Lajos Török

Implementation of PLL and FLL trackers for signals with high harmonic content and low sampling frequency

The accurate tracking of phase, frequency, and amplitude of different frequency components from a measured signal is an essential requirement for many digitally controlled equipment. The accurate and robust tracking of a frequency component from a complex signal was successfully applied for example in: grid connected inverters, sensorless motor control for rotor position estimation, grid voltage monitoring for ac-dc converters etc. Usually, the design of such trackers is done in continuous time domain. The discretization introduces errors which change the performance, especially when the input signal is rich in harmonics and the sampling frequency is close to the tracked frequency component. In this paper different discretization methods and implementation issues, such as Tustin, Backward-Forward Euler, are discussed and compared. A special case is analyzed, when the input signal is reach in harmonics and the sampling frequency is only 10 times larger than the tracked frequency component.

Robust control of boost PFC converter using adaptive PLL for line synchronization

The continuous development of the digital processing technology made advanced control strategies available for switched-mode power-supply applications. This paper presents the study and implementation of an adaptive Phased-Locked Loop (PLL)-based grid-fault tolerant control of a boost PFC converter. As the inductor current is synchronized to the rectified line voltage, by predicting the phase angle at each sampling sequence so the line current will follow the line voltage resulting in unity power factor. Tracking the phase angle of the rectified line voltage gives also the possibility to predict the next sampling value of the rectified grid voltage, avoiding in this way the compensation error caused by the delays of sampling and modulation. The proposed solution offers also noise immunity for the current controller to the line voltage disturbances.

High output LED-based profile lighting fixture

Recent developments in power light emitting diode (LED) industry have made LEDs suitable for being efficiently used in high intensity lighting fixtures instead of the commonly used high intensity discharge (HID) lamps. A high output LED-based profile-light fixture is presented in this paper. The system consists of a power supply with power factor correction (PFC), a LED-driver and an optical system designed for an overall high efficiency. An interleaved boost converter was chosen as PFC converter. A soft switching phase-shifted full-bridge converter with current doubler provides isolation from the grid and delivers the required voltage to the LED-driver which is a dual interleaved buck converter. Twelve high-power CBT-90 LEDs have been connected in a 4xRGB-configuration to deliver high output of saturated colors without the need for subtractive color filters. More than 6000 lm of fixture light output was measured.

Resonance Reduction for AC Drives With Small Capacitance in the DC Link

Pulse-width modulated ac drives equipped with a small dc-link capacitor are becoming an attractive solution for electric drive applications with moderate requirements for shaft dynamic performance. However, when these drives are fed from a weak grid, a resonance between the line side impedance and the dc-link capacitor appears. Due to this resonance, the total harmonic distortion and the partially weighted harmonic distortion of the line currents are increased, which may raise compatibility problems with the ac line harmonic standards. This paper proposes a novel dc-link voltage compensation method, which can reduce the amplitude of the aforementioned oscillation, while the large dc-link voltage variation, caused by the rectification, can be eliminated from the motor current. The method has been experimentally validated and the results show excellent performance.

Voltage ripple compensation for grid connected electrolyser power supply using small DC link capacitor

The purpose of this work was to investigate a three-phase-grid connected power supply using small DC link capacitor for electrolyser application. The hydrogen generation system requires low voltage and high current power supply. Thus the structure of the 3-phase power supply is defined as follows: a three phase rectification, a small DC-link capacitor and a phase-shifted full-bridge converter with current doubler rectification. Design constraints and control problems are investigated. The advantages and problems caused by the use of small DC link capacitor are presented. The control of the system is analysed from the grid current harmonic point of view and compensation solutions are discussed.

Efficiency and cost comparison of Si IGBT and SiC JFET isolated DC/DC converters

Silicon carbide (SiC) and other wide band gap devices are in these years undergoing a rapid development. The need for higher efficiency and smaller dimensions are forcing engineers to take these new devices in to considerations when choosing semiconductors for their converters. In this article a Si based converter and a SiC based converter is compared. Both converters are isolated DC/DC converters and were designed for 5 kW nominal outputs. Test setups for both converters were built and tested. The hardware differences between the two converters are described and performance is compared. An efficiency of above 97 % for the SiC JFET and over 90 % for the SI IGBT converter was measured. Cost differences between the two converters have been analyzed, showing that 772 days of operation are needed for the SiC converter costs to break even with the Si IGBT converter costs.

5kW phase-shifted full-bridge converter with current doubler using normally-off SiC JFETs designed for 98% efficiency

In this paper a 5kW step-down converter for low-voltage high-current application is presented using normally-off SiC JFETs as high voltage power switches, operating with efficiency close to 98%. Different low voltage side rectification solutions and loss estimations are also presented. As results show higher power density and efficiency can be achieved in medium- or high-power DC-DC applications by replacing silicone power devices with SiC alternatives.

Digital fuzzy logic and PI control of phase-shifted full-bridge current-doubler converter

Simple digital fuzzy logic voltage control of a phase-shifted full-bridge (PSFB) converter is proposed in this article. A comparison of the fuzzy controller and the classical PI voltage controller is presented and their effects on the converter dynamics are analyzed. Simulation model of the converter was built in Matlab/Simulink using PLECS. A 600W PSFB convert was designed and built and the control strategies were implemented in a 16 bit fixed point dsPIC microcontroller. The advantages and disadvantages of using Fuzzy logic control are highlighted.

Modelling and control of three-phase grid-connected power supply with small DC-link capacitor for electrolysers

These days electrolyzers are becoming more and more interesting due to the high demand for energy storage in form of hydrogen for renewable power generation using fuel cells. The design of a power supply for such a system is complex especially when the DC-link capacitance is reduced. By substituting the complex switching model of the power supply with a simplified one, the system dynamics can be better observed. The resonances caused by the small DC link capacitor and grid side inductance can be easier analyzed. A feed forward compensation method is proposed based on the simplified model of the system in order to minimize the effects of the DC link voltage ripple on the load voltage and current. The proposed method uses Frequency-Locked Loop (FLL) for estimating the fundamental component of the DC-link voltage ripple. Based on the reconstructed rectifier component a new feed-forward compensation signal is created, canceling in such a way the resonance introduced by the grid inductance and the DC-link capacitor from the feed-forward loop. The theoretical work has been validated through experiments on a 5 kW DC power supply used for electrolyser application.

Innovative use of power integrated modules for DC power supplies

In this article several innovative ways of utilizing Power Integrated Modules (PIM) as switching device in a DC power supply are presented. PIM have advantages in compactness of design, cost and fast prototype due to easier PCB layout. A PIM converter topology is chosen and designed resulting in an experimental setup. Results from the setup are presented showing the feasibility of using a PIM module as almost all power semiconductors in a DC power supply.