Tomas Kosan

Universal precharging method for dc-link and flying capacitors of four-level Flying Capacitor Converter

This paper investigates universal start-up procedure for Flying Capacitor Converter (FLC). Main part of this procedure is pre-charging of the dc-link and flying capacitors. This method is usable for voltage pre-charging in rectifier as well as inverter mode of the multilevel FLC converter. This specific feature is based on use of converter topology and modification of converter switching pulses control. The proposed control improvements are designed to control particularly multilevel converters. The control system is implemented in development platform Multi Level Converter (MLC) interface for a four-level multilevel converter with flying capacitors. Its performance is investigated and evaluated by selected experiments made on a developed converter prototype of the rated power of 30 kVA. This paper also discusses behaviour of converter on occurrence of safe restart and shut-down procedure.

Complete development platform for multi-level converters and complex control algorithms

This paper describes the modular development control platform including dedicated supporting tools. The platform was specially designed for the multi-level converters control therefore it provides up to 48 (plus 24 optional) of PWM outputs thanks to additional FPGA utilization. The combination of DSP enabled microcontroller and the FPGA allowed us to split the computational tasks between these parts which significantly helps with highly complex algorithms implementation. Fast application development is supported thanks to the software drivers covering broad range of elemental functions including communication, DMA transfers, AD service routines and basic user interface. Also an enhanced set of FPGA entities featuring various modulator functionalities are provided. Dedicated tools involves fully insulated JTAG interface with developed software allowing the platform to be programmed by a single JTAG emulator. An application example based on four level FLC converter is presented.

Implementation of SVPWM algorithm without trigonometric functions

This paper investigates topologically independent vector modulation for multilevel converters. The investigate vector modulation is Space Vector PWM (SVPWM) which was implemented in FPGA and also tested in development board MLC interface with low-voltage prototype of three-level Neutral Point Clamped (3L-NPC) converter. The main advantages and disadvantages which were found out during implementation and hardware tests are also described in this paper.

FPGA implementation of marginalized particle filter for sensorless control of PMSM drives

Marginalized particle filter is a stochastic filter combining Kalman filters with particle filters. It decomposes the model into linear and nonlinear part and applies the Kalman filter for the former and the particle filter for the latter. In effect, this allows to represent accurately the inherent non-Gaussianity and nonlinearity of the model. This allows estimation of the rotor position of the PMSM drive in the full speed range, including the standstill. The main disadvantage is its high computational cost. In this paper, we present an implementation of the marginalized particle filter in the field programmable logic array (FPGA). The parallel nature of the MPF algorithm allows to use pipelining which yields speedup in the order of magnitude in comparison to the DSP implementation. The sensorless control of the drive is implemented on a board with both DSP and FPGA, where the drive control runs on the DSP and the MPF estimator in the FPGA. Execution time of the estimator is thus negligible in the execution time of the sensorless control. Performance of the resulting sensorless control algorithm is evaluated on a developed drive prototype of rated power of 10.7kW.

Complete design of down-scale prototype of mining machine converter based on four-level voltage-source converter with flying capacitors

This contribution describes complete design of a three-phase four-level voltage-source converter for a new mining machine drive. Particularly, it is focused on development of a down-scale laboratory prototype of a converter with rated power of 30kVA. Moreover, the control system called REMCS which has been designed for control of the final full power prototype is also introduced. The proper function of the developed converter prototype is verified by selected experiments.

Active voltage balancing control with phase disposition PWM for 4-level flying capacitor converter

This contribution investigates three-phase four-level FLC based indirect frequency converter supplied from a 6kV AC-grid. It describes proposed active voltage balancing control of both output voltage-source inverter and input active rectifier with PD-PWM. The results are verified by experiments made on down-scale prototype of converter of rated power of 35kVA.

Control of single-phase AC/DC converter based on SOGI-PLL voltage synchronization

This paper introduces the advanced control designed for the single-phase AC/DC traction converter. This type of control provides direct current control and sufficient control of output voltage. The proposed control strategy is based on second order general integrator phase locked loop (SOGI-PLL), which is used for trolley voltage synchronization. In this case SOGI-PLL evaluates voltage position, amplitude and frequency. These data are used for precise and robust current control, which uses PR controller. The behavior of designed control and SOGI-PLL synchronization is analyzed by both simulations and experiments made on developed 1.5 kW laboratory prototype.

Complete solution of 4-level flying capacitor converter for medium-voltage drives with active voltage balancing control with phase-disposition PWM

This paper presents three-phase four-level FLC based electric motor drive for mining application supplied directly from a 6 kV ac-grid. It describes complete control algorithms of the drive with active voltage balancing control. The proposed control is verified by experiments carried out on down-scale drive prototype of rated power of 35 kVA.

Control of a Single-Phase Cascaded H-Bridge Active Rectifier Under Unbalanced Load

Cascaded H-bridge (CHB) converter technology is actually the most popular solution for grid-connected converters in both medium- and high-voltage applications. This paper introduces a new control of a single-phase CHB active rectifier. The control uses a direct grid current control based on adaptive resonant controllers. The resonant controllers are adapting to slow fluctuation of ac grid frequency. The challenging problem of CHB converters is dc-link capacitor voltage balancing especially under unbalanced load conditions. This paper presents a reliable voltage-balancing technique utilizing energy estimation of particular dc-link capacitor banks and simple prediction of the changes of their energies. A nonlinear behavior of the converter caused by power semiconductors voltage drops and dead-time effects is minimized by auxiliary adaptive resonant controllers. The resulting control has very good performance, including the operation under unbalanced load conditions, and achieves low total harmonic distortion of converter grid current. The theoretical results were verified by experiments made on the developed CHB active rectifier prototype with three power cells in cascade.

Grid impedance identification by current harmonics signal injection

This paper deals with grid impedance identification by current harmonics signal injection. The current signal is generated by the single phase H-bridge converter. The single phase H-bridge converter is connected in parallel to auxiliary winding of the Petersen coil. The voltage responses of converter for specific current harmonics are used for grid resonant frequency identification. This information is used as feedback for proper tuning of Petersen coil. Meanwhile the two harmonics current generation method is well known, this paper presents the twelve harmonics method. This solution provides more accurate resonant frequency estimation.