it has better fault tolerance. It any of the inverter fails, it can be easily bypassed and the drive will be still functional with reduced speed. Open loop v=f control and rotor flux oriented vector control schemes were used during the experimental verifi cation. TMS320F2812 DSP platform was used to execute the control code for the proposed drive schemes. For the entire range of operation, the carrier was synchronized with the fundamental. For the synchronization, the sampling period is varied dynamically so that the number of samples in a triangular region is fi xed, keeping the switching frequency around 1.2 KHz. The average execution time for the v=f code was found to be 20 S, where as for vector control it took nearly 100 S. The PWM terminals and I/O lines of the DSP is used to output the timings and the triangle number respectively. To convert the triangle number and the timings to IGBT gate drive logic, an FPGA (XC3S200) was used. A constant dead-time of 1.5 S is also implemented inside the FPGA. Opto-isolated gate drivers with desaturation protection (M57962L) were used to drive the IGBTs. Hall-effect sensors were used to measure the phase currents and DC bus voltages. An incremental shaft position encoder with 2500 pulse per revolution is also connected to the motor shaft, to measure the angular velocity. 1200 V, 75 A IGBT half-bridge module is used to realize the switches. The concepts were initially simulated and experimentally verifi ed using laboratory prototypes at low power. While these concepts maybe easily extended to higher power levels by using suitably rated devices, the control techniques presented shall still remain applicable.

This master‘s thesis focuses on optimization of power and control circuits of an inverter, which was developed at UVEE. The principle of function and circuit implementation of a single-phase inventer, various calculations (design of an LC filter, DC link capacitor, semiconductor elements and heat sink) are described in the thesis. A design of fast overcurrent protections, oscillator and saw signal generator is included. Furthermore, a printed circuit board was designed which was optimized by thermal simulation in the Workbench Ansys. Subsequently, the printed circuit board was mounted, debugged and verification measurements were performed on it. At the end of the thesis there is a documentation for the implemented equipment.

This thesis deals with DC motor control. Main goal was design and realization of DC motor controler module with feedback. The first part dwells on methods for DC motor control and HW design of control module. The second part describes development of software for the module, testing and sums up results.

This work is focused on single phase inverters, which are used for the conversion of the direct current to the alternating current and are nowdays used especially in systems of back-up power supply. The specific aim of this work is implementation of design hight power circuit of inverter include calculation of control algorithm. It describes the complete solution of power circuit. Next step is a analysis of problems concerning the digital control with help of signal processor which is used for solution of regulator structure. Check of the design and checkout of control algorithm is made in the form of simulation in the MATLAB Simulink. Debugged program algorithm is subsequently implemented into the signal microprocessor. The work results rate estimation functionality of inverter and solution of control algorithm.

Detta examensarbete har utförts på uppdrag av Terco. Tercos PST 2220Transmission Line and Distribution Module fungerar som en fysisk modellav ett verkligt transmissions- eller distributionsnät där fem olika typer av nätmed avseende på längd, spänningsnivå och skenbar effekt är möjliga. Idagfinns ett behov av en modell där användaren kan ställa in dessa parametrarså att modellen mer precist kan spegla vilka egenskaper det specifika nätethar. Här undersöks hur längden och dess inverkan på en ledning kan varierasi en modell.En presentation av hur transmissions- och distributionsnät fungerar ochbeskrivs teoretiskt lägger grunden till den modell och de två approximationersom kan beskriva ett helt näts egenskaper.Då R, L och C komponenterna behöver kunna varieras för att fysisktkunna realisera denna teoretiska modell undersöks vilka metoder som dettakan genomföras på. För detta undersöks två tillvägagångssätt, kaskadkopp-lad pi-modell och variabel aktiv-passiv reaktans.Flera aspekter som utrymme, kostnad och variabilitet gör att varia-bel aktiv-passiv reaktans är att föredra. Dess funktion som en varierbarspänningskälla, uppbyggd av switchar styrda med reglerteknik och puls-breddsmodulering gör att komponenterna R, L och C och dess egenskaperoch inverkan på en transmissionslinje kan åstadkommas. Resultatet är attde nödvändiga R,L,C komponenterna går att variera i storlek för att kunnaingå i en varierbar transmissionsledningsmodell.Resultatet och målen säkerställs med simuleringar där variabel aktiv-passiv reaktans visas kunna vidareutvecklas och praktiskt testas för att mo-dellera transmissions- och distributionsnät med olika längd. Nyckelord. Variabilitet, Inverterare, Impedans, DC-AC, Pulsbreddsmodu-lering, Övertoner, Transmissionsledning, Spänningsfall, Reaktiv effekt. / This diploma work has been carried out on behalf of Terco. TercosPST 2220 Transmission Line and Distribution Module works as a physicalmodel of a real transmission and distribution grid where five different typesof networks based on length, voltage and apparent effect are available. Thereis today a need of a model where the user self can adjust these parameters sothat the model more precisely can reflect the characteristics that the specificgrid has. Here it’s investigated how the length and its impact on a line canbe varied in a model.A presentation of how the transmission and distribution grid works andare described theoretically provides the basics for the different models thatcan describe a whole network and its properties.Since the R, L and C components needs to be able to be varied to be ableto physically realize this theoretical model, the different methods that thiscan be realized through are investigated. Two approaches are investigated,the cascaded pi-model and variable active-passive reactance (VAPAR).A number of aspects like space, cost and variability makes the variableactive-passive reactance the most suited solution. Its function as a variablevoltage source, made out of an four switches, operated with control techno-logy and pulse width modulation, makes it possible to imitate R, L and Csproperties and effect on a transmission line. The result is that the necessaryR,L,C components are made adjustable in order to be incorporated in aadjustable transmission lin model.The result and the goal are verified with simulations where variableactive-passive reactance is proved able for further development and practicaltests to model transmission and distribution lines with different length. Keywords. Variability, Inverter, Impedance, DC-AC, Pulse width modula-tion, Harmonics, H-bridge, Transmission line, Voltage drop, Reactive effect.