Vojtech Blahnik

Control of primary voltage source active rectifiers for traction converter with medium-frequency transformer

This paper deals with the new configuration of the traction converter with medium-frequency transformer intended for AC trolley wire fed locomotives. The main attention is paid to the primary serially connected single-phase voltage-source active rectifiers, which are directly connected to the trolley wire. This paper describes the control of the primary active rectifiers, presents simulation results as well as experimental evidence of designed low-voltage laboratory prototype of loco converter of rated power of 12 kW.

Compensation of low-frequency disturbances for traction converter with medium-frequency transformer for multi-system suburban units

The presented research deals with a new configuration of a main traction converter with medium-frequency transformer which is intended for modern multisystem suburban units and locomotives. This paper exactly introduces proposed control of primary voltage source active rectifiers with direct control of trolley-wire current and active damping of low-frequency disturbances at the converter ac side. The theoretical conclusions are verified by simulations and experiments made on developed small-scale laboratory prototype of traction converter of rated power of 12kW.

Current reference generator for single-phase shunt active power filters based on MGP-FIR

This paper describes three implementation alternatives of a multiplicative general parameter finite impulse response filter (MGP-FIR) used as a precise current reference generator for shunt-type active power filters. Compared to the traditional techniques that use fixed digital or analogue filters, the MGP-FIR is an adaptive and predictive algorithm for tracking typical frequency variations and thus avoiding the harmful phase shift of the fundamental sinusoid. This characteristic is essential for maximizing the harmonics reduction ability of the active power filter. The fixed subfilters of the MGP-FIR are pre-optimized by the use of a genetic algorithm. The harmonics reduction ability was verified by extensive simulations. Moreover, a laboratory prototype was developed and experimentally tested under typical non-linear loads. Compared to the previously presented articles on MGP-FIR-based current reference generators, this is the first time when real-valued or fixed-point coefficients are used with the MGP-FIR. In addition, we also improved the originally proposed amplitude detector. The results are compared with those presented earlier.

Elimination of dead-time effect causing current distortion of single-phase power converters

This paper describes constraints created by dead-times in single-phase voltage-source inverters working with medium and high switching frequencies (over thousands of Hertz). The dead-times cause distortion of a current at a converter ac side which is not acceptable especially in applications requiring high-precision current control. The control of voltage-source converter presented in this paper uses vector control in Cartesian coordinates which is offers very good dynamic properties. However, it is not able to naturally compensate the dead-time effects. Therefore, we complete this control by dead-time compensation block mitigating the unwanted distortion of converter ac current caused by dead-time effects using a nonlinear function generator. The behaviour of inverter control with proposed dead-time compensation and without compensation is reported in this paper.

Fuzzy energy management strategy for tram with supercapacitors

Energy storage systems (ESS) have large impact on efficiency and reliability of modern electric traction systems. This paper investigates the fuzzy energy management strategy for ESS based on supercapacitors (SC) for human driven trams. Operating the SC on board of a tram brings the following benefits: reduction of peak power demands, decrease of power consumption, improvement of performance and efficiency. Whereas the commonly used ESS Energy management strategies (EMSs) have been dealing without knowledge of vehicle position, the main interest of the presented research is put on the algorithm using the Global Positioning System (GPS). The tram position, located by a GPS module, is used to predict future energy demands and power flows. This information is used in the preparation of the supercapacitor energy level and its power flow control. The optimal ESS power flow with the respect to the tram position is a very complex problem. For this reason, soft computing techniques are used in this paper. The main part of the proposed ESS EMS is the Takagi-Sugeno Fuzzy controller (T-S Fuzzy). The T-S Fuzzy reduces problem dimensionality using the expert knowledge represented by the rules. The output membership functions were finaly optimized by the Differential Evolution (DE).

Current Source Based on H-Bridge Inverter with Output LCL Filter

Abstract The paper deals with a control of current source with an LCL output filter. The controlled current source is realized as a single-phase inverter and output LCL filter provides low ripple of output current. However, systems incorporating LCL filters require more complex control strategies and there are several interesting approaches to the control of this type of converter. This paper presents the inverter control algorithm, which combines model based control with a direct current control based on resonant controllers and single-phase vector control. The primary goal is to reduce the current ripple and distortion under required limits and provides fast and precise control of output current. The proposed control technique is verified by measurements on the laboratory model.

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.

Optimal control of single-phase voltage source active rectifier with emphasis on the minimal electromagnetic interference

This contribution presents comparison of two competitive control strategies for the single-phase voltage source active rectifier with emphasis on the minimal EMI. The first control is based on the PR controller with active damping of low-frequency disturbances at the converter ac side and the second control employs so-called hybrid delta modulation which naturally secures the sinusoidal waveform of the ac current. Results presented in this paper are confirmed by experiments made on developed laboratory prototype of the single-phase VSAR.

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.