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Middle-level control of FB-MMC converter in Delta connection
Kokeš, Petr
Control of a modular multilevel converter (MMC) is technically far more complicated than control of a standard 2-level converter. It is not only because of a great number of series-connected cells. For a MMC converter we need to cope with another control level (mentioned here as the middle-level control), which means balancing of voltages among MMC branches and the control of currents circulating inside this converter. For the Delta connected MMC with full H–bridge (FH) cells a convenient method for voltage balancing among all three MMC branches has been analysed and the appropriate control structure has been designed. Then the functionality of this balancing method has been verified using computer simulations and also tested with two MMC physical models operating as active power filters on 400V and 6kV grids.
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The small hydroelectric power station design
Kokeš, Petr ; Pěcha, Jiří (referee) ; Matoušek, Antonín (advisor)
The thesis deals with comprehensive design of the small hydroelectric power station in the particular site. There is the site description in the first part followed by evaluation of the hydroenergetic capacity of the watercourse and description of the inlet building and piping. Building and machinery part of the turbine hall is described in the next part. The electric part of the power station is worked up to wider scope and includes hydroalternator, switchgears incl. power for self-consumption, electric protections, cabling, transformer substation and high voltage inlet line. There is a description of the control system in the next part and economical evaluation of the investment is at the end.
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Commissioning of a laboratory model of modular converter in full Delta connection
Janovec, Jiří ; Kokeš, Petr ; Semerád, Radko
A laboratory model of MMC (Modular Multilevel Converter) was created and put into operation. The converter consists of series-connected FHB (Full H-bridge) cells and other necessary devices (for measurement, synchronization and pre-charging). The MMC was tested in topology of full Delta connection with 5 cells in each of 3 branches. The MMC was loaded for symmetrization of 1-phase 3.4kW resistive load (i.e. the branch current approached 5Amp rms). The power cells were completed with Slave units EPX and then controlled using TwinCat development system and EtherCat industrial data network. With the converter, control algorithms for symmetrization and compensation of 1-phase load for 3-phase power grid were tested.
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Protective circuits of PF converters
Hauptmann, R. ; Kokeš, Petr
Description and results of numerical simulations of circuits, which provide damage protection of the main power supply circuit for tokamak PF (Poloidal Field) coils under emergency conditions, is presented. In case of normal operation the protection circuits do not affect operation of the power supply circuitry. The protection circuits represent a separate system which is functionally independent of circuits and control of power converters. Functinality of this system is designed as a safety circuit - a fault of the protection system always causes safety shut-down of the device.
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Protective circuits of TF converters
Hauptmann, R. ; Kokeš, Petr
Description and results of numerical simulations of circuits, which provide damage protection of the main power supply circuit for tokamak TF (Toroidal Field) coils under emergency conditions, is presented. In case of normal operation the protection circuits do not affect operation of the power supply circuitry. The protection circuits represent a separate system which is functionally independent of circuits and control of power converters. Functinality of this system is designed as a safety circuit - a fault of the protection system always causes safety shut-down of the device.
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Stability Analysis of Power Transfer in PF Supply System of Compass-U Tokamak.
Kokeš, Petr ; Hauptmann, R.
Power transfer stability in supply circuits of PF (Poloidal Field) coils has been analysed. Proper energizing of these coils is necessary for COMPASS-U tokamak experiments. The analysis main method is linearization of a non-linear system in a steady-state working point. The steady state-points have been specified by the Institute of Plasma Physics ASCR so that the whole operating area of the tokamak would be involved. At first, a simplified numerical model has been set up and analysed, then the analysis of a complex model of the PF supply system has been carried out in several versions according to the requirements of the contractor.
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Lowest Level Control for FB-MMC Converter
Kokeš, Petr
The analysis and comparison of two basic methods for the lowest level control of the Delta-connected FB-MMC converter (Full Bridge, Modular Multilevel Converter) have been performed. The first method is the SA-PWM modulation (Sampled Average PWM) with cell voltage balancing of SORT-BAL type, where cells are sorted according to their voltages. The other is the PSC-PWM modulation (Phase Shifted Carrier PWM) with FBCK-BAL balancing, which uses feedback P-control of cell capacitors voltages.
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Software Implementation of Lowest Level Control for FB-MMC Converter
Kokeš, Petr
For FB-MMC converter (Full Bridge Cell, Modular Multilevel Converter), the software implementation of SA-PWM modulation (Sampled Average PWM) and SORT-BAL sorting type balancing of cell voltages have been designed. The report deals with the specifics of realizing control methods using the Beckhoff TwinCAT 3 system. The control structure was divided into explicitly defined function blocks for the Master controller as well as for the distributed EPX Slave units. Data transfer timing between the Master and the Slave units has been designed and the synchronization of EtherCAT link communication has been tested in practice. \n
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Cause of mechanical vibrations of Palašer synchronous motors and its removal
Pavelka, J. ; Šimek, J. ; Kobrle, P. ; Kokeš, Petr
The paper describes the procedure and the result of analysis of mechanical vibrations of mining machines at the Palašer mine in the Russian Federation. The cause of these vibrations was the change in the magnitude of the magnetic flux in the air gap. The simulations showed the possibility of eliminating these changes in\nmagnetic flux by injecting suitable voltages into the stator windings. The implementation of this injection is further described by torque variable component feed-direct compensation. Finally, oscillography records are presented before and after injection.
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Palaser Project - Back Effect of AFE Converter on Supply Grid Voltage.
Kokeš, Petr ; Adam, Z.
An input device of the Invert 7L frequency converter is the PWM rectifier, also called the AFE (Active Front End) converter. Higher harmonic voltages increase in the medium-voltage supply grid due to AFE operation. The report deals with the calculations and possibilities of reduction of these harmonics. Theoretical results are verified by numerical simulations and compared with measurements on a physical industrial installation.
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