Control of Static Converters for Grid-Side and Machine-Side Applications

The research activities summarized in this Ph.D. thesis are mainly referred to the power electronics field, with some extensions related to electric machines and electrical drives. The first chapter focuses on the analysis and control of an unconventional static converter able to extend a common 1-phase mains feeder into a standard 3-phase power supply featuring either a 3-wires or a 4-wires output, the latter including neutral. Such converter exhibits a complete power reversibility and permits to achieve a good power quality level both at the input and the output side. It is proposed as an attractive alternative to conventional solutions possibly available in the market, such as converters for drives supplied by 1-phase mains yet using 3-phase motors, thanks to the following benefits: greater simplicity, lower cost, inherent active-filter-like operation at supply side, low harmonic distortion at load side. Such converter might be then successfully applied in any application requiring a 3-phase standard supply when a 1-phase mains feeder is available. A theoretical analysis of the converter is presented as well as a semi-ideal simulation model implemented referring to different control strategies. Several simulation results are finally reported and commented, confirming the effectiveness of the proposed solution. The second chapter focuses on the real-time control of 3-phase single-dc-bus shunt active filters employed for the parallel compensation of harmonics, reactive components and unbalancing in the currents drawn by a power supply when generic 3-phase non-linear, non-resistive and unbalanced loads are connected. In particular, the specific issues related to applications featuring a high fundamental frequency, such as in aerospace ambit, were addressed, investigating an innovative improved dead beat digital control algorithm. Such solution was proposed and get ready mainly aiming to achieve a rather high bandwidth of the current control loop and a good reference tracking even when the number of commutations per fundamental period that can be used is rather low. In order to probe the performances of the proposed control strategy, a simulation model was first developed and a prototype system was finally get ready. The results obtained from several virtual and experimental tests are reported and commented referring both to standard industrial and much more demanding aerospace operative conditions, thus proving the validity of the proposed solution. The third chapter focuses on the real-time control of 3-phase multilevel shunt active filters employing a multilevel cascaded H-bridges structure, again mainly referring to applications featuring a high fundamental frequency such as in aerospace ambit. In fact, such power structures may permit to improve the equivalent converter performances while keeping at relatively low values the actual switching frequency of the power devices. In particular, the combined application of an innovative modulation technique and of a dead-beat strategy analogous to the one described in the previous chapter was investigated. A theoretical analysis of the proposed control strategy is reported, as well as several experimental results obtained from a prototype system purposely get ready and tested at both industrial and aerospace frequency, highlighting the potential of the proposed solution especially for the latter applications. The experimental activities related to chapters 2 and 3 were developed during a study period spent at the University of Nottingham, UK. The fourth chapter deals with the modeling and control of an innovative rotary-linear brushless machine. In particular, after its ideal analytical modeling and operation principle, its basic control strategy inspired to sinusoidal brushless machines is presented, reporting some simulation results. A more detailed simulation model based on the equivalent magnetic circuit approach is then presented, permitting to approximately take into account several secondary aspects neglected by the simpler basic sinusoidal model while remaining not much computationally intensive as a finite element model would be. Simulation results obtained by such model are reported and commented, highlighting its potential usefulness for both preliminary machine design purposes and for analyzing the operation of a complete drive. Finally, the fifth chapter presents the application of the same intermediate-level modeling approach described in chapter 4 to a consequent-pole brushless machine featuring an unconventional magnet-pole angular width ratio. After some considerations on the specific arrangement examined, which was conceived to achieve a better exploitation of the active materials, a simulation model of the machine is presented and numerical results are reported and commented, highlighting the usefulness of the proposed intermediate-level modeling approach.